Report 4 of 5: Sewage and Sunshine - India

Introduction

In the South, a tradition of using wastewater in ponds for growing fish is known to exist in many places. These wetland systems work effortlessly with the help of the knowledge of local farmers who are excellent performers in recovering wastewater nutrients to grow food. The fish ponds improve the quality of wastewater and act as stabilisation ponds for reducing biological and chemical toxicity of urban wastewater.

Untreated municipal waste is a serious cause of environmental concern. It can cause major pollution to the rivers, lakes or coastal areas in which it is disposed. Everyday 17 million gallons of sewage water pours out of Calcutta but none of the 11 million residents have to pay for sewage treatment because it is subsidised by a natural biological practice. A series of canals channel the water into the East Calcutta wetlands where a wastewater system, initially created by local fish farmers anxious to improve their yields, has revolutionised the concept of sewage treatment.

Integrated wetland systems (IWS)

Wetlands in urban areas are natural receptacles for wastewater because they harness the nutrients available in waste through fisheries and agriculture. The integrated wetland system project aims to provide a low-cost, ecologically balanced and community linked sanitation option for the poorer cities of the world with ample sunshine. It is a system that frees the river from domestic contaminants and can at the same time recover the wastewater nutrients with remarkable efficiency to grow fish. The system costs less than other technologies for treating sewage and recycling waste.

There are two types of IWS - the flow-through system and the abstracted flow system. The primary objective of the flow-through system is the treatment of wastewater and for the abstracted flow system, it is resource recovery.

In the flow-through system, the entire wastewater is transported through a pre-treatment system and is then detained in the recycling ponds for further treatment and for growing fish. Subsequently, the effluent from the recycling ponds is used for irrigation in downstream areas. The flow-through system needs less land to ensure adequate wastewater treatment and is particularly effective where cost of land is high.

The flow-through system can be divided into two types: minimum area or low cost system and large area system. In the minimum area system, the emphasis is on wastewater treatment and the area varies according to the effluent quality requirements. The large area system emphasises the need for aquaculture and requires an area three or four times that of the minimum area system.

In the abstracted flow system wastewater is abstracted from the outfall channel or receptacle stream and is used for growing fish or for irrigation, or both. In this case, the user can draw the wastewater as and when required.

Initial steps for implementing IWS projects

Evaluating wastewater loading: most of the subsequent steps depend on the volume of liquid which the system is expected to handle. It is also essential to identify the existing drainage system through which the effluent will finally flow down.

Local resistance to aquaculture will have to be identified before starting any project planning. Fish farmers are able to earn reasonable profit by selling fish to other markets so there is a tendency for fish to be harvested even where they are not locally consumed.

Ascertaining outfall direction: once appropriate project sites have been identified, it is necessary to carry out a base line survey, including hydraulic, soil, topographical and land use surveys.

Land acquisition formalities need to be completed in a legally valid manner appropriate to the country and place of the IWS.

Detailed project design: there needs to be an efficient programme of operation and maintenance support and the sustainability of the project should be protected against engineering and economic risks by safeguarding the constructions, facilitating stakeholders participation and upgrading the resource recovery system.

Major components of IWS

• Wastewater collection from cities through a sewerage system up to the IWS project site.
• Pumping of wastewater to lift it from below the ground and carry it up to the IWS project site, occasionally through a force main.
• Pre-treatment of wastewater to ensure safe aquaculture in recycling ponds.
• Primary recycling ponds are mixed flow reactors where the functions of nutrient removal and treatment of wastewater take place simultaneously.
• Secondary recycling ponds are the waterbodies within any user region which recycle effluent from primary recycling ponds and are used for growing fish or other commercial aquatic crops.
• Effluent irrigation in user regions that takes place on the downstream side of the outfall channel can be used for generating crops and planting trees. Fish can be cultured in ponds using the effluent. Linking user regions with the effluent channels will enhance the food security amongst the beneficiary communities and ensure larger participation of the stakeholders in IWS projects.

Issues to be considered during the selection of the project site will include:

• Amount of wastewater loading
• Quality of wastewater discharged
• Location of the terminal pumping station
• Location of potential user regions
• Location of the receptacle channel
• Area of the project site, cost of land and status
• Present land use of the project site
• Land use of the area adjoining the project site
• Lay of the land and relative relief of the project site
• Whether or not the site is being considered for any other development project

The quantity of waste to be treated is an important criterion for designing IWS. For estimating the quantity of wastewater it is necessary to consider:

• Per capita water consumption
• Existing population
• Future growth of population
• Industrial waste discharge
• Infiltration into the sewers

IWS in operation

The technique of using shallow wastewater ponds for recycling urban discharge is straightforward. The flow of wastewater into the shallow ponds is controlled and it is left in the ponds for up to ten days. During this time, light penetrates the water and reacts with the waste to create an environment rich in algae and plankton which is ideal for fish to feed on and grow in. The selection of fish species suitable for wastewater ponds needs to be carefully considered and there are specific criteria that should be met.

Maintenance is minimal but in order for the small fish to thrive, the water needs to be churned up and snails, which eat the algae, need to be picked out of the pond. Water hyacinth is used to stop the banks from eroding, but also needs to be kept under control. The biggest menace is from fish thieves so at night groups of men guard the ponds.

As well as the sewage being treated, the fish farmers are averaging yields of 10,000 tonnes of fish each year. The fish contain fewer pathogens than most other fish in the market and so are perfectly safe to eat. However, it is important to make sure that no industrial waste finds its way into the sewage canals. The "clean" water can be used for irrigation on the vegetable gardens nearby. Although pisciculture is the mainstay of IWS projects, planting trees and growing crops, vegetables and flowers ensures economic and ecological sustainability.

Advantages of IWS

In many cities in developing countries, the wetlands or natural depressions accumulate wastewater and become sources of health risk for humans. However, the planned use of these receptacles can change the waterlogged areas into sustainable technology for wastewater treatment and resource recovery. The following are advantages of such a wetland system:

• Reduced consumption of conventional energy – IWS is basically a solar reactor and completes most of its biochemical reaction with the help of the sun.
• ISW is a flexible system and can work with almost no-flow condition to full-flow condition with uniform proficiency and only minor adjustments.
• More efficient removal of pathogens – conventional mechanical sewage treatment plants are largely ineffective in removing pathogens whereas IWS can ensure a reasonable reduction because of the detention time it allows to the incoming wastewater.
• Enhancing food security – IWS includes pisciculture, horticulture and animal husbandry all of which have a common and rich nutrient base that is drawn from municipal wastewater.
• Contributes to rural development – completion of IWS projects triggers a chain of economic activities by providing enriched irrigation water in addition to the piscicultural units which form part of the system.
• Institutionalises participation of stakeholders – participation of the local people at all major levels of planning construction and maintenance is a basic need for successful running of the system.
• Longer life-span of the treatment facility – conventional sewage treatment plants are prone to damage and frequent breakdowns with a huge financial liability accruing in order to properly maintain such treatment plants. IWS is a revenue earner and proper management will not only make it self reliant but profitable. Furthermore, being a non- structural option, the problem of damage and breakdown hardly ever arises and the system can continue to work for any length of time without any major system disorder.
• Minimum construction time – IWS projects can be completed within 18 months compared to 5 years for a conventional sewage treatment plant.

For further information and to order a copy of the manual, please contact:
 

USAID/DISC, 1500 Wilson Blvd., Suite 1010, Arlington, VA 22209, USA. Tel: +1 703 351 4006 Document order #PN-ABU-593

This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.
 
 
 

The Mudialy Fishermen’s Cooperative Society (MFCS) Drawing support from the experience of the wetlands of eastern Calcutta, the MFCS have been successful in transforming a waterlogged area into a resource recovery eco-system in the south western fringe of the city of Calcutta and in demonstrating the sustainability of wetland option for wastewater treatment and resource recovery. There are 15 ponds of various sizes in the MCFS wetland area. Of these, 9 smaller ponds are used for improving the water quality before it enters the bigger ponds where the fish grow and further improvement of water quality takes place. About 100 members of the MCFS produce about 5.6 tonnes of fish per hectare per year from about 50 hectares of water area which once was a wooded area. In the process about 23 million litres of composite sewage is treated each day in the wetlands. The entire eco-system has been built without any financial help. The money earned from the sale of fish has given a gross per capita income of about US$3 per day which is more than three times the minimum daily agricultural wage in India. Municipal sanitation does not need to be a facility for which the government has to provide public money to run the system.

TVE/ Practical Action gratefully acknowledge support for the HANDS ON programmes from the UK's Department for International Development (DFID), the European Commission (EC), the UN Foundation and UNDP/The Equator Initiative in collaboration with the Government of Canada, IDRC, IUCN, BrasilConnects and the Nature Conservancy.