FINAL CLARIFICATION BY INTEGRATED FILTRATION WITHIN THE ACTIVATED-SLUDGE AERATION TANK

A laboratory sequencing batch reactor (SBR), integrating a novel filtr ation system, was used to treat wastewater from a cheese factory. For an average influent CODtot of 1,000 mg l(-1) and at an HRT of 8 d, the SBR-Filtration system yielded an overall efficiency of 94.5% in terms of COD removal, and an effluent suspended solids (SS) concentration d ose to 0 mg l(-1). Throughput fluxes as high as 443 l m(-2) h(-1) coul d be reached. No permanent clogging or decrease in permeability of the filtration step was observed over the 12 d testing period. The effect of solids concentration on filtration was assessed by increasing, ste pwise, the MLSS concentration in successive stages. The food to microo rganism ratio (F/M) was maintained almost constant by increasing the i nfluent load proportionately to the increase in biomass. This was done by adding powdered milk waste to the real wastewater. As a result of rapid increases in influent COD, changes in composition and loading ra tes, and a lack of nutrients during this phase of experiments, steady state conditions were interrupted. Consequently, the biomass would not flocculate well and the SVI increased. The decrease in filtration eff iciency was thought to be due to the transient biological state pof th e biomass, rather than to the concentration increase itself. An attemp t to corroborate this observation was made by systematically decreasin g the mixed liquor concentration in the reactor by dilution with water . Flux rates remained constant, regardless of the variation of MLSS co ncentration.