Effects Of Quick Harmless Chemical Treatment On Changes Of The Agricultural Characteristics And Heavy Metal Speciation In Rural Wastes

As the rural waste dumping amount increasing, the problem of low rate of harmless disposal and resource utilization of rural waste become very severe. This restricts the rural ecological environment construction and agricultural sustainable development. In China, the common treatment used in the disposal of livestock manure and other agricultural residues is biological fermentation method, which could realize resource utilization by producing organic fertilizer. However, this method has some limitations, such as the long process period, the large area occupied and the great impact on the adjacent environment during the processing because of emission of foul gas. The fast harmless chemical disposal technology was newly developed by Zhejiang Academy of Agricultural Sciences. Firstly, the core of the technology is disinfection the rural waste by using alkaline additives, then followed by adjustment pH value according to acid-base reaction theory, at the same time pathogenic microorganisms in residues were killed by the instantaneous high temperature and the niff molecules and water were removed. Eventually the purpose of harmlessness and reducing quantity of rural waste was achieved.In this paper, indoor simulation experiments were carried out to study the effects of on changes of the agricultural characteristics and heavy metal speciation in rural wastes. Pot experiment and field location test were used to investigate the influence of organic fertilizer produced by quick harmless chemical treatment on crop yield and quality, soil fertility and heavy metal accumulation. The results may provide theoretical basis for selection of best combination of quick chemical treatment and rational application of organic manure. The major results were as follows:1,In this study, the chemical treatment that combined with limestone powder and concentrated sulfuric acid has a strong killing effect on ascaris eggs and coliform organisms in household garbage, pig manure and chicken manure. After treating with different chemicals combination, death rate of ascaris eggs and colititre was below manure harmless Sanitary Standard (GB7959-1987). The contents of P2O5, K2O and organic matter in household garbage except for the low nitrogen content were within town refuse control standards for agricultural use (GB8172-87) after treating with fast harmless chemical method. The content of total nutrient and organic matter in pig manure and chicken manure exceeded the organic fertilizers industry standards (NY525-2002) after the chemical disposal. With the amount of limestone powder increasing from 3% to 7%, ammonia transformed from organic nitrogen in organic materials also increased. Adding concentrated sulfuric acid could inhibit ammonia release. When adding 4% concentrated sulfuric acid, it has a good performance in reduction of ammonia release.3% limestone powder+4% concentrated sulfuric acid was recommended as the best combination of the chemical treatment according to considering comprehensively from the factors of efficiency, nitrogen preservation and cost saving.2,After treating with different chemicals combinations, concentrations of heavy metals Cu, Zn, Pb, Cd and Cr in household garbage decreased slightly. The general trend of heavy metal concentrations decreased with the amount of chemical additive increasing because of dilution effect. Tessier sequential extraction was used to analyze Cu, Zn, Cr, Cd and Pb chemical species in household garbage. The results showed that limestone powder significantly reduced the content of stable organic compound (OM) and residual (RES) Cu, Zn, Cr, Cd and Pb in household garbage, while increased the content of labile exchangeable (EXE) heavy metals, especially increased the carbonate compound (CAR) heavy metal content significantly. The results maybe relate to the organic matter decomposition caused by adding limestone powder. The effect of limestone powder on heavy metal in Fe-Mn oxides (FeMnOx) form wasn't clear. Based on limestone powder treatment, additional sulfuric acid further reduced the OM and RES heavy metal content, while EXE heavy metal content changed not clearly. CAR heavy metal content decreased, which may relate to the dissolution of the carbonates. The results of chemical treatment with addition of exogenous heavy metal speciation in household garbage were consistent with the above conclusions.3,Three consecutive field experiment of soybeans-soybeans-horse bean showed that, compared with conventional fertilizer treatment, application of organic manure or organic and inorganic compound fertilizer produced by fast chemical treatment had no significant effect on the yield of the first two rotation crops, however there was significant differences in the third rotation crop yield. The yield of horse bean with household garbage and pig manure was 16.4% and 20.6% higher than that with conventional fertilizer respectively. The yield of horse bean with two organic-inorganic compound fertilizers was 6.1% and 7.7% higher than that with conventional fertilizer respectively. The crop yields in all the treatments reached a statistical significant level. Either organic manure or organic-inorganic compound fertilizer had an equivalent fertilizer efficiency with conventional pig manure. According to the results of crop quality and heavy metal contents, the crops were still safe even after three rotation continuous application of organic manure or organic-inorganic compound fertilizer produced by fast chemical treatment.4,Pot experiment also showed that application of chicken manure produced by biological fermentation or organic fertilizer made of town refuse produced by fast chemical treatment which accounted for 5%,10% and 15% soil weight significantly promoted the growth of amaranth (Amaranthus tricoclor L.) in red soil and fluvo-aquic soil. The fertilizer efficiency of chicken manure is better than that of organic fertilizer made of town refuse. Compared with conventional chemical fertilizer treatment, application of two organic fertilizers increased Cu and Zn concentration of amaranth in fluvo-aquic soil by 26.3%-36.0%,1.2%-20.3% respectively, which didn't exceed National Food Standard for the permission of Cu and Zn content in vegetables. The concentrations of Pb, Cr and Cd in amaranth plant with organic fertilizer treatments of were lower than that in control experiment, and there were no accumulation of these heavy metals in amaranth plant in organic fertilizer treatments. The concentration of Zn, Pb and Cd in amaranth plant with organic manure application in red soil decreased 42.7%-59.9%,0-48.9% and 4.1%-71.3% respectively, which reached a statistical significant level.5,Both the field and pot experiments indicated that application of organic manure increased the contents of organic matter, available phosphorus and potassium in soil, and improved soil fertility. Organic fertilizer made of town refuse produced by fast chemical treatment had a comparable efficiency with conventional organic manure. Compared with the original soil, all the contents of Cd, Pb, Cr, Hg and As increased in the treatment with three rotation continuous application of organic fertilizer. In the pot experiment, there was no significant heavy metal accumulation in red earth and fluvo-aquic soil in the treatments with organic manure accounting for 5% soil weight, while there was significant heavy metal accumulation in the treatments with organic manure accounting for 10% and 15% soil weight and the contents of Zn, Cd, Cr and Pb in both soils increased significantly.6,After amaranth harvesting, the pot soils were analyzed by Tessier sequential extraction. The results showed that the treatments with application of garbage fertilizer produced by chemical disposal and chicken manure decreased the most biological available EXE form of heavy metals, increased the stable OM and RES form of heavy metals in soils. Soil heavy metals content in CAR and FeMnOx speciation varied with pH value. The treatments with chicken manure reduced CAR-Cu and FeMnOx-Cu contents, while the treatments with garbage fertilizer increased CAR-Cu and FeMnOx-Cu content.