The Study On Sludge Reduction In The Biological Treatment For Gelatin High Calcium Wastewater

By adding green scale inhibitor polyepoxysuccinic acid (PESA) in the biological process is to treat gelatin wastewater in which Ca2+and CODCr concentration was1600mg/L and1500mg/L respectively, and to study its impact on the sludge concentration MLSS, sludge volume index SVI, effluent Ca2+retention rate, calcium content on the sludge and COD removal rate, and meanwhile to analyse its effect on the sludge reduction in the biological treating high calcium wastewater process. At the same time, through variation of pH in the biological response process and calcium constituents infrared analysis in sludge is to explore the mechanism of the precipitation of CaCO3, CaSO4, Ca3(PO4)2and CaHPC4. The experiment conducted a reactor without PESA (blank bioreactor) to present a contrast study. After23d experiments, the results showed:Start the biological aerated reaction after adding the PESA to the reactor, the COD removal rate was about60%-95%, namely that the PESA did not affect the treatment effect; MLSS was lower than blank bioreactor, sludge growth rate was135mg/L-d, while the blank bioreactor sludge growth rate was185mg/L·d, PESA inhibited sludge growth of50mg/L-d, the effect of reduction was27%; SVI rose0.85mL/g in18-20d and made the sludge volume release, it presentes a greater anti-calcium compression compressibility; Ca2+retention rate of effluent was above97%, it was higher than the blank bioreactor; Calcium content was5%-6%in the sludge, it was lower than the blank bioreactor, it shows that PESA can prevent the calcium salt precipitation coming from aeration process from attaching to the surface of the activated sludge, and keep good active sludge, so as to achieve the sludge reduction purpose. After20d, calcium content in the sludge was lower than5%in the reactor of adding PESA, calcium ion bridging function was weak, sludge floc began to collapse, SVI rose greatly, the sludge sedimentation performance declined, and the effluent was turbid, but still sank clearly after2h, it does not affect the effect of sludge reduction, thus the sludge retention time of the PESA reactor should be controlled at about20d.At the end of the biological reaction, excess sludge reduction effect of using alkali treatment was about11.64%, the content of the soluble organic substance SCOD was as high as1000mg/L, and making it back to the activated sludge system would make sludge load increase, and the cost also increased. But using PESA for sludge reduction did not increase equipments, space, and power consumption, and the sludge reduction effect could reach to27%.When the pH of the feed water was about8.2-8.3in the biological treatment system, the pH of the both reactors decreased firstly and then stabilized, when the pH of the feed water was about7.3-7.5, the pH of the two reactors increased firstly and then stabilized, finally the pH of inhibitor reactor stabilized at around7.65-7.75, while the pH of the blank bioreactor stabilized at around7.55-7.70; Stabilization trend of pH was mainly the regulation function of active sludge system itself and the buffer function of phosphates in wastewater; At the room temperature, first added HC1to dissolve calcium salt, then added NaOH to make the calcium salt re-precipitate, the pH of critical point which precipitated CaCCO3was7.62, the pH of critical point which precipitated CaSO4was6.03, the pH of critical point which precipitated Ca3(PO4)2was5.55, the pH of critical point which precipitated CaHPO4was5.12, the pH reached to its critical point which precipitated four kinds of calcium salt in biological aeration process, therefore the precipitation of calcium salt is inevitable; Active sludge was analysed by infrared after organic burning, the precipitated calcium salt was the mixture of CaCO3, CaSCO4, Ca3(PO4)2and CaHPCO4in biological aeration process, but in the PESA reactor, the main component of the calcium salt in the sludge was the mixture of CaCCO3and CaSO4, instead of Ca3(PO4)2and CaHPCO4. It indicates phosphates are dispersed by PESA, and proves adding PESA benefits to the reduction of the calcium salt in sludge system.