Characterization of Algal Organic Matter of Microcystis sp.: Disinfection By-Product (DBP) Formation Potential and Treatability

Abstract

Objectives This study was evaluated the disinfection by-product formation potential (DBPFP) in the algal organic matter of Microcystis sp. (M-AOM), which lives in the downstream Maeri area of Nakdong River, and the removal efficiency by each drinking water treatment process. Methods M-AOM were prepared by ultrasound/extraction/filtration using Microcystis sp. from Maeri area in the downstream of Nakdong River. M-AOM and Nakdong river water sample (N-NOM) were compared to removal efficiency of dissolved organic matter (DOM) and DBPFP in the coagulation/settlement (Coag./Sedi.), biological activated carbon (BAC) and granular activated carbon (GAC) processes. The treatment efficiency characteristics of DOM were evaluated by LC-OCD and fluorescence spectrophotometer. DBPFP was analyzed for trihalomethane formation potential (THMFP), haloacetic acids FP (HAAFP), haloacetonitrile FP (HANFP) and chloral hydrate FP (CHFP), respectively. Jar-tester was used for the Coag./Sedi., the BAC and GAC process were conducted using a laboratory scale acrylic column with an empty bed contact time (EBCT) of 20 min. Results and Discussion The contents of humic substances (HS) was high at 50.9% in N-NOM, whereas it was content 26.0% of biopolymers (BP) and LMW-acid (LMW-A) was high at 30.6% in M-NOM. In case of DBPFP, THMFP accounted for 59.5% of the total in N-NOM but CHFP and HANFP accounted for 49.6% and 23.3%, respectively in M-AOM. Thus, There were many differences in the composition of DOM and DBPFP of N-NOM and M-AOM. Both N-NOM and M-AOM showed a high removal efficiency of high molecular weight (HMW) organic matters (BP and HS) during the Coag./Sedi. process, whereas low molecular weight (LMW) organic matters (BB and LMW-org) was high during the GAC and the BAC processes, and the removal efficiency was somewhat different. Residual BP after Coag./Sedi. process was more easily removed by the biodegradation in BAC process rather than GAC process. THMFP and HAAFP which originated from AOM, were able to eliminated about 90% by the Coag./Sedi. process, which was very similar to the removal rate of BP and HS among DOM constituents and they were judged to be involved in THM formation. However, the removal rate of HANFP and CHFP was low, and it could be suspected that HANFP and CHFP formation were occurred in LMW organic matters showing low removal rate by the Coag./Sedi. process. The removal rates of CHFP and HANFP relatively high in the BAC process and total DBPFP showed high removal efficiency in the GAC process. Conclusions N-NOM had high contents of HS (50.9%), but M-AOM had high contents of BP (26.0%) and LMW-A (30.6%). THMFP accounted for 59.5% in total DBPFP of the N-NOM and CHFP (49.6%) and HANFP (23.3%) occupied high rate in the DBPFP of M-AOM. N-NOM and M-AOM were high removal from HMW organic matters (BP, HS) showed high removal efficiency by the Coag./Sedi. process, LMW organic matters showed high removal efficiency in the GAC and BAC processes. Also, residual BP after Coag./Sedi. was easily removed by biodegradation in the BAC rather than adsorption in the GAC process. THM and HAA formed in M-AOM could be removed about 90% by Coag./Sedi. process, whereas it was difficult to remove HANFP and CHFP by Coag./Sedi. process. CHFP and HANFP had relatively high removal efficiency in the BAC process and DBPFP removal was excellent overall in the GAC process. Key words: Microcystis sp., Algal Organic Matter (AOM), Disinfection By-Product, Drinking Water Treatment Process, Treatability