Matthias Plöchl

Bioenergy from permanent grassland--a review: 2. Combustion.

The aim of this review is to summarize current knowledge on suitability and sustainability of grassland biomass for combustion. In the first section grassland management for solid biofuel as well as information on harvest, postharvest and firing technology are described. An extensive grassland management system with one late cut and low level of fertilization is favored for grass as a solid biofuel. The grass harvest usually involves drying in the field and clearing with conventional farm machinery. Pelleting or briquetting improves the biofuel quality. Grass combustion is possible as stand-alone biomass-firing or co-firing with other fuels. Firing herbaceous biomass requires various specific adaptations of the different combustion technologies. In the second section economic and environmental aspects are discussed. Costs for biomass supply mainly depend on yields and harvesting technologies, while combustion costs are influenced by the size and technical design of the plant. Market prices for grass and possible subsidies for land use are crucial for profitability. Regarding biogeochemical cycles a specific feature of combustion is the fact that none of the biomass carbon and nitrogen removed at harvest is available for return to the grassland. These exports can be compensated for by fixation from the air given legumes in the vegetation and sufficient biomass production. Greenhouse gas emissions can be considerably reduced by grass combustion. Solid biofuel production has a potential for predominantly positive impacts on biodiversity due to the extensive grassland management.

Bioenergy from permanent grassland--a review: 1. Biogas.

Grassland biomass is suitable in numerous ways for producing energy. It is well established as feedstock for biogas production. The aim of this review is to summarize current knowledge on suitability and sustainability of grassland biomass for anaerobic digestion. In the first section grassland management for biogas feedstock as well as specifics of harvest, postharvest and digestion technology are described. Methane yields from grass are influenced by many factors. While the effects of some parameters such as grass species, cutting period and management intensity can be regarded as well known, other parameters such as preservation and processing still need investigation. In the second section economic aspects and environmental impacts are discussed. Profitability can be achieved depending on grass silage supply costs and the concept of anaerobic digestion and energy use. Grassland biomass for biogas production competes with other feedstock and other forms of grassland use, in particular animal husbandry. In developed countries a growing production of milk and meat is achieved with decreasing ruminant numbers, resulting in an increasing amount of surplus grassland with a remarkable bioenergy potential. In emerging and developing countries a rapidly rising demand for and production of milk and meat induce growing pressure on grasslands, so that their use for animal feed presumably will take priority over use for bioenergy. Grasslands provide a variety of essential environmental benefits such as carbon storage, habitat function, preservation of ground and surface water quality. When producing biogas from grassland these benefits will remain or even grow, providing appropriate grassland management is implemented. In particular, greenhouse gas emissions can be considerably reduced.

Simulating ozone detoxification in the leaf apoplast through the direct reaction with ascorbate

Abstract. This paper presents a mathematical model which enables the semi-quantification of ozone (O3) detoxification, based upon the direct reaction of the pollutant with ascorbate (ASC) located in the aqueous matrix associated with the cell wall (i.e. the apoplast). The model describes the uptake of ozone into the leaf and its direct reaction with ASC, taking into consideration the regeneration of dehydroascorbic acid in the cytosol, the rate of replenishment of cell wall ASC and the distribution of ASC between sub-cellular compartments – based upon the permeability of biomembranes to the neutral species, ascorbic acid and the pH of various sub-cellular compartments. The importance of various physico-chemical characteristics (e.g. stomatal conductance, mesophyll cell wall thickness and tortuosity, chloroplast volume, apoplast pH, ASC:O3 reaction stoichiometry) in mediating the flux of ozone to the plasmalemma is analysed. Model simulations, supported by experimental observations, suggest that the ASC concentration in the leaf apoplast is high enough to scavenge a significant proportion of the O3 taken up into the leaf interior, under environmentally relevant conditions. However, there is considerable variation between taxa in the potential degree of protection afforded by apoplastic ASC, emphasizing the need for an improved understanding of the reaction chemistry of O3 in the cell wall.

Concepts and profitability of biogas production from landscape management grass.

Landscape management grass is generally harvested late, resulting in unfavorable composition for many utilization purposes. This study explores various technical concepts of biogas production and their economic viability. The Lower Oder Valley National Park is taken here as an example. This National Park in North-East Germany comprises large grassland areas with conservation-related restrictions on management. The concepts of biogas production and use considered are: (1) decentralized digestion and use of biogas at five autonomous combined heat and power (CHP) units, (2) decentralized digestion and delivery of the biogas to a centralized CHP unit, (3) decentralized digestion, upgrading of the biogas and feeding into the natural gas grid, and (4) one central biogas plant with centralized CHP unit. Annual costs and revenues of biogas production were calculated for each alternative. Biogas production from landscape management grass meets the conservational demands of late cutting periods and under certain circumstances shows a profit.

Effects of thermobarical pretreatment of cattle waste as feedstock for anaerobic digestion.

Lab-scale experiments were conducted to assess the impact of thermobarical treatment of cattle waste on anaerobic digestion. Treatment was at temperatures of 140-220°C in 20K steps for a 5-min duration. Methane yields could be increased by up to 58% at a treatment temperature of 180°C. At 220°C the abundance of inhibitors and other non-digestible substances led to lower methane yields than those obtained from untreated material. In an extended analysis it could be demonstrated that there is a functional correlation between the methane yields after 30 days and the formation rate and methane yield in the acceleration phase. It could be proved in a regression of these correlation values that the optimum treatment temperature is 164°C and that the minimum treatment temperature should be above 115°C.

Energy balance, greenhouse gas emissions, and profitability of thermobarical pretreatment of cattle waste in anaerobic digestion.

In this study modeled full scale application of thermobarical hydrolysis of less degradable feedstock for biomethanation was assessed in terms of energy balance, greenhouse gas emissions, and economy. Data were provided whether the substitution of maize silage as feedstock for biogas production by pretreated cattle wastes is beneficial in full-scale application or not. A model device for thermobarical treatment has been suggested for and theoretically integrated in a biogas plant. The assessment considered the replacement of maize silage as feedstock with liquid and/or solid cattle waste (feces, litter, and feed residues from animal husbandry of high-performance dairy cattle, dry cows, and heifers). The integration of thermobarical pretreatment is beneficial for raw material with high contents of organic dry matter and ligno-cellulose: Solid cattle waste revealed very short payback times, e.g. 9 months for energy, 3 months for greenhouse gases, and 3 years 3 months for economic amortization, whereas, in contrast, liquid cattle waste did not perform positive replacement effects in this analysis.

Production of xylooligosaccharides from renewable agricultural lignocellulose biomass

Efficient utilization of lignocellulosic biomass requires pretreatment in order to liberate cellulose from lignin and disrupt its recalcitrant crystalline structure before effective enzymatic hydrolysis can take place. Three different pretreatment methods (pressure cooking with dilute alkali and dilute acid as well as alkaline extraction) to recover the xylooligosaccharides fraction from five different grass silage samples, whole crop rye silage and maize silage were compared. The predominant end products released were xylobiose, xylotetraose, xylopentaose and xylohexaose whereas the xylooligosaccharides release pattern differed with the substrate. Maximum values of xylooligosaccharides was found for grass silage 17.26 g/L, whole crop rye silage 3.06 g/L and for maize silage 5.77 g/L. Results reveal the production of high value by-products from agricultural biomass. Advantages of the green-biorefinery concept include a resulting liquid fraction after pretreatment with very low contents of inhibitors such as furfural, hydroxymethylfurfural (HMF) and phenolic compounds.

Hygiene and Sanitation in Biogas Plants.

The increasing number of agricultural biogas plants and higher amounts of digestate spread on agricultural land arouse a considerable interest in the hygiene situation of digested products. This chapter reviews the current knowledge on sanitation during anaerobic digestion and the hygienic status of digestate concerning a multitude of pathogens potentially compromising the health of humans, animals and plants. Physical, chemical and biological parameters influencing the efficiency of sanitation in anaerobic digestion are considered. The degree of germ reduction depends particularly on the resistance of the pathogen of concern, the processing conditions, the feedstock composition and the diligence of the operation management. Most scientific studies facing sanitation in biogas plants have provided data ascertaining reduction of pathogens by the biogas process. Some pathogens, however, are able to persist virtually unaffected due to the ability to build resistant permanent forms. As compared to the feedstock, the sanitary status of the digestate is thus improved or in the worst case, the sanitary quality remains almost unchanged. According to this, the spreading of digestate on agricultural area in accordance to current rules and best practice recommendations is considered to impose no additional risk for the health of humans, animals and plants.

Control and reduction of methane and nitrous oxide emissions within animal husbandry and manure application

Increasing the annual yield in dairy production would primarily reduce the emission of nitrous oxide and methane per unit milk. Considering decreasing numbers of lactations with increasing yields and the effects caused by replacement raising there will be an optimum annual yield of about 6000 kg milk a−1. The emissions from animal husbandry for fattening purposes can be reduced by decreasing the final body mass and hence the fattening period.

Exploring the Role of Extracellular Ascorbate in Mediating Ozone Tolerance

Tropospheric concentrations of ozone (O3) are known to pose a growing threat to the vitality of natural and managed ecosystems in many parts of the industrialized world (1,2). However, the mechanisms underlying the phytotoxicity of this ubiquitous air pollutant are just beginning to be unravelled (3,4,5).