GPS-X-based Evaluation Of The Carrying Capacity Of A~2O Process To Sewage With Low B/C And The Influence Of Receiving Beer Wastewater As Carbon Source

The reduction of carbon source concentration and the biodegradability of influent have universally plagued the operation of municipal wastewater treatment plants in China recently.Accepting an appropriate amount of food wastewater helps increase the concentration of carbon source and improve biodegradability of the influent of municipal wastewater treatment plants while saving the source and reducing the greenhouse gas（GHG）emissions caused by unnecessary energy consumption,but this is contrary to the relevant industrial wastewater discharge standards.At present,the Ministry of Ecology and Environment only allows beer producers and municipal wastewater treatment plants to agree on the discharge concentration of beer wastewater pollutant by signing written contracts to alleviate a series of problems（i.e.low BOD₅concentration in the influent）.However,due to the lack of theoretical reference and efficient assessment methods to identify the potential effluent risks,specific benefits,and optimal concentration and volume of beer wastewater,the measure has not been widely applied.Considering that A²O processes are sensitive to the carbon source concentration and biodegradability of sewage and have been widely applied,this study established an A²O process simulation model based on the sewage treatment process simulation platform of GPS-X by referring to the actual A²O process of a municipal wastewater treatment plant in Guangdong province,and studied the carrying capacity of the A²O process for low BOD5/COD（B/C）sewage impact caused by the rise of dissolved inert substances.According to the characteristic data of beer wastewater from an actual beer production enterprise,the scenario of an A²O process receiving wastewater with beer wastewater characteristics as an external carbon source was simulated.The impact of receiving wastewater with beer wastewater characteristics on the A²O process was analyzed in terms of effluent quality,economic benefits,and GHG emissions reduction.The conclusions are as follows:（1）Using actual values of process conditions and reasonable data of influent and effluent as much as possible may help to build a high quality model which is close to reality and reduce the difficulty of model calibration.25 parameters were sensitive to the observed indexes in 189 parameters analyzed.There may be a limit to calibrating the parameters by steady-state calibration alone,and dynamic calibration of parameters that fluctuate frequently in practice could significantly improve the fit of the simulated curves to the actual values.（2）When the simulated A²O process suffered from a continuous or random shock of sewage with low B/C caused by the elevated dissolved inert content,the Ammonia nitrogen and BOD₅of the effluent were not at the risk of exceeding the standard,while the effluent TN,TP and COD exceeded the standard in sequence.Reasonably reducing the dissolved oxygen concentration in aerobic tank and increasing the methanol dosage could reduce the over standard rates of TN and TP in the effluent of A²O process.The minimum over standard rates of TN and TP under certain process operating conditions were lower than that of COD,so it was reasonable to take a certain over standard rate of COD in the effluent as the carrying limit of A²O for low B/C sewage impact.If the effluent limit is set according to the Grade I-A Standard of Pollutant Discharge Standard for Urban Wastewater Treatment Plants（GB18918-2002）and the 5%of over standard rate of COD is regarded as the carrying capacity of A²O for shock of low B/C sewage,when the percentage of dissolved inert COD of the total COD（frsi）and B/C of the influent remained stable at 0.133 and 0.332,respectively,during 31 days,or there were 25days of influent with frsi and B/C of 0.136 and 0.330,respectively,or there were 20days of influent with frsi and B/C of 0.143 and 0.328,respectively,or there were 15days of influent with frsi and B/C of 0.151 and 0.324,respectively,or there were 10days of influent with frsi and B/C of 0.161 and 0.319,respectively,or there were 5days of influent with frsi and B/C of 0.189 and 0.308,respectively,the simulated A²O process reached the limit of treatment capacity for sewage.（3）Accepting a certain amount of beer wastewater can effectively improve the BOD₅concentration and biochemical properties of the influent.By receiving 1200m³/d of beer wastewater,the carbon source requirement of the simulated A²O process for denitrification and phosphorus removal could be met,and the effluent indexes concentrations met the Grade I-A Standard.As the flow rate of beer wastewater increased to 2700 m³/d（e.g.receiving all the beer wastewater of the beer enterprise）,the COD,BOD₅,Ammonia nitrogen,and TN of the effluent showed a slight increase,but the effluent indexes still did not exceed the Grade I-A Standard.The A²O process using methanol as the carbon source had a slightly higher TN removal rate and lower sludge production.Receiving 1200 m³/d and 2700 m³/d of beer wastewater as the carbon source could save（?）200.1 thousand of treatment costs（0.05（?）/m³）and（?）157.5thousand thousand of treatment costs（0.04（?）/m³）and reduce 734.7 t CO₂e（0.175kg CO₂e/m³）and 566.0 t CO₂e（0.135 kg CO₂e/m³）of GHG emissions for A²O process.Receiving the right amount of beer wastewater as a carbon source could not only avoid fossil source GHG emissions from the use of methanol,but also reduce CH₄and N₂O emissions of the A²O process.This study provides a new assessment tool and theoretical reference for wastewater plants to receive beer wastewater as a carbon source,and promotes the application of this measure to speed up the process of revising discharge standards for more categories of food wastewater.