Surplus Activated Sludge Dewatering Approach

With high-speed economic and social development, the capacity and efficiency of sewage treatment is increasing. Then a large amount of activated-sludge was produced. Activated-sludge has the main characteristic of high water content. Conditioning is needed to change the identity before disposal. Polyelectrolyte conditioning is a widely used conditioning method. It can speed up the rate of water separation and improve settlement performance significantly. However, it has a problem that higher water content in sludge cake after conditioning. This paper took removing the water in sludge as the main objective, studied the impact on sludge dewatering properties of two advanced sludge treatments, surfactant conditioning method and enzyme conditioning method.Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used for sludge conditioning. First, the extraction efficiency of extracellular polymeric substances (EPS) in the sludge was studied. Extraction mechanism of EPS was investigated by analyzing the calcium and magnesium ion and DNA content in the supernatant. Then dewatering properties, such as water content of sludge cake, settlement performance, filter performance, were studied to evaluate the impact of surfactants on the performance of sludge dewatering. By analyzing the sludge floc structure, the conditioning mechanism was explained. Experimental result showed that surfactants could extract EPS of sludge, reduce water content of sludge cake. CTAB has a better effect than SDS. Water content of sludge cake after filtering was decreased 10% when the CTAB dosage was 15%TS. sedimentation and filtration performances were also improved. In addition, combined technology of surfactant and polyelectrolyte showed that two reagents used for sludge conditioning in conjunction could both reduce water content and improve settlement performance.Enzymes, such as amylase, protease, cellulose, were used for sludge conditioning. The impact on activated-sludge dewatering properties and anaerobic digestion process were researched. Experimental result showed that enzymes can extract a certain amount of EPS, reduce water content of sludge cake and improve dewatering performance. Protease had a better effect than others. Enzymes could promote anaerobic digestion process; reduce water content of sludge cake and total solid content, organic content, and conducive to the disposal.