Formation characteristics of disinfection byproducts from four different algal organic matter during chlorination and chloramination

Comparative investigation of known and unknown disinfection by-product precursor removal and microbial community from biological biochar and activated carbon filters

Biological activated carbon filter (BAC) is one of the most effective technologies for removing disinfection by-product (DBP) precursors from water. Biochar is a lower-cost medium that has the potential to replace granular activated carbon in BAC applications, thus leading to the development of biological biochar filter (BCF). This study compared BCF with BAC for the removal of DBP precursors using column experiments. Both BCF and BAC achieved the removal of DBP precursors, resulting in concentrations of all DBP formation potential below the World Health Organization guideline values for drinking water. Bromodichloromethane and unknown DBP precursor removal by BCF was comparable to that by BAC. However, BAC removed more chloroform and dichloroacetontrile precursors than BCF. For microbial community analysis, cell numbers in a bottom layer (inlet) of BCF and BAC columns were higher than those in the top layer. The abundances of Nordella and a microbial genus from Burkholderiaceae at the bottom layer showed a strong correlation to the number of DBP precursors removed and were comparable in BCF and BAC. This finding likely contributes to the similarities between DBPs species removed and the removal performances of some known and unknown DBP precursors by BCF and BAC. Overall results from this study revealed that biochar can be served as a low-cost and sustainable replacement of activated carbon in water filter for DBP precursor removal.

A new concern raised from algal bloom: Organic chloramines in chlorination

Algal blooms have become a significant challenge in water treatment all over the world. In chlorination of drinking water, algal organic matter (AOM) leads to the formation of organic chloramines. The objectives of this review are to comprehensively summarize and discuss the up-to-date researches on AOM-derived organic chloramines and their chemical activities and toxicity, thereby drawing attention to the potentially chemical and hygienic risks of organic chloramines. The predominant algal species in water sources varied with location and season. AOM from cyanobacteria, green algae, and diatoms are composed of diverse composition. AOM-derived amino acids take a low portion of the precursors of organic chloramines. Both experimental kinetic data and quantum chemical calculation demonstrate the preferential formation of organic chloramines in the chlorination of model compounds (amino acids and peptides). Organic chloramines are persistent in water and can transform into dichloro- and trichloro-organic chloramines, unknown low-molecular-weight organic chloramines, and nitrogenous disinfection byproducts with the excess of free chlorine. The active chlorine (Cl+) in organic chloramines can lead to the formation of chlorinated phenolic compounds. Organic chloramines influence the generation and species of radicals and subsequent products in UV disinfection. Theoretical predictions and toxicological tests suggest that organic chloramines may cause oxidative or toxic pressure to bacteria or cells. Overall, organic chloramines, as one group of high-molecular-weight disinfection byproducts, have relatively long lifetimes, moderate chemical activities, and high hygienic risks to the public. Future perspectives of organic chloramines are suggested in terms of quantitative detection methods, the precursors from various predominant algal species, chemical activities of organic chloramines, and toxicity/impact.

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br-) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br-. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br-. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br-: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br- were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

Performance of public drinking water purifiers in control of trihalomethanes, antibiotics and antibiotic resistance genes

Point-of-use water purifiers are widely applied as a terminal treatment device to produce drinking water with high quality. However, concerns are raised regarding low efficiency in eliminating emerging organic pollutants. To enhance our understanding of the reliability and potential risks of water purifiers, the removal of trihalomethanes, antibiotics, and antibiotic resistance genes (ARGs) in four public water purifiers was investigated. In the four public water purifiers in October and November, the removal efficiencies of trichloromethane (TCM) and bromodichloromethane (BDCM) were 15%-69% (averagely 37%) and 6%-44% (averagely 23%). The levels of TCM and BDCM were lowered by all water purifiers in October and November, but accelerated in effluent compared to the influent in one public water purifier in December. The removal efficiencies of twelve antibiotics greatly varied with species and time. Out of twelve sampling cases, the removal efficiencies of total antibiotics were 25%-75% in ten cases. In the other two cases, very low removal efficiency (6%) or higher levels of antibiotics present in effluent compared to the influent were observed. Two public water purifiers effectively remove ARGs from water, with log removal rates of 0.45 log-3.89 log. However, in the other two public water purifiers, the ARG abundance accidently increased in the effluents. Overall, public water purifiers were more effective in removing antibiotics and ARGs compared to household water purifiers, but less or equally effective in removing trihalomethanes. Both public and household water purifiers could be contaminated and release the accumulated micro-pollutants or biofilm-related pollutants into effluent. The production frequency and standing time of water within water purifiers can impact the internal contamination and purification efficacy.

Formation characteristics and acute toxicity assessment of THMs and HAcAms from DOM and its different fractions in source water during chlorination and chloramination

The formation characteristics of trihalomethanes (THMs) and haloacetamides (HAcAms) from dissolved organic matter and its fractions were investigated during chlorine-based disinfection processes. The relationships between water quality parameters, fluorescence parameters, and the formation levels of THMs and HAcAms were analyzed. The fractions contributing most to the acute toxicity were identified. The trichloromethane (TCM) generation level (72 h) generally followed the order of Cl₂ > NH₂Cl > NHCl₂ process. The NHCl₂ process was superior to the NH₂Cl process in controlling TCM formation. Hydrophobic acidic substance (HOA), hydrophobic neutral substance (HON), and hydrophilic substance (HIS) were identified as primary precursors of 2,2-dichloroacetamide and trichloroacetamide during chlorination and chloramination. The formation of TCM mainly resulted from HOA, HON and HIS fractions relatively uniformly, while HOA and HIS fractions contributed more to the formation of bromodichloromethane and dibromomonochloromethane. UV₂₅₄ could be used as an alternative indicator for the amount of ΣTHMs formed during chlorination and chloramination processes. Dissolved organic nitrogen was a potential precursor of 2,2-dichloroacetamide during chlorination process. The fractions with the highest potential acute toxicity after the chlorination were water-dependent.

Algae impacted drinking water: Does switching to chloramination produce safer drinking water?

Harmful algal (cyanobacterial) blooms (HABs) are increasing throughout the world. HABs can be a direct source of toxins in freshwater sources, and associated algal organic matter (AOM) can act as precursors for the formation of disinfection by-products (DBPs) in drinking water. This study investigated the impacts of algae on DBP formation using treatment with chloramine, which has become a popular disinfectant in the U.S. and in several other countries because it can significantly lower the levels of regulated DBPs formed. Controlled laboratory chloraminations were conducted using live field-collected algal biomass dominated by either Phormidium sp. or Microseira wollei (formerly known as Lyngbya wollei) collected from Lake Wateree and Lake Marion, SC. Sixty-six priority, unregulated or regulated DBPs were quantified using gas chromatography (GC)-mass spectrometry (MS). The presence of HAB-dominated microbial communities in source waters led to significant increases in more toxic nitrogen-containing DBPs (1.5-5 fold) relative to lake waters collected in HAB-free waters. Compared to chlorinated Phormidium-impacted waters, chloraminated waters yielded lower total DBP levels (up to 123 μg/L vs. 586 μg/L for low Br^-/I^- waters), but produced a greater number of brominated, iodinated, and mixed halogenated DBPs in high Br^-/I^- waters. Among the DBPs formed in Phormidium-impacted chloraminated waters, dichloroacetic acid, trichloromethane, chloroacetic acid, chloropropanone, and dichloroacetamide were dominant. For Microseira wollei-impacted chloraminated waters, total DBP concentrations ranged from 33 to 145 μg/L (approximately 3-5 times lower than chlorination), with dichloroacetic acid, dichloroacetamide, and trichloromethane dominant. Overall, chloramination significantly reduced calculated cytotoxicity and genotoxicity in low Br^- and I^- waters, but produced 1.3 fold higher calculated cytotoxicity (compared to chlorine) with high Br^-/I^- waters due to increased formation of more toxic iodo- and mixed halogenated DBPs.

Application of fluorescence spectra and molecular weight analysis in the identification of algal organic matter-based disinfection by-product precursors

Algal organic matter (AOM) is considered to be threatening for the consumption of disinfectants and the formation of disinfection by-products (DBPs) during the disinfection process. Incompatible parameters in the conventional pretreatment of algal-laden water will lead to counterproductive results, such as AOM release. Therefore, the generation of AOM and its conversion to DBPs during pretreatment should be observed. The characteristics of DBPs from extracellular organic matter (EOM) and intracellular organic matter (IOM) were epitomized and simulation experiments were conducted in deionized (DI) water and source water under pretreatment conditions. Differences in DBP formation between the different backgrounds during chlorination and powdered activated carbon (PAC) treatment were investigated. Instead of monotonous excitation-emission matrix (EEM) spectra, molecular weight (MW) fractionation was simultaneously applied to elucidate the mechanisms of chlorination and PAC adsorption on AOM-based DBPs. The fluorescence regional integration (FRI) EEM results showed a clear correlation between the fluorescent properties and MW distribution of AOM. A decreasing trend was observed after a rapid increase in fluorescence intensity during the chlorination and PAC treatment of water samples in the simulation experiments in deionized (DI) water and source water. The DBP formation potential (FP) in the source water was consistent with the change in AOM during chlorination and PAC adsorption. In addition, EEM showed decent predictability of AOM-based trihalomethanes (THM) FPs (R² = 0.77-0.99) invoking a combination with MW fractionation. Macromolecular protein compounds were highly correlated with the formation of dichloroacetonitrile (DCAN) (R² = 0.89-0.98). These post-mortems results imply that EEM spectra are a useful tool for identifying AOM-based precursors to reveal the accurate environmental fate and risk assessments of AOM.