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What I’m going to talk about

Brief introduction to the history of wastewater

What a wastewater treatment plant looks like

The basic wastewater treatment processes

Sewage sludge – a whole new world



Why Treat Sewage??

A Potted History of Sewage Treatment in

the UK









1865 –Bazalgette’s first pumping stations

completed converting London from an opensewer to a city with proper sewerage,

transporting sewage to lower down in the

Thames.

Designed with enough capacity that it is stillenough capacity in it to still be in use today

The Thames Tideway is the modern

equivalent and is being constructed now,

almost 150 years later and is going to cost

£3.6 billion taking 15 years (the same asBazalgette) to build 22 miles of sewer

(compared to 100 miles for Bazalgette)

Bazalgette’s London



Still quite early for wastewater

treatment

1850’s – Typically water abstraction downstream of sewage

discharge points

Water treatment problem resolved by building moorland

catchment reservoirs and distribution system to take the

“clean” water to people’s taps.

1876 - Rivers Pollution Prevention Act – good idea but ahead

of its time because nobody knew how to treat sewage. Get out

clause which meant no improvements









……..and better

1960’s Mogden Formula introduced for traders as a method of

controlling trade loads by charging

1961 Rivers Prevention of Pollution Act – extended this to all existing

discharges

1974 Control of Pollution Act – An enabling Act which was brought into

law by Statutory Instruments. Act covered discharges to air, water,land and noise.

1977 – Pre 1937 discharges to sewer at last consented

From 1977 to present day most environmental law has been through

EC Directive although some of it has been included in 1991 Water Act

EC produced a black list of chemicals to be banned from discharges Also a red list of Chemicals to be controlled in discharges e.g. toxic

metals



……..and better

1990 & 1995- Environment Act and Environmental Protection Act

1998 UWWTD required wastewater treatment for all areas above

15,000 PE

River Quality Objective standards set to ensure rivers achieve required

classification. Standard dependant on available dilution in river and

upstream quality. Today standards are set by Stochastic models(statistically based e.g Monte Carlo Models)

2005- UWWTD increased to cover all works >2000 PE

2007 Environmental Permitting Regulations introduced

2009 – First River Basin Asset Management Programmes for the

Water Framework Directive. Environmental Permits get tighter





What is Sewage?

Screenings

Grit

Faecal matter

Urine

Water



What is Sewage?

Once all the screenings are

removed, the 0.5% that isn’t

water is:

The consent is usually centred

around

BOD

Ammonia

Solids

and sometimes

Phosphorus, organic chemicals

and metals

















Preliminary Treatment

Inlet works

CoarseScreens

(optional)

GritRemoval

(optional)

FineScreens

Sewer Primary

treatment

Screeningstreatment

ScreeningstreatmentGrittreatment





Getting the big stuff out

Coarse ScreensUsually around 25mm bars to take the big stuff out







Grit – Why’s it a problem?

• Problems with flow

measurement

• Erosion and wear of

downstream equipment,

pumps etc

• Settles and takes up

volume in sludge storage

• Reduces volume in

digesters – reduced

gas/energy production

Better here

Than here



How is Grit removed





And when it goes right



The Wastewater Treatment

Process


Primary Treatment





Primary Settlement

• Rely on gravity to settle out lighter SS material

• Circular or Rectangular constructions• Usual designs :

• minimum 2 hours retention at peak flow

• 30-50% removal of organic load and 60% of solids

• High calorific value removed and goes off to digesters toproduce energy









The Wastewater Treatment

Process


Primary Treatment

Secondary Treatment



Secondary TreatmentThe engine room of wastewater treatment

SecondaryTreatment

TertiaryTreatment/

Outfall

Sludge

Treatment

PrimaryTreatment









Trickling Filters

Advantages

• Simple and easy to operate

• Low or no power

• Relatively cheap to build

• Resilient and robust to change

and toxic shock• Very good for small works

• Adaptable

Disadvantages

• Large land take

• Not as efficient a removalprocess as suspended growth

• Not resistant to the cold

• Overgrowth and ponding



Activated Sludge (ASP)

Activated sludge consists of a mass of micro-organismswhich feed on pollutants inthe sewage. The bacteria issuspended in liquid and is

called “mixed liquor”, it ismixed with sewage andaerated in aeration basinsbefore passing to finalsettlement tanks where it issettled and the sludgereturned. The effluentproduced is of a highquality.



Activated Sludge (ASP)

• Sewage enters theaeration tank and mixeswith mixed liquor

• Bacteria eat the sewageand need to be fed with

air • More bacteria are bred

and old sludge needs tobe wasted to maintain abalance

• Sludge recycled aroundto ensure the mass of bacteria is maintained.





Activated Sludge (ASP)Advantages

• Very efficient producing a highquality effluent

• Common technique with a lotof industry knowledge

• Very adaptable to increasing

loads• Can be adapted for NutrientRemoval

Disadvantages

• Energy intensive

• More complicated to operatethan fixed film processes

• Produces more sludge thanfixed film













WHAT IS SLUDGE?

Mainly water (up to 99%)

Dissolved solids

Settled and suspended solids

Faecal matterBacteria and other micro-organisms

Nutrients (N, P, K)

Metals

Energy





SLUDGE PRODUCTION

Approx 1.2 million tonnes dry solidsproduced in UK annually this 165kg perperson per year

YWS production 150,000tds last year

S h t d d ith it ll



So… what do we do with it all

In 2004

62% Agricultural Land

19% Incinerated

11% Land Reclamation

7% Other (including composting)1% Landfill

Source: Water UK









Primary sludge

Bio

1º

2º

Secondary sludge

Tertiary

Humus typically 2% ds (1-3% )

SAS typically 0.6% ds (0.25-1.25% )

SOURCES OF SLUDGE





Primary sludge

Bio

1º

2º

Secondary sludge

Co-settled sludge

Tertiary sludge

TertiaryNormally returned asbackwash liquor

SOURCES OF SLUDGE



OBJECTIVES OF SLUDGEMANAGEMENT

Reduce volume (removal of water)

Reduce/remove odour

Stabilise organic material (BOD removal)

Remove pathogensReclaim useful by-products (biogas, soilconditioners)

Safe/appropriate disposal & recycling





>600 Sewage Treatment Works

50 Sludge Treatment CentresVarying degrees of treatment

Varying costs of treatment

Varying capabilities (sludgeintake, sludge output, day and

night operability)





TYPICAL SITE LAYOUTS







To achieve target dry solids with minimal solids lossin the filtrate

Target solids is 6% ds – thicker sludge is difficult topump

Filtrate is returned to the works and excessive solidscan cause compliance problems

THICKENING - aim













POLYMER

Added to sludge prior to mechanical thickening anddewatering

Poly adheres to sludge particles, causing the release of surface water, neutralisation of charge andconglomeration of small particles by bridging.

Many different types of polymer used eg cationic,ionic, single chain, cross linked

Type used depends on characteristics of solids (eg pH,age, source) type of mixing & dewatering device

pH, Alkalinity, water hardness, temperature, can affectperformance of polymers



Type of sludge is the primary factor affecting the typeand quantity of polymer required

Raw Primary sludge requires much less poly than SAS

Old sludge requires a higher poly dose than fresh

sludgePolymer concentration required for a sludge isdetermined in the lab by jar tests

NB sludge feed will vary therefore poly dose will

change

POLYMER





DIGESTION - requirements

Min 12d primary digestionMin 32ºCMin 14d secondary digestion

Code of Practice for the Agricultural Use of Sewage Sludge (1989)





Biogas

DIGESTION

Heatexchanger

Feed

Treated

sludge

Compressor









DEWATERING

Sludge feed

Polymer

Dewatered cakeFiltrate



DEWATERING







DEWATERING



Centrifuges

Feed

Bowl

Scroll

Beach

Weir plate





















Sludge as a marketable product



Technology exists its how you produce it and how you

sell it

Sludge as a marketable product

Biofert production at 13,200 tDS/annum

Sludge phytoconditioning

Biogas as a biofuel or supply to the gas grid

Ringsend 50% of energy from biogas

Sludge liquors as a product

Pearl & Crystal Green

Sludge Treatment as a resource



Sludge liquors – PEARL Process

Process that produces fertilizer byremoving nitrogen and

phosphorus from sludge liquors

Works by adding magnesium and

caustic soda to phosphorus rich

sludge liquors and passing themthrough an upflow column

The sludge liquors pass through

pellets of struvite that are re-

circulated around to act as seeds.

The pellet size is a function of retention time in the reactor





ANY

QUESTIONS??

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