The Security Control Of Biogas Slurry On Heavy Metals In The Application To Cirtus Trees

Biogas slurry has been extensively applied as a kind of good liquid organic fertilizer. But for the most part, the study about biogas slurry was stayed in a plainer level at present, which mechanism and safety was short of systematic research. In addition, as people pay more and more attention to the quality of agricultural products, the safety of them has become a hot spot which was concerned by many scholars. The toxic substances in biogas slurry, especially the content of toxic heavy metals would play a part of an important index to assess the quality. However, related study reports about the aspect were insufficient previously. So based on the current situation, the study tried to put forward new thinking and to lay the foundation for realizing the goal-the recharge of biogas slurry to farmland at the minimized ecological risk.The main nutrient status and heavy metals contents of the biogas slurry which was collected from the large and medium-sized piggeries in Chongqing were detected and surveyed in this article. And on that base, the load carrying capacity of different types of soil to biogas slurry and the combined impacts of the soil after biogas slurry application were researched in the paper. Meantime, the heavy metals security of biogas slurry applied on Trovita was analysed and estimated, in order to explore the effects of Trovita growth and the accumulation of heavy metals under the stress of Cu, Zn, Cr in biogas slurry. The major results were as follows:1. The study result indicated that the pH range of Biogas slurry was neutral to alkalescent. The tendency of principal nutrient elements contents of Biogas slurry was available N> available K> available P. And the average contents of the main heavy metals elements of Biogas slurry presented a certain trend:Zn>Cu>As>Cr>Pb>Cd>Hg. Moreover, the contents of main heavy metal elements in biogas slurry were different greatly. Especially, the difference of As status was the biggest, and its coefficient of variation was up to205.133%, and Cu, Zn, Cr to the next. And the variation rage of Pb was minimized, which coefficient of variation was only84.189%. Besides, compared to the standards of irrigation water quality, As was seriously far beyond the standard, and its amount exceeding by56.7%. Meanwhile, Cu、Zn exceeded the standard to different extent, and the safety of Hg、Pb、Cr、Cd were relatively more superior in agricultural industry. Generally speaking, the average contents of heavy metals elements comparatively increased after anaerobic fermentation. Among the heavy metals, only the correlation of As between biogas slurry and pig manure was obvious. However, the fundamental reason why the great differences existed between the contents of heavy metals would be studied in further researches.2. The bearing stress to biogas slurry was different among different types of soil. The bearing capacity of nutrient soil to biogas slurry was relatively large. And after biogas slurry applied by10times, the status of Cu, Zn, Cr, As was all still in the safety range. But to the paddy soil, just irrigated for5times, Cu began to appear the phenomenon of overweight. Furthermore, it was effective to reduce the content of Cr in slope soil for taking appropriate use of biogas slurry. But with the increasing time of biogas slurry application, Cr would continue to accumulate, so the bearing load of slope soil to biogas slurry should be less than5times.3. The content of soil organic matter would be increased and the enzyme activity in soil would be enhanced after biogas application. And with the constant irrigation of biogas slurry, the effect of strength also would be more obvious. So from this point of view, the application of biogas slurry played an important role in improving the physical properties to soil.4. The content of soil organic matter was related to phosphatase, urease and intertase activity, and the the relevance was significant. Compared with the paddy soil and slope soil, the status of soil organic matter and phosphatase, urease and intertase activity in nutrient soil were ranked No.1. Above all, the microbial populations were the biggest. And microbes played a good function of repairment to heavy metals in soil. Therefore, the bearing capacity of nutrient soil to biogas slurry was the strongest.5. Under the situation of being covered by plants, the content of Cu, Zn, Cr in soil was directly impacted by the concentration of Cu, Zn, Cr in biogas slurry. And after comprehensive comparison, the influence to the content of Cu, Zn, Cr in soil was outstandingly resulted from the concentration of Zn in biogas slurry. In addition, from the perspective of soil environmental quality, it was inaccurate to take the quality standards of irrigation water as the security restriction of heavy metals to biogas slurry. The limited content of Zn in biogas slurry should be below the standard for irrigation water-2mg/L.6. The status of Cr in fruits would be increased by the treatments of different heavy metals concentration in biogas slurry. And Cr in the fruit posed some serious potentially safety risks. In comparison, the security of Cu, Zn in fruits was relatively higher, but it was still needed to be tracked and identified in the long term. Besides, if taking the standards for irrigation water quality as the limited values for biogas slurry, it would make the content of Cr in fruits out of the standards. In light of this, standards for irrigation water quality was not suited to biogas slurry precisely. Especially, the safety standard for heavy mental in bioga slurry should tighten the limit on Zn.7. The correlation among the heavy metals concentration in biogas slurry and heavy metals pollution in soil, the safety of fruits quality was obvious. It was necessary to establish and improve the security control standards to guarantee the harmless circulation and efficient application of biogas slurry.8. The differences of the content of organic matters, catalase, invertase and urease activity caused by different heavy metals concentration were not significant, but the influence of soil phosphatase activity was relatively larger. In comprison, soil enzymes activity mostly influenced by the concentration of Cu in biogas slurry. In addition, under the compound stress of Cu, Zn, Cr, the soil catalase, phosphatase, urease activity were all restrained. Moreover, the higher concentration of Cu, Zn, Cr, the inhibition was greater. On the contrary, the invertase activity was activated, just the activation did not play a significant role.