الفهرس 
VERMREMEDIATION OF SEWAGE SLUDGE AND PRODUCTION OF SAFE NUTRIENT-RICH HUMUS FOR AGRO – FERTILIZATIONOnly 14 pages are availabe for public view
 |  | from | 22 |  |  |
| | | from | 22 | | |
Abstract
Combining some anthropogenic wastes in order to feed Lumbri’cus Allolobophora earthworms (LAEWs), which absorb and periodically accumulate the toxic trace elements in their tissues and increase the mineralization of the plant nutrients content in their habitat is a significant green technology. In view of the above background, this study aimed at investigating the role of EWs’ vermi-remediationin reducing the toxic trace elements contents and increasing mineralization of some macro and micro nutrients in the selected EWs’ bedding and feeding mixtures.
LAEWs’ Bedding and Feeding Mixtures: Original substrates that form a suitable multi- functional medium in which LAEWscan work, feed, produce casts, grow, reproduce, and survive were selected. The proposed LAEWs’ bedding and feeding substrates consist of the following organic materials and mineral mixtures to be recycled.Rice straw, calcareous soil and sandy soil that were mixed with oneof the following nitrogen source to form three LAEWs’ bedding andfeeding mixturesof: (1)sewage sludge,(2) cow dung, and (3) sewage sludge plus cow dung.Recycling these mixtures of rice straw, animal waste or municipal sludge and enough soil quantityby EWs for organic matter degradation and binding the released plant nutrients and toxic trace elements with the degraded organic ligands and soils matrices.
Treatments: The LAEWs were added to the three different beds and feeding mixtures to live in for nine weeks. Twelve wooden boxes were specifically designedto carry out the experiment. Four boxes were prepared for each treatment,three boxes were used as replicates and one box wasused as control per each nitrogen source. The boxes were designed with holes on twoopposite sidesand a perforated lid to provide more opportunity for air exchange with the ambient conditions.
Each box contains 500 g of calcareous soil, 500 g of sandy soil and 400g of shredded rice straw mixed withonenitrogen source consisting of the following: (i) - 400g sewage sludge; (ii) 400g cow dung; (iii) (200g sewage sludge + 200g cow dung).The moisture content of the LAEWs beds was adjusted to 65-70 % on volume bases.The wet bed was left to reach the ambient temperature of (13-15°C) before adding the LAEWsto the boxes. Forty flesh rosycolored adult LAEWs were placed on a filter paper in 100 ml glass beakers containing DW for gut evacuation, right afterthe defecated LAEWswere added to their beds. When the EWs were added to the boxes, the LAEWsdirectly invaded the feeding mixtures and thrive on the food stock.
Elements Contents in Beds: The initial and final total content of carbon, nitrogen, phosphorus, and potassium macronutrients; iron, manganese, zinc and copper micronutrient; and lead, cadmium, chromium and nickel toxic trace elements in the different treatments were analyzed to determine the stabilization and quality of the LAEWs’ beds.The same elements were analyzed in the LAEWs’ tissues and casts of the different treatments. Pathogen indicator was tested for sun dried sample of sewage sludge. The pH and EC in 1:10 solid: DW extracts were determined for the three feeding mixtures in absence or presence LAEWs’ at the end of the experiment. Earthworms were sorted from the wooden boxes after six and nine weeks for determining the LAEWs’’ growth biomass and multiplication indicators.
The obtained results indicated that the C/N ratios were11.40 for sewage sludge and 5.23 for Cow dung compared to 40.54 for rice straw while the soil samples have C/N ratios lower than 10. On the other hand, the sewage sludge, Cow dung and calcareous soil substrates suffer variable toxic level of lead compared to the permissible limits of Egyptian standards. In the mean time, sewage sludge and its mixture with cow dung suffer toxic level of Zn, Cu, Cr and Ni, while the calcareous soil sample suffer toxic level of Cu and Cd and the rice straw suffers toxic level of Cd.
Mixing the different substrates to produce the three feeding mixtures resulted in new initial nutrients and toxic trace elements contents. Also, the LAEWs’ feeding mixtures were subjected to changes in their compositions through nine weeks which resulted in another new nutrients and toxic trace elements contents.
The nutrients content and toxic trace elements, at which the LAEWs’ and the natural microorganisms were initially exposed to and live in for nine weeks in the different feeding substrates mixtures, was determined. In the feeding mixtures containing sewage sludge(Ss), sewage sludge plus cow dung (Ss+C.d), and cow dung (C.d), the total nitrogen and carbon content were resulted in initial C/N ratios of 19.07, 15.63 and 13.03, respectively, and were resulted in final C/N ratios of 7.26, 8.74, 6.96. This is because the sharp decrease relative to the initial total organic carbon content due to organic matter degradation, while the final total nitrogen content exhibits reasonable increases relative to the initial total nitrogen content due the LAEWs’ excretion of mucus and urine, that resulted in a sharp decline in the final C/N ratios compared to the initial C/N ratio. As expected, lower ratios of final C/N was observed in the different LAEWs’treatments compared to the control treatments.