Reducing Sludge Production By Using A Two-Stage Membrane Bioreactor

Excess sludge in biological wastewater treatment process is huge, besides, it usually has some toxicants, injurants and pathogenic microorganisms. So excess sludge must be properly disposaled. However, the disposal of excess sludge may account for 25-65% of the total plant operation cost. Thus increasing attention has been turned to look into potential technology for sludge reduction. One way to reducee excess sludge is to maximize and encourage the growth of organisms higher in the food chain, which feed on bacteria. Two-stage system can be used for culturing more microfauna in the second stage, such as protozoa and metazoa, and reducing the excess biomass production.The present study combine two-stage bioreactor with membrane bioreactor and use two control experimental installations, one is the common two-stage membrane bioreactor, the other is two-stage biofilm membrane bioreactor, to study the commined characteristics and efficiency of reducing sludge production over the controls. The results from the experiments are as following: (1) After the running of two control experimental installations are stablized, the removal of contamination characteristic in two control experimental installations approaches stabilization. The average removal efficiencies of CODcr, NH₄⁺-N and total phosphorus are respectively 96.6%, 82.5% and 59% in the common two-stage membrane bioreactor. The average removal efficiency of COD_Cr, NH₄⁺-N and total phosphorus are respectively 96.2%, 80.9% and 55.8% in the two-stage biofilm membrane bioreactor. (2)Before the predatory effect of microfauna has not impacted microorganism in the predator stage, the removal efficiency of nitrogen and phosphorus in the two-stage biofilm membrane bioreactor was higher than the common two-stage membrane bioreactor; but subsequently the removal efficiencies of nitrogen and phosphorus were lower than the common two-stage membrane bioreactor. (3)The efficiency of reducing sludge production is remarkable in two control experimental installations. The apparent sludge yield(Y_obs) in common two-stage membrane bioreactor and two-stage biofilmmembrane bioreactor is respectively 0.038 mgMLSS/mgCOD and 0.051 mgMLSS/ mgCOD, which is considerably lower than the yields generally obtained for treatment of similar wastewater in conventional treatment processes. Thus, two-stage membrane bioreactor can culture more microfauna, prolong the food chain in activated sludge and realize reducing sludge yield.