| The leachate from municipal solid waste incineration plants usually contains high concentrations of ammonia(NH4+-N,600-1200 rng/L)and organic matter(chemical oxygen demand(COD),50000-70000 mg/L),and therefore must be properly treated before being discharged.Anaerobic digestion is an effective treatment method to reduce organic compounds in incineration leachate,and also generates desirable biogas(CH4).However,during anaerobic digestion,the degradation of COD can lead to an increase in ammonia concentrations to levels as high as 1000-1800 mg/L in the anaerobically treated leachate leading to COD to nitrogen ratio(C/N)decreasing.The traditional approach used to enhance the removal of nitrogen and COD from anaerobically treated leachate involves anaerobic treatment supplemented with an aerobic process(anoxic-oxic(A/O)process).During the A/O process,it is often necessary for additional electron donors to be added to the leachate.The increasing free ammonia(FA)concentrations further inhibited the growth and activity of microorganisms.Anaerobic ammonia oxidation(Anarnmox)is an alternative nitrogen removal process.It is not necessary to supply any additional electron donors.And anaerobic ammonium oxidizing bacteria(AnAOB)can withstand high FA concentrations compared to the microorganisms in A/O process.Anammox process is considered a feasible process for the treatment of wastewater with a high ammonia content and low(C/N),such as that from anaerobically treated inc ineration leachate.However,practical application of the anammox process has been limited due to the extremely slow growth rate.AnAOB are also sensitive to fluctuating environmental conditions such as organic matter content,salinity,and heavy metals,which can inhibit their activity and result in insufficient wastewater treatment.Bio-electrochemical systems(BES)have been shown to enhance the performance of both conventional nitrification/denitrification systems by enriching for functional bacteria and increasing their bioactivities.Whether anaerobically treated leachate can be effectively treated with a partial nitrification/anammox process applied with BES still warrants investigation.Therefore,in this study,the partial nitrification/anammox process with BES were used to treat anaerobically treated leachate.The nitrogen removal effect of combined process and the enhancement mechanism of BES were explored.The effect of biological inhibit factor(NH4+,COD and NaCl)in anaerobically treated leachate and operating conditions(pH and temperature)on the specific Anammox activity(SAA)of sludge were explored by using static tests.The results showed that when NH4+ concentration was higher than 400 mg/L,COD concentration was higher than 200 mg/L,NaCl concentration was higher than 6000 mg/L,pH was higher than 8.5 or lower than 6.5 and operating temperature was lower than 25?,the SAA of sludge would decrease,indicating that the activity of AnAOB was inhibited.The effect of NH4+ and pH on SAA of sludge was mainly due to the high concentration FA and FNA,which was poisonous to AnAOB.The high concentration COD could provide sufficient electronic donor for denitrifying bacteria to consume more NO2-.The SAA of sludge would decrease referring to lack of NO2-.To accelerate the startup and maintain stable operation of combined process,the concentration of biological inhibit factor should be controlled lower than inhibition threshold.And the pH should be between 7 and 8,the optimal operating temperature was 35?.The effect of electron shuttle(AQDS,fulvic acid and Nano Fe3O4)on SAA of sludge was also explored by static test The results showed that all the electron shuttle could increase the SAA of sludge,indicating AnAOB had bioelectrical activity.To determine the optimal the applied electric potential(EP),effect of different electric potential difference(EPD)on the SAA of biofilm on the electrode was explored.The results showed that the applied EPD between 0 and 0.1V could increase the SAA When the EPD was 0.06V,the SAA was highest reaching to 151%.As a result,the 0.06V was the optimal EPD.An integral partial nitrification/anammox process with applied EP of 0.06V was applied to treat the anaerobically treated leachate.When the influent NH4+ concentration reached to 1000 mg/L,the total nitrogen(TN)removal efficiency was about 70%,15%higher than that of control group.The COD removal efficiency was 10%-20%higher than that of control group.The large macromolecules organic compounds with a molecular weight>20 kDa like fulvic-like acids and humic-like acids were partially biodegraded,the biodegraded product could be as electron donor for denitrification to further increase the TN removal efficiency.The extracellular polymeric substance(EPS)concentration reached to 236.7 mg/g VSS with applied EP,56%higher than that of control group,indicating that applied EP promoted the microorganism producing more EPS.And proteins(PN)versus polysaccharides(PS)on the electrode biofilms was 1.18,while the PN/PS was only 0.88 in control group.The increasing PN/PS allowed AnAOB to aggregate on the surface of the electrode.The abundance of AnAOB like Candidatus Kuenenia on the electrode was 2.66%,0.42%higher than that of control group.The abundance of Burkholderiales belonged to denitrification bacteria reached 22.4%,14.9%higher than that of control group.It revealed that the applied EP could increase the abundance of AnAOB and denitrification bacteria to enhance the TN removal effect of an integral partial nitrification/anammox process.At the same time,a two-stage partial nitrification/anammox process with applied EP of 0.06V was also used to treat the anaerobically treated leachate.When influent NH4+ concentration was 500 mg/L,NO2-concentration was about 650 mg/L,the TN removal efficiency reached 75.6%,35%higher than that of control group,COD removal efficiency was 10%-15%higher than that of control group.The large macromolecules organic compounds with a molecular weight>20 kDa like fulvic-like acids,humic-like acids and soluble microbial products(SMP)were partially biodegraded,the biodegraded product could also be as electron donor for denitrification to further increase the TN removal efficiency.The extracellular polymeric substance(EPS)concentration reached to 186.7 mg/g VSS with applied EP,60.6%higher than that of control group,indicating that applied EP stimulated the microorganism producing more EPS.And proteins(PN)versus polysaccharides(PS)on the electrode biofilms was 0.64,while the PN/PS was only 0.43 in control group.The increasing PN/PS allowed An AOB to aggregate on the surface of the electrode and increase the activity of AnAOB.The function enzyme concentration of AnAOB on the electrode like Nir enzyme,HZS enzyme,HDH enzyme and Cyt-c were respectively 39.6%,19.2%,22.3%and 30.1%higher than those of control group.The abundance of Candidatus Kuenenia,Candidatus Brocadia and Candidatus Jettenia were 13.01%,0.33%and 0.04%,while their abundance were only 7.22%,0.04%and 0.003%in control group.The abundance of Caldilinea belonged to denitrification bacteria reached to 8.3%,3.3%higher than that of control group.It revealed that the applied EP could improve the functional enzyme activity and increase abundance of AnAOB and denitrification bacteria to enhance the TN removal effect of anammox process. |
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