Efficient Photodegradation of Thiocyanate Ions in Mining Wastewater Using a ZnO-BiOI Heterojunction

Mining industries have long relied on cyanidation as the primary method for gold extraction, but this process generates thiocyanates as a problematic byproduct, posing challenges for wastewater treatment and recycling. The stability of thiocyanates makes their reduction or elimination in mining wastewater difficult. In this study, a p-n heterojunction of ZnO and BiOI was created and evaluated for its ability to photodegrade thiocyanate ions under simulated solar conditions. Various analytical techniques revealed a highly porous structure with a sponge-like morphology and agglomeration in the synthesized heterojunction. The compound exhibited crystalline patterns without impurity peaks, a slight red shift in absorbance, and Type IV isotherm adsorption. The synthesized heterostructure achieved the complete destruction of thiocyanate ions in less than 30 min. The investigation of different process parameters indicated that the destruction of the contaminant by the heterostructure was influenced by the initial thiocyanate concentration, which decreased as the thiocyanate concentration increased. The peak photodestruction reaction was observed at pH 7. By applying a pseudo-first-order kinetic model, it was found that increasing the catalyst mass to 15 mg raised the rate constant from 0.188 to 0.420 min-1, while increasing the pH to 10 led to a 3.5-fold reduction. The strong correlation between the observed data and the predicted values of the pseudo-first-order kinetic model was indicated by the observed (R2) values. The findings of this study hold potential significance for mining industries, as it offers a potential solution for eliminating cyanide and thiocyanates from mining wastewater. The elimination of thiocyanate generation in the cyanidation process is crucial for mining companies, making this study valuable for the industry.

Degradation pathway and microbial mechanism of high-concentration thiocyanate in gold mine tailings wastewater

As one of the inorganic pollutants with the highest concentration in the waste water of gold tailings using biohydrometallurgy, thiocyanate (SCN-) was effectively degraded in this research adopting a two-stage activated sludge biological treatment, and the corresponding degradation pathway and microbial community characteristics in this process were also studied. The results showed that SCN- at 1818.00 mg L-1 in the influent decreased to 0.68 mg L-1 after flowing through the two-stage activated sludge units. Raman spectroscopy was used to study the changes of relevant functional groups, finding that SCN- was degraded in the COS pathway. Based on 16S rRNA high-throughput sequencing technology, the microbial diversity in this system was analyzed, and the results indicated that Thiobacillus played a major role in degrading SCN-, of which the abundance in these two activated sludge units was 32.05% and 20.37%, respectively. The results further revealed the biological removal mechanism of SCN- in gold mine tailings wastewater.

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

Microbial degradation of thiocyanate (SCN^-) has been reported to suffer from instability highlighting the need for improved understanding of underlying mechanisms and boundaries. Respirometry, batch tests and DNA sequencing analysis were used to improve understanding of a mixed culture treating coke wastewater rich in SCN^-. An uncultured species of Thiobacillus was the most abundant species (26%) and displayed similar metabolic capabilities to Thiobacillus denitrificans and Thiobacillus thioparus. Thiocyanate was hydrolysed/oxidised to NH₄⁺-N, HCO₃^- and SO₄^2-. Nevertheless, at 360-2100 mg SCN^-/L a breakdown in the degradation pathway was observed. Respirometry tests demonstrated that NH₄⁺-N was inhibitory to SCN^- degradation (IC₅₀: 316 mg/L). Likewise, phenol (180 mg/L) and hydroxylamine (0.25-16 mg/L) reduced SCN^- degradation by 41% and ca. 7%, respectively. The understanding of the SCN^- degradation pathways can enable stable treatment efficiencies and compliance with effluent of <4 mg SCN/L, required by the Industrial Emissions Directive.

Bacterial community structure in rotating biological contactor treating coke wastewater in relation to medium composition

Biological wastewater treatment using biofilm systems is an effective way to treat difficult wastewater, such as coke wastewater. The information about the structure and the dynamics of this microbial community in biofilm, which are responsible for wastewater treatment, is relevant in the context of treatment efficacy and the biochemical potential to remove various pollutants. However, physico-chemical factors can influence the biofilm community significantly, causing performance disturbances. Therefore, we decided to examine the structure of microbial community in rotating biological contactor (RBC) biofilm during coke wastewater treatment and to investigate the possible shift in the community structure caused by the feeding medium change from synthetic to real coke wastewater. The experiment performed with high-throughput next-generation sequencing (NGS) revealed that bacteria commonly present in wastewater treatment plant (WWTP) systems, responsible for nitrite oxidizing, such as Nitrospira or Nitrobacter, were absent or below detection threshold, while Nitrosomonas, responsible for ammonia oxidizing, was detected in a relatively small number especially after shift to real coke wastewater. This research indicates that medium change could cause the change from autotrophic into heterotrophic nitrification led by Acinetobacter. Moreover, biofilm systems can be also a potential source of bacteria possessing high biochemical potential for pollutants removal but less known in WWTP systems, as well as potentially pathogenic microorganisms.