The vermicomposting for agricultural valorization of sludge from Algerian wastewater treatment plant: impact on growth of snap bean Phaseolus vulgaris L.

In the present study, vermicomposting of sewage sludges and their application in agriculture have been investigated. The impact of Eisenia fetida earthworms on the stabilization of these sludges during 7, 14 and 21 days was assessed. The final product was applied as soil amendment (set-1) to evaluate the effects on vegetative parameters (Chlorophyll, carotenoid, number of nodules, leaf weight, and plant height) of Phaseolus vulgaris.L bean. In the second test (set-2), the amendment was made with raw sludge. In the third test (set-3), the worms were added to the raw sludge at the time of spreading and left during the whole period of beans growth. In order to identify and better understand the behavior and role of worms with regard to sludge, their growth (weight and length), some pathogens and physico-chemical parameters were assessed during the vermicomposting. Results showed significant increase of earthworm weight of 10.62, 23.89 and 35.72 % after 7, 14 and 21 days of sludge vermicomposting, respectively, which explain their acclimatization. The vermicomposting caused a decrease of feacal coliforms number and organic matter (OM), an increase in electrical conductivity (EC) and stabilization in pH. Furthermore, significant differences were obtained for all plants vegetative parameters in soil amended with vermicomposts, compared to the control (unamended soil). Indeed, a significant increase of the chlorophyll level (a, b) was noted in the beans having undergone sludge spreading. However, worm-stabilized sludge for 7 days (set-1) showed the highest chlorophyll a and b levels about 16.1 and 24.64 μg/g, respectively, against 10.13 and 4.38 μg/g in the control. For the carotenoid, a significant decrease was observed compared to the control. Our experiments have also showed that the application of vermicomposted sludge significantly increases the number of nodules, leaf weight and plant height of Phaseolus Vulgaris L. snap beans.