Environmental Conditions and Effect of pH on Faecal Coliform Removal in Macrophyte and Algal Ponds

The environmental conditions within 3 pond systems comprising of water lettuce ( Pistia stratiotes ), duckweed ( Spirodela polyrhiza ) and algae (natural colonization), each operating in a series of four ponds were assessed specifically for temperature, pH, DO and total dissolved solids. The pH readings observed in the pond systems were simulated to determine the effect of different pH (4, 5, 7, 9 and 10), on faecal coliform removal in domestic wastewater. Acidic conditions prevailed in the water lettuce ponds and ranged from 4.3 to 6.3, duckweed ponds were neutral with values between 6.7 and 7.1. The algal ponds were mostly alkaline with pH values ranging from 7 to 10. The DO levels were low in the macrophyte ponds. The algal ponds had saturated levels of DO. The removal of faecal coliforms was lowest in the water lettuce ponds followed by duckweed and algal ponds respectively. The removal rates of faecal coliform at pH 7, 9 10 and the raw wastewater without pH adjustment under both sunlight and dark conditions were not significantly different. Removal rates at pH 5 were the lowest among all treatments. Under light conditions k (d -1 ) values of 1.5, 0.2, 1.3, 1.4, 1.4 and 1.4 were observed respectively for pHs of 4, 5, 7, 9, and 10 treatments and for the raw wastewater without pH adjustments. Under dark conditions the removal rates were 1.1, 0.5, 1.0, 1.2, 1.4 and 1.2 respectively for pH 4, 5, 7, 9, and 10 treatments and the raw wastewater pH without adjustment.