Impact Of Coagulation On Changes Of Biostability Of Secondary Effluent

Wastewater reclamation is an effective way to relieve water scarcity. However, th microbial regrowth in reclaimed water may leads to public health risks during storag and transportation. Assimilable organic carbon (AOC) is a crucial indicator fo evaluating the biological stability in water. Coagulation is commonly used in sewag regeneration process, but the current studies of its uncertain effects on AOC of treate water is still limited.The objective of this study was to systematically analyze the coagulation proces on removing organic matter in secondary effluent and investigate the changes in AOC under different water quality and operating condition. The resulting analysis of AOC changing mechanism provides a theoretical basis for optimizing wastewater treatmen process and guaranteeing the safety of reclaimed water.A secondary effluent sample from a municipal wastewater treatment plant ir Beijing was studied. Coagulation has effectively reduced the DOC and UV254 value of reclaimed water, but leads to elevation of AOC level. Compared with neutral and alkaline conditions, the removal efficiency of organic matter by coagulation was higher under acid condition, and with a slightest increase of AOC level. As temperatures rise, the removal rate of organic matter in the secondary effluent is gradually reduced, and AOC growth increased slowly; Ca2+ injection can remove the organic matters efficiently, and a high Ca2+ dosing is most effective at removing AOC; A lower concentrations of ammonia nitrogen (5 mg·L-1) is more conducive to the removal of DOC, but UV254 removal with little effect.After coagulation by different coagulants, including aluminum sulfate(Al2(SO4)3), ferric chloride(FeCl3) and polyaluminum chloride (PAC), the organic matters in secondary effluent could be removed at various removal efficacies. FeCl3 and Al2(SO4)3 had better effects than PAC1. Different coagulants, can effectively reduce the DOC and UV254 value of reclaimed water, but can lead to generally higher level of AOC. With the increase of coagulants dosage, the AOC level of water sample would increase first and lower down at a higher dosage. Add coagulant PAM is not avail at removing the organic substances in water, which may linked to the chemical substances relating to coagulant itself.