Removal Effect of Coagulating Sedimentation Method on Polyethylene Microplastics in Water

Microplastic is a new kind of pollutant.It exists widely in the aquatic environment and seriously endangers the aquatic ecosystem.In this study,the coagulating sedimentation method was used to remove microplastics in water.Polyethylene(PE)was selected as the representative of microplastics,polyferric sulfate(PFS),polyaluminum chloride(PAC)and aluminum sulfate(AS)were used as coagulant,and polyacrylamide(PAM)was used as coagulant aid to study the effects of pH,coagulant concentration and sedimentation time on the removal of PE by single and composite coagulant.The results showed that when the dosage of PFS was 0.5 g/L and pH was 5.0,the removal rate could reach 82.14%,which was better than PAC and AS,indicating that PFS had better coagulation and sedimentation performance for PE;the composite coagulant of PFS+PAC+AS(1 g/L+0.2 g/L+0.2 g/L,pH was 5.0)had the highest removal rate of PE,reaching 96.06%;the removal rate of PE increased with the increase in sedimentation time,but considering that the longer sedimentation time has less contribution to the improvement of removal rate,it is recommended that 4 h is appropriate.

Effects of Coagulation and Ozonation Pretreatments on Biochemical Treatment of Fluid Catalytic Cracking Wastewater

Fluid catalytic cracking (FCC) salty wastewaters, containing quaternary ammonium compounds (QACs), are very difficult to treat by biochemical process. Anoxic/oxic (A/O) biochemical system, based on nitrification and denitrification reactions, was used to assess their possible biodegradation. Because of the negative effects of high salt concentration (3%), heavy metals and toxic organic matter on microorganisms’ activities, some techniques consisting of dilution, coagulation and flocculation, and ozonation pretreatments, were gradually tested to evaluate chemical oxygen demand (COD), ammonia-nitrogen (ammonia-N) and total nitrogen (TN) removal rates. In this process of FCC wastewater, starting with university-domesticated sludge, the ammonia-N and TN removal rates were worst. However, when using domesticated SBR’s sludge and operating with five-fold daily diluted influent (thus reducing salt concentration), the ammonia-N removal reached about 57% while the TN removal rate was less than 37% meaning an amelioration of the nitrification process. However, by reducing the dilution factors, these results were inflected after some days of operation, with ammonia-N removal decreasing and TN barely removed meaning a poor nitrification. Even by reducing heavy metals concentration with coagulation/flocculation process, the results never changed. Thereafter, by using ozonation pre-treatment to degrade the detected organic matter of di-tert-butylphenol and certain isoparaffins, COD, ammonia-N and TN removal rates reached 92%, 62% and 61%, respectively. These results showed that the activities of the microorganisms were increased, thus indicating a net denitrification and nitrification reactions improvement.

Treatment of Wastewater from Dairy Farm by Coagulation Sedimentation

In order to evaluate the processing efficiency of coagulation sedimentation on wastewater from dairy farm and to provide reference for wastewater treat- ment, an experimental study was carried out to investigate effects of coagulant dosage, types, pH, dosage of coagulant aids PAM on removal rate of COD, turbidity and SS in wastewater from dairy farm. The results showed that PAC displayed higher effectiveness in treatment; the removal rates of COD, turbidity and SS were 61.4%, 86.6% and 94.5% respectively when pH was 11.0, PAC dosage was 150 mg/L, and PAM dosage was 4 mg/L. The results indicated that coagulation sedimentation could reduce organic content of wastewater effectively and alleviate the load of subsequent biochemical treatment.