Nitrogen Removal Of Digested Swine Wastewater By Micro-particle Biochar With Biofilm In Sequencing Batch Reactor

With the extensive and intensive development of livestock and poultry industries,although plentiful meat products have been produced to satisfy the high needs of human daily life,massive livestock and poultry manure emission have caused ecological environment pollution.In particular,a large quantity of piggery urine with rich nitrogen(N)and phosphorous(P)from large piggery farms in China has raised water eutrophication to damage aquatic organisms and even threaten human health,due to poor animal manure disposal further occurring surface runoff,except dry manure fertilization.However,the digested swine liquid is very high concentration of ammonia nitrogen(NH₄⁺-N)by way of simple fermentation pond in pig farm,especially in poor rural area.It can thus be seen that the digested liquid effluent is difficult to achieve the demand of‘discharge standard of pollutants for livestock and poultry breeding',which has to be further biological nitrogen removal.In this study,the livestock and poultry manure pollution with its potential risk was estimated and predicated from Chaohu Lake watershed at first.Then the digested swine wastewater in a pig farm of rural ecological breeding cooperatives near Chaohu Lake watershed was selected as research object.In the experiment,the novel micro-particle carriers were prepared and developed to enrich microorganism and cultivate biofilm in self-designed sequencing batch reactor(SBR).Whereafter,the partial nitration and denitrification(PND)pathways in wastewater treatment were explored by single factor test and Response Surface Methodology(RSM)in SBR,in order to remove nitrogen from the digested swine wastewater.Ultimately,the denitrifying bacteria was screened and identified from the biofilm of the micro-particle carriers,as well as the relationship among microbial diversity,community structure and environmental factors were analyzed and discussed,to understand the nitrogen removal mechanism of microgranular carrier biofilm for digested swine wastewater treatment.The major results of the dissertation are as follows:(1)Livestock and poultry manure with its risk were evaluated and forecasted in Chaohu Lake basin.The results indicated that the manure production was high in Chaohu Lake basin and the sum of production in Feixi and Feidong almost took up more 50%in the whole basin production.The pollution extent in the basin was quite serious which was achieved to level?even level?.The risk predication illustrated that the farmland of Feixi would be changed to a moderate pollution county due to livestock and poultry manure emission.In 2030,the mean risk level of water pollution would be approximately at 18 for Chaohu Lake watershed,which was suffered a moderate pollution of level?.The results implied that the runoff of livestock and poultry manure has become one of the important rea sons for the eutrophication of Chaohu Lake.(2)Micro-particle biochar carriers were developed and applied to accumulate microorganisms and cultivate biofilm in the experiment.Utilizing agricultural waste of rice husk and rice straw,four kinds of micro-particle carriers including rice husk biochar(RHB),modified rice husk biochar(MRHB),rice straw biochar(RSB)and modified rice straw biochar(MRSB)were prepared by cleaning,drying,charring,acid pickling,alkali washing,modifying,grinding and sieving.The four micro-particle carriers appeared abundant porosity through scanning electron microscope(SEM),their size was approximately in the range of 8.03 and 545.90?m based on laser particle size analyzer,existing hydroxyl,aromatic and oxygen-containing groups according to infrared spectrometer(FTIR),with diffraction peaks of amorphous structure in the light of X-ray diffractometer(XRD)analysis.The four micro-particle carriers were used to cultivate biofilm through microorganism enrichment.As a result,biofilm forming period in closed SBR was shorter than that in open SBR.COD removal efficiency was more than 85%in four micro-particle carriers with biofilm and NH₄⁺-N and TN removal rate in RHB and MRHB with biofilm were higher than that in RSB and MRSB with biofilm.COD,NH₄⁺-N and TN removal efficiency between and micro-particle carriers with biofilm and activated sludge(AS)showed a significant difference(P<0.05)based on analysis of variance(ANOVA).During biofilm formation in micro-particle carriers,biomass showed an increase tendency with a strong biochemical performance.Massive microorganism was accumulated to the four micro-particle carriers through microscopic observation.There were a plentiful of bacteria and extracellular polymeric substance(EPS)secretion in biofilm attached to micro-particle carriers.Those enzyme activities of catalase(CAT),dehydrogenase(TTC)and protease were higher in RHB and MRHB biofilm,thus they were stronger degradation capacity of COD,NH₄⁺-N and TN.(3)The pathway of PND to nitrogen removal using micro-particle biochar with biofilm was investigated based on single factor test and RSM.When single factor was separately controlled at influent COD of 3500 mg·L^-1,NH₄⁺-N of 511.23 mg·L^-1,5.87C/N,and 7.50 p H,3 L·min^-1 air aeration rate,COD,NH₄⁺-N and TN of RHB,MRHB and internal cycle RHB(I-RHB)with biofilm were achieved to the highest value.Based on RSM,the quadratic regression model was capable of describing response value regarding NH₄⁺-N and TN removal for I-RHB(P<0.0001).Factor interaction impact on NH₄⁺-N and TN removal rate of MHRB and I-RHB biofilm was in order of C/N>aeration rate>p H.The optimal parameters were C/N at 7.59,aeration rate at 2.9L·min^-1 and p H at 7.10.The verification result indicated that COD,NH₄⁺-N and TN removal efficiency,as well as nitrite accumulation rate(NAR)were high,realizing PND pathway,under the optimal conditions.(4)The results of micro-particle biochar with biofilm for nitrogen removal efficiency of digested swine wastewater through PND pathway indicated that the mean value of C/N and influent COD were separately at 7.77 and 2607.07 mg·L^-1,the average removal efficiency of COD for RHB and MRHB with biofilm was at 82.46%and 86.85%,respectively,which was 8.00%and 12.39%higher than that for AS.When the mean value of influent NH₄⁺-N and TN were severally at 337.05 mg·L^-1 and344.17 mg·L^-1,the average removal efficiency of NH₄⁺-N and TN for RHB with biofilm,as well as MHRB with biofilm,were separately at 58.96%and 57.74%,as well as 88.13%and 75.74%,which were higher than that of 8.99%and 8.00%,as well as 38.16%and 25.99%,for AS,respectively.At the same influent conditions,the mean COD,NH₄⁺-N and TN removal efficiency for I-RHB with biofilm were achieved to 85.30%,81.30%and 65.17%,compared with internal cycle AS(I-AS),higher 3.48%,24.37%and 14.72%,respectively.(5)The denitrifying bacteria from micro-particle biochar with biofilm after treatment of digested swine wastewater was screened and identified.The results indicated that a bacterial strain with nitrification and denitrification performance was obtained after three times enrichment,three times'preliminary screening and four times purification.The strain was considered as Acinetobacter oleivorans,according to 16S r DNA.The strain was inoculated into the culture medium of digested swine wastewater with initial 312.89 mg·L^-1 NH₄⁺-N and 405 mg·L^-1 TN.And the removal efficiency of NH₄⁺-N and TN for strain were at 69.86%and 75.07%,respectively,higher 13.56%and 16.09%than that with no strain liquid culture medium.Through Illumina Nova Seq sequencing,the results indicated that COD,NH₄⁺-N,DO and p H became major factors driving change of biofilm community structure.Most dominant bacterial community distributed in Protebacteria phylum with high abundance.It was found that Nitrosomonas and Nitrosospira,which belonged to ammonia oxidizing bacteria(AOB),without nitrite oxidizing bacteria(NOB).There were Acinetobacter,Comamonas,Pseudomonas,Arthrobacter,Bacillus,Flavobacterium and Corynebacterium,which exhibited heterotrophic nitrification and aerobic denitrification performance.