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2-Phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is an antiscalant that is widely used in reverse osmosis (RO) systems. Because of its high concentration in RO concentrate, eutrophication risk and anti-precipitation properties may affect subsequent treatments, therefore treatment strategies are needed to eliminate such substances. In this study, PBTCA was degraded by ozonation. The results show that PBTCA reacted with ozone molecules and hydroxyl radicals, with second-order rate constants of (0.12 ± 0.002) and (7.83 ± 1.51) × 108 L mol−1 s−1, respectively. The phosphorus in PBTCA (PP) was transformed into organic phosphorus except for PBTCA (PO), and inorganic phosphorus (PI); PO was further transformed into PI. The changes in the concentrations of these phosphorus forms were investigated by model simulation. Simulation showed that the rate of PP transformation into PO was 5.5 times higher than that into PI. PBTCA was ozonated much faster at alkaline pH than at acidic pH. This is ascribed to different amounts of ozone molecules and hydroxyl radicals, and their different reaction rates with PBTCA. Furthermore, anti-precipitation property was reduced during ozonation, as shown by the amounts and morphology changes of the precipitates. PBTCA concentration for 50% anti-precipitation (AP50) did not change during ozonation, indicating that the transformation products generated during ozonation did not have anti-precipitation effects. Phosphorus in PBTCA was removed by ozonation–coagulation treatment. Total phosphorus and inorganic phosphorus were removed efficiently by using ferric chloride as a coagulant. The coagulants tended to bind with inorganic phosphorus to form flocs. Meanwhile, flocs were more easily to aggregate and precipitate as anti-precipitation effect was gradually removed, thus more phosphorus was removed. A combination of ozonation and coagulation removed PBTCA effectively and simultaneously reduced its anti-precipitation property and phosphorus.

UV based advanced oxidation processes (UV-AOPs) that efficiently eliminate organic pollutants during water treatment have been the subject of numerous investigations. Most organic pollutants are not completely mineralized during UV-AOPs but are partially oxidized into transformation products (TPs), thereby adding complexity to the treated water and posing risks to humans, ecological systems, and the environment. While the degradation kinetics and mechanisms of pollutants have been widely documented, there is little information about the risks associated with TPs. In this review, we have collated recent knowledge about the harmful TPs that are generated in UV/H2O2 and UV photocatalysis, two UV-AOPs that have been studied extensively. Toxic and assimilable TPs were ubiquitously observed in more than 80% of UV-AOPs of organic pollutants, of which the toxicity and assimilability levels changed with variations in the reaction conditions, such as the UV fluence and oxidant dosage. Previous studies and modeling assessments showed that toxic and assimilable TPs may be generated during hydroxylation, dealkylation, decarboxylation, and deamination. Among various reactions, TPs generated from dealkylation and decarboxylation were generally less and more toxic than the parent pollutants, respectively; TPs generated from decarboxylation and deamination were generally less and more assimilable than the parent pollutants, respectively. There is also potential concern about the sensory-unpleasant TPs generated by oxidations and subsequent metabolism of microorganisms. In this overview, we stress the need to include both the concentrations of organic pollutants and the evaluations of the risks from TPs for the quality assessments of the water treated by UV-AOPs.

The effects of phosphonates, the heavily-used antiscalants in reverse osmosis systems, on microalgae are controversial, although they are harmless to most aquatic organisms. Herein, we assessed the inhibitory effects of etidronic acid (HEDP) and diethylenetriamine penta(methylene phosphonic acid) (DTPMP) on algal growth and revealed the mechanisms involved in both intrinsic toxicity and complexation. The phosphonates showed weak influences on Scenedesmus sp. LX1 in the first 4 d of cultivation. In contrast, a significant growth inhibition was observed subsequently with half maximal effective concentrations of 57.6 and 35.7 mg/L for HEDP and DTPMP, respectively, at 10 d. The phosphonates had little effect on cellular energy transfer and oxidative stress, quantified by adenosine triphosphate level and superoxide dismutase activity, respectively, demonstrating weak intrinsic toxicities to algal cells. Phosphonates blocked the algal assimilation of iron ions through complexation. Severe iron deficiency limited photosynthetic activity and caused chlorophyll decline, resulting in a functional loss of the photosystem followed by complete algal growth inhibition at the late cultivation stage. Our findings point to a potential ecological impact wherein harmful algal blooms are induced by the natural degradation of phosphonates due to the release of both iron and phosphate ions that stimulate algal regrowth after disinhibition.

UV based advanced oxidation processes (UV-AOPs) that efficiently eliminate organic pollutants during water treatment have been the subject of numerous investigations. Most organic pollutants are not completely mineralized during UV-AOPs but are partially oxidized into transformation products (TPs), thereby adding complexity to the treated water and posing risks to humans, ecological systems, and the environment. While the degradation kinetics and mechanisms of pollutants have been widely documented, there is little information about the risks associated with TPs. In this review, we have collated recent knowledge about the harmful TPs that are generated in UV/H

The disinfection performance of a flow-through electrode system (FES) was systematically evaluated using different carbonized (C1, C2, and C3) and corresponding graphitized (G1, G2, and G3) carbon fiber felt (CFF) electrodes. The physicochemical and electrochemical properties were characterized to identify the differences among CFFs. Graphitized CFFs (gCFFs) can achieve complete inactivation of Escherichia coli (>6 log) at the voltage of 3 V and flux of 120–3600 L/(m2 h) for high conductivity and chemical stability, while carbonized CFFs (cCFFs) only achieved around 1 log removal with obvious carbon corrosion. For the gCFFs, G1 (>6 log removal) with higher conductivity, better graphite structure, and larger surface area (related to fiber diameter and density) presented better disinfection performance at the flow rate of 30 mL/min than G2 (∼3 log) and G3(∼1 log). Furthermore, no regrowth and reactivation of bacteria occurred during the storage under visible light illumination after FES treatment. Three parallel FESs with G1 were operated continuously for one week (24 h per day, 7 days) treating the solution with an E. coli concentration ranging from 106 to 107 CFU/mL at the applied voltage of 3 V and the flow rate of 20 mL/min. No live bacteria were detected in the effluent of any of these three FESs. In-situ sampling experiments demonstrated that the inactivation of bacteria on anode was the dominant mechanism for FES treatment, which can be attributed to the sequential adsorption, direct-oxidation and desorption process on anode, instead of indirect oxidation by generating chemical oxidants. In addition, hydroxide ion generated from cathode reaction enhanced anode adsorption and inactivation of bacteria by providing alkaline environment. Combining the analysis results of material properties and disinfection performance, the gCFF-based FES was suggested to be a low-cost, high-efficiency, and safe alternative for future water disinfection.