Effect of Depth on the Performance of Algae-Based Wastewater Treatment Ponds

A pilot-scale treatment plant consisted of a UASB-septic tank followed by three parallel pond systems each consisting of three stabilization ponds of equal depth and with the same hydraulic retention time (HRT) of 28 days. The setting was intended to investigate the effect of pond depth on the performance of algae-based ponds (ABPs). The depth of the ponds in the first, second and third systems were 90, 60 and 30 cm, respectively. The average ambient temperature throughout the experimental period was 24.5 °C. The influent chemical oxygen demand (COD) to the UASB was 1275 ± 84 mg/L and the influent COD concentration to each pond system was 331 mg/L ± 69 mg/L. The results reveal that the performance of the ABPs was inversely proportional to the depth. COD removal efficiencies for the shallowest and deepest ponds were 54.0 ± 1.1% and 51.6 ± 3.2%, respectively. Higher ammonium (NH₄⁺) removal efficiencies were achieved in the shallowest pond instead of the deepest pond. The removal efficiencies of shallowest and deepest ponds were 64.5 ± 2.8% and 51.2 ± 1.9%, respectively. Furthermore, the removal efficiencies of total Kjeldahl nitrogen (TKN) in the shallowest and deepest ponds were 45.4 ± 3.1% and 61.1 ± 4.5%, respectively. Negative removal efficiencies for total suspended solids (TSS) were observed in ABPs.