Pilot Scale Experimental Study On Advanced Treatment Of Coking Wastewater

Coking wastewater is an industrial organic wastewater with high toxicity,high salt content and difficult biochemical degradation produced in a series of coal processing processes.It may have adverse effects on soil and surface water when discharged directly into the environment.In addition.With the shortage of water resources and the strict requirements of the state on environmental management and control,it is an imminent demand to realize the near-zero discharge of coking wastewater.This research takes coagulation and precipitation effluent of coking wastewater as the research object,adopts the combined process of"Ultrafiltration+Reverse osmosis+Forward osmosis/IM-Fenton"to treat it,studies the removal effect of the process on inorganic pollutants such as suspended matter,colloid and chloride ions and organic pollutants such as COD,ammonia nitrogen,total nitrogen and total phosphorus,analyzes the causes of membrane pollution and the cleaning and recovery effect.In addition,The recovery rate of wastewater,pharmaceutical cost,energy consumption and other economic indexes were also demonstrated.It provides a certain reference for the treatment of similar wastewater.Experimental results show:（1）When PTFE ultrafiltration membrane was used to remove coking wastewater coagulation-precipitation effluent,cross-flow filtration has more advantages,especially when the amount of wastewater is huge,the stability is higher and the operation cycle is longer.Suspended matter,colloid and some macromolecular organic pollutants were effectively removed.Turbidity and suspended matter of water production were less than0.1NTU and 20mg/L,respectively,with removal rates of 97-100%and 71.9%-98.1%.（2）According to the fitting model,SEM and atlas analysis,cake filtration and critical blocking are the main causes of membrane pollution.The pollutants mainly consist of ferric flocculants and some hydrophobic organics,which can easily lead to membrane pollution and blockage.After chemical cleaning,the recovery rate of membrane flux and specific flux reached more than 90%,and the trans-membrane pressure almost recovered to the level before operation.（3）When the RO membrane system was used to filter the ultrafiltration water,it was found that the contents of COD,ammonia nitrogen,TDS and chloride ions of the produced water were respectively less than 20mg/L,1.2mg/L,388mg/L and 127mg/L in the optimal operating conditions,and the removal rates reached 91.8%-99.2%,92.6%-97.58%,97.4%-98.13%and 95.7%-97.66%respectively.The effluent quality satisfies the quality standard of plant reuse water,and the recovery rate is stable at about75%.In addition,after chemical cleaning,the flux recovery rate of reverse osmosis membrane reached 97.24%,and the effluent pressure was reduced by 7.23%.The cleaning recovery effect was excellent.（4）When FO system was utilized to treat RO membrane concentrate,the treatment effect was good,but the energy consumption was high.It can reach 18.95kwh per ton of water,accounting for 74.46%of the total cost of UF+RO+FO combined process under the condition that the recovery rate is 69.83%-89.9%.In addition,when a new membrane needs to be replaced in the near future,the cost is higher.Therefore,exploring new technology,reducing energy consumption and improving membrane stability in long-term operation is one of the key problems faced by membrane treatment of coking wastewater.（5）When IM-Fenton technology was utilized to treat RO membrane concentrate,the optimal process parameters determined by single factor experiments were that activated carbon dosage is 1g/L,reaction time is 60min,p H is 3 and n（H₂O₂）:n(Fe²⁺)is 4:1.Under these conditions,the removal rates of COD,ammonia nitrogen,total nitrogen and total phosphorus were 64.8%,13.4%,41.36%and 91.23%respectively,which greatly reduced the content of organic pollutants and lightened the burden for subsequent treatment.It is of great significance for realizing zero discharge of coking wastewater.