The Control of DBPs Formation from Different Organics by Chloramine Disinfection

Abstract

The organics in the water after advanced treated and to be disinfected are classified basing on different characteristics. Compared with chlorination, the control of DBPs formation from different organics by chloramination is studied. The test results show that, the chloramine can reduces the TTHM and THAA formation from hydrophilic organics by 90.8% and 77.5%, and from organics with molecular size <1KDa by 84.0% and 74.2%. In addition, the reduction percentages of DBPs formation increases with the deceasing of molecular size. Introduction Since the chlorine disinfection byproducts (DBPs) are discovered in drinking water, the carcinogenic risk from them receives serious attention. However, the chlorine disinfection is still popular at most areas because of its low cost, easy operation and mature technology. So, the studies on how to control the DBPs in drinking water are more and more positively in china. The relative research [1] shows that, comparing with free chlorine, the chloramine disinfection could reduce the formation of DBPs. Natural organic matter (NOM), a complex mixed system, is the main precursor of the DBPs in water. So, the organics need to be classified and studied based on different characteristics. The common classification methods are membrane separation and resin separation [2]. In this paper, considering the water of Huangpu River is of high ammonia concentration and complex organics, the effluent from a pilot process in one water plant in Shanghai has been classified, and the control of chloramine disinfection on DBPs formation from different organics is studied for providing some theory for application of the chloramine disinfection. Test Material and Reagent The chloramine stock solution is prepared by sodium hypochlorite (NaClO) solution and ammonium chloride (NH4Cl) solution. In phosphate buffer of pH 8.3±0.1, the NaClO is added after the NH4Cl, then mixing for 30 minutes in dark place. The NH2Cl concentration is to be measured at every time the stock solution is used. The NaClO solution is for commercial, and the active chlorine concentration is titrated by iodometry method. The other reagents (NH4Cl, NaOH, and H2SO4) are analytically pure, so these solutions are prepared by deionized water. Testing Method The organics of the water samples are separated by membranes holding different molecular size (30×10Da, 10×10Da, 3×10Da, 1×10Da) [3], and the characteristics of formation into DBPs are studied. The resins of XAD-8 and XAD-4 are used to separate the hydrophilic and hydrophobic organics [4], and basing on structural analysis, the characteristics of formation into DBPs are studied too. International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 702 The water samples are added with chlorine and chloramine respectively both with a concentration of 3 mg/L, and stored in the 40 ML ampoules which are kept in constant temperature incubator. After 24 hours, the trihalomethanes (THMs) and haloacetic acids (HAAs) are measured. Analysis Method The DPD spectrophotometric method [5] is used for measuring the concentration of NH2Cl and the pH value is measured by PH meter named PHS-3C. The THMs are detected by liquid-liquid extraction and gas chromatography with EDC. The HAAs are detected by trace extraction derivative capillary gas chromatography [6]. Results and Discussion DBPs Formation from Different Kind of Organics According to the principle of the dissolution in the similar material structure, the highly polar organics have a strong affinity with water, and the weakly polar organics have a weak affinity with water, because H2O is polar molecular. So in this study, the organics of water samples are separated into hydrophilic, strongly hydrophobic and weakly hydrophobic organics. 1) Natural Organics Composition The water samples are taken from the effluent of the pilot process in a water plant in Shanghai, which takes the raw water from Huangpu River, and the TOC of the water sample is 3.83mg/L. Figure 1 shows the organics composition by percentage. Fig.1 Organics composition by percentage 2) Influence of Chloramine Disinfection Three groups of water samples with different organics are added with 3 mg/L chlorine and chloramines respectively, and the DBPs formation are measured after 24 hours. The results are indicated in figure 2 and 3. hydrophilic strongly hydrophobic weakly hydrophobic 0 5 10 15 20 25 30 DB P( ug /L ) Chlorination Chloramination Fig.2 Control of chloramine on the DBPs formation from different organics