Polyaluminum Chloride Research Articles

Chitosan enhances poly aluminum chloride flocculation system removal of microplastics: Effective, stable, and pollution free

Microplastics are a new type of pollutant that may enter the human body through drinking water so the effective removal of microplastics in water is of great significance. In this paper, natural organic polymer flocculant chitosan (CTS) was used to strengthen the traditional flocculant poly aluminum chloride (PAC) to remove microplastics. Then this study chose polyethylene terephthalate (PET) as representative microplastics and investigated the performance and mechanism of CTS enhancing PAC flocculation system. The experimental results showed that under the normal dosage, the PET removal rate of the PAC-CTS system in pure water was nearly three times that of the PAC system, and the PAC-CTS system's PET removal rate in tap water was even close to 90 %. The strengthening mechanism was analyzed by scanning electron microscope (SEM), Fourier transforms infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results indicated that the introduction of CTS improved the charge neutralization, adsorption, and purge flocculation in the PAC system to varying degrees, mainly strengthening the charge neutralization and adsorption. And the PAC-CTS system showed better adaptability to different influencing factors. What's more, compared with other flocculation systems, the PAC-CTS system had a better comprehensive evaluation for removing different types of microplastics in water.

Preparation of PVDF-PVP Composite Membranes for Oily Wastewater Treatment.

The oil and gas industry and related applications generate large quantities of oily wastewater, which can adversely affect the environment and human health if not properly handled. This study aims to prepare polyvinylidene fluoride (PVDF) membranes incorporated with polyvinylpyrrolidone (PVP) additives and utilize them to treat oily wastewater through the ultrafiltration (UF) process. Flat sheet membranes were prepared using PVDF dissolved in N,N-dimethylacetamide, followed by the addition of PVP ranging from 0.5 to 35 g. Characterization by scanning electron microscopy (SEM), water contact angle, Fourier transform infrared spectroscopy (FTIR), and mechanical strength tests were performed on the flat PVDF/PVP membranes to understand and compare the changes in the physical and chemical properties of the membranes. Prior to the UF process, oily wastewater was treated by a coagulation-flocculation process through a jar tester using polyaluminum chloride (PAC) as a coagulant. Based on the characterization of the membrane, the addition of PVP improves the physical and chemical properties of the membrane. The membrane's pore size becomes larger, which can increase its permeability and flux. In general, the addition of PVP to the PVDF membrane can increase the porosity and decrease the water contact angle, thereby increasing the membrane's hydrophilicity. With respect to filtration performance, the wastewater flux of the resultant membrane increases with increasing PVP content, but the rejections for TSS, turbidity, TDS, and COD are reduced.

Presence of SARS-CoV-2 in urban effluents in south-east Buenos Aires, Argentina, May 2020 to March 2022.

To implement and evaluate the use of wastewater sampling for detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in two coastal districts of Buenos Aires Province, Argentina. In General Pueyrredon district, 400 mL of wastewater samples were taken with an automatic sampler for 24 hours, while in Pinamar district, 20 L in total (2.2 L at 20-minute intervals) were taken. Samples were collected once a week. The samples were concentrated based on flocculation using polyaluminum chloride. RNA purification and target gene amplification and detection were performed using reverse transcription polymerase chain reaction for clinical diagnosis of human nasopharyngeal swabs. In both districts, the presence of SARS-CoV-2 was detected in wastewater. In General Pueyrredon, SARS-CoV-2 was detected in epidemiological week 28, 2020, which was 20 days before the start of an increase in coronavirus virus disease 2019 (COVID-19) cases in the first wave (epidemiological week 31) and 9 weeks before the maximum number of laboratory-confirmed COVID-19 cases was recorded. In Pinamar district, the virus genome was detected in epidemiological week 51, 2020 but it was not possible to carry out the sampling again until epidemiological week 4, 2022, when viral circulation was again detected. It was possible to detect SARS-CoV-2 virus genome in wastewater, demonstrating the usefulness of the application of wastewater epidemiology for long-term SARS-CoV-2 detection and monitoring.

Effects of different chemical agents on changes in sediment phosphorus composition and the response of sediment microbial community

Controlling the release of sediment phosphorus (P) using chemical agents is a promising method for controlling internal P in eutrophic lakes. However, mineral P formation and changes in the organic P composition after sediment amendment with P-inactivation agents remain poorly understood. Furthermore, little is known about the changes in the sediment microbial community composition after remediation. Here, various ratios of poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB) were added to nutrient-rich sediments and incubated. Sequential P extraction, solution/solid-state 31P nuclear magnetic resonance (NMR), and microbial analyses were periodically performed on the inactivated sediments. The results indicate that PAC and LMB effectively reduced sediment iron-bound P and organic P, respectively, markedly increasing the content of aluminum- and calcium-bound P in the sediment, respectively. Solid-state 31P NMR results confirmed the formation of rhabdophane (LaPO4. nH2O) in the LMB-amended sediment. Solution 31P NMR results showed that PAC preferentially reduced the organic P fractions of pyrophosphate, whereas LMB efficiently reduced the organic P fractions of orthophosphate, monoesters, and diesters in the sediment. Compared with the control sediment, PAC addition can cause short-term negative effects on sediment microbes at high doses, whereas LMB addition can increase bacterial diversity or richness in the sediment. These results provide a deeper understanding of the differences between PAC and LMB in internal sediment P control.

Investigation of coagulation and microfiltration for Danube water as the first step of make-up water production

A comparison of coagulation with two coagulants, poly-aluminum chloride (PACl) and ferric chloride (FeCl3), followed by microfiltration, was evaluated to obtain a better coagulant for an efficient pretreatment method for make-up water preparation from Danube water for thermal power plants. Efficiency was determined by chloride concentration and retention based on the total suspended solid content of the treated water samples. Results were compared to microfiltration working alone as a chemical-free pretreatment. Addition of PACl resulted in the lowest total suspended solid content (18.0 ± 1.3 mg/L), slightly lower than obtained for microfiltration alone (19.6 ± 2.5 mg/L) and significantly lower than for FeCl3 (25.0 ± 3.3 mg/L). Regarding the retention values, coagulation with PACl followed by microfiltration, microfiltration working alone and coagulation with FeCl3 followed by microfiltration represented retention values of 68%, 66.21%, and 56.89%, respectively. Considering the chloride concentration, it remained constant after microfiltration alone; meanwhile, adding coagulants showed a significant rise, ~ 6.4- and 5.7-times higher than the raw water's value after adding FeCl3 and PACl, respectively. From environmental viewpoint, microfiltration alone is recommended because it can provide a steady flux and low total suspended solid content without additional load of chloride ion which shall be eliminated in the further desalination step.

Algae-based treatment of a landfill leachate pretreated by coagulation-flocculation

Landfill leachate (LL) management is an urgent issue at recently closed Sisdol Landfill Site (SLS) used to dispose of solid waste generated in Kathmandu (Nepal) as untreated leachate is flowing directly to the nearby Kolpu River causing environmental and health concerns. This study aims to assess the potential of algae-based treatment of LL pretreated by optimized coagulation-flocculation (CF) for the removal of conventional pollutants such as biological oxygen demand (BOD5), chemical oxygen demand (COD), ammonia, nitrate, and phosphate. Response Surface Methodology (RSM) was used to optimize the operating variables (dose and pH) during the pretreatment of leachate by the CF process using ferric chloride (FeCl3.7H2O), alum (Al2(SO4)3.6H2O) and commercial poly aluminium chloride (PAC) as coagulants using a jar test apparatus. The pretreated LL was subjected to algal treatment using the mixed microalgae culture isolated and enriched from the wastewater collection pond and grown in artificial light. The combined physicochemical and algal treatment of LL from SLS achieved 62.93–72.43%, 74.93–75.55% and 87.58–93.40% and 73.63–86.73% removal for COD, BOD5, ammonium-nitrogen and phosphate, respectively. Thus, this research has proven the feasibility of a combined physiochemical and algae-based treatment of LL and also offers an exciting alternative to current treatment practices for LL.

A Comparison of a Conventional Chemical Coagulant and a Natural Coagulant Derived from Cassia fistula Seeds for the Removal of Heavy Metal Ions.

Cassia fistula seed-derived coagulant has been reported to exhibit high coagulating-flocculating activity, environmental friendliness, and cost-effectiveness for the wastewater treatment, especially of textile wastewater. For heavy metal removal, however, research focusing on evaluating the feasibility of this material is still limited. Therefore, this study reports jar-test experiments in which the Zn2+ and Ni2+ removal efficiency of C. fistula coagulant was assessed. Moreover, a comparison of coagulation performance using a conventional chemical coagulant and the natural coagulant was performed. Characterization of the C. fistula seed-derived coagulant revealed the presence of important functional groups and fibrous networks with rough surfaces. A bench-scale study indicated that the coagulation performance of the two coagulants depends strongly on the initial concentration of metal ions, pH level, and coagulant dosage. The C. fistula seed-derived coagulant was found to possess higher removal efficiency than polyaluminum chloride. This natural coagulant removed over 80% of metal ions at the optimal conditions of pH 5.0, a metal ion concentration of 25ppm, and a dosage of 0.8 and 1.6g/L for Zn2+ and Ni2+, respectively. This study shows that C. fistula seed-derived coagulant is a potential alternative to chemical coagulants and could be developed to provide an environmentally friendly, economical, and efficient wastewater treatment.

Anti-fouling performance and methane potential in coagulation-adsorption assisted biogas-spared anaerobic membrane preconcentration process

To preconcentrate domestic sewage and control membrane fouling, this study proposed a novel anaerobic membrane-based preconcentration (AnMPC) system and controlled fouling by coagulation-adsorption assisted biogas sparging. The effect of polyaluminium chloride (PACl) dosage on membrane fouling control and methane potential of preconcentrated domestic sewage was also investigated. Membrane fouling control was realized by the increase of particle-size (6.03%–40.65%) and the decline of soluble microbial product (11.10%–33.14%) with the rise of PACl addition. The minimum membrane filtration resistance of 1.15 × 1013 m−1 was obtained at the group with 10 mg/L PACl, which was 7.96%–28.20% lower than other groups. More than 75% of chemical oxygen demand (COD) could be preconcentrated, and the preconcentrated ratio increased by 4.22%–9.70% with the rise of PACl addition. Methane potential decreased by 5.40%–40.56% due to the inhibition of accumulated PACl. The pre-hydrolysis of domestic sewage during AnMPC could shorten fermentation time by 0.8–3.2 d. The group with 10 mg/L PACl addition was the optimal due to the excellent anti-fouling performance and the promising energy balance. This study could provide a promising membrane-based preconcentration method with high COD recovery and mild membrane fouling for sustainable treatment of domestic sewage.

Adsorption/precipitation prototype agent for simultaneous removal of phosphorus and organic micropollutants from wastewater

In this study, the effectiveness of a novel adsorbent/precipitant containing powdered activated carbon (PAC) and poly aluminum chloride (PACl) was evaluated for the simultaneous removal of organic micropollutants (OMP) and phosphorus. Results showed better performance with the prototype suspension at similar PAC/DOC doses, possibly due to changes in surface chemistry caused by PAC's suspension in the acid precipitant. Further lab tests with wastewater treatment plant (WWTP) effluent samples confirmed the prototype's effectiveness for different matrices. They highlighted the need for optimizing PAC content based on the total phosphorus and DOC content of the wastewater to use both PAC and PACl most efficiently. Full-scale testing at a specific PAC/DOC ratio of 2 over one month demonstrated the prototype's suitability for simultaneous phosphorus and OMP removal under real WWTP conditions. OMP removal increased by > 90 % for carbamazepine, > 50 % for diclofenac and metoprolol, and 30 % for benzotriazole; overall, > 80 % elimination was achieved for all investigated proxy substances. The full-scale experience confirmed that the prototype is easier to store and to apply. It can be immediately used in existing P-dosing systems without additional investment costs, making it advantageous over other OMP removal technologies.

Investigation of the microhole arrays generated by masked jet electrochemical machining with polyaluminum chloride electrolyte

Zirconium (Zr) alloy is a passivating metal with excellent general properties. The oxide films present on passivating metals make them resistant to corrosion by strong acid and alkali solutions, high-temperature water, and liquid metals. However, microfabrication of Zr alloy metal structures using existing machining methods suffers from low machining efficiency and poor machining quality. Electrochemical machining has advantages for processing Zr alloy metal microstructures. This study sought to evaluate the feasibility of masked jet electrochemical machining with a new electrolyte, polyaluminum chloride (PAC) of a microhole array in a Zr702 sheet. The dissolution behavior of Zr702 was analyzed with different concentrations of NaNO3, NaCl, and PAC. The electrochemical corrosion mechanism of Zr702 by using PAC was elucidated. A 2D model was established to analyze the evolution process of the sectional profiles of the microholes. Then, the effects of the main processing parameters were studied, and multifactor interaction response surfaces were analyzed. After optimizing the parameters, a high-quality microhole array was obtained with an average hole diameter of 152.11 μm, an average depth of 76.13 μm, a depth/diameter ratio of 0.501, a lateral corrosion coefficient of 2.023, a diameter variation coefficient of 1.71, and a depth variation coefficient of 2.87.

Surfactant-assisted air flotation: A novel approach for the removal of microplastics from municipal solid waste incineration bottom ash

The potential for the presence of microplastics (MPs) in municipal solid waste incineration bottom ash (MSWI-BA) has not been fully explored. In this study, surfactant-assisted air flotation separation in aqueous media was used to examine the removal of MPs and other pollutants from different particle size fractions of MSWI-BA. The use of 1 mmol L−1 sodium dodecylbenzene sulfonate (SDBS), at a liquid-solid ratio of 60:1, increased by 66 % the quantity of MPs floated from the MSWI-BA 0–0.3 mm fraction, as compared to pure water. The four most common shapes of the floated MPs were pellets, fragments, films and fibers, and the major polymers were polypropylene, polyethylene, polymethyl methacrylate, and polystyrene (approximately 450 μg g−1 BA). The flotation of <10 μm MPs increased by up to 7 % using this method compared to flotation in saturated NaCl solution. Reuse of the flotation solution with the SDBS concentration maintained resulted in reduced MPs removal abundance by 22 % in the fourth use as compared to the first use. MPs removal correlated positively to SDBS concentration and negatively to turbidity. Precipitation from the fourth flotation solution was evaluated using polyacrylamide (PAM) and polyaluminium chloride (PAC) for the purpose of promoting the regeneration and recycling of the flotation solution. This treatment reduced MPs abundance, turbidity, and potential heavy metals in the recycled flotation solution. It is estimated that 3.4 kg of MPs could be removed from each ton of MSWI-BA. The findings of this study contribute to a better understanding of the redistribution of MPs during MSWI-BA pre-use treatment and provides a reference for the practical application of surfactant-assisted air flotation separation.

Treatment of high-phosphorus load wastewater by column packed with non-burning compound filler/gravel/ceramsite: evaluation of performance and microorganism community.

Cost-effective and environmental-friendly substrates are essential for the constructed wetlands (CWs). In this study, the column test was used to explore the differences in pollutant purification performance, microbial community structure and abundance between non-burning compound filler and conventional CWs substrates (i.e. gravel and ceramsite) at low temperature (0-15℃). It was found that the maximum phosphorus removal efficiency of compound filler (99%) was better than gravel (18%) and ceramsite (21%). Besides, the proportion of aerobic heterotrophic bacteria capable of ammonium oxidation, nitrification and denitrification (i.e. Pseudomonas, Acinetobacter, and Acetoanaerobium) was enhanced by compound filler, which has an excellent potential for nitrogen removal in the subsequent purification process. These results demonstrated that the self-made non-burning compound filler was a potential substrate for CWs, which was of great significance for the resource utilization of solid wastes such as polyaluminum chloride residue.

Uncovering the regulation effect of modified clay on toxin production in Alexandrium pacificum: From physiological insights

As a common dinoflagellate, Alexandrium pacificum can produce paralytic shellfish toxins (PSTs). It can be removed from water by Polyaluminium chloride modified clay (PAC-MC), but it is unclear whether PAC-MC can prevent PSTs content and toxicity from increasing and whether PAC-MC can stimulate PSTs biosynthesis by A. pacificum. Effect of PAC-MC on PSTs and the physiological mechanism were analysed here. The results showed total PSTs content and toxicity decreased respectively by 34.10 % and 48.59 % in 0.2 g/L PAC-MC group at 12 days compared with control group. And the restriction of total PSTs by PAC-MC was mainly achieved via inhibition of algal cell proliferation, by affecting A. pacificum physiological processes and changing phycosphere microbial community. Meanwhile, single-cell PSTs toxicity did not increase significantly throughout the experiment. Moreover, A. pacificum treated with PAC-MC tended to synthesize sulfated PSTs such as C1&2. Mechanistic analysis showed that PAC-MC induced upregulation of sulfotransferase sxtN (related to PSTs sulfation), and functional prediction of bacterial community also showed significant enrichment of “sulfur relay system” after PAC-MC treatment, which might also promote PSTs sulfation. The results will provide theoretical guidance for the application of PAC-MC to field control of toxic Alexandrium blooms.

Microplastics removal from aquatic environment by coagulation: Selecting the best coagulant based on variables determined from a systematic review

The present study was carried out in the two phases of systematic review and experimental research. First, for the systematic review phase, Web of Science, Scopus, and PubMed as electronic databases were utilized to find research articles distributed up to March 5, 2021, related to the removal of microplastics by coagulation. In total, 104 publications were found, of which 14 were reviewed for deriving the variables and research design. Then, in the experimental phase, the experiment was carried out based on the variables derived from the systematic phase for three microplastic types (polyethylene, polystyrene, and polyamide) and five coagulants (polyaluminum chloride (PAC), ferric chloride (FeCl3), aluminum chloride (AlCl3), alum (Al(OH)3) and aluminum sulfate (Al2(SO4)3)) in bench scale study. The differences between removal efficiencies in terms of type, shape, concentration, and size of microplastics within the looked into article was analyzed utilizing ANOVA or Kruskal-Wallis test (for parametric or nonparametric analysis, respectively). The results of experimental phase show that the removal efficiency of different microplastics was significantly different, and it was equal to 65, 22, and 12% on average for PA, PS, and PE, respectively. These averages are much lower than the average removal efficiency calculated in the reviewed articles (78 and 52% for PS and PE, respectively). The removal efficiency of microplastics types by coagulants was not significantly different. As a result, a coagulant that has the lowest dose can be selected as the most suitable coagulant, which is Al(OH)3 in this study.

Molecular insights towards changing behaviors of organic matter in a full-scale water treatment plant using FTICR-MS

The changing behavior of organic matter in a full-scale water treatment process was characterized based on the three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Polyaluminum chloride (PAC) as a coagulant can help to effectively remove soluble microbial by-products-like and aromatic protein-like substances during coagulation and sedimentation, corresponding to tannin and coagulated aromatic regions. The leakage of soluble microbial products during sand filtration resulted in an increase in the intensity of biomass-like regions. Nitrogen-containing compounds have higher weighted average value of double bond equivalents (DBEw) and the modified aromaticity index (AImod-w) than nitrogen-free compounds. Water treatment can preferentially remove unsaturated nitrogen-containing compounds with more O atoms and higher-oxidation-state carbon. The dissolved organic carbon (DOC) and UV254 were not correlated well with changes in nitrogen-containing compounds due to the preferential removal of nitrogen-containing compounds. This study revealed the specificity of organic matter removal during water treatment, and it was helpful in optimizing treatment processes for various raw water to ensure water quality.

Anaerobic-aerobic treatment of high-strength and recalcitrant textile dyeing effluents

Eco-friendly treatment of complex textile and dyeing wastewaters poses a pressing environmental concern. An approach adopting different treatment paths and integrated anaerobic–aerobic processes for high-strength and recalcitrant textile dyeing wastewater was examined. The study demonstrated that over 97% of suspended solids (SS) and more than 70% of chemical oxygen demand (COD) were removed by polyaluminum chloride pre-coagulation of suede fabric dyeing stream. Up to 58% of COD and 83% of SS were removed through hydrolysis pretreatment of other low-strength streams. Notable COD removal of up to 99% from a feed of 20,862 mg COD/L was achieved by integrated anaerobic–aerobic treatment of high strength stream. Besides achieving high COD removal of 97%, the anaerobic granular sludge process demonstrated multi-faceted attributes, including high feed loading, smaller footprint, little sludge production, and good stability. The integrated anaerobic–aerobic treatment offers a robust and viable option for highly contaminated and recalcitrant textile dyeing wastewater.

Bioflocculants as Alternative to Synthetic Polymers to Enhance Wastewater Sludge Dewaterability: A Review

The dewatering process reduces the water quantity in sludge, allowing the decrease in its volume, which facilitates its storage, transport, stabilization, and improves the post-treatment efficiency. Chemical polymers including aluminum sulphate and polyaluminum chloride were applied as flocculants in the conditioning process in order to prepare sludge for dewatering. However, these synthetic polymers may cause risks for human health, and should be substituted with ecofriendly and safe materials. These materials include plant-based flocculants, animal-based flocculants, and microbial-based flocculants. Sludge dewaterability was evaluated by considering many parameters, such as moisture content (MC), dry solids (DS), specific resistance to filtration (SRF), capillary suction time (CST), and sludge volume index (SVI). The use of microorganisms for sludge dewatering is an available option, since many strains (R. erythropolis, A. ferrooxidans, P. mirabilis, T. flavus, etc.) demonstrated their ability to produce polymers useful for dewatering sludge from various origins (chemically treated primary sludge, activated sludge, anaerobically digested sludge, etc.). For plant-based flocculants, only okra (Abelmoschus esculentus), cactus (Opuntia ficus Indica), moringa (M. oleifera), and aloe (A. vera) plants are examined for sludge dewatering. Compared to synthetic polymers, plant-based flocculants showed a viable alternative to chemicals and a step forward in green sludge treatment technology. Among the animal-based flocculants, chitosan and aminated chitosan were able to reduce the SRF (SRF reduction rate &gt; 80%) of the anaerobically digested sludge. A new strategy using methylated hemoglobin also showed a significant enhancement in cake solid content of sludge (47%) and a decrease in sludge bound water content of 17.30%. Generally, extensive investigations are needed to explore and optimize all the related parameters (operating conditions, preparation procedure, production cost, etc.) and to choose the appropriate materials for large-scale application.

Optimalisasi Penjernihan Air PDAM Tirta Meulaboh Menggunakan Aluminium Sulfat (Tawas) dan Poly Aluminium Chloride (PAC)

This research aimed to determine the optimum coagulant that can be used to purify PDAM Tirta Meulaboh water which often has a cloudy color during the rainy season. The coagulants used are PAC and Tawas with the chemical formula Al2(SO4)3 and Poly Aluminum Chloride is known as PAC with the chemical formula Aln(OH)mCl(3n-m). The test was carried out by mixing 10 grams of alum and PAC which were dissolved in 1000 mL of water/aquades each. The treatment was carried out by dissolving each 1 mL in 1000 mL of PDAM water sample equal to 10 ppm. Variations in the addition of PAC/alum to each container were 10, 20, 30, 40, 50 and 60 ppm. Furthermore, rapid mixing was carried out at a speed of 100-150 rpm and slow at 20 rpm. The results showed that 10 ppm of PAC added to the sample produced turbidity of 5.2 NTU and pH 7.8, 20 ppm: 4.1 NTU and pH 7.5, 30 ppm: 3.8 NTU pH 7.3, 40 ppm : 2.3 NTU pH 7.2, 50 ppm: 1.5 NTU pH 7.1, 60 ppm: 0.8 NTU and pH 7.0. Samples added with 10 ppm of alum produced turbidity of 5.5 and pH 6.8, 20 ppm: 5.1 pH 6.7, 30 ppm: 4.5 pH 6.6, 40 ppm: 3.2 pH 6.6 , 50 ppm: 4.3 pH 6.4 and 60 ppm: 5.0 pH 6.3. The conclusions from this study indicate that PAC and alum coagulants can affect turbidity and pH levels of water, the optimal addition of PAC coagulant to purify water is 20 ppm, while the optimal addition of alum coagulant to purify water is 30 ppm.

Cake layer 3D structure regulation to optimize water channels during Al-based coagulation-ultrafiltration process

The variation in cake layer three-dimensional (3D) structures and related water channel characteristics induced by coagulation pretreatment remains unclear; however, gaining such knowledge will aid in improving ultrafiltration (UF) efficiency for water purification. Herein, the regulation of cake layer 3D structures (3D distribution of organic foulants within cake layers) by Al-based coagulation pretreatment was analyzed at the micro/nanoscale. The sandwich-like cake layer of humic acids and sodium alginate induced without coagulation was ruptured, and foulants were gradually uniformly distributed within the floc layer (toward an isotropic structure) with increasing coagulant dosage (a critical dosage was observed). Furthermore, the structure of the foulant-floc layer was more isotropic when coagulants with high Al13 concentrations were used (either AlCl3 at pH 6 or polyaluminum chloride, in comparison with AlCl3 at pH 8 where small-molecular-weight humic acids were enriched near the membrane). These high Al13 concentrations lead to a 48.4% higher specific membrane flux than that seen for UF without coagulation. Molecular dynamics simulations revealed that with increasing Al13 concentration (Al13: 6.2% to 22.6%), the water channels within the cake layer were enlarged and more connected, and the water transport coefficient was improved by up to 54.1%, indicating faster water transport. These findings demonstrate that facilitating an isotropic foulant-floc layer with highly connected water channels by coagulation pretreatment with high-Al13-concentration coagulants (having a strong ability to complex organic foulants) is the key issue in optimizing the UF efficiency for water purification. The results should provide further understanding of the underlying mechanisms of coagulation-enhancing UF behavior and inspire precise design of coagulation pretreatment to achieve efficient UF.

Simultaneous immobilization of ammonia and phosphorous by thermally treated sediment co-modified with hydrophilic organic matter and zeolite

The use of calcined sediments (CS) for thin-layer capping is an environment-friendly technology for controlling nitrogen (N) or phosphorus (P) release. However, the effects of CS derived materials and efficiency in controlling the sedimentary N/P ratio have not been thoroughly investigated. While zeolite-based materials have been proven efficient to remove ammonia, it is limited by the low adsorption capacity of PO43−. Herein, CS co-modified with zeolite and hydrophilic organic matter (HIM) was synthesized to simultaneously immobilize ammonium-N (NH4+-N) and remove P, due to the superior ecological security of natural HIM. Studies on the influences of calcination temperature and composition ratio indicated that 600 °C and 40% zeolite were the optimal parameters leading to the highest adsorption capacity and lowest equilibrium concentration. Compared with doping with polyaluminum chloride, doping with HIM not only enhanced P removal but also achieved higher NH4+-N immobilization efficacy. The efficiency of zeolite/CS/HIM capping and amendment in prohibiting the discharge of N/P from sediments was assessed via simulation experiments, and the relevant control mechanism was studied at the molecular level. The results indicated that zeolite/CS/HIM can reduce 49.98% and 72.27% of the N flux and 32.10% and 76.47% of the P flux in slightly and highly polluted sediments, respectively. Capping and incubation with zeolite/CS/HIM simultaneously resulted in substantial reductions in NH4+-N and dissolved total P in overlying water and pore water. Chemical state analysis indicated that HIM enhanced the NH4+-N adsorption ability of CS owing to its abundant carbonyl groups and indirectly increased P adsorption by protonating mineral surface groups. This research provides a novel strategy to control sedimentary nutrient release by adopting an efficient and ecologically secure remediation method to rehabilitate eutrophic lake systems.