Study on the Improvement Effects of the Petroleum Hydrocarbon Contaminated Loess by Common Agricultural Wastes

Abstract

Four agricultural wastes ( walnut shell, corn cob, soybean straw and wheat straw) were selected as the soil conditioners to treat the petroleum hydrocarbon contaminated loess in this study ,according to its difficulty to be treated quickly and completely once, the principal component function model was set up to confirm the optimal conditioner for soil improvement on the basis of data processing of principal component analysis(PCA) through 120 days’ indoor decomposition and analysis and SPSS software to analyze the dynamic changes of various soil properties and their relationships with oil content, The results were shown as following: Firstly, the petroleum ether was selected as the extraction agent to detect the content of petroleum hydrocarbon in loess soil by gravimetric method, it could found that there was a much more obvious linear relation between the actual values and the measured ones than other methods and its linear formula was (Y=0.63814+1.39684*X (R2=0.99416) by which the calculated accuracy rate of oil content was up to above 94% with the deviation value of 3.27% relative to the standard value, which indicated this detection method had a better reproducibility by using petroleum ether to extract the oil content of the petroleum hydrocarbon in loess soil. Secondly, compared with blank control group, adding walnut shell, corn cob, soybean straw and wheat straw could decrease the oil content inordinately by13.59%, 17.85%, 27.38% 15.21%, separately and lowered pH values (0.35,0.56,0.46,0.45) promoted soil respiration(66.32%, 216.94%, 1874.17%, 159.71%) and facilitate alkaline phosphatase activity(64.21%, 81.47%, 140.25%, 147.69% )respectively. Thirdly, with the decreasing oil content in the soil, he pH value and the urease activity decreased, oppositely, the soil respiration and the alkaline phosphatase activity increased by adding walnut shell, soybean straw and wheat straw to the soil simultaneously. The invertase activity which strengthened by adding corn cob, soybean straw and wheat straw to the soil, however, lowered in the walnut shell-added soil. The catalase activity increased in the soil added soybean straw and decreased in the soil added walnut shell, corn cob, and wheat straw oppositely. Meanwhile, adding corn cob, soybean straw and wheat straw simultaneously to the soil could promote invertase activity (8.89%, 117.06%, 3.08%) the result was soil catalase activity (1.77%, 40.72%, 1.10%) respectively; adding walnut shell merely to the soil can inhibit invertase activity (-9.44%) and soil catalase activity (-3.03%). Finally , the comparison expression of the aggregative principal component function model Y=0.61712Y1+0.18307Y2+0.15805Y3 was got by the SPSS software and through which the result we got was: soybean straw (Y=2.762)>corn cob (Y=0.360)>wheat straw (Y=-0.048)>walnut shell(Y=-1.175)> blank group (Y=-1.897), and the principal component analysis (PCA) showed that all of these four) agricultural wastes all had certain degree of soil improvement effect, in which the soybean straw and corn cob could much more significantly promote the improvement effect of the petroleum hydrocarbon contaminated loess soil. Presently, the domestic and foreign research direction for the petroleum contaminated soil remediation technologies mostly focused on the degradation of petroleum hydrocarbon removal, but for how to improve the biological and chemical properties of the oil contaminated soil has little attention, especially to improve the soil properties using agricultural waste of natural organic matter to improve the oil pollution of hydrocarbon contaminated soil was very rare now [1]. The common agricultural wastes had the advantages of low cost, fixed stability, no two pollution and other advantages, it is not only rich in C, N, P and other nutrients, but also have good affinity to soil enzyme and soil microorganisms, and in humic process can also release of dissolved organic matter into the soil, and the most of which was the common metabolic substrate of microbial degradation, which can be of persistent organic pollutants in soil (PAHs) have strong biological The ability to degrade so that both the purpose of the degradation of petroleum hydrocarbons in the soil can be improved, and the nature of the petroleum hydrocarbon contaminated soil can be improved by it [2]. Because of its large specific surface area, fine particles and poor permeability, the Loess in Northwest China makes its adsorption and retention ability of petroleum hydrocarbon pollutants very strong. When a large amount of petroleum hydrocarbons enter the loess, it will permeate rapidly to a certain depth, which not only changes the soil composition, but also gradually changes the ecology of the Loess surface and kills the microorganisms in the Loess [3]. Therefore, once the loess is polluted, it will be more difficult to control [4]. This study takes walnut shell, corncob, soybean straw, wheat straw four common agricultural wastes as conditioner; study the biochemical effects of different bulking agents on petroleum hydrocarbon contaminated loess soil and the improvement effect, so as to determine the characteristics of the four conditioners to provide a theoretical basis for its application in the Soil remediation field.