Experimental Study On Enhanced Phosphorus Removal Based On Preceding Phosphorus Recovery

In view of the traditional biological phosphorus removal method is difficult to stable standard, and lack of system in the presence of carbon source and removal of phosphorus and nitrogen removal of sludge age the contradiction of the requirement, the test is performed by chemical phosphorus recovery enhanced A2/O treatment of city sewage. The chemical phosphorus recovery test was studied, through the economic and technical feasibility analysis are compared in two aspects, optimized the phosphorus recycling precipitating agent. Water test and start up research was also carried out and the chemical phosphorus recovery side flow ratio, DO, mixed liquid recycle ratio, sludge return ratio on biological phosphorus removal effect were investigated.(l)The aluminum salt, ferric chloride, calcium hydroxide and magnesium chloride (guano act) were selected as chemical phosphorus recovery precipitating agent for the laboratory study, the results showed that polymeric aluminum chloride and struvite precipitation effect were good, but the guano method for recovering phosphorus from sludge amount, and capable of simultaneous removal of nitrogen and phosphorus, the formation of struvite stones can be directly used as fertilizer use, it has very large development space, so choose the guano act which could be used as phosphorus resource. For struvite the best pH value was10, the best Mg/P and N/P ratio was1.5. In the optimal case the removal rate of TP could reach89.3%.(2) The water test results showed that at constant temperature, different volume and different reflux ratio, the dissolved oxygen of the monitoring points which located above aeration was larger, conversely low; the dissolved oxygen of the anoxic tank kept constant along depth. When the aeration time was constant, the dissolved oxygen in oxidation ditch changed with reflux ratio with no special law; the dissolved oxygen in anoxic pond increased with reflux ratio. Reflux ratio was constant, the monitoring points of the dissolved oxygen increased as volume enlarged.(3)The removal rate for each pollutant was high in the late sludge culture, the average removal rates of COD, TN and TP were92.3%,68.5%and76%. In starting operation, the average removal rates of COD, TN and TP were91%,68%and80.6%,the effluent COD and TN reached the level of A, effluent TP could stable up to level B standard.(4) During the stable operation of the system, when the chemical phosphorus recovery side stream was0,5%,10%and15%, effluent COD changed little with lateral flow ratio increased. Effluent COD was always below50mg/L, the average value of effluent COD was40mg/L, the average removal rate of COD was92%. With flow ratio decreased, effluent TP increased, the removal rate increased. When S was5%and10%, effluent TP was below0.5mg/L, reached the level of A standard, when the S is10%, the lowest TP was obtained. When the side stream increased to15%, due to environmental temperature decreased, the effluent TP was rising, the removal rate was lower. The effluent TN was below15mg/L, the effluent TN was lowest when the the side stream was10%.Therefore chemical phosphorus recovery side flow ratio S taken as10%was more appropriate.(5)When DO was at0.5～6.25mg/L, the removal rate of TP and COD little with DO. But effluent TP was minimum when it was during0.5～6.25mg/L, so DO should be controlled in2～4mg/L.(6)The removal rate of TP increased with the mixed liquid recycle ratio rising between100%～400%, the effluent TP gradually reduced. During the running period, average value of effluent TP was0.71mg/L, the average removal rate of TP was89.5%. When the mixed liquid recycle was relatively low for100%,150%and200%, the removal rate of TP in the oxidation ditch was greater than that in the anoxic zone, and when the reflux ratio increased to300%and400%, the removal rate of TP in the anoxic zone on was greater. From the system of TP removal efficiency and energy consumption, mixed liquid reflux ratio of200%was quite appropriate. The effluent TP increased gradually with the sludge reflux ratio increased, the removal rate of TP was on a downward trend, effluent TP of anaerobic decreased. Considering the experiment, sludge return ratio of75%was more suitable for the test.