Gerhard Piringer

Corn stover for biogas production: Effect of steam explosion pretreatment on the gas yields and on the biodegradation kinetics of the primary structural compounds

This study evaluated the effect of steam explosion on the chemical composition and biomethane potential of corn stover using temperatures ranging between 140 and 220°C and pretreatment times ranging between 2 and 15min. Biodegradation kinetics during the anaerobic digestion of untreated and corn stover, pretreated at two different intensities, 140°C for 5min and 180°C for 5min, were studied in tandem. Results showed that pretreatment at 160°C for 2min improved the methane yield by 22%. Harsher pretreatment conditions led to lower hemicellulose contents and methane yields, as well as higher lignin contents, which may be due to the formation of pseudo-lignin. The biodegradation kinetics trial demonstrated that steam explosion enhances the degradation of structural carbohydrates and acid insoluble lignin.

Environmental hot spot analysis in agricultural life-cycle assessments - three case studies.

Present-day agricultural technology is facing the challenge of limiting the environmental impacts of agricultural production – such as greenhouse gas emissions and demand for additional land – while meeting growing demands for agricultural products. Using the well-established method of life-cycle assessment (LCA), potential environmental impacts of agricultural production chains can be quantified and analyzed. This study presents three case studies of how the method can pinpoint environmental hot spots at different levels of agricultural production systems. The first case study centers on the tractor as the key source of transportation and traction in modern agriculture. A common Austrian tractor model was investigated over its life-cycle, using primary data from a manufacturer and measured load profiles for field work. In all but one of the impact categories studied, potential impacts were dominated by the operation phase of the tractor’s life-cycle (mainly due to diesel fuel consumption), with 84.4-99.6% of total impacts. The production phase (raw materials and final assembly) caused between 0.4% and 12.1% of impacts, while disposal of the tractor was below 1.9% in all impact categories. The second case study shifts the focus to an entire production chain for a common biogas feedstock, maize silage. System boundaries incorporate the effect of auxiliary materials such as fertilizer and pesticides manufacturing and application. The operation of machinery in the silage production chain was found to be critical to its environmental impact. For the climate change indicator GWP100 (global warming potential, 100-year reference period), emissions from tractor operation accounted for 15 g CO2-eq per kg silage (64% of total GWP100), followed by field emissions during fertilizer (biogas digestate) application with 6 g CO2-eq per kg silage (24% of total GWP100). At a larger system scale that includes a silage-fed biogas plant with electricity generated by a biogas engine, silage cultivation operations are no longer the largest contributor; the most important contributor (49.8%) is methane slip from the exhaust of the biogas engine. In the third case study, the biogas plant model is energy system in an Alpine municipality of Western Austria is expanded to include a hypothetical system that uses mainly hay from currently unused alpine grassland in a local biogas plant. Here, the relative environmental impacts depend strongly on the fossil fuels that are assumed to be displaced by the local biogas plant; methane slip emissions from the exhaust dominate the impact of the hypothetical local biogas scenario. Taken together, the case studies demonstrate the potential and limitations of LCA as a technique to support decisions of agricultural stakeholders at a variety of scales. Choosing the proper system scale is key to a successful application of this method.