Effects of UV/H2O2 Oxidation Process on Disinfection By-products Formation for Algae and Activated Sludge
Date Issued
2014
Date
2014
Author(s)
Ou, Tai-You
Abstract
Chlorination has been widely used in drinking water supply systems for control of the growth of microorganisms; however, the formation of various disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs) in chlorination has been concerned due to their potential carcinogenicity and other adverse health effects. To avoid the generation of DBPs, advanced oxidation processes (AOPs) such as UV/H2O2 process have been applied as a substitute for pre-chlorination.
Most studies focused on the effects of UV/H2O2 on specific chemical pollutants; however, the influences on water quality after treating microorganisms by UV/H2O2 are still unclear. This study focuses on the changes of DBPs precursors and DBPs formation potential (DBPFP) after the treatment of activated sludge and algae by UV/H2O2 oxidation. Non-purgeable dissolved organic carbon (NPDOC) and dissolved organic nitrogen (DON) were measured; subsequently, DBPs including THMs, HAAs, HKs and HANs were analyzed after DBPFPs tests. Moreover, the effects of different initial H2O2 concentrations, initial pH disinfectants and the role of Br− were discussed. The characteristics of biological organic matter were also compared with which of anthropogenic organic matter (domestic sewage samples) and natural organic matter (ecological pond water samples).
After the UV/H2O2 oxidation, the experimental results showed that the organic matter was released from the samples of activated sludge and algae and soon was degraded, which caused that the NPDOC and DON of the tested samples could increase in the beginning and then decrease. The trends of DBPs were similar to that of NPDOC; however, the occurrence of highest THMs concentration was earlier to that of HAAs.
Comparing to using 0.05% and 0.01% initial concentrations of H2O2, using 0.1% H2O2 produced more NPDOC but could also keep on degrading the organic matter released from the microorganism samples. Higher NPDOC concentrations also could be produced when oxidation were conducted under the basic conditions. Moreover, there was no specific DBPs speciation from organic particulates with different sizes (0.22, 0.45 and 1.0 μm) after disinfection. Due to the stronger halogenation ability of bromine, the proportions of Br-DBPs and the concentrations of total DBPs could increase with the amounts of Br−.
Comparing the four different sources of organic matter, the highest DBPFP/NPDOC occurred in the domestic sewage samples; and then was in the activated sludge samples and the ecological pond water samples; the algae samples had the lowest DBPFP. Moreover, the dominant species shifted to HAAs form THMs in the samples of activated sludge and algae with the oxidation time. More HAAs could be generated in the domestic sewage while the ecological pond water samples could produce more THMs. The brominated species of THMs and HAAs could increase in all the samples after the addition of Br− moreover, the increased amount of DBPFP was much higher in the algae and the ecological pond water samples while the lower oxidizing capacity of HOBr reduced the DBPFP of the domestic sewage due to the higher demand of the domestic sewage for oxidation before halogen substitution. The DBPFP generated from the chloramination was much lower than which from the chlorination. HAAs became the dominant species in all the samples. However, the unchanged Br-HAAs concentrations caused the increased proportion of brominated species in HAAs.
Subjects
高級氧化
UV/H2O2
活性污泥
銅綠微囊藻
消毒副產物
Type
thesis
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