Coagulation Pretreatment Research Articles

Contribution of specific extracellular organic matter on membrane fouling in ultrafiltration and coagulation-ultrafiltration of algae-laden water

This study explores the specific impact of bound and dissolved extracellular organic matter (bEOM and dEOM), and their collective influence with algal cells on membrane fouling during ultrafiltration (UF) and coagulation-UF of algae-laden water. By characterizing the organic properties and adsorptive behaviors of bEOM and dEOM, and analyzing their subsequent impacts, we clarify their roles and contributions to membrane fouling. Our analyses revealed that bEOM, characterized by its higher molecular weight (MW) and hydrophobic nature, contains more protein-like substances compared to dEOM. Quartz Crystal Microbalance with Dissipation (QCM-D) analysis highlights significant differences in their adsorption behaviors, with bEOM demonstrating greater adhesion and higher adsorptive fouling potential. Despite bEOM's lower concentration relative to dEOM, at a ratio of 0.12–1, their contributions to irreversible membrane resistance are nearly identical, at 30.7% and 30.9% respectively, in the UF of algae-laden water. Coagulation pretreatment effectively reduces bEOM's fouling potential by forming larger flocs, thus minimizing its contact with the membrane. In terms of irreversible membrane resistance, the contributions are 6.5% from cells, 24.8% from bEOM, and 68.6% from dEOM. The presence of dEOM complicates coagulation efficiency due to its low MW components and high hydrophilicity. Using the Hermia model, atomic force microscopy (AFM), and scanning electron microscopy (SEM), we demonstrated how bEOM and dEOM modify membrane fouling mechanisms, particularly by influencing cake layer formation. These insights emphasize the distinct and significant contributions of bEOM and dEOM to membrane fouling, necessitating targeted strategies for their management to enhance the efficiency and sustainability of UF systems in water treatment facilities.

A membrane fouling control strategy based on a combination of pre-treatment mitigation and in-situ membrane surface regulation using a composite coagulant

Ultrafiltration technology (UF) is efficient in surface water treatment, but its development and widespread application are limited by membrane fouling. Herein, an efficient and stable polymerized ferric titanium coagulant (PFTC) was synthesized and used as a UF pretreatment agent in actual lake water treatment. The control mechanism of PFTC on membrane fouling was investigated from the perspective of organic removal efficiency and in-situ membrane surface regulation. PFTC demonstrated a remarkable affinity for soluble metabolic intermediates and hydrophilic proteins through complexation and hydrogen bonding force, achieving removal efficiencies of 66.4 % for UV254 and 81.3 % for DOC, respectively. The hydrophilic pollutants with high molecular weight and non-saturated structure could be preferentially removed by PFTC due to its diverse hydrolysates including positively charged Fe-based hydrolysates, amorphous Ti-based hydrolysates, and highly polymerized Fe-Ti copolymers. The flocs generated by PFTC exhibited strong hydrophilicity, allowing for the formation of a loose porous cake layer on the ultrafiltration membrane, which acted as a hydrophilic layer to enhance the anti-fouling performance of ultrafiltration membrane. With its dual function of contaminant removal and in-situ membrane surface regulation, PFTC alleviated 98.9 % of membrane fouling. This study provides new insights into membrane fouling control by coagulation pretreatment and efficient treatment of surface water.

Effects of coagulation pre-treatment on chemical and microbial properties of water-soil-plant systems of constructed wetlands

Chemical coagulation has gained recognition as an effective technique to enhance the removal efficiency of pollutants in wastewater prior to their entry into a constructed wetland (CW) system. However, its potential impact on the chemical and microbial properties of soil and plant systems within CWs requires further research. This study investigated the impact of using ferric chloride (FeCl3) as a pre-treatment stage for dairy wastewater (DWW) on the chemical and microbial properties of water-soil-plant systems of replicated pilot-scale CWs, comparing them to CWs treating untreated DWW. CWs treating amended DWW had better performance than CWs treating raw DWW for all water quality parameters (COD, TSS, TP, and TN), ensuring compliance with the EU wastewater discharge directives. Soil properties remained mostly unaffected except for pH, calcium and phosphorus (P), which were lower in CWs treating amended DWW. As a result of lower nitrogen (N) and P loads, the plants in CWs receiving FeCl3-amended DWW had lower N and P contents than the plants of raw DWW CWs. However, the lower loads of P into amended DWW CWs did not limit the growth of Phragmites australis, which were able to accumulate trace elements higher than CWs receiving raw DWW. Alpha and Beta-diversity analysis revealed minor differences in community richness and composition between both treatments, with only 3.7% (34 genera) showed significant disparities. Overall, the application of chemical coagulation produced superior effluent quality without affecting the properties of soil and plant of CWs or altering the functioning of the microbial community.

Rapid pretreatment strategy to control nanofiltration membrane fouling in recycling of real textile wastewater: Comparison and mechanisms

The recycling of textile wastewater by membrane technology often necessitates intricate pretreatment steps to prevent severe membrane fouling, which lead to prolonged process-flow and elevated operation expenses. This research focuses on a two-step coagulation (TS-Co) pretreatment-nanofiltration process for treating real textile wastewater and examines its mechanism for controlling membrane fouling. The findings indicated that the removal of organic pollutants from real textile wastewater could be enhanced through first coagulation under acidic conditions, and the secondary coagulation under neutral conditions further removed the residual organics and the metal coagulants released at first stage. This synergistic effect led to chemical oxygen demand (COD) and turbidity removal efficiencies of 56.31 % and 99.29 %, respectively, which were superior to those of ultrafiltration (UF) and conventional coagulation (C-Co) pretreatment. The foulant composition and correlation analysis confirmed that protein, humic acid, and polysaccharides were the primary pollutants causing the fouling of nanofiltration membrane. Interestingly, the removal efficiency of polysaccharides using TS-Co (63.72 %) was lower than that obtained using UF (95.57 %), while the TS-Co exhibited higher removal efficiencies for humic acid and protein (97.43 % vs. 49.90 %, and 96.99 % vs. 81.07 %, respectively), indicating its excellent performance to controlling membrane fouling. Additionally, the proposed short process-flow offers cost advantages over conventional long process-flow and shows promising application prospects.

Dynamic evolution of ultrafiltration membrane fouling affected by S(IV)–Fe(II)-activated permanganate pretreatment during a long-term operation

ABSTRACT The S(IV)–Fe(II)/PM pretreatment has demonstrated preliminary potential as an effective ultrafiltration (UF) pretreatment technology. However, a comprehensive understanding of its impact on UF membrane fouling control and the dynamic evolution of membrane fouling during prolonged operation is still lacking. In this study, a relatively prolonged fouling experiment was conducted. Results revealed that the S(IV)–Fe(II)/PM pretreatment exhibited superior performance over Al(III) coagulation pretreatment in mitigating the transmembrane pressure difference and addressing both reversible and irreversible membrane fouling. The application of a cluster analysis method to classify membrane fouling evolution stages further confirmed that S(IV)–Fe(II)/PM pretreatment effectively decelerated the rate of membrane fouling evolution. The surface cake layer of UF membranes pretreated with S(IV)–Fe(II)/PM exhibited greater looseness and smoothness. It also showed better results than Al(III) coagulation pretreatment in reducing the accumulation of organic foulants, controlling the Si content and reducing the total microorganisms and live microorganisms in the UF feed water. Variance Partitioning Analysis indicated that the combined contribution of organic, inorganic, and biological foulants was the most significant for UF membranes after S(IV)–Fe(II)/PM pretreatment (50.4%) and UF membranes after Al(III) coagulation pretreatment (70.2%). These findings underscore the efficacy of S(IV)–Fe(II)/PM pretreatment in controlling UF membrane fouling under prolonged operation.

Resource utilization of coal chemical waste salt by bipolar membrane electrodialysis with thermal pretreatment

The aim of this study is to explore the feasibility of applying bipolar membrane electrodialysis (BMED) to treat coal chemical waste salt with different pretreatments of organic pollutants. The organic content in the real waste salt reached 0.6 ± 0.1 % with a weight averaged molecular weight of 641 g/mol. Only 26.5 % of the total COD in a 250 g/L waste salt solution could be removed by the coagulation pretreatment, resulting in no apparent improvement in BMED performance. Thermal pretreatment at 850 °C for 180 min completely removed organics from the waste salt, resulting in efficient control of membrane fouling in the BMED. At the current density of 50 mA/cm2 and 250 g/L waste salt solution, the base concentration in the BMED with 850 °C pretreatment of waste salt was higher than that with 550 °C pretreatment and without any pretreatment (58.2 ± 1.0 vs. 56.0 ± 2.4 and 53.6 ± 2.0 g/L) within 180 min, respectively. The average current efficiency based on base productions with 850 °C pretreatment of the waste salt reached 91 ± 5 % in the BMED within 180 min. Our results should be useful for the resource utilization of coal chemical waste salt.

Combination of membrane bioreactor with chemical coagulation for the treatment of real pharmaceutical wastewater: Comparison of simultaneous and consecutive pre-treatment of coagulation on MBR performance

In this work, the combination of the coagulation process with the MBR system to reclaim effluent in pharmaceutical industries was investigated. In this research, comparison/concentration optimization of two modes of integrations, including simultaneous; one-step one pot, and consecutive coagulation MBR were investigated. Results showed that COD removal in simultaneous and consecutive modes at optimum values were 85 % and 95.8 %, respectively, which were considerably higher than that of control MBR; 53.89 %. The total fouling ratio for control MBR, simultaneous, and consecutive modes at optimum conditions were 70.69 %, 37.3 %, and 42.5 %, respectively, confirming that the integrated coagulation process and MBR system were considerably effective. Analyzing the secreted metabolite, e.g. protein, carbohydrate, and LB/TB-EPS ratio in the MBR tank as well as on the membrane surface showed that the charge-neutralization and entrapment of bio-foulants by aggregated clots during the coagulation hinder the adhesion of the biofouling agents on the membrane surface, therefore in-line with the flux attenuation trend, lower metabolite concentration results in less membrane fouling. It was found that simultaneous coagulative MBR with 100 mg/L FeCl3 concentration demonstrates better fouling mitigation in comparison with consecutive (even with poly aluminum chloride; PACl as coagulant aid) MBR, while the latter mode shows better performance in terms of wastewater treatment. These findings open avenues for future techno-economic assessments of a coagulation-assisted MBR, providing a cost-effective solution for treating high-strength wastewater on a larger scale.

Insights into coagulation, softening and ozonation pre-treatments for reverse osmosis membrane fouling control in reclamation of textile secondary effluent

Pre-treatment was an effective strategy to mitigate membrane fouling, while controversial fouling control performance and mechanism still restricted its application. Herein, coagulation, softening and ozonation pre-treatments were applied to mitigate reverse osmosis (RO) fouling in reclamation of textile secondary effluent. The results showed coagulation pre-treatment negligibly alleviated membrane fouling by dosing FeCl3 coagulant due to the low coagulation efficiency and dissolved organic carbon (DOC) removal (only 11 %) toward effluent organic matter (EfOM) with low molecular weight (2300–6145 Da). Unexpectedly, pre-ozonation caused more severe RO fouling with the increasing ozone doses owing to the enhanced bridging action of divalent cations between membrane and ozonated EfOM; however, the opposite phenomenon was observed when divalent cations were removed by softening due to the preferential removal of biopolymers, the decrease in molecular weight and hydrophobicity of EfOM. Especially, at ozone dose of 1.0 mg O3/mg DOC, flux loss and irreversible fouling resistance enhanced by 8.60 % and 25.4 %, but markedly reduced by 24.0 % and 41.2 % in the absence of divalent cations, respectively. Extended DLVO (XDLVO) theory further unveiled the different roles of pre-treatments in RO fouling control was mainly due to the variation of adhesion interfaces between RO membrane and foulants, especially for the Lewis acid-base (AB) interaction energy. We proposed that softening + ozonation pre-treatment was effective to control RO fouling. More importantly, the reclaimed water satisfy the national standard of China (GB/T 19923–2005) for industrial water reuse after softening + ozonation + RO membrane treatment, which is promising to reclaim textile wastewater.

Coagulation pretreatment coupled with indigenous microalgal-bacterial consortium system for on-site treatment of rural black wastewater

Improper treatment of rural black wastewater (RBW) presents substantial challenges, including the wastage of resource, environmental contamination, and economic consequences. This study proposed an integrated process for RBW treatment, consisting of coagulation/flocculation (C/F) pretreatment and subsequent inoculation of indigenous microalgal-bacterial consortium (IMBC) for nitrogen recovery, namely C/F-IMBC process. Specifically, the optimal C/F conditions (polyaluminium chloride of 4 g/l, polyacrylamide of 50 mg/l, and pH of 6) were determined through a series of single-factor experiments, considering CN, turbidity, and dissolved organic matter (DOM) removal, economic cost, and potential influence on the water environment. Compared to the sole IMBC system for RBW treatment, the proposed C/F-IMBC process exhibited a remarkable 1.23-fold increase in microalgal growth and a substantial 17.6–22.6 % boost in nitrogen recovery. The altered RBW characteristic induced by C/F pretreatment was supposed to be responsible for the improved system performance. In particular, the abundance of DOM was decreased and its composition was simplified after C/F pretreatment, based on the analysis for excitation-emission matrices with parallel factor and gas chromatography–mass spectrometry, thus eliminating the potential impacts of toxic DOM components (e.g., Bis(2-ethylhexyl) phthalate) on IMBC activity. It should also be noted that C/F pretreatment modified microbial community structure as well, thereby regulating the expression of nitrogen-related genes and enhancing the system nitrogen recovery capacity. For instance, the functional Cyanobacteria responsible for nutrient recovery was enriched by 1.95-fold and genes involved in the assimilatory nitrate reduction to ammonia pathway were increased by 1.52-fold. These fundamental findings are expected to offer insights into the improvement of DOM removal and nitrogen recovery for IMBC-based wastewater treatment system, and provide valuable guidance for the development of sustainable on-site RBW treatment technologies.

Enhanced separation and antifouling performance of ultrafiltration for surface water based on coagulation pretreatment by zirconium salts

Membrane fouling is the main challenge that limits ultrafiltration (UF) membrane long-term application. Coagulation, as an effective pretreatment method, not only reduces the pollutants loaded on the membrane surface, but also transforms membrane-pollutant contact into pollutant-floc reaction. Zircon (Zr) salts have drawn wide attention as a novel metal-based coagulant because of their excellent coagulation performance. In present study, three types of Zr coagulants zirconium tetrachloride (ZrCl4) and polyzirconium chloride (PZC), polyzirconium chloride/Poly dimethyl diallyl ammonium chloride (PZC/PDMDAAC) were estimated in terms of the coagulation removal of organic pollutants and the mitigation of membrane fouling. Results showed that the combination of PZC with alkalinity of 1.5 and PDMDAAC with molecular weight of 2.0–3.5 × 105 (abbreviated as PZC1.5/P2) presented the best coagulation performance under acidic and neutral conditions due to its better bridging affinity and sweeping ability. 8 mg/L dosage of PZC1.5/P2 could effectively remove turbidity (98.27%) and dissolved organic carbon (DOC) (59.04%) during the coagulation process. Furthermore, pre-coagulation by PZC1.5/P2 induced the transformation from cake filtration into thoroughly intermediate blocking and the removal of particulate matter would prevent reversible fouling-induced flux decline, whereas elimination of organic matter was beneficial for promoting UF efficiency by mitigating irreversible fouling. Besides, Derjaguin-Landau-Verwey-Overbeek (XDLVO) analysis showed that the foulants became more hydrophilic coagulated by PZC1.5/P2, and the adhesion between foulants and membrane surface was greatly weakened. All the improvement originated from the flocs structure contributed to the better UF performance with the improved normalize flux (J/J0) from 0.50 to 0.75, larger decrease in reversible and irreversible fouling by 82.27% and 91.27%, respectively. More importantly, PZC1.5/P2 exhibited excellent coagulation and membrane performances in the treatment of actual water from Wolf Mushan reservoir, which demonstrated that Zr-based coagulant is a promising coagulant for practical application in surface water purification.

Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles

The dissolution of silica and transparent exopolymer particles (TEP) can deposit on the membrane surface and cause serious membrane fouling in reverse osmosis (RO) technology. Coagulation, as a common pretreatment process for RO, can effectively intercept pollutants and alleviate membrane fouling. In this study, FeCl3 and AlCl3 coagulants and polyacrylamide (PAM) flocculants were used to explore the optimal coagulation conditions to reduce the concentration of silica and TEP in the RO process. The results showed that the two coagulants had the best removal effect on pollutants when the pH was 7 and the dosage was 50 mg/L. Considering the proportion of reversible fouling after coagulation, the removal rate of pollutants, and the residual amount of coagulation metal ions, the best PAM dosage was 5 mg/L for FeCl3 and 1 mg/L for AlCl3. After coagulation pretreatment, the Zeta potential decreased, and the particle size distribution increased, making pollutants tend to aggregate, thus effectively removing foulants. The removal mechanisms of pollutants by coagulation pretreatment were determined to be adsorption, electric neutralization and co-precipitation. This study determined the best removal conditions of silica and TEP by coagulation and explored the removal mechanism.

Insights into the control mechanism of different coagulation pretreatment on ultrafiltration membrane fouling for oily wastewater treatment

Oily wastewater treatment is necessary to reduce environmental pollution. Herein, a coagulation-ultrafiltration integrated process was used to remove emulsified oil. AlCl3, FeCl3, polyaluminum chloride (PAC), polyferric chloride (PFC), and polydimethyl diallyl ammonium chloride (PDMDAAC) were used in coagulation process. It was found that PAC was more effective than AlCl3 and Fe based coagulants in treating oil/water emulsions. Flocs formed in PAC+PDMDAAC, PDMDAAC+PAC, and PAC-PDMDAAC coagulation systems had different size, resistance, structure, and recovery ability, which was due to the changes in the dominant coagulation mechanism. The flocs formed by PAC-PDMDAAC composite coagulant were large and loose, indicating that bridging action and entrapment dominated the removal of oil droplets. PAC-PDMDAAC was efficient in reducing irreversible membrane fouling, while the PAC+PDMDAAC dual coagulation system performed well in controlling reversible fouling. The PDMDAAC+PAC system had a large adsorption resistance and a small cake layer resistance. The PAC-PDMDAAC system had a large polarization resistance. The different membrane resistance distribution was closely related to the discrepancy in coagulation behaviors. Therefore, the enhancement in coagulation performance is the key factor to alleviate membrane fouling. This study will provide theoretical guidance for the treatment of actual oily wastewater.

Revelation of the interaction between aluminum coagulants and natural organic matters in the dual-system during nanofiltration membrane scaling

Aluminum (Al) coagulants are widely and frequently applied to coagulation pretreatment before nanofiltration. However, the excess coagulants and residual natural organic matters (NOMs) might affect the gypsum scaling during nanofiltration process. This study investigated the nanofiltration membrane fouling process under Al coagulants and specific NOMs, including humic acids (HA), bovine serum protein (BSA), and sodium alginate (SA) in a dual-system. The flux and the particle size decreased significantly when both above were present. The gypsum crystallization on the membrane surface was enhanced, while the bulk crystallization was weakened. Zeta potential and the NICA-Donnan model showed that Al coagulants competed with Ca2+ to bind HA weakening the bulk crystallization of gypsum. Meanwhile, Al coagulants decreased the salt rejection rate. Interestingly, the BSA and SA alleviated the flux decrease. Furthermore, the characterization of the fouled membrane showed that the concentration of Ca2+ and SO42− on the membrane surface increased further in the presence of Al coagulants, the grain size reached 582.0 nm when both HA and Al were present, larger than the control group and when they were present in the feed solution alone. Finally, the modified Hermia model was introduced to analyze the mechanism of the interaction between Al coagulants and NOMs. It is suggested that the control of Al coagulants and HA is necessary for the coagulation pretreatment before nanofiltration.

Deep removal of fluoride from tungsten smelting wastewater by combined chemical coagulation-electrocoagulation treatment: From laboratory test to pilot test

Previous studies have shown that coexisting ions in tungsten smelting wastewater (TSW) will have a significant impact on fluoride removal by calcium ions. Therefore, in this work, the removal of fluoride from TSW by aluminum ions was studied. Electrocoagulation (EC) is essentially the use of aluminum ions to remove fluoride. The EC technology is widely favored by researchers due to its advantages of high treatment efficiency, simple operation, and easy automatic control. However, in the current research, EC technology as a deep defluorination method is mostly in the laboratory research stage, and there are few pilot test studies on large processing capacity, which slows down the industrial application of this technology to a certain extent. In this work, laboratory tests were carried out to study the removal of fluoride in wastewater by chemical coagulation and EC in detail. On this basis, the combined process of chemical coagulation pretreatment and EC advanced treatment was used to treat TSW with a capacity of 250–500 L/h. The results show that the coexisting ions in TSW have no effect on the defluorination of aluminum ions, and the optimal defluorination final pH of chemical coagulation and EC is 6–7. The pilot test could stably reduce the concentration of fluoride in TSW from 66 to 128 mg/L to less than 10 mg/L, and the total operating cost was 0.99–1.51 USD/m3 of wastewater. Cost analysis showed that the three items with the highest proportions in the chemical coagulation pretreatment costs were liquid caustic soda fee, aluminum sulfate fee, and solid waste treatment fee; while the three items with the highest proportions in the EC advanced treatment costs were aluminum plate loss fee, electricity fee, and solid waste treatment fee. This study is helpful to promote the application of EC advanced treatment technology in the defluorination of industrial wastewater.

Pre-treatment of landfill leachate via coagulation-flocculation: Optimization of process parameters using response surface methodology (RSM)

Wastewater treatment is achieved mainly through the regeneration of resources and energy from wastewater, especially using pre-treatment technologies. In this study, coagulation pre-treatment of landfill leachate was performed using polymeric iron sulfate (PFS) as coagulation. Moreover, the whole experimental process was divided into two parts. In the first phase, the effects of PFS dosing, initial pH and PAM dosing on the removal of chemical oxygen demand (COD), total phosphorus (TP) and UV254 from the leachate were assessed using one factor one experiment (OFAT); In the second phase, the individual and interactive effects of parameters on COD%, TP%, and UV254% were evaluated using response surface methodology (RSM). Numerical multiple response optimization was conducted using RSM to maximize COD%. The COD%, TP%, and UV254% at optimum condition (PFS dose of 12.18 g/L, initial pH of 8.12, and PAM dosage of 11.29 mg/L) reached 62.30 %, 95.79 %, and 83.45 %, respectively. The 3D-EEM showed the effluent from the leachate after mixing. The chemical properties significantly changed, and the concentration of hard-to-degrade substances, such as humic acid, decreased. FTIR and ESM-EDX were used to delineate the intrinsic mechanism of contaminant removal, demonstrating that hydroxyl bonds are crucial in the extraction of leachate and the aggregation of folcs.

Performance of gravity-driven membrane filtration for treatment of low-temperature and low-turbidity water: Effect of coagulation pretreatment

As a promising technology for decentralized drinking water treatment, performance of gravity-driven membrane (GDM) filtration for low-temperature and low-turbidity water purification and effects of coagulation pretreatment were investigated in this study. Flux development and permeate water quality of three GDM systems, i.e., control GDM without pretreatment, GDM with in-line coagulation (IC) pretreatment (IC-GDM), GDM with coagulation-sedimentation (CS) pretreatment (CS-GDM), were compared. Moreover, composition and morphology of bio-cake layer were characterized to explain underlying mechanisms for performance improvement by coagulation pretreatment. Results suggested that permeate flux of control GDM stabilized at ∼4.0 L/(m2·h) for raw water with relatively low temperature (8.1– 10.8 °C) and turbidity (1.15– 2.47 NTU). IC pretreatment increased stable flux by 65 %, although the bio-cake layer thickness in IC-GDM was increased by 71.7 %, probably due to a significant reduction (57.1 %) in extracellular polymeric substances (EPS) in the bio-cake layer. Meanwhile, CS pretreatment increased stable flux by 87.5 %, which can be attributed to 63.3 % reduction in EPS and 47.0 % decrease in bio-cake layer thickness. As for permeate water quality, dissolved organic matter (DOM) was significantly reduced by both IC and CS pretreatments, mainly due to transformation from dissolved state to particulates. Compared with control GDM, both IC and CS pretreatments resulted in decrease in microbial abundance and activity and changes in microbial community, probably due to decrease in bioavailable phosphate and DOM. This study suggested that both IC and CS pretreatments can be integrated with GDM filtration for efficient purification of low-temperature and low-turbidity water.

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.

Comparing Sedimentation, Flotation, and In-Line Pretreatment for Low-Pressure Membrane Fouling Reduction

Feed water pretreatment commonly is required for low-pressure membrane technologies employed in drinking water treatment applications to reduce membrane fouling and create stable operating conditions. Comparatively few studies have investigated coagulation–flocculation–dissolved air flotation (CF-DAF) pretreatment for drinking water applications, and none have compared CF-DAF, coagulation–flocculation–sedimentation (CF-S), and in-line coagulation (CF-IN) pretreatments using the same water. This study compared these three pretreatments for the filtration of a high dissolved organic carbon (DOC), high hydrophobic (HPO) surface water using a hydrophilic polyvinylidene fluoride (h-PVDF) ultrafiltration (UF) fiber. Multiday filtration tests were carried out using an automated bench-scale testing system operated in an outside-in configuration. CF-S and CF-DAF were found to be equally effective at mitigating membrane fouling, although CF-DAF pretreated water had a lower residual DOC and the greatest removal of UV254 absorbent organics. Compared with CF-DAF and CF-S, CF-IN pretreatment resulted in higher levels of total and irreversible fouling regardless of the applied coagulant dose. For all the pretreatments studied, irreversible membrane fouling was found to be strongly dependent on both the hydrophobicity of the feed water [in terms of specific UV absorbance (SUVA)] and the concentration of the 5–10-kDa DOC fraction, suggesting that the HPO humic organics were the principal foulant for this membrane–water combination. CF-IN pretreatment performance also was strongly impacted by the feed water zeta potential, suggesting that the characteristics of the formed flocculant particles are critical to the fouling behavior of the hybrid CF-IN-UF system.

Response Surface Optimization on Ferrate-Assisted Coagulation Pretreatment of SDBS-Containing Strengthened Organic Wastewater.

Sodium dodecylbenzene sulfonate (SDBS), an anionic surfactant, has both hydrophilic and lipophilic properties and is widely used in daily production and life. The SDBS-containing organic wastewater is considered difficult to be degraded, which is harmful to the water environment and human health. In this study, ferrate-assisted coagulation was applied to treat SDBS wastewater. Firstly, a single-factor experiment was conducted to investigate the effect of the Na2FeO4 dosage, polyaluminum chloride (PAC) dosage, pH and temperature on the treatment efficiency of SDBS wastewater; then, a response surface optimization experiment was further applied to obtain the optimized conditions for the SDBS treatment. According to the experimental results, the optimal treatment conditions were shown as follows: the Na2FeO4 dosage was 57 mg/L, the PAC dosage was 5 g/L and pH was 8, under which the chemical oxygen demand (COD) removal rate was 90%. Adsorption bridging and entrapment in the floc structure were the main mechanisms of pollution removal. The ferrate-assisted coagulation treatment of strengthened SDBS wastewater was verified by a response surface experiment to provide fundamental understandings for the treatment of the surfactant.

Effects of wastewater pre-treatment on clogging of an intermittent sand filter

Intermittent sand filters (ISFs) are widely used in rural areas to treat domestic and dilute agricultural wastewater due to their simplicity, efficacy and relative low cost. However, filter clogging reduces their operational lifetime and sustainability. To reduce the potential of filter clogging, this study examined pre-treatment of dairy wastewater (DWW) by coagulation with ferric chloride (FeCl3) prior to treatment in replicated, pilot-scale ISFs. Over the study duration and at the end of the study, the extent of clogging across hybrid coagulation-ISFs was quantified, and the results were compared to ISFs treating raw DWW without a coagulation pre-treatment, but otherwise operated under the same conditions. During operation, ISFs receiving raw DWW recorded higher volumetric moisture content (θv) than ISFs treating pre-treated DWW, which indicated that biomass growth and clogging rate was higher in ISFs treating raw DWW, which were fully clogged after 280 days of operation. The hybrid coagulation-ISFs remained fully operational until the end of the study. Examination of the field-saturated hydraulic conductivity (Kfs) showed that ISFs treating raw DWW lost approximately 85 % of their infiltration capacity in the uppermost layer due to biomass build-up versus 40 % loss for hybrid coagulation-ISFs. Furthermore, loss on ignition (LOI) results indicated that conventional ISFs developed five times the organic matter (OM) in the uppermost layer compared to ISFs treating pre-treated DWW. Similar trends were observed for phosphorus, nitrogen and sulphur, where proportionally higher values were observed for raw DWW ISFs than pre-treated DWW ISFs, with values decreasing with depth. Scanning electron microscopy (SEM) showed a clogging biofilm layer on the surface of raw DWW ISFs, while pre-treated ISFs maintained distinguishable sand grains on the surface. Overall, hybrid coagulation-ISFs are likely to sustain infiltration capacity for a longer period than filters treating raw wastewater; therefore, requiring smaller surface area for treatment and minimal maintenance.