| The present paper is aimed to meet the resource utilization of municipal sewage sludge to find a more simple economy vermitechnology, and expand the selection of earthworm species.Based on earthworm ecological function, direct vermicomposting of sewage sludge by two epigeic earthworm species (Eisenia foetida and Bimastus parvus) was conducted in a lab-scale experimental setup. The sewage sludge physiochemical properties, heavy metals, nutrients, bacteria aggregate, sludge reduction and earthworm biomass was tested during pot experiments with 30 days. The feasibility of vermicomposting technology to recycling dewatered sludge without any treatment by two epigeic earthworm species was investigated, and the performance was evaluated. The results are as follows:1:The sewage sludge was converted without any pretreatment and blending into good quality fertilizer-wormcast. The vermicompost was much darker, more fragmented, and porous than originally and had been processed into a homogeneous manure, after 30 days of earthworms activity. The water content, unit weight and porosity of wormcast were between 62.3%-64.7%,1.8 g.m-3-2.1 g.m-3 and 73.4%-76.3%.2. Vermicomposting significantly modified the physical and chemical properties and nutrients of different vermicultures tested (p<0.05).Vermicomposting resulted that pH declined upto 6.27 with B. parvus and 7.07 with E. foetida, while the electrical conductivity increased by 3.76-3.84 fold. Meanwhile, B. parvus produced 35.37%,15.28% and 31.92% increases in nitrogen, phosphorus, and potassium as well as 29.18% and 47.64% decreases in TOC and C/N ratio as compared to initial after 30 days of earthworm inoculation.In contrast, E. foetida produced 37.00%,18.93% and 20.16% increases in nitrogen, phosphorus and potassium as well as 27.00% and 46.86% decreases in TOC and C/N ratio as compared to initial after 30 days of earthworm activity.3. Vermicomposting of the epigeic species earthworms also caused significant reduction in total concentration of metals and bacteria aggregate (p<0.05). As compared to initial level, the reduction in total contents of Cu, Zn, Pb and Cr by E.fetida was 37.7%,38.8%,27.4% and 17.0% respectively. The reduction in total contents of Cu, Zn,Pb and Cr by B. parvus was 30.4%,29.3%,21.2% and 23.0% respectively.Nevertheless, Bioconcentration factors (BCFs) for metals (Zn, Cu, Pb and Cr) in different treatments were also calculated.The BCFs for B. parvus was 0.21,0.14,0.93 and 1.54 respectively as well as 0.25,0.22,0.97 and 0.48 respectively for E. fetida. Moreover, bacteria aggregate decreased with time in all the worm-worked vermireactors in the range of 99.92%-99.93%.4. At the end of experiment, the weight of system sludge reduction was 26.67%-27.14%, and the organic matter reduction was 23.45%-24.81% respectively for E. foetida and B. parvus. At the same time, the weight and cocoons with B. parvus and E. foetida showed significant increased, which the growth rate and the reproductive rate were 4.8 mg.d-1-5.8 mg.d-1 and 2.32 cocoon.d-1-3.65 cocoon.d-1 respectively.5. A comparative study on vermicomposting of sewage sludge between E. foetida and B. parvus resulted that both epigeic species earthworms showed same mineralization and decomposition rate. Vermicomposting of sewage sludge for 30 days resulted in significant difference (p<0.05) between the two species in their performance measured as loss pH and increase in total potassium.The change in electrical conductivity, nitrogen, phosphorus, TOC, C/N ratio, heavy metals and bacteria aggregate, sludge reduction and increase in number of earthworms and cocoons and weight of earthworms were non-significant (p>0.05).Our trials have demonstrated that the direct vermicomposting of sewage sludge could be an effective technology to convert into nutrient rich biofertilizer with E. fetida and B. parvus. On the basis of chemical analysis, the observations indicated the E. fetida to be similar in performance as B. parvus, in terms of Physiology the earthworm biomass of E. fetida were found to be the same as B. parvus. Overall, these results also indicate B. parvus may be a better adapted species for vermicompost directly.
|
PDF Full Text Request