Formation of Disinfection Byproducts from Algal Organic Matter Exposed to Monochloramine: Effects of Monochloramine Dosages, pH, and Bromide Concentrations

Abstract

The formation of volatile DBPs and haloacetic acids (HAAs) from algal organic matter (AOM) in different chloramination conditions (i.e., different monochloramine (NH 2 Cl) dosages, pH values, and bromide concentrations) was studied. In chloramination of AOM, HAAs were the major DBP species, followed by trihalomethanes (THMs), haloacetonitriles (HANs), and haloketones (HKs). The levels of THMs, HAAs, HKs, and HANs generated in chloramination were 75%, 69%, 68%, and 122% of those in chlorination, respectively. The concentrations of THMs and HAAs both doubled as the NH 2 Cl dosage doubled. The proportions of bromodichloromethane and dibromochloromethane in THMs and the proportions of dichloroacetic acid and trichloroacetic acid in HAAs increased with the NH 2 Cl dosage. Accelerating the pH value enhanced the formation of THMs, HAAs, and HANs, respectively, and favored the formation of brominated THMs. The HAN species distribution was unaffected by the NH 2 Cl dosage and pH. Increasing bromide levels slightly increased the yield of THMs and slightly decreased the yields of HAAs and HKs. The species shift from the chlorinated to the brominated was more significant for THMs and HANs than for HAAs. The THM-BSF and dichloroacetonitrile-BSF values were lower in chloramination than in chlorination. The high pH value and bromide level significantly accelerated the THM-BSFs. The maximum values of THM-BSFs and dichloroacetonitrile-BSF were 0.6 and 0.5.

Algal organic matter as a disinfection by-product precursor during chlor(am)ination: a critical review

“…In general, chlorination of AOM forms more DBPs than chloramination, with total DBPs from chloramination a maximum of 73% of that from chlorination. 65 In particular, chloramination of AOM reduced significantly the formation of 1,1,1-TCP, CH, HAAs, HANs, TCNM, HAcAms, and THMs compared to chlorination. 34,38,61 However, chloramination of AOM and/or natural waters can increase the formation of 1,1-DCP and DCA, 23 NDMA, 38 and CNCl 66 relative to chlorination.…”

“…DCAN decomposes faster in the presence of higher chlorine residuals and 1,1-DCP can be oxidized to 1,1,1-TCP. 69 Gu et al (2020) 65 increased the monochloramine dose from 1.3 to 2.6 Cl 2 : DOC (w w −1 ) and found an increment in THM and HAA yield of 1.2× and 2.0×, respectively. HAcAm formation varied when the chlorine dose increased from 2 to 6 mg L −1 , and decreased in the presence of excess free chlorine, most likely due to HAcAm decomposition.…”

“…Further, a pH increase from 7.0 to 9.0 increased the THM yield but reduced the formation of HAAs, HAL, CH, HK, HAN, and TCNM. 34,42,65 Hydrolytic decomposition of unstable DBPs (e.g., 1,1,1-TCP, CH, and DCAN) has higher rates at basic pH. 69 Furthermore, THM can be formed by the hydrolysis of 1,1,1-TCP, CH, and TCAA which explains why THMs typically increase at basic pH.…”

“…Further, a pH increase from 7.0 to 9.0 increased the THM yield but reduced the formation of HAAs, HAL, CH, HK, HAN, and TCNM. 34,42,65 Hydrolytic decomposition of unstable DBPs ( e.g. , 1,1,1-TCP, CH, and DCAN) has higher rates at basic pH.…”