Biogas And Organic Fertilizer Production From Azolla Pinnata R. Brown

Abstract

Biogas and organic fertilizer production from Azalla pinnata R . Brown supplementing cow dung and poultry droppings were studied in the laboratory batch digester (reactor) and in the outdoor " Mini-Biogas Plant" . In the laboratory studies, treatments considered using 20: 1 carbon-nitrogen ratio revealed that 50% Azalla supplementing 50% cow dung produced highest amount of biogas (22 L) followed by Azalla supplementing poultry droppings (20 L) and cow dung alone (16.5 L) after 45 days . When Azalla and cow dung alone were compared, Azalla produced lower amount of biogas because of longer time required to decompose than cow dung. Azalla appeared to have decomposed slower also when mixed with poultry droppings. When biogas from different treatments were compared in terms of percentage contributions by methane, Azalla s upplemented cow dung always prod uced higher amount (63-68%) followed by cow dung (51-66%), and Azalla supplemented poultry droppings (64-65%), later two are not significantly different from each other. Again Azalla alone or in combination contributed lowest amount even after 14 days. To obtain maximum biogas with high percentage of methane, Azalla plants were crushed manually and mixed thoroughly with cow dung and was used in the " Mini-Biogas Plant" developed. On an average 18.63 ± 1.92 L biogas was produced per day from day nine to 45 days of semi-continuous digester. Using about 20 L biogas produced in the " Mini-Biogas Plant", 250 g rice was cooked. The Mini-Biogas Plant developed may be further refined in future for performing better. 4 99 0 ~ fl Analysis of organic fertilizer produced from biogas residue (slurry) of laboratory di gester revealed that N , P, K and S concentrations were significantly higher in Azalia s upplemented cow dung compared to cow dung alone. Heavy metals were present but the concentrations were much lower than the acceptable limit. Using a mixture of 50% organic fertilizer obtained from Azalla supplemented cow dung residue with 50% recommended fertilizer doses (RFD) a much higher number of filled grains per pot and significantly higher 1000 grain weight (by 4.79%) were obtained in BRRI 28 rice variety compared to I 00% chemical fertilizer alone It appeared that Azalla supplemented cow dung mixture produced higher amount of biogas with higher concentration of methane and that the organic fertilizer produced from the residue mixed with 50% RFD was better than the 100% RFD of chemical fertilizers.