Waste water treatment and metal (Pb2+, Zn2+) removal by microalgal based stabilization pond system

A case study was undertaken for the treatment of domestic wastewater generated at village of Sanghol, Distt. Fatehgarh Sahib, Punjab (India), using a schematic designed algal and duckweed based stabilization pond system, which is discussed here for winter months only (November to March) as there was no growth of duckweeds and only algae dominated the whole system. A proficient increase in pH and dissolved oxygen was observed after the treatment with reduction in chemical oxygen demand and biochemical oxygen demand by 93% and 79% respectively. Chlorella sp. was the dominating algal species in the stabilization pond water during entire period and was studied for its Zn2+ and Pb2+ metal removal efficiency. 60–70% removal of Zn2+ was observed from culture medium containing 5–20 mg L−1 Zn2+, which declined to 42% at 50 mg L−1. A constant decline in cell number from 538 × 105 to 8 × 105 cells ml−1 was observed indicating zinc toxicity to Chlorella. Lead was maximally removed by 66.3% from culture medium containing 1 mg L−1. The lead removal efficiency was 45 50 % at higher 5 to 20 mg L−1 of external lead concentrations. The increase in cell number indicated no signs of Pb2+ toxicity up to 20 mg L−1. The maximum uptake (qmax) by live Chlorella biomass for both Zn2+ and Pb2+ was 34.4 and 41.8 mg/g respectively.