Sewage treatment plants directly emit gases from biological processes and indirectly from energy consumption and transport. Credit: Apurva Sharma
A study in Himachal Pradesh reveals that electricity consumption, and the treatment, transport and storage of sludge in sewage treatment plants (STPs) contribute significantly to greenhouse gas (GHG) emissions1.
Electricity consumption was responsible for the highest emissions, followed by the activated sludge process and sludge storage in landfill.
The study suggests that the use of renewable energy sources, such as solar energy, can reduce STP emissions, says a team at the Dr YS Parmar University of Horticulture and Forestry.
STPs directly emit gases from biological processes and indirectly from energy consumption and transport. The scientists assessed direct and indirect GHG emissions from 59 plants in the state. Of these, 24 treated less than 1 million litres of sewage daily, 26 treated between 1 and 3 million litres and the rest more than 3 million litres.
The plants which treated more than 3 million litres of sewage consumed more power and produced higher GHG emissions individually. However, the plants with 1 to 3 million litre and plants with less than 1 million litre capacities contributed greater amounts of GHG emissions since they outnumbered the larger plants in the state.
In addition to carbon dioxide, the plants emitted methane and nitrous oxide gases. Nitrous oxide has a much higher global warming potential than carbon dioxide.
Electricity consumption by the STPs accounted for 43% of GHG emissions, followed by activated sludge process at around 33%, landfill storage at 24% and transport at 2%.
