Biological Phosphorus And Nitrogen Removal In Single Stage Intermittent Aerated Biological Filter

Under intermittent aerated and continuous fed operation where the biofilmsystem was subjected to alternated anaerobic/aerobic condition, the effect of influentvolatile fatty acids (VFAs) concentrations, operation cycle and ammonium loads onthe biological nitrogen and phosphorus removal performance of the biofilter wasstudied.In the experiment, the influent velocity was5L/h with gas versus liquid ratio of8:1and hydraulic retention time (HRT) of1.3h, resulting in average COD,phosphorus and ammonium load of4.7,0.095,0.38~1.5g/(L·d) respectively. Resultsshow that:(1) Effective release and uptake of phosphorus was achieved in a operation cycle;(2) Higher influent VFAs contributed to more fluctuated and stronger P release inunaerated phase while the P uptake didn’t show obvious change, and lower VFAsdecreased both P release and uptake;P removal was improved when operation cyclewas compressed into6h, but opposite trend appeared when further compressed into5h;(3) Iinfluent VFAs and operation cycle had no significant effect on COD andammonium removal;with the increase of ammonium load, nitrogen removal inbiofilter increased first then decreased, the P release and uptake were obviouslyinhibited, and “nitrogen loss” was witnessed in the biofilter;(4) The pause of backwash decreased the phosphorus removal performancerapidly, but the consequent daily backwash operation recovered phosphorus removalto original level stepwise. When influent VFAs was100mg/L(calculated by CODvalue), operation cycle was6h and influent ammonium was20mg/L the filterperformed best in phosphorus removal, the phosphorus loading removal rate can be asmuch as0.059g/(L·d) at the aerated phase with those of COD and ammonium being3.8and0.28g/(L·d) respectively, and with average effluent phosphorus, COD andammonium concentrations being1.8,43.6and8.7mg/L.It is shown that sufficient and stable influent VFAs concentration, properoperation cycle, and more frequent backwash favored biological phosphorus removalperformance in the biofilter under intermittent aerated and continuous fed operation.Hourly effluent monitoring in a operation cycle indicated apparent C, N, Premoval trend as well as no sign of nitrate nitrogen accumulation in the filter. In thefirst hours of unaerated phase, the effluent COD and ammonium decreased sharply followed by stepwise increase, while P release came about and reached peak value inthe first2hours and then decreased. In the aerated phase, effluent C, N and Pdecreased stepwise and maintained low till end.A microbial spatial distribution model and the dissolved oxygen penetrationmethod were proposed according to the experimental phenomenons and reports inliteratures, and with the assitance of the metabolism of different microorganisms thebiological nitrogen and phosphorus removal mechanism was analysed, and part of theexperimental phenomenons were explained. Moreover, it was also found that it waswithin the biofilm that the alternation between anaerobic and aerobic condition wasrealized. It is hoped that the paper can provide reference and theoretical analyse forapplying biofilm process to nitrogen and phosphorus removal in wastewatertreatment.