Study On Biological Enhancement Technologies For Treating Typical Refractory Organic Pollutants From Coal Chemical Wastewater

Coal chemical wastewater,as a typical industrial refractory organic wastewater,contains numerous and complicated component which was toxic and inhibited on the activity of microorganisms.At present,the application of conventional biological process on the treatment of coal chemical wastewater was often unsatisfied due to low removal efficiency,instability and high operational cost?if using advanced treatment?.This work focuses on the enhancement of microbiological technologies for the removal of refractory organic pollutants from coal chemical wastewater.Firstly,as one of typical important nitrogenous heterocyclic compounds?NHCs?in coal chemical wastewater,pyridine was chosen due to its accumulated toxicity and high recalcitrance.Micro-aerobic condition and electro-assisted biological technologies were applied in order to enhance pyridine degradation and denitrification,respectively.Secondly,modified corncobs used as solid slow-release organic carbon sources and biofilm carriers were investigated to improve the refractory organic pollutants biodegradation based on absorption and co-metabolic mechanisms when treating the real bio-treated coking wastewater?BTCW?.Herein,the possible enhanced biodegradation technologies were explored according to the various conventional biological treatment sections,which provided a new thought for enhancing the biological removal efficiency of coal chemical wastewater.The detailed results are summarized as follows:?1?A sequencing batch biofilm reactor?SBBR?under micro-aerobic or anaerobic conditions was investigated to remove pyridine at various concentrations from synthetic wastewater.The results showed that over 98%of pyridine was degraded under micro-aerobic condition,while about 21%of pyridine was removed under anaerobic condition.Additionally,at least 60%of nitrogen located in the pyridine ring was transformed to ammonium.The observation of Scanning Electron Microscope?SEM?showed that abundant microorganisms were attached on the surface or inside of porous biocarriers under micro-aerobic condition.High-throughput sequencing analysis demonstrated that Azotobacter,unclassified?f?Rhodobacteraceae,Tolumonas and Trichococcus were the dominant species in the micro-aerobic system.The kinetic study at steady period showed that pyridine degradation was fitted well with the pseudo first-order model?R²>0.96?.?2?Membrane-free bioelectrochemical systems?MFBES?were developed to investigate the feasibility of the enhanced pyridine removal using nitrate as electron acceptor.The results indicated that high supplied voltage 1.2 V resulted in highest pyridine degradation with utilization of glucose as co-substrate,which was around15%?20%higher than the control experiment.The kinetic study at steady period showed that pyridine degradation was fitted well with the pseudo first-order model?R²>0.97?.Additionally,at least 75%of nitrogen located in the pyridine ring was transformed to ammonium.Compared with anaerobic degradation,the supplementary nitrate used as electron acceptor could improve the biodegradation of pyridine,whether both glucose?co-substrate?and pyridine or only pyridine were utilized as the carbon sources.When COD/NO₃^--N concentration ratio was 6 with pyridine as the only carbon sources,pyridine and NO₃^--N were completely degraded in 18 hours.MFBES with carbon brush as bioanode was the ideal for pyridine degradation.SEM observation showed that the biofilm was thicker and compact after electrical stimulation.Moreover,most of microorganisms were micrococcus and rod-shaped bacteria observed in the biofilm.High-throughput sequencing analysis demonstrated that the abundance and diversity of microorganisms increased in MFBES.Dominant pyridine-degrading bacteria,denitrifiers,and fermentative bacteria co-existed inside the MFBES.Electrical stimulation selectively enriched pyridine-degrading bacteria and denitrifiers,especially at the bioanode.Under the same applied voltage,different anode material configurations also affected the microbial community structure,and the carbon brush had better than the carbon felt in biofilm adhesion and charge transfer.?3?The quality of the real bio-treated coking wastewater?BTCW?is difficult to meet coking wastewater discharge standards and future wastewater recycling needs.In the advanced treatment stage,BTCW was treated by the solid slow-release organic carbon sources biological fixed-bed process,including the two up-flow fixed-bed bioreactors?UFBR?which were separately filled with alkali-pretreated or no alkali-pretreated corncobs used as solid slow-release carbon sources as well as biofilm carriers.Results showed that this UFBR process could significantly improve the biodegradability of BTCW and increase the C/N ratio.Thus,over 90%of residual nitrate in BTCW were removed stably.Furthermore,Gas Chromatography-Mass Spectrometer?GC/MS?analysis confirmed that the typical refractory organic pollutants decreased significantly after UFBR treatment.High-throughput sequencing analysis demonstrated that dominant denitrifiers,fermentative bacteria and refractory-organic-pollutants-degrading bacteria co-existed inside the UFBR system.Compared with no alkali-pretreated corncobs,alkali-pretreated corncobs provided more porous structure and much stable release of carbon to guarantee the growth and the quantity of the functional bacteria such as denitrifiers.This study indicated that the UFBR filled with alkali-pretreated corncobs could be utilized as an effective biological pre-treatment for the enhanced treatment of the BTCW.