Energy from Wastes – Achieving Self-sustenance in Sewage Treatment Plant


Technology for the recovery of energy from wastes – Achieving Self-sustenance in Sewage Treatment Plant

The successful operation of a Sewage Treatment Plant (STP) not only lies in achieving the desired standards but also in value addition through process & cost optimization during the plant’s lifecycle.

In developing countries, the % of non-operational plants in on the rise primarily due to interruptions in power supply. Further, due to financial issues, upkeep of the plant during the operations & maintenance phase is a hassle that hampers sustainability and performance.

This has driven the need to look for alternative sources of energy as well as options to optimize the operational expenditure. Such a thought requires the conviction that sewage is a resource with economic value and not a liability. Bio sludge produced in a STP is a valuable carbonaceous resource, which can be efficiently utilized for generation of energy with well-designed Sludge Treatment units employing Anaerobic digesters, Biogas holders and Biogas based energy generation systems. These systems are capable of generating green power to enable self-sustenance of the Plants.

The treatment of sewage is typically done through primary treatment for removal of solids/grit etc., followed by biological treatment in a conventional activated sludge system. The primary and excess bio sludge produced is thickened in thickeners and digested in anaerobic sludge digesters, producing methane rich biogas and well-digested bio sludge suitable for use as manure after dewatering in a centrifuge. The biogas produced is collected in a gas holder and used as fuel in biogas engine after stripping the biogas of hydrogen sulphide, which is corrosive in nature.

Some of the STPs are in successful operation for over ten years and are time tested references that testify to sustainability. A city which has pioneered this concept in India is Chennai. The Sewage Treatment Plants at Kodungaiyur and Perungudi in Chennai have been executed and maintained for over a decade by WABAG for Chennai Metropolitan Water Supply & Sewerage Board. In both the STPs, emphasis has been on sludge treatment and generation of power from biogas, utilizing the same to run the treatment process efficiently and reducing the electricity import from the State Electricity Grid.

Opting for such a resource recovery model not only ensures successful plant operation but also reduces the operational expenditure by installation of a bio energy mechanism which has a lucrative payback period of 3-4 years and by saving the cost in transporting sludge to distant landfills.

Further, such a model is aligned to the United Nations Sustainable Development Goal and helps the plant developer claim carbon credits under the clean development mechanism. Achieving even better results are possible through close monitoring and control of processes. Dedicated efforts by the technical support team ensure consistent operations of the plant for not only achieving the desired parameters but also sustain green energy production from non-fossil sources which helps protect the environment.