Control Strategies Of PN-Anammox Process For Treating Digested Effluent Of Swine Wastewater

Effluent from anaerobic digestion of swine wastewater still contains high ammonium concentration.The nitrogen must be removed for meeting strict national discharge standards at the region with limited land.Owing to a low ratio of chemical oxygen demand?COD?to ammoniumof digested effluent of swine wastewater,the traditional nitrification-denitrification process requires additional carbon and alkali resources,which lead to a high cost and low nitrogen removal efficiency.Compared to the traditional nitrification-denitrification process,partial nitrofication-anaerobic ammonia oxidatiion?PN-Anammox?process is widely used for decreasing the need for organic carbon requirement by 100%,high efficiency and low cost and floor space.However,there were many challenges in application of PN-Anammox process,e.g.longer start-up period,low or unstable nitrogen removal rate and poor effluent water quality.Hence,this paper studied the subject of“Control Strategies of PN-Anammox Process for Treating Digested Effluent of Swine Wastewater”.These control strategies,which were pulsed aeration for controlling PN process and the addition of zero-valent iron and granule sludge of PN-Anammox,were studied according to the challenges.This study also investigated the feasibility and performance of a PN-Anammox process to treat DPW,as well as its microbiological mechanisms.The results are listed as follows:?1?The influence of the different frequency of pulsed aeration on PN process for treating the digested effluent of swine wastewater in sequencing batch reactor?SBR?was investigated in this study.The match degree of effluent of PN process with Anammox process was compared.Moreover the energy efficiency of different frequency of pulsed aeration was also evaluated to select the optimal aeration strategy.The results showed that,in steady period,the nitrite accumulation rates?NAR?both were 90%and the activities of NOB were close to 0 in three reactors.It indicated NOB was successfully supressed by three aerated frequencies.Then,when the aerated frequency increased,the NO₂^--N concentration in effluent was increased.The ratio of NO₂-N:NH₄-N in effluent of R3(2 times h^-1)was1.35,which more matched Anammox process.The energy efficiency evaluation showed R1(6 times h^-1)had a highest actual oxygen transfer efficiency and dynamic efficiency,which decreased 29.6%and48.5%of energy demand compared to R2(3 times h^-1)and R3,respectively,when generated same DO.?2?The influence of zero-valent iron on PN-Anammox to treat digested effluent of swine wastewater was studied under different frequencies of pulsed aeration in SBRs.The results showed the ammonium conversion efficiencies were 93.2%,88.0%and 81.2%,NARs were 77.5%,89.3%and 90.6%,and total nitrogen removal efficiencies?TNREs?were 38.4%,45.3%and 51.3%in R1,R2 and R3,respectively.Although the highest NAR and TNRE were acquired in R3,the TNRE was lower than other literatures.All of this also indicated three reactors were in PN process,their productions can't be removal for the low activities of Anammox.Meanwhile,the no obvious increase of sludge concentrations and lower than30 mL g^-1 SS of sludge volume index were found in three reactors during 243 days of operation.Only the relative abundance of Nitrosomonas was higher than 1%in functional microbes.The reason can be listed:on the one hand,the low pH?4.0?which decided by the H⁺of PN process,inhibited the growth and metabolism of functional microbes.Low pH and high nitrite concentration induced high free nitrous acid which strong inhibit functional microbes,especially Anammox bateria.On the other hand,low pH also strengthen the corrosion of zero-valent iron.Which led to a high total iron concentration.The average total iron concentrations were high to 1009 mg L^-1,558 mg L^-1 and 319 mg L^-1 in R1,R2 and R3.High total iron concentration drastically deteriorated the PN-Anammox process.?3?The performance of the PN-Anammox process to treat digested effluent of swine wastewater was investigated by inoculating granule sludge of PN-Anammox and gradually shortening the HRT and enhancing the ammonium concentration during 390 days of operation.The results showed that the total nitrogen removal rate?NRR?and efficiency reached 3.9 kg-N m^-3 day^-1 and 73%,which were significantly higher than the levels reported previously.A high relative abundance of Nitrosomonas?4.2%?and functional microbes?12.15%?resulted in a high Anammox activity(1.25±0.1 g-N g VSS^-1d^-1),and a good settling ability(SVI,78.42 mL g^-1 SS)resulted in a high sludge concentration(VSS,11.01 g L^-1),which laid a solid foundation for the excellent performance.However,compared the NRR of treating synthetic wastewater(4.7 kg-N m^-3 day^-1),some components of digested effluent of swine wastewater may inhibit the activities of the sludge,such as heavy metals and antibiotics,which would result in a lower NRR value for treating digested effluent of swine wastewater.In conclusion,pulsed aeration could greater steady control the Pnprocess,compared continuous aeration.The addition of granule sludge of PN-Anammox could autotrophic remove ammonia from digested effluent of swine wastewater.The NRR(3.9 kg-N m^-3 day^-1)was significantly higher than the levels reported previously.The operation strategies could be the guidance for successful application of PN-Anammox process on digested effluent of swine wastewater.However,the components of digested effluent of swine wastewater inhibit the further increase of NRR,which need to further study.