Study On Initiation And Maintenance Of Limited Sludge Bulking Under Low Do In SBR Process

Activated Sludge Process is applied more and more extensively, with rate of treated sewage rising. As key problems to be solved, heavy energy consumption and sludge bulking have been attracting more and more attention of resaerchers. Theory of energy saving achieved by limited filamentous bulking under low DO (Limited sludge bulking for short.) can not only save energy but also improve water quality of effluent. And this theory has become a hot research topic since brought out, getting more and more recognition and attraction. However, there has been no systematic overall report on impact factor of starting limited sludge bulking because of short history and higher difficulty in studying.In order to surport practical applications of limited sludge bulking theory, effect of operation condition to starting limited filamentous sludge bulking was reseached using SBR process(Sequencing Batch Reactor Activated Sludge Process) in this paper, and nitrogen and phosphorus'removal effect was optimized after starting of limited filamentous sludge bulking. In addition, dominat filamentous bacteria was identified through methods of microorganism such as staining and experiment of sulgur accumulation, which is important to perfect limited sludge bulking theory. The conclusions are as follow:(1) Limited sludge bulking at low DO (0.3 mg/L) was induced at organic loading of 0.2 kgCOD/(kgMLSS·d) under operating ways of aerobic only, after short-term serious bulking,and was maintained as long as 40d. At the same time, COD, nitrogen and phosphorus were removed effectively. Specific gravity of activated sludge was increased by proliferation of phosphorus accumulating organisms (PAOs), which helped to resume state of limited sludge bulking after excessive sludge bulking.(2) Limited sludge bulking at low DO (0.3 mg/L) could also be induced under operating ways of A/O (Anoxic/Oxic). And DO of 0.5 mg/L couldn't induce limited sludge with worse effect of pollutant removal, but induced pin sludge instead. Removal rates of NH4+-N, TN and PO43--P were improved by longer aerobic stage, added post anoxic stage and external carbon source. And state of limited bulking hadn't been damaged; SVI was maintained about 170 mL/g during working under this pattern as long as 20d. And a system combining limited sludge bulking and effctive removal of nitrogen and phosphorus were realized. (3) Sludge bulking didn't occur because of neither low nor high temperature only under A/O pattern. Synergy effect of low or high temperature could both induce limited filamentous bulking at different DO value: 0.3mg/L at low temperature (10℃~15℃), and 0.8mg/L at high temperature(25℃~30℃). The difference was caused by dominant filamentous bacteria varing at different temperature: M. parvicella at low temperature, and H. hydrossis at high temperature with a few M. parvicella. M. parvicella in this paper was identified to be MPA223 by technique of FISH (Fluorescent in situ Hybridization).(4) Preliminary study on energy saving of limited bulking system at high temperature showed that method of limited sludge bulking (AR=5L)could save 63.6% aeration(AR) compared to normal state(AR=13.75 L), which provided reference for economic efficiency analysis when limited sludge bulking thoery applied in Wastewater Treatment Plant(WWTP).