Residual Sludge Reduction By Energy Uncoupled Metabolism

Worldwide, the activated sludge process is in common use for the treatment of wastewater, but it also generates a large quantity of excess sludge daily as a byproduct. In this paper, based on the increasing severe problem of sludge ultimate outlet, uncoupled metabolism under the presence of chemical uncoupler and dissipating energy intended for anabolism of cells mass provides a direct mechanism for reducing the yield of biomass. This method can reduce sludge production radically and virtually. The effectiveness of five metabolic uncouplers in reducing sludge production from activated sludge process was compared to screen effective, cheap and non-toxic available uncoupling chemicals and determined the optimal concentrations. The effects of addition of malonic acid and 2, 4, 6-trichlorophenol (TCP) on process performance and sludge reduction were also investigated. The effects of uncouplers on sludge characteristics and microorganism population in the sludge ecosystem were studied specially.In the second chapter, effects of five uncouplers [3, 3', 4' 5 -tetrachlorosalicylanilide (TCS), 2, 4, 6-trichlorophenol (TCP), 2, 4-dinitrophenol (DNP), aminophenol (AP) and malonic acid] on cell yields in batch cultures were compared and found that all five chemicals are good uncouplers in reducing sludge yield. The two chemicals DNP and AP were the most effective uncouplers and the sludge yields can be reduced by 63.75% and 62.39% respectively. The control rates of TCP, TCS and malonic acid were also more than 30%. The optimal concentrations of uncouplers reducing sludge yield were about 1.2, 4, 15, 20, 15 ppm respectively. Finally, TCP and malonic acid were determined as good uncouplers considering the following aspects: sludge reduction ratio, COD removal efficiency, effective concentration used and toxicity.The optimal concentrations of TCP and malonic acid and their effects on sludge observed growth yield and COD removal rate were investigated in batch activated sludge process. The results of batch operation demonstrated that the optimal concentrations of TCP and malonic acid were 4mg/l and 15mg/l. The sludge yield can reduce by 53.02% and 43.62% respectively with the optimal concentrations, butsubstrate removal rate were not inversely influenced. The results of dynamic experiment showed that specific substrate removal rate can be affected by TCP and malonic acid greatly, which can be improved by 26-30% and 8% with 4 mg/1 TCP and 15mg/l malomc acid respectively. The higher uncouple concentration, the higher specific substrate removal rate. The specific cell mass produced over unit time with TCP and malomc acid are lower than blank sample's. This showed that the catabolism and anabolism of microorganism can be uncoupled by uncouplers, which predicated there was an energy-spilling process for metabolic regulation and caused sludge reduction.The results of 70 days continuous operation of activated sludge process showed that excess sludge production with 4mg/l TCP was reduced by 47.83% and COD removal rate and sludge settlability were not influenced obviously. In the meanwhile, the excess sludge production with 15mg/l malonic acid was reduced by 30.08% and COD removal rate was not influenced obviously, but sludge settlability was influenced greatly and the SVI value reached 330 only after 5 days. So malonic acid can only be used as short-term or transition chemical.Sludge ecosystem was analysed by polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) and microscope. The results showed that the microorganism population in the sludge ecosystem had an obvious succession, which implied the uncouplers can effect microorganism population greatly. The diversification of microorganism population was the prime cause of the alteration of sludge settlability.