Bioflocculation And Trickling Filter Process For Sewage Treatment

Innovative low cost, energy and space efficient sewage treatment processes are necessary to deal with the sewage treatment issue in China. Conventional primary treatment is not sufficient to remove most organic pollutants from raw sewage. An innovative treatment process incorporating bioflocculation, for enhanced pretreatment, with the high rate trickling filter was proposed in this research project. Studies were performed to validate the concept, to demonstrate the treatment effectiveness and to define major process parameters.After 25 days culturing in a semi-continuous bioreaetor, the lab produced sludge was employed in bioflocculation pretreatment which accomplished 70% removal of chemical oxygen demand (COD) and 70-80% removal of suspended solids (SS). When the dissolved oxygen (DO) was at least 2 mg/L in the sludge activation tank, removals of COD and SS were at the highest level, while a DO of 5 mg/L was required to for effective removal of NH3-N;DO had no effect on phosphate removal. A DO of at least 2 mg/L was therefore employed in most of the test runs in this research.Relative to a low COD (100-250 mg/L) feed, less organic removal was observed in treating a high COD (400-800 mg/L) feed of septic tank effluent;such results suggested adsorption was the dominant COD removal mechanism. Bioflocculating effectiveness improved when the feed COD decreased;it was resistant to a shocking loading. Bioflocculation adsorption followed by the high rate trickling filter treatment resulted in a final effluent with a COD < 40 mg/L;its average removal rates for COD, PO₄³-P, and NH3-N were 84.7%, 65.5%, and 87% respectively.COD removal was stable and most effective at an organic loading of 3-7 kgCOD/kgMLSS·d. The treatment performance was adversely affected by increase influent flow rate. While the average COD removal continued at a high rate of 87.7% (effluent COD remained below 40 mg/L), the average NH3-N removal was 53.4% and the average PO₄^3--P was 49.7%.Sludge employed in bioflocculation exhibited the best adsorption rate at 20℃. Between 20-40℃, the adsorption rate decreased as the temperature went up;Adsorption equilibrium was attained in 20-30 minutes. Organic matters in suspended forms were more effectively removed by biosorption than soluble and colloidal forms. Microbe inhibitor was harmful to the bioflocculation pretreatment.