| Chloral hydrate?CH?,in terms of content,is the third disinfection by-product?DBP?in drinking water after trihalomethanes?THMs?and haloacetic acids?HAAs?.However,it has much more toxicity than THMs and HAAs and has aroused more and more attentions in recent years.The control for CH in drinking water is limited by O3-BAC advanced water treatment processalthough it can remove organic matter in water efficiently.In addition,researches on the precursors of CH were mainly focused on the model compounds so far,and the concentrations of specific precursors of CH such as humic acids,protein and amino acids in raw water and their removal by water treatment process w ere still unknown.This paper firstly revealed the concentration of specific precursors of CH in raw water and removal by water treatment processes.Sceondly,the control for CH enhanced by O3/H2O2 and O3/Ti O2 processes and the oxidation for CH by ozonation and catalyzed ozonation and its kinetic model were studied in this paper.Finally,the control for CH precursors in filtered water and specific precursors by O3-BAC,O3/H2O2-BAC and O3/Ti O2-BAC processes and its mechanism were investigated.The research on the concentration and removal of specifi c precursors revealed that: the average concentrations of total amino acids in A,B,C reservoirs were 6.31,5.02,13.50 ?g/L,respectively,in which the main amino acids in three reservoirs were aspartic acid,glutamic acid,cysteine and leucine.The aver age concentrations of humic acids in three reservoirs were 2.04?2.06?2.54 mg/L.The average concentrations of protein in three reservoirs were 0.12,0.11,0.10 mg/L,respectively.The removal ratios of protein and amino acids which has very low concentration in raw water by conventional process and biological activated carbon-ultrafiltration process was lower than O3-BAC process.The study on the oxidation of CH by ozonation and catalyzed ozonationrevealed that: The optimum dosage of O3 on the removal of CH was 1 mg/L,thus,56.4% of CH was removed by O3 oxidation process in this condition,and the oxidation for CH followed the first-order kinetic model.O3/H2O2 process significantly improved the removal of CH by O3 alone,in which 97.60% of CH was removed during the process at the mole ratio 0.5 of H2O2 and O3.The O3/Ti O2 process could improve the removal of CH by O3 alone,in which 73.38% of CH was removed by O3/Ti O2 process at the dosage 100 mg/L of Ti O2.Temperature and p H were the main factors which can impact the reaction rate of the oxidation for CH.With the higher temperature and p H,the faster reaction rates of oxidation of CH were occurred.The optimization on the control for CH precursors in raw water and specific CH precursors by O3-BAC,O3/H2O2-BAC and O3/Ti O2-BAC processes revealed that: 53.80% of CHFP for filtered water was removed by O3-BAC process at the dosage 1.5 mg/L of O3.While 79.10% and 65.34% of CHFP for filtered water were removed by O3/H2O2-BAC and O3/Ti O2-BAC processes at the mole ratio 0.5 of H2O2 and O3 and the dosage 100 mg/L of Ti O2,respectively.Thus,O3/H2O2 and O3/Ti O2 enhanced the removal of CHFP for filtered water by O3-BAC process.The mechanism of control for CH by O3-BAC process can be described as follows: O3 oxidation improved the proportion of biodegradable dissolved organic carbon and hydrophilic,aromatic protein-like organic matter in water and oxidized the aromatic organic matter at the same time,degraded soluble microbial by-product-like organic matter,hydrophobic organic compounds.Hence,the following BAC process removed organic matter in water more efficiently.O3/H2O2 process optimized the control for CHFP for filtered water by enhancing BDOC,hydrophilic compounds in water,and oxidized the refractory organic matter to turn to hydrophilic matter.On the other hand,O3/Ti O2 enhanced the mineralization of dissolved organic matter in water and converted the refractory and hydrophobic matter to biodegradable,hydrophilic matter.In general,O3/H2O2 has more efficient enhancement for the removal of CHFP for raw water and specific CH precursors than O3/Ti O2 by O3-BAC processes. |
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