Natural organic matter removal by coagulation during drinking water treatment: a review

Seasonal variations of natural organic matter (NOM) in surface water supplied to two coal-fired power stations

Global issues such as pollution and global warming have resulted in changes in water characteristics over the past 20 years. Natural organic matter (NOM) which is a major component in water systems has shown an increase globally. This increase in NOM concentration has negatively affected both water treatment processes and drinking water quality. It is subsequently critical to understand the seasonal variations and composition of NOM to be able to address issues related to NOM. In this study, techniques such as ultraviolet-visible spectroscopy, total organic carbon and liquid chromatography-organic carbon detection (LC-OCD) were used for characterisation and quantification of NOM. Two coal-fired power stations were selected for this study with each power station receiving water from a different source, i.e. power station A receives water from the Vaal River and power station B from the Nkomati River. Results from this study demonstrated that composition and concentration of NOM from these two water sources varied seasonally. Characterisation of NOM using the LC-OCD indicated that the different fractions of NOM, i.e. low molecular weight neutrals, low molecular weight acids, building blocks, humic substances and biopolymers, varied seasonally. The dissolved organic carbon concentration and specific ultraviolet absorbance values of the raw water at both power stations showed an increment amid the wet seasons and a decrease amid the dry seasons.

A review of long-term change in surface water natural organic matter concentration in the northern hemisphere and the implications for drinking water treatment

Reduced atmospheric acid deposition has given rise to recovery from acidification - defined as increasing pH, acid neutralization capacity (ANC), or alkalinity in surface waters. Strong evidence of recovery has been reported across North America and Europe, driving chemical responses. The primary chemical responses identified in this review were increasing concentration and changing character of natural organic matter (NOM) towards predominantly hydrophobic nature. The concentration of NOM also influenced trace metal cycling as many browning surface waters also reported increases in Fe and Al. Further, climate change and other factors (e.g., changing land use) act in concert with reductions in atmospheric deposition to contribute to widespread browning and will have a more pronounced effect as deposition stabilizes. The observed water quality trends have presented challenges for drinking water treatment (e.g., increased chemical dosing, poor filter operations, formation of disinfection by-products) and many facilities may be under designed as a result. This comprehensive review has identified key research areas to be addressed, including 1) a need for comprehensive monitoring programs (e.g., larger timescales; consistency in measurements) to assess climate change impacts on recovery responses and NOM dynamics, and 2) a better understanding of drinking water treatment vulnerabilities and the transition towards robust treatment technologies and solutions that can adapt to climate change and other drivers of changing water quality.

Suitability of Highly Polymerised Polyaluminium Chlorides (PACls) in the Treatment of Mixture of Groundwater and Surface Water

The aim of this study was to evaluate the effectiveness of the coagulation process using highly polymerised polyaluminium chlorides in reducing the level of pollution of water in a mixture of groundwater and surface water. The coagulants used were prehydrolysed polyaluminium chlorides with the trade names PAXHP908 and PAXXL1911 that had alkalinity 85% and different iron contents (<0.01% and 0.7%). The Al species distribution in the PACls (PAXXL1911 ad PAXHP908) samples were analysed by the Ferron complexation timed spectrophotometry. The content of polymer forms of aluminium (Alb) in the tested coagulants was 40%. The worse results in the removal of organic matter (TOC, DOC, UV254), iron, colour and turbidity in the coagulation process were produced by the PAXXL1911, possessing higher content of iron (0.7%). The lower usefulness of the PAXXL1911 was probably caused by the interaction of organic ligands present in the treated water and Fe(III) ions introduced into the water with the coagulant. The effectiveness of the coagulation process with the tested coagulants was also evaluated by measuring the electrokinetic potential ζ, which determines the stability of the colloidal system.

Removal of humic acid interference in soil enzymatic analysis using poly-γ-glutamic acid

Soil enzymes are biological indicators in environmental and agricultural monitoring. However, brownish humic acid (HA) in samples interferes significantly with various analytical methods, especially in optical-based techniques. Here, we implemented a coagulation-flocculation process to carry out continuously an enzymatic reaction without separation and transfer of a sample solution. The elimination of HA in a soil suspension using poly-γ-glutamic acid (PGA) by coagulation to minimize the HA interference in soil enzymatic analysis was investigated. As a result of the optimization of preliminary parameters, the removal efficiency of HA was > 92% in 100 mg L^-1 HA in neutral pH, using 100 mg L^-1 PGA and aluminum trivalent as a coagulant aid. However, the fluorescent intensity of the enzyme product (i.e., 4-methylumbelliferone) decreases by about 50% as HA was removed under the conditions used. A decrease in the enzymatic detection of 3,3',5,5'-tetramethylbenzidine (TMB) was not observed from treated samples even though the initial level of HA was different. The results suggested that the coagulation-flocculation approach is suitable for the reduction of HA interference, while maintaining target analyte detection. Therefore, the proposed sample treatment can be used to examine enzyme activity based on TMB product detection without regular standard addition calibration.

The removal of microplastics from water by coagulation: A comprehensive review

Drinking water treatment plants (DWTPs) and wastewater treatment plants (WWTPs) are the first and last hurdles for the prevention of microplastics (MPs) pollution, respectively. With coagulation as one of the most critical technologies for the removal of MPs in water treatment plants, there is an urgent need to gain an in-depth understanding of the mechanisms and influencing factors of MPs removal during coagulation. In this paper, the research progress of adopting coagulation in MPs removal in recent years is reviewed, the removal effect of coagulation in water treatment plants are compared, and the role of three coagulation mechanisms, i.e., charge neutralization, adsorption bridging, and sweep flocculation in MPs removal process are identified. The effect of coagulant performance, MPs characteristics, operation conditions and other parameters on the removal of MPs are systematically analyzed. It is found that the combined coagulation techniques have better removal efficiency, can better decrease MP pollution and meet strict discharge standards. Moreover, flaws in the application of coagulation technology are pointed out, and strategies to deal with them are also proposed. Hopefully, this review can not only contribute to a better understanding of the mechanism of MPs removal by coagulation technology, but also serve as a useful guide for future research on MPs removal.

Characteristics of dissolved organic matter in two alternative water sources: A comparative study between reclaimed water and stormwater

Reclaimed water and stormwater are two important alternative water sources to mitigate water resource shortage. They can be reused by discharging into drinking water sources. Due to different sources, characteristics of dissolved organic matter (DOM, a precursor of disinfection by-products, DBPs) present in reclaimed water and stormwater would be different. This study selected reclaimed water to compare with stormwater (including both stormwater runoff and rainwater) by investigating their DOM characteristics, including concentrations, aromaticity, molecular weight, hydrophobicity/hydrophilicity, composition and DBPs formation potential. The results showed that reclaimed water had higher dissolved organic carbon (DOC) concentrations (6.02-10.8 mg/L) than stormwater (3.62-5.48 mg/L) while SUVA₂₅₄ values of stormwater runoff (1.92-2.53 L/(mg-C·m)) were higher than reclaimed water (1.11-1.24 L/(mg-C·m)). Additionally, reclaimed water is more hydrophobic while stormwater runoff and rainwater are more hydrophilic. Although all water types included the highest fraction of DOM with molecular weight <1 kDa (43.0 %-77.5 %), reclaimed water primarily contained soluble microbial products (SMPs)-like and humic acid-like substances while stormwater runoff primarily contained humic acid-like DOM. In terms of DBPs, reclaimed water showed relatively higher formation potential than stormwater runoff while rainwater had the lowest DBPs formation potential. These results can contribute to effective water resource management. Particularly, when reclaimed water or/and stormwater are discharged into drinking water sources, these outcomes can help on efficient drinking water treatment.

Emerging technologies for enhanced removal of residual antibiotics from source-separated urine and wastewaters: A review

Antibiotic residues are of significant concern in the ecosystem because of their capacity to mediate antibiotic resistance development among environmental microbes. This paper reviews recent technologies for the abatement of antibiotics from human urine and wastewaters. Antibiotics are widely distributed in the aquatic environment as a result of the discharge of municipal sewage. Their existence is a cause for worry due to the potential ecological impact (for instance, antibiotic resistance) on bacteria in the background. Numerous contaminants that enter wastewater treatment facilities and the aquatic environment, as a result, go undetected. Sludge can act as a medium for some chemicals to concentrate while being treated as wastewater. The most sewage sludge that has undergone treatment is spread on agricultural land without being properly checked for pollutants. The fate of antibiotic residues in soils is hence poorly understood. The idea of the Separation of urine at the source has recently been propagated as a measure to control the flow of pharmaceutical residues into centralized wastewater treatment plants (WWTPs). With the ever increasing acceptance of urine source separation practices, visibility and awareness on dedicated treatement technologies is needed. Human urine, as well as conventional WWTPs, are point sources of pharmaceutical micropollutants contributing to the ubiquitous detection of pharmaceutical residues in the receiving water bodies. Focused post-treatment of source-separated urine includes distillation and nitrification, ammonia stripping, and adsorption processes. Other reviewed methods include physical and biological treatment methods, advanced oxidation processes, and a host of combination treatment methods. All these are aimed at ensuring minimized risk products are returned to the environment.

Advancements in laundry wastewater treatment for reuse: a review

Laundry related activities produce huge quantity of wastewater that is very rich in lint, dyes, surfactants, and detergents. The large amount of laundry wastewater (LWW) is generated by extensive human activities. LWW needs to be treated in order to tackle the challenging problem of water pollution and to accomplish water sustainability. To achieve this success, LWW can be reused for several purposes such as irrigation, construction activities, vehicle washing etc. However, there are several challenges in the reclamation of LWW like effective handling of the wastewater and meeting the regulatory criteria. Based on the literature review it seems that a single treatment process is not sufficient to treat LWW up to acceptable reuse standards. To that end, different treatment chains have been proposed: i) hybrid processes combining membrane filtration with adsorption; ii) advanced oxidation process using ultraviolet (UV) and hydrogen peroxide (H₂O₂); iii) coagulation-flocculation combined with sand filtration; iv) combination of ozonation process, adsorption, and ultrafiltration (UF). This review paper discusses the selection of suitable treatment technology depends on several factors: i) a well-designed equipment, ii) cost-effectiveness of treatment method and iii) desired characteristics of the treated water. The review paper also presents solutions for treatment and reclamation of LWW.

Waste to resource: use of water treatment residual for increased maize productivity and micronutrient content

Soil degradation, which is linked to poor nutrient management, remains a major constraint to sustained crop production in smallholder urban agriculture (UA) in sub-Saharan Africa (SSA). While organic nutrient resources are often used in UA to complement mineral fertilizers in soil fertility management, they are usually scarce and of poor quality to provide optimum nutrients for crop uptake. Alternative soil nutrient management options are required. This study, therefore, evaluates the short-term benefits of applying an aluminium-based water treatment residual (Al-WTR), in combination with compost and inorganic P fertilizer, on soil chemical properties, and maize (Zea mays L.) productivity and nutrient uptake. An eight-week greenhouse experiment was established with 12 treatments consisting of soil, Al-WTR and compost (with or without P fertilizer). The co-amendment (10% Al-WTR + 10% compost) produced maize shoot biomass of 3.92 ± 0.16 g at 5 weeks after emergence, significantly (p < 0.05) out-yielding the unamended control which yielded 1.33 ± 0.17 g. The addition of P fertilizer to the co-amendment further increased maize shoot yield by about twofold (7.23 ± 0.07 g). The co-amendment (10% Al-WTR + 10% C) with P increased maize uptake of zinc (Zn), copper (Cu) and manganese (Mn), compared with 10% C + P. Overall, the results demonstrate that combining Al-WTR, compost and P fertilizer increases maize productivity and micronutrient uptake in comparison with single amendments of compost and fertilizer. The enhanced micronutrient uptake can potentially improve maize grain quality, and subsequently human nutrition for the urban population of SSA, partly addressing the UN's Sustainable Development Goal number 3 of improving diets.

Unified understanding of intrinsic and extrinsic controls of dissolved organic carbon reactivity in aquatic ecosystems

Despite our growing understanding of the global carbon cycle, scientific consensus on the drivers and mechanisms that control dissolved organic carbon (DOC) turnover in aquatic systems is lacking, hampered by the mismatch between research that approaches DOC reactivity from either intrinsic (inherent chemical properties) or extrinsic (environmental context) perspectives. Here we propose a conceptual view of DOC reactivity in which the combination of intrinsic and extrinsic factors controls turnover rates and determines which reactions will occur. We review three major types of reactions (biological, photochemical, and flocculation) from an intrinsic chemical perspective and further define the environmental features that modulate the expression of chemically inherent reactivity potential. Finally, we propose hypotheses of how extrinsic and intrinsic factors together shape patterns in DOC turnover across the land-to-ocean continuum, underscoring that there is no intrinsic DOC reactivity without environmental context. By acknowledging the intrinsic-extrinsic control duality, our framework intends to foster improved modeling of DOC reactivity and its impact on ecosystem services.

Challenges in quantifying and characterizing dissolved organic carbon: Sampling, isolation, storage, and analysis

Despite the advancements in analytical techniques, there are still great challenges and difficulties in accurately and effectively quantifying and characterizing dissolved organic carbon (DOC) in environmental samples. The objectives of this review paper are (a) to understand the roles and variability of DOC along the water continuum; (b) to identify the constraints, inconsistences, limitations, and artifacts in DOC characterization; and (c) to provide recommendations and remarks to improve the analytical accuracy. For the first objective, we summarize the four ecological and engineering roles of DOC along the water continuum from source water to municipal utility, including nutrients and energy sources, controlling the fates of micropollutants, buffering capacity, and treatability and precursors of disinfection byproducts. We also discuss three major challenges in DOC analysis, including spatial and temporal variations, degradability and stability, and unknown structures and formulas. For the second objective, we review the procedures and steps in DOC analysis, including sampling in diverse environmental matrices, isolation of DOC fraction, storage and preservation techniques, and analyses on bulk chemical characteristics. We list and discuss the available options and evaluate the advantages and disadvantages of each choice. Last, we provide recommendations and remarks for each stage: sampling, isolation, storage, and analysis.

MEUF for removal and recovery of valuable organic components present in effluents: A process intensified technology

In recent years, the domain of the research space in novel separation process has been led by membrane systems as a panacea providing multifarious benefits of high separation efficiency, elimination of extreme process conditions, sustainability, and environment friendliness coupled with high operational flexibility. In this niche area, often, ultrafiltration is touted as a robust separation technique due to its high separation efficiency, membrane stability, and lower operating costs. The only drawback of relatively large pore size can be overcome by combining surfactant addition, leading to development of integrated processes termed as Micellar Enhanced Ultrafiltration. MEUF processes isolate and selectively separate valuable organics present in effluent streams. The process characteristics fit the bill as a typified example for process intensification Technology interventions for recycling of surfactants can enhance the cost-competitiveness of the process. This has the potential to develop into a broad-spectrum effluent treatment option with a change of surfactants for target contaminants. Here, in this review, we attempt to critically examine the unique features of this technology, development of spin-offs with wide-ranging applications. Specifically applications in removal of hazardous, and persistent components like dissolved organics have been critically studied. The focus was to highlight the crux of the novel technologies highlighting the efficacy and the underlying concept of process intensification. PRACTITIONER POINTS: Role of MEUF as a sustainable process intensifying separation technique for removal and recovery of organics. Novel process development using MEUF. Comparative performance analysis to assess efficacy. Discussions on future integrative process development. Sustainability aspect of MEUF with possibility of byproduct recovery.

Studies of Protein Wastes Adsorption by Chitosan-Modified Nanofibers Decorated with Dye Wastes in Batch and Continuous Flow Processes: Potential Environmental Applications

In this study, reactive green 19 dye from wastewater was immobilized on the functionalized chitosan nanofiber membranes to treat soluble microbial proteins in biological wastewater. Polyacrylonitrile nanofiber membrane (PAN) was prepared by the electrospinning technique. After heat treatment, alkaline hydrolysis, and chemically grafted with chitosan to obtain modified chitosan nanofibers (P-COOH-CS), and finally immobilized with RG19 dye, dyed nanofibers were generated (P-COOH-CS-RG19). The synthesis of P-COOH-CS and P-COOH-CS-RG19 are novel materials for protein adsorption that are not deeply investigated currently, with each of the material functions based on their properties in significantly improving the adsorption efficiency. The nanofiber membrane shows good adsorption capacity and great recycling performance, while the application of chitosan and dye acts as the crosslinker in the nanofiber membrane and consists of various functional groups to enhance the adsorption of protein. The dyed nanofibers were applied for the batch adsorption of soluble protein (i.e., lysozyme), and the process parameters including chitosan’s molecular weight, coupling pH, chitosan concentration, dye pH, dye concentration, and lysozyme pH were studied. The results showed that the molecular weight of chitosan was 50 kDa, pH 5, concentration 0.5%, initial concentration of dye at 1 mg/mL dye and pH 12, lysozyme solution at 2 mg/mL at pH 8, and the maximum adsorption capacity was 1293.66 mg/g at a temperature of 318 K. Furthermore, thermodynamic, and kinetic studies suggested that the adsorption behavior of lysozyme followed the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model. The optimal adsorption and desorption conditions based on batch experiments were directly applied to remove lysozyme in a continuous operation. This study demonstrated the potential of dyed nanofibers as an efficient adsorbent to remove approximately 100% of lysozyme from the simulated biological wastewater.

Plant-based coagulants/flocculants: characteristics, mechanisms, and possible utilization in treating aquaculture effluent and benefiting from the recovered nutrients

The increasing intensification of the aquaculture industry requires the development of new strategies to reduce the negative impacts of wastewater on the environment. Plant-based coagulants/flocculants, regarded as one of the environmentally friendly technologies for wastewater treatment, show good performance in the removal of suspended solids from wastewater. The aforementioned technology involves the utilization of plants as coagulants/flocculants in the treatment process and produces nontoxic sludge as treatment by-products. The produced sludge could be converted into valuable compounds used in agriculture. This review summarizes coagulation-flocculation by using plant-based coagulants/flocculants, its mechanisms, operational factors that control the treatment process, and its application in the treatment of wastewater, especially aquaculture effluent. Moreover, this work discusses the potential utilization of aquaculture sludge as a valuable compound used in agriculture. The presented review aims to emphasize the potential of using plant-based coagulants/flocculants in the treatment of aquaculture effluent and explore the potential of using the produced sludge as fertilizer for plants to solve problems related to sludge handling and the toxicity of inorganic coagulants in a recirculating aquaculture system. This paper concluded that utilization of recovered nutrients in the form of solids is feasible for agricultural purposes, while a hydroponic system can be used to reclaim the nutrients in the form of solution.

Recent advances of bismuth titanate based photocatalysts engineering for enhanced organic contaminates oxidation in water: A review

Over more than three decades, the scientific community has been contentiously interested in structuring varying photocatalytic materials with unique properties for appropriate technology transfer. Most of the existing reported photocatalysts in the literature show pros and cons by considering the type of application and working conditions. Bismuth titanate oxides (BTO) are novel photocatalysts that raised recently towards energy and environmental-related applications. Most recent advances to developing bismuth titanate-based photocatalysts for the oxidation of organic pollutants in the water phase were reviewed in this report. To counter the potential drawbacks of BTO materials, i.e., rapid recombination of photoproduced charges, and further promote the photoactivity, most reported approaches were discussed, including creating direct Z-scheme junctions, conventional heterojunctions, metal/non-metal doping, coupling with carbon materials, surface modification and construction of oxygen vacancies. In the end, the review addresses the future trends for better engineering and application of BTO based photocatalysts towards the photodegradation of organic pollutants in water under controlled lab and large scales conditions.

A pilot-scale study of the integrated floc-ultrafiltration membrane-based drinking water treatment process

Although applications of the integrated ultrafiltration (UF) membrane have been investigated for years, most studies have been conducted at the lab scale. Here, a case study on the integrated Fe-based floc-UF process was presented. To enhance membrane performance, both pre-filtration (bag filter) and pre-oxidation were used as pretreatments to remove particles and inhibit the development of microorganisms. Results showed that the integrated process operated stably with pre-treatments, and the UF membrane fouling behavior could be divided into three different phases: slow increase rate (phase I), medium increase rate (phase II), and fast increase rate (phase III). In comparison to those in phases II and III, both natural organic matters and colloids were the main membrane fouling mechanisms during phase I, as the pollutants were not successfully removed by flocs initially. With the continuous injection of flocs, a loose cake layer became the main fouling mechanism during phase II, resulting in the deterioration of membrane fouling. During phase III, however, microorganisms (e.g., Proteobacteria) were inevitably nourished within the cake layer and played an important role in aggravating the degree of membrane fouling. During this integrated membrane-based process, several operating factors, including floc concentration, sludge discharge frequency, and the aeration rate during backwashing, played important roles in determining membrane performance. In addition, except for oxygen consumption, all the effluent quality parameters met the drinking water criteria followed in China (GB5749-2006).

Release and removal of algal organic matter during prechlorination and coagulation treatment of cyanobacteria-laden water: Are we on track?

A better understanding of the physicochemical properties and fate of algae-derived organic matter (AOM) in water treatments significantly benefits the control of algae-derived disinfection byprodcuts and process parameter optimization. In this study, we conducted a comprehensive investigation of the release and treatability of dissolved organic matter during prechlorination and postcoagulation treatments of cyanobacteria-laden source water via size-exclusion chromatography-tandem diode array detector, fluorescence detector and organic carbon detector. The results revealed that the allochthonous humic substances could protect algal cell membrane from damage during prechlorination at a low level of chlorine dose. Due to the release and oxidation of biopterins during prechlorination of M. aeruginosa cells, the variation of the humic-like fluorescence can be used to indicate the chlorine dose for a sufficient membrane damage of algae cells. The prechlorination of M. aeruginosa cells induced minimal release of large MW biopolymer fractions but much more release of low MW fractions E1 and E2 (i.e., unknown carbonaceous substances and fluorescent nitrogenous biopterins). The physically extracted AOM contained a large proportion of biopolymers and could not well represent those released during prechlorination treatment. During coagulation, the negative effect of humic substances on the coagulant demand to achieve algae removal was more remarkable than AOM released by prechlorination. The high-MW biopolymers and humic substances can be removed over 50% by coagulation. Among the low-MW carbonaceous fractions, E1 released by prechlorination can also be effectively removed via coagulation while fractions C, D (possibly oligopeptides or secondary aromatic metabolites & low MW acids) and nitrogenous biopterins were recalcitrant to coagulation. This study highlights the differences of AOM properties between physical extraction and prechlorination and provides a basis for drinking water treatment plants to give more attention to the recalcitrant low MW fractions in coagulation when treating algae-laden source water.

Photocatalytic disinfection of Coliforms and degradation of natural organic matters in river water using titanate nanotubes

In this study, we synthesized and modified titanate nanotubes (TNTs) under different conditions of acid rinsing and calcination. The produced materials were then characterized by transmission electron microscopy, X-ray diffraction, ultraviolet-visible spectroscopy, temperature programmed desorption, inductively coupled plasma atomic emission spectroscopy, and Brunauer-Emmett-Teller analysis. The activity of material was evaluated via its application for disinfection of Coliforms and removal of natural organic matters (NOMs) in river water. Results showed that TNTs rinsed at pH 1.6 and calcined at 500°C had the highest removal efficiency for the treatment of Coliforms and NOMs in Sai Gon river water, possibly due to its high surface area, crystallinity, and surface acidity. The application of this TNTs material for the treatment of waters from Dong Nai River and Mekong River also show high removal efficiency, which could meet the quality standard for supply water, suggesting the potential of TNTs for practical drinking water treatment.

Effect of Fe(II)-Activated Peroxymonosulfate (PMS) on the Performance of Ultrafiltration (UF) Process for Secondary Effluent Treatment and Reuse

The secondary effluent of the wastewater treatment plant is considered as one of the reused water sources and needs advanced treatment to meet increasingly stringent water treatment standards. Ultrafiltration, as one of the most widely used advanced treatment technologies, is limited due to membrane fouling, and coagulation and pre-oxidation have received extensive attention as pretreatment methods to alleviate membrane fouling. This research proposes a new method of Fe(II)-activated peroxymonosulfate (PMS) coagulation and a pre-oxidation system coupled with ultrafiltration (UF) to treat secondary effluent from sewage plants, separately evaluating the treatment effect under different molar ratios of Fe(II)/PMS. The Fe(II)/PMS decontamination mechanism and membrane fouling control effect were elucidated through pollutant removal efficiency, membrane morphology, membrane flux trend, and membrane fouling resistance distribution. According to the experimental results, the optimal effect of organic matter removal and membrane fouling mitigation was achieved at the Fe(II)/PMS dosage of 60/60 μM/μM (molar ratio 1:1). The efficiency of pretreatment methods in removing organics and fluorescent components and mitigating membrane fouling followed the order of Fe(II)/PMS > Fe(III) > inactivated PMS. Fe(II)/PMS could produce a synergistic effect in a high concentration state (60 μM), relying on the dual effects of coagulation and oxidation to alleviate membrane fouling. Coagulation and pre-oxidation by Fe(II)/PMS significantly reduced the clogging of membrane pores and the proportion of irreversible resistance, effectively controlling membrane fouling and improving effluent quality. SEM images further confirmed its effectiveness, and EPR results unequivocally indicated that its synergistic mechanism was mediated by •OH and SO4•−. The research results can provide ideas for advanced wastewater treatment and secondary effluent reuse.

Potential risks and approaches to reduce the toxicity of disinfection by-product - A review

Water contamination through anthropogenic and industrial activities has led to the emergence and necessity of disinfection methods. Chlorine and bromine gases, often used to disinfect water, resulted in the by-product formation by reacting with organic matter. The Disinfectant by-products (DBP) led to the formation of Trihaloaceticacid (TAA), Trihalomethane (THM), and other minor components. The release of chemicals has also led to the outbreak of diseases like infertility, asthma, stillbirth, and types of cancer. There are new approaches that are found to be useful to compensate for the generation of toxic by-products and involve membrane technologies, namely reverse osmosis, ultrafiltration, and nanofiltration. This review mainly focuses on the toxicology effects of DBPs and various approaches to mitigate the same. The health hazards caused by different DBPs and the various treatment techniques available for the removal are discussed. In addition, a critical comparison of the different removal techniques was discussed.

Tannin-based coagulants: Current development and prospects on synthesis and uses

Population growth, industrialization, urbanization, and agriculture lead to a decrease in the availability of clean water. Coagulation/flocculation is one of the most common operations in water, urban wastewater, and industrial effluents treatment systems. Usually, this process is achieved using conventional coagulants that have their performance affected by pH, are poorly biodegradable, produce a huge volume of sludge, and are associated with degenerative diseases. As a substitute for these chemicals, natural coagulants have been highly researched for the last ten/fifteen years, especially the tannin-based (TB) ones. This review paper highlights the advantages of using these greener products to treat different types of water, wastewater, and effluents, especially from dairy, cosmetics, laundries, textile, and other industries. TB coagulants can successfully remove turbidity, color, suspended solids, soluble organic (chemical/biochemical oxygen demand) and inorganic matter (total phosphate, and heavy metals), and microorganisms. TB coagulants are compatible with other treatment technologies and can be used as coagulant-aid to reduce the consumption of chemicals. TB coagulants can reduce operating costs of water treatment due to less alkalinity consumption, as pH adjustment is sometimes unnecessary, and the production of a smaller volume of biodegradable sludge. TB coagulants can be synthesized by valorizing wastes/by-products, from the bark of some specific trees and skins/pomace of different fruits and vegetables. The strengths, weaknesses, opportunities, and threats (SWOT) on TB coagulants are discussed. The progress of TB coagulants is promising, but some threats should be overcome, especially on tannin extraction and cationization. The market competition with conventional coagulants, the feasibility of application in real waters, and the reluctance of the industries to adapt to new technologies are other weaknesses to be surpassed.

Unraveling the Role of Anthropogenic and Natural Drivers in Shaping the Molecular Composition and Biolability of Dissolved Organic Matter in Non-pristine Lakes

Lakes receive and actively process terrestrial dissolved organic matter (DOM) and play an important role in the global carbon cycle. Urbanization results in elevated inputs of nonpoint-source DOM to headwater streams. Retention of water in lakes allows time for alteration and transformation of the chemical composition of DOM by microbes and UV radiation. Yet, it remains unclear how anthropogenic and natural drivers impact the composition and biolability of DOM in non-pristine lakes. We used optical spectroscopy, Fourier transform ion cyclotron mass spectrometry, stable isotopic measurements, and laboratory bioincubations to investigate the chemical composition and biolability of DOM across two large data sets of lakes associated with a large gradient of urbanization in lowland Eastern China, encompassing a total of 99 lakes. We found that increased urban land use, gross domestic products, and population density in the catchment were associated with an elevated trophic level index, higher chlorophyll-a, higher bacterial abundance, and a higher amount of organic carbon with proportionally higher contribution of aliphatic and peptide-like DOM fractions, which can be highly biolabile. Catchment areas, water depth, lake area: catchment area, gross primary productivity, δ¹⁸O-H₂O, and bacterial abundance, however, had comparatively little linkage with DOM composition and biolability. Urban land use is currently intensifying in many developing countries, and our results anticipate an increase in the level of biolabile aliphatic DOM from nonpoint sources and accelerated carbon cycling in lake ecosystems in such regions.

Fate and removal efficiency of polystyrene nanoplastics in a pilot drinking water treatment plant

Occurrence of microplastics and nanoplastics in aquatic systems, as well as in water compartments used to produce drinking water have become a major concern due to their impact on the environment and public health. Nanoplastics in particular, in regard to their fate and removal efficiency in drinking water treatment plants (DWTP), which ensure water quality and supply drinking water for human consumption have been, by far, rarely investigated. This study investigates the removal efficiency of polystyrene (PS) nanoplastics in a conventional water treatment plant providing drinking water for 500'000 consumers. For that purpose, a pilot-scale DWTP, located within the main treatment plant station, reproducing at a reduced scale the different processes and conditions of the main treatment plant is used. The results show that filtration process through sand and granular activated carbon (GAC) filters in the absence of coagulation achieves an overall nanoplastic removal of 88.1%. The removal efficiency of filtration processes is mainly attributed to physical retention and adsorption mechanisms. On the other hand, it is found that coagulation process greatly improves the removal efficiency of nanoplastics with a global removal efficiency equal to 99.4%. The effective removal efficiency of sand filtration increases considerably from 54.3% to 99.2% in the presence of coagulant, indicating that most of PS nanoplastics are removed during sand filtration process. The higher removal efficiency with the addition of coagulant is related to nanoplastics surface charge reduction and aggregation thus significantly increasing their retention in the filter media.

Rapid and Efficient Removal of Anionic Dye in Water Using a Chitosan-Coated Iron Oxide-Immobilized Polyvinylidene Fluoride Membrane

Anionic dyes are one of the most serious contaminants in water as these molecules are known to be toxic to many living organisms. Herein, we report the development of functionalized polyvinylidene fluoride membranes modified with chitosan-coated iron oxide nanomaterials (Fe-PVDF) for the efficient treatment of anionic dye-contaminated water. Aqueous solutions of anionic dyes could be captured rapidly by passing through the functionalized membrane under reduced pressure. Under neutral conditions, Fe-PVDF showed a maximum removal capacity of 74.6 mg/g for Evans blue (EB) through the adsorption process. In addition, the adsorption capacity was significantly enhanced up to 434.78 mg/g under acidic conditions. The adsorption process for EB matched well with the Langmuir model, indicating monolayer adsorption of the dye to the membrane surface. Moreover, Fe-PVDF can be reusable by a simple washing step in an alkaline solution, and thus, the composite membrane was applied several times without a significant decrease in its adsorption performance. The same composite membrane was further applied to the removal of five other different anionic dyes with high efficiencies. The adsorption mechanism can be explained by the electrostatic interaction between the positively charged chitosan and the negatively charged dye as well as the affinity of the sulfate groups in dye molecules for the surface of the iron oxide nanoparticles. The easy preparation and rapid decolorization procedures make this composite membrane suitable for efficient water treatment.

Assessing the performance of coral reef-like floc towards the removal of low molecular weight organic contaminant

The removal of low molecular weight (MW) organics by coagulation is always a challenge in water treatment. In this study, we proposed a novel coagulation strategy: continuous dosing coagulation (CDC). The metallic coagulant and alkali were continuously dosed into water that was pre-acidized, rather than adding all the coagulant and alkali at once as in conventional coagulation (CC). The CDC process promoted the removal of different low MW organics, performing 15% better than the CC process. The best performance occurred at initial pH 6 and the coagulant dosing rate was 2 mg/(L·min). Under optimal conditions, the continuously dosed coagulant formed medium polymer Al in the early stages, which bound low MW organics to form complexes. Then, the subsequently dosed coagulant could adhere to the primary complexes and form coral reef-like surfaces with higher zeta potential and specific surface area. Each freshly formed surface bound contaminants and covered the previous surface. As a result, more dissolved low MW organic contaminants were included in the interior of flocs. However, in the CC process, all the coagulant was dosed at once, resulting in the rapid formation of aluminum hydroxide clusters, which had cotton-like surfaces with fewer binding sites. To achieve similar organic removal in treating secondary effluent, the CDC dosage was half of the CC dosage, indicating the potential economic benefits. The CDC process is a promising technology and the application in various water treatments should be further investigated.

The influence of environmental factor on the coagulation enhanced ultrafiltration of algae-laden water: Role of two anionic surfactants to the separation performance

With the acceleration of urbanization and the improvement of people's living standards, more chemicals that humans rely on are entering the city and surrounding water bodies. Anionic surfactants are one of the essential products for human beings. It is also one of the inducements that cause the eutrophication. The algae-laden water caused by eutrophication is a headache in the traditional water treatment process. To solve the problem, ultrafitration combined process was widely investigated to treat the algae-laden water. The presence of stimuli, low concentration anionic surfactant, probably interfere the performance of ultrafiltration process during algae-laden water treatment. In this study, the influence of two typical anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (LAS), on the performance of coagulation-enhanced ultrafiltration was investigated. The aluminum sulfate hydrate and iron sulfate hydrate were respectively employed as coagulant. Based on the residual turbidity and zeta potential, 4 mg/L Al and 8 mg/L Fe were determined as the optimal coagulant dosage. The floc morphology confirmed that Al-algae flocs with lower fractal dimension (D_f) were looser and more porous compared to Fe-algae flocs. More coagulant was depleted by LAS due to the better hydrophobicity of LAS. During the filtration process, LAS caused a larger flux reduction compared with SDS regardless of the coagulant that was used. More organic compounds penetrate into membrane pores and block the pores with the presence of LAS since algal cell aggregation was weakened. Finally, the rejection of organic compounds by the coagulation-enhanced ultrafiltration process was studied, and the co-existing surfactants can cause effluent deterioration. Therefore, the presence of surfactants has a negative effect to the ultrafiltration treatment of algae-laden water.

Changes in molecular dissolved organic matter and disinfection by-product formation during granular activated carbon filtration by unknown screening analysis with Orbitrap mass spectrometry

The minimization of disinfection by-product (DBP) formation by the removal of its precursors before water disinfection is a highly effective approach. Granular activated carbon (GAC) filtration is widely used for water treatment, but our understanding of molecular dissolved organic matter (DOM) remains insufficient. This research investigates the removal of DOM and the minimization of DBP formation by pilot-scale coal- and coconut-based granular activated carbon filtrations (coAC and ccAC, respectively) using unknown screening analysis with Orbitrap mass spectrometry. DOM adsorption rates by both GACs were fitted with pseudo-second order models with initial adsorption rates of 0.005 mg g^-1 min^-1 and 0.022 mg g^-1 min^-1 for ccAC and coAC, respectively. Based on observations, ccAC was more effective in the removal of dissolved organic carbon and prolonged adsorption longer than coAC, as the breakthrough of coAC was found on Day 10. ccAC removed compounds with carbon, hydrogen, and oxygen (CHO features) with a wide range of oxidation states, as indicated by the carbon oxidation state (C_os), and a wide range of unsaturation, as indicated by oxygen subtracted double bond equivalent per carbon ([DBE-O]/C), while coAC selectively removed only those CHO features with less oxidized characters. Less oxidized compounds (low C_os) were preferentially removed with less contact time, while more oxidized compounds needed more contact time to adsorb on the GACs. A biofilm was developed on Day 60, and many CHO features were found to have increased after GAC treatment on Day 60, indicating the formation of microbial products. Chlorination resulted in a decrease in many CHO and CHO with Cl atom (CHOCl) features and the formation of CHOCl DBPs more than CHO DBP features. ccAC was effective in the minimization of trihalomethane (THM) and CHOCl DBP feature formations on Day 10 and Day 60, while coAC was found to be much less effective.

Classical and Recent Developments of Membrane Processes for Desalination and Natural Water Treatment

Water supply and water treatment are of major concern all around the world. In this respect, membrane processes are increasingly used and reported for a large range of applications. Desalination processes by membranes are well-established technologies with many desalination plants implemented in coastal areas. Natural water treatment is also well implemented to provide purified water for growing population. This review covers various aspects of desalination: membranes and modules, plants, fouling (scaling, biofouling, algal blooms), cleaning, pretreatment (conventional and membrane treatments), energy and environmental issues, renewable energies, boron removal and brine disposal. Treatment of natural water focuses on removal of natural organic matter, arsenic, iron, nitrate, fluoride, pesticides and herbicides, pharmaceutical and personal care products. This review underlines that desalination and natural water treatment require identical knowledge of membrane fouling, construction of large plants, cleaning procedures, energy and environmental issues, and that these two different fields can learn from each other.

Molecular investigation on changing behaviors of natural organic matter by coagulation with non-targeting screen using high-resolution mass spectrometry

Natural organic matter (NOM) can tremendously influence the purification efficiency of the drinking water treatment process. Coagulation was the first and primary process of NOM removal in the drinking water treatment process. The interaction between coagulants and NOM molecules remains unclear. Three typical coagulants (Al₁₃, FeCl_3, and AlCl₃) were used to investigate the effects on NOM removal. The measurement of NOM was conducted using 15 T Electrospray Ionization coupled Fourier-Transform-Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR MS). The coagulation process altered the mass peak numbers as well as relative intensity of the peaks which were positively correlated with TOC value. The lignin-like compound was the most abundant moiety in raw water. Al-based coagulants remove more unsaturated larger compounds (lower KMD and higher carbon number). Al₁₃ remove the unsaturated hydrocarbons preferably. FeCl₃ is more reactive with NOM molecules and removes more fully saturated compounds. These findings revealed the coagulation removal mechanism of NOM with different structural characteristics and advise the practical use of coagulants for various raw water with different NOM characteristics.

Wastewater Treatment Using Novel Magnetic Nanosponges

Modern agricultural activities and concentrated animal feeding operations (CAFOs) are two of the major sources of groundwater contamination that affect the quality of drinking water. Conventional water quality improvement methods include direct filtration, coagulation/settling treatment techniques, membrane-based systems, and absorption-based systems. However, to date, there are no efficient and cost-effective processes available for water treatment. This study developed an innovative nanotechnology-based technique to improve groundwater quality. Magnetic nanosponges (MNSs) were synthesized and characterized using two different magnetic nanoparticles along with polymeric coagulants. The efficiency of MNSs in removing pollutants in wastewater collected from local diary and swine CAFO lagoons was investigated. Standard water quality evaluation parameters, such as the total organic content (TOC), turbidity, total suspended solids (TSS), and biological oxygen demand (BOD), were measured prior to and after treatment with MNSs. The results demonstrate the potential of MNSs to improve the quality of groundwater and support the development of a cost-effective best management practice (BMP) that also employs traditional coagulants at CAFOs and other wastewater treatment plants.

Biological ion exchange as an alternative to biological activated carbon for natural organic matter removal: Impact of temperature and empty bed contact time (EBCT)

Biofiltration is a widely used process in drinking water treatment plants to remove natural organic matter (NOM). A novel biofiltration process using ion exchange resins as supporting media (i.e., biological ion exchange or BIEX) has been demonstrated to provide a superior performance compared to conventional biological activated carbon (BAC). In order to optimize the performance of BIEX filters, the impact of temperature and empty bed contact time (EBCT) on NOM removal was systematically studied. In the present study, bench-scale BIEX filters were set up in parallel with BAC filters and operated at different temperatures (i.e., 4 °C, 10 °C and 20 °C) and EBCTs (i.e., 7.5 min, 15 min and 30 min). Higher average dissolved organic carbon (DOC) removal was achieved in BIEX filters (73 ± 6%) than BAC filters (22 ± 9%) at the steady state with an EBCT of 30 min. Higher temperatures improved NOM removal in both BAC and BIEX filters, with the impact being greater at lower EBCTs (i.e., 7.5 min and 15 min). Higher EBCTs could also improve NOM removal, with the impact being greater at lower temperatures (i.e., 4 °C and 10 °C). DOC removal for BIEX and BAC filters can be modeled with a first-order kinetic model (R² = 0.93-0.99). BAC had a higher temperature activity coefficient than BIEX (1.0675 vs. 1.0429), indicating that temperature has a greater impact on BAC filtration than BIEX filtration. Overall, temperature and EBCT must be considered simultaneously for biofilters to efficiently remove NOM.

Sustainable utilization of water treatment residue as a porous geopolymer for iron and manganese removals from groundwater

Raw water is a significant resource for industrial water usage, but this water is not directly suitable for use due to the presence of contaminants. Therefore, pre-treatment is essential. The treatment generates water treatment residue (WTR) which consists of silt, clay and undesirable components. Most WTR is conventionally disposed of in landfill. In addition, the presence of iron (Fe) and manganese (Mn) in groundwater can result in a reddish-brown color and undesirable taste and odour. A number of expensive and complex technologies are being used for the removal of such iron and manganese. Due to the high Al₂O₃ and SiO₂ content in WTR, therefore, this research proposes the use of WTR as the source material for geopolymer production for Fe/Mn removal. With the availability of free alkali in the geopolymer framework, the OH^--releasing behavior of the WTR-based geopolymer was investigated by the precipitation of Fe(II) ion. The WTR-based geopolymer was calcined at 400 °C and 600 °C to obtain a strong geopolymer matrix with the ability to remove Fe/Mn ions. The results show that the WTR-based geopolymer has the potential to remove Fe from Fe-contaminated water. Hydroxide ions are released from the geopolymer and form an Fe(OH)₃ precipitate. Geopolymer with a calcination temperature of 400 °C provides total removal of the Fe after 24 h of immersion. In addition, the existence of Fe(OH)₃ helps to coprecipitate the Mn(OH)₂ in the Fe/Mn solution leading to a significant reduction of Mn from the solution. The pH value and retention time play an important role in the final metal concentration. The final pH of the solution is close to 8.5, which is the recommended value for boiler water. This method offers an alternative use of WTR in making a porous geopolymer for groundwater Fe/Mn removal using a simple method.

Alleviation of Ultrafiltration Membrane Fouling by ClO2 Pre-Oxidation: Fouling Mechanism and Interface Characteristics

In order to alleviate membrane fouling and improve removal efficiency, a series of pretreatment technologies were applied to the ultrafiltration process. In this study, ClO₂ was used as a pre-oxidation strategy for the ultrafiltration (UF) process. Humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were used as three typical organic model foulants, and the mixture of the three substances was used as a representation of simulated natural water. The dosages of ClO₂ were 0.5, 1, 2, 4, and 8 mg/L, with 90 min pre-oxidation. The results showed that ClO₂ pre-oxidation at low doses (1–2 mg/L) could alleviate the membrane flux decline caused by humus, polysaccharides, and simulated natural water, but had a limited alleviating effect on the irreversible resistance of the membrane. The interfacial free energy analysis showed that the interaction force between the membrane and the simulated natural water was also repulsive after the pre-oxidation, indicating that ClO₂ pre-oxidation was an effective way to alleviate cake layer fouling by reducing the interaction between the foulant and the membrane. In addition, ClO₂ oxidation activated the hidden functional groups in the raw water, resulting in an increase in the fluorescence value of humic analogs, but had a good removal effect on the fluorescence intensity of BSA. Furthermore, the membrane fouling fitting model showed that ClO₂, at a low dose (1 mg/L), could change the mechanism of membrane fouling induced by simulated natural water from standard blocking and cake layer blocking to critical blocking. Overall, ClO₂ pre-oxidation was an efficient pretreatment strategy for UF membrane fouling alleviation, especially for the fouling control of HA and SA at low dosages.

Chemically enhanced primary treatment of dairy wastewater using chitosan obtained from shrimp wastes: optimization using a Doehlert matrix design

Dairy operations generate large volumes of polluted wastewater that require treatment prior to discharge. Chemically enhanced primary treatment (CEPT) is a widely utilized wastewater treatment strategy; but it requires the use of non-biodegradable coagulants that can lead to toxic-byproducts. In this study, chitin from shrimp shell waste is extracted and converted into chitosan. Chitosan was demonstrated to be a natural, low-cost alternative coagulant compatible with the CEPT. Following treatment, dissolved air flotation allowed for the removal of turbidity, COD, and UV₂₅₄ from the synthetic dairy effluent (SDE). Doehlert matrix was used to optimize the chitosan dosage and pH of the CEPT; as well as to model the process. The mechanisms behind the coagulation-flocculation were revealed using zeta potential analysis. FTIR spectroscopy was utilized to confirm the functional groups present on the chitosan. Chitosan with a degree of deacetylation equal to 81% was obtained. A chitosan dose of 73.34 mg/L at pH 5.00 was found to be optimal for the removal of pollutants. Removals of COD, turbidity and UV₂₅₄ were 77.5%, 97.6%, and 88.8%, respectively. The amount of dry sludge generated to treat 1 m³ of SDE was 0.041 kg. Coagulation-flocculation mechanisms involved in chitosan-mediated treatment of SDE involve the neutralization of electrostatic charges carried on the amine groups present in cationic chitosan at pH 5.00. Doehlert matrix proved to be a useful tool in optimizing parameters throughout the coagulation-flocculation process. Chitosan from shrimp waste is a low-cost, eco-friendly coagulant alternative for the removal pollutants from dairy effluent using the CEPT.

Combination of Coagulation, Adsorption, and Ultrafiltration Processes for Organic Matter Removal from Peat Water

The high content of natural organic matter (NOM) is one of the challenging characteristics of peat water. It is also highly contaminated and contributes to some water-borne diseases. Before being used for potable purposes, peat water must undergo a series of treatments, particularly for NOM removal. This study investigated the effect of coagulation using aluminum sulfate coagulant and adsorption using powdered activated carbon (PAC) as a pretreatment of ultrafiltration (UF) for removal of NOM from actual peat water. After preparation and characterization of polysulfone (Psf)-based membrane, the system’s performance was evaluated using actual peat water, particularly on NOM removal and the UF performances. The coagulation and adsorption tests were done under variable dosings. Results show that pretreatment through coagulation–adsorption successfully removed most of the NOM. As such, the UF fouling propensity of the pretreated peat water was substantially lowered. The optimum aluminum sulfate dosing of 175 mg/L as the first pretreatment stage removed up to 75–78% NOM. Further treatment using the PAC-based adsorption process further increased 92–96% NOM removals at an optimum PAC dosing of 120 mg/L. The final UF-PSf treatment reached NOM removals of 95% with high filtration fluxes of up to 92.4 L/(m2.h). The combination of three treatment stages showed enhanced UF performance thanks to partial pre-removal of NOM that otherwise might cause severe membrane fouling.

Removal of inorganic pollutants using electrocoagulation technology: A review of emerging applications and mechanisms

Electrocoagulation (ECoag) technique has shown considerable potential as an effective method in separating different types of pollutants (including inorganic pollutants) from various sources of water at a lower cost, and that is environmentally friendly. The EC method's performance depends on several significant parameters, including current density, reactor geometry, pH, operation time, the gap between electrodes, and agitation speed. There are some challenges related to the ECoag technique, for example, energy consumption, and electrode passivation as well as its implementation at a larger scale. This review highlights the recent studies published about ECoag capacity to remove inorganic pollutants (including salts), the emerging reactors, and the effect of reactor geometry designs. In addition, this paper highlights the integration of the ECoag technique with other advanced technologies such as microwave and ultrasonic to achieve higher removal efficiencies. This paper also presents a critical discussion of the major and minor reactions of the electrocoagulation technique with several significant operational parameters, emerging designs of the ECoag cell, operating conditions, and techno-economic analysis. Our review concluded that optimizing the operating parameters significantly enhanced the efficiency of the ECoag technique and reduced overall operating costs. Electrodes geometry has been recommended to minimize the passivation phenomenon, promote the conductivity of the cell, and reduce energy consumption. In this review, several challenges and gaps were identified, and insights for future development were discussed. We recommend that future studies investigate the effect of other emerging parameters like perforated and ball electrodes on the ECoag technique.

Effect of the Recycling Process on Drinking Water Treatment: Evaluation Based on Fluorescence EEM Analysis Using the Peak-Picking Technique and Self-Organizing Map

The recycling process is applied in many water treatment plants (WTPs), although this process can lead to adverse effects. The effect of the recycling process on the characteristics of dissolved organic matter was evaluated based on a fluorescence excitation-emission matrix using the peak-picking technique and self-organizing map (SOM). In this study, an evaluation of two WTPs, one with and one without a recycling system, was carried out. Both WTPs show moderate efficiency during the coagulation–flocculation process in removing DOC, fulvic acid-like, humic acid-like, and tryptophan-like substances. The recycling process causes increased values of fulvic acid-like, humic acid-like, and tryptophan-like substances and specific ultraviolet absorbance (SUVA) after the filtration process of about 31.0%, 35.7%, 22.2%, and 6%, respectively. Meanwhile, the WTP without recycling showed a reduction in the level of fulvic acid-like, humic acid-like, and tryptophan-like substances and SUVA by 23.3%, 52.9%, 27.8%, and 21.1%, respectively. Moreover, SOM analysis based on the peak-picking technique can determine differences in sample clusters due to the recycling process.

Low-pressure UV-initiated synthesis of cationic starch-based flocculant with high flocculation performance

A kind of starch-based flocculant (starch-graft-poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride], denoted St-g-PDMC-LPUV) has been synthesized by low-pressure ultraviolet initiation and was employed to remove humic acid (HA) for water purification. The physicochemical characteristics of starch and St-g-PDMC-LPUV were characterized by FT-IR, ¹H NMR, XRD, TGA, SEM and BET to confirmed the successful grafting DMC onto starch. Effects of flocculant dosage, pH, the adding amount of Fe₃O₄, initial HA concentration and stirring speed were investigated systematically. The prepared St-g-PDMC-LPUV flocculant with non-toxic, biodegradability and environmental friendliness exhibited effective performance for removing HA from water in a wide pH range (5-10). The flocculation mechanism was attributed to the effective collision between function groups of the St-g-PDMC-LPUV flocculant and HA by charge neutralization, adsorption, bridging and patching.