Formation Of 2,6-dichloro-1,4-benzoquinone From Chlorination Of Chlorella Vulgaris And Its Algal Organic Matter

Disinfection by-products (DBPs), a class of substances with carcinogenic, teratogenic and mutagenic effect to human health, are produced during the disinfection of drinking water. It is important to control the formation of DBPs for drinking water safety. Halobenzoquinones (HBQs), is a new class of emerging DBPs, which is considered to have high correlation to bladder cancer formation by quantitative structure toxicity relationship (QSTR). Moreover,2,6-Dichloro-1,4-benzoquinone (2,6-DCBQ) has been detected to be the most prevalent HBQ in disinfected water. Surface water, as the main source water in China, are micro-pulluted by algae blooms. Thus, algae and algal organic matter (AOM) have been considered as crucial precursors of DBPs in water treatment. However, there are still no reports about HBQs generation from algae and AOM.Based on the establish of analysis method of 2,6-DCBQ, we selected Chlorella vulgaris, an unicellular green alga generally detected in surface water, as representative alga, and investigated 2,6-DCBQ formation process of C. vulgaris and AOM. Then, we discussed the impacts of water quality conditions (pH, water temperature and common ions) and the chlorination process conditions (Cl/TOC and reaction time) to 2,6-DCBQ formation. Then, we characterizated the intracellular organic matter (IOM) and the extracellular polymeric substances (EPS), the two part of AOM, by ultraviolet (UV) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and three-dimensional fluorescence spectroscopy (3D-EEM) repectively. Moreover, the formation characteristics of 2,6-DCBQ from IOM and EPS was compared. By selecting bovine serum albumin (BSA), fish oil and starch as surrogates for the biochemical components of protein, lipid and polysaccharide respectivly, the formation characteristics of 2,6-DCBQ from the three surrogates were compared. Furthermore, we extracted the total protein from C. vulgaris and studied the formation characteristics of 2,6-DCBQ from the total protein, then established a relationship between 2,6-DCBQ yields and the content of total protein. Research results are as follows:(1) The analytical method of 2,6-DCBQ was established by using HPLC-UV with the limit of detection of 12?g/L, the linear range and the recoveries of this method was 40-200 ?g/L and 79.3%-95.6%, respectively. With comparison to 2,6-DCBQ analysis by HPLC-MS/MS, HPLC-UV method is accurate and simple, and is suitable for 2,6-DCBQ analysis from high concentration of algae in this study.(2) C. vulgaris can generate 2,6-DCBQ in chlorination process, and the yields of 2,6-DCBQ increased with the reaction time and reached steady after 72 h with the maximum yield of 2.12 ?g/mg TOC. When the pH range from 6.0 to 9.0,2,6-DCBQ yields increased firstly and then decreased with the rise of pH (ranged from 0.25 to 2.12 ?g/mg TOC), reaching a maximum at pH 8.0. Moreover, determination of dissolved organic carbon (DOC) and particle size distribution in the system showed that the maximum concentration of DOC and more material (the particle size of the material was smaller than algal cells) emergenced at pH 8.0, which indicate that algal cells were susceptible to decompose and release IOM under this pH, and thus leading to more 2,6-DCBQ yields.(3) The factors influence on the yields of 2,6-DCBQ are as follows:1) The yields of 2,6-DCBQ elevated with water temperature rising from 5? to 35?, which was more obvious when the water temperature below 25?.2) The yields of 2,6-DCBQ significantly increased with the increase of Cl/TOC (4:1-20:1), which were 3.27 ?g/mg TOC with Cl/TOC 20:1, while were just 1.23 ?g/mg TOC with Cl/TOC 4:1.3) Ca2+ significantly inhibited the yields of 2,6-DCBQ with maximum inhibition rates of 35.9%, and F- (0-0.9 mg/L) has a slight inhibition (-9%), while other commom ions have little influence on the formation of 2,6-DCBQ.(4) The UV showed the AOM contain a low SUVA254 value, and FTIR and 3D-EEM spectroscopy demonstated that protein, polysaccharide and lipid are the main components of IOM and EPS. In addition, the measurement results show that the ratio of protein and polysaccharide in IOM (0.46 ±0.03) was more than 3.5 times of EPS. These results indicate that IOM of C. vulgaris is mainly composed of protein, while EPS is mainly composed of polysaccharide.(5) The IOM and EPS can generate 2,6-DCBQ in chlorination process. The 2,6-DCBQ generation potential of IOM and EPS were 2.32 ?g/mg TOC and 0.67 ?g/mg TOC, respectively. The generation potential of IOM was twice of EPS, which showed that IOM is the major precursor of generating 2,6-DCBQ in chlorination of AOM, however, the contribution of EPS can not be ignored.(6) The chlorination results of BSA, fish oil and starch showed that the 2,6-DCBQ generation potential of BAS was 2.32 ?g/mg TOC, while the fish oil and starch substantially does not generate 2,6-DCBQ, which indicate that the protein is the main biochemical component to yield 2,6-DCBQ. Thus, we further extracted the total protein from C. vulgaris, and the chlorination results demonstated that the 2,6-DCBQ generation potential was 1.89 ?g/mg TOC. Furthermore, the yields of 2,6-DCBQ showed a good correlation with the total proteins extracted from C. vulgaris (R2=0.98).