Avadi Sewage Treatment Plant: Sustainable off-grid sewage treatment in Chennai

The Tamil Nadu Police Housing Corporation (TNPHC) has successfully constructed an off-grid sewage treatment plant (STP) to improve living conditions in the police housing colony in Avadi, a suburb of Chennai. This sewage treatment plant has not only solved the problem of sewage disposal but also provided a pond of treated water for fishing, vegetable cultivation and recharging of groundwater. It treats 12 lakh litres of sewage every day with no negative discharge, produces manure, recharges groundwater, removes the source of foul odour and waterborne diseases, and beautifies the area.

Rationale

The lack of sewage treatment facilities was a major concern for residents of the police quarters in Avadi, a suburb of Chennai under the municipality of Thiruvallur district. The police colony, constructed by the Chennai Public Works Department (PWD) in 1966, occupies an area of 1,000 acres and houses approximately 12,500 residents from 2,000 households. However, as the Avadi area does not fall under Chennai city limits, it was notconnected to the underground sewer system and had to dispose of its sewage through septic tanks.

The problem with this arrangement was that the percolation of water from the septic tank to the subsoil was little, as the soil was largely clayey. This resulted in heavy stagnation of wastewater around the police quarter area, which became a source of foul odour andwaterborne diseases, causing severe inconvenience to residents.

The residents complained to the TNPHC, a state-level nodal body in charge of all police-related construction matters. After studying the area and the problems faced,a decision was taken to construct an off-grid STP that would transform waste into useful material.

Objective

The STP was constructed with the objective of treating and reusing the sewage water generated in the Avadi police quarters.

Key Stakeholders

The programme is being implemented by the TNPHC with the financial support of the Government of Tamil Nadu, and the beneficiaries are the residents of Avadi.

Implementation Strategy

The approach followed for implementation involved focussing on the basics initially, testing the essential viability of the project and then, if successful, scaling it up. Thus, the first goal of the project was to contain the existing damage and treat the sewage that was being generated. Emphasis was also placed on building a robust system that would be as maintenance-free as possible. Accordingly, the methodology of activated sludge control was chosen for deployment due to its simplicity and reliability. The method uses air and abiological floc composed of bacteria and protozoa to treat sewage. A contractor was selected through an open tendering process to construct the STP using this method. Unplasticised Polyvinyl Chloride (UPC) material was used in construction, as it does not corrode easily and requires less maintenance.

Phase I of the project began in 2003, with the target of treating 2 lakh litres of water daily and constructing a pond to store the treated water and use it to recharge the groundwater table. The project was completed in 2004. Phase II began in 2011 and had the target oftreating 10 lakh litres of water daily. An additional STP was constructed for this purpose by 2012.

After the construction of the treatment plant, its maintenance was handed over to the members of the police colony. Constables and pump operators were trained for three months by the implementing agency.

The STP in Avadi is now almost maintenance-free. The process flow for the system is illustrated in Figure 2.

Resources Utilised

Details about the resources utilised in the construction of the STP in Avadi are presented in Table 1.

Table 1: Resources used in establishing the STP in Police Colony (Avadi)

Impact

Treatment of sewage, removal of odour and diseases: The immediate outcome of the STP in Avadi has been to treat 12 lakh litres of sewage every day with no negative discharge, produce manure, recharge groundwater, remove the source of foul odour and waterborne diseases, and beautify the area.

Production of economically valuable items: The water produced by the STP is being used for cultivation of bananas, coconuts and vegetables; fish like katla, kapis and logu; and beema bamboo, which is used in the production of furnace oil, paper, cloth, ornamental items and mats. This fast growing, thorn-free plant generates high levels of oxygen and also acts as a green boundary wall. The 1,000 beema saplings brought from Hosur, Bengaluru, will be ready for harvesting in five years. The products cultivated at the site are used in police canteens and are made available to the colony’s residents at subsidised rates.

Key Challenges

Residents of the police colony were initially reluctant to use the treated water. To address this issue, senior police officers were involved in building a consensus leading to acceptance of the initiative. The Additional Director General (Police), Inspector General (Prisons) and aformer Police Commissioner of Chennai visited the field site, held discussions with the residents of the colony and encouraged them to use the treated water. The unutilisedland around the plant was divided into plots that were to be used for cultivation. Three teams were formed to carry out the cultivation, and within six months the land reaped a harvest of bananas. The culture of cultivation caught on, and kitchen gardens irrigated by the pond arenow a common sight in the colony. Subsequently, the TNPHC introduced fish cultivation in the pond by providing seeds and feed. However, residents showed reluctance in consuming the fish. To deal with this, the previous strategy of involving highlevel leadership was successfully used again. In fact, the Additional Director General (Police) set an example by consuming some of the fish himself. This encouraged many of the residents to follow suit.

Replicability and Sustainability

The STP in the police quarters in Avadi successfully converts waste into useful material. It replenishes the environment, produces economically valuable items and removes a major source of inconvenience for the community. The set-up costs for the plant were drawnfrom the funds earmarked for waste disposal in the housing project. The STP’s maintenance cost is low, and there is no requirement for additional allocations.

The fruits of the project are directly available to the community, which also has a stake in maintaining the system.

The Government of Tamil Nadu recognised the value of the initiative and replicated it in several other locations in the state. In 2010-2011, it launched a project in MaduraiCentral Prison. The plant cost Rs 45 lakh and has a treatment capacity of 2 lakh litres. The treated water is being used to cultivate vegetables. The government has decided to scale up and implement the model in all the prisons of the state. Similar projects have alreadybeen implemented in the Tamil Nadu Police Academy in Vandalur and in Kumarasampatti quarters in Salem district. There are plans to use the Avadi model in the construction of 2,673 houses for uniformed service personnel under the Own Your House scheme inMalakottiyur near Chennai.

Conclusion

The construction of the STP in Avadi shows how off-grid or isolated systems for sewage treatment can effectively manage sewage in a way that converts waste into useful products and also recharges the environment. Having already been replicated at several sites in Tamil Nadu, the model offers a proven strategy for responsible and productive sewage disposal.