Transformation Of Disinfection Byproduct And Its Precursors During The Wastewater Regeneration Processes And The Controlling Research

As a potential water resource,urban sewage has the advantages of reliable and stable water supply as well as a great significance for solving water shortage and the contradiction between water supply and demand.The disinfection process is an important part for the safety of the water regeneration,but which was also accompanied with the risk of disinfection byproducts?DBPs?.In this study,DBPs precursors in the municipal water treatment process was analyzed and characterized.The migration and transformation of precursors in different treatment processes were studied and the formation of chlorination DBPs was explored.Furthermore,DBPs precursors in the biotreatment process were analysed according to their molecular weight?MW?and polarity.The changes of precursors during the biotreatment process and the relationship between DBPs and precursors were investigated.Moreover,an ozone-ceramic membrane system was built to treat the secondary effluent,and the mechanism of membrane filtration,ozone pre-oxidation and the combined ozone-ceramic membrane on the formation of DBPs were studied.The main results are as follows:?1?Primary treatment?sedimentation?could effectively remove hydrophobic humic acid through the mutual exclusion between hydrophobic fraction?HPO?with water.The removal of humic acid would lead to the obvious reduction of carbonaceous disinfection byproduct formation potential?C-DBPFP?.In addition,nitrogenous disinfection byproduct formation potential?N-DBPFP?was found to be increased due to the increase of DON/DOC value.Although secondary treatment?biotreatment?was effective in removing humic acid and aliphatic hydrocarbons,it could produce a large amount of soluble microbial products?SMP?,which led to the enhancement of HPO percentage.And the accumulation of SMP resulted in the significant increase of C-DBPFP and N-DBPFP.Humic acid and hydrophobic SMP could be removed by the advanced treatment?cloth filtration?,leading to the reduction of HPO percentage and the increase of HPI percentage.The decrease of humic acid and hydrophobic SMP would cause the reduction of C-DBPFP and N-DBPFP in the advanced treatment.?2?Further researches were carried out to study the changes of DBPs precursors and DBPs during the biotreatment process.Results indicated that the reversed A²/O process could not only effectively remove the dissolved organic carbon?DOC?and dissolved total nitrogen in the wastewater,but also affect the molecular weight?MW?distribution and hydrophilic-hydrophobic property of dissolved organic matter?DOM?.The accumulation of low MW and HPO DOM was possibly due to the formation of SMP-like matters in the reversed A²/O treatment,especially in the anoxic and aerobic processes.Moreover,DOM in the wastewater displayed high C-DBPFP in the fractions of MW > 100 k Da and MW < 5 kDa,and revealed an increasing tendency of N-DBPFP with decrease of MW.For those polarity based fractions,HPO fraction of wastewater showed significantly higher C-DBPFP and N-DBPFP than hydrophilic and transphilic fractions.Therefore,although the reversed A²/O process could remove most DBP precursors by DOC reduction,they led to the enhancement of DBPFP with the formation and accumulation of low MW and HPO DOM.?3?An ozone-ceramic membrane system was built to study the mechanism of membrane,pre-oxidation and combined O₃-ceramic membrane on the formation of DBPs from secondary effluent.The results indicated that the small pore ceramic membrane?0.1 ?m and 0.05 ?m?was effective in the removal of C-DBP and N-DBP precursors.The removal rate of C-DBP precursors and N-DBP precursors for 0.1 ?m and 0.05 ?m ceramic membranes were 61.85%,68.10% and 53.59%,58.85%,respectively.O₃ pre-oxidation could remove C-DBP and N-DBP precursors to some extent,but the removal rate was low,which were 36.74% and 28.86%,respectively,when O₃ dosage was 5 mg/L.The combined O₃-ceramic membrane process could effectively alleviate membrane fouling?relative to individual ceramic membrane filtration?and increase the removal rate of C-DBP and N-DBP precursors?relative to individual O₃ preoxidation?.When O₃ dosage was 5 mg/L,after running for 6h,transmembrane pressure of 0.05 ?m and 0.1 ?m ceramic membranes were 21.5 kPa and 15 kPa,respectively,and the service life of ceramic membrane was nearly doubled.Under such condition,the removal rates of C-DBP precursors for 0.05 ?m and 0.1 ?m ceramic membranes were 59.20% and 53.25%,and which of N-DBP precursors were 43.50% and 41.45%.