Disinfection By-product Formation Potential Research Articles

Removal of Microcystis aeruginosa and control of algal organic matters by potassium ferrate(VI) pre-oxidation enhanced Fe(II) coagulation

The problem of cyanobacteria blooms during potable water production has generated wide concern. Ferrate(VI) serving as a pre-oxidation tactic was first applied to enhance conventional Fe(II) coagulation for Microcystis aeruginosa-laden water treatment at lab scale. Results demonstrated that ferrate(VI) pre-oxidation could successfully destabilize algae cells through destroying the protective organic layer. The residual ferrate(VI) together with post-added Fe(II) could provoke a comproportionation reaction, where large amounts of Fe hydrolyzates [Fe(OH)3] are formed. The in-situ Fe(OH)3 with abundant reactive surface is responsible for the promotion of flocs growth by facilitating the clustering and cross-linking of algal organic matters (AOM) and cyanobacteria cells, simultaneously resulting in satisfactory reductions in OD680, turbidity and UV254. Overdose of ferrate(VI) could cause severe cell destruction along with the release of intracellular organic matter (IOM), which may impair the water quality by increasing the concentration of dissolved organic carbon (DOC) and the disinfection by-products formation potential (DBPFP). Meanwhile, considering the Fe residual in settled water, the optimal ferrate(VI) dose (20 µM) and Fe(II) dose (80 µM) were proposed. Besides, the synergistic effect of both the degradation by ferrate(VI) and the adsorption by in-situ Fe(OH)3 contributed to the removal of DOC and Microcystin-LR. This study suggests that ferrate(VI) might be a potential candidate for pre-treatment to assist Fe(II) coagulation when addressing algae-laden water.

The combined influence of hydrophobicity, charge and molecular weight on natural organic matter removal by ion exchange and coagulation

Three different source waters were investigated using virgin and pre-used anion exchange resins, coagulation, and ion exchange combined with coagulation (IEX&Coagulation). The hydrophobicity, size distribution and charge of natural organic matter (NOM) were used to evaluate its removal. Dissolved organic carbon (DOC) removal by pre-used IEX resin was 67–79%. A consistent ratio of different hydrophobicity fractions was found in the removed DOC, while the proportion and quantity of the molecular weight fraction around 1 kDa was important in understanding the treatability of water. For pre-used resin, organic compounds were hypothesised to be restricted to easily accessible exchange sites. Comparatively, virgin resin achieved higher DOC removals (86–89%) as resin fouling was absent. Charge density and the proportion of the hydrophobic fraction were found to be important indicators for the specific disinfection byproduct formation potential (DBP-FP). Treatment of raw water with pre-used resin decreased the specific DBP-FP by between 2 and 43%, while the use of virgin resin resulted in a reduction of between 31 and 63%. The highest water quality was achieved when the combination of IEX and coagulation was used, reducing DOC and the specific DBP-FP well below that seen for either process alone.

Assessment of the chlorine demand and disinfection byproduct formation potential of surface waters via satellite remote sensing

The ability of satellites to assess surface water quality indicators such as colored dissolved organic matter (CDOM) suggests that remote sensing could be a useful tool for evaluating water treatability metrics in considering potential drinking water supplies. To explore this possibility, 24 surface water samples were collected throughout Minnesota, USA with wide ranging values of CDOM (a440; 0.41–27.9 m-1), dissolved organic carbon (DOC; 5.5–47.6 mg/L) and specific ultraviolet absorbance at 254 nm (SUVA254; 1.3–5.1 L/mg-M). Laboratory experiments were performed to quantify chlorine demand and the formation of two classes of halogenated disinfection byproducts (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), using the uniform formation conditions (UFC) test. Chlorine demand and THMUFC were linearly correlated with CDOM (R2 = 0.97 and 0.91, respectively), indicating that CDOM is a useful predictor of these parameters. On the other hand, data comparing di- and tri-HAAUFC with CDOM were better fit by a logarithmic relationship (R2 = 0.73 and 0.87, respectively), while mono-HAAUFC was linearly correlated with CDOM (R2 = 0.46) but only for low-to moderately-colored waters (a440 ≤ 11 m−1). The correlations relating chlorine demand and DBPUFC values with CDOM were coupled with satellite CDOM assessments to estimate chlorine demand and DBPUFC values for all surface waters larger than 0.05 km2 in the state of Minnesota, USA. The resulting maps suggest that only 21.8% of Minnesota lakes would meet both the THM and HAA maximum contaminant levels, but only when pre-disinfection treatment removes 75% of DBP precursors. There are limitations to determining CDOM using satellites for high color surface waters (a440 > 11 m−1), however, leading to underpredicted values for CDOM, chlorine demand, and DBPUFC. Overall, the results demonstrate the potential benefits of satellite remote sensing for assessing potential drinking water sources and water treatability metrics.

Comparative Analysis of Different Disinfection Techniques Performances in Drinking Water Treatment Plant Using a Process Simulation Software Hayder Mohammed Issa

The performance of chlorination disinfection in drinking water treatment is facing challenges with the potentiality to produce disinfection by-products. Seeking safer drinking water quality is related to increasing demands by consumers who are looking for better assurances about the quality of the water they drink. In this study, a water treatment process simulator of WatPro 4.0 was used under certain influent conditions to evaluate possibilities for alternating an existing chlorination disinfection process in a drinking water treatment plant (DWTP-Efraz 2) in March 2014 at Erbil, North Iraq. The evaluation was made in terms of effluent water quality and disinfection by-products formation potentials. The studied disinfection processes are; chlorination, ozonation, and ultraviolet. In the chlorination process simulation, the predicted effluent water quality was verified by the analysis and testing results of the effluent treated water goes out from the plant (Efraz-2). Results showed that each of the studied disinfection processes has its own environmental and limitation pros and cons. Ultraviolet disinfection process meets the required standards of the lowest potential of disinfection by-products. Ozonation included a lower risk than chlorination in the formation of disinfection by-products from the dissolved organic matter. The other parameters of water quality showed close characteristics for all the three disinfection processes. The results obtained in this work gives further insight into the performance of water treatment plant design and encourage the application of water treatment simulators as tools for disinfection process development.

Ozonation of Coking Wastewater Effluent to Remove Disinfection By-Product Precursors Using an O3 Fluidized Bed Reactor

Various types of dissolved organic matter (DOM) exist in the effluent of coking wastewater treatment plants. These can become precursors for disinfection by-products (DBPs) during chlorination in downstream drinking water treatment plants, representing a significant threat to the water supply. In this study, an O3 fluidized bed reactor (FBR) process is proposed to stabilize and reduce the number of precursors of haloacetonitriles (HANs) and trihalomethanes (THMs) in coking wastewater effluent. It was found that higher O3 concentrations resulted in lower amounts of precursors. Analysis of dissolved organic carbon (DOC) and total organic carbon (TOC), as well as three-dimensional excitation-emission matrix (3D EEM) fluorescence spectroscopy, showed that O3 preferentially decomposed DOM containing unsaturated and aromatic components. Ozonation also changed the species of organic compounds in the effluent. Furthermore, nitrogenous organic compounds such as nitrogen-containing heterocyclic compounds and nitrile were quickly oxidized. Amines were first increased then decreased, while the olefin and phenol, which contain unsaturated functional groups, were also selectively oxidized by ozonation. Organic acids and alkanes were formed during ozonation; however, these intermediate compounds showed relatively low formation potential for HANs and THMs. Therefore, the precursors can be mineralized or converted to organic compounds, which are less likely to form disinfection by-products. These results indicate that the ozonation treatment of coking wastewater effluent can effectively minimize disinfection by-product formation potential (DBPFP), reducing risks to the downstream water supply.

Photochemical release of dissolved organic matter from particulate organic matter: Spectroscopic characteristics and disinfection by-product formation potential

In this study, we investigated the photochemical release of dissolved organic matter (DOM) from the particulate organic matter (POM) of soil and litter leaves (broad leaves; coniferous leaves) and compared the releasing characteristics of the DOM using UV-visible and fluorescence spectroscopy. The disinfection by-product formation potential (DBPFP) of the released DOM was also examined. Additional dissolved organic carbon (DOC) was released by UV irradiation for all POM sources (10.58 ± 2.7 mg-C L−1 g−1 for BL, 8.32 ± 2.6 mg-C L−1 g−1 for CL, and 0.20 ± 0.1 mg-C L−1 g−1 for soil). The excitation-emission matrix combined with parallel factor analysis results showed that the photo-released DOM from soil was mainly humic-like components (C1, C3) produced by photodesorption, resulting in high trihalomethane formation potential, while protein-like component (C2) was the major component of the photodissolved DOM from litter leaves, resulting in high haloaceticacid formation potential. Further, DBPFP from soil and litter leaves showed high correlation with humic-like components (C1+C3) and SUVA254, respectively. In conclusion, this study demonstrates that significant amounts of DOM could be released from POM under UV irradiation, although the characteristics and DBP formation of the photo-released DOM were highly dependent upon the POM source.

Impact of Different Combinations of Water Treatment Processes on the Concentration of Disinfection Byproducts and Their Precursors in Swimming Pool Water.

To mitigate microbial activity in swimming pools and to ensure hygienic safety for bathers, pool systems have a recirculating water system ensuring continuous water treatment and disinfection by chlorination. A major drawback associated with the use of chlorine as disinfectant is its potential to react with precursor substances present in pool water to form harmful disinfection byproducts (DBPs). In this study, different combinations of conventional and advanced treatment processes were applied to lower the concentration of DBPs and their precursors in pool water by using a pilot-scale swimming pool model operated under reproducible and fully controlled conditions. The quality of the pool water was determined after stationary concentrations of dissolved organic carbon (DOC) were reached. The relative removal of DOC (Δc cin-1) across the considered treatment trains ranged between 0.1 ± 2.9% and 7.70 ± 4.5%, where conventional water treatment (coagulation and sand filtration combined with granular activated carbon (GAC) filtration) was revealed to be the most effective. Microbial processes in the deeper, chlorine-free regions of the GAC filter have been found to play an important role in the degradation of organic substances. Almost all treatment combinations were capable of removing trihalomethanes to some degree and trichloramine and dichloroacetonitrile almost completely. However, the results demonstrated that effective removal of DBPs across the treatment train does not necessarily result in low DBP concentrations in the basin of a pool. This raises the importance of the DBP formation potential of the organic precursors, which has been shown to depend strongly on the treatment concept applied. Irrespective of the filtration technique employed, treatment combinations employing UV irradiation as a second treatment step revealed higher concentrations of volatile DBPs in the pool compared to those employing GAC filtration as a second treatment step. In the particular case of trichloramine, results confirm that its removal across the treatment train is not a feasible mitigation strategy because it cannot compensate for the fast formation in the basin.

Throughfall Dissolved Organic Matter as a Terrestrial Disinfection Byproduct Precursor

More than half of the drinking water supply in the United States originates from forest watersheds, where terrestrial dissolved organic matter (DOM) is known as an important disinfection byproduct (DBP) precursor. Throughfall-derived DOM, a significant portion of terrestrial DOM, has seldom been evaluated for its formation potential of DBPs. Here, we collected throughfall and leaf extracts of an evergreen (loblolly pine, Pinus taeda L.) and a deciduous tree species (turkey oak, Quercus cerris L.) in South Carolina to explore their seasonal DOM quantity, optical properties, and DBP formation potential. Elevated dissolved organic carbon (DOC) from rainwater (1.2 ± 0.4 mg/L) to pine (26.0 ± 19.7 mg/L) and oak throughfall (38.8 ± 37.8 mg/L) indicated canopy can be a significant DOM source. DOM aromaticity (indicated by specific ultraviolet absorbance at 254 nm) was higher in oak than pine throughfall and higher in throughfall than leaf extracts. The throughfall DOM characteristics were seasonally more stable ...

Performance of BAC for DBPs precursors’ removal for one year with micro-polluted lake water in East-China

ABSTRACT Effectiveness of biological activated carbon (BAC) filter in removing disinfection byproducts (DBPs) precursors of micro-polluted lake water for one year was conducted. The formation potential (FP) of DBPs (trihalomethanes (THMs), haloacetic acids (HAAs) and Nitrosamines (NAs)), dissolved organic carbon (DOC), molecular weight (MW) distribution and excitation emission matrix fluorescence (EEM) of dissolved organic material (DOM) in the influent and effluent of BAC were determined. The results indicated that the removal efficiency (RE) of DOC ranged from 42.9–28.3%. Neither virgin GAC nor long-term operated BAC could efficiently dispose of THMs and HAAs precursors (RE from 35.2–18.8%, from 42 to 8.4%, respectively), however, BAC still showed good ability in removal of NAs precursors after a year operation, of which RE just dropped from 81.7–69.6%. There was strong correlation between RE of NAs precursors and DOC with small MW (<0.5 kDa). The removal of HAAs precursors showed relatively close relation to aromatic protein-like components and soluble microbial pollutants (SMPs). Weak direct relationship was found between the water quality parameters and THMs precursors.

Higher functionality of bacterial plasmid DNA in water after peracetic acid disinfection compared with chlorination

Peracetic acid (PAA) is an emerging disinfectant with a low disinfection by-product formation potential, but how PAA destroys gene function after killing bacteria remains to be studied. Bacterial plasmid DNA is a mobile genetic element that often harbors undesirable genes encoding antibiotic resistance and virulence factors. Even though PAA efficiently kills bacteria, bacterial plasmids and other mobile genetic elements might still be intact and functional after PAA disinfection, posing potential public health and environmental risks. This study evaluated the impact of PAA disinfection on the functionality of plasmid DNA in vivo and compared the results with those from chlorination. We delivered a plasmid DNA harboring two antibiotic resistance genes to Escherichia coli TOP10 to form an antibiotic-resistant bacterium (ARB). The planktonic ARB was treated with PAA and chlorine to find the minimum doses inhibiting the regrowth of the strain. PAA and chlorine stopped the regrowth at 8 ± 1 mg PAA·L−1 and 20 ± 9 mg Cl2·L−1, respectively. The functionality of the plasmid DNA after PAA and chlorine disinfection was then determined at higher doses in vivo. Neither PAA nor chlorine completely destroyed the plasmid DNA. However, chlorine was more efficient than PAA in eliminating the plasmid DNA. PAA at 25 mg PAA·L−1 reduced the transforming activity of the plasmid DNA by less than 0.3 log10 units, whereas chlorine at 25 mg Cl2·L−1 reduced the transforming activity by approximately 1.7 log10 units. Chlorine had a more pronounced impact on the functionality of the plasmid DNA because it oxidizes or destroys bacterial components including plasmid DNA faster than PAA. In addition, environmental scanning electron microscopy shows that chlorination desiccated the cells resulting in the flat cellular structure and possibly more complete loss of plasmid DNA, whereas PAA disinfection had a less impact on cell structure and morphology. This study demonstrates that more plasmid DNA remains functional in water after PAA disinfection than after chlorination. These functional genetic elements could be acquired by other microorganisms via horizontal gene transfer to pose potential public health and environmental risks.

Effects of KMnO4/NaHSO3 pre-oxidation on the formation potential of disinfection by-products during subsequent chlorination

Bisulfite-activated permanganate oxidation (PM/BS) technology is an emerging oxidation process that can rapidly oxidize organic contaminants and degrade some permanganate-resistant organic contaminants. For the first time, the influences of PM/BS technology as a pre-oxidation process on the formation potentials of disinfection by-products (DBPFPs) during chlorination of humic acid (HA) solution and three natural water samples were investigated. The results revealed that PM/BS pre-oxidation only slightly affected the DBPFPs of HA in the absence of Br- although it changed the structure of HA according to the fluorescence characterization result. With the presence of Br-, PM/BS pre-oxidation enhanced the generation of trihalomethanes but inhibited that of nitrogenous DBPs (N-DBPs) during chlorination of HA. The toxic risk analysis showed that the toxicity of the generated DBPs from chlorinating HA solution without Br- only changed slightly after PM/BS pre-oxidation but it was decreased by 14% in the presence of 150 μg/L Br− due to PM/BS pre-oxidation. This should be associated with the inhibiting effect of PM/BS pre-oxidation on the generation of N-DBPs and several haloacetic acids in the presence of Br-. Because of the complex matrix of natural water samples, PM/BS pre-oxidation had minor influence on the amount and the potential toxicity of DBPs generated during chlorination. The above results suggested that PM/BS technology could be an alternative of the drinking water pretreatment.

Control wildfire-induced Microcystis aeruginosa blooms by copper sulfate: Trade-offs between reducing algal organic matter and promoting disinfection byproduct formation

Elevated levels of nutrients due to wildfire ash input into stream waters will likely cause algal blooms. When source water is impeded by algae and requires immediate restoration, copper algaecides are usually applied. Previous studies indicate that Cu2+ can promote reactivity of dissolved organic matter in forming disinfection byproducts (DBPs). However, it is unclear that how DBP formation is changed after the treatment of post-fire algal bloom by copper algaecide. In this study Microcystis aeruginosa was cultured in the medium containing black and white ash water extracts (BE and WE) to study DBP concentrations before and after 4-days exposures to low and high copper sulfate (0.5 and 1.0 mg-Cu/L). Dissolved organic matter (DOM) was characterized by UV-VIS absorption and fluorescence spectroscopy and chlorination/chloramination-based DBP formation potential (FP) experiments. DOM concentrations and algal population in the treatments were lower than that in control, regardless of types of water extract. N-nitrosodimethylamine FP in the treatments were 4–6 times higher than the control (0.23–0.34 vs. 0.05–0.06 μg/L), while haloacetonitrile FP revealed no significant difference (132–191 vs. 167–185 μg/L). Trade-offs between reducing algal population and promoting DBP-FP were more pronounced for the solutions containing BE than WE. Low copper concentration was as effective as high concentration in inhibiting algal growth while minimizing promotion of DBP formation. The results can serve to support risk evaluations of algal population and DBP concentration when wildfire-induced algal bloom is left untreated and treated by copper algaecides.

Impact of carbon-based nutrient enhancement on biofiltration performance for drinking water treatment

Incorporation of a carbon-based nutrient enhancement strategy for drinking water biofiltration is an attractive option, especially for source waters which contain recalcitrant organics. This study compared biofilters that were operated in parallel and individually enhanced with amino acids (including alanine, phenylalanine, and tryptophan), inulin, and sucrose to increase biomass concentration and promote biodegradation of dissolved organic carbon (DOC) in the source water, including disinfection by-product (DBP) precursors. Biomass activity was characterized by measuring adenosine tri-phosphate (ATP), dissolved oxygen (DO) consumption, and through the use of laccase and esterase enzyme assays. Performance was evaluated in terms of headloss, turbidity, pH, DOC, UV254, and DBP formation potential (DBP FP). The introduction of carbon-based nutrients significantly increased biomass activity, where ATP values peaked at 976 ng/g of filter media, 853 ng/g, and 513 ng/g for amino acids, inulin, and sucrose-spiked biofilters, respectively, while a non-spiked control only reached 104 ng/g. DO utilization by the enhanced biofilters was significantly higher than the control, with a strong correlation between ATP and DO uptake observed for all filters (R2 > 0.74). Laccase and esterase enzyme activities of enhanced biofilters were also elevated (p > 0.05), suggesting greater biodegradation potential. Operational parameters such as headloss development and turbidity control were not impaired by carbon supplementation strategies or an increase in biomass concentration and activity. However, the enhancement strategy did not provide improvement in terms of source water carbon removal (DOC and UV254) or DBP FP when treated filters were compared to a control.

Natural organic matter removal from algal-rich water and disinfection by-products formation potential reduction by powdered activated carbon adsorption

Algal blooms intensified operational problems in water treatment due to the increases of taste- and odor-causing compounds and natural organic matter (NOM). Effects of powdered activated carbon (PAC) addition during algal blooms on NOM removal was investigated in this study using an algal-rich water. Water quality analyses including dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254) and specific UV absorbance (SUVA) were performed to elucidate characteristics of NOM removal by PAC adsorption. Variations of MW distributions and emission/excitation matrix (EEM) spectra with increasing PAC dosages were also measured. In addition, formation potential (FP) of trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs) was evaluated with increasing PAC dosage. The correlations between disinfection by-products formation potential (DBPFP) and water qualities such as DOC, UV254, SUVA, and EEM spectra were also investigated to identify factors associated with DBPFP. The PAC addition was effective to remove NOM, especially low molecular weights NOM and proteinaceous substances with weak aromatics. The PAC addition showed the consistent reduction of THMFPs, HAAFPs, and HANFPs with increasing PAC dosage while the greater reduction of HAN precursors was eminent compared to the other two FPs. The close correlations between UV254 and the three DBPFPs were obtained. The low molecular weight (i.e., 1–700 Da) NOM and three fluorescence spectra peaks, i.e., T1, A and C peaks, also showed high correlation factors with the three DBPFPs. Those analyses with high correlations with DBPFPs would provide useful information to reduce DBPs during algal blooms.

Unlocked disinfection by-product formation potential upon exposure of swimming pool water to additional stimulants

Anthropogenic organics are known to be responsible for the formation of harmful disinfection byproducts (DBPs) in swimming pool water (SPW). The research explored an important scenario of SPW with no additional anthropogenic organic input. With stimulations by residual chlorine or additional chlorine and extended incubation, the formation of DBPs, especially chloroform, was significantly induced. Similar observations were found by investigating synthetic SPW made with sweat and urine. The presence of urine led to a massive formation of chloroform, as noted by an approximate 19-fold increase after 165-day incubation with a shock chlorine dose. The research suggests that consistent residual chlorine and long water retention as two typical features of SPW could unlock the DBP formation potential of anthropogenic organics. Thus, limiting the introduction of anthropogenic organics may not have an immediate effect on reducing DBP levels, because their reactions with chlorine can be slow and long-lasting. Pool management should prioritize on control of urine and improving air ventilation. This work is useful to deepen understandings about DBP formation in SPW and provide implications for pool management and prospective legislation.

Understanding Organic Nonpoint-Source Pollution in Watersheds via Pollutant Indicators, Disinfection By-Product Precursor Predictors, and Composition of Dissolved Organic Matter.

The analytical techniques and instrumentation used to assess agricultural and rural nonpoint-source organic pollution loading are usually complex and expensive. There has been a strong demand for alternative methodologies to determine the presence and composition of organic pollutants and to predict their levels. In the current work, we investigated a simple and inexpensive approach combining excitation-emission matrix and support vector machine that measures pollution and predicts the levels of precursors to disinfection by-products, which are organic pollutants derived from agricultural and rural nonpoint sources in small watersheds. Through parallel factor analysis, a four-component model was developed to explain the composition of dissolved organic matter in water impacted by nonpoint-source pollution. Support vector classification and support vector regression with model components can use fluorescence properties as proxy indicators for nonpoint-source pollution. When the model components are used as input variables, formation potential of disinfection by-products can be predicted. This method provides water utilities managers with tools to control pollution, supervise aquatic environments, and ensure the safety of drinking water.

Decrease in the chloride disinfection by-products (DBPs) formation potential in water as a result of coagulation process

Decrease in the chloride disinfection by-products (DBPs) formation potential in water as a result of coagulation process

Evaluation of NOM Characteristics and Disinfection By-Products (DBPs) Formation Potential in Nakdong River Basin

Evaluation of NOM Characteristics and Disinfection By-Products (DBPs) Formation Potential in Nakdong River Basin

Fluorescence Spectra Predict Microcystin-LR and Disinfection Byproduct Formation Potential in Lake Water.

Disinfection byproducts (DBPs) and algal toxins can be expensive to monitor and represent significant potential risks to human health. DBPs, including haloacetic acids and trihalomethanes, are possible or probable human carcinogens. Microcystin-LR-produced by cyanobacteria-is linked with various adverse health effects. Here we show that fluorescence spectra predict both microcystin-LR occurrence and DBP formation potential (DBPfp) in lake water. We compared models with either fluorescence spectra or a suite of water quality predictors as inputs. A regularized logistic regression model with fluorescence spectral inputs correctly classified 94% of test data with respect to microcystin-LR occurrence, with a 96% probability of correctly ranking a detect/nondetect pair. Regularized linear regression predicted DBPfp based on fluorescence inputs with a combined R2 of 0.83 on test data. A gradient-boosted classifier with seven water quality inputs was comparable in detecting microcystin-LR (91% correct), as was UV254 in predicting DBPfp (combined test R2 = 0.84), but no single parameter matched fluorescence spectra over both predictive tasks. Results highlight the potential for multiparameter monitoring via fluorescence spectroscopy, extending previous work on predicting DBPs alone. As a high-frequency monitoring tool, this approach could supplement mass spectrometric methods that may only be applicable at low frequency due to resource limitations.

A comparison of trichloromethane formation from two algae species during two pre-oxidation-coagulation-chlorination processes

Microcystis aeruginosa (M. aeruginosa) commonly blooms in summer while Cyclotella meneghiniana (C. meneghiniana) outbreaks in fall in water reservoirs of Southeast China. Pre-oxidation has been demonstrated to enhance the algae removal from chemical coagulation processes. However, excessive dosage of pre-oxidant can increase the disinfection by-products formation potential (DBPsFP). Additionally, the DBPs formation mechanisms from algae during the pre-oxidation-coagulation-chlorination processes have not well elucidated. In this study, the objectives were to investigate the trichloromethane (TCM) formation, the changes of water quality indexes, and the morphology changes of algal cells from M. aeruginosa or C. meneghiniana contaminated water during potassium permanganate (KMnO4) or chlorine (Cl2) pre-oxidation-coagulation-chlorination disinfection. The results showed that the TCM yield for two algal species decreased with the dosage increase of KMnO4 pre-oxidation, but increased with the dosage increase of pre-chlorination. Therefore, the 2.0 mg/L KMnO4 or 0.5 mg/L Cl2 was proposed as the optimal dosage for preventing both M. aeruginosa blooms in summer and for C. meneghiniana outbreaks in fall. M. aeruginosa exhibited a slightly higher TCM yield than C. meneghiniana in these treatment processes. Based on the release of potassium (K) ion and SEM analysis, KMnO4 had less damage on cell integrity than Cl2 at the dosage ≤2.0 mg/L. In addition, C. meneghiniana was easier to be disrupted by both pre-oxidants than M. aeruginosa, combining with subsequent coagulation led to different value of dissolved organic carbon (DOC), UV–visible absorbance (UV254) and turbidity.