Metal-bearing Wastewaters Research Articles

Self-coagulating polyelectrolyte complexes for target-tunable adsorption and separation of metal ions

Metal-containing wastes in aquatic environments lead to public health hazards and valuable resource lose. Metal-bearing wastewater must be treated to remove heavy metals or recover precious metals. To achieve these, target-tunable adsorbents that bind cationic and anionic metal species were developed through facile polyelectrolyte complexation using polyethylenimine (PEI) and polyacrylic acid (PAA). Utilizing the properties of the two polyelectrolytes and pKa variabilities, stable tunable adsorbents were fabricated in water without additional solvents. The homogenous complex adsorbents were strategically synthesized via dissolution in 0.1 M NaOH and drop-wise addition of 1 M HCl, followed by crosslinking with glutaraldehyde. Consequently, the adsorbents in alternating weight ratios of 4:1 and 1:4 (PEI:PAA) exhibited good tunability and adsorption properties. The maximum single metal adsorption capacities were 1609.7 ± 49.6 and 558.6 ± 9.67 mg/g for gold and cadmium, respectively. The pseudo-second-order model fitted the kinetics data more appropriately and was recognized as the rate controlling step. In a binary mixture, gold selectivity was observed to be influenced by adsorption-reduction mechanism, which was elucidated by XRD and XPS. Moreover, the adsorbents demonstrated NO3– sequestration properties, a feat deemed important for environmental remediation of nitrate ions. Finally, sequential separation was achieved with ethylenediaminetetraacetic acid (EDTA) and acidified thiourea.

Sustainable Electrochemical Extraction of Metal Resources from Waste Streams: From Removal to Recovery

Due to the widespread application of heavy metals in steel making, electronics, batteries, leather tanning, and catalysis, considerable toxic heavy metal-bearing wastewater and solid waste are dire...

Synergistic removal of cadmium and organic matter by a microalgae-endophyte symbiotic system (MESS): An approach to improve the application potential of plant-derived biosorbents

Plant-derived materials as environmentally friendly biosorbents to remove heavy metals from wastewater have been extensively studied. However, the chemical oxygen demand (COD) increase caused by the plant-derived biosorbent has not been considered previously. In this study, water hyacinth was used as biosorbent to remove Cd(II) from wastewater. About 66% of Cd(II) was removed by the biosorbent with a maximum biosorption capacity (qmax) of 21.6 mg g−1. However, the COD of the filtrate increased from 0 to 292 mg L−1 during this process. Subsequently, endophytes, microalgae and the microalgae-endophyte symbiotic system (MESS) were assessed for the simultaneous Cd(II) and COD removal. Among these three systems, the MESS achieved the best performance. After 3 d of inoculation, the extent of total Cd(II) removal increased to 99.2% while COD decreased to 77 mg L−1. This study provides a new insight into the application of a plant-derived biosorbent in combination with microalgae and endophytes for the effective treatment of heavy metal-bearing wastewater.

High adsorptive potential of calcined magnetic biochar derived from banana peels for Cu2+, Hg2+, and Zn2+ ions removal in single and ternary systems.

The use of banana peel as a sustainable and low-cost precursor for the fabrication of effective biochar was exploited. Here, calcined magnetic biochar (CMB) was fabricated and characterized. CMB possesses surface acidic functional groups (-OH and COO-), porous structures, high saturation magnetization (39.55 emu/g), and larger surface area than the non-magnetic biochar (CB). The CMB adsorption performance (72.8, 75.9, and 83.4 mg/g for Zn2+, Cu2+, and Hg2+, respectively at pH 6) in a single component was described suitably by pseudo-second order kinetic model, Langmuir, and Redlich-Peterson adsorption isotherms. Notably, the selectivity factor values in the extended Langmuir isotherm indicated that CMB has higher adsorption affinity toward Hg2+ than Cu2+ and Zn2+ in the multi-component system. Owing to its high adsorption efficiency and fast and easy separation, the calcined magnetic biochar is considered promising and effective for the purification of heavy metal-bearing wastewater.

Fractionation and leachability of Fe, Zn, Cu and Ni in the sludge from a sulphate-reducing bioreactor treating metal-bearing wastewater.

This work presents and discusses experimental results on the characterisation and metal leaching potential of a biogenic, metal-rich sulphidic sludge, generated in a sulphate-reducing bioreactor, operated to treat acidic synthetic solutions bearing Fe, Zn, Ni and Cu. The sustainability of the metal removal bioprocess strongly depends on the fate of the sludge. To propose appropriate management practices, a detailed characterisation of the sludge is necessary. The granulometry, chemical composition and mineralogy of the sludge were initially determined. The mobility of the metals was assessed via a modified Tessier experimental procedure. The leachability of the sludge metal content was determined via a standard compliance method (EN 12457-2) and experiments designed to evaluate the effect of pH and time on metal leaching from the sludge. The sludge metal content sums up to 69.5% dw, namely iron (14.8%), zinc (18.7%), nickel (17.7%) and copper (18.2%) and, based on the criteria set by European Union, the sludge is characterised as hazardous and inappropriate for landfilling without any pretreatment. The sludge consists mainly of very fine poorly crystalline aggregates of Fe, Zn, Cu and Ni sulphides. The fine grain size, the poorly crystalline structure and the oxidation of sulphide upon exposure to water/air render the high metal content of the sludge recoverable.

FTIR spectroscopy and scanning electron microscopic analysis of pretreated biosorbent to observe the effect on Cr (VI) remediation

ABSTRACTVarious chemical and physical treatments have been applied to indigenously isolated cyanobacterial strain, Lyngbya putealis HH-15, to observe the effect on chromium removal capacity. Pretreatment with hydrochloric acid (99.1%) and nitric acid (98.5%) resulted in enhanced chromium removal as compared to untreated control biosorbent (98.1%). Pretreatment with acetic acid (97.9%), methanol (97.0%), calcium chloride (96.0%), hot water (95.2%), and sodium hydroxide (93.9%) did not improve the chromium removal capacity of biosorbent. Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) analysis identified changes in biomass functionality and availability after physical and chemical modification—the results of which were in agreement with metal removal studies. In conclusion, this acid-treated biosorbent represents a suitable candidate to replace conventional removal technologies for metal-bearing wastewaters.

Kinetic modelling of cadmium and lead removal by aquatic mosses

Because biosorption is a low cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In the present study, the performance of the aquatic moss Fontinalis antipyretica for removing cadmium and lead from simulated wastewaters has been evaluated. Five kinetic models (first-order, pseudo-first-order, Elovich, modified Ritchie second-order and pseudo-second-order) were fitted to the experimental data and compared. Previously, the effect of parameters such as the initial solution pH, contact time, and initial metal ion concentration on biosorption was investigated. The initial pH of the solution was found to have an optimum value in the range of 4.0-6.0. The equilibrium sorption capacity of cadmium and lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L-1, the uptake capacity of the moss, at equilibrium, is the same for both metals (4.8 mg g-1). Nevertheless, when the initial concentration increases up to 100 mg L-1, the uptake of Pb(II) was higher than 78%. The pseudo-second order biosorption kinetics provided the better correlation with the experimental data (R² ≥ 0.999).

Hybrid Sargassum-sand sorbent: A novel adsorbent in packed column to treat metal-bearing wastewaters from inductively coupled plasma-optical emission spectrometry

Laboratory batch and column experiments were carried out to examine the efficiency of algal-based treatment technique to clean-up wastewaters emanating from inductively coupled plasma-optical emission spectrometry (ICP-OES). Chemical characterization revealed the extreme complexity of the wastewater, with the presence of 14 different metals under very low pH (pH = 1.1), high conductivity (6.98 mS/cm), total dissolved solid (4.46 g/L) and salinity (3.77). Batch experiments using Sargassum biomass indicated that it was possible to attain high removal efficiencies at optimum pH of 4.0. Efforts were also made to continuously treat ICP-OES wastewater using up-flow packed column. However, swelling of Sargassum biomass leads to stoppage of column. To address the problem, Sargassum was mixed with sand at a ratio of 40: 60 on volume basis. Remarkably, the hybrid Sargassum-sand sorbent showed very high removal efficiency towards multiple metal ions with the column able to operate for 11 h at a flow rate of 10 mL/min. Metal ions such as Cu, Cd, and Pb were only under trace levels in the treated water until 11 h. The results of the treatment process were compared with trade effluent discharge standards. Further the process evaluation and cost analysis were presented.

Bioremediation of industrial effluents containing heavy metals using brewing cells of Saccharomyces cerevisiae as a green technology: a review

The release of heavy metals into the environment, mainly as a consequence of anthropogenic activities, constitutes a worldwide environmental pollution problem. Unlike organic pollutants, heavy metals are not degraded and remain indefinitely in the ecosystem, which poses a different kind of challenge for remediation. It seems that the "best treatment technologies" available may not be completely effective for metal removal or can be expensive; therefore, new methodologies have been proposed for the detoxification of metal-bearing wastewaters. The present work reviews and discusses the advantages of using brewing yeast cells of Saccharomyces cerevisiae in the detoxification of effluents containing heavy metals. The current knowledge of the mechanisms of metal removal by yeast biomass is presented. The use of live or dead biomass and the influence of biomass inactivation on the metal accumulation characteristics are outlined. The role of chemical speciation for predicting and optimising the efficiency of metal removal is highlighted. The problem of biomass separation, after treatment of the effluents, and the use of flocculent characteristics, as an alternative process of cell-liquid separation, are also discussed. The use of yeast cells in the treatment of real effluents to bridge the gap between fundamental and applied studies is presented and updated. The convenient management of the contaminated biomass and the advantages of the selective recovery of heavy metals in the development of a closed cycle without residues (green technology) are critically reviewed.

Modelling of lead removal by an aquatic moss

Aquatic bryophytes are frequently used as biomonitors for trace metals in aquatic ecosystems. Nevertheless, their special characteristics also allow using them as biosorbents to clean industrial wastewaters. As biosorption is a low cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In this study, the ability of the aquatic bryophyte Fontinalis antipyretica to remove lead from simulated wastewaters was evaluated. Three kinetic models (pseudo-first order, pseudo-second order and Elovich) were fitted to the experimental data and compared by the F-test. Previously, the effect on biosorption of parameters such as the initial solution pH, contact time and initial metal ion concentration was investigated. The initial pH of the solution was found to have an optimum value is in the range 4.0-6.0. The equilibrium sorption capacity of lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L⁻¹, the uptake capacity at equilibrium was 4.8 mg g⁻¹. Nevertheless, when the initial concentration increased up to 100 mg L⁻¹, the uptake of lead was 10 times higher. The pseudo-second order biosorption kinetic model provided the better correlation with the experimental data (R²=1.00). The applicability of the Langmuir and Freundlich adsorption isotherms to the present system was also assessed. The maximum lead sorption capacity by Fontinalis antipyretica was 68 mg g⁻¹.

Removal of Pb(II) from wastewaters by Fontinalis antipyretica biomass: Experimental study and modelling

Aquatic bryophytes are frequently used as biomonitors for trace metals in aquatic ecosystems. Nevertheless, their special characteristics also allow using them as biosorbents to clean industrial wastewaters. As biosorption is a low-cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In this study, the ability of the aquatic bryophyte Fontinalis antipyretica to remove lead from simulated wastewaters was evaluated. Previously, the effect on biosorption of parameters such as the initial solution pH, contact time and initial metal ion concentration was investigated. The biosorption process is highly pH-dependent, and the favorable pH for maximum Pb2+ adsorption on the aquatic moss was found to have an optimum value in the range 4.0–6.0. The equilibrium sorption capacity of lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L−1, the uptake capacity at equilibrium was 4.8 mg g−1. Nevertheless, when the initial concentration increased up to 100 mg L−1, the uptake of lead was 10 times higher. Maximum adsorption rates were achieved almost in the first 10–20 min of contact, and a further increase in the contact time had a negligible effect on the Pb2+ sorption. Three kinetic models (pseudo-first order, pseudo-second order and Elovich) were fitted to the experimental data and compared by the F-test. The pseudo-second order biosorption kinetic model provided the better correlation with the experimental data (R 2 = 1.00). Probably the chemisorption is the rate-limiting step and the biosorption mechanism follows a pseudo-second order reaction model. The applicability of the Langmuir and Freundlich adsorption isotherms to the present system was also assessed. The equilibrium experimental data of lead sorption was very well described by the Langmuir model with R 2 values exceeding 0.993. The maximum lead sorption capacity by Fontinalis antipyretica attained a value of 68 mg of lead ions per gram of aquatic moss.

Study on the purification property of pyrite and its spectra on the processing of metal-bearing wastewater

The purification property of pyrite was discussed by using in situ attenuated total reflection-Fourier transform infrared spectroscopy. Results showed that there might be dissolution–adsorption precipitation equilibrium of heavy metals on the surface of pyrite, which is dependent on the surface oxidation of pyrite and the neutralization reaction of carbonate within pyrite. If there was excessive carbonate within pyrite, the “dissolution” of metals would be less than that of the “adsorption precipitation,” making pyrite exhibit its purification property. Based on this property, pyrite was used to process simulated wastewater containing Pb2+, Hg2+, Cd2+, Cr(VI) and Cu2+. Results showed that the efficiencies of metal removal exceeded 96%. In addition, reflectance spectroscopy and absorption spectroscopy were also utilized to investigate the simulated metal-bearing wastewater treatment process. Analysis by diffused reflectance infrared Fourier transform spectroscopy confirmed that the superficial hydroxyl groups in pyrite reacted with metal ions during the wastewater treatment process. Reflectance spectroscopy in the visible region was used to characterize the variation in particle size and specific surface area of pyrite during the wastewater treatment process, which explained its increasing activity when reutilized. Further, analysis by absorption spectroscopy and X-ray photoelectron spectroscopy indicated that the process involved when using pyrite for the treatment of Cr(VI)-containing wastewater was an adsorption–precipitation process.

Nickel Removal from Waters Using a Surfactant-Enhanced Hybrid Powdered Activated Carbon/Microfiltration Process. II. The Influence of Process Variables

This study focused on the removal of nickel ions from aqueous solution using a surfactant-enhanced (SE) powdered activated carbon (PAC)/microfiltration (MF) hybrid membrane process. The main objective of the research is to investigate the technical performance of the process under the influences of all relevant process variables namely process time, recycling time, pH, temperature, PAC concentration, surfactant concentration, nickel concentration, cross-flow velocity, and transmembrane pressure, thus to reveal its applicability to water problems involved in heavy metal pollution. The concentrations of PAC, surfactant, metal, and H+ ion were determined as significant process stream variables, while transmembrane pressure and temperature came into prominence as significant operating variables. ANOVA calculations indicated that the total influences of these six variables on process performance realized in a range of about 93−98%. Nickel concentration and PAC amount in the feed were established as the most influential variables for nickel rejection, and surfactant rejection and permeate flux, respectively. The increase of PAC from 0.1 to 4 g/L led to a flux decline of about 60%. The most critical parameter for process performance was the mass ratio of PAC to surfactant (PAC/surfactant) per unit mass of metal removed. The process which may be effectively operated in continuous cross-flow filtration mode within a short filtration time of 30 min has crucial advantages compared to high pressure driven membrane processes and offers a promising alternative to remove heavy metal pollutants from drinking waters and metal bearing wastewaters.

Selective removal of heavy metals from metal-bearing wastewater in a cascade line reactor.

This paper is a part of the research work on 'Integrated treatment of industrial wastes towards prevention of regional water resources contamination - INTREAT' the project. It addresses the environmental pollution problems associated with solid and liquid waste/effluents produced by sulfide ore mining and metallurgical activities in the Copper Mining and Smelting Complex Bor (RTB-BOR), Serbia. However, since the minimum solubility for the different metals usually found in the polluted water occurs at different pH values and the hydroxide precipitates are amphoteric in nature, selective removal of mixed metals could be achieved as the multiple stage precipitation. For this reason, acid mine water had to be treated in multiple stages in a continuous precipitation system-cascade line reactor. All experiments were performed using synthetic metal-bearing effluent with chemical a composition similar to the effluent from open pit, Copper Mining and Smelting Complex Bor (RTB-BOR). That effluent is characterized by low pH (1.78) due to the content of sulfuric acid and heavy metals, such as Cu, Fe, Ni, Mn, Zn with concentrations of 76.680, 26.130, 0.113, 11.490, 1.020 mg/dm3, respectively. The cascade line reactor is equipped with the following components: for feeding of effluents, for injection of the precipitation agent, for pH measurements and control, and for removal of the process gases. The precipitation agent was 1M NaOH. In each of the three reactors, a changing of pH and temperature was observed. In order to verify. efficiency of heavy metals removal, chemical analyses of samples taken at different pH was done using AES-ICP. Consumption of NaOH in reactors was 370 cm3, 40 cm3 and 80 cm3, respectively. Total time of the experiment was 4 h including feeding of the first reactor. The time necessary to achieve the defined pH value was 25 min for the first reactor and 13 min for both second and third reactors. Taking into account the complete process in the cascade line reactor, the difference between maximum and minimum temperature was as low as 6 degrees C. The quantity of solid residue in reactors respectively was 0.62 g, 2.05 g and 3.91 g. In the case of copper, minimum achieved concentration was 0.62 mg/dm3 at pH = 10.4. At pH = 4.50 content of iron has rapidly decreased to < 0.1 mg/dm3 and maintained constant at all higher pH values. That means that precipitation has already ended at pH=4.5 and maximum efficiency of iron removal was 99.53%. The concentration of manganese was minimum at pH value of 11.0. Minimum obtained concentration of Zn was 2.18 mg/dm3 at a pH value of 11. If pH value is higher than 11, Zn can be re-dissolved. The maximum efficiency of Ni removal reached 76.30% at a pH value of 10.4. Obtained results show that efficiency of copper, iron and manganese removal is very satisfactory (higher than 90%). The obtained efficiency of Zn and Ni removal is lower (72.30% and 76.31%, respectively). The treated effluent met discharge water standard according to The Council Directive 76/464/EEC on pollution caused by certain dangerous substances into the aquatic environment of the Community. Maximum changing of temperature during the whole process was 6 degrees C. This technology, which was based on inducing chemical precipitation of heavy metals is viable for selective removal of heavy metals from metal-bearing effluents in three reactor systems in a cascade line. The worldwide increasing concern for the environment and guidelines regarding effluent discharge make their treatment necessary for safe discharge in water receivers. In the case where the effluents contain valuable metals, there is also an additional economic interest to recover these metals and to recycle them as secondary raw materials in different production routes.

Characterization of carbonated tricalcium silicate and its sorption capacity for heavy metals: A micron-scale composite adsorbent of active silicate gel and calcite

Adsorption-based processes are widely used in the treatment of dilute metal-bearing wastewaters. The development of versatile, low-cost adsorbents is the subject of continuing interest. This paper examines the preparation, characterization and performance of a micro-scale composite adsorbent composed of silica gel (15.9 w/w%), calcium silicate hydrate gel (8.2 w/w%) and calcite (75.9 w/w%), produced by the accelerated carbonation of tricalcium silicate (C 3S, Ca 3SiO 5). The Ca/Si ratio of calcium silicate hydrate gel (C–S–H) was determined at 0.12 (DTA/TG), 0.17 ( 29Si solid-state MAS/NMR) and 0.18 (SEM/EDS). The metals-retention capacity for selected Cu(II), Pb(II), Zn(II) and Cr(III) was determined by batch and column sorption experiments utilizing nitrate solutions. The effects of metal ion concentration, pH and contact time on binding ability was investigated by kinetic and equilibrium adsorption isotherm studies. The adsorption capacity for Pb(II), Cr(III), Zn(II) and Cu(II) was found to be 94.4 mg/g, 83.0 mg/g, 52.1 mg/g and 31.4 mg/g, respectively. It is concluded that the composite adsorbent has considerable potential for the treatment of industrial wastewater containing heavy metals.

A Study of the Operating Parameters of a Sulphate-Reducing Fixed-Bed Reactor for the Treatment of Metal-Bearing Wastewater

An upflow fixed-bed sulphate-reducing reactor has been set up and monitored for the treatment of metal-bearing wastewater. Zinc has been chosen as the target metal to be sequestered from influent water stream at initial concentrations ranging from 50 to 400 mg/l and initial pH values ranging from 3 to 5. Main operating parameters of the reactor, such as the composition and content of electron donor, electron acceptor, sulphate and metal removal capacity, have been monitored during ten months of continuous operation. The results obtained have shown that the reactor has a considerable capacity of completely reducing sulphates for initial concentrations up to 7,200 mg/l, completely removing soluble zinc for initial concentrations up to 400 mg/l and completely removing Total Organic Carbon (TOC), for initial concentrations up to 1,500 mg/l.

폐슬러지를 이용한 흡착·부상 공정에 의한 중금속 제거

Waste sludge may be used to recovery wastewater contaminated with heavy metals. The waste sludge is an inexpensive readily available source of biomass for biosorption with metal-bearing wastewater. The biosorption of heavy metals such as Pb(II), Cu(II), Cr(II), and Cd(II) onto waste sludge was investigated in batch ex­periments and waste sludge loaded heavy metals was separated by dissolved air flotation. The biosorption equi­bria of heavy metals could be described by Langmuir and Freundich isotherms. The adsorption capacity for waste sludge was in the sequence of Pb(II)>Cr(II)>Cu(II)>Cd(II). The system attained equilibrium about 20 min. The Langmuir and Freundlich adsorption model effectively described the biosorption equilibrium of Cu(II) and Cr(II) ions on waste sludge. Maximum adsorption capacity of Cu(II) and Cr(II) were 196.08 and 158.73 mg/g, respectively. Solid-liquid separation efficiencies were kept above <TEX>$95\%$</TEX> on waste sludge loaded heavy metals, and were decreased with pH increasing.

Removal of Bi, Cd, Co, Cu, Fe, Ni, Pb, and Zn from an Aqueous Nitrate Medium with Bis(2-ethylhexyl)phosphoric Acid Impregnated Kapok Fiber

Bis(2-ethylhexyl)phosphoric acid (D2EHPA) impregnated fiber (SIF) using a commercial oil sorbent made of kapok fiber as the support has been prepared by a wet method, and its ability to remove metal ions of Bi(III), Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II), and Zn(II) from single-metal nitrate solutions has been evaluated in comparison with D2EHPA-impregnated resin using XAD7HP as the support (SIR) and solvent extraction with D2EHPA dissolved in a nonpolar organic solvent (SX), where the amount of D2EHPA in each system was the same. The results are summarized as follows: (i) the removal of each metal by SIF proceeds via cation exchange as in the cases of SIR and SX; (ii) the pH value at 50% metal removal, pH50, by SIF increases in the order Fe(III) < Bi(III) < Zn(II) < Pb(II) < Cd(II) < Cu(II) < Co(II) < Ni(II), and this order agrees with those by SIR and SX; (iii) the pH50 value for each metal increases in the order SIF < SIR ≪ SX; (iv) the loading capacity of Zn(II) by SIF is 1.5 times higher than that by SIR; (v) SIF can be used many times after regeneration by acid treatment as in the case of SIR. The removal rates for Cd(II), Cu(II), Pb(II), and Zn(II) decrease in the order SX > SIF > SIR. In conclusion, SIF is more advantageous than SIR and SX in terms of the amount of D2EHPA necessary for achieving a certain removal percentage and than SIR in terms of the removal rate; thus, the application of SIF to metal-bearing wastewater treatment is highly expected.

Advances in biotreatment of acid mine drainage and biorecovery of metals: 1. Metal precipitation for recovery and recycle.

Acid mine drainage (AMD), an acidic metal-bearing wastewater, poses a severe pollution problem attributed to post mining activities. The metals usually encountered in AMD and considered of concern for risk assessment are arsenic, cadmium, iron, lead, manganese, zinc, copper and sulfate. The pollution generated by abandoned mining activities in the area of Butte, Montana has resulted in the designation of the Silver Bow Creek-Butte Area as the largest Superfund (National Priorities List) site in the U.S. This paper reports the results of bench-scale studies conducted to develop a resource recovery based remediation process for the clean up of the Berkeley Pit. The process utilizes selective, sequential precipitation (SSP) of metals as hydroxides and sulfides, such as copper, zinc, aluminum, iron and manganese, from the Berkeley Pit AMD for their removal from the water in a form suitable for additional processing into marketable precipitates and pigments. The metal biorecovery and recycle process is based on complete separation of the biological sulfate reduction step and the metal precipitation step. Hydrogen sulfide produced in the SRB bioreactor systems is used in the precipitation step to form insoluble metal sulfides. The average metal recoveries using the SSP process were as follows: aluminum (as hydroxide) 99.8%, cadmium (as sulfide) 99.7%, cobalt (as sulfide) 99.1% copper (as sulfide) 99.8%, ferrous iron (sulfide) 97.1%, manganese (as sulfide) 87.4%, nickel (as sulfide) 47.8%, and zinc (as sulfide) 100%. The average precipitate purity for metals, copper sulfide, ferric hydroxide, zinc sulfide, aluminum hydroxide and manganese sulfide were: 92.4, 81.5, 97.8, 95.6, 92.1 and 75.0%, respectively. The final produced water contained only calcium and magnesium and both sulfate and sulfide concentrations were below usable water limits. Water quality of this agriculturally usable water met the EPA's gold standard criterion.

Binary biosorption of iron(III) and iron(III)-cyanide complex ions on Rhizopus arrhizus: modelling of synergistic interaction

Many heavy metal-bearing wastewaters also contain their metal cyanide complex ions. Although the biosorption of single or multi-metal ions to various microorganisms has been extensively studied, very little attention has been given to the bioremoval and the expression of the adsorption equilibrium and kinetics of metal–metal cyanide complex ion systems. In this study, the simultaneous biosorption of iron(III) (ferric) cations and iron(III)-cyanide complex (ferricyanide) anions to Rhizopus arrhizus from binary mixtures was studied and compared with single metal and metal cyanide complex ion situation in a batch stirred system. The effects of initial pH and single and dual-component concentrations on the biosorption kinetics and equilibrium uptake of each component, both singly and in mixture were investigated. The working pH value for both species was determined as 2.0. Multi-component biosorption studies were also performed at this pH value. The biosorption rates and equilibrium uptakes of iron(III) or iron(III)-cyanide complex ions increased by the presence of increasing concentrations of the other ion up to 200 mg l −1 for iron(III) and up to 1000 mg l −1 for iron(III)-cyanide complex ions. This situation showed a synergistic interaction between these ions. The Freundlich, Langmuir and Redlich–Peterson adsorption models were used to predict the mono-component equilibrium uptake and model parameters were estimated by the non-linear regression. It was seen that the mono-component adsorption equilibrium data fitted very well to the mono-component Langmuir and Redlich–Peterson models for both the components at moderate ranges of concentration. A modified synergistic Langmuir model was proposed for dual-component system and model parameters were also estimated by the non-linear regression. The pseudo second-order kinetic model was applied to single and multi-component experimental data assuming that the external mass transfer limitations in the system can be neglected and biosorption is sorption controlled.