Christine Idler

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.

Effects of ensiling, silage additives and storage period on methane formation of biogas crops.

Effects of the ensiling process, storage periods of up to 1 year and several chemical and biological silage additives on biomethanation were assessed for maize, sorghum, forage rye and triticale with the aim to identify optimised conditions for silage production of crops used as feedstock in biogas plants. Ensiling, prolonged storage and biological silage additives showed positive effects on methane yield of up to 11%. These could be attributed to increases in organic acids and alcohols during ensiling. A regression model including acetic acid, butyric acid and ethanol accounts for 75-96% of the variation in methane yield. Storage periods of up to 1 year for properly ensiled crops could be possible without losses in methane production, considering the increase in methane yield and the losses of dry matter during this period. However, taking storage losses into account silage additives showed little effect on methane production.

Biogas crops grown in energy crop rotations: Linking chemical composition and methane production characteristics

Methane production characteristics and chemical composition of 405 silages from 43 different crop species were examined using uniform laboratory methods, with the aim to characterise a wide range of crop feedstocks from energy crop rotations and to identify main parameters that influence biomass quality for biogas production. Methane formation was analysed from chopped and over 90 days ensiled crop biomass in batch anaerobic digestion tests without further pre-treatment. Lignin content of crop biomass was found to be the most significant explanatory variable for specific methane yields while the methane content and methane production rates were mainly affected by the content of nitrogen-free extracts and neutral detergent fibre, respectively. The accumulation of butyric acid and alcohols during the ensiling process had significant impact on specific methane yields and methane contents of crop silages. It is proposed that products of silage fermentation should be considered when evaluating crop silages for biogas production.

Improving aerobic stability and biogas production of maize silage using silage additives

The effects of air stress during storage, exposure to air at feed-out, and treatment with silage additives to enhance aerobic stability on methane production from maize silage were investigated at laboratory scale. Up to 17% of the methane potential of maize without additive was lost during seven days exposure to air on feed-out. Air stress during storage reduced aerobic stability and further increased methane losses. A chemical additive containing salts of benzoate and propionate, and inoculants containing heterofermentative lactic acid bacteria were effective to increase aerobic stability and resulted in up to 29% higher methane yields after exposure to air. Exclusion of air to the best possible extent and high aerobic stabilities should be primary objectives when ensiling biogas feedstocks.

Fibre boards and composites from wet preserved hemp

It is absolutely necessary to reduce plant investments and processing costs in order to make natural fibres more attractive for farmers and industry. Conventional hemp fibre production is based on field drying and straw retting – connected with a high weather risk. Therefore, a novel weather-independent technique has been developed. Hemp is harvested by means of a chopper followed by anaerobic storage. A pilot plant with a processing capacity of 300 kg h −1 (dm) fibre material has been built up and tested. The whole plant material can be processed to products like insulation materials, fibre boards or granulate for injection moulding.

Wet Processing of Hemp: An Overview

Normally, the production of fibers from agricultural fiber crops is based on field drying and retting of plant straw. As weather conditions at the usual harvest time are often problematical for harvesting and retting, the development of weather-independent supply chain technologies is very important. The weather risk can be avoided, if, e.g., hemp after being harvested with a conventional forage harvester is directly processed to final products, or stored by wet preservation. Furthermore advantageous is that the whole plant material without any loss is processed to final products like fiber boards, insulation materials, or fibrous materials for natural fiber reinforced composites. Especially for this purpose a pilot plant has been built up and is tested till present. The investigations have shown that conventional technologies of ensiling are capable for the preservation of hemp for more than one year.

Microorganisms for the Production of Lactic Acid and Organic Lactates

Biorefineries consider lactic acid as one of the most promising platform chemicals which are being extensively used in a wide range of food and nonfood applications. Since lactic acid is produced via biotechnological processes, the microbial strains are in the focus of interest, besides all the other aspects of raw materials, fermentation mode, etc.

Storage Problems of Poplar Chips from Short Rotation Plantations with Special Emphasis on Fungal Development

Abstract - There are several problems in storing wood chips freshly harvested from short rotation plantations, which result in quality losses as well as in dry matter and energy losses. The factors influencing the degradation of raw material are examined in this paper with special focus on fungal development. An excessive growth of fungi is connected to dry matter losses and also to an increased health risk during raw material handling. The following factors were measured during 6 months storage of poplar wood chips depending on particle size: box temperature, moisture content, pH-value, appearance of fungi in the storage and the concentration of fungal particles in the air. The results show a close connection between particle size, temperature and attack of fungi. During the storage mesophilic and termophilic species of the genera Alternaria, Aspergillus, Cladosporium, Mucor and Penicillium appeared. The concentration of fungal particles is the highest for fine chips and decreases in bigger particles. There was a special focus on the investigation of the properties of coarse chips (G 50), which represent a good compromise between handling, storage losses and health risk due to fungal development. Kivonat - Rövid vágásfordulójú nyár apríték tárolási problémái, különös tekintettel a kifejlődő gombákra. Frissen kitermelt rövid vágásfordulójú fafajokból előállított apríték tárolása során számos probléma merül fel, melyek eredménye minőség-, szárazanyag- és energiaveszteség. Ebben a tanulmányban a nyersanyag-degradációt befolyásoló tényezők kerültek vizsgálatra, különös tekintettel a kifejlődő gombákra. Ezek rendkívüli elszaporodásának köszönhető a szárazanyag-veszteség mellett a nyersanyag kezelése során fellépő, megnövekedett egészségügyi kockázat is. Nyár faapríték hat hónapos tárolása folyamán az aprítékméret függvényében a következő tényezők mérése zajlott: a tárolón belüli hőmérséklet, nedvességtartalom, pH, a tárolóban megjelenő gombák és azok száma a levegőben. Az eredmények szoros összefüggést mutatnak, különösen az aprítékméret, a hőmérséklet és a gombák száma közt. A tárolás során mezofil és termofil gombák fejlődtek. A következő nemzetségekhez tartozó fajok voltak megfigyelhetők: Alternaria, Aspergillus, Cladosporium, Mucor, Penicillium. A gombák száma a finom aprítéknál volt a legmagasabb, ami az aprítékméret növekedésével csökkent. A kutatás folyamán különös szerepet kapott a középfinom apríték tulajdonságainak vizsgálata (G 50), mely kompromisszumos megoldást jelent a kezelés, tárolási veszteségek és a kifejlődő gombáknak köszönhető egészségügyi kockázatok között.

Bacterial community dynamics during ensiling of perennial ryegrass at two compaction levels monitored by terminal restriction fragment length polymorphism

The purpose of this study was to investigate the effects of compaction and air infiltration on the bacterial community structure during the fermentation process and the aerobic exposure phase of grass silage.