Conventional Water Treatment Processes Research Articles

Molecular-Level Insights on the Facet-Dependent Degradation of Perfluorooctanoic Acid.

Perfluorooctanoic acid (PFOA) has raised significant health concerns due to its high ecotoxicological risks and difficulties in removal by conventional water treatment process. Previous studies have demonstrated that photocatalytic techniques exhibit great potential in PFOA removal. However, the underlying mechanism of the degradation process has not been fully understood, particularly the contribution of the facet effects of catalysts. In this study, a combination of experiments and first-principles calculations were conducted to shed light on the facet-dependence of the interfacial interactions and oxidation during the PFOA degradation process. We proved that the interfacial interaction was essential in initiating the hole-dominated degradation process, and the {110}R3̅c facet of hexagonal In2O3 features the strongest interaction with PFOA. The overall defluorination rate was mainly controlled by the hole-dominated oxidation processes under UV irradiation, which were further attributed to the electronic structures and reaction site distributions of different In2O3 surfaces. This study provides molecular-level insights on the facet-dependent PFOA catalytic degradation process, which can guide the rational design of photocatalysts to achieve superior decontamination efficiency.

Azole and strobilurin fungicides in source, treated, and tap water from Wuhan, central China: Assessment of human exposure potential

Fungicides are widely used in agriculture worldwide. However, data on the occurrence of fungicides in drinking water are scarce. This study aimed to determine the occurrence of 12 selected fungicides in drinking water, the removal efficiency of conventional water treatment processes for fungicides, and the risk of fungicide exposure. In this study, source water (February and July), treated water (February and July), and tap water samples (February, April, July, and October) were collected from Wuhan, central China, in 2019. Seven of the twelve selected fungicides were 100% detected in the three types of water samples; tricyclazole was found with the highest concentrations in the source water phase (median: 15.2 ng/L; range: 4.21–67.9 ng/L). The concentrations of the 12 selected fungicides remaining in the treated water samples (median proportion of the remaining content: 77.5%) revealed that most of the target analytes may not be removed efficiently by conventional water treatment processes, though they could be removed efficiently by advanced treatment. Higher concentrations of the fungicides were observed in samples collected in July (median: 38.7 ng/L; range: 12.5–85.8 ng/L), followed by those in October (median: 21.8 ng/L; range: 10.2–58.8 ng/L), February (median: 9.82 ng/L; range: 5.63–93.3 ng/L), and April (median: 7.13 ng/L; range: 6.23–91.1 ng/L). The health risk assessment implied that estimated daily intake of these fungicides through tap water ingestion might pose a low risk to consumers, though risk associated with infant exposure to the fungicides requires further attention. This study provides baseline data on the occurrence, removal efficiencies, and seasonal variations of the selected fungicides in tap water from central China.

Investigating use of chlorine dioxide for pre-treatment of raw water from polluted sources at Morton Jaffray Water Treatment Works, Harare, Zimbabwe

Abstract Raw water quality deterioration has affected capabilities of Conventional Water Treatment Processes (CWTP) in many countries. CWTP used at Morton Jaffray Water Treatment Works (MJWTW) in Harare have proven ineffective due to pollution. The study investigated the use of chlorine dioxide (ClO2) as an alternative pre-treatment chemical. Its effectiveness was compared to that of calcium hypochlorite (Ca(CIO)2) used at MJWTW. Grab raw water samples from MJWTW were collected between January and March 2020 and pre-treated with ClO2 and Ca(CIO)2 followed by jar tests with alum to determine pre-treatment effectiveness. Parameters analyzed included electrical conductivity (EC), total dissolved solids (TDS), total solids (TS), turbidity, chemical oxygen demand (COD), pH and total algae counts (TAC). The raw water had mean TDS (264 mg/L), TS (440 mg/L), turbidity (7.1 NTU), COD (85 mg/L), pH (7.9) and TAC (28.4 × 106 cells/mL). The optimum alum dosage without pre-oxidation was 80 mg/L. Pre-oxidation with 0.075 mg/L ClO2 reduced alum dosage to 60 mg/L. This ClO2 dosage was compared to a Ca(CIO)2 dosage of the same concentration and strength at 5 and 15-minutes contact time before alum dosage at 60 mg/L. The treated water quality parameter levels proved better performance for ClO2 compared to calcium hypochlorite.

Extractive removal and recovery of bisphenol A from aqueous solutions using terpenoids and hydrophobic eutectic solvents

Bisphenol A (BPA) is a widely used chemical that is found in wastewaters and surface water due to its ineffective removal by conventional water treatment processes. BPA being an endocrine disruptor, regulations and different technologies have been proposed for its treatment. In this work, the use of natural solvents such as terpenoids and eutectic solvents is presented, envisioning a BPA extraction from aqueous solutions based on the hydrophobicity of these sustainable solvents. First, an initial screening of 43 solvents was performed by molecular simulation using the COSMO-RS method. BPA extraction from aqueous solutions was experimentally evaluated with initial BPA concentrations of 5–100 mg/L, and several solvent-to-feed ratios at 303.2 K. Extraction yields > 99% were obtained with eucalyptol, geraniol, and (menthol + camphor) eutectic solvent outperforming conventional solvents. Eucalyptol, geraniol, and (menthol + camphor) have been used in a scaling-up evaluation and reuse in 6 consecutive cycles observing yields in all stages above 98.5% at solvent-to-feed ratios ranging 0.01–0.05. Besides, the solvents were regenerated using back-extraction with NaOH, providing yields above 99.5%. The regenerated solvents showed similar yields to those obtained with fresh solvent, and their chemical stability was checked through FTIR analysis. BPA was recovered by precipitation from the aqueous back-extraction solution, showing by FTIR that no degradation occurs during the extraction, back-extraction, and precipitation processes. For the first time, the complete cycle of extraction with solvent reuse, back-extraction, and precipitation of BPA using eutectic solvents and terpenoids has been studied.

Removal Behavior of Protein-like Dissolved Organic Matter During Different Water Treatment Processes in Full-Scale Drinking Water Treatment Plants

Protein-like dissolved organic matter (pDOM), which is ubiquitous in natural waters, is a critical precursor of nitrogenous disinfection byproducts. Recently, the control and elimination of pDOM have been a growing concern during drinking water treatment processes. In this study, a high-performance size exclusion chromatography system coupled with photo-diode array, fluorescence detector, and online organic carbon detector (HPSEC-PDA/FLD/OCD) was used to determine the removal behaviors of different-sized pDOM from two full-scale drinking water treatment plants (DWTPs). Coagulation and activated carbon adsorption were selected for bench-scale experiments to further assess the removal behavior of pDOM during conventional water treatment processes. The results showed that different-sized pDOM fractions exhibited different removal characteristics. Pre-oxidation can effectively remove some tyrosine-like and tryptophan-like components with high MW, and as the oxidization effect was enhanced, more high MW fractions decomposed into low MW ones. Conversely, some aliphatic pDOM fractions in high MW (e.g., aliphatic proteins) were not subject to pre-oxidation removal. The coagulation-sedimentation unit was efficient in removing high MW fractions, specifically tryptophan-like fractions. Additionally, some pDOM components may be released during coagulation. pDOM with low MW and high hydrophobicity were easily removed during activated carbon filtration. However, long-term operation of the activated carbon filter may breed microorganisms, resulting in the partial release of pDOM fractions. Moreover, UV disinfection processes promoted the degradation of low MW pDOM components. Due to the complex water quality and uncontrollable microbial activities, the aforementioned water treatment units did not exhibit a synergistic effect on pDOM removal. In comparison with humic-like substances, pDOM was susceptible to water quality changes, and its removal was limited in the surveyed DWTPs. Therefore, DWTPs must strengthen pDOM monitoring in influent and effluent and adjust the operating parameters of different treatment units in a timely manner. Moreover, the combination of advanced water treatment processes, such as ozone-biological activated carbon process and nanofiltration, should also be considered to strictly control pDOM component removal.

Microplastic removal in conventional drinking water treatment processes: Performance, mechanism, and potential risk

The effectiveness of traditional drinking water treatment plants for the removal of Microplastics (MPs) in the size range of tens of micrometers is currently uncertain. This study investigated the behavior and removal efficiency of four different sized polystyrene MPs (10−90 μm in diameter) in a simulated cascade of coagulation/sedimentation, sand filtration, and UV-based oxidation over technically relevant time frames. In the coagulation and sand filtration steps, the larger the MP size, the better it was removed. The coagulant type and water characteristics (i.e., pH and the presence of natural organic matter) influenced the coagulation efficiency for MPs. X-ray microcomputed tomography technique and two-site kinetic modeling were used to identify the mechanisms involved in sand filtration. The MPs > 20 μm could be completely retained in sand by straining, while the attachment to the sand surface was likely responsible for the retention of MPs < 20 μm. However, approximately 16% of 10 μm MPs injected passed through the sand, which were further fragmented by UV oxidation. UV/H2O2 treatment promoted the MP fragmentation and chemical leaching more significantly than UV treatment, resulting in a higher toxicity for UV/H2O2-treated water. Our findings pave the way for deeper understanding of how MPs behave and transform in a sequential drinking water treatment process.

Effects of temperature and microorganism densities on disinfection by-product formation

This study investigated the role of microorganisms on the correlation between temperature changes and disinfection by-product formation in natural waters. Climate changes have resulted in an increase in the global surface temperature. Studies have revealed that increases in temperature may change the composition of dissolved organic matter (DOM), which may contain major disinfection by-product (DBP) precursors. This change in the DOM composition may affect DBP formation after conventional water treatment processes. Understanding the role of microorganisms in DOM composition as well as DBP formation and speciation is critical for controlling DBP formation. In this study, laboratory stimulatory experiments were conducted on water samples from various sources, at various temperatures, and with various microbial concentrations. The results revealed a decreasing trend of dissolved organic carbon (DOC), trihalomethane formation potential (THMFP), and haloacetic acid formation potential (HAAFP) at high temperature incubations irrespective of microbial concentrates. This result may be attributed to the fact that microorganism activities or concentrations in water increase at higher temperatures, which may result in higher DOC consumption and lower DBP formation. Water samples spiked with bacteria concentrates exhibited higher THMFP or HAAFP reduction than did samples without bacteria concentrates. A higher biomass in water may contribute to a higher consumption of DOC and consequently lower DBP formation potentials, especially at high incubation temperatures.

Recycled reverse osmosis membrane combined with pre-oxidation for improved arsenic removal from high turbidity waters and retrofit of conventional drinking water treatment process

End-of-life reverse osmosis membranes could be now recycled (UFr) by a low-cost oxidative treatment producing a membrane with properties similar to ultrafiltration. Its efficiency for arsenic, iron and manganese removal from contaminated surface water was compared to submerged (UFs) and pressurized (UFp) ultrafiltration modules as strategies for a safe drinking water supply. The processes were preceded by a pre-oxidation stage, assessing their permeate flux and fouling under high turbidity conditions (100–1000 NTU). The pre-oxidation was effective in converting soluble species into colloids and complexes that were latter removed by UF units even under high turbidity conditions (1000 NTU). From all filtration units, the UFr was capable to retain even the complexes formed with manganese, being the only system capable to attain the threshold values for all three contaminants. The highest permeate flux of UFp came along with the highest flux decay among all three configurations. Despite the lower permeate flux (71.8–65.2 L/m2h, for 100 and 1000 NTU, respectively) and shorter membrane lifespan for UFr, the process still presented the lowest operating cost (US$/m³ 0.310) and highest rate of return compared to the other configurations (UFs: US$/m³ 0.337 and UFp: US$/m³: 0.328). The advantages of UFr could be extended to environmental aspects as diminishes the disposal of end-of-life membranes in landfills whilst attaining the technical and economical pre-requisites for novel technologies being sought for a safe drinking water supply.

Metformin (Glucophage) Biodegradation: Insights from Microbiome and Biochemical Analyses

Metformin is the most prescribed type 2 diabetes medication in the United States and in many countries worldwide. In diabetes patients, this drug has been shown to alter the gut microbiome resulting in improved glucose metabolism. More recently, metformin has been proposed to have anti-aging and antiviral properties making the drug a potential candidate to treat other health conditions. Metformin and its proposed “dead-end” product, guanylurea, are not fully metabolized by humans and enter municipal wastewater where they cannot be removed through conventional water treatment processes. These compounds have been detected in surface waters around the world and are currently considered emerging pollutants. This study examined a bacterial consortium enriched from activated sludge which demonstrated the ability to utilize metformin as a sole source of nitrogen, as well as to degrade metformin to its transformation product, guanylurea. Metagenomic sequencing yielded an 18 Mb assembly distributed over 7,440 contigs with an average GC content of 64%. 16S rRNA analysis suggested the presence of Sphingopyxis, Pseudomonas mendocina, Microbacterium, and Mesorhizhobium species within the consortia. Bioinformatic analysis led to the identification of three relevant enzymes involved in metformin metabolism: guanylurea hydrolase, carboxyguanidine deiminase, and allophanate hydrolase. Biochemical studies revealed that these proteins catalyze the degradation of guanylurea to ammonia and carbon dioxide. Protein sequence analyses and structural modeling studies are currently in progress to identify a candidate gene(s) encoding the enzyme initiating the metabolism of metformin. This research presents the first evidence for a biochemical pathway associated with the microbial degradation of guanylurea. Significantly, it also advances understanding of the microbial capacity for metformin biodegradation. These findings could lead to the development of practical biotechnological applications to improve water treatment processes and provide insight into the effects of metformin on human microbiome metabolism.

One-Step Reverse Osmosis Based on Riverbank Filtration for Future Drinking Water Purification

The presence of newly emerging pollutants in the aquatic environment poses great challenges for drinking water treatment plants. Due to their low concentrations and unknown characteristics, emerging pollutants cannot be efficiently removed by conventional water treatment processes, making technically, economically, and environmentally friendly water purification technologies increasingly important. This article introduces a one-step reverse osmosis (OSRO) concept consisting of riverbank filtration (RBF) and reverse osmosis (RO) for drinking water treatment. The OSRO concept combines the relatively low-cost natural pretreatment of river water with an advanced engineered purification system. RBF provides a continuous natural source of water with stable water quality and a robust barrier for contaminants. With the pre-removal of particles, organic matter, organic micro-pollutants (OMPs), and microbes, RBF becomes an ideal source for a purification system based on RO membranes, in comparison with the direct intake of surface water. OSRO treatment removes almost 99.9% of the particles, pathogens, viruses, and OMPs, as well as the vast majority of nutrients, and thus meets the requirements for the chlorine-free delivery of drinking water with high biostability. The OSRO treatment is cost effective compared with the standard conventional series of purification steps involving sprinkling filters, softening, and activated carbon. Artificial bank filtration (ABF), which functions as an artificial recharge in combination with a sand filtration system, is proposed as an alternative for RBF in the OSRO concept to supply drinking water from locally available resources. It is also suggested that the OSRO concept be implemented with wind power as an alternative energy source in order to be more sustainable and renewable. An OSRO-based decentralized water system is proposed for water reclaiming and reuse. It is suggested that future water treatment focus on the combination of natural and engineered systems to provide drinking water through technically efficient, financially feasible, resource reusable, and environmentally relevant means.

Optical Characterization of Ciprofloxacin Photolytic Degradation by UV-Pulsed Laser Radiation.

Ciprofloxacin is one of the most prescribed antibiotics in treating bacterial infections, becoming an important pollutant of the wastewaters. Moreover, ciprofloxacin is hard to be destroyed by conventional water treatment processes; therefore, efficient treatments to destroy it are needed in water decontamination. This study offers insights into the performance of 266 nm laser beams on the photodegradation of ciprofloxacin. An Nd:YAG laser was used that emitted 266 nm at an energy of 6.5 mJ (power of 65 mW) and ciprofloxacin water solutions were irradiated up to 240 min. The irradiated solutions were investigated by UV-Vis and FTIR absorption spectroscopy, pH assay, and laser-induced fluorescence. An HPTLC densitometer was used to characterize the laser-induced fluorescence and fluorescence lifetime of photodegradation products. The UV-Vis absorption, FTIR, and laser-induced fluorescence spectra showed the degradation of ciprofloxacin. Moreover, HPTLC densitometry offered the fluorescence and fluorescence lifetime of ciprofloxacin and its three photoproducts as well as their relative quantification. From the FTIR spectra, the molecular structure of two out of three photoproducts was proposed. In conclusion, the laser irradiation method provided the efficient photodegradation of ciprofloxacin, whereas the analytical techniques offered the proper means to monitor the process and detect the obtained photoproducts.

Comparative evaluation of 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, and 2,4,6-trichloroanisole degradation by ultraviolet/chlorine and ultraviolet/hydrogen peroxide processes

2-Isopropyl-3-methoxypyrazine (IPMP), 2-Isobutyl-3-methoxypyrazine (IBMP), and 2,4,6-Trichloroanisole (TCA) are the primary emerging taste and odor (T&O) compounds in water systems with low thresholds (ng L−1). The selected T&O compounds are known to be difficult to remove using conventional water treatment processes. In this study, we compared the removal characteristics of the three T&O compounds using UV/Cl2 and UV/H2O2. The removal rates of the three compounds by direct photolysis at 254 nm were less than 10%, even at a high UV dose (approximately 1000 mJ cm−2). Under conditions of an oxidant injection volume of 5 mg L−1 and UV dose of 1000 mJ cm−2, the degradation rate of the target compounds in the UV/H2O2 process exceeded that of the UV/Cl2 process. Moreover, the results revealed that pH has a significant impact on the removal of the T&O compounds during the UV/Cl2 process. The IPMP, IBMP, and TCA were found to be more reactive with hydroxyl radicals than reactive chlorine species (RCS). A predictive tool was developed to determine the optimal operating condition using the generalized reduced gradient (GRG) nonlinear solver. In the UV/H2O2 process, the EED value for 90% removing rate was 0.156 kWh m−3 for the IPMP, 0.135 kWh m−3 for the IBMP, and 0.154 kWh m−3 for the TCA, respectively. In case of the UV/Cl2, the EED value for 50% removing rate was 0.174 kWh m−3 for the IPMP, 0.138 kWh m−3 for the IBMP, and 0.169 kWh m−3 for the TCA, respectively.

Different Adsorption Behavior between Perfluorohexane Sulfonate (PFHxS) and Perfluorooctanoic Acid (PFOA) on Granular Activated Carbon in Full-Scale Drinking Water Treatment Plants

Perfluorinated compounds (PFCs) in water have detrimental effects on human health, and the removal rate of these compounds by conventional water treatment processes is low. Given that the levels of PFCs have been regulated in many regions, a granular activated carbon (GAC) adsorption process has been used in drinking water treatment plants to maintain concentrations of PFCs, perfluorohexyl sulfonate (PFHxS), and perfluorooctanoic acid (PFOA), below 70 ng/L. However, it was found that these concentrations in the final product water in local water utilities unexpectedly increased because of inappropriate operation and maintenance methods of GAC, such as its inefficient regeneration and replacement cycle. In this study, the changes in PFC concentration were monitored and analyzed in raw and final water of two large-scale water treatment plants for eight months. Additionally, the correlation of the GAC replacement cycle with the removal efficiency of PFHxS and PFOA was investigated in a total of 30 GAC basins of two drinking water treatment plants. A lab-scale experiment with a coconut-shell-based GAC column showed the possibly different mechanism of removal between PFHxS and PFOA, indicating that the sulfonate-based PFCs may be a limiting factor in GAC replacement cycle for PFCs removal.

Variations of disinfection byproduct precursors through conventional drinking water treatment processes and a real-time monitoring method

In this investigation, raw water (RW), settled water (SW), and filtered water (FW) collected from a drinking water treatment plant were fractionated into 24 natural organic matter (NOM) fractions with varying molecular weights and hydrophobicity. The yields of disinfection byproducts (DBPs) obtained during the chlorination of the NOM fractions were explored. Results revealed that the 0–1 kDa, 5–10 kDa, and hydrophobic DBP precursors dominated RW. Hydrophobic fractions cannot be effectively removed, which contributed to the high DBP precursors remaining in the FW. The optional optical parameters, including UVA (UV340, UV360, and UV380), UVB (UV280, UV300, and UV310), and UVC (UV254, UV260, and UV272), were analyzed to determine the DBP yields during chlorination of different NOM fractions. Results revealed that UVC could be applied to indicate the regulated DBP yields of the humified precursors. Contrary to the generally accepted view, for biologically derived precursors, their regulated DBPs and dichloroacetonitrile correlated better with UVA (e.g. UV340). Moreover, PARAFAC analysis was applied to decompose an array of 24 EEM spectra. Good linear correlations were found between the PARAFAC components and most DBP yields. Furthermore, four fluorescence parameters were proposed via a modified fluorescence picking method, which can serve as excellent surrogates of PARAFAC components. These fluorescence parameters were found to be effective in indicating most DBP yields. Finally, the fluorescence intensity at excitation wavelength/emission wavelength = 310/416 nm was found to be a promising built-in parameter for the real-time monitoring of DBP precursors, regardless of the humification degree of the precursors.

Potential Impacts on Treated Water Quality of Recycling Dewatered Sludge Supernatant during Harmful Cyanobacterial Blooms.

Cyanobacterial blooms and the associated release of cyanotoxins pose problems for many conventional water treatment plants due to their limited removal by typical unit operations. In this study, a conventional water treatment process consisting of coagulation, flocculation, sedimentation, filtration, and sludge dewatering was assessed in lab-scale experiments to measure the removal of microcystin-LR and Microcystis aeruginosa cells using liquid chromatography with mass spectrometer (LC-MS) and a hemacytometer, respectively. The overall goal was to determine the effect of recycling cyanotoxin-laden dewatered sludge supernatant on treated water quality. The lab-scale experimental system was able to maintain the effluent water quality below relevant the United States Environmental Protection Agency (US EPA) and World Health Organisation (WHO) standards for every parameter analyzed at influent concentrations of M. aeruginosa above 106 cells/mL. However, substantial increases of 0.171 NTU (Nephelometric Turbidity Unit), 7 × 104 cells/L, and 0.26 µg/L in turbidity, cyanobacteria cell counts, and microcystin-LR concentration were observed at the time of dewatered supernatant injection. Microcystin-LR concentrations of 1.55 µg/L and 0.25 µg/L were still observed in the dewatering process over 24 and 48 h, respectively, after the initial addition of M. aeruginosa cells, suggesting the possibility that a single cyanobacterial bloom may affect the filtered water quality long after the bloom has dissipated when sludge supernatant recycling is practiced.

Degradation mechanism of tris(2-chloroethyl) phosphate (TCEP) as an emerging contaminant in advanced oxidation processes: A DFT modelling approach

As a typical toxic organophosphate and emerging contaminant, tris(2-chloroethyl) phosphate (TCEP) is resistant to conventional water treatment processes. Studies on advanced oxidation processes (AOPs) to degrade TCEP have received increasing attention, but the detailed mechanism is not yet fully understood. This study investigated the mechanistic details of TCEP degradation promoted by OH by using the density functional theory (DFT) method. Our results demonstrated that in the initial step, energy barriers of the hydrogen abstraction pathways were no more than 7 kcal/mol. Cleavage of the P–O or C–Cl bond was possible to occur, whilst the C–O or C–C cleavage had to overcome an energy barrier above 50 kcal/mol, which was too high for mild experimental conditions. The bond dissociation energy (BDE) combined with the distortion/interaction energy (DIE) analysis disclosed origin of the various reactivities of each site of TCEP. The systematic calculations on the transformation of products generated in the initial step showed remarkable exothermic property. The novel information at molecular level provides insight on how these products are generated and offers valuable theoretical guidance to help develop more effective AOPs to degrade TCEP or other emerging environmental contaminant.

Stray particles as the source of residuals in sand filtrate: Behavior of superfine powdered activated carbon particles in water treatment processes

Although superfine powdered activated carbon has excellent adsorption properties, it is not used in conventional water treatment processes comprising coagulation–flocculation, sedimentation, and sand filtration (CSF) due to concerns about its residual in treated water. Here, we examined the production and fate of very fine carbon particles with lacking in charge neutralization as a source of the residual in sand filtrate after CSF treatment. Almost all of the carbon particles in the water were charge-neutralized by coagulation treatment with rapid mixing, but a very small amount (≤0.4% of the initial concentration) of very fine carbon particles with a lesser degree of charge neutralization were left behind in coagulation process. Such carbon particles, defined as stray carbon particles, were hardly removed by subsequent flocculation and sedimentation processes, and some of them remained in the sand filtrate. The concentration of residual carbon particles in the sand filtrate varied similarly with that of the stray carbon particles. The stray and residual carbon particles were similarly smaller than the particles before coagulation treatment, but the residual carbon particles had less charge neutralization than the stray carbon particles. The turbidity of water samples collected after sedimentation was not correlated with the residual carbon concentration in the sand filtrate, even though it is often used as an indicator of treatment performance with respect to the removal of suspended matter. Based on these findings, we suggest that reduction of the amount of stray particles should be a performance goal of the CSF treatment. Examining this concept further, we confirmed that the residence time distributions in the coagulation and flocculation reactors influenced the concentration of stray carbon particles and then the residual carbon particle concentration in sand filtrate, but found that the effect was dependent on coagulant type. A multi-chambered-reactor configuration lowered both the stray carbon particle concentration after coagulation treatment and the residual carbon particle concentration in sand filtrate compared with a single-chambered reactor configuration. When a normal basicity PACl that consisted mainly of monomeric Al species was used, the stray carbon particle concentration was decreased during coagulation process and then gradually decreased during subsequent flocculation process because the monomeric Al species were transformed to colloidal Al species via polymeric Al species. In contrast, when a high-basicity PACl that consisted mostly of colloidal Al species was used, coagulation treatment largely decreased the stray carbon particle concentration, which did not decrease further during subsequent flocculation process. These findings will be valuable for controlling residual carbon particles after the CSF treatment.

Heterogeneous Fenton-like reaction followed by GAC filtration improved removal efficiency of NOM and DBPs without adjusting pH

This paper explores the removal of natural organic matter (NOM) and disinfection by-products (DBPs) in drinking water by heterogeneous Fenton-like oxidation and granular activated carbon (GAC) filtration in a pilot scale test without adjusting pH of the water. pH of the used water in this study was from 7.5 to 8.7. Comparing with conventional water treatment processes, heterogeneous Fenton-like reaction and GAC filtration increased the removal rate of dissolved organic carbon (DOC), NOM with different apparent molecular weight (AMW) (F1-F7) and with different compositions (C1-C5) to 75.11%, 88.65% and 58.73%, respectively. Moreover, heterogeneous Fenton-like reaction and GAC filtration increased the removal rate of DBPs to 88.18%. The multivariate statistical analysis indicated that haloacetic acids (HAAs) and haloketones (HKs) mainly came from fulvic-like and humic-like NOM with AMW lower than 1.5 K Da. These substances with AMW between 1.5 K Da and 3.5 K Da were the main precursors of trihalomethanes (THMs). The main precursors of halonitriles (HANs) were soluble microbial byproduct-like (SMP-like), tyrosine-like and tryptophan-like substance with the AMW between 3.5 K Da and 4.5 K Da. Overall, without adjusting pH of water, heterogeneous Fenton-like reaction and GAC filtration improved the removal efficiency of NOM and DBPs, and controlled the genotoxicity of drinking water.

Dead-end ultrafiltration as a cost-effective strategy for improving arsenic removal from high turbidity waters in conventional drinking water facilities

Dead-end ultrafiltration (UF) was integrated to a conventional drinking water treatment process (pre-oxidation, coagulation-flocculation, decantation and sand filtration) as a strategy for arsenic control in drinking water. Different turbidities (control, 300 and 1000 NTU) and arsenic concentration (0.015 – 0.4 mg/L) were considered, in addition to the interference of iron and manganese on arsenic removal as these metals occur concomitantly. The efficiency of coagulation-flocculation processes was assessed, stablishing multilinear regression models for predictive purposes. These are processes highly dependent on surface water quality, in which the average removal of arsenic, iron and manganese decreased as their initial concentration increased, although the removal of colour and turbidity seems not to be a major concern. The results reinforced the limitation of conventional treatment process for attaining the threshold values especially for arsenic and manganese, an issue overcame by the implementation of an UF (RAs: 96.9% RMn: 88.9% and RFe: 99.7%). Not only the efficiency in attaining the threshold values, but the UF performance was reassured by its operation stability, that showed no expressive flux decay (J/J0 > 0.93). A sensitive analysis demonstrated that the implementation of an UF becomes more economically attractive in facilities of a greater treatment flowrate. As the treatment capacity increase (0.108 – 12,690 m3/h) the operating costs decreases (0.98 – 0.81 US$/m3). The overall results suggested that UF can be used to retrofit drinking water treatment plants in view of the increased concentration of arsenic, and other ions as iron and manages, in drinking water sources.

Technologies Employed in the Treatment of Water Contaminated with Glyphosate: A Review.

Glyphosate [N-(phosphonomethyl)-glycine] is a herbicide with several commercial formulations that are used generally in agriculture for the control of various weeds. It is the most used pesticide in the world and comprises multiple constituents (coadjutants, salts, and others) that help to effectively reach the action’s mechanism in plants. Due to its extensive and inadequate use, this herbicide has been frequently detected in water, principally in surface and groundwater nearest to agricultural areas. Its presence in the aquatic environment poses chronic and remote hazards to human health and the environment. Therefore, it becomes necessary to develop treatment processes to remediate aquatic environments polluted with glyphosate, its metabolites, and/or coadjutants. This review is focused on conventional and non-conventional water treatment processes developed for water polluted with glyphosate herbicide; it describes the fundamental mechanism of water treatment processes and their applications are summarized. It addressed biological processes (bacterial and fungi degradation), physicochemical processes (adsorption, membrane filtration), advanced oxidation processes—AOPs (photocatalysis, electrochemical oxidation, photo-electrocatalysis, among others) and combined water treatment processes. Finally, the main operating parameters and the effectiveness of treatment processes are analyzed, ending with an analysis of the challenges in this field of research.