| Present biological wastewater treatment in China generates a large amount of sewage sludge.The spreading of sludge containing reductive sulphides,insoluble metal sulphides on soil has resulted in a second pollution and is a waste of resource unless it is timely disposed.These processes are based on the oxidation of sulfur, reduced sulfur compounds or ferrous ion by chemolithotrophic bacteria which converts them into soluble sulphates.In the so-called iron-based process,microbial desulphurization experiments under different conditions have been carried out for the municipal sludge based on the screening,identification and researches on biological characteristics of the desulphurization microbes.Ferrous-oxidizing bacteria strain NF-01 was isolated from the acid coal waste rock slurry,which was characterized of oxidation of different substrates such as ferrous,sulfur,sodium thiosulfate.Morphologic,biochemical,physiological and 16S rDNA sequence analysis indicated NF-01 belonged to the branch of Acidithiobacillus, and the close relative to Thiobacillusferrooxidans TK(DQ062114),with a similarity of 98.86%.In contrast,it was 98.70%identical to type strain ATCC23270.It indicated that NF-01 was in close proximity to Thiobacillus ferrooxidans which belonged to Acidithiobacillus spp.,and not in the same envolutionary branch with A.thiooxidans CMTT-32.Ferrous ion oxidation indicates the growth rules of Thiobacillus ferrooxidans. Biooxidation experiments were studied to upgrade the conditions of desulphurization, displaying series of results about the optimum critical point of different factors such as temperature at 28℃,pH value about 2.5,inoculation concentration 10%,initial ferrous concentration about 9 g/L with a shorter lagging phase and high growth activity,when the ferrous oxidation rate reached 0.4200 g/L·h-1.Presumed by plasmid extract and agarose gel electrophoresis of molecular biology level explore test, experimental results indicated that the oxidizing ability of Thiobacillus ferrooxidans to ferrous and sulfur may be only related with the nuclear chromosome DNA,and the heredity substance of Thiobacillus ferrooxidans is the nuclear chromosome DNA.In order to reduce the precipitates produced during culture of strain NF-01 in modified 9K medium,medium was optimized by altering the components of 9K medium rationally.Meanwhile,the strain was adapted by sequential adaptive culture and isolation via continuous culture.The ferrous oxidation rate reached 0.3376 g/L·h-1, which is similar to the original type.Moreover,the precipitate came into being at latest,and it was the least,which was in accordance with the report mentioned.This paper intends to present the results of T.ferrooxidans on desulphurization from sewage sludge in the iron-based bioleaching process.Desulphurization tests under different conditions have been carried out to study the effect on the rate of biodesulphurization.The fluctuations between ferrous and ferric were monitored during the bioleaching process.Mixed cultures (NF-01 and NH-2) at different inoculation proportion ratio was to determine if they could affect the leaching activity of T.ferrooxidans and compare their desulphurization rates.Desulphurization results showed the optimal growth conditions and desulphurization effects of strain NF-01 during the sewage sludge bioleaching.Leaching sulphate concentration was increased more rapidly when inoculation concentration superinduced.The differences of desulphurization rate between 10%and 25%were not obvious with the extension of leaching time, and then stabilized.When initial pH value was about 3.5,sulphate concentrations reached as high as 6.4300 g/L.Lower sewage sludge density causes higher desulphurization effect per gram of sewage sludge,but it would go with lower desulphurization amount.Satisfactory effect could be achieved at 5%sludge density.In biodesulphurization process of sludge,iron concentrations were kept in a dynamic equilibrium.The mutual interaction of NF-01 and NH-2 can accelerate the leaching of sulphate and the desulfurization of sludge.The best inoculation proportion ratio of NF-01 and NH-2 was 2:3 with leaching sulphate concentration as high as 8.0000 g/L.Results from the present study is to contribute to understand desulphurization disciplines and mechanisms, and the role of bioleaching microorganisms in heap bioleaching of sewage sludge. |
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