Tomasz Żelaziński

THE IMPACT OF EXTRUSION ON THE BIOGAS AND BIOMETHANE YIELD OF PLANT SUBSTRATES

The objective of the present work was to determine the effect of pretreatment by extrusion on the biogas and biomethane yield of lignocellulosic substrates such as maize silage and maize straw silage. The biogas yields of the substrates before and after treatment were compared. Moreover, energy efficiency of pretreatment by extrusion was analyzed in order to assess the applicability of the process in an agricultural biogas plant. Extrusion tests were carried out in a short single-screw extruder KZM-2 in which the length-to-diameter ratio of the screw was 6:1 and rotational speed was 200 rpm. The biogas yield tests of the plant substrates after extrusion were carried out in a laboratory scale, using 15 biofermenters operated in a periodic manner, at a constant temperature of 39°C (mesophilic digestion) and controlled pH conditions. The gas-emission analysis was performed using a certified gas analyzer from Geotech GA5000. Pretreatment by extrusion was observed to improve the quantity of methane generated: in terms of fresh matter for maize silage subjected to extrusion, the methane yield was 16.48% higher than that of the non-extruded silage. On the other hand, maize straw silage after extrusion gave 35.30% more methane than did the same, non-extruded, material. Differences in yields relative to dry organic matter are also described in this paper. Taking into account the amount of energy that is spent on pretreatment and the generated amount of methane, the energy balance for the process gives an idea of the economics of the operation. For maize silage, energy efficiency was lower by 13.21% (-553.2 kWh/Mg), in contrast to maize straw silage, where the increase in energy was 33.49% (678.4 kWh/Mg). The obtained results indicate that more studies on the pretreatment and digestion of maize silage are required in order to improve the efficiency of its use for making biogas. To fully utilize its potential, it is necessary to know thoroughly the effect of the extrusion process and of biogas production on energy efficiency at different conditions.

Impact of bioethanol additive on the properties of stretchable starch films

Impact of bioethanol additive on the properties of stretchable starch fi lms. The objective of the study was to examine the impact of bioethanol additive on mechanical properties of stretchable starch fi lms. The test consisted of adding bioethanol to the plasticizer, constituting a mixture of water and glycerol. Mass proportion of plasticizer to raw starch was 8 : 1 (800 g/100 g). Bioethanol used for the tests was a raw distillate, obtained directly from an agricultural distillery, containing 90% ethanol. The mixture obtained from these ingredients was heated to the temperature of 80°C, and then poured into Petri dishes and dried. The quality of starch coating obtained was assessed by calculating the Young’s modulus and the maximum puncture force with a cylindrical penetrometer. The strength tests were conducted for dried samples and for samples exposed directly to water. For this purpose, the samples were kept in an aqueous environment for 6 h and 6 days, and strength tests were conducted every 1 h and 24 h, respectively. It was found that under exposure to water, the quality of products changed over time, and increase in alcohol content resulted in increase in the value of Young’s modulus of the starch coating.