| Coking wastewater composition is complex, it not only contains ammonia nitrogen, cyanide, phenolic compounds and other inorganic contaminants, while also containing heterocyclic compounds and polycyclic aromatic hydrocarbons and many other refractory organic pollutants.It is difficult to biological treatment. Most of domestic enterprises adopt pretreatment, biological treatment and advanced treatment combination technology to treat coking wastewater, the traditional biological treatment process (A2/O and A2/O2, etc.) have long flow and high operating cost. Upflow Blanket Filter (UBF) is a new type of composite reactor, the upper packing layer and the lower sludge bed in two parts, the combination of the packing layer and the sludge bed can not only improve the amount of microbes in the reactor, and also make the reactor has a stronger ability to resist impact load, improve the stability of operation. This study intends to realize simultaneous denitrification and methanogenesis in UBF, incorporating A1 and A2 in the traditional process, removing organic matter and nitrogen at the same time by denitrification and methanogenesis, shortening the process, saving energy consumption.Prepare the simulated coking wastewater according to certain proportion of the typical components of coking wastewater phenol, quinoline, pyridine, indole (phenol:quinoline:pyridine:indole=76:18:4:2; in COD equivalent).Anaerobic granular sludge as the inoculated sludge, under the temperature of 35±2℃,use the UBF to treat simulated coking wastewater, adding NaNO3 in water to simulate the backflow of nitrification liquid and realize simultaneous denitrification and methanogenesis.Analysis on UBF startup conditions, the optimization of operating conditions, organic substrate competition and substrate degradation kinetics, get the following results:1. Anaerobic granular sludge as the inoculated sludge, under the temperature of 35±2℃, start the UBF with the simulated coking wastewater, culturing activated sludge and biological film simultaneously. On the basis of realize methanogenesis, join nitrate nitrogen to coupling denitrification. After four months of culture resulted in simultaneous denitrification and methanogenesis, along with stable operation and a high efficiency of denitrification and decarburization, the removal efficiency of COD and nitrate nitrogen are above 85% and 99%.2. Research on denitrification and decarburization effect on different hydraulic retention time (HRT) levels(24-4.3h), the best HRT of UBF is 7.2h. When HRT is 7.2h, COD and nitrate nitrogen removal efficiency reached 94% and 99%. Even if the HRT longer, removal rate almost unchanged. When below 7.2h, removal efficiency of COD decreased.3. Research on reactor operating effect under different levels of inflow COD/NO3--N(25～3), concluded the adaptive inflow COD/NO3--N level is 4-12. Within the scope, COD and nitrate nitrogen removal efficiency reached 94% and 99%.When inflow COD/NO3--N> 12, COD degradation rate decrease. When inflow COD/NO3--N<4, lack of carbon source, denitrification reaction was not complete, therefore caused NO2--N accumulation.4. By studying denitrification and decarburization effect at different ascending velocity (0.5～5m/h) drew the following conclusions:the adaptive ascending velocity is 1.5-3.5m/h. When ascending velocity is too high or too low, COD significantly increased, decarburization effect dramatically declined.5. When the UBF ran under the adaptive conditions(HRT=7.2h, inflow COD/NO3-N=10, ascending velocity=2m/h), the removal efficiency of COD and NO3-N are 94.7% and 99.7%. The removal efficiency of COD and NO3-N of lower sludge bed are 67% and 99%.6. Carbon balance analysis in the UBF obtained following conclusions: denitrification almost concentrate sludge bed, methanogenesis throughout the UBF. When the inflow COD/NO3-N levels were 15 and 8, the rates of denitrification contribution to COD removal are 26.1% and 47.79%. Methanogenesis contribution rates are 73.9% and 52.21%.7. Monod mode has a strong characterization of COD degradation rule in the process of anaerobic digestion, model parameters is obtained by Matlab curve fitting:Largest degradation rate is 3.456d-1, half-saturation constant is 253.62mg/L, concentration of refractory material is 100.8mg/L.8. Then differential model based on Monod model was used to fit the change in the concentration of NO3-N and NO2-N and COD respectively, model parameters were as follows:The maximum degradation rates are 1.13 d-1 and 0.66d-1.The half-saturation constant of NO3-N and NO2-N are 2.0 mg/L and 2.5 mg/L. The half-saturation constant of organic substrate based upon NO3-N and NO2-N are 90.8 mg/L and 96.8 mg/L,denitrification refractory organic matter concentration is 79.8 mg/L... |
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