Stabilization of Sewage Sludge by Vermi Composting by Sonakshi Gurung
Abstract
Toxic concentrations of heavy metals have been reported to be present in STPs as many industries dispose their waste directly in domestic sewers without prior treatment and thus they are carried to the sludge generated during the treatment processes. This sludge is directly fed to fields without any proper analysis or treatment which ultimately enters the food chain. This problem can be handled by biodegradation methods to lessen its threat to the environment. This study used one such technique of vermi composting for stabilizing the toxic sludge. Aerobic sewage sludge was assembled from the SBR unit of sewage treatment plant situated at Bhattian, Ludhiana. The work aimed at reducing the heavy metal content (Cr, Cd, Ni and Pb) from aerobic sewage sludge by the vermicomposting method using earthworm Eisenia foetida with the different activators (Cow Dung, Poultry Manure and Horse Dung) at 50:50 proportion by mass for 105-day period. Vermi-beds of size 3´×3´×0.5´ were set up and the raw material was inserted in the said proportions. The lab and field analysis were performed on regular intervals. The parameters considered for the study were pH, moisture content, total carbon, total nitrogen, C/N ratio, total potassium, total phosphorus and the heavy metals (Cr, Ni, Cd and Pb). The results showed that both cow dung and poultry manure are commensurable for causing the decomposition of the sewage sludge and were better than horse dung. And for stabilizing the heavy metals, cow dung acted as the best activator. The lab analysis depicted high values of chromium which made it the main toxic element that needed removal. The study further showed that there are high heavy metal contents in the activator themselves which contribute to the high values in the pit material at the initial stages but still considering their stabilization effect they are added. the sewage sludge waste but in case of heavy metals, cow dung acts as the best stabilization material.
