Effects of different secondary biological treatment processes followed by flocculation and sand-filtration on subsequent DBPs control from sewage treatment plants

摘要

The nature and chlorine reactivity of dissolved organic matter (DOM) in reclaimed water from sewage treatment plants (STPs) are quite important for assessing the risk of wastewater reuse. Elucidating relation between DOM and its fractions characterization with different treatment processes is quite important for selection of treatment processes focusing on disinfection by-products (DBPs) control. In this study, four classical STPs in Beijing (A similar to D) with different secondary biological treatment processes but all with flocculation and sand-filtration as advanced treatment process were selected to investigate DBPs formation potentials and DOM characterization variation during these processes and their relation. Chloroform, dichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) dominated among four trihalomethanes (THMs) and nine haloacetic acids (HAAs) formation potentials respectively during chlorination of both secondary and sand-filtration effluents with the order of TCAA chloroform DCAA. Both THMs and HAAs formation potentials were positively related with DOC percentage for the hydrophobic fractions in the DOM. The bromine incorporation in THMs was obviously higher than that in HAAs. The especially higher bromine incorporation in D STP was probably due to the higher SUVA value in this STP with SBR as secondary biological treatment process comparing to those in the other three STPs. DOC and bromide removal, SUVA decrease were important elements for selecting secondary treatment process considering DBPs control. Flocculation and sand-filtration performed not well in removing DBPs precursors especially for chloroform and DCAA except for C STP, which had higher hydrophobic fraction percentage removal and molecular weight decreasing during the advanced treatment process. FTIR analysis revealed that flocculation and sand-filtration probably removed more aliphatic structures than aromatic or COO- structures. The absorption ratio of aromatic C=C, COO-/aliphatic CH3 peaks in D STP was the highest among the four STPs, which was consistent with the highest bromine incorporation in this STP.