An integrated biological approach for treatment of cyanidation wastewater

Solar-assisted selective separation and recovery of precious group metals from deactivated air purification catalysts

The mitigation of environmental and energy crises could be advanced by reclaiming platinum group precious metals (PGMs) from decommissioned air purification catalysts. However, the complexity of catalyst composition and the high chemical inertness of PGMs significantly impede this process. Consequently, recovering PGMs from used industrial catalysts is crucial and challenging. This study delves into an environmentally friendly approach to selectively recover PGMs from commercial air purifiers using photocatalytic redox technology. Our investigation focuses on devising a comprehensive strategy for treating three-way catalysts employed in automotive exhaust treatment. By meticulously pretreating and modifying reaction conditions, we achieved noteworthy results, completely dissolving and separating rhodium (Rh), palladium (Pd), and platinum (Pt) within a 12-h time frame. Importantly, the solubility selectivity persists despite the remarkably similar physicochemical properties of Rh, Pd, and Pt. To bolster the environmental sustainability of our method, we harness sunlight as the energy source to activate the photocatalysts, facilitating the complete dissolution of precious metals under natural light irradiation. This eco-friendly recovery approach demonstrated on commercial air purifiers, exhibits promise for broader application to a diverse range of deactivated air purification catalysts, potentially enabling implementation on a large scale.

Cloning and heterologous expression of Fusarium oxysporum nitrilase gene in Escherichia coli and evaluation in cyanide degradation

Cyanide is widely utilized in the extraction of precious metal extraction even though it has been deemed as the most toxic compound. Fusarium oxysporum has been shown to degrade cyanide through the activity of the Nitrilase enzyme. In this study, the coding sequence of nitrilase gene from F. oxysporum genomic DNA was optimized for cloning and expression in E. coli. The pUC57 containing synthetic optimized nitrilase gene was transferred into E. coli DH5α strain. This nitrilase gene was sub-cloned into pET26b (+) expression vector containing an in-built His-tag at the C-terminal end to facilitate its purification. The recombinant plasmid, pETAM1, was confirmed by PCR, digestion pattern, and sequencing. The recombinant protein was overproduced in E. coli BL21 (DE3). The results of the SDS-PAGE pattern and Western blot analysis confirmed the expression of the expected recombinant protein. For expression optimization of Nitrilase protein, M16 orthogonal experimental design of the Taguchi method was used. The effect of induction time, temperature and IPTG concentration were examined using four levels for each factors. Estimation of the amount of the expressed protein was calculated via densitometry on SDS-PAGE. The enzyme activity and expression in E. coli proved to be successful since there was ammonia production when potassium cyanide and acrylonitrile were used as substrates while the highest enzyme activity of 88% was expressed at 30 °C. The Km and Vm values of the expressed Nitrilase enzyme were determined to be 0.68 mM and 0.48 mM/min respectively.

Study on the performance of Anerinibacillus sp. in degrading cyanide wastewater and its metabolic mechanism

Cyanide extraction dominates the gold smelting industry, which leads to the generation of large amounts of cyanide-containing wastewater. In this study, Aneurinibacillus tyrosinisolvens strain named JK-1 was used for cyanide wastewater biodegradation. First, we tested the performance of JK-1 in degrading cyanide under different conditions. Then, we screened metabolic compounds and pathways associated with cyanide degradation by JK-1. Finally, we explored the potential JK-1-mediated cyanide degradation pathway. Our results showed that the optimal pH and temperature for cyanide biodegradation were 7.0 and 30 °C, respectively; under these conditions, a degradation rate of >98% was achieved within 48 h. Untargeted metabolomics results showed that increased cyanide concentration decreased the abundance of metabolic compounds by 71.1% but upregulated 32 metabolic pathways. The Kyoto Encyclopedia of Genes and Genomes enrichment results revealed significant changes in amino acid metabolism pathways during cyanide degradation by JK-1, including cyanoamino acid metabolism, β-alanine metabolism, and glutamate metabolism. Differential metabolic compounds included acetyl-CoA, l-asparagine, l-glutamic acid, l-phenylalanine, and l-glutamine. These results confirmed that cyanide degradation by JK-1 occurs through amino acid assimilation. This study provides new insights into the mechanism of cyanide biodegradation, which can be applied in the treatment of cyanide wastewater or tailings.

Metal mobility and bioaccessibility from cyanide leaching heaps in a historical mine site

Unlike acidic sulfide mine wastes, where metal/loid mobility and bioaccessibility has been widely studied, less attention has been paid to alkaline cyanide heap leaching wastes. Thus, the main goal of this study is to evaluate the mobility and bioaccessibility of metal/loids in Fe-rich (up to 55%) mine wastes resulting from historical cyanide leaching activities. Wastes are mainly composed of oxides/oxyhydroxides (i.e. goethite and hematite), oxyhydroxisulfates (i.e. jarosite), sulfates (i.e., gypsum, evaporitic sulfate salts), carbonates (i.e., calcite, siderite) and quartz, with noticeable concentrations of metal/loids (e.g., 1453-6943 mg/kg of As, 5216-15,672 mg/kg; of Pb, 308-1094 mg/kg of Sb, 181-1174 mg/kg of Cu, or 97-1517 mg/kg of Zn). The wastes displayed a high reactivity upon rainfall contact associated to the dissolution of secondary minerals such as carbonates, gypsum, and other sulfates, exceeding the threshold values for hazardous wastes in some heap levels for Se, Cu, Zn, As, and sulfate leading to potential significant risks for aquatic life. High concentrations of Fe, Pb, and Al were released during the simulation of digestive ingestion of waste particles, with average values of 4825 mg/kg of Fe, 1672 mg/kg of Pb, and 807 mg/kg of Al. Mineralogy may control the mobility and bioaccessibility of metal/loids under rainfall events. However, in the case of the bioaccessible fractions different associations may be observed: i) the dissolution of gypsum, jarosite and hematite would mainly release Fe, As, Pb, Cu, Se, Sb and Tl; ii) the dissolution of an un-identified mineral (e.g., aluminosilicate or Mn oxide) would lead to the release of Ni, Co, Al and Mn and iii) the acid attack of silicate materials and goethite would enhance the bioaccessibility of V and Cr. This study highlights the hazardousness of wastes from cyanide heap leaching, and the need to adopt restoration measures in historical mine sites.

An Overview of Emerging Cyanide Bioremediation Methods

Cyanide compounds are hazardous compounds which are extremely toxic to living organisms, especially free cyanide in the form of hydrogen cyanide gas (HCN) and cyanide ion (CN−). These cyanide compounds are metabolic inhibitors since they can tightly bind to the metals of metalloenzymes. Anthropogenic sources contribute significantly to CN− contamination in the environment, more specifically to surface and underground waters. The treatment processes, such as chemical and physical treatment processes, have been implemented. However, these processes have drawbacks since they generate additional contaminants which further exacerbates the environmental pollution. The biological treatment techniques are mostly overlooked as an alternative to the conventional physical and chemical methods. However, the recent research has focused substantially on this method, with different reactor configurations that were proposed. However, minimal attention was given to the emerging technologies that sought to accelerate the treatment with a subsequent resource recovery from the process. Hence, this review focuses on the recent emerging tools that can be used to accelerate cyanide biodegradation. These tools include, amongst others, electro-bioremediation, anaerobic biodegradation and the use of microbial fuel cell technology. These processes were demonstrated to have the possibility of producing value-added products, such as biogas, co-factors of neurotransmitters and electricity from the treatment process.

Removal of ammonia nitrogen and phenol by pulsed discharge plasma combined with modified zeolite catalyst

In this work, the removal of ammonia nitrogen and phenol by pulsed discharge plasma (PDP) and modified zeolite was investigated. The Fe-zeolite and Mn-zeolite catalysts were prepared by the impregnation method. Catalysts' morphology, specific surface area, and chemical bond structure were characterized. Based on the pollutants removal experiments, Fe-zeolite (0.01) in the PDP system had better catalytic oxidation of phenol and adsorption effect of ammonia nitrogen. The removal efficiency of the pollutants increased with the increase of discharge voltage and solution conductivity, but decreased with the increase of discharge distance. During the plasma discharge process, the pH value in the solution decreased, and the solution conductivity gradually increased. After PDP/Fe-zeolite system treatment, the toxicity of the wastewater was significantly reduced. This study provided a new treatment method for inorganic and organic pollutants treated by PDP.

Partially treated domestic wastewater as a nutrient source for tomatoes (Lycopersicum solanum) grown in a hydroponic system: effect on nutrient absorption and yield

Using effluent from the anaerobic baffled reactor (ABR) of the decentralised wastewater treatment system (DEWATS) as a sole nutrient source is not sufficient for tomato plants grown in hydroponic system. The study investigated the effects of commercial hydroponic fertilizer mix (CHFM) combined with ABR effluent on tomato growth and yield. A media-based hydroponic technique consisting of three treatments, namely, ABR effluent, CHFM, and ABR effluent combined with CHFM (ABR + CHFM (50:50 v/v) was used. The results showed that plant growth parameters, biomass, fruit yield and shoot nutrient content were significantly higher in tomato plants fed with CHFM and ABR + CHFM than those grown in ABR effluent. Addition of 50 % dose of CHFM in ABR wastewater (ABR + CHFM) increased shoot N, K, Ca and Zn. These results indicated that adding 50% CHFM can alleviate nutrient deficiencies when partially treated wastewater from anaerobic digester is used as a nutrient source for hydroponic tomato cultivation.

Laser-Plasma Spatiotemporal Cyanide Spectroscopy and Applications

This article reports new measurements of laser-induced plasma hypersonic expansion measurements of diatomic molecular cyanide (CN). Focused, high-peak-power 1064 nm Q-switched radiation of the order of 1 TW/cm 2 generated optical breakdown plasma in a cell containing a 1:1 molar gas mixture of N 2 and CO 2 at a fixed pressure of 1.1 × 10 5 Pascal and in a 100 mL/min flow of the mixture. Line-of-sight (LOS) analysis of recorded molecular spectra indicated the outgoing shockwave at expansion speeds well in excess of Mach 5. Spectra of atomic carbon confirmed increased electron density near the shockwave, and, equally, molecular CN spectra revealed higher excitation temperature near the shockwave. Results were consistent with corresponding high-speed shadowgraphs obtained by visualization with an effective shutter speed of 5 nanoseconds. In addition, LOS analysis and the application of integral inversion techniques allow inferences about the spatiotemporal plasma distribution.

Hydroponic technology as decentralised system for domestic wastewater treatment and vegetable production in urban agriculture: A review

Water scarcity, nutrient-depleted soils and pollution continue to be a major challenge worldwide and these are likely to worsen with increasing global populations particularly, in urban areas. As a result, environmental and public health problems may arise from the insufficient provision of sanitation and wastewater disposal facilities. Because of this, a paradigm shifts with regard to the sustainable management of waste disposal in a manner that could protect the environment at the same time benefits society by allowing nutrient recovery and reuse for food production is required. Hence, the use of urban wastewater for agricultural irrigation has more potential, especially when incorporating the reuse of nutrients like nitrogen and phosphorous, which are essential for crop production. Among the current treatment technologies applied in urban wastewater reuse for agriculture, hydroponic system is identified as one of the alternative technology that can be integrated with wastewater treatment. The integration of hydroponic system with municipal wastewater treatment has the advantage of reducing costs in terms of pollutants removal while reducing maintenance and energy costs required for conventional wastewater treatment. The efficiency of a hydroponic system with regard to municipal wastewater reuse is mainly linked to its capacity to allow continuous use of wastewater through the production of agricultural crops and the removal of pollutants/nutrients (nitrogen and phosphorus), resulting to increased food security and environmental protection. Moreover, the suitability of hydroponic system for wastewater treatment is derived from its capacity to minimize associated health risks to farmers, harvested crop and consumers, that may arise through contact with wastewater.

Interaction of cyanate uptake by rice seedlings with nitrate assimilation: gene expression analysis

Cyanate (CNO^-) has been produced in the environment through either natural or anthropogenic sources. However, due to industrialization, it has been led more over-loads. In this study, interaction of CNO^- uptake by rice seedlings with nitrate assimilation was investigated using gene expression analysis after an acute phytotoxicity assay. Our results showed that CNO^- exposure caused inhibition on relative growth rates of plants. CNO^- analysis demonstrated that rice seedlings had higher potential for CNO^- uptake and the removal rates showed a zero-order kinetic. PCR analysis exposed that OsCYN transcript was not significantly induced by CNO^- treatments in rice tissues and CNO^- exposure also repressed gene expression of the collaborative enzyme carbonic anhydrase (CA), suggesting that assimilation of CNO^- initiated by the enzyme cyanase (CYN) in rice seedlings was an enzyme-limitation reaction. Gene expression of other enzymes involved in nitrate metabolism was tissue-specific under CNO^- exposure, suggesting that rice seedlings were able to trigger its intrinsic regulative and responsive mechanisms to cope up with uneven N conditions. Significant upregulation of three OsGDH isogenes, except for OsGDH1 in roots, was detected in both rice materials with enhancing CNO^- concentrations, suggesting that GDH may play a primary role to maintain the balance of C and N in plants under CNO^- exposure. In conclusion, because the innate pool of CYN activity was non-sufficient to degrade exogenous CNO^- by rice seedlings, CNO-derived ammonium only can serve as a supporting N source to support growth of rice seedling under non-effective doses of CNO^- exposure.

Immobilization of E. coli expressing Bacillus pumilus CynD in three organic polymer matrices

Cyanide is toxic to most living organisms. The toxicity of cyanide derives from its ability to inhibit the enzyme cytochrome C oxidase of the electronic transport chain. Despite its high toxicity, several industrial processes rely on the use of cyanide, and considerable amounts of industrial waste must be adequately treated before discharge. Biological treatments for the decontamination of cyanide waste include the use of microorganisms and enzymes. Regarding the use of enzymes, cyanide dihydratase (CynD), which catalyzes the conversion of cyanide into ammonia and formate, is an attractive candidate. Nevertheless, the main impediment to the effective use of this enzyme for the biodegradation of cyanide is the marked intolerance to the alkaline pH at which cyanide waste is kept. In this work, we explore the operational capabilities of whole E. coli cells overexpressing Bacillus pumilus CynD immobilized in three organic polymer matrices: chitosan, polyacrylamide, and agar. Remarkably, the immobilized cells on agar and polyacrylamide retained more than 80% activity even at pH 10 and displayed high reusability. Conversely, the cells immobilized on chitosan were not active. Finally, the suitability of the active complexes for the degradation of free cyanide from a solution derived from the gold processing industry was demonstrated.

Recent Developments in the Photocatalytic Treatment of Cyanide Wastewater: An Approach to Remediation and Recovery of Metals

For gold extraction, the most used extraction technique is the Merrill-Crow process, which uses lixiviants as sodium or potassium cyanide for gold leaching at alkaline conditions. The cyanide ion has an affinity not only for gold and silver, but for other metals in the ores, such as Al, Fe, Cu, Ni, Zn, and other toxic metals like Hg, As, Cr, Co, Pb, Sn, and Mn. After the extraction stage, the resulting wastewater is concentrated at alkaline conditions with concentrations up to 1000 ppm of metals. Photocatalysis is an advanced oxidation process (AOP) able to generate a photoreaction in the solid surface of a semiconductor activated by light. Although it is well known that photocatalytic processes can remove metals in solution, there are no compilations about the researches on photocatalytic removal of metals in wastewater with cyanide. Hence, this review comprises the existing applications of photocatalytic processes to remove metal and in some cases recover cyanide from recalcitrant wastewater from gold extraction. The use of this process, in general, requires the addition of several scavengers in order to force the mechanism to a pathway where the electrons can be transferred to the metal-cyanide matrices, or elsewhere the entire metallic cyanocomplex can be degraded by an oxidative pathway.

Synergic effect of adsorption and biodegradation enhance cyanide removal by immobilized Alcaligenes sp. strain DN25

A high efficiency and stability polyurethane-foam (PUF)-immobilized cell system was constructed to remove cyanide based on simultaneous adsorption and biodegradation (SAB). The performance of the PUF-immobilized system was evaluated by comparison with the freely suspended cell system. The SAB system exhibited more effective and robust, and could still remain degradation activity even at 40 °C or pH 11.0. The SAB system completely removed 500 mg CN^-/L within 8 h at 30 °C, pH 8.0, and 120 rpm, whereas 12 h were required for the free cells system. Moreover, the SAB system showed apparent superiority in removing higher concentration cyanide up to 1200 mg CN^-/L. A continuously stirred tank bioreactor (CSTR) was successfully designed and steadily operated with approximately 85% of the total average removal efficiency for 52 days at an influent cyanide concentration of 100-200 mg/L, which demonstrated a favorable reliability. Cyanide removal process could be well described using a pseudo first-order model, and the higher apparent rate constants (k) of the immobilized cells showed the synergic effect of adsorption and biodegradation significantly enhanced cyanide removal. Preliminarily, it was found that the foam characteristic might play a not negligible role on the cyanide-degrading enzyme expression of strain DN25 in the SAB system.

Overview of the state of the art of processes and technical bottlenecks for coal gasification wastewater treatment

CGWW is major waste stream resulting from a number of activities of the low/medium temperature gasification unit that occurs during the production of natural gas. The resulting effluent contains a broad spectrum of organic and inorganic contaminants and exerts a negative influence on the environment, mainly due to the presence of toxic and refractory compounds. So far, various technologies have been applied for treatment of CGWW, while few reviews are available in the literature. Thus, this review attempts to offer a comprehensive picture about CGWW. An overview about pretreatment, biological and advanced processes for treatment of CGWW is presented, and the degradation mechanism of toxic and refractory pollutants is also elaborated. Technical bottlenecks existing in the operation of coal chemical industries, including foam proliferation, odors and biotoxicity risk, are detailed analyzed. Finally, the prospects of treatment for CGWW are discussed based on the concept of "wastewater is money". The review can be provided as an effective technical support for the construction and operation of coal gasification industries.

Single microbial fuel cell reactor for coking wastewater treatment: Simultaneous carbon and nitrogen removal with zero alkaline consumption

The use of several individual reactors for sequential removal of organic compounds and nitrogen, in addition to the required alkaline addition in aerobic reactors, remain outstanding technical challenges to the traditional biological treatment of coking wastewater. Here, we report the utilization of a single microbial fuel cell (MFC) reactor that performs simultaneous carbon and nitrogen removal with zero alkaline consumption, as evidenced by the results of the batch-fed and continuous-flow experiments. The MFC exhibited faster reaction kinetics for COD and total nitrogen (TN) removal than the same configured reactor analogous to the traditional aerobic biological reactor (ABR). At a hydraulic retention time (HRT) of 125 h, the efficiencies of COD and TN removal in the MFC reached 83.8±3.6% and 97.9±2.1%, respectively, much higher than the values of 73.8±2.9% and 50.2±5.0% obtained in the ABR. Furthermore, the degradation in the MFC of the main organic components, including phenolic compounds (such as phenol, 2-methylphenol, 3-methylphenol, 4-methylphenol, and 2,4-dimethlyphenol) and nitrogenous heterocyclic compounds (such as quinolone, pyridine, indole, and isoquinolone) was greater than that in the ABR. The enhancing effect was attributed to the ability of the MFC to self-adjust the pH. It was also manifested by the increased abundances of heterotrophs, nitrifiers, and denitrifiers in the MFC. The correlations between the current density and the rates of COD and TN removal suggest that the extent of the current from the anode to the cathode is a critical parameter for the overall performance of MFCs in the treatment of coking wastewater.

Microbial communities associated with the co-metabolism of free cyanide and thiocyanate under alkaline conditions

This study focused on the identification of free cyanide (CDO) and thiocyanate (TDO) degrading microbial communities using a culture-dependent and independent approach. Culturable microbial species were isolated from the CDOs (n = 13) and TDOs (n = 18). The CDOs were largely dominated by Bacillus sp. while the TDOs were dominated by Bacillus sp., Klebsiella oxytoca, Providencia sp. and Pseudomonas sp. However, 16S rRNA amplicon gene-sequencing revealed the complexity and diversity of the microbial communities in contrast to the organisms that were detected using culture-dependent technique. Overall, the organisms were mainly dominated by Myroides odoratimimus and Proteus sp. at 37.82 and 30.5% for CDOs, and 35.26 and 17.58% for TDOs, respectively. The co-culturing of the CDOs and TDOs resulted in biochemical changes of key metabolic enzymes, and this resulted in the complete degradation of CN- and SCN- simultaneously; a phenomenon which has not been witnessed, especially under alkaline conditions. Current ongoing studies are focused on the application of these organisms for the biodegradation of CN- and SCN- in a continuous system, under changing operational parameters, to assess their effectiveness in the biodegradation of CN- and SCN-.

Enhanced biodegradation of phenol in a novel cyclic activated sludge integrated with a rotating bed bioreactor in anoxic and peroxidase-mediated conditions

Cyclic activated sludge integrated with a rotating bed bioreactor (CASIR) was used for phenol biodegradation. The effects of phenol loading rate, mixed liquor suspended solids (MLSS) concentration, media filling ratio, hydraulic retention time (HRT) and salinity were investigated for phenol degradation and COD removal. In the second phase of the study, the microbial content of the bioreactor was induced by hydrogen peroxide injection for in situ generation of peroxidase. For investigating the above-mentioned parameters, the bioreactor was operated for 535 days and residual phenol, nitrate and COD were measured daily. The variation of the dehydrogenase activity and peroxidase activity of suspended biomass and attached film were also monitored during the bioreactor operation. Complete degradation of phenol at the loading rate of 667 g m⁻³ d⁻¹ was achieved in anoxic conditions. Addition of media to the bioreactor to form active attached biofilm led to the increase in tolerance of the bioreactor on organic loading shocks. It was found that increasing the salinity of the wastewater did not affect the performance of the bioreactor. Investigating dehydrogenase activity proved that the attached biofilm was more involved in phenol degradation, compared with the suspended biomass. However, after switching to peroxidase-mediated conditions, the organic loading tolerance of the bioreactor considerably increased and complete degradation of phenol at the loading rate of 2000 g m⁻³ d⁻¹ was reached. After adaptation of the microorganisms for hydrogen peroxide, the peroxidase activity of 290 U g_biomass⁻¹ was observed in the bioreactor. Accordingly, the H₂O₂-induced microbial cells in cyclic activated sludge could be considered as a promising technique for enzymatic degradation of phenol and corresponding COD.

Cyclic activated sludge integrated with a rotating bed bioreactor (CASIR) was used for phenol biodegradation.

Exploring anaerobic environments for cyanide and cyano-derivatives microbial degradation

Cyanide is one of the most toxic chemicals for living organisms described so far. Its toxicity is mainly based on the high affinity that cyanide presents toward metals, provoking inhibition of essential metalloenzymes. Cyanide and its cyano-derivatives are produced in a large scale by many industrial activities related to recovering of precious metals in mining and jewelry, coke production, steel hardening, synthesis of organic chemicals, and food processing industries. As consequence, cyanide-containing wastes are accumulated in the environment becoming a risk to human health and ecosystems. Cyanide and related compounds, like nitriles and thiocyanate, are degraded aerobically by numerous bacteria, and therefore, biodegradation has been offered as a clean and cheap strategy to deal with these industrial wastes. Anaerobic biological treatments are often preferred options for wastewater biodegradation. However, at present very little is known about anaerobic degradation of these hazardous compounds. This review is focused on microbial degradation of cyanide and related compounds under anaerobiosis, exploring their potential application in bioremediation of industrial cyanide-containing wastes.

Expression of the cyanobacterial enzyme cyanase increases cyanate metabolism and cyanate tolerance in Arabidopsis

Cyanate and its derivatives are considered as environmental hazardous materials. Cyanate is released to the environment through many chemical industries and mining wastewater. Cyanase enzyme converts cyanate into CO₂ and NH₃ in a bicarbonate-dependent reaction. At low cyanate concentrations, the endogenous plant cyanases play a vital role in cyanate detoxification. However, such cyanate biodegradation system is probably insufficient due to the excess cyanate concentrations at contaminated sites. In this study, we have transferred the activity of the cyanobacterial cyanase into Arabidopsis thaliana plants in order to enhance plant resistance against cyanate toxicity. The enzyme was shown to be active in planta. Transgenic plants exposed to cyanate, either applied by foliar spray or supplemented in growth medium, showed less reduction in pigment contents, antioxidant enzymes, carbohydrate contents, and reduced levels of plant growth retardation. Plant growth assays under cyanate stress showed enhanced growth and biomass accumulation in cyanase overexpressors compared to control plants. Results of this study provide evidence for developing novel eco-friendly phytoremediation systems for cyanate detoxification.