Bogdan Dubis

Theoretical and observed biogas production from plant biomass of different fibre contents

The methane productivity of silage of four crop species -Zeamays L., Sorghumsaccharatum, Miscanthusxgiganteus and Miscanthussacchariflorus - was investigated. The experiments revealed that at a hydraulic retention time of 60days the volumetric methane yields from the Z.mays L. or S.saccharatum silages were higher than those from the Miscanthusxgiganteus or M.sacchariflorus silages because of the higher crude fibre content in Miscanthus spp. However, at comparable lignin concentrations in the feedstock, methane productivity for M.sacchariflorus (0.19+/-0.08L/g volatile solids) was twice that of Miscanthusxgiganteus (0.10+/-0.03L/g volatile solids). The efficiency of cellulose conversion varied from 83.6% (S. saccharatum) to 52.1% (Miscanthusxgiganteus), and hemicellulose from 88.9% (Z. mays L.) to 59.7% (Miscanthusxgiganteus). Conversion of cellulose and hemicellulose depended on the ratio of these polysaccharides to the lignin concentration of the feedstock.

Effect of different nitrogen fertilizer treatments on the conversion of Miscanthus × giganteus to ethanol

Miscanthus×giganteus is a perennial rhizomatous grass which is used as a biofuel crop. Due to its high yields, low production costs, resistance to low temperatures, low soil requirements and, above all, high cellulose content, miscanthus can be a useful resource for ethanol production. The aim of this study was to determine the effect of two fertilization regimes (sewage sludge/mineral NPK) during miscanthus cultivation on the chemical composition of biomass, the content of major lignocellulosic factions and the effectiveness of miscanthus conversion to bioethanol. The results indicate that fertilization treatments influenced biomass yield and the content of major lignocellulosic fractions. Bioethanol production was higher when hydrolysis and fermentation processes were conducted separately than when saccharification and fermentation were conducted simultaneously. Ethanol production increased by 30% and 40% in response to sewage sludge and NPK (equivalent nitrogen content=160kgN/ha) fertilization, respectively, in comparison with unfertilized crops.

PRODUCTION OF BIOGAS USING MAIZE SILAGE SUPPLEMENTED WITH RESIDUAL GLYCERINE FROM BIODIESEL MANUFACTURING

Abstract The aim of this study was to investigate the influence of residual glycerine (5 and 10% w/w) from the biodiesel industry, used as a co-substrate, on biogas production from maize silage. The experiments were conducted in a laboratory-scale, single-stage anaerobic digester at 39ºC and hydraulic retention time (HRT) of 60 d. Addition of 5% residual glycerine caused organic load rate (OLR) to increase to 1.82 compared with 1.31 g organic dry matter (ODM) L-1d-1 for maize silage alone. The specific biogas production rate and biogas yield were 1.34 L L-1d-1 and 0.71 L g ODM-1 respectively, i.e. 86% and 30% higher than for maize alone. Increasing the residual glycerine content to 10% increased OLR (2.01 g ODM L-1d-1), but clearly decreased the specific biogas production rate and biogas yield to 0.50 L L-1d-1 and 0.13 L g ODM-1 respectively. This suggested that 10% glycerine content inhibited methanogenic bacteria and organics conversion into biogas. As a result, there was accumulation of propionic and valeric acids throughout the experiment.