| As China is a big country of livestock and poultry, livestock manure has become an important raw material for organic fertilizer production. However, the heavy metals content in manure organic fertilizer always exceed the standards. It brings not only an increasing risk of heavy metal pollution in soil, but also harm to human health, for heavy metals may be absorbed by crops. The problem has become one of the bottlenecks restricting organic fertilizer production. Therefore, in the production process of manure organic fertilizer, how to passivate heavy metals is significant to environmental protection and industrial development.This study did a tracing analysis of the heavy metals in manure organic fertilizer on the North China Plain. It revealed the extent of heavy metals exceeding the standards. We used pig manure as the research object, set different fermentation process, optimized process parameters, added amendment and conducted passivation process. We completed a systematic research on the physicochemical properties of organic fertilizer, as well as the transformation characteristics and passivation of heavy metals. The main research achievements are as follows:1. We chose the North China Plain as research scope, conducted sample investigations and analysis on manure, commercial organic fertilizer, and fodder on livestock and poultry farms, and then did a tracing analysis of the heavy metals by principal component analysis. The results showed that average contents of Cu, Pb, Zn, Cd, Cr, Hg, As, Ni in commercial organic fertilizer were 69.22, 87.40, 274.58, 0.21, 45.42, 0.33, 3.21, 16.50 mg/kg, respectively. Additionally, 80.56% of all samples contented excessive Pb. The average contents of the heavy metals in manures were 301.6, 27.2, 736.3, 0.04, 57.7, 0.016, 1.6, 9.4 mg/kg, respectively. Additionally, 2.17%, 13.04%, 2.17% of all samples contented excessive Cr, Pb, As, respectively. The average contents of heavy metals in fodder were 87.03, 6.32, 297.90, 0.02, 13.89, 0.01, 0.65, 3.00 mg/kg. Additionally, 60.38%, 54.72%, 41.51%, 39.62% of all samples contented excessive Cu, Zn, Pb, Cr, respectively. Principal component analysis and correlation analysis showed that, the risk of heavy metal pollution mainly caused by the application of fodder with high Cu, Pb, Zn, Hg.2. This study revealed the effects of different fermentation technology(natural ventilation fermentation, forced ventilation fermentation and anaerobic dry fermentation) on the activities of heavy metals in the compost process. As fermentation processing, with the temperature higher than 50 ? during high-temperature period, 10 days duration, p H maintaining at 8.0, EC less than 2 m S/cm, and the seed germination rate index reaching 117%, the physicochemical property indexes of forced ventilation fermentation were obviously better than those of natural ventilation fermentation and anaerobic dry fermentation. All the different fermentation processes significantly affected morphological changes of Cu, Zn, Pb. The passivation abilities of the three different fermentation processes from high to low are forced ventilation fermentation>natural ventilation fermentation>anaerobic dry fermentation. The passivation rates of Cu, Zn, Pb caused by forced ventilation fermentation were 45.42%, 46.29% and 38.35%, respectively.3. This study revealed the effect of different process parameters(moisture, ventilation rate, the cycle of fermentation) on heavy metal activities during composting. A static forced aeration composting experiment was conducted, with initial moisture content values of 60%, 65%, 70%, and ventilation rates of 0.05, 0.1, 0.2 m3/min·m3, as well as fermentation periods of 20 d, 35 d, 50 d. The results showed that different process parameters affected physicochemical property of compost significantlly. The analysis of variance on the distribution rates of Cu, Pb, Zn showed that, the ventilation rates significantly influenced the passivation effects of exchangeable Cu(p=0.02) and Pb(p=0.040), however, the water content significantly influenced the passivation effect of exchangeable Zn(p=0.009). The two optimized fermentation process parameters had been found: a initial moisture content of 65%, a ventilation rate of 0.1 m3/min·m3, a fermentation period of 50 days; a initial moisture content of 65%, a ventilation rate of 0.2 m3/min·m3, a fermentation period of 20 days. For the two optimized fermentation process parameters, the high temperature duration were 12 days and 8 days, the p H value were 8.0 and 7.6, the EC value were 3.86 and 3.75 m S/cm, the GI value were 64.95% and 144.05%, respectively. The passivation rates of exchangeable Cu, Pb, Zn, Cd were 86.13%, 52.37%, 18.42%, 40.37% and 83.57%, 63.46%, 56.17%, 46.41%, respectively.4. This study revealed the effects of different conditioners(pig manure, pig manure+ corn straw, pig manure + sawdust) on the activity of heavy metals during composting. High temperature aerobic fermentation process was conducted, with a material moisture content of 65%, a ventilation rate of 0.2 m3/min·m3, a the fermentation cycle of 30 d. The results showed that adding straw or sawdust could significantly improve the physical and chemical properties of compost, the high temperature duration were 5 days, the p H value were 8.6 and 8.7, the EC value were 1.79 and 1.72 m S/cm, the GI value were 118% and 142%, respectively. The addition of corn straw and sawdust improved the passivation effect on heavy metal, and the passivation rates of Cu, Pb, Zn, Cd were-3. 9%, 42.8%,-0.2%, 73.2% for addition of corn straw, and the passivation rates were 60.5%,-18.1%, 52.8%, 89.9% for addition of sawdust respectively.5. This study revealed the effects of different passivation materials(sawdust biochar, corn straw biochar, peanut shell biochar, Fujian humic acid, Jia Bowen humic acid, peat) on the heavy metal activity during composting. High temperature aerobic composting was conducted with pig manure and straw, and the different morphological characteristics of Cu, Pb, Zn and Cd were studied. The results showed that the compose with biochar, peanut shell or Fujian humic acid didn't reached the compost standards. The p H value was less than 6.0 for addition of peanut shell biochar, the EC values were more than 4.0m S/cm for addition of peanut shell biochar and Fujian humic acid, the GI values were less than 80% for addition of corn straw biochar, peanut shell biochar, Fujian humic acid. The passivation rates on Cu were 0%, 24.31%, 65.79%, 14.70%, 47.78%, 25.35% for addition of sawdust biochar, corn stalk biochar, peanut shell biochar, Fujian humic acid, Jia Bowen humic acid, peat, resecptively. The passivation rates on Pb were 13.09%, 57.20%, 46.20%,-1.25%, 47.54%, 4.08%, resecptively. The passivation rates on Zn were 55.42%, 18.08%, 13.66%,-17.13%, 64.94%, 50.28%, resecptively. The passivation rates on Cd were 94.67%, 49.93%, 25.09%, 47.39%, 87.36%,-6.90%, resecptively.To sum up, on the North China Plain, Cr, Pb and As in manure and commercial organic fertilizer exceed the standard. The risk of heavy metal pollution in organic fertilizer came mainly from feed additive. Through a series of optimization and selection, the optimized fermentation process parameters with the best passivation effect on heavy metals were found: a high temperature aerobic composting process; a initial moisture content of 65%; a ventilation rate of 0.2 m3/min·m3; a fermentation period of 20 days; adding straw or sawdust as bulking agents; choosing sawdust biochar and Jia Bowen humic acid as the passivation material. This study provided theoretical and technical references to heave metal passivation technology and the scale application manure of organic fertilizer. |
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