Alkaline Fermentative Short-chain Fatty Acids Produced From Excess Activated Sludge As The Carbon Sources Of Biological Nutrients Removal

In our previous research work,it has been known that the fermentation of excess activated sludge at alkaline condition would produce large amount of short chain fatty acid(SCFA),protein,carbohydrate,ammonia nitrogen and soluble ortho-phosphorus (SOP).In this paper,the recovery of nitrogen and phosphorus from alkaline fermentation liquid of excess activated sludge was discussed.The removal performances of phosphorus and nitrogen when using fermentation liquid and acetic acid as carbon sources of SBR process were investigated and compared with each other.And the variations of SCFA,nitrogen,phosphorus,glycogen,PHA during one cycle in the SBRs were also studied.First,the influence factors and optimal conditions for nitrogen and phosphorus recovery were investigated.Ammonia nitrogen and phosphorus can be recovered though struvite formation by adding Mg to the fermentation liquid at alkaline condition.Mixing time was not the significant factor for phosphorus recovery.In the phosphorus recovery process,phosphorus removal efficiency increased with pH from 8.0 to 10.0,and Mg/P molar ratio from 1.2-1.8,and there was no significant increase after pH 10.0 and Mg/P 1.8.At the optimal conditions for phosphorus recovery,that is, pH 10.0 and Mg/P 1.8,after mixing for 2 min,the phosphorus removal efficiency was 92.8%.In the simultaneous nitrogen and phosphorus recovery process,at pH 9.5-10.5, Mg/N 1.0-1.8,P/N 0.8-1.2,ammonia nitrogen removal efficiency increased with all these three factors rising,and Mg/N and P/N were significant influence factors. However,Phosphorus removal efficiency improved with both pH and Mg/N rising, but decreased with P/N increasing.The optimal conditions for nitrogen and phosphorus recovery were obtained with response surface methodology(RSM).At this conditions,that is,Mg/N 1.8,pH 10.0,P/N 1.13,ammonia nitrogen and phosphorus removal efficiency was 73.6%and 82.2%,respectively. Second,the fermentation liquid after nitrogen and phosphorus recovery and acetic aicd were used as carbon sources of microbe in SBR for enhanced biological phosphorus removal(EBPR)and both nitrogen and phosphorus removal process. Their nitiogen and phosphorus removal efficiency,variations of nitrogen,phosphorus, SCFA,glycogen and PHA during one cycle were discussed.In the anaerobic/aerobic EBPR process,the phosphorus removal efficiency of SBR driven by fermentation liquid and acetic acid was 98.7%and 71.1%, respectively.The sythensis PHA in the SBR driven by fermentation liquid was 2.11mmol-C/gVSS,which was less than that of driven by acetic acid(3.65 mmol-C/gVSS).The former would synthesize 0.57 mmol-C glycogen and took in 15.19 mg-P when decomposed 1mmol-C PHA,but the latter would produce 0.67 mmol-C glycogen and just absorbed 8.45 mg-P.Therefore,the SBR driven by fermentation liquid had better PHA utilization ratio.This may be the reason why the SBR driven by fermentation liquid had better phosphorus removal efficiency than driven by acetic acid.In the anaerobic/aerobic/anoxic/aerobic/anoxic/aerobic SBR nitrogen and phosphorus removal process,during the first and second anoxic stage,the denitrofication rates in the SBR driven by fermentation liquid,which was 1.97 and 1.41mgNO_x-N/gVSS·h,respectively,were more than that of driven by acetic acid (1.84 and 1.1 mgNO_x-N/gVSS·h).From the endogenous denitrification research,it was found that the former carbon source would reduce more nitrogen than the latter carbon source when degraded the same amount of PHA.Although the synthesis PHA in the SBR driven by fermentation liquid was less than in the SBR driven by acetic acid,the former had a better PHA ultilization ratio for phosphorus and nitrogen removal and then resulted in a better removal performance.The SOP and TN removal efficiency of the former SBR was 95.3%and 87.2%,while that of the latter SBR was 81.5%and 73.9%,respectively.Furthermore,it was found that the phosphorus uptake in both SBR,and for both processes(EBPR,nitrogen and phosphorus removal processs)were coincided with first-order kinetics.The SBR driven by fermentation liquid had greater uptake rate. The degradation of acetic acid in the SBR driven by acetic acid,and both the acetic and propionic acid in the SBR driven by fermentation liquid were in accord with the first-order kinetics,too.The propionic acid degradation rate in the SBR driven by fermentation liquid was greater than its acetic acid degradation rate.Moreover,the SBR driven by fermentation liquid had better acetic acid reduceing rate than that of SBR using acetic acid as carbon source.For this research,the toxicity of fermentation liquid as carbon source to microorganisms was investigated.Through observing the SOUR and dehydrogenase activity of the activated sludge in the two SBRs,it was found that the fermentation liquid had no toxicity influence to the microorganisms.Although there were some heavy metals in the fermentation liquid,no heavy metals was detected from the effluent of SBR.At last,comared with the SBR driven by municipal wastewater without adding fermentation liquid as carbon source,the SBR driven by municipal wastewater with complementary fermentation liquid had better phosphorus and nitrogen removal performance.The phosphorus removal efficiency was 94.9%vs.60.27%for EBPR process.The SOP and TN removal efficiency for nitrogen and phosphorus removal process was 97.2%and 80.9%for SBR driven by fermentation liquid,and 43.9%and 63.5%for SBR driven by acetic acid.Low COD concentration wastewater could gain perfect treatment performance when adding fermentation liquid as complementary substrate.