| Heavy metal pollution from livestock and poultry manure is one of the environmental problems that need to be solved urgently.Based on the technology of bio-leaching using A.ferrooxidans LX5,the paper explored the effect of bio-leaching on the heavy metals removal in pig manure and the changes of its nutrient content and dehydration performance,showed the results of NaBH4 and stable pH for bio-synthesis schwertmannite,and the effects of the arsenic adsorption,analyzed the mechanism of schwertmannite adsorption and bio-mineralization coprecipitation of heavy metals in the leaching solution after bio-leaching.The effect and application prospect of removing heavy metals from leaching solution by chemical precipitation method were also expounded.The results showed as follows:(1)The effects of NaBH4 on biogenic mineralization,mineral adsorption and photocatalytic properties were investigated by adding NaBH4 in three batches in the filtrate after the biosynthesis of schwertmannite.The results showed that after adding 1.25 g·L-1 and 1.67 g·L-1 NaBH4 in three batches,the total Fe precipitation rate of the 2treatments reached 47.0% and 62.7%,respectively,and the production of secondary iron minerals were 8.92 g·L-1and 10.34 g·L-1.Generated minerals are schwertmannite(the first batch),schwertmannite mixture with sodium jarosite(the second batch),sodium jarosite(the third batch)respectively.The specific surface areas of synthesized minerals when adding 1.25g·L-1 and 1.67 g·L-1 NaBH4 to two treatment groups in three batches were 14.17 m2·g-1 and20.02 m2·g-1 in the first batch,32.95 m2·g-1 and 42.74 m2·g-1 in the second batch,0.84 m2·g-1and 13.68 m2·g-1 in the third batch.In the arsenic removal experiment,it basically conforms to that the larger the specific surface area is,the better the adsorption effect is.(2)Adjusted the pH of the system every 3 h to 2.50,2.70,2.90,3.10 and 3.30 during the biosynthesis of schwertmannite,respectively,and investigated its effects on the synthesis of schwertmannite and the performance of arsenic removal.The results showed that the total Fe precipitation was 26.5% in the control treatment system,the mineral production was 5.21 g·L-1,and the specific surface area was 3.18 m2·g-1.The total Fe precipitation increased to 88.4%,95.2%,95.7%,97.8% and 95.8% in the five treatments with adjusted pH every 3 h.The mineral production increased to 17.45,18.62,18.32,18.02 g·L-1 and 17.10 g·L-1.The specific surface area increased to 3.61,29.20,31.22,68.03 m2·g-1 and 90.67 m2·g-1,and the mesopore specific surface area at 2-20 nm contributed the most.Only a small amount of schwertmannite was converted to goethite in the three treatments with pH adjusted to 2.90,3.10 and 3.30.In the experiments of actual arsenic containing wastewater(27.4 μg·L-1)and simulated arsenic containing wastewater(1000 μg·L-1),the larger the specific surface area,the better the adsorption effect.(3)Taking pig manure from a farm in Taigu District,Shanxi Province as the research object,the effects of multiple batches of biological leaching of pig manure on its heavy metal leaching and dehydration performance were investigated.It was found that the biological leaching of original pig manure could not be carried out smoothly even the A.f accounted for 50%.After centrifugation for 3 times,pig manure bioleaching could be carried out well.The leaching rates of Cu,Zn and Mn were 100%,97.3% and 96.2%,respectively.The specific resistance decreased from 1.95×1013 m·kg-1 to 0.17×1012 m·kg-1.The contents of organic matter,total N,total P and total K in pig manure decreased by 53.0%,31.8%,72.3% and 74.9%,respectively.In the batch experiment,the treatment of A.f: leaching liquid: centrifugation pig manure = 1:1:2 can carry out in multiple batches of biological leaching.The leaching rates of Cu in the three batches were 100%,and the Zn and Mn were more than 99% and 95%.After biological leaching,the specific resistance of each treatment was 0.11×1012-0.27×1012 m·kg-1,which was easy to dehydrate.Bioleaching could cause partial nutrient loss in pig manure.The contents of organic matter,total N,total P and total K in pig manure decreased by 23.3%~30.8%,32.3%~38.3%,67.9%~71.4% and 76.3%~79.4%,respectively.(4)When took 1 g·L-1 schwertmannite synthesized by adjust pH 2.50-3.30 into the leaching solution system(pH=2.20),the removal efficiency of Cu,Zn and Mn was 10.9%-15.7%,9.8%-12.2%,6.8%-8.6%,respectively,while the pH was adjusted to 8 by Ca(OH)2,the Cu and Zn were precipitated completely,added 1 g·L-1 schwertmannite again,the removal efficiency of Mn was enhanced to 11.4%-21.4%.The results of this study clarify the parameters of biological leaching of pig manure in multiple batches,and reveal the regular mechanism of NaBH4 and stable pH on the synthesis of schwertmannite.Furthermore,this paper also reveals the effect of chemical precipitation on the removal of heavy metals from the leaching solution after biological leaching.The related research results can provide theoretical support for harmless treatment and resource utilization of pig manure,synthesis and application of schwertmannite. |
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