Experimental Study On The AO-AAO-coagulation-adsorption To Treat The Wastewater Collected From Passenger Trains

The characteristics of wastewater from the excrement collector of passenger train are high concentration of organic,ammonia nitrogen,phosphorus,SS and chromaticity.It has been difficult to treat the wastewater independently.In this paper,the AO-AAO process,in which the anaerobic tank was added behind the second-stage anoxic,was beneficial to the enhanced biological phosphorus removal as the core process,supplemented by the coagulation adsorption advanced treatment process,and formed a new combined process to treat passenger train toilet waste water.The goal of wastewater treatment was to meet the first level A criteria of the Pollutant Discharge Standard for municipal wastewater treatment plant(GB18918-2002).The external carbon source addition dosages of the first anoxic tank,the second anoxic tank and the anaerobic tank were obtained by experiment of enhancing biological nitrogen and phosphorus removal in the AO-AAO model device.The nitrogen and phosphorus balance of AO-AAO process was analyzed.The beaker test was conducted with the coagulation and adsorption to remove total phosphorus,COD,and chromaticity in the effluent of AO-AAO process.And the dosages of PAC and powdered activated carbon were obtained.According to the experiment results,the train toilet sewage treatment station could be designed and analyzed economically.The research results are summarized as follows:(1)The AO-AAO process was applied to treat the wastewater from the excrement collector of passenger train.When the HRT of the process was 10.86d,the reflux ratio of the mixed liquid was 750%,the sludge reflux ratio was 200%,the external carbon source dosages of the first anoxic tank,the second stage anoxic tank and the anaerobic tank were 0.9g COD/L,2.8g COD/L and 2.2g COD/L respectively,the removal rates of COD,total nitrogen,ammonia nitrogen and total phosphorus were more than 95%,99%,99.5%and 95%respectively.Moreover,ammonia nitrogen and total nitrogen in the effluent could meet the first level A criteria of the Pollutant Discharge Standard for municipal wastewater treatment plant.(2)The simultaneous coagulation and adsorption by combining addition of PAC and powdered activated carbon were applied to treat the effluent of AO-AAO process.When the coagulation and adsorption reaction time was 0.5h,the dosage of powdered activated carbon was 250mg/L,and the dosage of PAC was 200mg/L,the COD,total phosphorus,and chromaticity of the advanced treated wastewater could meet the level A criteria.The chromaticity in the effluent of the AO-AAO process was mainly manifested by urine pigments.(3)The results of nitrogen and phosphorus balance analysis on the AO-AAO process showed that the nitrogen balance rate was 90.1%and 77.2%of the total nitrogen was removed by nitrification-denitrification,and the phosphorus balance rate was 90.3%and 86.1%of phosphorus was discharged from the system as excess sludge.(4)The economic estimation of the station to treat train toilet sewage with a capacity of 250m~3/d showed that the project investment index was 16,200 RMB yuan/m~3,and the operating cost index was 20.8 RMB yuan/m~3.Compared with the scheme of levying environmental protection tax to discharge the train toilet sewage to municipal sewers directly,the project investment to treat the wastewater independently would be recouped when the station was operated more than 6 months.The"AO-AAO-coagulation adsorption"process was an optional process to treat the wastewater collected from passenger trains.The research obtained could provide reference for the design and operation of sewage treatment stations with similar water quality.