The Influence Of Bioleached Sludge Land Utilization On The Crops Growth And Ecological Environment

Tannery sludge containing valuable nutrients and organic matter could be used as aorganic fertilizer for plant growth and soil amendment. Land utilization of tannery sludge isa potential approach for this sludge disposal. But the presence of high levels of poisonousmetal Cr in tannery sludge often limits its use on the farmland. The Cr in tannery sludge isabout 1ï¼…-4ï¼…on a dry weight basis. In the past two years, a technologically feasibleprocess so-called bioleaching was used successfully to remove Cr from tannery sludge withAcidithiobacilli species in our group with almost 90ï¼…of Cr removal efficiency from thetannery sludge. In the light of higer level of Cr in tannery sludge, tannery sludge cannot beapplied directly to the land.A series of laboratory studies, field and greenhouse experiments were conducted toassess the effect of land utilization of tannery sludge to the growth as well as the ecologicalenvironment influence. Pot experiments showed that along with primitive tannery sludgequantity increase, ryegrass biomass, chlorophyll and height increase. And descend when therate of sludge is 25ï¼…, but is still finer than comparison treatment. After the addedchromium joins, the content of chromium in soil is 2000mg.kg^-1, the ryegrass growth startsto restrains. And when the content achieved 4000mg.kg^-1, the ryegrass was obviouslyrestrained; the ryegrass could not grow nearly. Along with the tannery sludge quantityincrease, the chromium content of ryegrass didn't increase obviousiy; but the addedchromium treatments were obvious. Bioleathed sludge to the ryegrass growth always wasthe promotion; but to the primitive tannery sludge, the third crops of ryegrass biomassdescended actually; moreover along with the increase of quantity, the scope which dropsincreased. The ryegrass hight, chlorophyll, root system vigor and so on had the samechange tendency with the ryegrass biomass.From the content of chromium of Ryegrass, we can know that bioleached sludgeapplication in the amount and timing of the application of chromium absorption ryegrass little effect while the treatments of primitive sludge were very clear. At the same time,bioleached sludge had simulative effect for the absorption of N, P and K of ryegrass, thetannery sludge restrained the nutrient absorption in the latter part. The treatments thatmingled with sludge had the same influence to the physical and chemical properties of soils.However, the total chromium content in soil of the tannery sludge increased obviously.With the increase in the amount of sludge applied, along with a large number of trivalentchromium into the soil, but there were little soil available chromium, the effective state ofchromium content in soil just 4.62mg.kg^-1 after four months of the 25ï¼…tannery sludge,were more than 52.98ï¼…compared with the same amount of bioleachied sludge and therewere no hexavalent chromium detected in the soil.Field experiment showed that the negative effects of applying directly tannery sludgeinto soil on growth of the rice. The yield of rice was observed decreased by 27.10ï¼…compared with the control. However, bioleached tannery sludge increased rice yield andimproved rice growth including enhancing the number of rice tilling, the chlorophyllcontent, and fresh weight and yield respectively. The highest yield was obtained for thetreatment of applying bioleached tannery sludge accompanied by fertilizer with the increaseof 20.02ï¼…compared with the control. In addition, either tannery sludge or bioleachedtannery sludge increased soil fertility as exhibiting the increase of soil N and organic matter.But the application of Cr-rieh tannery sludge resulted in soil Cr pollution. The applicationof bioleached tannery sludge hardly accumulated Cr in the treated soils. Correspondingly,the content of Cr in rice grain didn't exceed 1 mg.kg^-1, a limited level in rice grain proposedby Ministry of Health of the People's Republic of China, when Cr in tannery sludge wasremoved through bioleaching and then bioleached sludge was applied.Under the cultivated situation, the mineralization rate of bioleached sludge wasincreased with time, but after the ninth week, the rate of mineralization did not changebasically and it reached to top in the sixth week or the eighth week, different sludgeapplication, different mineralization rate.This paper showed that the trivalent chromium in original tannery sludge was mostlyadsorbed by the soil, but compared with bioleached sludge, it inhibited the growth of cropssignificantly; moreover, the effective state chromium in the soil was also higher than thetreatments of bioleached sludge. The bioleached sludge promoted the growth of ryegrassand increased soil N, P and other nutrients. Clearly, the tannery sludge land use must bedisengaged from Cr before using; biological leaching technology is economic way and offers a broad prospect for land use.