Studies on the Removal of Phosphate from Drinking Water by Electrocoagulation Process

New Zein Protein Composites with High Performance in Phosphate Removal, Intrinsic Antibacterial, and Drug Delivery Capabilities

Herein, poly(N-(4-aminophenyl)methacrylamide)-carbon nano-onions [abbreviated as PAPMA-CNOs (f-CNOs)] integrated gallic acid cross-linked zein composite fibers (ZG/f-CNOs) were developed for the removal/recovery of phosphate from wastewater along with controlled drug delivery and intrinsic antibacterial characteristics. The composite fibers were produced by Forcespinning followed by a heat-pressure technique. The obtained ZG/f-CNOs composite fibers presented several favorable characteristics of nanoadsorbents and drug carriers. The composite fibers exhibited excellent adsorption capabilities for phosphate ions. The adsorption assessment demonstrated that composite fibers process highly selective sequestration of phosphate ions from polluted water, even in the presence of competing anions. The ZG/f-CNOs composite fibers presented a maximum phosphate adsorption capacity (qmax) of 2500 mg/g at pH 7.0. This represents the most efficient phosphate adsorption system among all of the reported nanocomposites to date. The isotherm studies and adsorption kinetics of the adsorbent showed that the adsorption experiments followed the pseudo-second-order and Langmuir isotherm model (R2 = 0.9999). After 13 adsorption/desorption cycles, the adsorbent could still maintain its adsorption efficiency of 96-98% at pH 7.0 while maintaining stability under thermal and chemical conditions. The results mark significant progress in the design of composite fibers for removing phosphates from wastewater, potentially aiding in alleviating eutrophication effects. Owing to the f-CNOs incorporation, ZG/f-CNOs composite fibers exhibited controlled drug delivery. An antibiotic azithromycin drug-encapsulated composite fibers presented a pH-mediated drug release in a controlled manner over 18 days. Furthermore, the composite fibers displayed excellent antibacterial efficiency against Gram-positive and Gram-negative bacteria without causing resistance. In addition, zein composite fibers showed augmented mechanical properties due to the presence of f-CNOs within the zein matrix. Nonetheless, the robust zein composite fibers with inherent stimuli-responsive drug delivery, antibacterial properties, and phosphate adsorption properties can be considered promising multifunctional composites for biomedical applications and environmental remediation.

Coagulation as an effective method for cyanobacterial bloom control: A review

Eutrophication, the over-enrichment with nutrients, for example, nitrogen and phosphorus, of ponds, reservoirs and lakes, is an urgent water quality issue. The most notorious symptom of eutrophication is a massive proliferation of cyanobacteria, which cause aquatic organism death, impair ecosystem and harm human health. The method considered to be most effective to counteract eutrophication is to reduce external nutrient inputs. However, merely controlling external nutrient load is insufficient to mitigate eutrophication. Consequently, a rapid diminishing of cyanobacterial blooms is relied on in-lake intervention, which may encompass a great variety of different approaches. Coagulation/flocculation is the most used and important water purification unit. Since cyanobacterial cells generally carry negative charges, coagulants are added to water to neutralize the negative charges on the surface of cyanobacteria, causing them to destabilize and precipitate. Most of cyanobacteria and their metabolites can be removed simultaneously. However, when cyanobacterial density is high, sticky secretions distribute outside cells because of the small size of cyanobacteria. The sticky secretions are easily to form complex colloids with coagulants, making it difficult for cyanobacteria to destabilize and resulting in unsatisfactory treatment effects of coagulation on cyanobacteria. Therefore, various coagulants and coagulation methods were developed. In this paper, the focus is on the coagulation of cyanobacteria as a promising tool to manage eutrophication. Basic principles, applications, pros and cons of chemical, physical and biological coagulation are reviewed. In addition, the application of coagulation in water treatment is discussed. It is the aim of this review article to provide a significant reference for large-scale governance of cyanobacterial blooms. PRACTITIONER POINTS: Flocculation was a promising tool for controlling cyanobacteria blooms. Basic principles of four kinds of flocculation methods were elucidated. Flocculant was important in the flocculation process.

Comparative Investigation of Phosphate Adsorption Efficiencies of MOF-76 (Ce) and Metal Oxides Derived from MOF-76 (Ce)

Phosphate pollution is a very challenging problem for the water environment. Phosphate mixed with water in various ways causes eutrophication. To sustain life in aquatic systems, phosphate ions must be cleaned. Therefore, it is very important to remove phosphate in wastewater. Here, an adsorption method has been tried for the removal of phosphate. MOF-76 (Ce), a cerium-based metal-organic framework, was synthesized by a hydrothermal method. Since metal oxides are known to be successful in phosphate adsorption, CeO2 nanoparticles were also obtained by pyrolysis of this MOF structure. The phosphate adsorption efficiencies of both adsorbents were compared. The characterization methods (SEM, FTIR, XRD, and TGA) were applied to adsorbents. The kinetic, isotherm, and thermodynamics studies were applied to experimental results. At 298 K, the adsorption capacity of MOF-76 (Ce) is higher than that of CeO2, according to Langmuir isotherm qm values. The qm values are 72.97 and 55.71 mg/g, respectively. Both adsorbents follow the pseudo second-order kinetic model. It has been found that MOF-76 (Ce) has a pH-selective property in phosphate adsorption. No change was observed in the phosphate adsorption capacity of CeO2 with pH. In terms of thermodynamics, the endothermic reaction is valid for both adsorbents.

Study on influencing parameters and long-term operation of electrocoagulation phosphorus removal from small rural domestic sewage

Excessive discharge of phosphorus can produce eutrophication in aquatic environments, damaging public health, the living environment, and the economy. The conventional mechanical-biological phosphorus removal methods are not suitable for small rural domestic sewage due to the features of small scale, scattered distribution, intermittent emission, and large fluctuation. This work evaluated electrocoagulation (EC) with industrial steel as electrodes on small rural domestic sewage. Results showed that the best performance was achieved at a current density of 1 mA/cm², electrode distance of 2 cm, electrode number of 2, pH of 7, and Hydraulic Retention Time of 30 min, respectively. Under optimum conditions, the EC process removed 93.91% phosphorus while consuming around 0.25 kWh/m³ of electricity. In addition, the electrode passivation of EC was further investigated; the long-term research found that the phosphorus removal efficiency only decreased by 4.34% after 10 days of continuous flow operation, and the operational energy consumption was 0.07 kWh/m³ at a Cl^- concentration of 500 mg/L.

Removal of nutrients and other emerging inorganic contaminants from water and wastewater by electrocoagulation process

The continual discharge of emerging inorganic pollutants into natural aquatic systems and their negative effects on the environment have motivated the researchers to explore and develop clean and efficient water treatment strategies. Electrocoagulation (EC) is a rapid and promising pollutant removal approach that does not require any chemical additives or complicated process management. Therefore, inorganic pollutant treatment via the EC process is considered one of the most feasible processes. The potential developments of EC process may make the process a wise choice for water treatment in the future. Thus, the present study mainly focuses on the use of EC technology to remove nutrients and other emerging inorganic pollutants from water medium. The operating factors that influence EC process efficiency are explained. The major advancement of the EC technique as well as field-implemented units are also discussed. Overall, this study mainly focuses on emerging issues, present advancements, and techno-economic considerations in EC process.

Removal of phosphorus in wastewater by sinusoidal alternating current coagulation: performance and mechanism

The effects of initial total phosphorus (TP) concentration, current density, conductivity and initial pH value on the removal rate of TP and energy consumption, as well as the behaviour and mechanism of phosphorus removal, were investigated by sinusoidal alternating current coagulation (SACC). The flocs produced by SACC were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy FTIR and X-ray photo electron spectroscopy. The thermodynamic and kinetic behaviours of phosphorus removal by iron sol adsorption were also studied in detail. In a self-made SACC reactor equipped with five sets of parallel iron electrodes spacing 10 mm, the removal rate of TP reached 90.9% for a pH 7.0 wastewater with 5 mg dm^-3 TP (κ = 800 μS cm^-1) after being treated for 60 min by applying 2.12 mA cm^-2 sinusoidal alternating current. Compared with direct current coagulation (DCC), SACC exhibits a higher removal efficiency of phosphorus due to the stronger adsorption of the produced flocs. It was found that the adsorption in the SACC process follows pseudo-second-order kinetic with the involvement of the intra-particle model. The adsorption of iron sol to phosphorus was an endothermic and spontaneous process, and its adsorption behaviour can be characterized with Langmuir and Redlich-Peterson isothermal adsorption models. SACC may be employed for the treatment of more complex wastewater combined with biological and/or electrochemical techniques.

Molecular insights into formation of nitrogenous disinfection byproducts from algal organic matter in UV-LEDs/chlorine process based on FT-ICR analysis

Eutrophication is a globally concerned issue, which brings algal cells and algal organic matter (AOM) into drinking water treatment plants. AOM is an important branch of nitrogenous disinfection byproduct (N-DBP) precursors. The variation of AOM composition in UV-LEDs/chlorine process, and its relationship with N-DBP formation still remain much uncertainty. Herein, we used fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to investigate AOM transformation in UV-LEDs/chlorine process, with UV₂₈₅ and UV₃₆₅ as light source, and screen for typical precursors of N-DBPs. We found that more nitrogen-containing compounds were generated after UV-LEDs/chlorine process, leading to the larger formation of N-DBPs in postchlorination. Compounds such as lignin, proteins, and amino sugars tends to be oxidized by reactive species in UV-LEDs/chlorine process. Further, compounds with higher O/C and higher weighted average double bond equivalence (DBE_w) are easier to form N-DBPs, including dichloroacetonitrile and trichloronitromethane. Also, influence factors including pH, UV fluence, post-chlorination time and bromide concentration on N-DBP formation were evaluated. The results show that N-DBP formation generally followed the order of UV₂₈₅/chlorine-postchlorination, UV₃₆₅/chlorine-postchlorination, and direct chlorination. Our study provides comprehensive information on N-DBP formation from AOM in UV-LEDs/chlorine-postchlorination from molecular levels.

Concept of Flocks Fragmentation and Averaging Method for the Application of Electrocoagulation in Process for Coke Oven Wastewater Treatment

The main objective of the article is to develop the concept of flock fragmentation and the averaging method for the application of electrocoagulation in the process of treating wastewater from coke ovens. The designed solution was part of an innovative system for the coke oven wastewater treatment process. The system is dedicated to removing the hazardous elements and compounds from wastewater from leaching ashes in municipal waste incineration plants. The design of the process and its automatization was based on a quantitative simulation method. The balance equations of mass, energy, and momentum of transport, complemented by the kinetics of the related reaction, are used during the calculation of the process. The main result achieved is a practical solution-the reactor's scheme, classified due to a patent procedure in the Polish Patent Office.

Coagulation removal of phosphorus from a southern China reservoir in different stages of algal blooms: Performance evaluation and AlP matching principle analysis

Due to excessive nutrient discharge, many reservoirs in southern China suffer from eutrophication and harmful algal blooms. Several methods for phosphorus (P) removal have been proposed, including coagulation, adsorption, and biological methods. Among these methods, coagulation is preferable because of its quick effect, simple operation, and low cost. To investigate the effect and mechanism of coagulation on dephosphorization in reservoir water, the performances of Al-based (AlCl₃ and polyaluminum chloride (PACl)) and Fe-based coagulants (FeCl₃ and FeSO₄) were evaluated in this work. For reservoir water with a total phosphorus (TP) concentration of approximately 0.080 mg/L, aluminum salts showed stable advantages in dephosphorization. AlCl3 reduced the TP level by over 90% when treating the water sample collected at the initial stage of algal blooms, and PACl reduced by over 80% during the blooming stage. To reveal the dephosphorization mechanism and AlP matching principle, synthesized water samples were prepared and treated with AlCl₃ and [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺ (Al₁₃). While simulating the water quality characteristics of reservoir water, important influencing factors were considered. The factors include P content (dissolved phosphorus (DP) and particulate phosphorus (PP)), pH, and extracellular organic matter (EOM). The pH was set to 7.66 and 8.29, with PP proportion set to 20%, 50%, and 80%. Simulated water treatment results indicated that, except for the coagulants species, pH significantly affected the dephosphorization efficiency. Moreover, the effects of P speciation and EOM were confirmed. Based on the coagulation performance and coagulation product characterization, chemical precipitation and inner-sphere complexation were estimated to be the most predominant way that DP and PP match with Al and were efficiently removed by Al-based coagulants.

Magnetically attracted iron scrap anode based electrocoagulation for phosphate removal

This study shows the effectiveness of a novel electrocoagulation process using magnetically attracted iron scrap anodes for phosphate removal from aqueous solution. The effect of contact time, reaction temperature, dose of iron scrap, initial phosphate concentration, applied voltage, pH, magnetic force, and the species of competing anions on the efficiency of phosphate removal and the reaction products has been investigated. The techniques of XRD, XPS, and VSM were used to characterize the elemental composition and the types of the reaction products in order to clarify the interaction between novel anode and phosphate ions. The removal of phosphate was fitted by a pseudo first-order reaction kinetic model. The results showed that magnetically attracted iron scrap anodes were electrodissoluted under an applied potential and reacted with phosphate into Fe-hydroxo-phosphate complexes. The work suggested that electrocoagulation using magnetically attracted iron scrap anodes had the potential to become a promising technique for phosphate precipitation.

Electron storage and resupply modes during sulfur cycle enhanced nitrogen removal stability in electrochemically assisted constructed wetlands under low temperature

In this work, an electrochemically assisted vertical flow constructed wetland (E-VFCW) achieved efficient PO₄^3--P (92.9-96.6%), NO₃^--N (50.8-91.8%) and TN (38.8-73.1%) removal from synthetic sewage effluent within 1-12 h at 12 °C. Abiotic reduction, Fe(II)-, S- and H₂-dependent denitrification, as well as coupling of fermentation, acetogenesis and heterotrophic denitrification might facilitate NO₃^--N removal in the E-VFCW. Particularly, electron resupply for NO₃^--N reduction by the in-situ deposited FeS, FeS₂ and S⁰ in the E-VFCW would occur during electron supply-demand disequilibrium situations (e.g., lower HRT or temperature). Stoichiometric results suggested that 21.7-278.7 mmol e^- d^-1 from the in-situ deposited S contributed to NO₃^--N reduction under HRT of 1-6 h at 12 °C, which improved the resilience capabilities of the E-VFCW to temperature and nitrogen loads fluctuations. Overall, this work provides new insights into the modes of S cycle mediating NO₃^--N conversions in the E-VFCW under low temperature.

Evaluation of phosphorus removal from a lake by two drinking water treatment plants

The impact of drinking water treatment plants on phosphorous in a lake has never been previously reported. In this mass balance study, phosphorus removal by a conventional plant and a membrane plant on Lake Simcoe was monitored. Approximately 16 kg of phosphorus per year were removed from the lake by the membrane plant, representing 72% of the influent phosphorous load to the plant. The membrane plant did not practice coagulation, so approximately two-thirds of the removal was via circulation of the treated water to the municipal wastewater treatment plant where phosphorous was removed. The remaining third was removed by the membranes. The conventional plant removed approximately 10 kg of phosphorus per year, representing 92% of the influent phosphorus loading. In this plant, polyaluminum chloride coagulation and subsequent sludge removal were responsible for approximately two-thirds of the phosphorous removal, with the remainder removed via circulation of the treated water to the municipal wastewater treatment plant.

Treatment and characterization of phosphorus from synthetic wastewater using aluminum plate electrodes in the electrocoagulation process

The main objective of this study is treatment and characterization of phosphorus from synthetic wastewater using aluminum electrodes in the electrocoagulation process. EC experimental setups were designed and different parameters were optimized. The maximum amounts of phosphorus removal efficiencies were observed at pH 7. The phosphorus removal efficiency increases from 85.16 to 97.65% as the temperature increases from 15 to 45 °C, beyond this temperature, there is small effect on removal efficiency. Pollutant removal efficiency increases with an increase in the electrolysis time. At lower initial concentrations the removal efficiencies reached to their maximum values while at the highest initial concentration, the phosphorus removal efficiency was decreased. The increase of current density improves the efficiency of phosphorus removal. Energy and aluminum consumption decreases with increasing initial concentration of phosphorus. Field Emission Scanning Electron Microscope (FESEM) image analysis demonstrated very fine structures for aluminum hydroxide/oxyhydroxides and aluminum phosphate. The existence of the different elemental composition in the sludge was proved by the help of Energy Dispersive X-ray Analysis (EDXS), indicating that the aluminum, oxygen and phosphorus were present in the product. From X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and Raman analyses of the sludge product, it is concluded that the chemical speciation of the by-products can be mostly aluminum hydroxide and aluminum phosphate.

The variation of flocs activity during floc breakage and aging, adsorbing phosphate, humic acid and clay particles

The mechanism of removal of humic acid, phosphate and kaolin particles by coagulation with alum and PACl or adsorption by their pre-formed precipitates was investigated, and it was found that the coagulation mechanisms for monomeric Al at neutral pH and polymeric Al₁₃ at alkaline pH were very similar. The removal of phosphate and humic acid by coagulation with alum or PACl did not change with stirring time (between 1 min and 15 min), independent of the dose and species of coagulants. However, for adsorption of these impurities by pre-formed precipitates, the results were significantly different. Both Al³⁺ and nano-sized Al₁₃ could precipitate and form aggregates at pH 7 and pH 9, respectively, and their precipitates became less active (fewer binding sites on the surface of precipitate) with the increase of shear time or shear rates before adsorbing pollutants. Thus, although the total surface area increased (the average size of flocs became smaller) at higher applied shear rates or longer shear time, the removal efficiency of humic acid and phosphate decreased. Also, from the MW distributions, it was confirmed that less humic acid was removed by the adsorption on alum precipitate pre-formed with longer shear time. Chemical groups (OH₂and OH) on the surface of precipitate determined the removal efficiency of phosphate and humic acid, and the activity of precipitate become lower as a result of higher applied shear and longer shear time. This is confirmed be due to some crystallization of the amorphous precipitate, forming inactivated hydroxyl. When kaolin was added 10 min after the alum or PACl precipitate formed, the precipitates captured kaolin particles only on their surface, whereas when alum was added to kaolin suspensions particles were trapped within the growing flocs. When alum/kaolin flocs were broken at high shear rate re-growth of flocs decreased with increasing shear time, but after a short breakage period, long aging of broken flocs had little effect on floc regrowth.

Effective adsorption of trace phosphate and aluminum in realistic water by carbon nanotubes and reduced graphene oxides

In this study, carbon nanotube (CNT) and reduced graphene oxide (rGO) were studied for their potentials as novel adsorbents for trace concentrations of phosphorus and aluminum in water and wastewater. Static adsorption results demonstrated that CNT and rGO employed in this study removed up to 65.6% of total dissolved Al and 98.9% of P from a natural surface water and a secondary wastewater effluent. Hydrogen-bonding interactions between CNT/rGO and oxyanions were hypothesized to contribute to the adsorption process. Accordingly, acetaminophen (AAP), a pharmaceutical compound known to form hydrogen bonding with CNT, was spiked into the real water as a competitor for P and Al adsorption. Subsequent sorption results showed that the presence of AAP reduced Al and P adsorption by CNT and rGO by 9.3%-18.4% and 11.2%-18.2%, respectively. These results suggest that hydrogen bonding interactions with CNT/rGO influenced the adsorption of P and Al species. In addition, pH effect investigation on Al/P removal further verified the above opinion. Overall, this study provided important evidence and insights into CNT/rGO adsorption of P and Al species from water and wastewater, which expanded our understanding on the ability of carbonaceous nanomaterials for advanced water and wastewater treatment.

A Review of Fouling Mechanisms, Control Strategies and Real-Time Fouling Monitoring Techniques in Forward Osmosis

Forward osmosis has gained tremendous attention in the field of desalination and wastewater treatment. However, membrane fouling is an inevitable issue. Membrane fouling leads to flux decline, can cause operational problems and can result in negative consequences that can damage the membrane. Hereby, we attempt to review the different types of fouling in forward osmosis, cleaning and control strategies for fouling mitigation, and the impact of membrane hydrophilicity, charge and morphology on fouling. The fundamentals of biofouling, organic, colloidal and inorganic fouling are discussed with a focus on recent studies. We also review some of the in-situ real-time online fouling monitoring technologies for real-time fouling monitoring that can be applicable to future research on forward osmosis fouling studies. A brief discussion on critical flux and the coupled effects of fouling and concentration polarization is also provided.

Treatment of industrial estate wastewater by the application of electrocoagulation process using iron electrodes

In this study electrocoagulation (EC) of industrial estate wastewater taken from the inlet of wastewater treatment plant was investigated using sacrificial iron electrodes. Employing a pole changer to homogenous consumption of electrodes, studies on the parameters such as current density, supporting electrolyte concentration and initial pH, which have significant effects on COD removal and hence the energy consumption, were performed. Hydrogen peroxide was used in different concentrations to observe its effects on COD removal efficiency and the energy consumption. Sludge productions were also calculated for all experiments. COD removal efficiency of ∼92% was obtained at the best experimental conditions (i = 30 mA/cm², SE = 3 mM Na₂SO₄, pH = original pH (∼6) of the wastewater, 1500 mg/L H₂O₂) with an energy cost of €3.41/m³ wastewater treated and the sludge production of 5.45 g per g COD removed.

Arsenic removal by electrocoagulation process: Recent trends and removal mechanism

Arsenic contamination in drinking water is a major issue in the present world. Arsenicosis is the disease caused by the regular consumption of arsenic contaminated water, even at a lesser contaminated level. The number of arsenicosis patients is increasing day-by-day. Decontamination of arsenic from the water medium is the only one way to regulate this and the arsenic removal can be fulfilled by water treatment methods based on separation techniques. Electrocoagulation (EC) process is a promising technology for the effective removal of arsenic from aqueous solution. The present review article analyzes the performance of the EC process for arsenic removal. Electrocoagulation using various sacrificial metal anodes such as aluminium, iron, magnesium, etc. is found to be very effective for arsenic decontamination. The performances of each anode are described in detail. A special focus has been made on the mechanism behind the arsenite and arsenate removal by EC process. Main trends in the disposal methods of sludge containing arsenic are also included. Comparison of arsenic decontamination efficiencies of chemical coagulation and EC is also reported.

Electrochemical oxidation of iron and alkalinity generation for efficient sulfide control in sewers

The addition of iron salts is one of the most commonly used dosing strategies for sulfide control in sewers. However, iron salts decrease the sewage pH which not only reduces the effectiveness of sulfide precipitation but also enhances the release of residual sulfide to the sewer atmosphere. Equally important, concentrated iron salt solutions are corrosive and their frequent transport, handling, and on-site storage often come with Occupational Health and Safety (OH&S) concerns. Here, we experimentally demonstrated a novel sulfide control approach using electrochemical systems with parallel placed iron electrodes. This enabled combining anodic dissolved iron species release with cathodic hydroxyl anion production, which alleviates all the aforementioned concerns. A long-term experiment was successfully carried out achieving an average sulfide removal efficiency of 95.4 ± 4.4% at low voltage input of 2.90 ± 0.54 V over the course of 8 weeks. This electrochemical method was demonstrated to successfully achieve efficient sulfide control. In addition, it increases the sewage pH, thereby overcoming the drawbacks associated with the pH decrease in the case of conventional iron salt dosing. Ferrous ions were produced at an overall coulombic efficiency (CE) of 98.2 ± 1.2%, whereas oxygen evolution and direct sulfide oxidation were not observed. Short-term experiments showed that increasing either inter-electrode gap or current density increased the cell voltage associated with the increase in the ohmic drop of the system. Overall, this study highlights the practical potential of in-situ generation of dissolved iron species and simultaneous hydroxyl anion generation for efficient sulfide control in sewers.

Synergy of flocculation and flotation for microalgae harvesting using aluminium electrolysis

Microalgae are often used as feedstock for renewable biofuel production and as pollutant up-takers for wastewater treatment; however, biomass harvesting still remains a challenge in field applications. In this study, electro-flocculation using aluminium electrolysis was tested as a method to collect Chlorella vulgaris. The electrolysis products were positively charged over a wide pH range below 9.5, which gave them a flocculation potential for negatively charged microalgae. As flocculants were in-situ generated and gradually released, microalgae flocs formed in a snowballing mode, resulting in the compaction of large flocs. When higher current density was applied, microalgae could be harvested more rapidly, although there was a trade-off between a higher energy use and more residual aluminium in the culture medium. Benefits of this flocculation method are twofold: the phosphate decrease in post-harvesting could improve nutrient removal in microalgae based wastewater treatment, while the ammonium increase may favor microalgae recovery for medium recycling.

Intensified nitrate and phosphorus removal in an electrolysis -integrated horizontal subsurface-flow constructed wetland

A novel electrolysis-integrated horizontal subsurface-flow constructed wetland system (E-HFCWs) was developed for intensified removal of nitrogen and phosphorus contaminated water. The dynamics of nitrogen and phosphorus removal and that of main water qualities of inflow and outflow were also evaluated. The hydraulic retention time (HRT) greatly enhanced nitrate removal when the electrolysis current intensity was stabilized at 0.07 mA/cm². When the HRT ranged from 2 h to 12 h, the removal rate of nitrate increased from 20% to 84%. Phosphorus (P) removal was also greatly enhanced-exceeding 90% when the HRT was longer than 4 h in the electrolysis-integrated HFCWs. This improved P removal is due to the in-situ formation of ferric ions by anodizing of sacrificial iron anodes, causing chemical precipitation, physical adsorption and flocculation of phosphorus. Thus, electrolysis plays an important role in nitrate and phosphorus removal. The diversity and communities of bacteria in the biofilm of substrate was established by the analysis of 16S rDNA gene sequences, and the biofilm was abundant with Comamonadaceae and Xanthomonadaceae bacteria in E-HFCWs. Test results illustrated that the electrolysis integrated with horizontal subsurface-flow constructed wetland is a feasible and effective technology for intensified nitrogen and phosphorus removal.

Phosphorus removal and recovery from dairy manure by electrocoagulation

Removal of 96.7% of phosphorus from dairy manure via electrocoagulation with low carbon steel electrodes.

Zr(IV) loaded cross-linked chitosan beads with enhanced surface area for the removal of nitrate and phosphate

In this work, a new method namely silica dissolution method, has been adapted to increase the surface area of the cross-linked chitosan beads. Zr(IV) was loaded in the cross-linked chitosan beads in order to make it selective for the nitrate and phosphate anions from aqueous solutions. Zr(IV) loaded cross-linked chitosan beads prepared by normal method (ZrCB) and silica dissolution method (SD-ZrCB) were characterised using N2 adsorption/desorption studies, SEM, EDAX, XRD, FTIR, TGA, DTA and water regain property. The SD-ZrCB exhibited higher N2 adsorption, water regain property as well as anion adsorption capacity than ZrCB. Batch method was adapted for the adsorption studies. The nitrate and phosphate adsorbed SD-ZrCB was regenerated using 0.025M NaCl solution. There was not much drop in adsorption capacities up to 10th regeneration cycle. Freundlich adsorption isotherm was the best fit adsorption isotherm among Freundlich, Langmuir and Dubinin-Radushkevich (D-R) isotherms which have been used to fit the nitrate and phosphate adsorption data. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of adsorption process.

Arsenic Removal from Natural Groundwater by Electrocoagulation Using Response Surface Methodology

Contamination of natural groundwater by arsenic (As) is a serious problem that appears in some areas of Northern Central Mexico (NCM). In this research, As was removed from NCM wells groundwater by the electrocoagulation (EC) technique. Laboratory-scale arsenic electroremoval experiments were carried out at continuous flow rates between 0.25 and 1.00 L min−1using current densities of 5, 10, and 20 A m−2. Experiments were performed under galvanostatic conditions during 5 min, at constant temperature and pH. The response surface methodology (RSM) was used for the optimization of the processing variables (flow rate and current density), response modeling, and predictions. The highest arsenic removal efficiency from underground water (99%) was achieved at low flow rates (0.25 L min−1) and high current densities (20 A m−2). The response models developed explained 93.7% variability for As removal efficiency.

Recovery of hydrogen and removal of nitrate from water by electrocoagulation process

The present study provides an optimization of electrocoagulation process for the recovery of hydrogen and removal of nitrate from water. In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. Aluminum alloy of size 2 dm(2) was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. The results show that a significant amount of hydrogen can be generated by this process during the removal of nitrate from water. The energy yield calculated from the hydrogen generated is 3.3778 kWh/m(3). The results also showed that the maximum removal efficiency of 95.9% was achieved at a current density of 0.25 A/dm(2), at a pH of 7.0. The adsorption process followed second-order kinetics model. The adsorption of NO3(-) preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. Thermodynamic studies showed that adsorption was exothermic and spontaneous in nature. The energy yield of generated hydrogen was ~54% of the electrical energy demand of the electrocoagulation process. With the reduction of the net energy demand, electrocoagulation may become a useful technology to treat water associated with power production. The aluminum hydroxide generated in the cell removes the nitrate present in the water and reduced it to a permissible level making the water drinkable.

Oxidized multiwalled carbon nanotubes as adsorbent for the removal of manganese from aqueous solution

A batch adsorption process was applied to investigate the removal of manganese from aqueous solution by oxidized multiwalled carbon nanotubes (MWCNTs). In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. MWCNT with 5-10-nm outer diameter, surface area of 40-600 m(2)/g, and purity above 95 % was used as an adsorbent. A systematic study of the adsorption process was performed by varying pH, ionic strength, and temperature. Manganese-adsorbed MWCNT was characterized by Raman, FTIR, X-ray diffraction, XPS, SEM, and TEM. The adsorption efficiency could reach 96.82 %, suggesting that MWCNT is an excellent adsorbent for manganese removal from water. The results indicate that second-order kinetics model was well suitable to model the kinetic adsorption of manganese. Equilibrium data were well described by the typical Langmuir adsorption isotherm. Thermodynamic studies revealed that the adsorption reaction was spontaneous and endothermic process. The experimental results showed that MWCNT is an excellent manganese adsorbent. The MWCNTs removed the manganese present in the water and reduced it to a permissible level making it drinkable.

Removal of copper from water by electrocoagulation process--effect of alternating current (AC) and direct current (DC)

PURPOSE AND AIM: In general, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of copper from water using magnesium alloy as anode and cathode.

MATERIALS AND METHODS

Magnesium alloy of size 2.0 dm(2) was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. Copper adsorbed magnesium hydroxide coagulant was characterized by SEM, EDAX, XRD, and FTIR.

RESULTS

The results showed that the optimum removal efficiency of copper is 97.8 and 97.2 % with an energy consumption of 0.634 and 0.996 kWh/m(3) at a current density of 0.025 A/dm(2), pH of 7.0 for AC and DC, respectively. The adsorption of copper is preferably fitting the Langmuir adsorption isotherm for both AC and DC respectively. The adsorption process follows the second-order kinetics model with good correlation. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

CONCLUSIONS

The magnesium hydroxide generated in the cell removes the copper present in the water, reducing the copper concentration to less than 1 mg/L, making it safe for drinking. The results of the scale-up study show that the process was technologically feasible.

Biofouling of water treatment membranes: a review of the underlying causes, monitoring techniques and control measures

Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategies. This paper highlights the underlying causes of membrane biofouling and provides a review on recent developments of potential monitoring and control methods in water and wastewater treatment with the aim of identifying the remaining issues and challenges in this area.

Enhanced trace phosphate removal from water by zirconium(IV) loaded fibrous adsorbent

This study was investigated for the trace phosphate removal at high feed flow rate by ligand exchange fibrous adsorbent. The zirconium(IV) loaded bifunctional fibers containing both phosphonate and sulfonate were used as a highly selective ligand exchange adsorbent for trace phosphate removal from water. The precursory fiber of the bifunctional fibers was co-grafted by polymerization of chloromethylstyrene and styrene onto polyethylene coated polypropylene fiber and then bifunctional fibers were prepared by Arbusov reaction followed by phosphorylation and sulfonation. Phosphate adsorption experimental work was carried out in column approach. Phosphate adsorption increased with decreasing the pH of feed solutions. An increase in the feeds flow rate brings a decrease in both breakthrough capacity and total adsorption. The effect of competing anions on phosphate adsorption systems was investigated. The experimental findings reveal that the phosphate adsorption was not affected in the presence of competing anions such as chloride and sulfate despite the enhancement of the breakthrough points and total adsorption. Due to high selectivity to phosphate species, low concentration level of phosphate (0.22 mg/L) was removed at high feed flow rate of 450 h(-1) in space velocity. The adsorbed phosphate on the Zr(IV) loaded fibrous column was quantitatively eluted with 0.1 M NaOH solution and then the column was regenerated by 0.5M H2SO4 for the next adsorption operation. During many adsorption-elution-regeneration cycles, no measurable Zr(IV) was found in the column effluents. Therefore, the Zr(IV) loaded bifunctional fibrous adsorbent is to be an effective means to treat wastewater to prevent eutrophication in the receiving water bodies for long time without any deterioration.

Effects of alternating and direct current in electrocoagulation process on the removal of cadmium from water

In practice, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of cadmium from water using aluminum alloy as anode and cathode. The results showed that the removal efficiency of 97.5 and 96.2% with the energy consumption of 0.454 and 1.002 kWh kl(-1) was achieved at a current density of 0.2A/dm(2) and pH of 7.0 using aluminum alloy as electrodes using AC and DC, respectively. For both AC and DC, the adsorption of cadmium was preferably fitting Langmuir adsorption isotherm, the adsorption process follows second order kinetics and the temperature studies showed that adsorption was exothermic and spontaneous in nature.

Optimization of electrocoagulation process for the simultaneous removal of mercury, lead, and nickel from contaminated water

PURPOSE AND AIM: The present study provides an optimization of electrocoagulation process for the simultaneous removal of heavy metals such as mercury, lead, and nickel from water. In doing so, the thermodynamic, adsorption isotherm and kinetic studies were also carried out.

MATERIALS AND METHODS

Magnesium alloy, magnesium, aluminum, and mild steel sheet of size 2 dm(2) were used as anode and galvanized iron as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. Mercury-, lead-, and nickel-adsorbed magnesium hydroxide coagulant was characterized by SEM and EDAX.

RESULTS

The results showed that the maximum removal efficiency was achieved for mercury, lead, and nickel with magnesium alloy as anode and galvanized iron as cathode at a current density of 0.15 Å/dm(2) and pH of 7.0. The adsorption of mercury, lead, and nickel are preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. The adsorption process follows second-order kinetics. Temperature studies showed that adsorption was endothermic and spontaneous in nature.

CONCLUSIONS

The magnesium hydroxide generated in the cell removes the heavy metals present in the water and reduces to a permissible level, making it drinkable.