Mathematical Simulation Of Vegetation-activated Sludge Process For Domestic Wastewater Treatment

The hybrid vegetation-activated sludge process（V-ASP）has being received moreand more concern since that it is an innovative ecological wastewater treatmentinvolved of microorganisms, vegetation and small fauna to be implemented indecentralized sewage treatment. In the present work, the typical V-ASP system,Canna-SBR process was used to treat domestic wastewater, and classic ASM2D modelwere employed to establish the V-ASP model through model development, parametersestimation, and sensitivity analysis. The developed model was used to predict thetreatment performance, and to evaluate the influential profiles by operational factors,and to propose the stabilities adjustment strategies. The results herein would be veryuseful for V-ASP system and give practical guideline for real application.Considering that the Canna-SBR process comprised of the conventional SBR andtypical vegetation, while without any chemicals dosage for phosphorus precipitation,the mathematical model developed based on ASM2D omitted the components（MeOHand MeP）and reaction kinetics (precipitation of P and Fe（OH）3, and re-suspension ofP and Fe（OH）3）related with chemically P removal. In addition, the vegetationfunction was affiliated in terms of vegetation mass （Xve）, vegetation growthstoichiometric parameters （Yve、iN,ve、iP,ve） and kinetics coefficients （KNH4,ve、KNO3,ve、KCOD,ve、KP,ve）. The developed model included five SBR phases, i.e. feeding,anaerobic, aerobic and anoxic, and withdrawn steps. From the verification betweenmathematical model and experimental results, the deviation of COD, TN, NH4+-N andTP was20%,5%,8%and10%, all of which were acceptable for model prediction andapplication.Series of batch tests were carried out to estimate the major kinetics coefficients andstoichomestrical parameters. It was obtained that the half-saturation coefficients ofCanna to the COD, NH4+-N, NO3--N and PO43--P was42.4mg/L、0.46mg/L、0.47mg/Land0.18mg/L, respectively. In addition, the Canna possesses the specific growth rate（ve） and yield coefficient （Yve） was0.0003d-1and0.17, respectively, while theycontained the N（iN,ve）and P（iP,ve）content ranged around0.03and0.005. Moreover,the yield coefficient of heterotrophy and maximum specific growth rate of autotrophy is0.678and1.04d-1, respectively.With the developed model, the reflective characteristic and correlation ofCanna-SBR system with the operational conditions were evaluated, and was comparedwith those in conventional SBR process. It was revealed that the Canna-SBR system have higher resistance against the influent loading fluctuation and operational conditionvariation in contrast with the conventional SBR, reflected by that it could achieve stableeffluent quality when the C/N ratio decreased to3.27or HRT shorten to6h. However,when the operational temperature decreased below10℃or the C/N below3, thecapability of pollutants removal by vegetation would be inhibited significantly.The Canna-SBR system has to confront the unstability problem when the lowsurrounding temperature, low C/N and MLSS content. Thus, the stability adjustmentstrategies were proposed with the assistant of mathematical model. The results showedthat: i）for the low C/N ratio, additional carbon source dosage and HRT prolong wouldbe effective to recovery the system. The carbon source dosage for the Canna-SBRsystem was more than10%lower than the SBR needed, since that this process couldkeep high removal efficiency even the C/N below3.27. This results may indicate thatthe V-ASP system would have energy or chemical saving benefit apart from theirlandscape function, ii）for the low temperature situation, HRT prolonging and extraheating methods for the system would be needed, iii）for the low MLSS, decreasing ofsludge discharge to keep high MLSS in the system would be useful for the stability,although the minimum MLSS of the Canna-SBR system could be lower compared withthe conventional SBR. To sum, the results herein would be very important for theecological decentralized wastewater treatment technologies.