Processes And Equipments Of Restaurant Wastewater Treatment And Oil Grease Recovery

Restaurant wastewater is a kind of high concentration organic wastewater, whichis harmful to the environment. In this study, investigations of large canteens’wastewater quality characteristics and emission rules were taken. In addition,treatment of oil and grease, chemical oxygen demand(COD) and suspended solid (SS)were studied, too. Meanwhile, preliminary recovery technologies of oil and greasewere explored.Surverys show that the restaurant wastewater was acid and had much organics,which included oil and grease of308~3236mg/L, SS of287~14318mg/L and CODCrof1470~10690mg/L. The concentrations of linear alklybezene sulfonates (LAS),ammonia nitrogen (NH3-N) and total phosphorus (TP) are low, which were0.33~13.84mg/L,1.6~64.7mg/L,1.1~43.5mg/L, respectively.The process of oil separation and pressurized dissolved air flotation was used totreat restaurant wastewater. When the hydraulic retention time (HRT) was1h, theremoval effciency of oil and grease, SS, COD was80%,44%,44%, respectively. Theeffluent of oil separation process was treated by pressurized dissolved air flotationprocess. The best condition was PAC dosage of50mg/L and reflux ratio of50%.The effluent of oil separation process was also treated by electro-coagulation andflotation process. It showed that it had a high removal efficiency (99%) of oil andgrease under the conditions of inter-electrode distance of3.6cm, reaction time of34min, current density of43A/m2in the model of response surface methodology. Whenwastewater conductivity was less than2980μs/cm, electro-coagulation played thedominant role, and the contribution rates ranged from68.1%to72.5%. When thewastewater conductivity was above3480μs/cm, electro-flotation played the dominantrole and the contribution rates ranged from51.6%to65.8%. The concentration of AlTincreases with the increasing of wastewater conductivity, reaction time and currentdensity. Active ingredient Alb%increases with the increasing of reaction time andcurrent density, which reaches the largest as wastewater conductivity of2980μs/cm.Pilot study of electro-coagulation and flotation process was also taken. Under theconditions which was current of30A and HRT of20min, the concentration of oil andgrease and SS met the standard with the concentration less than100mg/L and400mg/L, repectively. At that time, the power consumption of1m3was0.4kW h/m3.Compare with pressurized dissolved air flotation, electro-coagulation and flotation has the advantages of smaller palce, lower investment and simple management. Soelectro-coagulation and flotation is recommended as the fine treatment of restaurantwastewater.The process of evaporation and filtration was used to recover greaves from theoil separation tank. And the recovery rate was around80%. However, scum from theelectro-coagulation and flotation tank should add some acid to lower the pH todissolve the floc of Al first. And then it was the same recovey proesss with thegreaves, while the recovery rate was around50%. Among all the process, the recoveryrate of oil and grease was over70%.