Utilization of semi‐natural grassland through integrated generation of solid fuel and biogas from biomass. I. Effects of hydrothermal conditioning and mechanical dehydration on mass flows of organic and mineral plant compounds, and nutrient balances

Abstract

The use of semi-natural grasslands for the production of renewable energy through conventional conversion techniques faces major limitations because of chemical and physical properties of the biomass. A new conversion procedure was developed which separates the biomass, as silage, into a liquid phase for biogas production and into a solid fraction to be used as fuel. Separation (mechanical dehydration) is carried out with a screw press after mashing with water (hydrothermal conditioning). The effect of hydrothermal conditioning at different temperatures (5, 60 and 80°C) and mechanical dehydration on mass flows of plant compounds into the press fluid was investigated for five grassland pastures typical of mountain areas of Germany. Results show that 0AE18 of the crude fibre was transferred into the fluid, whereas more digestible organic compounds, such as crude protein and nitrogen-free extract, showed mass flows of 0AE40 and 0AE31 respectively. While 0AE52-0AE89 of potassium (K), magnesium (Mg) and chloride (Cl), which are detrimental for the combustion of the press cake, were transferred into the press fluid, more than 0AE50 of calcium, which has positive combustion properties, remained in the press cake. Significantly (P < 0AE05) higher mass flows were detected at conditioning temperatures of 60°C (K and Mg) and 80°C (crude fibre and nitrogen-free extract) compared with the 5°C treatment. Because of the separation of solids and liquids, high proportions of P (0AE61-0AE74) and K (0AE64-0AE85) but only 0AE32-0AE45 of nitrogen exported from the grassland would be recycled with an application of the digestates from the anaerobic digestion of the press liquid.

The Effect of the Invasive Plant Species Lupinus polyphyllus Lindl. on Energy Recovery Parameters of Semi-Natural Grassland Biomass

“…Compared to other research results from semi-natural grassland biomass [9,10,18,19], the mineral concentration values for the L0 biomass are within the expected range for biomass harvested in June; however, the values for the L100 samples for Ca, Mg and N were considerably higher. This corresponds with previous findings, which likewise found higher mineral content, particularly for Ca, Mg and N [20,21], in legumes and other dicotyledonous plants compared to grasses.…”

“…Wachendorf et al [9] observed methane yields with a mean value of 218 L N ·CH 4 ·kg −1 VS for five semi-natural grassland areas, and Piepenschneider et al [25] measured values of 222 L N ·CH 4 ·kg −1 VS for urban road-side cut material from the city of Kassel, Germany. While these values were slightly lower than the values reported in this study, higher methane yields (285-388 L N ·CH 4 ·kg −1 VS) have also been reported by Richter et al [26] for samples from an alluvial meadow with successive harvesting dates, with the tendency of decreasing methane yields with progressing sward maturity.…”

“…In order to maintain biodiversity in semi-natural grasslands of lower mountain regions, it is necessary to find a use for the biomass, which is flexible in terms of cutting date and forage quality, and also insensitive to toxic compounds. One option could be the Integrated Generation of Solid Fuel and Biogas from Biomass (IFBB [9]). The system produces a press fluid (PF) for anaerobic digestion and a press cake (PC) for combustion.…”

Bioenergy from “surplus” land: environmental and socio-economic implications

“…In some instances, a positive environmental effect may be achieved by using the vegetation already growing on the land for bioenergy rather than using the land for the cultivation of energy crops. Wachendorf et al (2009) showed that semi-natural grassland in Europe can be used for bioenergy production by separating the silage harvested into a liquid fraction for biogas production and a solid fraction for combustion. Similarly, baler technology now exists for harvesting biomass from brushlands.…”

The estimated nutritive value of three common grassland species at three primary growth harvest dates following ensiling and fractionation of press-cake

“…lactic acid, amino acids). Wachendorf et al (2009) reported that fractionation reduces herbage water content and the concentration of minerals, and leads to the enrichment of fibrous constituents in the press-cake fraction. Similarly, reported that > 0.55 of the N and ash was removed from the press-cake fraction relative to the fresh material pre-ensiling.…”