Backwash Water Research Articles

Role of Titanium Dioxide-Immobilized PES Beads in a Combined Water Treatment System of Tubular Alumina Microfiltration and PES Beads.

The membrane process has a limit to the decay of various pollutants in water. To improve the problem, the roles of backwashing media and titanium dioxide (TiO2) photocatalyst-immobilized-polyethersulfone (PES) beads' concentration were investigated in a combined system of tubular alumina MF and the PES beads for advanced drinking water treatment. The space between the outside of the MF membrane and the module inside was filled with the PES beads. UV at a wavelength of 352 nm was irradiated from outside of the acryl module. A quantity of humic acid and kaolin was dissolved in distilled water for synthetic water. Water or air intermittent backwashing was performed outside to inside. The membrane fouling resistance after 3 h process (Rf,180) was minimum at 30 g/L of the PES beads for water backwashing, and at 40 g/L for air backwashing when increasing the PES beads from 0 to 50 g/L. The irreversible membrane fouling resistance after physical cleaning (Rif) was at the bottom at 5 g/L of the PES beads for water backwashing, which was 3.43 times higher than minimal at 40 g/L of the PES beads for air backwashing. The treatment effectiveness of turbidity increased when increasing the PES beads' concentration from 0 to 50 g/L; however, it reached a maximum at 98.1% at 40 g/L and 99.2% at 50 g/L for water and air backwashing, respectively. The treatment effectiveness of UV254 absorbance, which was dissolved organic matter (DOM), increased dramatically when increasing the PES beads; however, it reached a peak of 83.0% at 40 g/L and 86.0% at 50 g/L for water and air backwashing, respectively. Finally, the best PES beads' concentration was 20~30 g/L to minimize the membrane fouling; however, it was 50 g/L to remove pollutants effectively. The water backwashing was better than the air at treating DOM; however, the air backwashing was more effective than the water at removing turbid matter and reducing membrane fouling.

Application of Chitosan and Its Derivatives as Bioflocculants for Iron and Turbidity Removal from Filter Backwash Water

The present study aimed to investigate the potential application of chitosan (CS) and its two derivatives, dialdehyde chitosan (DCT) and carboxymethyl chitosan (CMC), as new flocculants in the purification of filter backwash water. The main objective of the work was to remove the disadvantages and inconveniences associated with using synthetic flocculants, mainly based on polyacrylamide, by using biodegradable and non-toxic biopolymer flocculants. The chitosan derivatives were obtained in the process of the chemical modification of this polysaccharide. CS was oxidated with periodate in acetic acid solution to obtain DCT with a degree of substitution (DS) of 44.29%. For the CMC synthesis, after the alkaline activation of chitosan, the solution was treated with monochloroacetic acid (MCA) at 60 °C for 3 h, leading to carboxymethylated chitosan formation with a DS of 49.55%. Characterizations of the flocculants using Fourier transform infrared (FT-IR) spectroscopy, 13C nuclear magnetic resonance (13C NMR) spectroscopy, and an elementary analysis confirmed the successful modification of the chitosan. The morphology and thermal stability of the samples were investigated using scanning electron microscopy (SEM) and a thermogravimetric analysis (TGA), respectively. Moreover, the biopolymer materials were studied in a series of flocculation jar tests for filter backwash water samples collected at a water treatment plant (WTP) in Kutno, Poland. CMC turned out to be a particularly effective agent in an optimal amount of 0.2 mg/L, achieving nearly 99% iron removal and 98.26% turbidity removal efficiency rates, which indicates that chitosan–based materials can be ecological alternatives for polyacrylamide flocculants, effectively removing the impurities of iron ions.

Effect of Zeolux and Filters Backwash Water (FBWW) on Plant Growth and Yield of Sage (Salvia Officinalis) Plant

<p>Jordan is one of the few countries with constricted water resources, having one of the lowest per capita water levels in the world (Ministry of Agriculture, 2015). Jordan's available water resources per person are predicted to fall from less than 160 m3/capita/year to roughly 90 m3/capita/year by 2025, placing the nation in the acute water shortage category. Massive volumes of filter backwash water (FBWW) are created and wasted in Jordan. The use of FBWW to Sage (Salvia Officinalis) plant germination under controlled conditions with various dilution treatments would reduce water waste while also providing an alternate irrigation water supply. The effects of Zeolux as a soil amendment on the productivity and a variety of agronomic parameters of a Sage (Salvia officinalis) irrigated with fresh and FBWW were also studied. Various clay-zeolux mixtures were tested to achieve this goal. The combination soil mix of 25% zeolux and 75% clay watered with FBWW had the greatest results in terms of plant height, number of branches, fresh weight, dry weight, and root dry weight. The results reveal that the addition of zeolux to clay enhanced the yield and agrarian characteristics of plants cultivated in the soil. The results demonstrate that employing FBWW increased plant growth features greatly, and zeolux increases the favorable impact of FBWW irrigation on plant output. The study's main results will help to preserve valuable drinking water supplies while also increasing the yield of irrigated plants by using treated FBWW for irrigation.</p>

Fouling mitigation in membrane bioreactors by nanobubble-assisted backwashing

Widespread application of membrane bioreactors (MBRs) is still difficult because of the problem of membrane fouling, which increases operational and maintenance costs. A novel approach to mitigate fouling in MBRs, nanobubble-assisted backwashing (NBB), is presented in this paper. Nanobubbles generated in this study had an average diameter of about 150 nm, and some of the nanobubbles could pass through the pores of microfiltration (MF) membranes used for MBRs. Therefore, nanobubbles introduced from the permeate side during backwashing might exhibit cleaning effects for membranes since applications of nanobubbles for cleaning of various materials such as protein-coated gold electrodes and stainless steel have been reported. The effectiveness of NBB was compared with that of tap water backwashing (TWB) and chemically enhanced backwashing (CEB) using 50 ppm NaClO. Experiments were carried out by using three bench-scale MBRs installed at a local wastewater treatment plant. The three MBRs were operated in parallel with identical operating conditions except for backwashing conditions. Polyethylene glycol (PEG) granular materials were inserted in each membrane tank to scour the membrane surface. Regardless of the variation of the feed, NBB always exhibited better cleaning performance than TWB, and the cleaning efficiency of NBB was sometimes comparable to that of CEB. The degree of reversible fouling observed with TWB was 424 % higher than that with NBB, indicating that NBB is much more effective than TWB for the control of reversible fouling. It was also found that NBB could mitigate irreversible fouling even in the absence of a thick protective layer on the surface of the membrane. It was attempted to reveal the mechanism by which NBB enhances the cleaning effect by carrying out comprehensive analysis of the distribution of filtration resistance, mixed liquor suspension and the fouling layer. Significant changes in microbial activity of the mixed liquor suspension and sludge properties in the MBRs were not observed when NBB was carried out. The results of the analysis suggested that NBB made the structure of the fouling layer more porous, possibly facilitating the removal of the fouling layer from the membrane.

Low-pressure air plasma-assisted acrylic grafted polyetherimide ultrafiltration membranes with excellent oil-water separation and high anti-fouling performances

This paper reports the first surface modification of polyetherimide (PEI) ultrafiltration membranes using low-pressure air plasma-treated surfaces to induce acrylic acid (AA) graft polymerization, significantly improving their retention and fouling resistance properties. The successful formation of graft layers was verified by water contact angle (WCA) measurement of hydrophilic changes and Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis of the surface chemistry. Scanning electron microscopy (SEM) was used to analyze the morphological features, and atomic force microscopy (AFM) was tested for changes in surface roughness. The overall property changes after grafting were evaluated by mechanical tests and filtration tests. Methyl tert-butyl ether (MTBE) was chosen to measure the oil-water separability. The results showed that the membrane surface obtained PAA dense graft layer and improved hydrophilicity (CA from 57.62° to 29.26°) with no loss of tensile properties. In addition, the modified grafted membranes showed a high retention rate of BSA of 95.1 %, while the rejection rate of MTBE increased from 31.8 % to 75.9 %. Notably, PEI-g-AA fully recovered the permeability by simple water backwashing, exhibiting excellent antifouling performance. Therefore, this communication demonstrates that graft modification on the surface of PEI membranes is feasible and effective, and provides a new idea of PEI modification, which is valuable for exploring the development of high-efficiency ultrafiltration membranes.

Application of UF and RO for power plant's wastewater treatment and recycling for environmental sustainability

Abstract Global indicators have warned of freshwater scarcity in Asia. However, the utilization of freshwater resources has skyrocketed for commercial and industrial purposes without any strategy for recycling and reuse. The power plant's wastewater/reject mainly consisted of cooling tower blowdown water and reverse osmosis (RO) plant reject water. Due to the high turbid nature of reject water, pretreatment was carried out to achieve SDI15 <3 by employing multimedia filters (MMF), activated carbon filters (ACF) and ultrafiltration (UF). Operational parameters of RO membranes were optimized (11.5 bar, 29 °C) to achieve maximum water recovery along with higher rejection rates of critical scale forming species such as 81% total dissolved solids (TDS), 73% calcium hardness and 72% silica (Si). After accounting for backwash water and other concentrate rejections, the membrane treatment plant has achieved an appreciable recovery rate of more than 44%. The RO membrane-treated water was then incorporated in the cooling tower and a 16% reduction in freshwater makeup was achieved. Reduction of microbial growth rate as well as corrosion and scaling in the cooling tower was observed due to the reuse of treated water. This is to confirm here that brackish water RO membranes can act as a strong contender for reject water reclamation and effective utilization.

Distribution, Tansformation, and Fate of Per-and Polyfluoroalkyl Substances in Drinking Water Treatment

Per-and polyfluoroalkyl substances (PFASs) are present in surface water, tap water, and even commercial drinking water and pose a threat to human health. In this study, the occurrence and transformation of 14 PFASs were studied in large drinking water treatment plants (DWTPs) with Taihu Lake as the source, and the results showed that a total of 10 PFASs were detected in the water samples, indicating that PFAS were widely distributed in drinking water. The total concentration of PFASs in raw water was 127.4 ng·L-1, with the highest concentration being that of pentadecafluorooctanoic acid (PFOA, 49.8 ng·L-1). Pre-ozone caused a reverse increase in the concentration of PFASs, which may have been due to the presence of precursors or conversion from short to long chains. PFASs were not effectively removed by conventional treatment processes, andozone-biological activated carbon (O3-BAC) had a dominant role in the removal of PFASs (20.74%) from DWTPs. O3-BAC, the main removal process for DWTPs, contained high concentrations of PFASs in the backwash water with similar distribution characteristics to the raw water. Using a pilot plant, five common filter backwash water treatment processes were compared, and the results showed that GAC-ultrafiltration could adsorb and retain a certain amount of PFASs while ensuring a high removal rate of turbidity (99.08%). The 3D-EEM analysis indicated that GAC-ultrafiltration could also remove most of the fluorescent micro-pollutants, and for raw water containing high concentrations of PFASs DWTPs, it is practical to use it as a filter backwash water reuse treatment process.

Evaluating membrane cleaning for organic fouling in direct contact membrane distillation

To find an effective cleaning method for organic fouling in membrane distillation (MD), this work focused on the fouling characteristics of humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA), and the cleaning efficiency of deionized (DI) water flushing, NaCl flushing, NaOH flushing and DI water backwashing. The results showed that when Ca2+ was absent from the feed solution, severe fouling was observed for HA and BSA, while SA led to slight fouling due to its hydrophilicity. The addition of Ca2+ alleviated the fouling for HA, but intensified the fouling for SA and BSA. There was a transition from cake filtration to complete blocking in membrane fouling mechanism for most MD tests. NaOH flushing resulted in irreversible fouling ratio of 48–60% after fouling by HA and BSA, while DI water flushing can recover 70% of flux decline caused by SA without Ca2+ present in the feed. For the three organics, only 8–15% of fouling was removed after DI water backwashing. The differences in the cleaning efficiency of the four cleaning methods were further verified by the positive correlation between irreversible fouling ratio and surface energy parameter, as well as Scanning electron microscopy and Fourier transform Infrared analysis of the membranes used in this study.

Use of hollow fibre membrane contactors to remove dissolved gases from effluents of UASB reactors treating sewage after its conditioning with dynamic membrane filtration

Dissolved gases in the effluent of anaerobic reactors, such as dissolved methane (D-CH4) and sulphide (S2−), are a drawback for anaerobic-based sewage treatment plants. Hollow fibre membrane contactors (HFMCs) have been tested for the removal of these compounds, and this paper evaluated a novel configuration with pressurised dynamic membrane modules (PDMMs) for conditioning an anaerobic effluent (from UASB reactor fed with sewage) as a means to reduce HFMCs clogging and fouling. Three PDMMs were used for the anaerobic effluent conditioning before two types of HFMCs (dense and microporous membranes). An automated backwash with a tap water cleaning protocol complemented with a chemical cleaning protocol (NaOH and citric acid) was applied for fouling control. The microporous HFMC could not maintain a stable performance (D-CH4 and S2− removal drop of 30 % and 40 %, respectively, in 10 days of operation), arguably due to membrane wetting, meanwhile the dense HFMC showed a more stable behaviour (removal efficiencies close to 100 % and 90 % for S2− and D-CH4, respectively in >30 days). The water backwash removed an important fraction of the entrapped organic solids. Meanwhile, the NaOH cleaning was efficient in removing inorganic compounds. Citric acid contributed to the removal of calcium and phosphate.

Backwashing of granular media filters and membranes for water treatment: a review

AbstractFilter backwashing is a supplemental part of a drinking water treatment (DWT) facility to wash the filter bed at regular intervals using water or air scour/water by fluidizing the filter bed. Deposited material induces clogging the filter pores and enhances head loss in the bed. Biofiltration has been extensively utilized to decrease organic matter and manage the occurrence of disinfection by-products within drinking water sources. Biological rapid sand filters are frequently utilized to eliminate ammonium from groundwater provinces with the purpose of meeting drinking water requirements. Biological activated carbon (BAC) filters need to be backwashed to wash and enhance the treatment capability by detaching both restrained materials and residual biomass. The reclamation of activated carbon-used backwash water (UBW) was managed by exercising an ultrafiltration (UF) procedure.

Characterization of DOM and disinfection by-products precursors in biological activated carbon filter backwash water from drinking water treatments

Abstract Biological activated carbon filter backwash water (BAC FBW) removes pollutants from BAC filters in drinking water treatment plants. Characterizing the dissolved organic matter (DOM) in BAC FBW is of great significance for the recycling and treatment of backwash water. DOM pollution was monitored over a year using three-dimensional excitation–emission matrix fluorescence spectra. The dissolved organic carbon (DOC) concentration and fluorescence results showed that the DOC concentration reached the lowest value of 1.95 mg/L in the summer. The relative abundances of fluorescence components had a direct relationship with temperature variations. The soluble microbial products were enhanced greatly during cold seasons, while fulvic-acid-like and humic-acid-like compounds remained constant. Disinfection by-products (DBPs) formation potential and cytotoxicity were evaluated. The total haloacetonitriles (HANs), trihalomethanes (THMs), halonitromethanes (HNMs), and haloacetaldehyde (HALs) formation potentials ranged from 35.5 to 47.3 μg/L, 95.1 to 126 μg/L, 4.95 to 8.06 μg/L, and 43.4 to 53.0 μg/L in BAC FBW, respectively. Among all DBPs included in the calculation, the order of contribution to cytotoxicity was HANs > HALs > THMs > HNMs, respectively. Especially, HANs were much higher than the other DBPs, which should be controlled to avoid the biological risk of effluent quality.

Pilot-scale biofiltration of 1,4-dioxane at drinking water-relevant concentrations

1,4-Dioxane is a drinking water contaminant of emerging concern. Because conventional and many advanced drinking water treatment technologies are ineffective for 1,4-dioxane removal, cost-effective technologies for the removal of 1,4-dioxane at drinking water-relevant concentrations are needed. In this research, a gravity-fed, cometabolic biofiltration system was developed to degrade 1,4-dioxane that was spiked into coagulated, settled surface water at a concentration of ∼10 µg/L. Objectives were to determine whether cometabolic degradation of trace levels of 1,4-dioxane can be sustained using n-butane as primary substrate and whether filter media properties and empty bed contact time (EBCT) affect biofiltration efficiency. A mixed culture of bacteria derived from the Cape Fear River basin and previously enriched using isobutane served as inoculum for biologically active filters. Two granular activated carbons (GACs) with different grain sizes and one carbonaceous resin were used as attachment media, and n-butane served as the primary substrate for biologically active filters. Non-inoculated controls with the same media were evaluated in parallel to distinguish between biological and adsorptive removals of 1,4-dioxane. For the duration of the pilot study (>3 months), 1,4-dioxane was degraded in inoculated biofilters receiving n-butane. In control filters containing larger and smaller grain GAC, 1,4-dioxane broke through completely within 750 and 1250 bed volumes, respectively, corresponding to 15 to 30 days of operation at an EBCT of 30 min. 1,4-Dioxane removal increased with increasing EBCT in all biologically active filters. At an EBCT of 30 min, the biologically active GAC filter containing the larger-grain GAC removed on average 87% of 1,4-dioxane at pseudo steady-state. When the hydraulic loading rate was decreased to achieve an overall EBCT of 60 min, 1,4-dioxane was removed to <1 µg/L in the biologically active GAC filter containing the larger-grain GAC. Activity-based labeling showed the presence of catalytically active monooxygenases in backwash water from biologically active filters that degraded 1,4-dioxane. Amplicon sequencing results showed that while taxa shifted after the initial inoculation of biologically active filters, taxa in biologically active filters remained more similar to the inoculum than those in the non-inoculated control filters. Overall, results of this research demonstrate that cometabolic degradation of 1,4-dioxane at trace levels is possible for extended periods of time in inoculated biofilters that receive n-butane as primary substrate.

Quality Assessment of Sludge from Filter Backwash Water in Swimming Pool Facilities

Swimming pools are examples of water-intensive facilities, where solutions for reducing economic and environmental costs are searched with increased frequency. One of the solutions supporting savings is the recovery of water from wastewater, including backwash water obtained while rinsing the filter bed. The study objective was the qualitative and quantitative assessment of post-coagulation sludges, the main pollutant found in the washings. During the analyses, assessment of the sedimentation capabilities of the sludges was performed (gravitationally), particle size distribution was assessed (particle size distribution analyser) and assessment of phytotoxicity with the use of plant indicators in short-term tests was performed (Lemna minor, Lepidium sativum, Sinapis alba, Raphanus sativus). The samples were collected from two independent circulations, which differed in terms of capacity and type of coagulant used. The tested post-coagulation sludges were characterized by high content of total suspended solids: in samples from Circuit 1 from 251 to 128 mg/L, in Circuit 2 from 489 to 228 mg/L. However, the sedimentation processes enabled significant separation of sludges. The hydrolyzed coagulant contributed to the improvement of sedimentation capabilities of the sludges. Despite the fact that in many samples low sludge concentrations favored stimulation of plant growth, the post-coagulation sludges can constitute a hazard to plant growth, particularly in the long-term perspective.

Characterization and chlorine reactivity of particulate matter released by bathers in indoor swimming pools

Disinfecting swimming pool water is essential for preventing waterborne diseases. An unforeseen consequence of treating water with disinfectants is the formation of disinfection by-products (DPBs) that can cause harmful effects to health through the interactions between the added disinfectant and organic matter in the water. The present work focuses on the chlorine reactivity with particles released by bathers. Such particles are collected in the filter backwash water of swimming pools and this study intends to distinguish DPBs generated from dissolved chemicals from those formed by particulate matter. Therefore, filtered and unfiltered backwash waters were collected from several swimming pools, analysed physicochemically and chemically, and then chlorinated as is (79 mgL−1) and as diluted suspensions (36.2 and 11.9 mgL−1) at varying concentrations of chlorine (1.2 mg and 24 mgCl2L−1). Utilizing a DPD colorimetric technique and GC-ECD, respectively, the kinetics of chlorine consumption and DPBs production have been investigated. Up to 25.7 μgL−1 of chloroform was produced within 96 h at 1.2 mgCl2L−1, followed by haloacetic acids (HAAs) and haloacetonitriles (HANs). Within 96 h, the concentration of trichloroacetic acid reached a maximum of 231.8 μgL−1 at a chlorine concentration of 231.8 μgL−1. The formations of 0.13 μmol THMs, 0.31 μmol HAAs, and 0.04 μmol HANs per mg of dissolved organic carbon (DOC) were finally determined by correlating the organic content of particles with the nature of the DBPs generated. Comparing the quantities of DBPs generated in filtered and unfiltered samples helps us conclude that ∼50% of DBPs formed during the chlorination of swimming pool water are derived from particles brought by bathers.

Recirculation of Backwash Water in the Water Treatment Plant for the Needs of the Combined Heat and Power Plant

Recirculation of Backwash Water in the Water Treatment Plant for the Needs of the Combined Heat and Power Plant

Molecular characterization of disinfection byproduct precursors in filter backwash water from 10 drinking water treatment plants

Organic matter reacts with chlorine forming disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetamides (HAMs), haloacetic acids (HAAs), and haloacetonitriles (HANs). Filter backwash water (FBW) is either released back to the environment or recycled to the head of the treatment plant after solids settling and the remaining dissolved organic matter is a significant pool of DBP precursors that are not well understood. We characterized dissolved organic matter in FBW from 10 treatment plants and low molecular weight (MW < 1 kDa) organic matter contributed the most to DBP formation. We demonstrated overall similarity of the molecular composition (e.g., elemental ratios, m/z, DBE) of the 10 samples of FBW by Fourier transform ion cyclotron resonance mass spectrometry. Aromatic and more highly oxidized compounds preferentially reacted with chlorine, forming DBPs. Low MW (<450 Da) aliphatic compounds, and highly unsaturated and phenolic compounds were the primary precursors of THMs, HANs, and HAMs, and the formation potentials (FPs) of these groups of DBPs were correlated with multiple individual molecular formulae. HAA FPs were correlated with low MW, highly unsaturated and phenolic compounds. These advances in the understanding of the molecular composition of DBP precursors in FBW may develop the effective strategies to control DBP formation and limit impacts on the quality of finished water, and can be expanded to understanding DBP precursors in drinking water sources.

Evaluation of water consumption in rapid sand filters backwashed under varied physical conditions

Egypt suffers from water scarcity. In water treatment plants using sand filters, a significant amount of treated water is consumed, estimated at 10%–15% of the filtered water during backwashing. The objective of this study is to determine the most effective way to reduce the amount of treated water used for backwashing. The methodology of this study was to evaluate the effects of air and water rates, treated water turbidity of 1.6 NTU or slightly higher synthetic turbidity of 4.0 NTU, and media type with single or dual media on reducing treated water consumption during rapid sand filter backwashing procedures. The experimental set up was a bench-scale filter operated at a filtration rate of 189 m3/m2/day. Backwashing with the right water and air rates reduce water usage by 18%, enhanced process performance, and reduced the ripening period. Backwashing using synthetic turbid water recovered 100% of the treated water and improved the ripening duration without affecting backwashing efficiency. This study concluded that backwashing the dual media filter with silica sand and activated carbon achieved the highest treated backwash water consumption by approximately 60%. While anthracite coal was utilized as a dual-media filter, the least reduction in treated water consumption was discovered.

Evaluation of a novel integrated membrane biological aerated filter for water reclamation: A practical experience

The use of treated wastewater in addition to solving the problem of water shortage, can increase soil fertility and reduce the use of chemical fertilizers. We aim to provide a high-quality effluent to feed membrane system, reduce treatment costs and enhance the efficiency of wastewater recycling. All experiments were conducted on a novel integrated membrane biological aerated filter (IMBAF) consisting of a down flow cylindrical biological aerated filter (BAF) filled by silica and a novel sand-coated polystyrene granules (SCP), followed by ultrafiltration (UF) and reverse osmosis (RO) membranes. IMBAF reactor, with 73.6L volume, was operated for 270 days (in three 90-day stages) with different conditions of returning backwash water. Accordingly, BAF generated high quality water for feeding UF membrane with 94.2%, 68%, 54.4%, 91.2%, and 99.95% of turbidity, 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), oil and grease (O&G), fecal coliform (FC) removal, respectively. At the end of stage 3, 99.88% of influent was recycled by UF and only 0.12% was disposed of as sludge. The BAF and UF module efficiently promote the quality of water entering RO system. After 75 days of continuous operation, the increase in trans-membrane pressure (TMP) and also decrease in RO membrane permeability were about 14% and 9.4%, respectively, indicating low clogging of the membrane. The use of BAF structure designed in this study increases the wastewater recycling rate, decreases membrane clogging and thereby reduces the costs of concentrate disposal and chemical cleaning.

Development of arsenic removal unit with electrocoagulation and activated alumina sorption: Field trial at rural West Bengal, India

In the present study, electrocoagulation (EC) with iron electrodes along with adsorption by activated alumina has been evaluated as a treatment process for arsenic removal from groundwater. Batch scale experiments were performed with iron electrodes to assess the removal efficiency of electrocoagulation. The effects of inter-electrode distance and electro-charge loading (ECL) were evaluated on arsenic removal. EC was able to decrease the arsenic concentration in the aqueous phase below 10 ppb at ECL of 60 coulomb/L with 1 cm inter-electrode distance. The optimal condition was obtained by Response Surface Methodology (RSM) with the help of central composite design (CCD). The regression equation and analysis of variance were originated using Design-Expert software and F value (131.56), p-value (<0.05), and desirability value of 1 were obtained for the optimized model. Activated alumina adsorption has also been shown to be a promising arsenic removal technology (As5+) with 15 min of equilibrium time. An arsenic removal system was designed with EC unit, sand filter, and activated alumina column in series for field application. The field unit was able to deliver safe water to the local community. During the operation, the electrodes were passivated, and calcium-based deposition was found on the cathodes. Periodic electrode reversal was able to minimise the passivation. Due to the accumulation of ferric hydroxide flocs, the pores of the filter bed become clogged and they must be cleaned by backwashing. The Backwash system should be continued until the water runs clear. An arrangement of a suitable soak pit is made to contain the backwash water avoiding any environmental contamination. EC could be able to deliver safe water locally in rural areas at affordable prices due to its high efficiency and low operation and maintenance costs.

Experimental study on coal blockage removal based on pulverized coal blockage

The generation and transport of coal powder has caused great harm to coal reservoir channeling conductivity, affecting the capacity of coalbed methane wells, causing the failure of engineering equipment and great distress to production, while current unblocking methods have many shortcomings. In this study, a series of laboratory experiments on coal samples' plugging and reverse-water/gas injection replacement of pulverized coal to unblock coal samples under three-dimensional stress conditions were carried out using a gas–liquid–solid three-phasedisplacement simulation system. In addition, the characteristics of the change of coal permeability and coal powder output under different plugging pressures and unplugging media and pressures were explored. Furthermore, the influence of medium difference on coal powder migration and its mechanism were analyzed. The results were as follows: (1) under the same pressure, the gas carrying capacity for pulverized coal in the pores and fissures of raw coal is much greater than that of water; (2) only when the reverse-gas injection pressure is greater than or equal to the plugging pressure can the coal be unblocked. The reverse-gas injection unblocking the coal body has three stages such as gas-drive-water, gas-drive-water and pulverized coal, and gas production stages (complete unblocking stage of the coal body). The migration difficulty determines the output order of products; (3) during reverse injection hydrolysis of coal plugging, the liquid-phase permeability (LPP) of coal showed “fluctuation–stability” characteristics. The final liquid-phase permeability is lower than the initial value, which is related to the competition between the secondary bridging blockage of pulverized coal particles (PCP) at the pore shrinkage of coal caused by the change in water flow seepage velocity and backwashing, and the pulverized coal's unblocking, redistribution, and capture caused by the local pressure build-up.