The effect of nutrients on extracellular polymeric substance production and its influence on sludge properties

The effect of nutrients on extracellular polymeric substance (EPS) production and its impact on sludge properties and removal efficiencies were investigated in an in-depth field survey of wastewater treatment plants. Thereafter, laboratory studies were performed to evaluate the effect of a combination of nutrients - nitrogen and phosphorus and operational conditions on EPS production, and sludge settling and dewatering characteristics. Multiple regression analysis was performed to assess the effect of variables in nutrient operational conditions on the EPS production and sludge properties. The field survey revealed that although filamentous micro-organisms were found in most of the sludge samples, they did not always cause sludge bulking. Further, it was observed that EPS production was lower in anaerobic than in aerobic processes. An evaluation of the effect of the deficiency and excess of nitrogen and phosphorus was conducted in batch experiments on synthetic wastewater with glucose as the carbon source. The study revealed that the EPS components, namely proteins and carbohydrates had a more profound effect on sludge properties compared to total EPS, with protein being more significant than carbohydrate. Both nitrogen deficiency (COD: N < 100:2) and nitrogen excess (COD: N > 100:10) improved the sludge properties. The optimum phosphorus ratio determined was COD:P, ranging from 100:3 to 100:5, at which sludge properties in terms of settling, dewatering and the final clarification improved. WaterSA Vol.29(4) 2003: 437-442