Gravity-driven Membrane Systems Research Articles

Microplastics affect membrane biofouling and microbial communities during gravity-driven membrane filtration of primary wastewater

Recently, gravity-driven membrane (GDM) filtration has been adopted as an alternative solution for decentralized wastewater treatment due to easy installation and maintenance, reduced energy and operation cost, and low global warming impact. This study investigated the influence of microplastic size (0.5–0.8 μm and 40–48 μm) and amount (0.1 and 0.2 g/L) on the membrane performance and microbial community in GDM systems for primary municipal wastewater treatment. The results showed that dosing microplastics in the GDM systems led to 9–54% lower permeate flux than that in the control. This was attributed to more cake formation (up to 6.4-fold) with more deposition of extracellular polymeric substances (EPS, up to 1.5-fold) and divalent cations (up to 2.1-fold) in the presence of microplastics, especially with increasing microplastic amount or size. However, the dosed microplastics promoted formation of heterogeneous cake layers with more porous nature, possibly because microplastics created void space in the cake and also tended to bind with divalent cations to reduce EPS-divalent cations interactions. In the biofilm of the GDM systems, the presence of microplastics could lower the number of total species, but it greatly enhanced the abundance of certain dominant prokaryotes (Phenylobacterium haematophilum, Planctomycetota bacterium, and Flavobacteriales bacterium), eukaryotes (Stylonychia lemnae, Halteria grandinella, and Paramicrosporidium saccamoebae), and virus (phylum Nucleocytoviricota), as well as amino acid and lipid metabolic functions. Especially, the small-size microplastics at a higher dosed amount led to more variations of microbial community structure and microbial metabolic functions.

Effects of cations on biofilms in gravity-driven membrane system: Filtration performance and mechanism investigation

The gravity-driven membrane (GDM) system is desirable for energy-efficient water treatment. However, little is known about the influence of cations on biofilm properties and GDM performance. In this study, typical cations (Ca2+ and Na+) were used to reveal the combined fouling behavior and mechanisms. Results showed that Ca2+ improved the stable flux and pollutant removal efficiency, while Na+ adversely affected the flux. Compared with GDM control, the concentration of pollutants was lower in Ca-GDM, as indicated by the low biomass, proteins, and polysaccharides. A heterogeneous and loose biofilm was observed in the Ca-GDM system, with roughness and porosity increasing by 43.06 % and 32.60 %, respectively. However, Na+ induced a homogeneous and dense biofilm, with porosity and roughness respectively reduced by 17.48 % and 22.04 %. The richness of bacterial communities increased in Ca-GDM systems, while it decreased in Na-GDM systems. High adenosine triphosphate (ATP) concentration in Ca-GDM system was consistent with the abundant bacteria and their high biological activity, which was helpful for the efficient removal of pollutants. The abundance of Apicomplexa, Platyhelminthes, Annelida and Nematoda increased after adding Ca2+, which was related to the formation of loose biofilms. Computational simulations indicated that the free volumes of the biofilms in Ca-GDM and Na-GDM were 13.7 and 13.2 nm3, respectively. The addition of cations changed intermolecular forces, Ca2+ induced bridging effects led to large and loose floc particles, while the significant dehydration of hydrated molecules in the Na-GDM caused obvious aggregation. Overall, microbiological characteristics and contaminant molecular interactions were the main reasons for differences in GDM systems.

Exploration of ferrate (VI) pretreatment and ultrasonication combined with gravity-driven membrane filtration for shale gas wastewater treatment

Gravity-driven membrane (GDM) filtration has gained attention as a promising technology for the decentralized treatment of wastewater. However, one major limitation of GDM filtration is its relatively low permeate flux. In this work, we investigated the application of GDM filtration, combined with ferrate (VI) pretreatment and ultrasonication, for the shale gas wastewater (SGW) treatment, and evaluated their respective impacts on the GDM performance. The results of our study revealed that ultrasonication played a significant role in enhancing the flux of GDM filtration, with an observed increase of 265%. This improvement can be attributed to the effective removal of pollutants from the membrane surface and the reduction of the fouling layer thickness caused by ultrasonication. Compared to a GDM alone, ferrate (VI) pretreatment could notably change the microbial community structure and reduce the extracellular polymeric substances accumulation, which may be linked with an enhancement in stable flux. Ferrate (VI) pretreatment selectively enriched particular microorganisms in SGW, which might perform a role in specific organics degradation. These findings provide valuable insights and suggestions for enhancing the overall performance of GDM systems in wastewater treatment. Notably, the ultrasonically enhanced GDM system, which confers the characteristics of simple operation, low energy supply and no chemical pollution, has great application potential in wastewater treatment.

Oxidants-assisted gravity-driven membrane (GDM) process for manganese removal from surface water: Rapid maturation and manganese oxide regulation

The rapid maturation of the gravity-driven membrane (GDM) process for manganese removal from surface water is critical to its practical application. In this study, KMnO4 and NaClO were used to investigate their effects on the start-up period of the GDM process for treating manganese-containing surface water. The start-up period of the GDM system with KMnO4 (24 days) was shorter compared to that with NaClO (40 days). After the addition of KMnO4 and NaClO, the stable flux of the GDM system was significantly improved, and the bio-cake layer became more porous, which was ascribed to the reduction of proteins in the extracellular polymeric substances (EPS). The active manganese oxide (MnOx) in the bio-cake layer was identified as δ-MnO2. The addition of the oxidants increased the proportion of Mn(III) with high catalytic oxidation activity in δ-MnO2, where the assisted effect of KMnO4 (43.7%) was superior to that of NaClO (27.8%). The development of δ-MnO2 in the natural filtration state was ascribed to the enrichment of manganese oxidizing bacteria (MnOB). The biological action only accounted for 9.4%–12.3% of the manganese removal and was not dominant. The difference in the start-up period of the GDM process was dependent on the autocatalytic oxidation of Mn(III) in δ-MnO2 in the bio-cake layer. These findings provided acceptable and practical strategies for the rapid and safe manganese removal in the GDM process.

Fabrication of nanoclay embedded adsorptive electrospun nanofiber membrane for removal of trace organic molecules

This study aims to fabricate nanoclay (NC) embedded polyacrylonitrile (PAN) adsorptive electrospun nanofibers (Ads-ESNs) as high performance membranes for organic micropollutants (OMPs) removal. Ads-ESN were tested using a comprehensive protocol included adsorption in batches (static) and during filtration (dynamic). The filtration performance of Ads-ESNs was tested using gravity driven membrane (GDM) filtration using methylene blue (MB) as an adsorbate of similar characteristics to OMPs. The characterization was carried using SEM-EDS, FTIR and BET N2 adsorption/desorption technique. Addition of NC increased fiber diameters from 164 to 355 nm and surface areas from 12.9 to 45.9 m2/g. Accordingly, Ads-ESNs had 7 times higher adsorption capacity than PAN-ESN with isotherms fitting to Langmuir model (R2 = 0.9511–0.9899). The kinetics showed that adsorption in Ads-ESNs followed pseudo 1st and 2nd order indicating the occurrence of physisorption and chemisorption mechanisms simultaneously. pH and temperature effect were investigated and the results showed that highest adsorption occurred at pH 7 and 25 °C. The GDM system was operated at constant permeate flow rates of 1.0, 2.0 and 4.0 mL/min at 50mbar. MB rejection was over 90% at 1.0 and 2.0 mL/min of flow rates indicating the effect of applying lower flow rate and higher contact time. The adsorption capacities of Ads-ESN were different at static and dynamic adsorption due to different equilibrium states achieved at both adsorption modes. The fabricated Ads-ESNs showed outstanding removal performance for trace organic molecules even after four adsorption+filtration/regeneration cycles. Overall, this study demonstrated the potentials of combining membrane filtration and adsorption in a single-step process at same entity.

Gravity-driven membrane system treating heavy metals-containing secondary effluent: Improved removal of heavy metals and mechanism

This study aimed at investigating the removal performance of the gravity-driven membrane (GDM) system in treating the heavy metals-containing secondary effluent, as well as evaluating the respective roles of Fe and Mn addition on the removal of heavy metals. GDM process with the formation of biocake layer exerted effective removals of Cr, Pb and Cd, with an average removal efficiency of 98%, 95% and 40%, respectively, however, after removing the biocake layer, the removal efficiencies of Cr, Pb and Cd reduced to 59%, 85% and 19%, respectively, indicating that the biocake layer played a fundamental role in removing heavy metals. With the assistance of Fe, the removal efficiency of heavy metals increased, and exhibited a positive response to the Fe dosage, due to the adsorption by the freshly generated iron oxides. On the contrary, the Mn involvement would result in the reduction of Cd removal due to the competitive adsorption of residual dissolved Mn2+ and Cd. Furthermore, the addition of a high dosage of Fe increased the diversity of eukaryotic communities and facilitated the elimination of heavy metals, however, the involvement of Mn would lead to a reduction in microbial diversity, resulting in a decrease of heavy metal removal efficiency. These findings are expected to develop new tactics to enhance heavy metal removal and promote widespread application of GDM technology in the fields of deep treatment of heavy metals-containing wastewater and reclamation of secondary effluent.

Enhanced permeation performance of biofiltration-facilitated gravity-driven membrane (GDM) systems by in-situ application of UV and VUV: Comprehensive insights from thermodynamic and multi-omics perspectives

Biofouling is a major challenge limiting the practical application of biofiltration-facilitated gravity-driven membrane (GDM) systems in drinking water treatment. In this study, ultraviolet irradiation, including ultraviolet (UV) and vacuum ultraviolet (VUV) irradiation, was used for in-situ purification of membrane tanks to control membrane biofouling. After using UV and VUV, the permeate flux increased significantly by 26.1% and 78.3%, respectively, which was mainly due to the decreased cake layer resistance (Rc). The permeability of the biofouling layer improved after UV and VUV application, as evidenced by the increased surface porosity and decreased thickness. The contents of loosely bound extracellular proteins (LB-PN) and tightly bound extracellular proteins (TB-PN) in the biofouling layer were reduced after UV and VUV irradiation. The decreased LB-PN and TB-PN improved the interfacial free energy between the fouling itself and between the fouling and the membrane, which contributed to the reduction of interfacial cohesion and adhesion, resulting in a looser and thinner biofouling layer and a cleaner membrane. The concentration of protein-like material in the membrane tank decreased after UV and VUV irradiation, significantly altering the bacterial community structure on the membrane surface (Mantel's r > 0.7, p < 0.05). The changes in the metabolic state were responsible for the differences in the LB-PN and TB-PN contents. The inhibition of “Alanine, aspartate and glutamate metabolism” and “Glycine, serine and threonine metabolism” reduced amino acid biosynthesis, which restricted the secretion of LB-PN and TB-PN. Critical genera in the Proteobacteria phylum, such as Hirschia, Rhodobacter, Nordella, Candidatus_Berkiella, and Limnohabitans, were involved in metabolite transformation. Overall, the in-situ application of UV and VUV can be an effective alternative strategy to mitigate membrane biofouling, which would facilitate the practical application of biofiltration-facilitated GDM systems in drinking water treatment.

Performance Evaluation of a Pilot-Scale Aerobic Granular Sludge Integrated with Gravity-Driven Membrane System Treating Domestic Wastewater

This study describes a novel integration of aerobic granular sludge (AGS) with a gravity-driven membrane (GDM) system at a pilot scale with a treatment capacity of approximately 150 L per day to treat raw domestic wastewater. The treatment performance and energy consumption of the AGS-GDM system were compared to the neighboring full-scale aerobic membrane bioreactor (AeMBR), treating the same wastewater at about 4000(±500) m3 per day. The AGS-GDM system demonstrated superior nutrient (nitrogen and phosphorus) removal as compared to the AeMBR. The GDM unit was continuously supplied with AGS-treated effluent. The GDM unit started with high [ >20 L per m2 per h (LMH) ] flux, which gradually declined. The flux remained quite stable after 15 days reaching 3 LMH after 35 days without any physical or chemical cleaning. Our results suggest that AGS-GDM is a viable technology for decentralized wastewater treatment and reuse in water-scarce regions. The AGS-GDM could easily replace conventional AeMBR technology in the wastewater treatment and reclamation market.

Integrating gravity-driven ceramic membrane filtration with hydroponic system for nutrient recovery from primary municipal wastewater

In this study, a gravity-driven membrane (GDM) filtration system and hydroponic system (cultivating basil and lettuce) were combined for nutrient recovery from primary municipal wastewater. The GDM system was optimized by increasing the periodic air sparging flow rate from 1 to 2 L/min (∼15 hr per 3–4 days), resulting in a ∼52% reduction of irreversible fouling. However, the total fouling was not alleviated, and the water productivity remained comparable. The GDM-filtrated water was then delivered to hydroponic systems, and the effects of hydroponic operation conditions on plant growth and heavy metal uptake were evaluated, with fertilizer- and tap water-based hydroponic systems and soil cultivation system (with tap water) for comparison. It was found that (i) the hydroponic system under batch mode facilitated to promote vegetable growth with higher nutrient uptake rates compared to that under flow-through feed mode; (ii) a shift in nutrient levels in the hydroponic system could impact plant growth (such as plant height and leaf length), especially in the early stages. Nevertheless, the plants cultivated with the GDM-treated water had comparable growth profiles to those with commercial fertilizer or in soils. Furthermore, the targeted hazard quotient levels of all heavy metals for the plants in the hydroponic system with the treated water were greatly lower than those with the commercial fertilizer. Especially, compared to the lettuce, the basil had a lower heavy metal uptake capability and displayed a negligible impact on long-term human health risk, when the treated water was employed for the hydroponic system.

Long-term operation and biofouling of graphene oxide membrane in practical water treatment: Insights from performance and biofilm characteristics

The widespread research of graphene oxide (GO) membranes has revealed the need to investigate their long-term performance and associated biofouling behavior in practical water treatment conditions. In this study, we have evaluated the long-term operation of GO membranes from the perspective of filtration performance and biofilm characteristics, based on two representative GO membranes (V-GO and P-GO, fabricated by vacuum and pressure filtration, respectively) with different surface properties and a natural surface water, using a gravity driven membrane system. The results showed that the GO membranes were capable of achieving sustainable water purification over 45 days of operation, associated with a complete rejection for biopolymers and desirable removal for fluorescent organic matters. Furthermore, the V-GO membrane with a rougher surface, reduced hydrophilicity and higher sheet-edge exposure than that of the P-GO membrane formed a highly heterogeneous and porous biofilm with high permeability, despite its greater biofilm thickness and extracellular polymeric substances (EPS) contents. In contrast, the P-GO membrane biofilm exhibited a thin but dense structure, and therefore an increased hydraulic resistance (∼1.5 times greater than V-GO membrane). The microbial community analysis revealed that bacteria related to biofilm formation was richer in V-GO biofilm. While bacteria associated with the degradation of organic matters and the aggregation of microorganisms accounted for a greater proportion in P-GO biofilm. These factors were responsible for forming a thick biofilm for V-GO, and a thin but high resistance biofilm for P-GO membrane. Our findings highlight the sustainable water purification performance of the GO membranes, and the P-GO membrane can alleviate biofilm formation but not necessarily reduce biofouling during the long-term filtration, while this was opposite in case of the V-GO membrane.

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.

Regulation of bacterial behavior to mitigate membrane fouling in gravity-driven membrane system: The beneficial effects of gravity-driven up-flow slow biofilter

Membrane fouling has been a challenge for the practical application of gravity-driven membrane (GDM) systems. In this paper, gravity-driven up-flow slow biofilter (GUSB) was used before the GDM system to mitigate membrane fouling, and the spatial distribution of the fouling characteristics was investigated. The cake layer resistance (Rc) and membrane pore resistance (Rp) were reduced after GUSB pretreatment, resulting in a 62% increase in permeate flux. In the membrane module vertical direction, Rc and Rp declined sequentially from top to bottom. The ratio of protein to polysaccharide (PN/PS) was highly negatively correlated with nanoparticle size (Pearson's r = −0.89), and was the key factor shaping the bacterial community (Mantel's r = 0.95). The increased relative abundance of functional bacteria (such as Candidatus_Obscuribacter genus) and metabolic functions (amino acid, carbohydrate, and energy) was associated with the structure and composition of the biofouling layer. Rc has the highest weight ratio (0.699) for membrane resistance. Nanoparticle size influenced surface porosity and composition of the biofouling layer by regulating bacterial community diversity and metabolic functions, which indirectly determined membrane resistance (indirect effect coefficient = −2.018). This study would spark a wider application of GDM in drinking water treatment, and provided a comprehensive explanation for the membrane fouling mechanism.

Less pressure contributes to gravity-driven membrane ultrafiltration with greater performance: Enhanced driving efficiency and reduced disinfection by-products formation potential

Gravity-driven membrane (GDM) systems have been well developed previously; however, impacts of driving (i.e., transmembrane) pressure on their performance received little attention, which may influence GDM performance. In this study, we evaluated 4 GDM systems via altering the transmembrane pressure from 50 mbar to 150 mbar with 2 groups, treating surface water in Beijing, China. Results showed that less driving pressure was more favorable. Specifically, compared to groups (150 mbar), groups under a pressure of 50 mbar were found to have greater normalized permeability and lower total resistance. During the whole operation period, the quality of effluents was gradually improved. For example, the removal efficiency of UV254 was significantly improved; particularly, under low driving pressure, the removal efficiency of UV254 in PES GDM system increased by 11.91%, as compared to the corresponding system under high driving pressure. This observation was consistent with the reduction on disinfection by-products (DBPs) formation potential; groups under 50 mbar achieved better DBPs potential control, indicating the advantages of lower driving pressure. Biofilms were analyzed and responsible for these differences, and distinct distributions of bacteria communities of two GDM systems under 50 and 150 mbar may be responsible for various humic-like substances removal efficiency. Overall, GDM systems under less pressure should be considered and expected to provide suggestions on the design of GDM systems in real applications.

Influence of powdered activated carbon on gravity-driven ultrafiltration for decentralized drinking water treatment: Insights from microbial community and biofilm structure

Gravity-driven membrane (GDM) filtration, an appealing approach for decentralized drinking water treatment, tolerates the development of membrane biofilms for the benefit of low energy consumption and stable flux. In this study, the effect of introducing powdered activated carbon (PAC) on the biofilm generated during long-term GDM filtration was investigated. The results indicated that the addition of PAC significantly enhanced the removal of dissolved organic compounds (DOC) (31 %), whereas only 15.7 % removal was achieved in the control GDM system without PAC. The improved permeate quality was attributed to the combined effects of adsorption and biodegradation of organic compounds by PAC. However, the presence of PAC reduced the permeability of the GDM system by 39 % compared to the control one, which was related to the synergetic effect of the increased extracellular polymeric substances (EPS) content and the decreased metazoan amounts (especially Nematoda) in the biofilm. A large number of substrates adsorbed by PAC facilitated the growth of bacteria and hence intensified the secretion of EPS. Meanwhile, the deposition of PAC on the membrane surface limited the movement space of metazoans, leading to a denser and flatter biofilm basal structure. Furthermore, fewer metazoans meant less predation on bacteria, which also contributed to bacterial reproduction. In addition, an enhanced removal efficiency of ammonia nitrogen was observed in the PAC/GDM system, corresponding to a much higher abundance of Nitrospira in bacterial community. This study links microbial community to hydraulic resistance of biofilm and has practical implications for the application of GDM processes.

Ultrasonication-assisted fouling control during ceramic membrane filtration of primary wastewater under gravity-driven and constant flux conditions

This study investigated the feasibility of using ultrasonication as a ceramic microfiltration membrane fouling control strategy during gravity-driven membrane (GDM) filtration and constant flux filtration of primary municipal wastewater. The fouling model fitting curves revealed that initial intermediate pore blocking was dominant in the GDM system, followed by cake filtration; while cake filtration was dominant during constant flux filtration with a continuously increasing pattern. In the GDM system, periodic ultrasonication cleaning achieved higher cake resistance reduction (∼60 % vs ∼ 26 %) and led to lower specific cake resistances (0.2–2.0 × 107vs 29.6–59.3 × 107 m/mg) compared to periodic backwash. Ultrasonication-facilitated fouling mitigation effectiveness was related to cake properties (such as cake foulant density and porosity) and improved with extending ultrasonication duration. The foulant examination indicated that ultrasonication may result in porous cake nature by cake expansion and facilitate detaching particulate foulants and soluble organics (such as biopolymers) from the membrane. Cost analysis revealed that with commercial ceramic membranes, ultrasonication-facilitated GDM systems are economically feasible for treating wastewater at a household scale (∼1.1 EUR/m3 water), while ultrasonication-facilitated constant flux filtration systems are favorable at a small-community scale (∼0.5 EUR/m3 water). Furthermore, it was predicted that the use of low-cost recycled ceramic membranes would allow GDM systems as economical decentralized wastewater treatment processes due to their lower water production cost (∼0.16 EUR/m3 water) with easy operation and maintenance.

Gravity-Driven Membrane as seawater desalination pretreatment: Understanding the role of membrane biofilm on water production and AOC removal

Gravity-Driven Membrane (GDM) is considered an emerging seawater reverse osmosis desalination pretreatment. The objective of this study was to assess the GDM process performance under different operating conditions and to evaluate the impact of membrane biofilm on the produced water quantity and quality. Three lab-scale submerged GDM systems (UF12h, UF24h and MF24h) were tested under different conditions of Hydraulic Retention Time (HRT) (12 h/24 h) and membrane pore size (Microfiltration/Ultrafiltration). The best water quality in terms of Assimilable Organic Carbon (AOC) was achieved with the longer HRT (24 h), where significant AOC was removed by the biofilm developed on the membrane. The next generation sequencing indicated that a longer HRT increased the abundance of Proteobacteria and Planctomycetes in the biofilm, which due to their biodegradation capability yielded to the highest AOC removal (~50–55 %). Furthermore, the use of microfiltration led to the highest water production (9.1 L/m2/h) due to larger membrane pore size, and a less dense biofilm. These findings indicate that employing a microfiltration membrane and 24 h HRT provides the best performance in terms of water quantity and AOC-removal. This study demonstrates that controlling GDM design and operation enabled manipulation of the biofilm proprieties yielding to high water production and high AOC-removal.

Potential negative effects of illumination on gravity-driven membrane system in treating sulfamethoxazole-containing water

Sunlight illumination could affect the stability and sustainability of the gravity-driven membrane (GDM) system. In this study, sunlight-based GDM and GDM were compared to treat sulfamethoxazole (SMX)-contained water. Results indicated that the removal of DOC, SMX and fluorescent pollutants became worse due to the bacteria activity limited by algae proliferation in sunlight-based GDM. But the total phosphorus (TP) removal rate increased by 74.72% due to algal assimilation. Algae promoted a thick and sticky biofilm with enrichment of extracellular polymeric substances (EPS), and the biofouling layer possessed the highest fluorescence intensity of pollutants. Long-term illumination reduced the biodiversity and richness in the biofouling layer. Pseudomonas was dominant in the sunlight-based GDM (71.3%), while Acinetobacter and Saccharimonadales were more prevalent in the GDM blank, which were related to SMX degradation. Besides, algae reduced the degradation pathways of SMX. Considering the application of GDM in rural areas, long-term illumination should be avoided.

Impact of Gravity-Driven Membrane Filtration Water Treatment Systems on a Rural School in Indonesia

Improving access to safe drinking water in developing countries is still a challenge and Gravity-Driven Membrane (GDM) filtration systems may be a sustainable solution. Two rural schools in West Java Indonesia were studied, one as a control site and another having an installed GDM system. Chemical and microbiological water quality data were collected for an initial 3-month period at the GDM site and a final sampling at the study’s conclusion (6 months) at both sites. After the initial 3-month period, health surveys were conducted with students self-reporting incidences of diarrhea for 3 months at both school sites. An analysis of the chemical parameters indicated that both schools had good water quality. An average 2-log reduction of fecal indicator bacteria at the GDM site was observed, with the control site having numbers that exceeded the upper detection limits (&gt;3.38 log CFU/100 mL). Student diarrhea incidence at the GDM site declined from 0.077 at the survey onset to 0.052 at the latter half of the survey period, while the control site had a diarrhea incidence of 0.077 throughout. The results indicate that GDM technology can serve as a practical water filtration technology, improving access to safe drinking water for rural populations.

Influence of operation modes on gravity-driven membrane process in treating the secondary effluent: Flux improvement and biocake layer property

A low flux level of the gravity-driven membrane (GDM) process constrained its extensive application in treating the secondary effluent. In this study, different operation modes were introduced to the GDM process without aeration, backwashing, and chemical cleanings, hoping to develop simple and economic flux regulating strategies, and their influences on the filtration performances and biocake layer characteristics were systematically investigated. The results indicated that the stable fluxs in the intermittent GDM systems elevated by 40%–100% relative to the continuous GDM case, attributing to the synergetic effects of forming more permeable, mushroom-like structures and reducing the concentrations of EPS and SMP within biocake layers. The quantitative analysis of biocake layer properties suggested that the structural parameters of porosity and absolute roughness were closely related to the flux variation compared to the thickness and relative roughness. Besides, the intermittent GDM system generated an apparent detachment of the biocake layer from the membrane surface along with a persistent flux increase than in the continuous GDM case during long-term filtration, achieving its self-sustained operation in a higher flux level without any interferences. The periodical flux recovery and decline occurred daily in each intermittent GDM system since the biocake layer attached to the membrane surface was mainly reversible. Although there were no significant differences in removing dissolved organic pollutants under different operation modes, the manganese removals decreased by 0%–25% in the intermittent GDM filtrations compared to the continuous GDM scenario. The optimized daily operation mode was 16 h on / 8 h off (operation of 16 h, interruption of 8 h), considering the trade-off effects between membrane flux level and water production. These findings provide a new simply-feasible optimized GDM process operation strategy and benefit promoting the application of the GDM system in the reclamation of wastewater.

Insight into biofouling mechanism in biofiltration-facilitated gravity-driven membrane (GDM) system: Beneficial effects of pre-deposited adsorbents

The membrane fouling triggered by biofouling layer is the critical factor limiting the application of biofiltration-facilitated gravity-driven membrane (GDM) system in decentralized drinking water treatment. Powdered activated carbon (PAC) and alumina (AA) were used to mitigate membrane fouling by pre-deposition. Pre-deposited PAC and AA improved the stable flux of the biofiltration-facilitated GDM systems, increasing by 9.6% and 17.0%, respectively. The removal of dissolved organic carbon, UV254 and protein-like material was sequentially enhanced by pre-deposition of PAC and AA, respectively. Pre-deposited AA performed better than pre-deposition of PAC in restricting the adhesion of soluble microbial products to the membrane. After pre-deposition of PAC and AA, the porosities of the biofouling layers increased by 0.78% and 2.51%, and the protein/polysaccharide ratio in extracellular polymeric substances (EPS) decreased from 111.8% to 53.4% and 39.8%, respectively. The protein in tightly bound EPS showed a significant positive (p < 0.05) relationship with the total membrane resistance and genus Acidovorax. Zoogloea was the core genus among the bacterial communities related to EPS production. Overall, pre-deposition of PAC and AA can be a simple and effective strategy to alleviate membrane fouling in biofiltration-facilitated GDM.