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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