| Coal chemical wastewater（CCW）is a kind of typical toxic,harmful and intractable industrial wastewater with complex components,high concentration of nitrogen pollutants and poor biodegradability.With the increasingly strict access conditions and environmental protection standards（especially the requirements for total nitrogen concentration）of coal chemical industry,the difficulty of CCW disposal has been heightened.Biological processes are still the main technology for CCW treatment,as they possess the advantages of lower operating costs.However,the widely used anoxic/aerobic/aerobic biological denitrification process shows its disadvantages in practical engineering.It is urgent to develop and apply a new treatment process with high efficiency and low cost,to fundamentally solve the urgent situation that shutdown and rectification of enterprise.In addition,community structure determines the efficiency of CCW treatment.Relevance understanding of the structural diversity and functional correlation and the interaction of microbial populations in the system are still very limited,this restricts the efficiency of CCW treatment system considerably.To this end,the research on the performance and microecology mechanism during biological treatment of CCW is the key for improving wastewater treatment efficiency,reducing processing costs and protecting the ecological environment.The object of this study was two typical coal chemical wastewaters,and the biological process of a step-feeding two-stage A/O（SF-A/O）treatment for coking wastewater and integrated PN/A treatment for coal gasification wastewater（CGW）was developed and the efficiency of engineering application was analyzed.And the control optimization strategy of the stable operation for the two processes in practical projects was comprehensively analyzed.In addition,the differences of microbial community structure,biodiversity and community function prediction related to pollutant degradation in the system were revealed by means of molecular biology.And the characteristics and succession law of dominant denitrification microorganisms,and the interaction relationship between bacteria in the system was discussed.Finally,the comprehensive evaluation of several biological denitrification processes was carried out by using the life cycle assessment and the construction of analytic hierarchy process model to select the most appropriate engineering technology scheme.It provides a scientific and quantitative decision-making basis for the process optimization,technology comparison and operation management of CCW treatment for enterprise.The main results obtained are as follows:（1）A SF-A/O process was developed and firstly applied at full-scale to treat CCW.It showed that the SF-A/O process displayed a greater removal efficiency than the A/O/O process,especially in nitrogen removal.The reduction of NO3-and co metabolism of carbon source have strengthened the degradation of high molecular weight PAHs.The abundance in Thiobacillus,SM1A02,and Thauera could be the main reason why SF-A/O was superior to A/O/O in treating TN.The microbial community structure of SF-A/O was similar among stages in system and was less affected by environmental factors,which may have been one of the important factors in the system’s strong stability.（2）The feasibility of treating CGW by integrated PN/A process was verified for the first time.The NRR of CGW treatment by pilot scale IFAS system was reach 0.65±0.09 kg N/（m3·d）.And the three dominant An AOB was coexist in the system,and different distribution characteristics of the denitrification microorganisms in biofilm and flocs was found.Based on the results of pilot experiment,the integrated PN/A process was firstly applied at full-scale to treat CGW with low carbon nitrogen ratio（the value lower than 0.5）and high nitrogen（the concentration of TN was 655.4±187.6mg/L）.The project was successfully started after commissioning for 120 days,and the initial NRR can reach 0.37±0.14kg N/（m3·d）.Different from the results of pilot experiment,there was only one dominant An AOB bacteria in the full-scale system.Combined with the long-term operation results of pilot and full-scale project,the control strategies of inhibiting NOB and realizing stable shortcut nitrification process are excavated.（3）The construction results of molecular ecological network for potential microbial interaction in integrated PN/A system of CGW was show that it likely led to closer and more complex networks with the continuous maturity of biofilm.There was more competition among species with similar niche,and the relationship between microbial species was more single and closer.Most of the key microorganisms were mainly involved in the degradation of organic matter and denitrification,to cooperate with the stability of anammox reaction.And the relatively low abundances species could act as important roles in the anammox system.（4）The environmental impact of CCW biological treatment technology was mainly reflected in terrestrial ecotoxicity,global warming potential,human non carcinogenic toxicity and fossil resource scarcity.And the pollutant discharge related to the power production required to operate the CCW biological treatment system,the direct discharge of wastewater and the pollutants discharged in the process of reagent production were determined as the main factors of the overall environmental impact for several treatment schemes.The total environmental impact of the integrated PN/A system was significantly lower than that of the other three processes,especially in its contribution to global warming potential and fossil resource scarcity.（5）The results of the analytic hierarchy process show that the weights of the four treatment schemes were 0.753,0.663,0.748 and 0.814,which means that the A/O/O process has the least benefit to CCW treatment.Overall,integrated PN/A has the greatest advantages,but its evaluation results at the management level and technical level were not optimal.In addition,the SF-A/O process shows the same advantages as the integrated PN/A in terms of technical performance.Moreover,the results of AHP variability analysis show that the integrated PN/A process have exhibit an excellent stability. |
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