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31/01/2017
Anaerobic Digestion Economic Feasibility
Study: Generating energy from waste,
sewage and sargassum seaweed in the
OECS
CPI Report Number: CPI-SP-RP-141
Compiled By
Michelle Morrison, CPI
Daniel Gray, The Caribbean Council
Confidential | A report on behalf of The Foreign and
Commonwealth Office
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The Centre for Process Innovation is the UK’s national
technology and innovation centre
to serve and support the process manufacturing industries. We
are chosen by key
industry leaders and SMEs to develop, prove, prototype and scale
up the next
generation of products and processes.
with no down time in production as all of the process
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We help our clients to produce better products with
increased quality and performance. We can create
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We enable companies to decrease capital and
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4 CONFIDENTIAL
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5 CONFIDENTIAL
Contents
1 Revision
History.............................................................................................................
7
2 Glossary
........................................................................................................................
8
3 Executive summary
.......................................................................................................
9
4 Background, Approach & Objectives
...........................................................................
10
4.1 Background
....................................................................................................................................
10
4.2 Approach & objectives
...................................................................................................................
12
5 Existing Information
.....................................................................................................
15
5.1
Energy............................................................................................................................................
15
5.1.1 St. Lucia
....................................................................................................................................
15
5.1.2 Grenada
....................................................................................................................................
17
5.2 Waste resources
............................................................................................................................
18
5.2.1 St. Lucia
....................................................................................................................................
18
5.2.2 Grenada
....................................................................................................................................
22
5.3 Water treatment
.............................................................................................................................
24
5.3.1 St. Lucia
....................................................................................................................................
24
5.3.2 Grenada
....................................................................................................................................
25
5.4 Sargassum
.....................................................................................................................................
26
6 Anaerobic Digestion
....................................................................................................
29
6.1 Biogas production
..........................................................................................................................
29
6.2 Applications & Benefits
..................................................................................................................
30
6.3 Planning and Permitting for AD
.....................................................................................................
31
7 Biochemical methane potential
....................................................................................
33
7.1 Introduction
....................................................................................................................................
33
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6 CONFIDENTIAL
7.2 Methodology
..................................................................................................................................
33
7.2.1 Feedstock preparation
..............................................................................................................
33
7.2.2 Substrate blends and controls
..................................................................................................
33
7.2.3 Biogas volumes and composition
.............................................................................................
35
7.3 Treatment of data
..........................................................................................................................
35
7.3.1 Theoretical methane potential
..................................................................................................
35
7.3.2 Higher heating values & energy content
..................................................................................
35
7.4 Results
...........................................................................................................................................
36
7.5 Conclusions from the BMP
............................................................................................................
40
8 Energy yield & Economics
...........................................................................................
41
8.1 Energy potential – St Lucia
............................................................................................................
41
8.2 Energy potential – Grenada
...........................................................................................................
44
8.3 Economic case
..............................................................................................................................
47
8.3.1 Explanation of terms
.................................................................................................................
49
8.3.2 Discounted cash flow modelling results
...................................................................................
50
8.3.3 Biomethane as LPG replacement
............................................................................................
53
8.3.4 Conclusions from the energy yield and economic modelling
................................................... 54
9 Conclusions
.................................................................................................................
56
9.1.1 Viability of AD as a waste treatment and energy generation
technology in the OECS ............ 56
9.1.2 Policy recommendations for St. Lucia and Grenada
................................................................
57
10 Next Steps
...................................................................................................................
58
11 Appendix
.....................................................................................................................
60
11.1 St. Lucia Data compiled by the Caribbean Council
.......................................................................
60
11.2 Grenada Data compiled by the Caribbean Council
.......................................................................
67
11.3 St Lucia Waste tonnage data
........................................................................................................
79
11.4 Written Responses to Questions
...................................................................................................
80
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1 Revision History
Revision Prepared by Checked by Approved by Comment
[001] Michelle Morrison Emma Stokes Daniel Gray Initial
version.
[002] Daniel Gray Polly Hatfield Chris Bennett Comments and
edits from The Caribbean Council following discussion.
[003] Daniel Gray Polly Hatfield Michelle Morrison
Additions from The Caribbean Council to Section 5 and 9.
Creation of Section 10.
[004] Michelle Morrison Daniel Gray Chris Bennett Further
modelling and research from the CPI for Section 8 & 9.
[005] Daniel Gray Michelle Morrison Chris Bennett Final
Approval
[006] Michelle Morrison Daniel Gray Chris Bennett Addition of
responses to queries following Webinar Presentation on 25/01/17
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2 Glossary
AD Anaerobic Digestion
BMP Biochemical Methane Potential
BOE Barrel of Oil Equivalent
CF Cash flow
CH4 Methane
CHP Combined heat and power
CO2 Carbon dioxide
COD chemical oxygen demand
CSTR Continuously stirred tank reactor
CV Calorific value
DCF Discounted cash flow (model)
FiT Feed in tariff (for electricity)
FW Food waste
GDP Gross domestic product
GWh Giga watt hours
HHV Higher heating value
H2S Hydrogen sulphide
IRR Internal rate of return
kW kilowatts
kWh kilowatt hours
LPG Liquefied petroleum gas
MJ Mega joules
MW Megawatts
MWh Megawatt hours
NPV Net present value
OM MSW Organic matter fraction of municipal solid waste
P Profit
PV Photo voltaic
SBY Specific biogas yield
SLSWMA St Lucia Solid Waste Management Authority
SMY Specific methane yield
STP Standard temperature and pressure (273K, 1.01325 bar)
TMP Theoretical methane potential
Tons Imperial measurement of mass
TPA Metric tonnes per annum
TS Total solids
US$ United States dollars
VS Volatile solids
XC$ Eastern Caribbean dollars
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3 Executive summary
Small island developing states in the Caribbean face serious
challenges relating to 1) waste management; 2)
sewage treatment and; 3) energy sustainability. At present, all
too often, inefficient and poorly planned delivery
of these key services is having a negative impact on the quality
of people’s lives and the environment. Action
across the public and private sector is needed regionwide to
address these issues in a cost-effective, controlled
and sustainable manner.
Anaerobic Digestion (AD) is a technology which can provide real
benefits to all three areas of concern and
which is currently not being deployed in the Caribbean. This
report seeks to study how anaerobic digestion
could be used in a Caribbean context to treat biogenic waste,
including sewage sludge and in the process,
generate renewable energy in the forms of electricity, heat and
biomethane gas for fuel. AD can be
implemented at all scales and there are existing and well proven
technologies available at all scales of delivery.
For the purposes of this study, St Lucia and Grenada were taken
as examples of developing island states.
They both exhibit all three problems and could benefit from an
AD solution. Available information on St Lucia
has been used to provide an initial estimate of the available
tonnage of potential AD feedstocks; 66,000 tpa of
biogenic waste (not including agricultural, food or drinks
processing, brewery/distillery or slaughterhouse
waste) could yield between 46,400,000 and 72,300,000 MJ of
energy, the equivalent of 13 GWh of power.
Corresponding data on Grenada indicate that there could be
46,000 tonnes per annum of biomass waste
available for treatment through AD which could yield 81,500,000
MJ of energy or the equivalent of 22.5 GWh
of power.
AD could also provide a waste treatment solution for beached
Sargassum, a growing problem throughout the
Caribbean. Available information on Sargassum natans and
fluitans, the two species of primary concern across
the Caribbean, is sparse. The small BMP assessment carried out
showed that ‘old’, beached Sargassum,
when milled to a powder and digested, had a very low BMP at 61
m3/tonne VS added (compare with food
waste at 421 m3/tonne VS added). In spite of Sargassum’s low
SMY, it could still be treated through AD, as an
amendment to a plant taking other wastes as its primary
feed.
Regarding economic viability of an AD approach to energy
generation, modelling suggested that it should be
possible to make a financial return on implementing AD
technology in St Lucia and Grenada. The percentage
contribution to electricity and/or heat supply made by AD would
be relatively small but significant. In St Lucia,
AD could provide up to 6%, possibly more if all potential
feedstocks for AD were treated. In Grenada, that rises
to around 11%.
Varying levels of financial interventions would be required, to
help AD investment yield positive returns. Small
scale projects need more incentives to be financially viable,
such as generation tariffs and gate fees (where
possible), plus state aid or capital grants. Large scale plants
could make a return with less incentives and no
gate fee for waste, depending on the energy content of the
waste. Small community scale projects may be the
answer in hard-to-reach communities and could double up as both
energy generation and sewage treatment.
Technology at the back end to dewater and purify the digestate
could also deliver grey water for non-potable
uses.
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Taken together with other renewable sources, such as solar PV
and thermal, plus wind, these renewables
have high potential to replace a large fraction of fossil fuel
derived energy, creating more sustainable and
resilient island nations, not completely dependent on, or at the
mercy of wildly fluctuating energy markets.
Policy development would need to look at how to structure an
energy generation tariff system and remuneration
levels for electricity and heat sales. Examination of existing
systems and their faults would be useful. This may
require thought on how best to capture the organic fraction of
municipal and commercial waste. As a potentially
valuable source of energy, a source-segregated approach would be
the ideal option but this is not without its
challenges. There will need to be some policy and regulation in
place for the use of digestate (on land), to
ensure environmentally responsible application. Education of the
public is also a major challenge, together
with the logistics of collection. A Food Waste Study could help
identify the issues and prepare options for
moving forward. In this respect, there are European examples to
draw on, both in terms of the technologies
involved, and the associated public education campaigns.
As explored in Section 10 (Next Steps), further research,
experimentation and investment is required to take
forward the use of waste-to-energy anaerobic digestion solutions
in the Caribbean. This includes additional
experimentation with samples of Sargassum and more in-depth
techno-economic studies into the economic
viability of AD plants in the region. Finally, supplementary
research on the politico-economic landscape in
individual OECS states would enhance the policy making process,
and help identify which of the Scenarios
covered in this report are most likely to gain support among
civil society.
4 Background, Approach & Objectives
4.1 Background
In March 2016, a meeting, Harnessing the Economic Benefits of
Sargassum, was organised by the British
Virgin Islands Government and Virgin Unite together with the
Foreign and Commonwealth Office, the
Caribbean Council and the Organisation of Eastern Caribbean
States and held in the British Virgin Islands.
The meeting was arranged in order to discuss the problems
arising from inundations of the pelagic seaweed
Sargassum and also to discuss potential solutions to its
management, which could derive financial and societal
benefit for the communities of the British Virgin Islands (and
the wider Eastern Caribbean archipelago).
The problems highlighted included; the loss of economic activity
for the local fishermen, unable to access or
move their boats during inundations and limited or no access to
fishing grounds; detrimental impacts on the
tourism industry, so vital to the islands, due to lack of access
to popular beach resorts; odour issues resulting
from the breakdown of the beached Sargassum and the consequent
release of trace amounts of the ‘bad-egg’
smelling gas, hydrogen sulphide (humans can detect H2S at very
low levels), also deterring visitors. Out at sea
the mats of floating Sargassum offer a vital habitat as a
nursery for a variety of fish species, invertebrates and
young turtles and well as a safe stopping off point for
migratory species. However, once in the coastal zone it
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11 CONFIDENTIAL
has a negative impact on the ecosystem, where coastal fauna can
become trapped in the decaying weed;
there have been many sightings of dead turtles and fish.
Although Sargassum has been landing throughout the Caribbean and
along sections of the Mexican coast for
several years, tracking and more importantly predicting its
arrival is proving to be a complex and difficult task.
Many of the affected nations are now working together, not only
to try and devise an early warning system for
the entire region but also to develop methods of management.
Currently, there is no publicly available data on
how much Sargassum is being washed up, neither as volume or
mass. Historically, there have always been
periods where Sargassum has beached in the Caribbean but the
scale of these events was much smaller than
that seen in recent years. The first major, problematic
inundation occurred during 2011, with large annual
influxes subsequently until 2015, when there was another major
inundation1. 2016 appears to have been less
problematic, with lighter influxes landing later on in the
season. Unfortunately, the massive variation in quantity,
location and timing of influxes has resulted in significant data
gaps, which are only now starting to be
addressed. At this time it is not possible to say anything on
quantities of Sargassum available for treatment or
the regularity of supply in any one place. One consequence of
this lack of data and the difficulty of obtaining
good data on these points, is that management strategies to deal
with the invasive Sargassum to deliver a
monetary value, which might involve the installation of
processing plant [to produce energy, chemicals] at some
cost, are difficult to justify on an economic basis.
Intermittency of supply is a very important consideration and
so, allied to availability is the important question of how to
effectively store the material that does land, so that
it can be processed through time whilst maintaining its active
ingredients.
The topics covered in this feasibility arose out of the
Sargassum meeting in the BVI. However, these are
recurring themes across developing states and small island
nations. Grenada hosted the first Caribbean Waste
to Energy Technology Expo & Conference in January 2016,
sponsored by CARICOM Secretariat/GIZ REETA
– German Federal Enterprise for International Cooperation (GIZ)
Renewable Energy and Energy Efficiency
Technical Assistance Programme (REETA); Caribbean Community
Climate Change Centre (CCCCC)/SIDS
DOCK; the United Nations Industrial Development Organization
(UNIDO); the Swedish Energy Agency (SEA);
and the World Intellectual Property Organization (WIPO).
It has already been recognised that appropriate, effective and
sustainable waste management, both of solid
and liquid wastes, is a vital tool in the battle for sustainable
and financially viable communities. As the effects
of climate change become apparent, experienced more keenly in
some developing island nations, the drive to
improve resilience can largely be met by effective waste
management and the implementation of renewable
energy initiatives, which make use of waste resources. A diverse
toolbox of technologies for waste
management and energy generation (including solar and wind)
would improve resilience across a number of
other sectors including environmental management, management of
fresh water resources, health, education
and skills and job opportunities.
On the 30 September 2015 the United Nations (UN), announced the
entry into force of the SIDS DOCK Treaty,
giving legal recognition to the intergovernmental sustainable
energy and climate resilience organisation
established by Heads of State and Government of Small Island
Developing States (SIDS) in 2009, in order to
help finance climate change adaptation through the
transformation of their countries to low carbon economies.
1 E. Doyle, E. and J. Franks. 2015. Sargassum Fact Sheet. Gulf
and Caribbean Fisheries Institute.
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12 CONFIDENTIAL
The concept paper, “Toward the Development of a Caribbean
Regional Organic Waste Management Sub-
Sector”, of the 1st Caribbean Waste to Energy Technology Expo
& Conference gives a very good summary of
the problems faced by developing island states in the Caribbean
and how an emerging and effective waste
strategy could help alleviate against those issues2. There are a
number of other useful documents which detail
some of the work completed thus far.3,4
The management of fresh water resources is becoming a pressing
issue for many islands. Increases in
population, brought on by improved living standards and greater
economic activity, have resulted in greater
demand on existing fresh water resources. The consequence of
this has been increased contamination and
degradation of water bodies, both fresh water and marine, due to
poor waste water treatment strategies. Again,
governments are recognising waste water treatment as an
important issue but limited financial resources
makes implementing better collection and treatment systems very
difficult; not enough revenue is raised
through taxation to cover the capital expenditure. In 2013, it
was estimated that as much as 85% of the waste
water entering the Caribbean Sea was untreated and around 50% of
households across the region were not
linked to a formal and regulated sewer connection4. The end
result of the release of poorly controlled primary
treated and untreated sewage to the nearshore, is the inevitable
eutrophication of those receiving water bodies,
which contributes to the continuing build-up of algae on reefs
and on land, the contamination of ground water
reserves and surface water bodies.
4.2 Approach & objectives
In the big picture, an approach which seeks to treat energy,
waste and water resources as interlinked, would
be more likely to result in a well-planned, cost-effective and
efficient set of services, where wastes from one
process are used as feeds for another, where mass and energy
flows can be maximised and recycled to close
process loops, where possible. This preliminary feasibility
study will look at the potential contained within
biogenic wastes, sewage sludge and invasive Sargassum, for
treatment by anaerobic digestion (AD). This
process is described in more detail later in the report but the
main products from the process are renewable
energy in the form of biomethane and a material called
digestate, which generally tends to be used as a useful
replacement for chemical-based fertilisers, either whole or
separated into its liquid and solid components.
Figure 1 is a simple process flow diagram which shows the feed
materials for an AD treatment system, the
pre-treatment steps which might be required and the outputs.
Also included is an option for the treatment of
wastes more suitable to a thermal treatment technology, such as
gasification, though this option is not
considered in any detail in this study. A combination of
recycled wastes, AD for waste biomass (not including
woody material) and a thermal treatment technology for other
residual wastes not suitable for AD or recycling,
2 SIDSDOCK, January 2016, ‘Toward the development of a Caribbean
regional organic waste management sub-sector. available at:
http://sea.sidsdock.org/download/wte_expo_library/background_papers/REGIONAL-WASTE-MANAGEMENT-MEETING-CONCEPT-PAPER-REVISED-JAN-2016.pdf
3 Caribbean Renewable Energy Development Programme, GIZ, October
2013, ‘A Review of the Status of the Interconnection of Distributed
Renewables to the Grid in CARICOM Countries’. Available at:
http://www.credp.org/Data/CREDP-GIZ_Interconnection_Report_Final_Oct_2013.pdf
4 SIDSDOCK, May 2015, ‘Toward the development of a Caribbean
regional organic waste management sub-sector’. Available at:
http://sea.sidsdock.org/download/wte_expo_library/background_papers/01-14-16-DRAFT-NOT-FOR-CIRCULATION-DRAFT-REGIONAL-WASTE-MANAGEMENT-.pdf
http://sea.sidsdock.org/download/wte_expo_library/background_papers/REGIONAL-WASTE-MANAGEMENT-MEETING-CONCEPT-PAPER-REVISED-JAN-2016.pdfhttp://sea.sidsdock.org/download/wte_expo_library/background_papers/REGIONAL-WASTE-MANAGEMENT-MEETING-CONCEPT-PAPER-REVISED-JAN-2016.pdfhttp://www.credp.org/Data/CREDP-GIZ_Interconnection_Report_Final_Oct_2013.pdfhttp://www.credp.org/Data/CREDP-GIZ_Interconnection_Report_Final_Oct_2013.pdfhttp://sea.sidsdock.org/download/wte_expo_library/background_papers/01-14-16-DRAFT-NOT-FOR-CIRCULATION-DRAFT-REGIONAL-WASTE-MANAGEMENT-.pdfhttp://sea.sidsdock.org/download/wte_expo_library/background_papers/01-14-16-DRAFT-NOT-FOR-CIRCULATION-DRAFT-REGIONAL-WASTE-MANAGEMENT-.pdf
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13 CONFIDENTIAL
could provide a neat solution to an island’s waste management.
However, this would require significant
financial investment and a strategic approach to addressing
planning and regulation of integrated services.
This is possible and recent events, which have included multiple
agencies working in an interdisciplinary way,
indicate that the political will is gaining momentum.
Figure 1. Linear process flow diagram to illustrate the key
components of an approach centred on anaerobic digestion as
treatment
technology but also including an illustration of where/how
gasification might fit into the overall approach. The products from
gasification
are not detailed beyond syngas in this report.
Of the biomass feed materials listed in Figure 1, Sargassum
presents its own challenges. As with any intended
seaweed application there will be questions of supply regarding
constancy, regularity and quality. Businesses
hoping to make use of beached Sargassum will need to find ways
around these particular issues, in the same
way that businesses which harvest natural and farmed seaweeds
need to. There are a number of potential
commercial routes to exploitation, depending on the chemical
composition of the seaweed. Some seaweeds
lend themselves to certain applications and the application of
seaweed as an energy crop is again being
studied5 (after a lull of 20-30 years following some initial
studies). The SeaGas Project is looking at the financial
and practical viability, across the supply chain, of farming
Saccharina latissima for bioenergy production; there
is a large element of practical work studying the digestion
characteristics but also the very important step of
how best to preserve the Saccharina so that it doesn’t degrade
over time, once harvested. This work could
inform a similar approach to preserving Sargassum fluitans &
natans. There may be the possibility to derive
5 The SeaGas Project. IUK IB Catalyst funded for 2015-2018.
Centre for Process Innovation (lead partner), with SAMS, Queen’s
University Belfast, CEFAS, Eunomia and ADAS, on behalf of The Crown
Estate.
Process Schematic
Sargassum(Periodic)
Organic waste Fraction
Agriculture Wastes
WWT Biosolids
Sorting & segregating
Drying (open air) & Milling,
Ensiling
Shredding/maceration
Pasteurisation
Mechanical/physical pre-
treatment
ANAEROBICDIGESTION
Recyclates
BIOGAS/
DIGESTATE
CHP
Cooling Electricity
Grey Water Soil/Plant improver
(BIO)RESOURCE PRE-TREATMENT TREATMENT PRODUCTS
Gasification
Plastics, tyres, waste oils,
woody materials
Vehicle fuel
Residual waste
Syngas
Michelle Morrison
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14 CONFIDENTIAL
higher value end products from Sargassum but its use as a feed
for bioenergy would tie in well with the bigger
picture for energy and waste.
Anaerobic digestion is a biological process which runs
continuously, providing base load power, hence it
requires daily feeding. Washed up Sargassum we know would not
provide that constancy of supply. However,
the other biogenic materials suggested in Figure 1 are available
on a regular basis and could form the basis
of the feedstock for an AD process. All of these biogenic
materials have some calorific value i.e. they contain
a certain amount of energy which can be utilised to produce
power. This energy value is at present not routinely
recovered but lost in linear and open ended processes.
There is then a possible approach to managing both biogenic
wastes generated in a location and the invasive
Sargassum. The aim of this feasibility study is to investigate
the potential for establishing anaerobic digestion
as a waste treatment technology in St Lucia and Grenada, in
particular, and whether stranded Sargassum
could be fed into the AD treatment process. The objectives of
the study are as follows:
To take information from the public domain regarding waste
materials on St Lucia and Grenada and to
assess how much is available, what the energy content might be
and what proportion of renewable energy
could potentially be realised by implementing AD as a treatment
technology
To carry out some preliminary practical work to assess the
biochemical methane potential of Sargassum
fluitans which was washed up on a beach in St Lucia
To model a number of scenarios regarding the size of an AD
operation (based on tonnage throughput),
to assess their financial viability
To discuss the benefits and drawbacks of anaerobic digestion
against other treatment techniques, namely
thermal treatment (pyrolysis, gasification, incineration)
To highlight where there are data gaps which impede more
accurate analysis
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15 CONFIDENTIAL
5 Existing Information
Data existing in the public domain was collated by the Caribbean
Council (Project Lead) and included the
following items (Appendix 1 for the full data spreadsheet
prepared by the Caribbean Council, including
references to sources of information):
Energy –
o current demand and generation
o fuel import data including consumption and cost
o power plants – how many and size
Waste –
o Information on waste collection methods
o Waste type and annual tonnage
o Current waste disposal techniques
o Costs of waste disposal
o Recycling activities
o Waste water treatment
Policy regarding energy and waste management
Sargassum - unfortunately though not unexpectedly, there was no
information forthcoming on Sargassum
with regards to tonnages, temporal and spatial movements,
landing locations or periods of strandings.
There is also scant data on chemical composition of the species
of interest.
5.1 Energy
5.1.1 St. Lucia
There is a reasonable amount of information available regarding
energy generation, consumption and demand.
The headline figures are as follows:
Diesel is the main source of all power generation for St Lucia
and around 10.2% of St Lucia’s GDP is
spent on importing fuel. The cost of this is of the order of
US$130M per annum
Total energy imported and produced: 3061 BOE/day in 2012 (Ref
Appendix 1)
o Only 2% equivalent to 61 BOE/day from renewables
(combustion)
o The remaining 98% equivalent to 3000 BOE/day from imported
fossil fuel
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16 CONFIDENTIAL
Of that 3061 BOE/day, around 1468 BOE/day were lost during
distribution, generation and
transmission, which, at around US$55/barrel equates to
US$81k/day and approximately 2334MWh
power per day, lost.
The remaining 1592 BOE/day were utilised between transport needs
and electricity demand, at 41%
and 55%, respectively.
The energy generator is State-owned (LUCELEC) and controls and
operates two power stations on the island;
Union Power Station, which can provide up to 2.5MW of
diesel-fuel based power, if required; and Cul-de-Sac
Power Station at 86.2MW, which comprises: 3 units of 6-7 MW
(diesel-fuel-based); 4 units of 9.3 MW (diesel-
fuel-based) and; 3 units of 10.3 MW (diesel-fuel-based).
Electricity generation in 2013 was at 382.9 GWh, of which
LUCELEC used 4.8 GWh and 334.4 GWh were
used across commercial, residential and industrial applications.
The difference between generated and used
electricity was accounted for by 8% losses from the system for
that year. Figure 2 illustrates how electricity
generation increased over 23 years, from 1990 to 2013 but
appeared to plateau between 2010 and 2013.
Figure 2. Increasing electricity generation in St Lucia.
In 2010, the World Bank forecast an increase in required
electrical capacity from 95 MW in 2015 to 148 MW
in 2027, in order to cover the peak demand projected. If this is
to be met in any sustainable way, there will
need to be a mixed tool box of energy generating technologies.
Diversification of the energy supply will help
build in resilience to both fluctuations in the oil market and
some of the effects of climate change.
The most recent figures for 2015 show that, of the 88.4 MW
available capacity, demand peaked at 59 MW, a
0.2% increase in peak demand over 2014. Total electricity sales
were 337.5 GWh for 2015, of which 57% was
to the commercial sector (including hotels) and 34% to domestic
users. The number of domestic consumers
at year end was 59,766. That equates to an average annual
consumption of 1.94 MWh per domestic consumer
(household). In contrast the commercial average annual
consumption was at 27 MWh per business consumer.
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17 CONFIDENTIAL
5.1.2 Grenada
There is a reasonable amount of information available regarding
energy generation, consumption and demand.
The headline figures are as follows:
The electricity price in Grenada is among the highest in the
Caribbean, costing $0.37 USD/kWh. 55%
of this comes from the costs associated with imported fossil
fuel, including LNG.
Diesel and LNG are the main sources of all power generation for
Grenada. 6% of Grenada’s GDP is
spent on importing fuel. The cost of this is of the order of
US$130M per annum.
Total energy imported and produced: 2785 BOE/day in 2011 (Ref
Appendix 1)
o 7% equivalent to 185 BOE/day from renewables (combustible
renewable, waste and solar
energy)
o The remaining 93% equivalent to 3000 BOE/day from imported
fossil fuel
Of that 2785 BOE/day, around 774 BOE/day were lost during
distribution, generation and
transmission, which, at around US$99.8/barrel equates to
US$77.2k/day and approximately
1230MWh power per day, lost.
The remaining 2011 BOE/day were utilised between transport needs
and electricity demand, at 41%
and 58%, respectively.
The energy generator is GRENLEC. It is a private-public entity,
with the state holding a 21% stake, and US-
based WRB Holding serving as the majority shareholder. GRENLEC
holds exclusive license of generation,
transmission, distribution, and sale of electricity until 2073,
though it does not have an exclusive right on small-
scale self-generated electricity. GRENLEC controls and operates
a total of five diesel-fuel-based power
stations, namely:
Queen’s Park: 25.2 MW capacity
Grand Anse: 18 MW capacity
St. George’s University: 2.8 MW capacity
Carriacou: 3.17 MW capacity
Petite Martinique: 0.483 MW capacity
Electricity generation in 2015 was at 204 GWh. Figures from 2013
indicate that GRENLEC used 6.1 GWh of
the total capacity, while 175.8 GWh was used across 5,961
commercial, 37,916 residential and 35 industrial
customers. The difference between generated and used electricity
was accounted for by 7.5% losses from the
system for that year, as well as some spare capacity.
While peak energy demand has declined in recent years in the
wake of the global financial crisis, energy
demand is expected to double by 2028. To meet this demand,
Grenada will need to diversify its energy mix.
Diversification of the energy supply will help build in
resilience to both fluctuations in the oil market and some
of the effects of climate change.
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18 CONFIDENTIAL
Figure 3. Electricity demand in Grenada.
5.2 Waste resources
5.2.1 St. Lucia
Residential, commercial, and industrial waste collection
services are privatized.
St Lucia Solid Waste Management Authority (SLSWMA) is
responsible for coordinating and integrating
systems for the collection, treatment and disposal of the
island’s solid waste, from both household and
government establishments (i.e schools, hospitals, health
centres, prisons, and government offices). The
SLSWMA sub-contracts out the collection of waste to five
contractors, who each work in specific waste
collection regions, as shown in Figure 3.
Figure 4. Waste collection areas of St Lucia colour-coded to
show the five contractors’ working areas.
0
20
40
60
80
100
120
140
160
180
200
2002 2004 2006 2008 2010 2012 2014
Electricity Demand and Peak Demand in Grenada 2003-2013
Electricity Demand (GWh) Peak Demand (MWh)
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19 CONFIDENTIAL
SLSWMA operates two solid waste disposal facilities; Deglos
Sanitary Landfill in the north of St Lucia and
Vieux-Fort Waste Management Facility, in the south.
The Deglos Sanitary Landfill received 53,500 tons (48,534
tonnes) of solid waste in the year 2013-2014 (Figure
4). It opened in March 2003 and was designed to be operational
over a 25 year period, according to current
waste management practices. The site occupies around 9.5
hectares and receives an average of 4,000 tons
(3,629 tonnes) per month. This facility also has a leachate
collection and treatment system.
Figure 5 St Lucia, Deglos Sanitary Landfill (North).
BOX 1
A “Sanitary Landfill” (SL) is understood to mean the spacing,
placement, and compacting of waste on an
impermeable bed and its daily covering with a layer of earth or
another inert material in order to control the
proliferation of vectors, gas emissions and leaching so as to
avoid environmental contamination and protect
people’s health. A SL is the product of an engineering project,
with controlled access, weighing, and no
informal recyclers on site.
Source: IDB, 2010.
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20 CONFIDENTIAL
Figure 6 Vieux-Fort Waste Management Facility (South), St
Lucia.
The Vieux-Fort facility occupies 7.4 hectares and received
21,000 tons (19,050 tonnes) over the same period
(Figure 5). It does not have a leachate collection and treatment
system, unlike Deglos, and is referred to as a
Controlled Dumpsite.
There are no waste transfer stations on the island, so there is
little opportunity to sort the waste before it arrives
at the landfill sites. Instead of picking lines at a waste
transfer station, SLSWMA has formalised arrangements
with waste pickers at the Vieux Fort Solid Waste Management
Facility. The waste pickers recover material
such as ferrous metal, scrap wire, and wood6. There has been an
increase in recycling activity over the last
few years with most recycled materials going for export; there
is only limited recycling of materials for reuse
on the island. Recycled materials comprise metals, plastics,
paper, card, electronics and batteries.
There is currently no separation of organic matter from the
municipal or commercial mixed waste fraction for
St Lucia, neither at source nor through waste separation
technologies. Mixed municipal and commercial waste
is delivered to landfill and buried, resulting in acidic
leachate from the degradation of the organic material,
6 Saint Lucia Waste Management Authority, March 2015, ‘Annual
Report’. Available at:
http://www.sluswma.org/images/pdf/Annual%20Report%202014-2015.pdf
BOX 2
Controlled dumpsites refer to open air dumps that are controlled
to some extent or to sanitary landfills that
have been gradually abandoned over the years.
Source: IDB, 2010.
http://www.sluswma.org/images/pdf/Annual%20Report%202014-2015.pdf
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21 CONFIDENTIAL
which is collected and treated at Deglos, and release of methane
to the atmosphere. As a consequence, there
appears to be no data available on food waste in particular or
the percentage fraction of organic material
contained within the mixed municipal and commercial waste.
Records are kept on tonnages of waste arisings
and those which might have an organic element are given in Table
1 (the complete table of waste arisings is
given in Appendix 2).
Table 1. Waste tonnages of material which might contain organic
matter.
Waste
Category
2011/12 2012/13 2013/14 2014/15
Beach cleaning 249.6 270.43 400.7 407
Commercial 14,857 14,191 10,582 9,846
Condemned
foods 321.7 403.7 1,170 268
Farm waste - - 605 571
Green waste 4,273 7,451 6,647 7,065
Hotel waste - - 6,082 6,398
Residential/
institutional 34,480 31,952 33,903 32,929
TOTAL (tons) 54,181 54,268 59,390 57,484
TOTAL (tonnes) 49,152 49,231 53,878 52,148
There is some data on the organic waste fraction from Grenada7,
which we can use as a proxy for St Lucia
given the similarity in population size and GDP, though St Lucia
has a larger tourism sector. The study on
Grenada found the organic fraction accounted for around 27% of
the total municipal waste arisings. Another
source (SLSWMA, 2008. No further detail provided) put the
organic waste fraction as high as 45% of the total
annual waste collection for St Lucia. Taking a range of
percentage content for the organic fraction, the tonnage
of organic matter can be estimated; if the total municipal waste
fraction is taken to be 52,148 tonnes per annum,
the tonnage of organic matter could lie between 14,000 tpa and
23,500 tpa for 2014/15. The Food & Agricultural
Organisation (FAO) publishes figures on its website regarding
food wastage. Figure 6 is taken from the FAO
website and shows how the mass of waste per capita varies across
major population groups.
Figure 7. FAO data on food waste generated per capita of
population.
7 German Corporation for International Cooperation (GIZ), June
2015, ‘Regional waste-to-energy collaborative’. Available at:
http://irena.org/EventDocs/T2%20BW2E%2004%20Andreas%20Taeuber%2020150623%20long%20version.pdf
http://irena.org/EventDocs/T2%20BW2E%2004%20Andreas%20Taeuber%2020150623%20long%20version.pdf
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22 CONFIDENTIAL
The Caribbean islands designated as developing states are
possibly similar in per capita food waste to South
& Southeast Asia. Grenada generates around 27% organic waste
as a percentage of the total8. If we assume
that a third of the total waste generated in St Lucia is
biogenic, then around 104 kg/person/year of organic
waste would be generated. If we consider a third of the total
given in Table 1, the per capita figure drops to 84
kg/person/year of organic waste. In the EU the mean per capita
figure was around 179 kg/person/year of food
waste9 in 2010, which is significantly less than the value in
Figure 7, which may be more recent. The differences
in data highlight the inherent problems with extrapolating data
across large populations where there is a lot of
variability within any one area. A more accurate and reliable
approach would be to conduct on-the-ground
surveys of waste arisings, documenting the data over an extended
period. In the UK there is the Waste Data
Flow database, which is completed by council collection services
and a fairly accurate reflection of waste
arisings in the municipal and some commercial sectors, where
councils collect the waste. There are other
waste arisings which do not fall under council authority and
many of these are picked up by the UK Environment
Agency, through waste licensing regulations and permits.
For the purpose of the modelling in this study, the organic
waste per capita has been assumed to lie between
84 and 104 kg/person/year. Taking these per capita values, the
potential tonnage of organic matter lies
between 15,700 and 19,500 tpa. This compares fairly well with
the earlier estimates using percentage OM of
the MSW fraction (14,000 and 23,500 tpa).
It has also been assumed that the organic fraction is 100% food
waste. It is assumed that there are currently
no markets for organic wastes.
5.2.2 Grenada
Solid Waste Management in Grenada is the responsibility of the
Grenada Solid Waste Management Authority
(GSWMA), which is part of the Ministry of Health. This
organisation is funded by levies on both imported
products and household electricity bills. The latter levy, of
10%, applies where household electricity
consumption exceeds 100kWh. Although this levy is currently
sufficient for the management and disposal of
solid waste, it will not provide sufficient funds to facilitate
the developments needed to implement a waste-to-
energy programme.
Solid waste collection is outsourced to private firms who do
charge for waste collection services, although
GSWMA does not charge fees for waste drop-off and disposal in
order to avoid incentivising illegal waste
disposal.
8 SIDSDOCK, ‘Toward the development of a Caribbean regional
organic waste management sub-sector’, May 2015. Available at:
http://sea.sidsdock.org/download/wte_expo_library/background_papers/01-14-16-DRAFT-NOT-FOR-CIRCULATION-DRAFT-REGIONAL-WASTE-MANAGEMENT-.pdf
9 European Commission, 2010, ‘Preparatory Study on Food Waste
across the EU 27’. Available at:
http://ec.europa.eu/environment/eussd/pdf/bio_foodwaste_report.pdf
http://sea.sidsdock.org/download/wte_expo_library/background_papers/01-14-16-DRAFT-NOT-FOR-CIRCULATION-DRAFT-REGIONAL-WASTE-MANAGEMENT-.pdfhttp://sea.sidsdock.org/download/wte_expo_library/background_papers/01-14-16-DRAFT-NOT-FOR-CIRCULATION-DRAFT-REGIONAL-WASTE-MANAGEMENT-.pdfhttp://ec.europa.eu/environment/eussd/pdf/bio_foodwaste_report.pdf
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23 CONFIDENTIAL
Waste collection in Grenada is divided geographically into five
separate zones:10
Zone 1: South and north of St George’s and St George’s Town
Zone 2: St David and South St Andrew
Zone 3: St Andrew and St Patrick East
Zone 4: St John, St Mark and St Patrick’s West
Zone 5: Carriacou and Petite Martinique
There is currently one landfill site on Grenada at Perseverance,
but this has reached capacity11. GSWMA and
the Caribbean Development Bank (CDB) are currently working
together to rehabilitate disused landfill sites,
although it is estimated that these new landfill cells would
reach their capacity limits within 7 years without a
reduction in overall quantity of waste production. GSWMA also
operates a further landfill site at Dumfries on
the island of Carriacou. The precise amount of waste received at
Carriacou is not known, but is estimated to
be less than 2,000 tonnes per year. Neither of these landfill
sites has been technically engineered or
constructed using established industry techniques.12
At present there are very few procedures or facilities in place
to enable the sorting and separation of waste. In
2013, per-capita waste in Grenada amounted to 1.02kg/day. By
2014, this had increased to 1.08kg/day. The
three largest contributors to overall waste composition in 2009
were as follows:13
Organic waste: 27.1%
Site cleaning waste: 21.3%
Plastics: 16.4%
However major stakeholders surveyed by the German Corporation
for International Cooperation (GIZ)
predicted that the quantity of plastic in circulation in Grenada
was likely to have increased alongside the growth
in formal and informal start-up food production businesses in
the aftermath of 2004’s hurricane Ivan, which
generally use plastic packaging.
Overall, there is little sorting and separation of waste
products in Grenada, which results in a high amount of
litter.14 Salvaging of recyclable products in Grenada
constitutes a significant source of informal employment,
whereby glass bottles are taken from cities and landfill sites,
and exchanged for a refund of XCD0.25 per
item.15
10 German Corporation for International Cooperation (GIZ), 2016,
‘Reducing the input of plastic litter into the ocean around
Grenada’. Available at:
https://www.giz.de/en/downloads/giz2016-marine-litter-instruments-grenada.pdf
11 Ibid. p.9 12 Ibid. p.11 13 Ibid. p. 11 14 Ibid. p.12 15 Ibid.
p.11
https://www.giz.de/en/downloads/giz2016-marine-litter-instruments-grenada.pdf
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24 CONFIDENTIAL
5.3 Water treatment
5.3.1 St. Lucia
In St Lucia the Water and Sewerage Company (WASCO) is mandated
by law to develop and manage the
water supply and sewerage services in St Lucia. Only 24% of the
public receives a 24-hour supply of potable
water, the majority of residents and establishments in St Lucia
utilize individual on-site systems (pit latrines,
septic tanks and soak aways) for sewage treatment and disposal.
There are two sewerage systems in St
Lucia16:
Castries
o Primary sewage collection and disposal system in the city of
Castries, which serves around
15% of the Castries population, including the business
district.
Rodney Bay
o Collection, treatment and disposal of sewage waste, using an
Advanced Integrated Aeration
Pond system, serving around 13% of the residential population of
St Lucia and hotels in the
north of the island
o Treated effluent from the system is discharged via an earth
drain to a ravine which leads to
the ocean on the East Coast of St Lucia
o It currently operates under-capacity
The importance of effective waste water treatment cannot be
overstated. There is recognition that incomplete
coverage of effective waste water treatment is causing
environmental damage and poses a human health risk.
Illnesses which can be contracted through bathing in
contaminated water or through consumption of
contaminated shellfish are gastro-enteritis, dermatitis, viral
hepatitis, wound infections, cholera, typhoid fever,
and dysentery. In St Lucia there are still communities with no
effective waste water treatment, where raw
sewage is discharged directly into receiving water courses,
eventually draining out to sea. This has resulted in
nearshore waters, off certain parts of the St Lucian coastline
being deemed unfit for human bathing, due to
elevated levels of faecal coliforms. The primary effect can be
severe ill health but an important secondary
effect is the negative impact this has on the tourism industry.
A report from January 201610 addresses these
issues for a specific community in St Lucia. The WWT options for
Canaries is discussed in the report; there
are a range of topographical and areal constraints, which make
options for treatment more challenging.
As with the organic solid waste fraction, the data on tonnages
of WWT Biosolids or primary sewage sludge
and septage is not complete. Therefore, another estimation has
had to be made for the purpose of modelling.
The Canaries report states that the waste effluent flow is in
the region of 95 L/person/day; another source
suggests an effluent rate of 227 L/person/day – this high value
includes hotels and commercial uses, which
has been estimated to generate up to 10x more effluent per head
than the residents of the island. The latter
16 Island Water Technologies. ‘Assessment Of Wastewater
Infrastructure And Go-Forward Options For The Village Of Canaries,
St. Lucia’, January 2016. Available at:
http://islandwatertech.com/wp-content/uploads/2016/07/Canaries-Wastewater-Report-2016.pdf
http://islandwatertech.com/wp-content/uploads/2016/07/Canaries-Wastewater-Report-2016.pdf
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25 CONFIDENTIAL
rate is also extrapolated across the Caribbean region17. These
estimates have been used to calculate a
possible range for tonnage of sewage. The population of St Lucia
is 187214 (as of 13/11/2016), thereby
delivering an annual tonnage of sewage effluent between 17,800
tonnes and 42,500 tonnes.
5.3.2 Grenada
The UNEP Caribbean Environment Programme describes regional
sanitation in the Caribbean as largely
inadequate, with poor quality services and insufficient access.
This has the potential to impact extremely
negatively on public health.18 Grenada has historically suffered
due to its poor sanitation system: in the 1980s,
many shallow reefs around Grenada were degraded and became
overgrown with algae. This is believed to
have arisen as a result of a combination of sewage,
agro-chemical pollution, and sedimentation caused by
coastal development.19
The information below is adapted from pages 30-34 of
Waste-to-Energy Scoping Study for Grenada, a report
published in March 2015 by Renewable Energy and Energy
Efficiency Technical Assistance (REETA) and
German Corporation for International Cooperation (GIZ).20
This report highlighted several obstacles facing researchers
investigating the scale and functionality of the
current system. As the most recent comprehensive study into
wastewater management in Grenada dates from
1999 (Wastewater Management Project, 1998-1999), there is
limited up-to-date information available. Some
information nonetheless remains unchanged since the publication
of that report.
The National Water and Sewerage Authority (NAWASA) has
responsibility for maintaining national water
supply and overseeing domestic wastewater management. Grenada
does not have an officially legalised
effluent standard, but instead draws on and partially applies
standards outlined in a 1998 document from
Trinidad & Tobago, relating to industrial effluent
standards.
As is the case in St Lucia, there are two sewerage systems in
Grenada.
1) St Georges
o Sewered system with fall out pipe at the Stadium Bridge
o Fall out point: approximately 500m offshore
o Average flow: 130.000 gal/day (2013)
2) Grand Anse
o Sewered system with a fall out pipe at Point Salines
17 Caribbean Environmental Health Institute for UNEP/CAR-RCU,
2009, ‘Financial Assessment for Wastewater Treatment and Disposal
(WWTD) in the Caribbean’. Available here. 18 United Nations
Environment Programme (The Caribbean Environment Programme),
Undated, ‘Wastewater, Sewage and Sanitation’. Available at:
http://www.cep.unep.org/publications-and-resources/marine-and-coastal-issues-links/wastewater-sewage-and-sanitation
19 Ibid, citing Smith et al, 2000 20 German Corporation for
International Cooperation (GIZ), and Renewable Energy and Energy
Efficiency Technical Assistance (REETA), March 2015,
‘Waste-to-Energy Scoping Study for Grenada’. Summary available at:
http://sea.sidsdock.org/download/wte_expo_library/Waste-to-Energy_Potential_Grenada_150316.pdf
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwj584PX0-TQAhUFymMKHebLD48QFggdMAA&url=http%3A%2F%2Fwww.cep.unep.org%2Fcontent%2Fgef-crew-caribbean-regional-fund-for-wastewater-management-unep-iadb-gef-partnership-project%2Fmicrosoft-powerpoint-financial-assessment-ww-treatment.pdf%2Fat_download%2Ffile&usg=AFQjCNGEva3urt2LGU5TP3jQ46oIgirMFg&sig2=6o96QK7LUNuVK-YyrrHe0A&cad=rjahttp://www.cep.unep.org/publications-and-resources/marine-and-coastal-issues-links/wastewater-sewage-and-sanitationhttp://sea.sidsdock.org/download/wte_expo_library/Waste-to-Energy_Potential_Grenada_150316.pdf
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26 CONFIDENTIAL
o Fall out point: Approximately 300m off shore
o Average flow: 660.000 gal/day (2013)
o This system receives a lot of wastewater generated in hotels
(which tends to be less polluted
than domestic wastewater.) This effect may, however, be offset
by the fact that there are a
number of industries and a brewery also connected to the
system.
These two systems meet the needs of approximately 45% of
households in Grenada. The other 55% of the
country depend on pit latrines and cesspit systems. In Grenada,
most domestic septic tanks only receive waste
from the toilet flushing system: other liquid waste, including
from showers and kitchen usage, is diverted to
‘soakaways’ or gardens. NAWASA oversees and provides licences
for the operations of tanker companies,
who empty these pit latrines/ cesspit systems into either the St
Georges or Grand Anse sewage system. These
septic tanks and pit latrines are emptied, on average, every 3-5
years. NAWASA does not monitor the amount
of septage (solid waste) which is collected by these tankers and
subsequently released into the national
sewage system.
Wastewater in Grenada is released into the sea with little to no
treatment. The fall out point at Point Salines is
problematic, as it releases much of the effluent it carries much
closer to the shore than its intended endpoint
(located 300m out to sea), as it has previously sustained
significant storm damage.
In theory, wastewater emitted into the ocean receives ‘marine
treatment’: it is released at a sufficient depth to
dilute and oxidise it as it moves towards the water surface. In
practice, however, increased organic load and
changing currents have combined to make this wastewater damaging
for marine environments. It is generally
accepted that current fall out points are in need of extension
in order to protect marine wildlife and tourist
attractions, and that Grenada’s wastewater system as a whole is
in need of significant modernisation and
improvement. However, high initial start-up costs, high running
costs and a shortage of space for a full-scale
waste treatment plant are all cited as reasons for apparent
national reluctance to make the necessary changes.
5.4 Sargassum
There are many applications for seaweed and the East and
South-East Asians have been exploiting seaweeds,
at a vast commercial scale for over a century, mainly for food
production. Data from the FAO indicates that, in
2014 out of a total global production of 27.3M tonnes (wet
weight) of seaweed, approximately 26.7M tonnes
came from the Far East, with 26M tonnes produced between China
and Indonesia alone, almost all of which
was in a marine setting. The only producer in Western Europe was
Ireland with 100 tonnes. Norway harvests
the most seaweed in Europe at around 155k tonnes, but this is
all from natural stocks.
The value of this global market stood at just over US$5.5B per
annum in 201421 and has been estimated at
US$11B in 20163. In 2014, US$5B of this was used for human
consumption, mainly across Asia; the remainder
of the market was generated through the extractions of compounds
such as the phycocolloids (alginates, agars
21 Food and Agriculture Organisation of the United Nations,
2014, ‘Fishery and Aquaculture Statistics’. Available at:
http://www.fao.org/3/a-i5716t.pdf
http://www.fao.org/3/a-i5716t.pdf
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27 CONFIDENTIAL
and carrageenens), some specific compounds with medical
applications, cosmetics and such uses as animal
feed in agriculture. According to one market analyst22, the
market is predicted to rise sharply over the next 5
years, up to US$17B. Hence, the market is predicting a strong
and growing demand for seaweed products.
How does this relate to invasive inundations of seaweed, which
are uncontrolled, irregular and difficult to
process? It demonstrates that there are markets at a commercial
scale for certain seaweeds and that there
may be a similar potential for the Sargassum of the
Caribbean.
The available data on Sargassum and in particular the species
which dominate across the Caribbean, S.
fluitans and S. natans, is very sparse. Information in the
literature focuses on the ecological aspects of these
holopelagic seaweeds, trying to understand the origins and
movements of the mats/rafts of Sargassum and
approaches that have been taken to manage the seaweed once it
comes into conflict with human activities.
There are a number of approaches to managing Sargassum which can
be implemented. Most methods at this
time are concerned with removal and disposal, composting and
allowing the material to degrade naturally on
the beach (a good approach where the beach is off the tourist
trail). These methods are becoming more
sustainable as the negative impacts of standard techniques such
as beach clearance by heavy moving
vehicles, have become clear. A recent publication23 out of
collaborative work by CERMES, CAR-SPAW-RAC
and GCFI provides some insight and advice on successful and
sustainable Sargassum management. There
are some small private and commercial enterprises which use
applications of Sargassum to land as a fertiliser
or as a horticultural plant stimulant e.g. Algas Organics and
their Sargassum extract. This small company has
shown some very positive results and their Sargassum extract is
being marketed locally in St. Lucia. The
potential of Sargassum natans and fluitans is only now being
investigated to assess its potential as a revenue
stream.
Chemical composition data is sparse for Sargassum natans &
fluitans but the following four tables (tables 2 –
5) represent some of the work done and published.
Table 2. Ultimate analysis of Sargassum species
Species C H O N Ash Source Reference
1Sargassum natans 25.9 5.57 24.18 3.58 nd Guangdong,
China Shuang W et al, 2013
2Sargassum muticum 33.36 4.85 24.01 5.46 31.85 Kent,UK Milledge
&
Harvey, 2016
3Sargassum fluitans 34.29 5.27 54.53 1.15 23.55 St Lucia,
Caribbean CPI, 2016
Sargassum fluitans nd nd nd nd 19 BVI,
Caribbean CEVA, 2016
1Sargassum was dried from fresh sampling. 2Sargassum was
processed from fresh frozen samples 3Sargassum used was collected
from a beach in St Lucia. It was around 2 months old and dried
through exposure on the beach. nd = not determined
22 Markets and Markets, undated, ‘Commercial Seaweeds Market
worth 17.59 Billion USD by 2021’. Available at:
http://www.marketsandmarkets.com/PressReleases/commercial-seaweed.asp
23 Ecomar Belize, 2016, ‘Sargassum Management Brief’. Available at:
http://www.ecomarbelize.org/uploads/9/6/7/0/9670208/sargassum_management_brief__-__cermes_-_august_24_2016_final[2]_copy.pdf
http://www.marketsandmarkets.com/PressReleases/commercial-seaweed.asphttp://www.ecomarbelize.org/uploads/9/6/7/0/9670208/sargassum_management_brief__-__cermes_-_august_24_2016_final%5b2%5d_copy.pdfhttp://www.ecomarbelize.org/uploads/9/6/7/0/9670208/sargassum_management_brief__-__cermes_-_august_24_2016_final%5b2%5d_copy.pdf
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Table 3. Carbohydrate content of Sargassum species
Species Mannitol Laminarin Fucans Glucose Total
sugars Alginic
acid Source Reference
Sargassum muticum
7.7 0.3 8 2.2 18.2 16.7 Isle of Wight
Gorham & Lewey, 1984
Ascophyllum 8.886 13.25 5.956 nd nd 17.18 Not
provided
Faulkner, Ocean Harvest
Sargassum fluitans
10.245 12.6 6.19 nd nd 15.55 BVI,
Caribbean
Faulkner, Ocean Harvest
nd = not determined
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6 Anaerobic Digestion
6.1 Biogas production
Anaerobic digestion is the breakdown of complex organic matter
such as proteins, carbohydrates and lipids
(fats) into smaller organic molecules, eventually resulting in
the production of biogas. This process of
degradation takes place in the absence of oxygen i.e.
anaerobically and is facilitated by a complex population
of bacteria and archaea. The conversion of complex organic
matter into biogas is a relatively slow process
compared with aerobic digestion (composting) but the result is a
gaseous product which comprises around
60% (50 – 70% range) methane and 40% (30 – 50% range) carbon
dioxide and also a digestate, which can
be used as an effective fertiliser or plant stimulant. The
biogas generated has an energy value due to the
methane content and can be passed through various boilers and
engines to produce electricity and or heat.
Generally, 1m3 of biogas has a calorific value of around 22 MJ
m-3 (6kWh), which can be upgraded by scrubbing
the gas to remove the CO2 and other impurities to produce
biomethane, which has a calorific value of 36 MJ
m-3 (10kWh). Therefore, by knowing what the biogas and methane
yields are for a particular feedstock (or
blend of feeds), it is possible to then calculate how much
energy could be produced. In reality, the maximum
potential is never reached for a number of reasons:
Efficiency of the AD conversion process is not 100%
The efficiency of a CHP engine to convert methane to electricity
is around 35 – 40%. Quite often the 50%
heat produced through CHP is not utilised. There is the
potential to make use of this heat either for heating
space or cooling through refrigeration.
The efficiency of a boiler to produce heat is around 85%
There are other small process losses from the system, which can
amount to as much as 15%
In light of these process efficiencies and losses, it becomes
very important to try to optimize the AD process
to produce the best possible methane yield. Process optimization
involves studying the plant data generated
over a period, making adjustments to operating conditions (as
suggested by the data) and possibly introducing
further technology at the front end to help release more of the
feed’s active components. However, before
optimization there is the important step of achieving a steady
state of operation.
In the recent past there has been a failure to understand the
sensitivity of AD. Not all feeds are equal, in fact
feed types vary enormously in their chemical composition and
this variability can prove to be quite a challenge
for AD operators. The microbial population in any AD plant is
sensitive to changes in chemical composition
e.g. salt content or fat content, pH and temperature. Small but
significant changes can shock the system and
cause it to fail and there have been many instances of this in
the UK over the last 20 years. Ideally, once
established, with a reasonably consistent feedstock, any AD
plant should operate at a steady state, producing
fairly constant and consistent biomethane yields. Hence, the
importance of a stable feedstock cannot be
underestimated.
Biogas yields are governed by a number of factors; the type of
organic matter used to feed the digestion
process; the operating conditions of the AD plant, in particular
the temperature, pH, the amount of time the
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materials spends in the digester (retention time), the amount of
bioavailable organic matter loaded into the
digester per day (organic loading rate) and whether any nutrient
amendments are required; the requirement
or desirability of any pre-treatment technology to treat the
feed before it reaches the digester. Getting all these
elements right so that the best yields can be realised is an
important and at times lengthy process.
6.2 Applications & Benefits
AD technology has been used for decades, from the first AD plant
built in a leper colony in India in 1859 and
the early Victorian waste water treatment systems in the UK for
treating sewage sludge, first established in
1895, to a broader application today which includes the use of
other biomass wastes and also purpose-grown
energy crops, such as maize, sugar beets and grass silage to
produce biogas. The rate of uptake of this
technology has been variable across continents and countries but
the technology is now considered to be
proven and well established.
AD benefits from a number of attributes which compare favourably
with other waste treatment solutions. In St
Lucia and other Caribbean states, thermal treatment is being
considered for the MSW waste arisings. Thermal
treatment comprises incineration, pyrolysis and gasification.
The benefits of AD can be summarised as follows:
Well suited to wet feedstocks – a ‘wet’ AD system generally
handles feed materials with ≤ 15% total solids
(TS), whereas a ‘dry’ AD system can handle TS content between 15
% and 40%. No drying of feed is
required for AD, which saves on operating costs.
AD makes use of biological processes to break down organic
matter and so does not require a large
energy input. Generally, the process itself can generate more
than enough energy to be able to run itself
by taking off the small parasitic load from the power generated
through the engine.
AD can be applied at a range of scales, from micro-digestion
(< 10kW) for individual households, small
scale (10 – 250kW) for small communities or businesses, to
medium scale (250 – 1MW) for larger
business, towns and finally larger scale (>1MW) for
municipal, centralised applications. The economic
viability at this range of scales is variable and generally
harder to make money on for the smaller scale
operations. However, making a quick return may not always be the
driving force behind a project. More
importantly might be delivering environmental improvement,
improving the health of the community,
reducing waste disposal costs, off-setting expensive and
volatile fossil fuel imports and becoming more
resilient as a community; a slower, lower return on investment
might be seen as acceptable under these
drivers.
O&M costs are generally much lower than any of the thermal
treatment options, as is the initial investment
on an AD plant of similar capacity. The difference in capex is
an order of magnitude, a few US$M for AD
compared with multiples of US$10M for thermal treatment. Thermal
treatment only becomes financially
viable at large scale.
Easier process control, with no requirement for high
temperatures, pressures or sterility. ‘Ease’ of process
control, should not be equated with ‘no control’; an AD system
can be shocked and fail if the composition
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of the influent feed is not adequately managed. Inconsistent and
variable feed will upset the balance of
microbes within the system and cause the production of biogas to
change and the quality (%CH4) to
change. This could directly impact power generation and
financial return.
AD technology could address current problems with sewage
treatment as it is possible to treat raw sewage
and sewage which has undergone some degree of waste water
treatment (primary and or secondary
sludge). This may form part of a water treatment and recycling
solution for more remote communities.
Community waste (food, sewage, agricultural) could be treated
through a small AD plant – there are some
very nice solutions on the market for small and micro systems.
The resulting digestate could be dewatered
either through mechanical/physical separation or more passively
over a longer period of time. There are
systems which will treat the sewage first, separating the liquid
and solids; the liquids could pass through
a passive water treatment system based on bioreactors with
plants; the solids could be fed into an AD
plant. For small communities, there could be a number of options
for combining waste water treatment
with energy generation.
Thermal treatment is being considered as a solution for waste
management and energy provision. This
technology definitely has a place for treating certain types of
waste, which cannot be readily disposed of
via other means, such as waste wood, discarded tyres, used
engine oil and the residual municipal waste
fraction. However, this technology is not the ideal treatment
option for wet biomass wastes. Biogenic
wastes not only have an energy value, they also contain macro
and micronutrients, which pass through
an AD process almost unchanged; these useful components would be
lost through thermal treatment.
Thermal treatment is an expensive treatment option, which
provides a return on investment when
implemented either at large scale or supported by generous
tariffs and gate fees for waste. Capex costs
are much greater than for AD; 40,000 tpa incineration plant, can
cost around US$40M24, compared with
US$4+M for a 30,000 tpa AD plant (this study).
Incineration is straight forward combustion with excess oxygen,
at high temperature, generating CO2 and
water as gases (harmful other components are scrubbed out).
Gasification is the sub-stoichiometric partial
combustion of waste to produce syngas – a mixture of H2, CO and
CH4. Part of the reason why gasification
requires greater financial intervention and incentives to give a
positive return is that syngas has a much
lower calorific value than biogas from AD; syngas values tend
between 4 – 10 MJ/Nm3, compared with
biomethane at 38 MJ/Nm3 (biogas at 22 MJ/Nm3).
6.3 Planning and Permitting for AD
In the UK, there are regulations in place which govern where
plants can be located or rather, where they cannot
be located. There are also regulations on how to operate the
plant to protect both human health and the
environment. All waste operators have to apply for and fulfil
the conditions of an Environmental Permit or, for
very small operations, an Environmental Exemption. There are
annual charges associated with these permits,
which contribute to the costs of administering and enforcing the
regulations.
24 Waste to Energy International, 14 September 2015, ‘Cost of
incineration plant’. Available at:
https://wteinternational.com/cost-of-incineration-plant/
https://wteinternational.com/cost-of-incineration-plant/https://wteinternational.com/cost-of-incineration-plant/
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An application for planning consent, in the UK, addresses
particular issues by way of an Environmental Impact
Assessment (EIA). An EIA will consider the following elements
and make a judgement, based on knowledge
and evidence, on the following aspects of the proposed
development;
Any planning policies which support the development and any
policy documents relating to renewable
energy, climate change, greenhouse gas emissions etc.
The waste type and tonnage throughput
The footprint of the intended development, its location and the
boundary of the parcel of land in which it
would sit and in which any operations connected with the
development, would take place
How far away would be the nearest residents, water extraction
boreholes, water courses, any sensitive
land uses (sites of special scientific interest etc)
What the impacts on the local community would be from traffic
(waste trucks), odour (from the untreated
waste), noise (traffic and any waste moving vehicles), pests
(requirement for proper control of wastes),
and would there be a loss of amenity value, for instance, would
the development involve taking over a
park, which is used for recreation? The destination of the
digestate would also be discussed as would the
proposed use of the energy liberated from the process.
Some of these aspects might be applicable to a development in St
Lucia and Grenada. The planning stage
provides the community with the opportunity to view the plans
and ask questions of the developer. It also
provides an opportunity to register support or rejection of the
proposal. Hence, in the UK, the planning process
is an important time for trying to get the community on board,
answering their questions and concerns so that
they have the facts of the proposal.
Environmental Permitting is concerned with the details of
operation and regulates how a plant is run, what
records are maintained, controls on waste, air quality, health
and safety. There is guidance to help operators
comply with the conditions of their permits. To ensure that new
operations do not result in potentially harmful
activities to either humans or the environment, some measure of
regulation and control may need to be devised
for the developing island states.
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7 Biochemical methane potential
7.1 Introduction
A biochemical methane potential assessment is a methodology
which is used to determine the maximum
methane yields potentially achievable from any given feedstock.
The test is always a batch experiment, where
a known amount of feed and inoculum are digested anaerobically
and the volume and quality of the resulting
biogas measured over an incubation period. This test is not
representative of plant situations and cannot,
should not be used to scale a full scale process. However, it
does provide useful information on the suitability
of a potential feedstock for treatment through AD. If further
investigations are carried out in bench scale or pilot
scale digesters, the BMP data can be used as a benchmark against
which the efficiency of the digestion
process to produce methane, can be assessed.
7.2 Methodology
7.2.1 Feedstock preparation
The Sargassum test material was received as dry fronds. A
sieving test showed the material to be around one
third by weight beach sand.
The sample for the BMP was washed several times with distilled
water to remove the bulk of the sand. The
washed sample was then dried overnight at 80 C in an air oven
and then ground up in a Nutribullet. Grinding
reduced the sample to a fine powder but with a significant
amount of larger, harder particulates ranging in size
up to about 2-3 mm. The whole ground sample was used for the
BMP.
7.2.2 Substrate blends and controls
In Table 6, the composition of the set of substrates for the BMP
experiment are set out. The inoculum was
digestate from another seaweed/food waste AD experiment and the
loading of each batch was determined
from the analysis of the raw materials VS components. Batches
were loaded according to a number of blend
ratios calculated from the VS of Sargassum, Saccharina and FW
and then a final 1:1 VS ratio of inoculum to
feed.
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Table 6.Treatment compositions for each BMP experiment, as
calculated for an approximate 600 mL volume. The blend ratios (*)
are calculated on a VS basis as the sargassum [and Saccharina] was
dried. Where SW = seaweed, Sm = Sargassum fluitans, Sl = Saccharina
latissima and FW = food waste . The FW was not dried but added as a
wet slurry.
Treatment Set Inoculum SW FW
(mL) (g) (mL)
Inoculum DI Blank 1 600 0 0
FW only C1 560 0 40
Sm only C2 592 8 0
Sl only C3 591 9 0
Sm + FW 1:1* B1 575 4 21
Sm + FW 2:1 B2 581 6 14
Sm + FW 3:1 B3 583 6 11
Sm + FW 1:2 B4 570 3 27
The substrate weights or volumes, as appropriate, for each
treatment were calculated and then prepared to