Mechanism Of Characteristic Pollutant Removal From Wastewater Containing Phenols And Ammonia By Algal–bacterial Symbiotic System

Coal chemical wastewater contains a large number of toxic and harmful pollutants,the primary ones being phenols and ammonia.After biochemical treatment,some phenols and nitrogen-containing heterocyclic substances retained in the effluent increase the difficulty and cost of subsequent treatments,such as advanced oxidation and reverse osmosis.Therefore,establishing stable and efficient biochemical treatment systems is the key to ensuring the reliable operation of subsequent treatment processes and achieving“zero liquid discharge.”Accordingly,this study screened bacteria and algae in terms of the degradation performance of phenolic substances,and built an algal–bacterial symbiotic system to further treat biochemically aerobic wastewater.Analyses of the pollutant composition,community structure,and functions of the microbial communities helped clarify the pollutant degradation mechanism of the algal–bacterial symbiotic system,and the removal of the refractory pollutants in the wastewater by the microorganisms was further improved.The main results of this research are as follows:?1?A high-efficiency phenol-degrading bacterium H2-2,was selected from coal gasification wastewater and identified as Rhodococcus sp.The simultaneous degradation of phenol and p-cresol by strain H2-2,antioxidant enzyme activity,and gene expression of phenol hydroxylase and catechol-1,2-dioxygenase,have been studied.The H2-2 strain had a tolerance of 1000 mg/L to both phenol and p-cresol.The initial concentration of p-cresol was 300 mg/L when the initial concentration of phenol was less than 500 mg/L.Both pollutants could be completely removed,and the expression of phenol hydroxylase gene and catechol-1,2-dioxygenase gene reached their highest levels at 48 h.The biotoxicity and superoxide dismutase activity of the solution after degradation were significantly reduced.However,when the phenol concentration exceeded 500 mg/L,the degradation of both was inhibited.?2?The co-metabolic properties of Chlorella vulgaris?C.vulgaris?in phenol and p-cresol,including the removal of phenols and ammonia-nitrogen,antioxidant enzyme activity,and phenol hydroxylase activity have been studied.The highest tolerance concentrations of C.vulgaris to phenol and p-cresol were 800 mg/L and 400 mg/L,respectively.During the co-metabolic process,the initial concentration of p-cresol was 300mg/L,and a low concentration of phenol?100 mg/L?significantly promoted the degradation of p-cresol.Moreover,p-cresol promoted the removal of high phenol concentrations.In addition,the change in phenol concentration had no significant effect on the ammonia-nitrogen removal rate,which was approximately 60%.As an exogenous nutrient of C.vulgaris,NaHCO₃ could increase the phenol hydroxylase activity and then enhance the co-metabolism of phenol and p-cresol.?3?The algal–bacterial symbiotic system was constructed in a moving bed biofilm bioreactor,and its effect on coal chemical wastewater treatment was analyzed.The composition of the coal chemical wastewater and degradation of the pollutants,the composition of the microbial community in the reactor and its change,the distribution of genes related to the nitrogen cycle,and phenol degradation were studied.The results showed that after two-stage aerobic treatment,the water quality of the coal chemical wastewater was obviously improved.In the control group aerobic reactor,the removal rates of chemical oxygen demand?COD?,ammonia-nitrogen,and total nitrogen were 66.25%,51%,and 62.01%,respectively,while in the algal–bacterial symbiotic reactor,the removal rates of COD,ammonia-nitrogen,and total nitrogen were 70%,63%,and 58.71%,respectively.It can be seen that the algal–bacterial symbiotic system was more advantageous for the removal of COD and ammonia-nitrogen.The pollutants were effectively removed in the control group aerobic reactor and algal–bacterial symbiotic reactor.The analytical results of Gas chromatography–mass spectrometry and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry results showed that compared with the control group,the high molecular weight CHO and CHON heterocyclic soluble pollutants were degraded effectively and converted into low molecular weight pollutants in the algal–bacterial symbiotic system.Among the three reactors,the most abundant microorganisms were found on the surface of the packing,and the abundance of the microbial communities was also high.In the control group aerobic reactor,Ferrovibrio,Xanthobacter,and Methyloversatilis were the dominant strains,whereas Sphingomonas,Pseudomonas,and Rhodococcus were the dominant species in the algal–bacterial symbiosis reactor.Although the microbial communities in the water and paddings of all three reactors exhibited the potential to degrade phenols as well as heterocyclic and condensed ring pollutants,the degradation effects on the latter two pollutants in the algal–bacterial symbiotic system were superior.