The Safety Technology For Municipal Wastewater Reclamation By Advanced Municipal Wastewater Treatment O₃-BAF

With the development of environmental pollution and shortage of water resource,wastewater reclamation has become of increasing importance. Promotion of wastewaterreclamation has become an important policy as well as strategy of China to cope withwater shortage problems. However, the chemical and hygienic risks accompanied withwastewater reclamation have to be reduced to an acceptable level. The removal ofharmful persistent organic compounds (POPs) as well as harmful microorganisms isrequired to ensure the safety of wastewater reuse. The conventional coagulation-sedimentation-sand-filtration treatment for wastewater reclamation mainly focuses onthe removal of suspended solids. Chlorine has long been used for the mostlydisinfection of municipal wastewater . Formation of many harmful disinfection by-products, however, has caused public concerns over the risk of chlorine disinfection .And further, the residual chlorine could cause severe damage toward hydro-ecosystem.In this study, two ozonation-biofilters (O3-BAF) was constructed for the advancedtreatment of municipal wastewater, and the pollutant removal efficiency, thestabilization of the system, and the safety of treated water were evaluated over long-term test. The results are summarized as follows. 1. Safety evaluation index system for reclaimed water The system includes conventional parameters like DOC, CODMn, UV254, NH3-N,etc., POPs like organotins, NP , etc., bioassay indexes like UMU, Ah acceptor, ER, etc.,and the exposure of carassius auratus(determinationof fish growth and VTG) 2. Characteristics of secondly effluent from the municipal wastewater treatmentplant (MWTP) The quality of the secondly effluent from the MWTP was quite stable: 30～40mg/L CODCr, 8.8～12.2 mg/L BOD5, 10.0～15.9 mg/L TOC, 7.8～9.5 mg/L SS, 25～32 cu chrama, 2.55～39.89mg/L NH3-N, 0.29～0.31 BOD5/CODCr. With successivecoagulation-sedimentation-sand-filtration treatment(15mg/L Al2O3), the CODCr,BOD5 and SS was 23～34mg/L, 6.44～10.26mg/L and 5.1～7.8 mg/L, respectively ;NH3-N was less than 10mg/L ; the ratio of BOD5/CODCr was 0.26～0.33. 3.Ozonation-biofiltration ( BAC and BCF) systems for wastewater reclamation III重庆大学博士学位论文 Ozonation can effectively improve the quality of the secondly effluent, theoptimum ozone dose was 5mg/L, and the optimum reactive time 5-10 min.; theoptimum EBCTof following biofiltration is 10-15min. Under an ozone dose of 5mg/L, reactive time of 10min and BAF's EBCT of 10min,the removals of CODMn, DOC,UV254 and chroma by O3-BAC and O3-BCF were30.6%, 27.7%, 47.5%, 80% and 28.3%, 23.8%, 41.3%, 79%, 80.1% , respectively. Itseffluent quality was 3.8mg/L, 4.1mg/L, 0.053cm-1, 2.0cu and 3.9mg /L, 4.3mg/L,0.059cm-1, 2.1cu of CODMn, DOC,UV254, and chroma; at the same time SDI (siltdensity index) was <4, indicating that the treated effluent was suitable to be used as thefeeding water of RO (reverse osmosis) systems. 4.Microorganismsafety The number of total bactica and E.coli were 106～109 MPN/L and 103～106MPN/L in secondly effluent, and decreased to 105～108 MPN/L and 102～105 MPN/Lafter successive coagulation-sedimentation-sand-filtration treatment. The inactivation efficiency of E.coli using ozone increased with increase of ozonedose. Complete inactivation of E.coli requires an ozone dose of at least 12mg/L. 5.Chemcialsafety Ozonation led to the effective removal of EDCs like MBT, DBT and NP etc., andthe removal of NP was above 99.99%. Ozonation-biofiltration can decrease the death and aberration ratio of carassiusauratus, and its ecological risk. 6.Analysis of microbial communities in the biofilters PCR-DGGE results demonstrated that the micobial community in the BAC andBCF was very similar and stable over the time and space spans. 7. Cost performance assessment In terms of pollutant removal, BAF and BAC demonstrated similar performance.However,...