Study On Two-stage Anaerobic Process Pretreating Coal Chemical Industry Wastewater

As the continous development of China's economy, the demand for oil and natural gas rose sharply, giving the external conditions for the development of coal chemical industry. However, a great deal of wastewater was generated during the production processes of coal chemical industry. The component of the wastewater was very complex, phenolics were the main organic pollutents, a variety of toxic harmful and prohibitive pollutants were included. It would cause significant damage to the environment unless it was treated effectively. Nowadays, anoxic-oxic treatment process was most commonly used to treat the coal chemical industry wastewater after ammonia and phenol were recovered, but the effect was not ideal.Two-stage mesophilic anaerobic process was used to treat the synthesis wastewater from coal chemical industry in this paper. The following aspects are studied:⑴The start-up of the two-stage mesophilic anaerobic system and the aerobic biodegradability improvement of the coal chemical wastewater by the two-stage mesophilic anaerobic system;⑵The effect of HRT, influent concentration, OLR and upflow velocity on the system efficiency;⑶The stability of the system under the shocks of influent COD concentration, influent flow rate, influent total phenol concentration and pH;⑷BP network model was used to preliminary simulate the efficiency of the system. The main conclusions are as follows:The start-up of the system was completed after 168 days. The influent concentration of COD and total phenol were about 2500mg/L and 525mg/L, respectively, the removal of them were about 50% and 48%. After its effluent was treated by aerobic process for 32h, The COD and total phenol concentration were 288.2±12.2mg/L和46.4±4.8mg/L, respectively. When the HRT of single anaerobic reactor was extended from 24h to 36h, the COD removal rate was increased from 49.8% to 51.9%, the effect was limited. The results also showed that, when the up flow velocity in the reactors was increased from 0.042m/h to 0.126m/h, the COD removal rate of the system was decreased from 49.8% to 31.3%. The raise of the influent COD concentration would greatly influence the performance of the system. When the influent COD concentration suddenly increased from 2500mg/L to 4757.6mg/L, the first stage anaerobic reactor was almost completely inhibited, but the pollutants removal of the second stage anaerobic reactor was greatly enhanced, the COD and total phenol removal rate both reached over 25%. The stability of the system was guaranteed when the concentration shock was happened. The impact of influent flow rate shock was smaller than that of influent concentration shock, and the needed recovery time was shorter. When the shock concentration of total phenol was 656mg/L, the COD removal rate of the system was still over 30%, and the needed recovery time was only about 10 days. pH shock for short time would not make serious impact on the system, and the total phenol removal would be improved under lower pH value. BP network model was used to preliminary simulate the COD removal efficiency of the system. The influent COD and OLR were used as inlet, COD removal efficiency as outlet, the simulation results was excellent.