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

Abstract

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 NH 4 +-N, HCO 3 and SO 4 2-. Nevertheless, at 360-2100 mg SCN-/L a breakdown in the degradation pathway was observed. Respirometry tests demonstrated that NH 4 +-N was inhibitory to SCNdegradation (IC 50 : 316 mg/L). Likewise, phenol (180 mg/L) and hydroxylamine (0.25-16 mg/L) reduced SCNdegradation by 41% and ca. 7%, respectively. The understanding of the SCNdegradation pathways can enable stable treatment efficiencies and compliance with effluent of <4 mg SCN/L, required by the Industrial Emissions Directive.

Enhancing the removal of pollutants from coke wastewater by bioaugmentation: A scoping study

“…Alkalinity addition led to a reduction in phenol concentration to 0.3 mg L –1 allowing compliance with the <0.5 mg L –1 emission limit. Ammonia‐nitrogen concentrations were expected to increase as a result of SCN – degradation . Alkalinity addition, however, led to ammonia‐nitrogen removal (Table ) which was consistent with the stimulation of autotrophic nitrifying bacteria.…”

“…Ammonia-nitrogen concentrations were expected to increase as a result of SCNdegradation. 9,39 Alkalinity addition, however, led to ammonia-nitrogen removal ( Table 5) which was consistent with the stimulation of autotrophic nitrifying bacteria.…”

“…As SCNdegraders are autotrophic in nature, the improved SCNremoval through biostimulation may be associated with the increased concentrations of the required micronutrients or inorganic carbon associated with alkalinity addition, which may in turn be utilized by autotrophic thiocyanate degraders present in the biomass. 23,39 A bioaugmentation dose of 0.1 g L -1 resulted in a similar degradation trend to control conditions in the first 13 h. However, final SCNconcentrations at 25 h were higher than under control conditions at 4.3 ± 2 mg L -1 . The addition of bioaugmentation product at 0.1 g L -1 therefore offered no benefit to SCNdegradation over a 25 h period.…”

“…), a genusknown to be involved in SCN – degradation. As SCN – degraders are autotrophic in nature, the improved SCN – removal through biostimulation may be associated with the increased concentrations of the required micronutrients or inorganic carbon associated with alkalinity addition, which may in turn be utilized by autotrophic thiocyanate degraders present in the biomass …”

“…Figure shows the OTU abundance for the bioaugmentation product, indigenous activated sludge biomass, batch test effluent combined with river water and batch test effluent combined with river water after 24 h. It can be observed that the indigenous activated sludge biomass was characterized by a high abundance of an uncultured species of Thiobacillus (26%), an uncultured species of Mizugakiibacter (13%), an ambiguous species of Rhodanobacter (11%) and an ambiguous species of Comamonas (12%). Thiobacillus is associated with the degradation of SCN – , whereas Mizugakiibacter and Rhodanobacter have been associated with their iron‐oxidising and nitrate‐reducing abilities . Comamonas bacteria have been associated with a wide range of abilities including the degradation of phenol…”