Improvement of coal gasification reverse osmosis concentrate treatment by Cu-Co-Mn/AC catalytic ozonation.

Approximately 20% of concentrate will be produced from coal gasification wastewater after reverse osmosis treatment. The organic matter contained in the concentrate affects its evaporation crystallisation; therefore, the refractory organics must be removed. In this study, Cu-Co-Mn/AC catalytic ozonation was used to treat reverse osmosis concentrate (ROC). With the addition of the Cu-Co-Mn/AC catalyst, the production of ·OH increased by 82 µmol/L, thereby enhancing the ozonation performance. The pH, ozone dosage, and catalyst dosage all affected the catalytic ozonation performance. By constructing a response surface model, it was found that the catalyst dosage had the most significant effect on the catalytic ozonation performance. The predicted optimal reaction conditions were pH = 9.02, ozone dosage = 1.08 g/L, and catalyst dosage = 1.33 g/L, under which the chemical oxygen demand (COD) removal reached a maximum of 81.49%.

Bacterial diversity evolution process based on physicochemical characteristics of sludge treating hydroquinone during acclimation.

Hydroquinone is one of the main pollutants in coal-gasification wastewater, which is biologically toxic and difficult to remove. The aerobic biodegradation rate, organic toxicity, and microbial community structure at different acclimation stages of degradation of hydroquinone by activated sludge were investigated. In each acclimation cycle, the removal of hydroquinone reached 100% after 5 days, indicating that high-concentration hydroquinone in the activated sludge could be completely biodegraded. When the microbial flora was inhibited by the influent hydroquinone, the enzyme system experienced stress conditions and led to the secretion of secondary metabolites, extracellular protein of 5-10 kDa mainly contributing to the sludge organic toxicity. Microbial diversity analysis showed that with the increase of the concentration of hydroquinone, ß-Proteus bacteria such as Azoarcus and Dechloromonas gradually accumulated, which improved the removal of hydroquinone with aerobic activated sludge in the sequencing batch reactor (SBR) system. As the inhibition degree exceeded the appropriate tolerance range of microorganisms, bacteria would secrete much more secondary metabolites, and the organic toxicity of sludge would reach a relatively high level.

Study on the differences in sludge toxicity and microbial community structure caused by catechol, resorcinol and hydroquinone with metagenomic analysis.

The aerobic biodegradation rate, organic toxicity and microbial community structure of activated sludge acclimated by catechol, resorcinol and hydroquinone were investigated, to study the relationship between microbial structure and sludge organic toxicity caused by phenolic compounds. At the stable operation stage, the degradation rates of the dihydroxy benzenes in a single sequencing batch reactor (SBR) cycle were followed the order: resorcinol (89.71%) > hydroquinone (85.64%) > catechol (59.62%). Sludge toxicity bioassay indicated that the toxicity of sludge was catechol (45.63%) > hydroquinone (40.28%) > resorcinol (38.15%). The accumulation of secondary metabolites such as 5-10 kDa tryptophan and tyrosine protein substances caused the differential sludge toxicity. Microbial metagenomic analysis showed that the toxicity of sludge was significantly related to the microbial community structure. Thauera, Azoarcus, Pseudomonas and other Proteobacteria formed in the sludge during acclimation. Catechol group had the least dominant bacteria and loop ring opening enzyme genes (catA, dmpB, dxnF, hapD) numbers. Therefore, the degradation of catechol was the most difficult than resorcinol and hydroquinone, resulting the highest sludge toxicity.