Research On Carbon Source And Phosphorus Recovery From Excess Sludge Of Biofilm Process

Biofilm wastewater treatment process,as a highly efficient wastewater treatment process,is widely used in municipal and industrial wastewater treatment.Excess sludge of biofilm wastewater treatment process(biofilm sludge)is the by-product of biofilm wastewater treatment process,which is mainly composed of detached biofilm,suspended solids,microbial metabolites and a variety of toxic substances,such as pathogenic bacteria,pathogens,organic pollutants,and etc.In order to avoid the secondary environmental pollution and application limitation caused by biofilm sludge,it is of great importance to properly treat and dispose biofilm sludge.Biofilm sludge is a potential resource due to its rich nutrients contents such as organic matters and phosphorus(P).The paper investigated the carbon source and phosphorus recovery from biofilm sludge,which was of great significance for sludge valorization and resource utilization of biofilm sludge.Firstly,the paper investigated the feasibility of biofilm sludge to produce VFAs via hydrolysis acidification.The VFAs production process condit ions including mixing speed,inoculum and biofilm sludge concentration were systematically studied.The results showed that VFAs production from biofilm sludge via hydrolysis acidification was feasible and biofilm sludge was a potential carbon source.The maximum VFAs productivity of 363.16 mg COD/g VSS from biofilm sludge(VSS concentration of 5.41 g/L)was achieved at mixing speed of 150 rpm on the third day with no additional inoculum.Identification of phosphorus fractions of biofilm sludge and P releas e and transformation in biofilm sludge treatment related to p H was investigated by with sequential extraction scheme and P-31 nuclear magnetic resonance spectroscopy(31P-NMR).P recovery by calcium salt precipitation method and ferrous ion precipitation method was studied.Results showed that inorganic Psolid(IPsolid)occupied most in solid phase of raw biofilm sludge(69.21% total P solid)and the content of releasable and bioavailable P(part of IPsolid and organic Psolid)was 15.56 mg P/g TSS(90.57% of total Psolid),suggesting that biofilm sludge could be a potential P source.The optimum conditions for P release in biofilm sludge treatment process were p H=5 and p H=10,respectively,under acidic and alkaline conditions,and the corresponding maximum concentrations of orthophosphate-P were 72.44 mg/L and 76.84 mg/L.Moreover,p H played an important role on P transformation and redistribution in the treatment process.The suitable process conditions for P recovery by calcium salt precipitation method was reaction time of 3min,initial p H of 10 and Ca2+/PO43--P of 4 and the suitable process conditions for P recovery by ferrous salt precipitation method was reaction time of 10 min,initial p H of 8 and Fe2+/PO43--P of 2,which were obtained by single factor experiment.The characteristics of biofilm sludge carbon source were studied and a strategy to produce biofilm sludge carbon source was proposed.The effect of biofilm sludge carbon source on pollutant removal of biofilm wastewater treatment process and the performance of biofilm wastewater treatment process were investigated.The results showed that the addition of biofilm sludge carbon source could promote the pollutant removal of biofilm wastewater treatment process.The removal efficiency of ammonia nitrogen,total nitrogen,chemical oxygen demand and total phosphorus were enhanced to some extent of biofilm wastewater treatment process.In order to improve and deepen the understanding of the biofilm sludge carbon source recovery and utilization,the paper conducted models based on data-driven methods and predicted the performance of VFAs production from biofilm sludge under different process conditions and pollutants removal of biofilm process before and after biofilm sludge carbon source addition,which provided theoretical and technical support for conditions optimization of biofilm process,operational stability analysis,process performance prediction,and etc.The paper constructed the model for biofilm sludge VFAs production prediction based on e Xtreme Gradient Boosting(XGBoost)method and investigated the prediction performance under different process conditions.Moreover,contrast model based on traditional Gradient Boosting Decision Tree(GBDT)method verified the applicability and effectiveness of the proposed model for biofilm sludge VFAs production prediction based on XGBoost method.Root mean square error(RMSE),mean absolute error(MAE)and mean relative error(MRE)were adopted for evaluating the accuracy and fitness of the prediction model.MRE of the prediction model under different mixing speeds,inoculum and biofilm sludge concentration were 15.86%,16.30% and 20.56%,respectively.Moreover,prediction model of performance of biofilm wastewater treatment process was constructed by SDAE-XGBoost(Stacked denoising auto-encoder)method to study the pollutant removal performance prediction of biofilm wastewater treatment process.RMSE of the prediction model of ammonia nitrogen,total nitrogen,chemical oxygen demand and total phosphorus removal were 0.50 mg/L,1.48 mg/L,10.01 mg/L and 0.22 mg/L,respectively.Contrast model based on backpropagation neural network,support vector regression,extreme learning machine,SDAE,XGBoost method verified the applicability and effectiveness of the proposed model for pollutant removal performance prediction of biofilm wastewater treatment process.