Abstract

Lagoons have been traditionallyused in India for decentralized treatment of domestic sewage. These are cost effective as they depend mainly on the natural processes without any external energy inputs.  This study focuses on the treatment efficiency of algae based sewage treatment plant (STP) of 67.65 MLD (million litres per day) capacity considering the characteristics of domestic wastewater (sewage) and functioning of the treatment plant, while attempting to understand the role of algae in the treatment. STP performance was assessed by diurnal as well as periodic investigations of key water quality parameters and algal biota. STP with a residence time of 14.3 days perform moderately, which is evident from the removal of total COD – Chemical Oxygen Demand (60%), filterable COD (50%), total BOD – Biochemical Oxygen Demand (82%) and filterable BOD (70%) as sewage travels from the inlet to the outlet. Furthermore, nitrogen content showed sharp variations with Total Kjeldahl Nitrogen (TKN) removal of 36%; Ammonium N (NH₄-N) removal efficiency of 18%, nitrate (NO₃–N) removal efficiency of 22% and nitrite (NO₂–N) removal efficiency of 57.8%. The predominant algae are euglenoides (in facultative lagoons) and chlorophycean members (maturation ponds). The drastic decrease of particulates and suspended matter highlights heterotrophy of euglenoides in removing particulates.

Keywords: algae, sewage treatment, euglena, facultative pond, nutrient, carbon capture, bio-volume