Experimental Study On Startup And Performance Characteristic Of The Microaerobic EGSB Reactor Treating Coking Wastewater

A conventional activated sludge process has problems to treat the coking wastewater because of the presence of toxic and inhibitory compounds. Poor settle-ability problem was reported at high loading rates in an activated sludge process. The removal efficiencies for ammonia and CN were very low. In the biofilm process, the poor settle-ability problems could not be observed, the removal efficiencies of COD and phenol are relatively high but the removal efficiencies of ammonia, SCN and CN were still low because of the presence of toxic and inhibitory compounds. The A2/O biological treatment system is frequently used in order to treat coking wastewater for the toxic organic compounds and NH3-N removal. But there are problems which are inherent to an anaerobic/aerobic treatment sequence since the anaerobic transformation of toxic organic compounds is often incomplete. The metabolites of anaerobic treatment may also be inhibitory to the methanogens themselves, resulting in declining anaerobic treatment efficiencies and adding to the load on the downstream aerobic treatment system. The EGSB reactor had the particular advantage in treatment of industry wastewaters containning many refractory, but which could not ensure the ammonia removal effect. Through introducing the limited-oxygen concept, the two-stage EGSB reactors could simultaneously attain high COD and ammonia removal when treating coking wastewater. In this paper, the start-up for the microaerobic EGSB reactor seeded with municipal digestion sludge,the operation characteristic and miciobiology property, the operation influence factors, and the pollutant removal mechanism were studied in details.The EGSB reactor seeded with municipal digestion sludge and little loose granules lack of nutrition could startup within 10d using brewery wastewater. The granules formed in the EGSB reactor had good settlement property,high methanogenic activity and abundant microbes species. It was the key factor for the quickly forming of the granular sludge to add little loose granules lack of nutrition.With the two-stage EGSB reactor configuration treating actual coking wastewater containing many toxicant and refractory organic compounds, the fast start-up mode was feasible to formed granular sludge with brewery wastewater through seeding digestion sludge and little loose granules lack of nutrition and then to acclimatize the granules with actual coking wastewater. Gradually increasing the coking wastewater supplement ratio was an effective acclimation approach, and the startup of the EGSB reactor treating coking wastewater could achieve within 6 months.The two-stage microaerobic EGSB reactor treating actual coking wastewater could have high COD and ammonia removal efficiencies, and the effluent COD and ammonia concentrations were 52.7mg.L-1 and 12mg.L respectively. And both met the effluent standard.The removal of the nitrate (NO3-) was mostly accomplished in the EGSBⅠ,and the EGSBⅡwas mainly used to enrich the nitrite (NO2-). But the denitrification process was not strengthened in the EGSBⅡ, and it was essential to accomplish shortcut denitrification of the nitrite. The two-stage microaerobic EGSB reactor could successfully remove toxicant and refractory organic compounds from the coking wastewater, and the effluent phenol, CN and SCN concentrations were all under 0.5mg.L-1. The EGSBⅠand EGSBⅡcould all achieved high COD removal efficiency of 70%-90%. But the phenol and CN removal was mainly accomplished in the EGSBⅠ, and the SCN and ammonia was mostly removed in the EGSBⅡ.The removal of the pollutants in the actual coking was presented a phenol+CN+COD/SCN+ammonia treatment sequence. In particular, the removal effect of the SCN had directly influence on the removal effect of other contaminations, especially on the ammonia and TN removal. The two-stage mocroaerobic EGSB reactor had very strong supporting loads shock ability of COD, ammonia, phenol, CN and SCN, and which was suitable.for the treatment of actual coking wastewater.The operation influence factors of the two-stage microaerobic EGSB reactor treating actual coking wastewater were investigated. It was found that the oxygenation flow rate had to be added gradually in order to increase the COD removal efficiency for the start-up operation process of the microaerobic EGSB reactor. The COD and ammonia removal efficiencies were distinctly higher using the continuous oxygenation way than using the intermittent oxygenation method. It was feasible for the microaerobic EGSB reactor control to combine the control factors of the oxygenation flow rate and the ORP. An air supply of 5000ml.min-1 was suitable, and the ORP was about 50mV. Because of the very strong ability of supporting loads shock, the two-stage microaerobic EGSB reactor had prominent advantage of treating actual coking wastewater with regular water quality changes. The two-stage microaerobic EGSB reactor could be solely used to highly efficiently treat coking wastewater. And which also could be combined with the A2/O biological treatment system to strengthenly treat the coking wastewater. The optimal values of the influent flow, recycle rate,HRT and Vup were 1.5L.h-1,15-22.5L.h-1,8h and 2.1-3.1m.h-1,respectively. It was more suitable to control the sludge concentration in the microaerobic EGSB between 15g.L-1 and 25g.L-1.For the actual pH value of 7.5-8.5, the microaerobic EGSB reactor could run well. Low temperature had no influence on the operation effect of the microaerobic EGSB reactor treating coking wastewater. But with a large temperature fluctuation range, the the COD removal efficiency decreased distinctly and however could revover very quickly. And thus the microaerobic EGSB reactor had very strong supporting temperature shock ability when treating actual coking wastewater. The supplement of NaHCO3 could observably increase the COD and ammonia removal efficiency of the microaerobic EGSB reactor treating coking wastewater.The substrate-utilization dynamic model of the microaerobic EGSB reactor treating coking wastewater at the startup operation stage and the stable operation stage was founded. And synchronously dynamics constants of the microaerobic EGSB reactor at varied operation stage were calculated. At the startup operation stage, the dynamics constants value of vmax,KI,KS,Vmax/KS,KS/KI were 7.34×10-3,197.76,19.53,3.7×10-4 and 0.10, respectively.and for the stable operation stage, the dynamics constants value of vmax,KI,KS,Vmax/KS,KS/KI were 2.4×10-2,66.64,44.07,5.4×10-4 and 0.66, respectively. And which indicated that the geanules in the microaerobic EGSB reactor could gradually adapt and then highly efficienctly remove the toxic or inhibitory compounds. Increasing the liquid upflow velocity Vup could make the maximum specific substrate removal rate vmax increasing and the half-saturation coefficient KS decreasing and thus strengthen the operation effect of the microaerobic EGSB reactor.