Operation of an activated sludge plant for fellmongery wastewater treatment : a thesis submitted in partial fulfilment of the requirements of the degree of Master of Technology in Environmental Engineering at Massey University, Palmerston North, New Zealand

Abstract

Activated sludge is one of the most common wastewater-treatment processes used to reduce pollutant loads on the receiving environment. For efficient operation, there must be an effective process control and operation strategy in place to ensure that process problems are avoided. This research is a case study into the process control and operation of an activated sludge plant used for fellmongery wastewater treatment. Analysis of the pretreated fellmongery wastewater showed that it is characterised by high total and volatile suspended solids concentrations, and high organic nitrogen concentrations. The plant was experiencing frequent problems that were attributed to the high influent suspended solids load coupled with ineffective solids management. Operation of bench-scale simulations showed that solids retention time (SRT) control at 5 or 10 days will produce acceptable effluent suspended solids concentrations and soluble chemical oxygen demand (COD) removal. Soluble COD removal for both 5 and 10 days was high at 85 and 80 % respectively at a hydraulic retention time of 6.4 days. Effluent suspended solids concentrations were 100 and 157 g/m 3 respectively. A steady state control model was developed based on, mass balances of biochemical oxygen demand (BOD) and volatile suspended solids (VSS), process performance equations, and the solids retention time (SRT). The model used three control points, the clarifier underflow pump, the clarifier influent pump and the waste sludge pump. The model was incorporated into an off-line Activated Sludge Operation Program (ASOP) to provide a user-friendly interface between the plant and operator. The main output from ASOP includes values for the three control points and suggestions to help avoid problems. A process control and operation strategy was developed using ASOP, the knowledge gained in this research, and an operation manual developed from accepted operation practises.