Dilute Effluents Research Articles

Competitive recovery of copper ions using ethyl acetoacetate modified chitosan/organo-functionalized alginate hydrogel beads: kinetics and isothermal sorption studies

Surface functionalization of chitosan using some chelating ligands not only improves sorption capacity but also induces selectivity into the biopolymer. The current study is based on the facile synthesis of ethyl acetoacetate modified chitosan and surface-functionalized alginate composite beads (EAA-MCSA). Chemical modification of sodium alginate was carried out to graft amino thiocarbamate moiety (-OCSNHNH2) to entrench selectivity and specificity across the linear chains of preliminary polysaccharide. Biosorbent (EAA-MCSA) was thoroughly characterized by FT-IR and SEM analysis and employed in the form of composite hydrogel beads for competitive Cu(II) recovery. Newly grafted aminothiocarbamate (-OCSNHNH2) and 1,3-dicarbonyl moieties (-COCH2CO-) are supposed to act as potential chelating sites for enhanced Cu(II) sorption. Kinetic data could be well depicted using pseudo-second order rate law (R2 = 0.99, qexp≈qe,th = 85.25 mg/g, k2 = 0.45–1.17 ×10−2 g/mg.min−1) and sorption data was found in close agreement with Langmuir adsorption isotherm (R2 = 0.99, qm= 390.21 mg/g at 298 K and pH = 6.0, KL= 0.44–0.49 ×10−2 L/mg). The ΔG° values (−20.75, −21.10, −21.30 and −21.50 kJ/mol) and positive ΔH° (−7.63 kJ/mol) designated the sorption process as spontaneous and exothermic, respectively. Hence, EAA-MCSA could be a better sorbent for adsorptive remediation of Cu(II) from dilute effluents.

Effective Usage of Biochar and Microorganisms for the Removal of Heavy Metal Ions and Pesticides.

The bioremediation of heavy metal ions and pesticides is both cost-effective and environmentally friendly. Microbial remediation is considered superior to conventional abiotic remediation processes, due to its cost-effectiveness, decrement of biological and chemical sludge, selectivity toward specific metal ions, and high removal efficiency in dilute effluents. Immobilization technology using biochar as a carrier is one important approach for advancing microbial remediation. This article provides an overview of biochar-based materials, including their design and production strategies, physicochemical properties, and applications as adsorbents and support for microorganisms. Microorganisms that can cope with the various heavy metal ions and/or pesticides that enter the environment are also outlined in this review. Pesticide and heavy metal bioremediation can be influenced by microbial activity, pollutant bioavailability, and environmental factors, such as pH and temperature. Furthermore, by elucidating the interaction mechanisms, this paper summarizes the microbe-mediated remediation of heavy metals and pesticides. In this review, we also compile and discuss those works focusing on the study of various bioremediation strategies utilizing biochar and microorganisms and how the immobilized bacteria on biochar contribute to the improvement of bioremediation strategies. There is also a summary of the sources and harmful effects of pesticides and heavy metals. Finally, based on the research described above, this study outlines the future scope of this field.

A novel pre-dilution, swirling jet diffuser to enhance effluent mixing: Hydrodynamics and dilution performance

Diffusers are widely-used to quickly dilute effluents in receiving water bodies. This study proposed a novel diffuser that pre-mixes effluent with ambient water before discharging and that uses the swirling jet to further enhance near-field dilution. The nozzle of the diffuser was examined in two ambient flow conditions: co-flow and counter-flow that are commonly-met in the environment such as oceans due to tidal effect. Physical experiments were first conducted in co-flow on its dilution performance and hydrodynamics, using heated water as the effluent. A 3-D CFD model was developed and calibrated the co-flow scenarios, and then used to investigate the diffuser in counter-flow. The results showed that the nozzle can effectively reduce the maximum temperature rise of the effluent by about 50 % before discharging. The swirling jet from the outlet has a larger shear area, half-width and entrainment rate, enabling the effluent to be rapidly diluted to a minimum of around 10 times at x/D = 6 in co-flow, whereas the dilution for conventional nozzles is about 1 because of the potential core. The flow amplification ratio (α) decreases gradually with increasing velocity ratio in co-flow but increases with increasing velocity ratio in counter-flow. The counter-flow reduces the water drawn into the device; however, the pre-dilution effect at the outlet remains stable. The near-field dilution in counter-flow was significantly enhanced than that in co-flow. Environmental regulations at outfalls and mixing zones can be more easily met using this novel diffuser.

Synthesis of hybrid biosorbent based on 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and organo-functionalized calcium alginate for adsorptive removal of Cu(II)

The present study is based on the synthesis of a novel hybrid biosorbent using 1,2-cyclohexylenedinitrilotetraacetic acid modified crosslinked chitosan and amino-thiocarbamate moiety functionalized sodium alginate (CDTA-CS/TSC-CA). The fabricated sorbent was employed to investigate the efficient recovery of Cu(II) from aqueous media. CDTA-CS/TSC-CA was characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Analysis confirmed the successful modification of both biopolymers and subsequent loading of Cu(II) ions. CDTA-CS/TSC-CA was casted in the form of hydrogel beads having different CDTA-CS to TSC-CA mass ratios i.e., 10.0–40.0% by mass. The hydrogel beads 4CDTA-CS/TSC-CA with CDTA-CS/TSC-CA mass ratio of 40.0% was found most effective for copper sorption. Equilibrium sorption results showed that initial concentration of copper, medium pH, contact time, sorbent dosage and temperature influenced the sorption capacity (qe). Rate of sorption data was interpreted using different kinetic models and found best fitted with pseudo second order rate expression (R2 ≈ 0.99), illustrating that the rate determining step includes the electron density transfer from sorbent coordination sites to central copper ions. Crank's RIDE equation and Elovich chemisorption model (ECM) revealed the presence of two sorption phases, initially rapid sorption followed by comparatively a slow uptake. Equilibrium sorption data was well depicted by Langmuir model and maximum monolayer adsorption capacity (qm) was computed as 276.53 mg·g−1 at 298 K. Standard Gibbs free energy change, ∆G° (−19.99, −20.18 and −20.36 kJ/ mol), standard enthalpy change, ∆H° (−8.95 kJmol) and standard entropy change, ∆S° (0.04 kJ/mol K−1) values suggested that the adsorption process is spontaneous and exothermic. Hence, 4CDTA-CS/TSC-CA was found efficient biosorbent for copper removal from its dilute effluents.

The relationship between the pH value of dilute effluent streams and system durability in the separate bed electrodeionization process

The successful application of electrodeionization (EDI) for the preparation of ultra-pure water has been encouraging researchers to explore its feasibility in the treatment of heavy metal electroplating wastewaters. Based on the separate bed membrane stack, the relationship between the pH of dilute effluent streams and its long-term operation stability was investigated. The pH, conductivity, electric current and voltage were recorded on-line with cupric ions contents measured off-line. The microstructure and morphology of ion exchange resins and membranes were studied with infrared spectroscopy and scanning electron microscopy. It is the adsorption saturation in the cation exchange resins-filled compartment (CR-cell) that results in the acidity of dilute effluent waters due to the consumption of hydroxide ions in the anion exchange resins-filled compartment (AR-cell). The periodic change of acidity and alkalinity of dilute effluents was caused by the alternative processes of adsorption saturation and hydrolysis regeneration in CR-cell. The conversion of quaternary amines into tertiary ones of the anion resins and membranes owing to hygro-thermal aging weakened alkaline and shortened the acid-base change period. Increasing stack voltage and intermittent leaching play an important role in prolonging the service life of EDI, and make it feasible to remove heavy metal ions from industrial wastewaters.

Interfacial Catalysis in Biphasic Carboxylic Acid Esterification with a Nickel-Based Metallosurfactant

A metallosurfactant catalyst was developed to address the requirements for the utilization of low-molecular-weight carboxylic acids from dilute effluents. The catalyst Ni(DBSA)2 combines transition...

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Effluents containing heavy metals are hazardous to human health and the environment even at low concentrations. It is costly and unsustainable to use conventional methods to remove heavy metals from dilute effluents. Microalgal biomass owing to its high metal biosorption capacity, is a promising alternative biosorbent for treating dilute heavy metal solutions. However, the application of freely suspended algal biomass for metal removal has a number of drawbacks such as small particle size, low chemical resistance, low mechanical strength, and difficulty in separation of biomass and effluent. The present article reviews the techniques used to address these drawbacks. It also discusses the key factors affecting biosorption efficiency including initial concentration of metal ions, contact time, solution pH, solution temperature, biosorbent concentration, agitation rate, and competing ions. Biomass cross-linking with appropriate agents such as polysolfane, formaldehyde, or chlorohydrin could improve mechanical strength, chemical resistance, and separation of the biomass from the effluent. However, cross-linked biomass usually shows low sorption capacity and slow rate of metal uptake. These disadvantages could be minimized by using physical and/or chemical pretreatments prior to biomass cross-linking. Alkaline detergent, sodium hydrogen carbonate without autoclaving, sodium hydroxide or sodium carbonate plus autoclaving, or supercritical carbon dioxide at mild conditions are among the most effective pretreatments. Apart from liberating more latent metal binding sites on the biomass, supercritical CO2 could also improve the porosity of the biomass thereby improving sorption rate of the cross-linked biomass. High sorption capacity and rapid metal uptake will allow substantial reduction in size of biosorption columns, which will consequently improve the economic and sustainability features of algal-based metal biosorption processes.

Recovery of Silver from Dilute Effluents via Electrodeposition and Redox Replacement

In this study, the electrodeposition-redox replacement (EDRR) method was studied for the recovery of minor concentrations of silver from dilute solutions. The parameter optimization was carried out with synthetic solutions similar to silver oxide button battery recycling effluents, consisting of sulfuric acid and concentrated base metal (10 g·L−1 H2SO4, 60 g/L Zn2+) with a minor amount of silver (100 ppm) and a varying amount of Fe3+ ions. Results of these experiments were analyzed both electrochemically and by use of SEM-EDS. The role of dissolved Fe3+ ions was studied by varying the concentration from 0 to 1000 ppm and the results showed that although the presence of Fe ions decreased silver recovery efficiency, final product purity was found to increase slightly. The EDRR process was also found to be more effective for Ag recovery and has less energy consumption when Fe3+ concentrations are relatively low (≤ 100 ppm) when compared with conventional direct current electrowinning. In the final stage, silver was successfully recovered via EDRR, using the optimized conditions, from a real pregnant leaching solution (PLS) obtained from the leaching of silver oxide batteries.

Wastewater treatment and reuse in urban agriculture: exploring the food, energy, water, and health nexus in Hyderabad, India

Nutrients and water found in domestic treated wastewater are valuable and can be reutilized in urban agriculture as a potential strategy to provide communities with access to fresh produce. In this paper, this proposition is examined by conducting a field study in the rapidly developing city of Hyderabad, India. Urban agriculture trade-offs in water use, energy use and GHG emissions, nutrient uptake, and crop pathogen quality are evaluated, and irrigation waters of varying qualities (treated wastewater, versus untreated water and groundwater) are compared. The results are counter-intuitive, and illustrate potential synergies and key constraints relating to the food–energy–water–health (FEW–health) nexus in developing cities. First, when the impact of GHG emissions from untreated wastewater diluted in surface streams is compared with the life cycle assessment of wastewater treatment with reuse in agriculture, the treatment-plus-reuse case yields a 33% reduction in life cycle system-wide GHG emissions. Second, despite water cycling benefits in urban agriculture, only <1% of the nutrients are able to be captured in urban agriculture, limited by the small proportion of effluent divertible to urban agriculture due to land constraints. Thus, water treatment plus reuse in urban farms can enhance GHG mitigation and also directly save groundwater; however, very large amounts of land are needed to extract nutrients from dilute effluents. Third, although energy use for wastewater treatment results in pathogen indicator organism concentrations in irrigation water to be reduced by 99.9% (three orders of magnitude) compared to the untreated case, crop pathogen content was reduced by much less, largely due to environmental contamination and farmer behavior and harvesting practices. The study uncovers key physical, environmental, and behavioral factors that constrain benefits achievable at the FEW-health nexus in urban areas.

Sorption of Rare Earth Metal Ions (La(III), Nd(III) and Er(III)) using Cellulose

Background: Rare earth elements, REEs, are used for many high-tech applications; the rarefaction of the resource requires developing methods for their recovery from low-grade sources and their recycling from waste materials. Sorption processes, including biosorbents, represent an interesting method for their recovery from dilute effluents. Keywords: Cellulose, sorption isotherms, uptake kinetics, rare earth metal ions, metal desorption, sorbent recycling, sorption thermodynamics.

Characterisation of potential aquaculture pond effluents, and physico-chemical and microbial assessment of effluent-receiving waters in central Ghana

An understanding of specific aquaculture systems and the impacts of their management practices leads to sound and cost-effective policies to protect the aquatic environment. Water samples were collected in 2009 from fish ponds, streams that receive effluents directly from ponds and reference streams in Ghana to assess potential environmental impacts of pond aquaculture. Although relatively dilute, fish ponds had higher levels of all physico-chemical variables measured compared to those of locations upstream and downstream of farms, and to reference locations. Total nitrogen and BOD5 were most clearly statistically significant. Of 292 earthen fish ponds surveyed in central Ghana, approximately 92% were used for either Oreochromis monoculture or Oreochromis–Clarias polyculture. These had similar pond water (i.e. potential effluent) quality but different management practices. The study ponds had the potential to pollute effluent-receiving streams, but their actual impacts will depend on how pond effluents are managed. Conventional treatment of effluents from these small-scale, low-volume operations, which discharge relatively dilute effluents infrequently, might not be cost-effective.

Bipolar membrane electrodialysis and ion exchange hybridizing for dilute organic acid solutions treatment

In this work, treatment of very dilute effluents of organic acids by means of an electro-membrane hybrid process is studied. Dilute organic acids effluents are generated by numerous processes. Converting such effluents into pure more concentrated fluxes is a key step in the valorization process. An experimental study has been performed to recover acetic acid by bipolar membrane electrodialysis (BMED). The experiments performed when coupling BMED and ion exchange have clearly demonstrated that hybridization reduces energy consumption. This improvement is due to the decrease of the electrical resistance of the diluted compartment thanks to the ionic conductivity provided by the resins. The effect of back diffusion on the current efficiency was also studied. In the case of acetic acid effluent treatment, investigation of the influence of the resin initial form showed that hydroxyl and acetate initial forms result in very close performances. It is therefore useless regenerating the resin bed.

Integrated culture of silver kob Argyrosomus inodorus and bloodworm Arenicola loveni loveni in abalone farm effluent

South African abalone Haliotis midae farms utilise large volumes of seawater (c. 500–1 500 l s–1) and produce relatively dilute effluents that are potentially suitable for the integrated culture of other species. To test this hypothesis, a marine finfish, silver kob Argyrosomus inodorus, and a detritivorous polychaete, bloodworm Arenicola loveni loveni, were cultured in abalone farm effluent and the results compared to controls reared in unused seawater. The silver kob were fed a nutritionally complete pelleted diet whereas the bloodworm were placed in shallow tanks with a low water velocity that allowed suspended organic solids to settle for the detritivorous worms to feed on. Silver kob growth rate (0.48% body weight d–1; SE = 0.01%), mortality (1.8 ± 0.5%), feed conversion ratio (3.0 ± 0.2) and protein efficiency ratio (1.0 ± 0.1) did not differ significantly between the effluent and control treatments. Bloodworm reared in abalone effluent grew well on the particulate organic waste matter in the effluent (0.39% body weight gain d–1; SE = 0.07%), whereas those in the seawater control lost weight at 0.19 ± 0.04% body weight d–1 over the experimental period. Bloodworm mortality did not differ significantly between effluent (6 ± 3%) and unused seawater (11 ± 8%) treatments. The faster growth of bloodworm in the abalone farm effluent was ascribed to the higher deposition rate of enriched organic solids (182 ± 56 g m–2 d–1) compared with those grown in the seawater control (46 ± 13 g m–2 d–1). It was concluded that abalone farm effluent is potentially suitable for the culture of both bloodworm and silver kob.

Recovery of high-purity silver directly from dilute effluents by an emulsion liquid membrane-crystallization process

An emulsion liquid membrane (ELM)-crystallization process, using hypophosphorous acid as a reducing agent in the internal aqueous phase, has been developed for the purpose of recovering high-purity silver directly from dilute industrial effluents (waste rinse water). After pretreatment with HNO 3, silver in waste rinse water can be reliably recovered with high efficiency through the established process. The main parameters in the process of ELM-crystallization include the concentration of carrier in the membrane phase, the concentration of reducing agent in the internal aqueous phase, and the treatment ratio, which influence the recovery efficiency to various extents and must be controlled carefully. The results indicated that more than 99.5% (wt.) of the silver ions in the external aqueous phase were extracted by the ELM-crystallization process, with an average efficiency of recovery of 99.24% (wt.) and a purity of 99.92% (wt.). The membrane phase can be used repeatedly without loss of the efficiency of recovery.

THREE-DIMENSIONAL ELECTRODES FOR THE REMOVAL OF METALS FROM DILUTE SOLUTIONS: A REVIEW

Electrochemical processes utilizing three-dimensional (3-D) electrodes have significant potential for a variety of applications, particularly for the treatment of dilute effluents. The use of electrons to reduce the metal species from solution can be regarded as “cleaner” technology than the use of a chemical reagent, which would further contaminate the waste stream. Literature detailing the studies of these electrodes has been extensively published. A review of such literature is presented, summarizing the various types of 3-D electrodes and certain design considerations.

Mercury Sorption on Chitosan

Mercury sorption on chitosan was investigated in batch and continuous systems. Chitosan sorption properties were determined through sorption isotherms. Langmuir and Freundlich equations were used for the modeling of isotherms at pH 5. In batch systems, maximum sorption capacities reached 550 mg Hg/g. Sorption kinetics have been studied as a function of sorbent particle size and stirring rate. Dynamic removal of mercury was tested in a fixed bed reactor investigating the following parameters: particle size, column size, flow velocity and metal ion concentration. Clark and Adams-Bohart models were evaluated for the simulation of breakthrough curves. This study shows that chitosan is an effective sorbent for the treatment and recovery of mercury from dilute effluents at near neutral pH.

Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Carbon felt is a potential material for electrochemical reduction of chromates. Very dilute solutions may be efficiently treated due to its large specific surface area and high porosity. In this work, the up-scaling of this technology is investigated using a new type of separated cell and once-through flow of industrial rinse water. A significant enhancement of the process is obtained due to copper deposition during long-term operation. The co-deposition and re-solution of copper occurs depending on the inlet chromate concentration. When previously deposited copper is present a current-free reduction of chromate takes place resulting in current efficiencies apparently above 100%. Very high space time yields are obtained even for effluents at low concentration and optimised conditions (high flow rates and pH 2). The economic feasibility of the technology is also considered. Continuous, single-pass operation results in lower energy requirements than batch processing. The economic potential of the process is also evaluated in comparison with chemical detoxification of chromate. The operating costs for the electrochemical treatment of very dilute effluents on a carbon felt electrode are 30% lower than for the chemical method.

Modelling potentials, concentrations and current densities in porous electrodes for metal recovery from dilute aqueous effluents

One-dimensional steady-state models have been developed for the recovery of Pb(II) ions from lead–acid battery recycling plant effluent by simultaneous lead and lead dioxide deposition, including oxygen evolution/reduction and hydrogen evolution as loss reactions. Both monopolar and bipolar reactor with porous graphite electrodes were modelled, as a design aid for predicting spatial distributions of potentials, concentrations, current densities and efficiencies, as well as specific electrical energy consumptions and by-pass currents. Since the industrial effluent contains a large excess of supporting electrolyte (Na2SO4), the electrical migrational contribution to reactant transport rates was neglected and the current density–potential relationship was described by the Butler–Volmer equation, allowing for both kinetic and mass transport control. The models were implemented and the governing equations solved using commercial finite element software (FEMLAB). The effects were investigated of electrolyte velocity, applied cathode potential, dissolved oxygen concentration and inlet Pb(II) ion concentration on single-pass conversion, current efficiency and specific electrical energy consumptions. According to model predictions, de-oxygenation of the inlet process stream was found to be crucial to achieving acceptable (i.e. >0.8) current efficiencies. Bipolar porous electrodes were also determined to be inappropriate for the recovery of Pb(II) from effluents, as the low concentration involved resulted in the predicted fraction of current lost as by-pass current, i.e. current not flowing in and out of the bipolar electrode, to be greater than 90% for the ranges of the variables studied.

Modelling Oxygen Transport in a Reedbed-constructed Wetland Purification System for Dilute Effluents

This paper describes a simple model of oxygen supply to aerobic microorganisms in a horizontal reedbed-constructed wetland. The model simulates oxygen transport through the water by diffusion and convection, and via the macrophyte plants to the microorganisms that reside on their roots. The model also describes nitrogen (N) transformation processes for organic material with high biological oxygen demand (BOD), ammonium and nitrate. Some of these transformation processes are aerobic and therefore constrained if the oxygen supply is inadequate. Parameter values have been selected for equations describing oxygen transport and N transformation rates to fit data from a functioning reedbed processing sewage from a rural community. This reedbed achieves a large reduction in ammonium concentration in the effluent. Since it is unlikely that so much ammonium could have been lost by volatilisation alone, this implies rapid transport of oxygen to the microorganisms to convert the ammonium to nitrate. This rate is substantially higher than that which can be explained by diffusion and convection through the water alone, suggesting an important role for oxygen transport via the plants to the roots.

NF270, a new membrane having promising characteristics and being suitable for treatment of dilute effluents from the paper industry

A good nanofiltration membrane for the paper mill waters is hydrophilic, having both high retention and high permeability, and it should be resistant to fouling and temperature increase. The membrane should also withstand alkaline and acidic cleaning and mechanical wear. Membranes having all these properties do not exit. Based on laboratory- and pilot-scale experiments one promising membrane is the NF270 from Dow. The membrane is rather hydrophilic and it has fairly high retention and permeability. However, its resistance to temperature is not sufficient for all applications in the paper industry. By using this membrane or other similar NF membranes in the high-shear cross-rotational CR-filter fluxes above 100 L/(m 2 h) and retentions over 80% for conductivity and total carbon are obtainable with many rather dilute effluents from the paper industry.