Applicatoin Research On Urban Sludge Treatment By The Earthworm

It would have a bad effect on the environment and human health if sewage sludge will not be improperly disposed, but the potential of sewage sludge as resource is tremendous owing to their rich nutrients and organic matter.This study measures and analysis the sewage sludge characteristic of Wenjiang area. Carring on the single factor test from the three aspects of earthworm on the density, thickness of sludge added and material carbon and nitrogen ratio, we can obtain the best earthworm on the density, the best thickness of sludge added and the best material carbon and nitrogen ratio. Carrying on the orthogonal design experiment of the three factors, we can obtain the optimal level combination of three factor. Carrying on wheat germination experiment in the flower pot with wormcast and nutritional soil matrix, we can observe the morphological characteristics of wheat malt and statistics the germination rate and growth rate. The main contents and conclusions are as follows:(1) Through the measure of the sewage sludge characteristic, it is concluded that the organic matter, total nitrogen, total phosphorus and total potassium were 54.99± 9.87%,2.42±0.66%, 0.90±0.25% and 0.67±0.06% on average. The contents of alkaline hydrolysis nitrogen, available phosphorus and available potassium were 2.42±0.66%、0.90±0.25%and 0.67±0.06% on average. respectively, accounted for 6.42%,5.47% and 61.53% of total nitrogen, total phosphorus and total potassium. The order of the heavy metal content from high to low was Zn> Cu> Cr> Pb> Cd. Its average content were 545.14 mg/kg,148.74 mg/kg,90.79 mg/kg,28.8 mg/kg,4.80 mg/kg. In general, the sewage sludge obtain rich nutrition, lower heavy metal content than the limit, great utilization value.(2) After the earthworm treatment, sludge pH had a significant rise, the content of total nitrogen and total phosphorus decreased significantly, total potassium content had a significant rise, organic matter is greatly reduced, alkaline hydrolysis nitrogen, available phosphorus and available potassium had a significant rise, heavy metals content of Cu, Zn, Pb, Cr, Cd is significantly reduced.(3) Through different earthworm on the density test, it is concluded that with the increase of earthworms on the density, the earthworm weight ratio first increased then decreased. The wormcast pH was ever growing. Total nitrogen and total phosphorus first increases then decreases. Total potassium content was ever growing. Organic matter content was ever decreasing. The content of alkaline hydrolysis nitrogen, available phosphorus and available potassium first increased then decreased. Heavy metal content gradually reduced. Earthworm biomass incrementary ratio and earthworm weight ratio was the highest on the earthworm density of 50 g/kg, so it is the most suitable earthworm density. In 50g/kg density, total nitrogen and total phosphorus content in wormcast was significantly lower than other groups. alkaline hydrolysis nitrogen, available phosphorus and available potassium content were the highest. The greater the earthworm on the density, the more significant heavy metal accumulation effect by earthworm,the better heavy metal reduction effect by earthworm.(4) By different sludge thickness test, with the increase of thickness of sludge added, earthworm weight ratio roughly showed a trend of first increase then decrease. The content of alkaline hydrolysis nitrogen, available phosphorus and available potassium in wormcast first increased then decreased. The decreases amplitude of Cu, Zn content gradually reduced. Earthworm biomass incrementary ratio and earthworm weight ratio was the highest of 10 cm sludge thickness, so it is the most suitable sludge thickness. In wormcost pH of 8 cm sludge thickness is significantly higher than other processing. Total nitrogen, total phosphorus and organic matter content in wormcost of 10 cm is significantly lower than other groups. Total potassium content was significantly higher than other groups. Alkaline hydrolysis nitrogen, available potassium content reaches maximum value. In general, of the sludge thickness of 10 cm, quick-acting nutrient growth effect in wormcast is better. In wormcost, Pb, Cd, Cr of the 10-12 cm sludge thickness, the effect of reduction was the best. Taken together, in the sludge thickness of 10 cm, heavy metal accumulation effect by earthworm was the more significant, heavy metal reduction effect by earthworm was the better.(5) Through the test of the different material carbon and nitrogen ratio, it is concluded that with the increase of material carbon nitrogen ratio, the earthworm weight ratio roughly showed a trend of first increase.then decrease. Material carbon and nitrogen ratio had significant effect on earthworm growth. With carbon nitrogen ratio of 20, earthworm weight ratio was the highest, so it may be the most suitable material carbon and nitrogen ratio.(6) Through 3 factors 3 levels orthogonal design test, it was concluded that carbon and nitrogen ratio, the sludge thickness and density of earthworms, three factors on the effect size of earthworm weight ratio is carbon and nitrogen ratio> density> thickness, C/N ratio of 20, thickness of 10 cm, density of 50 g/kg is the optimal condition combination of the earthworm treatment sludge, the growth of earthworm was fastest at this time.(7) Through wheat germination experiment and wheat seedling growth test in the wormcast and nutritional soil, it was concluded that in wormcast wheat seedling germination rate was faster, complete germination time is shorter than in the nutritional soil, but the germination rate is lower than the nutritional soil. Compared with nutritional soil, wheat seeding growth in wormcast was faster.