Research On Technology Of Coagulation-MAP-Sonoelectrochemistry Combined Process Treatment Train’s Fecal Sewage

The toilets were widely installed on the ordinary trains with the improvement of people’s hygiene requirements.And closed toilets were used on EMU trains due to more strict requirements.The closed toilets has changed the "disposable discharge" of the toilet fecal sewage in-line,which reduces the pollution to the environment along the railway.However,the closed toilets also produce a large amount of high-concentration fecal sewage,which can be met emission standards through conventional biotreatments.Therefore,it is necessary to find an effective and fast treatment process for fecal sewage collected from the train.In this paper,the coagulation-MAP-sonoelectrochemistry combined process was used to investigate the treatment efficiency of train fecal sewage.The effects of coagulation,MAP and ultrasonic electrochemistry on the removal of COD,ammonia nitrogen,total phosphorus and SS were investigated by single factor experiments,and the parameters of the ultrasonic electrochemical were optimized by the response surface.Thus,the fecal sewage was treated by a combined process and biotreatment in this study.There were four types of coagulants used in the coagulation treatment of train fecal sewage as:polyaluminum chloride,polyferric sulfate,ferric chloride,and chitosan.The results showed that the removal rates of COD,TP and SS of fecal sewage by conventional inorganic coagulant were higher than those by chitosan,and the highest removal rates were obtained in polyferric sulfate.The effects of the four coagulants on ammonia nitrogen were all very poor,but the chitosan was less affected by pH and the produced sludge could be used as a compost material.And the single factor experiment analysis suggested that in terms of chitosan,the optimal pH was 8 and the optimal dosage was 600 mg/L.The removal rates of COD and ammonia nitrogen in the process of sonoelectrochemistry of fecal sewage were mainly affected by current density,chloride ion concentration and pH.The removal rates of COD and ammonia nitrogen increased with the increase of current density.The acidic condition promoted the removal of organic matters and COD,while the alkaline condition enhanced the removal of ammonia nitrogen.In the electrochemical process,chloride ion was an excellent electrolyte,which could not only increase the conductivity,but also remove ammonia nitrogen and organic matters by indirect oxidation as it could be converted into a variety of active chlorine in electrochemical action.The response surface was used to optimize the ultrasonic electrochemistry.The variables were ultrasonic power,current density,chloride ion concentration,and pH value.And the ammonia nitrogen and COD removal rates were used as the response values.The optimal optimization conditions were as followed:the plate spacing,the current density,the initial,the chloride ion concentration,the ultrasonic power was,the reaction time were 2 cm,0.09 A/cm2,7,4.51 g/L,30 W/L and 180 min,the COD and ammonia nitrogen removal rates were 86.86%and 85.72%,respectively.The recovery rate of oxidized water was significantly higher than those of the other two kinds of sewage,by comparing the phosphorus recovery of raw water,coagulated water and oxidized water.While the optimal pH was 10,the optimal stirring time was 8 min,and the molar ratio of Mg:P was 1.4.The recovery rate of phosphorus reached 98.86%,and it was feasible to recover high phosphorus concentration in fecal wastewater by MAP method.After the treatment by the whole process,the removal rates of COD,ammonia nitrogen and orthophosphate reached 99.7%,99%,and 97.4%,respectively.And the effluent quality could reach the secondary standard in the Pollutant Discharge Standard for Urban Sewage Treatment Plants(GB18918-2002).