The Initial Studies On Nitrogen And Phosphorus Removal By Periphyton

As a key component of aquatic ecosystems,periphyton can absorb nitrogen and phosphorus contaminants,maintain matter metabolism and ecosystem balance in waters.Meantime,for its natural ability,namely, attaching on substrates and being harvested easly,it has become the research focus in recent decades.This paper has studied the removal of nitrogen and phosphorus in polluted urban waters by filamentous periphyton and unicellular periphyton through designing a simple wastewater treatment system,under the near-natural conditions.The main conclusions were summarized as follows,(1)Filamentous periphyton in the wastewater treatment system showed nitrogen and phosphorus removal efficiency,and the average removal rates of NH₄⁺-N,NO₃^--N,TN,PO₄^3-P and TP reached 60.5%, 52.4%,68.4%,71.9%and 74.0%,respectively.But unicellular periphyton just had significant removal effect on NH₄⁺-N and TN,the average removal rates were respectively 32.0%and 46.6%,while the removal rate of TP was relatively low(30.9%). (2)Removal rates were significantly correlated with the concentrations of nitrogen and phosphorus flowing into the system.As the concentrations of NH₄⁺-N and NO₃^--N were larger than 7.78,1.38 mg·L^-1respectively,over 50%of NH₄⁺-N,NO₃^--N can be removed by filamentous periphyton.While,more than 60%of TN was removed as the concentration of TN was larger than 13.70 mg·L^-1.High PO₄^3--P(＞75%) and TP removals(＞75%)were occured as the concentrations were above 0.66 and 1.60mg·L^-1,respectively.For unicellular periphyton,its maximum removals of NH₄⁺-N(81.0%)and TN(65.0%)occurred when the corresponding influent concentrations were 10.90 mg·L^-1and 11.67 mg·L^-1,respectively,and high TP removal(＞50%)appeared under low influent TP concentration(＜0.2 mg·L^-1).Moreover,the results of pollution load analysis showed that NH₄⁺-N,TN and TP load rates of unicellular periphyton positively impacted on the corresponding removal rates.The maximum removals of NH₄⁺-N(81.0%)and TN(65.0%) occurred at the corresponding loads of 0.87 mg NH₄⁺-N·g Chla^-1·d^-1and 0.40 mg TN·g Chla^-1·d^-1,respectively.(3)The ratio of TN:TP of the water treatment system ranged from 5.3～20.6,which satisfied with growth need of filamentous periphyton to effectively absorb nitrogen,phosphorus contaminants.During the experiments,filamentous periphyton growed well in sewages,and its biomass was increased signicantly with nitrogen and phosphorus removal rates.The maximum removals of NH₄⁺-N,NO^3--N,TN,PO₄^3--P and TP were occurred as the Chla concentrations were 1.14,1.01,1.00,0.84,and 1.02 mg·g^-1,respectively.(4)Both filamentous periphyton and unicellular periphyton showed significant effects on TSS and Chla removal and increase of DO concentration.(5)Under SE medium conditions,unicellular periphyton had significant absorption effect on nitrogen,nutrient the average removal rate for TN and NH₄⁺-N could reach above 20%,while NO₃-N increased, and the phosphorus absorption rate was still low(＜10%).(6)Unicellular periphyton has also shown good adaptability to sewages,with remarkable increases of Chla(58.2%)and biomass (54.0%).It was also observed that community compositions were successfully changed from original unicellular Bacillariophytes and chlorophytes dominated community to filamentous and unicellular Cyanobacteria dominated community.