Characterisation of thiocyanate degradation in a mixed culture activated sludge process treating coke wastewater

Degradation of thiocyanate by Fe/Cu/C microelectrolysis: Role of pre-magnetization and enhancement mechanism

Thiocyanate (SCN-), a non-volatile inorganic pollutant, is commonly found in various types of industrial wastewater, which is resistant to hydrolysis and has the potential to be toxic to organisms. Premagnetized iron-copper-carbon ternary micro-electrolytic filler (pre-Fe/Cu/C) was prepared to degrade SCN-. Pre-Fe/Cu/C exhibited the most significant enhancement effect on SCN- removal when magnetized for 5 min with an intensity of 100 mT, and the SCN- removal rate was the highest at an initial pH of 3.0 and an aeration rate of 1.6 L/min. The electrochemical corrosion and electron transfer in the pre-Fe/Cu/C system were confirmed through SEM, XPS, FTIR, XRD, and electrochemical tests. This resulted in the formation of more corrosion products and multiple cycles of Fe2+/Fe3+ and Cu0/Cu+/Cu2+. Additionally, density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) were utilized to illustrate the oxygen adsorption properties of the materials and the participation of reactive oxygen species (1O2, ·O2-, and ·OH) in SCN- removal. The degradation products of SCN- were identified as SO42-, HCO3-, NH4+, and N2. This study introduced the use of permanent magnets for the first time to enhance Fe/Cu/C ternary micro-electrolytic fillers, offering a cost-effective, versatile, and stable approach that effectively effectively enhanced the degradation of SCN-.

Molecular level insight of thiocyanate degradation by Pseudomonas putida TDB-1 under a high arsenic and alkaline condition

It is a big challenge to bioremediate thiocyanate pollution in the gold extraction heap leaching tailings and surrounding soils with high contents of arsenic and alkali. Here, a novel thiocyanate-degrading bacterium Pseudomonas putida TDB-1 was successfully applied to completely degrade 1000 mg/L thiocyanate under a high arsenic (400 mg/L) and alkaline condition (pH = 10). It also leached the contents of thiocyanate from 1302.16 to 269.72 mg/kg in the gold extraction heap leaching tailings after 50 h. The maximum transformation rates of S and N in thiocyanate to the two finial products of SO₄^2- and NO₃^- were 88.98 % and 92.71 %, respectively. Moreover, the genome sequencing confirmed that the biomarker gene of thiocyanate-degrading bacterium, CynS was identified in the strain TDB-1. The bacterial transcriptome revealed that critical genes, such as CynS, CcoNOQP, SoxY, tst, gltBD, arsRBCH and NhaC, etc. in the thiocyanate degradation, S and N metabolisms, and As and alkali resistance were significantly up-regulated in the groups with 300 mg/L SCN^- (T300) and with 300 mg/L SCN^- and 200 mg/L As (TA300). In addition, the protein-protein interaction network showed that the glutamate synthase encoding by gltB and gltD served as central node to integrate the S and N metabolism pathways with thiocyanate as substrate. The results of our study provide a novel molecular level insight for the dynamic gene expression regulation of thiocyanate degradation by the strain TDB-1 with a severe arsenic and alkaline stress.

A newly developed consortium with a highly efficient thiocyanate degradation capacity: A comprehensive investigation of the degradation and detoxification potential

Thiocyanate-containing wastewater harms ecosystems and can cause serious damage to animals and plants, so it is urgent to treat it effectively. In this study, a new efficient thiocyanate-degrading consortium was developed and its degradation characteristics were studied. It was found that up to 154.64 mM thiocyanate could be completely degraded by this consortium over 6 days of incubation, with a maximum degradation rate of 1.53 mM h^-1. High-throughput sequencing analysis showed that Thiobacillus (77.78%) was the predominant thiocyanate-degrading bacterial genus. Plant toxicology tests showed that the germination index of mung bean and rice seeds cultured with media obtained after thiocyanate degradation by the consortium increased by 94% and 84.83%, respectively, compared with the control group without thiocyanate degradation. Cytotoxicity tests showed that thiocyanate without degradation significantly decreased the Neuro-2a cell activity and mitochondrial membrane potential; induced reactive oxygen species generation and apoptosis; increased the cellular Ca²⁺ concentration; and damaged the cell nucleus and DNA. Furthermore, the thiocyanate degradation products produced the consortium were almost totally non-toxic, revealing the same characteristics as those of the control using distilled water. This study shows that the consortium has a high degradation efficiency and detoxification characteristics, as well as great application potential in bioremediation of industrial thiocyanate-containing wastewater.

Treatment of thiocyanate-containing wastewater: a critical review of thiocyanate destruction in industrial effluents

Thiocyanate is a common pollutant in gold mine, textile, printing, dyeing, coking and other industries. Therefore, thiocyanate in industrial wastewater is an urgent problem to be solved. This paper reviews the chemical properties, applications, sources and toxicity of thiocyanate, as well as the various treatment methods for thiocyanate in wastewater and their advantages and disadvantages. It is emphasized that biological systems, ranging from laboratory to full-scale, are able to successfully remove thiocyanate from factories. Thiocyanate-degrading microorganisms degrade thiocyanate in autotrophic manner for energy, while other biodegrading microorganisms use thiocyanate as a carbon or nitrogen source, and the biochemical pathways and enzymes involved in thiocyanate metabolism by different bacteria are discussed in detail. In the future, degradation mechanisms should be investigated at the molecular level, with further research aiming to improve the biochemical understanding of thiocyanate metabolism and scaling up thiocyanate degradation technologies from the laboratory to a full-scale.

Metabolic engineering of Oryza sativa for complete biodegradation of thiocyanate

Industrial thiocyanate (SCN^-) waste streams from gold mining and coal coking have caused serious environmental pollution worldwide. Phytoremediation is an efficient technology in treating hazardous wastes from the environment. However, the phytoremediation efficiency of thiocyanate is very low due to the fact that plants lack thiocyanate degradation enzymes. In this study, the thiocyanate hydrolase module was assembled correctly in rice seedlings and showed thiocyanate hydrolase activity. Rice seedlings engineered to express thiocyanate degrading activity were able to completely remove thiocyanate from coking wastewater. Our findings suggest that transforming the thiocyanate hydrolase module into plants is an efficient strategy for rapid phytoremediation of thiocyanate in the environment. Moreover, the rice seedlings expressing apoplastic or cytoplasmic targeted thiocyanate hydrolase module were constructed to compare the phytoremediation efficiency of secretory/intracellular recombinant thiocyanate hydrolase. The most obvious finding from this study is that the apoplastic expression system is more efficient than the cytoplasm expression system in the phytoremediation of thiocyanate. At last, this research also shows that the secreted thiocyanate hydrolase from engineered rice plants does not influence rhizosphere bacterial community composition.

A Simple Analysis Method of Specific Anammox Activity Using a Respirometer

Anaerobic ammonium oxidation (anammox) is a biological nitrogen removal process with attractive prospects, such as no carbon addition, less aeration, lower greenhouse gas generation, and lower sludge production. However, it is difficult to maintain a stable anammox process since the anammox bacteria have a slow growth rate and high sensitivity to many factors. Therefore, it is very important to analyze and maintain the anammox activity as a process indicator for its successful operation. The conventional method for measuring the concentration of nitrogen compounds, such as ammonium, nitrite, or nitrogen gas is inconvenient during the reaction time for specific anammox activity (SAA) analysis, which can result in an inaccurately determined SAA due to the substrate loss and temperature change. In this study, a respirometer was utilized to analyze the SAA. The SAA values from a respirometer (rSAA) showed a similar pattern to the SAA values (mSAA) from the conventional method. All of the SAA analyses showed the highest value at 35 °C with a granule size of <1 mm. Statistical analysis showed no significant differences regardless of the analysis method, since the p-values for the t-test and Wilcoxon rank-sum test were >0.05. Therefore, the respirometer can be used as a simple and efficient tool for SAA analysis. Moreover, the operating maintenance and management of the anammox process can be improved due to the simple SAA analysis in the field.

The importance of utilizing nitrate (NO3-) over ammonium (NH4+) as nitrogen source during detoxification of exogenous thiocyanate (SCN-) in Oryza sativa

Thiocyanate (SCN^-) is a nitrogen-containing pollutant, which can be involved in the nitrogen (N) cycle and interferes with plant growth. The current study highlights a new insight into the N (nitrate [NO₃^-] and ammonium [NH₄⁺]) utilization ways in rice seedlings under SCN^- exposure to clarify the interactive effect on uptake and assimilation between these N-containing chemicals. Phenotypically, relative growth rates (RGR) of NO₃^--fed seedlings were significantly higher than NH₄⁺-fed rice seedlings at the same SCN^- concentration. Both N fertilizations have no significant influence on SCN^- content and its assimilation in rice seedlings. However, significant accumulation of NO₃^- and NH₄⁺ were detected in shoots prior to roots under SCN^- stress. Enzymatic assay and mRNA analysis showed that the carbonyl sulfide (COS) pathway of SCN^- degradation occurred in both roots and shoots of NO₃^--fed seedlings but only evident in roots of NH₄⁺-fed seedlings. Moreover, the effect of SCN^- on the activity of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT) was negligible in NO₃^--fed seedlings, while GOGAT activity was significantly inhibited in shoots of NH₄⁺-fed seedlings. Nitrogen use efficiency (NUE) estimation provided positive evidence in utilizing NO₃^- over NH₄⁺ as the main N source to support rice seedling growth during detoxification of exogenous SCN^-. Overall, SCN^- pollution has unexpectedly changed the rice preference for N source which shifted from NH₄⁺ to NO₃^-, suggesting that the interactions of SCN^- with different N sources in terms of uptake and assimilation in rice plants should not be overlooked, especially at the plant N nutritional level.

Respirometry tests in wastewater treatment: Why and how? A critical review

Respirometry tests are a widely employed method in wastewater treatment field to characterize wastewater streams, assess toxic/inhibitory effects to the biomass, calibrate mathematical models. Respirometry can allow to fractionize the chemical oxygen demand (COD) in biodegradable and inert fractions, but also provide information related to biomass kinetics and stoichiometry through standardized laboratory techniques. Considering the increasing number of emerging contaminants detected in wastewater effluents, such as pharmaceuticals, personal care products and pesticides, respirometry can be a useful tool to promptly assess any toxic or inhibitory effect in wastewater treatment plants (WWTPs) operations. Beside conventional activated sludge (CAS), in recent years respirometric methods have been applied to innovative fields, such as moving-bed bio-reactors (MBBRs), fungi and microalgae, exploiting natural remediation methods. In particular, respirometry application to microalgae, through the so-called photo-respirometry, has been investigated in the latest years in the treatment of high-nutrient loaded streams, allowing resource recovery in biomass form. In this work, respirometric methods are first introduced from a theoretical basis and then critically discussed by considering the experimental apparatus, the available characterization protocols and the fields of application; the most recent literature findings on respirometry are coupled with authors' experience in the field. A comparison between physicochemical methods and respirometry is made, considering common protocols for WWTP modelling and calibration. The future research needed on the topic is finally outlined, including the coupling of respirometry with microbial community analysis, potentially leading to an enhanced process understanding, an extended respirometry utilization to get specific kinetic and stoichiometric parameters for modelling purposes, and a wider respirometry application as diagnosis tool in WWTP operations.

Biological treatment of coke plant effluents: from a microbiological perspective

During coke production, large volume of effluent is generated, which has a very complex chemical composition and contains several toxic and carcinogenic substances, mainly aromatic compounds, cyanide, thiocyanate and ammonium. The composition of these high-strength effluents is very diverse and depends on the quality of coals used and the operating and technological parameters of coke ovens. In general, after initial physicochemical treatment, biological purification steps are applied in activated sludge bioreactors. This review summarizes the current knowledge on the anaerobic and aerobic transformation processes and describes key microorganisms, such as phenol- and thiocyanate-degrading, floc-forming, nitrifying and denitrifying bacteria, which contribute to the removal of pollutants from coke plant effluents. Providing the theoretical basis for technical issues (in this case the microbiology of coke plant effluent treatment) aids the optimization of existing technologies and the design of new management techniques.

Anammox reactor exposure to thiocyanate: Long-term performance and microbial community dynamics

Anaerobic ammonium oxidation (anammox) is an autotrophic denitrification process that has broad application potential for treating coking wastewaters. The present study estimated the effects of thiocyanate (SCN^-), a common pollutant in coking wastewaters, on anammox processes and microbial communities in anammox reactors for over two years of continuous exposure. The addition of SCN^- (from 50 to 200 mg L^-1) showed negative effects on the denitrification performance of the anammox reactors. In SCN^--dosed reactors, increased effluent ammonium concentrations indicated the occurrence of SCN^--based biodegradation processes. Microbial analysis revealed that the anammox species almost disappeared in the reactor dosed with SCN^- at over 100 mg L^-1. Instead, an abundance of chemolithoautotrophic bacteria belonging to the Thiobacillus genus demonstrated a linear increase with SCN^- addition. The competition between anammox species and SCN^--degrading microorganisms was expected to dominate the inhibition effects of SCN^- addition on the performance of anammox reactors.