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SYNOPSIS
Comparative Study of Appropriate
Decentralised Wastewater Treatment System for
Urban Residential Use
Devendra Anil Deshpande
SA0711
Guided by
Ar. Surya Kakani
Master of Architecture (M. Arch) in Sustainable Architecture
Faculty of Architecture
CEPT University
May, 2013
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Comparative Study of Appropriate Decentralised
Wastewater Treatment System for Urban Residential Use
1. INTRODUCTION & PURPOSE OF STUDY
Every substance & every organism in nature has its role to
play in an ecosystem.
Nothing in nature is waste, refused parts or substances by one
component are potential
resource of another. In view of rapid urban growth capacities of
centralised wastewater
treatment systems are falling short. Decentralised wastewater
treatment systems identifies
potential resource content of wastewater & uses different
components of the ecosystem to
extract these resources for purification of water as well as
resource generation.
The focus of this research is a comparative study of
decentralised wastewater
treatment systems Decentralised Wastewater Treatment System
(DEWATS), Decentralised
on Site Waste Management system (DOSIWAM), Urine Diversion
Toilets (UDTs),
Biosanitizer Eco-chips (Biocatalyst) and combination of DOSIWAM,
UDT & Biosanitizer.
Such a study is important in order to understand resource
generation & resource offset
potentials of wastewater. The approach adopted in this
dissertation includes comparative
study of different decentralised treatment systems based on
parameters namely, processes
involved in treatment, space requirement, resources generation,
limitations & combination
with other systems.
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Aim
To asses & calculate possibilities of using appropriate
Decentralised Wastewater
Treatment systems in urban residential area, for the identifying
potentials of resource
generation & offset through system.
Objectives
o To find possibilities of retrofitting & calculating
appropriate decentralised wastewater
treatment systems in urban situations.
o To find appropriateness of decentralised systems in terms of
space requirement,
quality of treatment & quantity of resource generation.
o To cross examine the existing policies, rules &
regulations for decentralised treatment
systems on the basis of result of the study cases.
Hypothesis
Decentralised wastewater treatment systems need optimum
infrastructure &
technologies, and can efficiently be used in urban situations,
for treatment of waste water as
well as for generation & offset of energy & usable
resources.
Scope
o The study will be focussed on the urban group housing.
o Assessment of decentralised treatment systems will be based on
Theoretical
calculations.
Limitations
o The study will not include laboratory analysis of the influent
& effluent of the
treatment system.
o Calculation of water & resources is based on the
standards.
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Methodology:
o Data collection of different decentralised wastewater
treatment system from case-
studies & literature review. Selection of criteria of
appropriateness of the system
based on different parameters of the selected study cases.
o Comparative analysis & preparation of matrix of
decentralised treatment systems
based on appropriateness criteria.
o Selection of different decentralised treatment systems &
combination of decentralised
treatment systems from the matrix for applied calculations based
on appropriateness
criteria, for 2 high-density urban group housing projects.
o Review of existing policies for decentralised treatment
systems in Eco Housing
Criteria, Pune.
o Suggestions for use of decentralised treatment systems for
group housing in urban
area.
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2. DECENTRALISED WASTEWATER TREATMENT SYSTEMS
2.1.DOSIWAM System (Decentralised Onsite Waste Management)
DOSIWAM is a sustainable, eco-friendly, hygienically safe
sanitation process based
on natural biodegradation which converts waste to wealth. In
this system every grain of solid
& every drop of liquid is treated hygienically by bio
digestive process& natural aeration and
end products are returned to the soil in horticulture or
agriculture in an ecological sustainable
manner. End products from DOSIWAM are Biogas, Organic fertilizer
& Stabilised clean
water.
Space Requirement for Biogas plant -
Total space required = 2.65 cu.m. (for 25 persons).
Resource Generation per year
Biogas 35 lit. / Person / day gives 63.875 cu.m. of bio gas per
year / family.
Water usage reduction instead of 10 lit. / Flush system uses
2.17 lit. / flush,
therefore, 14,289 lit. Water can be saved.
Water for irrigation considering 20 lit./head/day for bathing
& 45lit./head/day for
washing, grey water generated = 65 lit./head/day. Therefore, 1,
18, 625 lit. of treated
& stabilised water can be made available from stabilisation
tank for irrigation or
horticulture in 1 year.
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2.2.Urine Diversion Toilets - Ecosan Toilets /(UDTs)
Ecosan concept is based on segregation of different flow streams
at source & reuse of
treated water & generated resource after appropriate
treatment. Worldwide many Ecosan
projects have already been implemented, however there is still
lack of practical experiences
with medium to large scale projects.
Space Requirement Double Vault Type (for 1 family)
2 compartments, each Compartment 0.9 x 1.2 m. ht. 1.0 m. (Under
toilet seat)
Resource Generation per year (By 1 family)
Urine 1 lit/person/day gives 1825 lit/yr. for 1 family (5 users
x 365 days).
Manure 0.3 kg/person/day with 45% less moisture gives 136.90
kg/yr. (0.3kg. x
5users x 365 days x 0.25 actual solid content)
Water saving person urinates 4 to 5 times a day, with 4 lit. of
water per flush.
Therefore, 29,200 lit/yr. water can be saved (4 times x 4 lit x
5 users x 365 days).
Offset of 43 days water usage (considering 135/day/head).
2.3. DEWATS (Decentralised Wastewater Treatment System)
DEWATS stands for DEcentralised WAstewater Treatment System.
This system based
on different natural treatment techniques put together in
different combination according to
the need like, gravity, micro-organisms, temperature, reeds etc.
The system consists of 4
different steps of processing namely, Primary Treatment septic
tank, Secondary Treatment
anaerobic baffle reactor, Tertiary Treatment reed bed, Polishing
Pond.
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Space Requirement (for 1 family)
Anaerobic Digestion 1.50 sq.m. / cu.m. (4 to 6 days) (Minimum
requirement)
Reed Bed 5.00 sq.m. /cu.m. (2 to 3 days) (Minimum
requirement)
Polishing Tank 1.20 sq.m. / cu.m. (1 to 2 days) (Minimum
requirement)
Total Area requirement 7.70 sq.m. / cu.m. (10 to 11 days)
(Minimum requirement)
Resource Generation per year (By 1 family)
Treated Water offset requirement of non-potable water for 7
months.
Cultivation of usable biomass like bamboo, khus etc.
Biosanitizer Eco-chips - (Biocatalyst)
This bio-catalyst is extracted from thorough understanding of
traditional ecological
practices based on eco-logic. When damaged traditional
ecological practices were analysed
based on eco-logic, it is found that nitrates are of critical
importance in all processes.
Space Requirement (for 1 family)
100 lpcd wastewater generation requires 3 sq.m. Septic tank.
(Min. requirement).
Required HRT is 12 hrs.
Resource Generation per year (By 1 family)
100 lpcd wastewater will generate 182.5 cu.m. of oxygen rich
water, which has
quality of soil nourishment as well as treating other types of
garbage because in has
high level of active oxygen.
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3. COMPARISON, ANALYSIS & CALCULATIONS
Criteria of analysis of appropriateness of the decentralised
system are drawn based on
case studies & literature review of different decentralised
treatment systems,
1. Working Principles of the System
Treatment processes involved.
Treatment capacity.
Type of building where system can be used.
Retrofitting of system to existing building.
2. Requirements of the System
Space.
Time (HRT).
Capital investment.
Operation & maintenance.
3. 3-R achieved by the system
Water use reduced at source.
Quantity of treated water.
Reuse of treated water.
Resources generation.
4. Advantages of system.
5. Limitations of the system.
6. Combination with Other System to Improve Performance of the
System.
Different decentralised treatment systems are compared &
analysed based on
appropriateness criteria. From this comparison following
decentralised treatment systems &
combination of decentralised treatment systems are found to be
effective for use in urban
residential use.
After applied calculations of the decentralised wastewater
treatment systems to group
housing it is found that, combination of DOSIWAM, Biosanitizer
& Urine Diversion is most
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ideal system for group housing in terms of resource generation.
But combination of the
DOSIWAM & Biosanitizer is most practical system for
wastewater treatment in terms of
resource generation, space requirement & O & M
Figure - Schematic Drawing Showing Space Requirement for
Decentralised Treatment Systems - Group
Housing 1
Project Details
Redesign of Jayshefali Group Housing, Shivaranjani Char Rasta,
Ahmedabad.
Site Area 10,416 sq.m.
Total Built up Area 17,962 sq.m. (G+9 Floors)
Nos. of Units 201
Nos. of Residents 853
Population Density 819 persons/ha.
Water Usage 115.2 cu.m./day
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3.1.Practical Issues Involved in Application of Decentralised
Systems
Effluent from DOSIWAM system is not nutrient free & hence,
it is not odour free as
well as not suitable for human contact. Therefore it cannot be
used for purposes like
washing, flushing & bathing. Also it cannot be recharged to
the ground water table.
Stabilised water can only be used for irrigation &
gardening, but for high-density
area, quantity of water is huge and cannot be only used for
gardening.
Grey & Brown waters from UDTs need to be treated in other
systems. As well as
market availability of urine diversion flush toilets is
fundamental issue.
Reduction of flushing water quantity from 40 lpcd to 5 lpcd is
crucial, due to flushing
requirements of conventional toilet pans. If excess water goes
into biogas plant, solid
content of the faeces will decreased & pH value will
increase, under this condition
biogas will not be generated efficiently.
Operation & Maintenance of decentralised treatment system is
major issue at group
housing level.
3.2.Review of Policies for Wastewater Treatment in Pune.
Low flow faucets (non-mandatory) & Dual flush Cistern
(mandatory)
Treatment of Grey Water (mandatory) & Treatment of Grey
& Black water
(non-mandatory)
Reuse of Grey Water (partially mandatory)
Disinfectants & Antiseptics
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4. CONCLUSION / INFERENCES
Wastewater is mixture of refused resources & nutrients by
humans. Wastewater
generation cannot be calculated precisely because of urban
growth & diverse water
consumption. Due to continuous urban growth, capacities of
centralised wastewater treatment
systems are falling short.
Decentralised treatment systems are evolved from natural
chemical & biological
processes, which separate nutrients from wastewater & return
it as potential resources.
Different decentralised treatment systems separate different
resources from wastewater. If
appropriate combinations in correct sequence of treatment are
used, then wastewater can be
treated more efficiently with maximum possible extraction of
resources.
Decentralised treatment systems cannot replace centralised
treatment systems in an
urban area, as excessive treated water needs to be carried away
from the city, but these
systems can reduce the load on centralised system to large
extent.
Decentralised systems need O & M. In case of DOSIWAM, use of
disinfectants,
antiseptics or excessive water will cause failing of the system.
Therefore lifestyle change is
major factor for use of decentralised systems.
Existing policies should be revised based on principle that
decentralised treatment
systems generate resources as well as reduces requirement of
flushing water.
Just as transportation is the back bone of urban planning, water
& wastewater
thinking need to be incorporated as an important matrix which
may potentially allow newer
city forms.
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