Study On The Formation Characteristics And The Risk Assessment Of The By-products During The Ozonation Of Raw Water Of Pearl River

With the increasing contamination of drinking water resource, it is essential to find newsdrinking water trearment process. Ozonation, as an advanced treatment technology ofdrinking water, has been thoroughly researched and widely applied. Then a new problem isappeared, that is carcinogenic by-products like formaldehyde and bromate may formed duringozonation. It will be more beneficial to the safety of drinking water and the widespreading ofozone technology in drinking water treatment, if the formation characteristics of theby-products can be known and the generating capacity of the by-products can be predictedbefore.In this thesis, simulation experiments in deionized water were conducted to studyinfluential factors of the formation characteristics of formaldehyde and bromate; Theorthogonal experiments, different water quality of raw water experiments and Contrastexperiments of two kinds of different ozone/activated carbon process were conducted with theraw water from Pearl River, Dongjiang River, Xijiang River and Beijiang River, to study theinfluence of the operating conditions, the conditions of water quality and the processconditions on the formation characteristics of formaldehyde and bromate; Ozone/activatedcarbon process experiments were conducted with the raw water which was influenced bytidewater from Zhongshan City Southern Town to establish predicting models of bromateformation. Main research conclusions are as follows.When other parameters were kept unchanged, crylic acid with double bond structureproduced the most formaldehyde after the oxidation by ozone, while tartaric acid withsaturated straight-chain and aniline with aromatic ring produced no formaldehyde. Makingacrylic as the precursor of formaldehyde, the formation had a linear relation with acrylicconcentration; With the increasing of ozone dosage, the formation of formaldehyde increasedfirst, when [O₃]₀/[acrylic]₀>0.57mg/mg reduced; Within the range of pH of natural water, theformation of formaldehyde had no obvious change with the change of pH; Hardness increasedthe formation of formaldehyde; Alkalinity, to some extent, restricted the formation of theformaldehyde. As to bromate, crylic acid and aniline inhibited the formation of bromate,while tartaric acid enhanced its formation; Parachlorobenzoic-acid（pBCA） can effectively restrain hydroxyl radicals, thus can reduce the formation of bromate; The formation ofbromate increased with the increasing of hardness and alkalinity.According to orthogonal experiments with the raw water from Pearl River, the bestprocess of controlling formaldehyde was as follows: ozone dosage during pre ozonation was0.89mg/L, amount of coagulant was15mg/L, ozone dosage during later ozonation was4.59mg/L, residence time in the activated carbon was14min; As to the best process of controllingbromate, ozone dosage during pre ozonation was0.51mg/L, coagulant dosage was45mg/L,ozone dosage during later ozonation was2.28mg/L, residence time in the activated carbonwas8.4min.With the same total ozone dosage, the pre ozonation/conventional processing/afterozone/GAC process led more formaldehyde and bromate formation than the conventionalprocessing/after ozone/activated carbon process.The bromate formation models indicated that increasing pH, initial bromideconcentration, ozone dose or alkalinity will increase bromate formation, it was find that therelative importance order of variable contributing to increasing bromate formation was:pH>O₃dose>IC>Br-（[Br-]₀>50μg/L）; Increasing ammonia concentration will decreasebromate formation; In the models, the influence of organic matter to bromate formation wasnot apparent.In wet season, the risk of bromate formation exceeded the standard was infinitesimal,and there was almost no risk of formaldehyde formation that exceeded the standard of, afterthe raw water from water head site of Pearl River Delta Area was treated by ozone/activatedcarbon process. The risk of bromate formation exceeded the standard was exist, after thewater influenced by salt tide was treated by ozone/activated carbon process.