Adsorbents from Methane Fermentation Sludge

The product gas (the biogas) of the CH4 fermentation mainly consists of CH{4} and CO{2}. In the CH{4} fermentation, a large amount of sludge is yielded and the valuable utilisation of the sludge is desired. Therefore, we prepared the adsorbate from the sludge char at 673-1273 K. The prepared char was used for the recovery of CH{4} from biogas and for the humidity control. We investigated the influence of the carbonisation temperature on the pore structure of the sludge char and on the adsorption property. The pore size distribution of the char prepared at 673-773 K was very sharp and the pore size range was between 0.40 and 0.43 nm. The amount adsorbed of CH{4} was much smaller than that of CO{2} and especially, the amount of adsorbed CH{4} on the char prepared at 1173 K was very small. The adsorption rate of CO{2} was 20 times faster than that of CH{4} on the char prepared at 773 K and it was found that this char was suitable for the recovery of CH{4} from biogas. In the adsorption isotherm of the water vapour on the sludge char, the specific surface area of the sludge char was much smaller than that of the commercial activated carbon (commercial AC), but the amount adsorbed on the sludge char was larger than that on the commercial AC and at the high humidity, the amount adsorbed on the sludge char increased rapidly. Therefore, it was found that the sludge char was suitable for the humidity control.