Reduction Of Excess Sludge Production By Uncoupled Metabolism In Activated Sludge Process

Worldwide, the activated sludge process is in common use for the treatment of wastewater, which also generates a large quantity of excess sludge daily as a byproduct that requires additional processing and disposal and may account for up to 60% of total plant operation costs. In this paper, based on the increasing severe problem of sludge ultimate outlet, uncoupled metabolism under the presence of protonphore or aerobic-anoxic recycle occurs and dissipating energy intended for anaboiism of cells mass provides a direct mechanism for reducing the yield of biomass. Reduction of yieid of cell and lysis of cell by endogenous respiration with physical, chemical and biological means result in low to zero excess sludge discharge from wastewater treatment plant. This method can reduce sludge production radically and virtually. The effectiveness of eight metabolic uncouplers in reducing sludge production from activated sludge process were compared to screen effective, cheap and non-toxic available uncoupling chemicals and determined the long-term uncoupler effects of 3,3',4',5-tetrachlorosalicylanilide(TCS) in activated sludge batch cultures. The effects of addition of TCS on process performance and sludge characteristics were also investigated. The activated sludge process with addition of TCS. oxic-settling-anoxic(OSA)process and OSA with addition of TCS combined process were studied in continuous operation with emphasis.In the second chapter, effects of 8 uncoupling chemicals[ o-chlorophenol(oCP), m-chlorophenol(mCP), 2, 4-dichlorophenol]DCP), 2, 4, 5-trichlorophenol(TCP), p-nitrophenol(pNP), m-nitrophenol(mNP), 2,4-dinitrophenol(DNP) and TCS] on cell yields in batch cultures were compared and found that all eight chemicals are good uncouplers in reducing sludge yield. Nitrophenol chemicals were better thanchlorophenols. The two chemicals DNP and pNP were the most effective uncouplers of activated sludge respiration with control rates of 89.16% and 83.77% respectively. The control rates of oCP, TCP, mNP and TCS were also more than 60%. The acidity constant(pATa)of a metabolic uncoupler highly influenced its effectiveness in sludge reduction, i.e. metabolic uncoupler with a lower pKa value has a higher potential to reduce sludge production which confirmed the theoretical analysis that uncoupler weaken the proton motive potential producing ATP. The optimal concentrations of uncouplers reducing sludge yield were about 10 ppm. When the uncoupler concentration was constant, sludge yield increased with the increasing sludge concentration. High sludge concentration would weaken the effect of uncoupler. Therefore, the specific uncoupler concentration, i.e. the ratio of uncoupler concentration to sludge concentration was a better parameter to choose uncoupler.In the third chapter, the effect of addition of liquor TCS, solid TCS and addition mode of solid TCS on excess sludge production in batch activated sludge process, process performance and sludge characteristics were investigated. The results of 40 day batch operation demonstrated that TCS of 3.6 mg/l can reduce sludge production by 54.3%, but substrate removal rate was not inversely influenced and effluent total nitrogen and NH3-N concentrations were comparative with the control test. SVI values of sludge were increased slightly. Although compared with the control sludge, the sludge was loose; the settlability of sludge was not affected. Specific oxygen uptake rate(SOUR) and dehydrogenase activity of sludge were higher than those of control sludge, which showed that TCS can activate microbial in sludge to promote energy spilling which resulting in sludge yield reduction. Filamentous bacteria were still present in the control reactor, while this did not occur in the reactor with addition of TCS. The results of PCR-DGGE technology suggested that the microbialpopulation was changed. The effect of dosing solid TCS was better than that of liquor TCS. but COD removal rate was decreased a little. Effluent TN and NH3-N concentrations were the same wi...