| Biofilm processes have now widely applied in domestic wastewater treatment,while they have various problems such as low efficiency in nitrogen removal and easy biofilm detachment.Since being advantageous in hydraulic characteristics,specific surface area and dispersibility,soft micro-sized inorganic basalt fiber could adsorb,enrich and immobilize microbes on the surface,forming an aggregate called bio-nest,with the size more than 10 cm.When applied in single reactor or unit,it could simplify reactor configuration,incorporate aerobic/anoxic or aerobic/anoxic/anaerobic functions into bio-nest,achieving nitrogen removal effectiveness.The purpose of this study aimed to construct multifunctional single reactor,i.e.,BF bio-nest reactor,with the contents listed as follows:(1)Performance optimization of bio-nest reactor.Single factor experiments were conducted to investigate the effects of hydraulic retention time(HRT),carrier horizontal spacing(HS)and dissolved oxygen(DO)on contaminant removal efficiencies,while biological contact oxidation and ordinary activated sludge reactor were used as the controls.Subsequently,orthogonal experiments were carried out to determine the optimal operating parameters in bio-nest reactors,meanwhile A/O process was used as the control.Results from single factor experiments showed that HRT was not important in COD removal efficiency of the three groups of reactors,but significant in ammonia nitrogen and total nitrogen removal.DO was more important in reactor operation,making ammonia nitrogen and total nitrogen removal efficiencies reaching 57.1% and 55.7% at DO of 1.5 mg/L,but adverse to ammonia nitrogen and total nitrogen removal at concentration of more than 3.5 mg/L.HS significantly affected total nitrogen removal effectiveness through arrangement density.orthogonal experiments showed that the optimal parameters were obtained at HRT,DO and HS of 12 h,2.5 mg/L and 20 cm.(2)Effectiveness and mechanism of BF bio-nest reactor in nitrogen removal.Besides organic removal,bio-nest reactor was used to investigate nitrogen removal mechanism of bio-nest,with biological contact oxidation and A/O process as the controls.Results showed that bio-nest reactor achieved COD,ammonia nitrogen and total nitrogen removal efficiencies of 93.2%,84.9% and 73.5% at optimal conditions.Bio-nest had higher specific oxygen uptake rate and dehydrogenase activities at the outer regions,suggesting that enhanced organic removal capability was ascribed to abundance of heterotrophic bacteria.High-throughput sequencing showed that the genera included heterotrophic nitrifying genera(e.g.,Nitrosomonas,Comamonas),denitrifying genera(e.g.,Ottowia,Candidatus?Saccharimonas,Brachymonas,Rhodanobacter,Limnobacter,Azoarcus),autotrophic denitrifying genera(e.g.,Hydrogenophaga),as well as aerobic denitrifying genera(e.g.,Thauera),which together accounted for 20.5% of the obtained sequence reads,much higher than that in other two reactors.(3)Applicability of bio-nest reactor.Three kinds of real wastewater(domestic,printing and dyeing,as well as carbon nanotube producing)were used to evaluate bio-nest's capability in real wastewater treatment.The results showed that bio-nest did well in domestic wastewater treatment,with COD,ammonia nitrogen and total nitrogen removal efficiencies of 88.0%,86.1% and 70.8%.Furthermore,it showed good resistance to loading impact and capability in contaminant removal,with COD,ammonia nitrogen and total nitrogen removal efficiencies of 85.0%,90% and 72.7% for printing and dyeing wastewater.By contrast,because of the higher ammonia nitrogen loading rate,bio-nest had an ammonia nitrogen and removal efficiency of no more than 55.0%,but had relatively higher COD and total nitrogen removal efficiencies of 81.0 % and 68.8% for carbon nanotube producing wastewater. |
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