Acidification During Aerobic Treatment Of Digested Swine Wastewater And Improvement Strategy

Digested effluent from anaerobic treatment of swine wastewater still contains high concentration pollutants,especially ammonia nitrogen,which can not meet the strict national discharge standards.Generally,it need to aerobicall treat further in the region with limited land.The results of aerobic treatment is poor due to acidification.Aiming at this problem,on the basis of previous research,this paper studied the subject of“Acidification during Aerobic Treatment of Digested Swine Wastewater and Improvement Strategy”.Using Sequence Bath Reactor?SBR?,this dissertation investigated the acidification during aerobic treatment of digested effluent of swine wastewater and its influence on the removal of pollutants.The new strategy to improve the acidification and the treatment efficiency were explored.The improvement mechanism was also analyzed.The results are listed as follows:?1?Acidification during aerobic treatment of digested effluent of swine wastewater and its effect on pollutant removal were investigated.The results showed,at influent chemical oxygen demand?COD?and NH₄⁺-N concentrations of 540 mg/L and 400 mg/L,respectively,all reactors with HRTs?Hydraulic Retention Times?of 1.25,2.5,and 5d experienced acidification because of nitrification,and the lowest p H values reached approximately 6.0.The COD removal efficiency were-22.1,-14.3 and 3.23%,and NH₄⁺-N removal efficiency were 70.1,77.0 and 80.7%in reactors with HRTs of 1.25,2.5 and 5 d,respectively.Almost no total phosphorus?TP?was removed.When HRTs were lengthened to 7.5,10 and12.5 d,COD removal reached 4.34,5.46 and 8.88%,respectively,and NH₄⁺-N removal reached 81.1,82.3 and 83.0%,respectively.Although longer HRT increased the removal of NH₄⁺-N,it decreased the nitrogen removal loading rate.Low pH not only inhibit the growth and metabolism of microorganisms,but also influence the availability of substrates and toxicity?free nitrite?of nitrifying bacteria.Acidification was also responsible for leakage of phosphate from microbial cells and the dissolution of precipitated phosphorus.?2?A pilot experiment was conducted to study the effect of improvement strategy that the SBR was inoculated with anaerobic ammonia oxidation sludge?AN?,using addition of raw swine wastewater?RW?to digested effluent as a reference.High throughput sequencing technology of Miseq was also employed to analyze the variation of microbial community in two improvement strategies.Compared to treating digested swine wastewater directly,the efficiency of AN and RW increased 60.2%and 102.6%for COD removal respectively,11.1%and 73.3%for total inorganic nitrogen?TIN?removal respectively.The improvement of RW was the most obvious.The relative abundance of the Nitrosomonas of control group?CG??7.9%?and AN group?4.2%?was higer than RW group?0.79%?.The relative abundance of enrichment ammonia oxidizing bacteria?AOB?was less than nitrite oxidizing bacteria?NOB?in RW group,while the CG group and AN group showed the opposite trend.It indicated that NO₂^--N was accumulated in CG group and AN group,and there was little accumulation of NO₂^--N in RW group.The enrichment of anaerobic ammonia oxidation bacteria?Anammox?only appeared at the AN group.But the relative abundance of Anammox bacteria was low?Candidatus Brocadia=0.05%?,resulting in lower efficiency of autotrophic nitrogen removal.?3?Another pilot experiment was conducted to study the effect of improvement strategy of adding zero-valent iron?iron shavings??IS?to mixed liquid of SBR,using adding alkali?Na₂CO₃??AA?as a reference.Compared to treating digested swine wastewater directly,the efficiency of IS and AA increased 13.2%and 0.6%?corrected for NO₂^--N interference?for COD removal respectively,22.7%and 22.5%for NH₄⁺-N removal respectively,91.7%and 10.5%for total inorganic nitrogen?TIN?removal respectively,72.6%and 11.9%for total phosphorus?TP?removal respectively.At stable stage,IS presented the highest removal efficiencies of COD,NH₄⁺-N,TIN and TP up to 82.7%,100%,98.2%and 81.2%,respectively.The improvement of IS was the most obvious.?4?By means of detection of the concentration of Fe²⁺and Fe³⁺in effluent of the reactor,electron microscope scanning to sludge,analysis of elements and mineral,conversion activity test of sludge to different substrates,and high throughput sequencing technology,the mechanism of improvement of ammonia nitrogen removal in aerobic treatment process of digested effluent by addtion of zero-valent iron?iron shavings?was studied.The results showed that ammonia oxidation,nitrite oxidation,heterotrophic denitrification and anaerobic oxidation of iron in SBR?aerobic/anoxic?treatment system contributed to higgh removal of TIN after adding zero-valent iron?iron shavings?.In conclusion,adding zero-valentine iron?iron shavings?can observably improve aerobic treatment of digested effluent of swine wastewater.COD and ammonia nitrogen concentration in effluent can meet the discharge standards prescribed by the China?GB18596-2001?.The improvement strategy of adding zero-valent iron could be expected to form a new technology for nitrogen and phosphorus removal from wastewater.The new process has a broad application prospect.The mechanism need to be further studied to provide theory for the perfect and practical application of the new process.