Disinfection By-Products Formation from Chlor(am)ination of Algal Organic Matter of Chlorella sorokiniana.

Eutrophication in water reservoirs releases algal organic matter (AOM), which is an important precursor of disinfection by-products (DBPs) formed during water treatment. Chlorella sorokiniana is a microalgae which flourishes under conditions of high light intensity and temperature, thus its prevalence in algal blooms is expected to increase with climate change. However, Chlorella sorokiniana AOM has not been previously investigated as a DBP precursor. In this context, this study evaluated the effect of AOM concentration, humic acid (HA), and pH on DBP formation from chlor(am)ination of AOM Chlorella sorokiniana. DBP yields determined by linear regression for trichloromethane (TCM) and chloral hydrate (CH) were 57.9 and 46.0 µg·mg DOC-1 in chlorination, while the TCM, CH, dichloroacetonitrile (DCAN), 1,1,1-trichloropropanone (1,1,1-TCP), and chloropicrin (CPN) concentrations were 33.6, 29.8, 16.7, 2.1, and 1.2 µg·mg DOC-1 in chloramination. Chloramination reduced the formation of TCM and CH but increased CPN, DCAN, and 1,1,1-TCP yields. AOM Chlorella sorokiniana showed a higher DBP formation than 9 of 11 algae species previously investigated in the literature. At basic pH, the concentration of TCM increased while the concentration of other DBP classes decreased. Bromide was effectively incorporated into the AOM structure and high values of bromine incorporation factor were found for THM (1.81-1.89) and HAN (1.32) at 1.5 mg Br·L-1. Empirical models predicted successfully the formation of THM and HAN (R2 > 0.86). The bromide concentration had more impact in the model on the DBP formation than AOM and HA. These results provide the first insights into the DBP formation from AOM chlor(am)ination of Chlorella sorokiniana.

Screening of new adsorbents to remove algal organic matter from aqueous solutions: kinetic analyses and reduction of disinfection by-products formation.

The algal organic matter (AOM) is a problem in water treatment. Although the adsorption process is extensively applied to drinking water treatment, little information is known about the potential of new adsorbents to remove AOM. Herein, this work evaluated the removal of AOM and its main compounds (dissolved organic carbon (DOC), carbohydrate, and protein) by new adsorbents-mesoporous silica (SBA-16), graphene oxide material from citric acid (CA), and sugar (SU), and a composite of CA immobilized on sand (GSC). In general, the removal efficiencies followed the order of SBA-16 > CA > SU or GSC for DOC, carbohydrate, and protein. At environmental condition (5 mg DOC·L-1 and pH 8), high removals were reported for SBA-16 (88.8% DOC, 80.0% carbohydrate, and 99.6% protein) and CA (70.0% DOC, 66.7% carbohydrate, and 89.7% protein), while moderate removals were found for SU (60.5% DOC, 47.9% carbohydrate, and 66.5% protein) and GSC (67.4% DOC, 60.8% carbohydrate, and 57.4% protein). Based on these results, further analyses were done with SBA-16 and CA. Both adsorbents' efficiencies decayed with the pH increment of the test water. Disinfection by-products reductions found using SBA-16 - trihalomethanes (58.2 to 94.7%) and chloral hydrate (48.7 to 78.8%) - were higher than the ones using CA-trihalomethanes (45.2 to 82.4%) and chloral hydrate (40.1 to 70.8%). This study showed the potential of applying these adsorbents for AOM removal, and further investigations are suggested to increase the adsorption capacity of these adsorbents.

Acute toxicity of disinfection by-products from chlorination of algal organic matter to the cladocerans Ceriodaphnia silvestrii and Daphnia similis: influence of bromide and quenching agent.

Algal organic matter (AOM) in water reservoirs is a worldwide concern for drinking water treatment; once it is one of the main precursors for disinfection by-products formation (DBPs). In this context, this study investigated the ecotoxicity of DBPs from chlorination of AOM to Ceriodaphnia silvestrii and Daphnia similis (Crustacea, Cladocera). The bioassays evaluated three scenarios, including the AOM extracted from Chlorella sorokiniana, the quenching condition used in the tests, and the DBPs formed after the chlorination of the two test waters with AOM (with and without bromide presence). The results showed that AOM has no toxic effects for the tested species under typical environmental concentration (5 mg∙L-1). However, since AOM is a potential precursor of DBPs, the toxicity of two test waters (TW-1 and TW-2) after the chlorination process (25 mg Cl2·L-1, for 7 days, at 20 °C) was tested. The sample with higher toxicity to the tested species was TW-1, in which chloroform and chloral hydrate were quantified (615 and 267 µg∙L-1, respectively). However, TW-2 showed lower concentration of chloroform and chloral hydrate (260 and 157 µg∙L-1, respectively), although bromodichloromethane, dibromochloromethane, and bromoform were also detected (464, 366, and 141 µg∙L-1, respectively). Although free chlorine is highly toxic to the tested species, the quenching conditions also affected the organisms' survival due to the use of ascorbic acid and the presence of reaction intermediates. Nonetheless, both species were more affected by TW-1 and TW-2 than the quenching condition. These results endorse the importance of removing the AOM before the disinfection process to avoid the formation of DBPs. In addition, ecotoxicological analyses could provide a more comprehensive assessment of water quality, especially considering the challenges of quantifying DBPs and other emerging contaminants.