| H2S and NH3have a strong pungent odor, corrosive and toxicity, which are commoncomponents of exhaust gas from the industries such as waste processing, petrochemical andprotein fermentation. Therefore, their emission must be strictly controlled. Because ofchemical method with stability and high efficiency and biological method with energy savingand innocuousness, desulfurization and denitrification technology which combines theadvantages of two methods appears to be most promising.In the indirect biological oxidation procedure, H2S was removed by multiplex catalysisof Acidithiobacillus ferroxidans and Fe3+,moreover, NH3was removed by acidic absorption,which achieving close circulation of the iron ions and offering nitrogen source to microbialgrowth. In this paper, a bio-chemical reactor with two stage design was used to remove H2Sand NH3. The culture condition was optimized, effect and stability of immobilization wereinvestigated, and the joint operation of the reactor to purify gas was researched. The mainconclusions were as follows:(1) The effects of material type and concentration of nitrogen source and initial pH ongrowth of swimming cells and generation of precipitate were studied. It showed that(NH4)2HPO4was the optimum nitrogen source and its concentration in0.33~1g·L-1was asuitable range for cell growth of Acidithiobacillus ferroxidans. At1g·L-1, average oxidationrate of Fe2+was0.225g·(L·h)-1; dissolved Fe3+increased to7.67g·L-1; and precipitation was1.17g·L-1. Therefore, the optimal concentration of (NH4)2HPO4was1g·L-1. And it wasdetermined that the initial pH at2.0best corresponded with the actual needs. By this time,average oxidation rate of Fe2+was0.2g·(L·h)-1, maximum generating of Fe3+increased to7.85g·L-1, concentration of precipitation was1.01g·L-1.(2) The impacts of different concentration of (NH4)2HPO4on effect and stability ofimmobilization were investigated. It showed that optimal concentration to immobilize cells ofAcidithiobacillus ferroxidans was0.33g·L-1. The stability of the immobilized biological towerwas analyzed by dynamics to determine the half-life of the system for205days.(3) The effects of inlet concentrations of NH3in2.90~13.52mg·L-1on removalefficiency of H2S and physicochemical properties of the absorption liquid were researched,when steady operation of chemical absorber was being in progress. It showed that NH3didnot directly affect the removal of H2S. As NH3was absorbed into the liquor, pH rose gradually,change of NH4+concentration was ascend in first and descend at last, and dissolved Fe3+reduced. The changes of pH, NH4+and Fe3+were more marked with the increment of NH3concentration. When its concentration reached13.52mg·L-1, growth rate of pH was0.034h-1,cumulative NH4+maximally increased by1.38g·L-1, final concentration of NH4+was0.33g·L-1and concentration of Fe3+was reduced by1.74g·L-1. (4) The change of constituents of systemic circular fluid under the influence of removalof H2S and NH3was investigated, when the joint reactor kept running stable. It showed thatMg2+and P were reduced by absorption of H2S and NH3and meanwhile NH4+wasaccumulated. By the end of running, Mg2+and P held a considerable surplus of78.58%and91.11%and concentration of NH4+remained greater than0.33g·L-1. It could fulfill therequirements for biological reuse without additional Mg2+, P, and NH4+. Furthermore, Usingcirculating fluid to culture the microbe was studied and ratio of dosing circulating fluid of25~50%was obtained for industrialization application. |
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