Monitoring biofouling based on aerobic respiration in reverse osmosis system.

A monitoring method of biofouling in reverse osmosis (RO) system was proposed based on the fluorescent signal of resorufin, which is reduced by nicotinamide adenine dinucleotide released from viable cells during aerobic respiration. The fluorescent signal of resorufin reduced by planktonic cells and microorganisms of biofilm showed linearity, indicating its feasibility to monitor biofouling in a RO system. For the application of the method to the lab-scale RO system, the injection concentration of resazurin and the injection flow rate were optimized. Biofilm on RO membranes continuously operated in a lab-scale RO system was estimated by resorufin fluorescence under optimized detection condition. As a result, resorufin fluorescence on RO membrane showed a significant increase in which the permeability of RO system decreased by 30.48%. Moreover, it represented the development of biofilm as much as conventional biofilm parameters such as adenosine triphosphate, extracellular polymeric substances, and biofilm thickness. The proposed method could be used as a sensitive and low-cost technology to monitor biofouling without autopsy of membranes.

Comparison of formation of disinfection by-products by chlorination and ozonation of wastewater effluents and their toxicity to Daphnia magna.

This study compared the two most frequently used disinfectants (i.e., chlorine and ozone) to understand their efficiency in wastewater effluents and the ecotoxicity of disinfection by-products created during chlorination and ozonation. Four trihalomethanes (THMs) and nine haloacetic acids (HAAs) were measured from a chlorine-disinfected sample and two aldehydes (i.e., formaldehydes and acetaldehydes) were analyzed after ozonation. Chlorination was effective for total coliform removal with Ct value in the range of 30-60 mg-min/L. Over 1.6 mg/L of ozone dose and 0.5 min of the contact time presented sufficient disinfection efficiency. The concentration of THMs increased with longer contact time (24 h), but that of HAAs showed little change with contact time. The measured concentration of formaldehyde at the ozone dose of 1.6 mg/L and the contact time of 9 min showed the greatest value in this study, approximately 330 µg L(-1), from which the corresponding ecotoxicity was determined using an indicator species, Daphnia magna. The ecotoxicity results were consistent with the toxicological features judged by occurrence, genotoxicity, and carcinogenicity. Both the disinfection efficiency as well as the DBP formation potential should therefore be considered to avoid harmful impacts on aquatic environments when a disinfection method is used for wastewater effluents.

Oxidant production from corrosion of nano- and microparticulate zero-valent iron in the presence of oxygen: a comparative study.

In aqueous solution, zero-valent iron (ZVI, Fe(0)) is known to activate oxygen (O2) into reactive oxidants such as hydroxyl radical and ferryl ion capable of oxidizing contaminants. However, little is known about the effect of the particle size of ZVI on the yield of reactive oxidants. In this study, the production of reactive oxidants from nanoparticulate and microparticulate ZVIs (denoted as nZVI and mZVI, respectively) was comparatively investigated in the presence of O2 and EDTA. To quantify the oxidant yield, excess amount of methanol was employed, and the formation of its oxidation product, formaldehyde (HCHO), was monitored. The concentration of HCHO in the nZVI/O2 system rapidly reached the saturation value, whereas that in the mZVI/O2 system gradually increased throughout the entire reaction time. The mZVI/O2 system exhibited higher yields of HCHO than the nZVI/O2 system under both acidic and neutral pH conditions. The higher oxidant yields in the mZVI/O2 system are mainly attributed to the less reactivity of the mZVI surface with hydrogen peroxide (H2O2) relative to the surface of nZVI, which minimize the loss of H2O2 by ZVI (i.e., the two-electron reduction of H2O2 into water). In addition, the slow dissolution of Fe(II) from mZVI was found to be partially responsible for the higher oxidant yields at neutral pH.