Effects of cellulose rich waste paper on fuel and mechanical properties of biogas digestate -derived briquettes.

Abstract

This study investigated the creation of a waste disposal channel as well as provision of a green energy source through employing waste paper and biogas digestate as feedstock in the production of fuel briquettes. This would not only contribute to solving energy poverty, disposal problems but also improve farmers’ income in Uganda through creation of a tradable item. Response surface methodology was employed to optimize fuel and mechanical properties of the developed briquettes. Linear models were found to best fit the responses of higher heating value, compressive strength and moisture content whereas quadratic models were found to best fit the responses of ash content and bulk density. Waste paper mass was found to have the most significant influence on ash content and higher heating rate. Waste paper also had the most significant influences on bulk density followed by compression force used. Moisture content was mainly influenced by waste paper mass followed by compression force applied. Optimum parameters were found to be; waste paper to digestate mass ratio (269: 1000), compression force (1530.81 N), and drying time (10.5 days). Development of briquettes using the optimum parameters resulted into ash content (22.686% db.), higher heating value (14.731 MJ/kg), bulk density (562.719 kgm-3), compressive strength (9.873 Nmm-2), and moisture content (5.466 % wb). The briquettes developed using the optimum parameters were mechanically strong with a drop test strength of 93.12%. The briquettes had a better thermal efficiency (52%) compared to eucalyptus wood (31%) and eucalyptus charcoal (36%) as well as a lower specific fuel consumption requirement. The cost of production for one-kilogram mass of briquettes was determined as $ 0.22615. If waste paper – digestate char derived briquettes replaced eucalyptus wood and derived charcoal, cost savings of $ 328.5 and $ 216.23 would be realized for every one ton of either fuel forgone. Emissions reductions of up to 1248.5 kg CO2 and 1589 kg CH4 per 2 tons of mixed waste employed would be realized.