Utilisation of unused biomass resources from grassland areas and landscape management in Europe, e.g. roadside green cuttings or endemic plants that suppress biodiversity via anaerobic digestion has been explored in INTERREG IV B funded COMBINE-Converting Organic Matters from European urban and natural areas into storable bio-Energy project.
Anaerobic digestion is a biological decomposition process, where breakdown of organic matter occurs in absence of oxygen. It proceeds in four stages involving four different groups of microorganisms. The final product of the decomposition is biogas. The residues from the digestion can be used, after being stabilized, as fertiliser depending on the composition of the input material. Pehlken, et al. (2015) investigated the option to partially replace maize in biogas plants by grassy material from cultural landscape conservation by a stakeholder alliance in two model regions in Germany. Landscape conservation biomass was confirmed to be interesting for the use in digestion as it created more than 50 % of the feedstock for the biogas fermenter in one of the their model regions in Germany (Pehlken, et al., 2015).
The utilisation of unused biomass resources from grassland areas and landscape management in Europe via anaerobic digestion
Utilisation of unused biomass resources from grassland areas and landscape management in Europe, e.g. roadside green cuttings or endemic plants that suppress biodiversity via anaerobic digestion has been explored in INTERREG IV B funded COMBINE-Converting Organic Matters from European urban and natural areas into storable bio-Energy project. One of the aims of this project is increasing the efficiency of biomass supply chains, through the addition of a year-round heat sink in distributed biogas or anaerobic digestion plants by new harvesting and conditioning techniques. This project is based on IFBB technology which stands for the integrated generation of solid fuel and biogas from biomass, developed at the University of Kassel in the early 2000s.
The first commercial full scale IFBB technology based plant has already started its operation in 2013 in Baden-Baden, Germany. The substrates processed at the Baden-Baden plant include branches, brushwood, leaves, grass, garden waste, municipal green waste etc. In the first step, the delivered material at receiving station of plant is sorted into three categories 1. grass and leaves 2. material contaminated with soil and 3. wood and brushwood. Larger wood and brushwood are chopped and passed through several sieving stages. The wood chips with 2-4 cm are marketed and smaller parts are compressed to briquettes or added to silage processing. The green material that consists of grasses, leaves etc. is minced and stirred within a tossing tub and afterwards pressed and packed in 500 kg silage bales that facilitate storage and transportation to the biogas plant located at a distance of 1.5 km otherwise, a clamp silo facility is on-site. At the hydrothermal conditioning unit, which is the core of IFFB processing, the silage is conditioned/mashed by adding warm water (~40 oC) in 1:4 ratio (silage:water). The material is mixed with pulper to open up the cell walls of the fibrous material of silage. With a pump line the mashed silage suspension is transferred to two buffering reservoirs and homogenized again to prevent segregation during pumping. Remaining sand particles settle to the bottom. From reservoirs, the mashed biomass suspension is pumped into the separation unit where the fibrous, lignin-rich solid part (press cake) is separated from the silage liquid (press fluid) by a screw press. The press fluid contains not only the easily digestible ingredients but also minerals that are detrimental for combustion, > 80 % of Cl and K and > 50 % of S and Mg from the biomass is transferred in the fluid. To use the press cake for combustion and energy production, the separated press cake is then passed through a belt dryer in order to reduce its water content from 50-60 % to 15-17 %. The waste heat from the combined heat and power plant of the biogas plant is supplied to belt dryer. The dried press cake is then compressed to briquettes for easier transportation and could be blended with wood to further improve solid fuel and briquette quality. These briquettes are usable in furnaces suitable for wood firing, determined by the German Federal Pollution Control Act (4. BlmSchV) and the corresponding control regulation TA Luft. To cover the complete internal heat demand of the facility, a portion of the dried press cake is combusted in the heating plant (2x 420 kW effective heat output) of the Eigenbetrieb Umwelttechnik of the city of Baden-Baden. The surplus heat could be exported into a district heating network. The easily biodegradable press fluid is directly fed into the hydrolyse stage of the biogas plant. A surplus of about 30 % electricity is available after covering the complete station supply of the facilities and the sewage plant with the produced electricity. In addition, the Baden Baden plant generates a wide variety of marketable products e.g. wood briquettes, wood chips, grass briquettes, un-pressed grass silage etc. (DANUBEENERGY, 2016).
Within biochemical Bio-Refinery, lignocellulosic biomass is refined into intermediate outputs (cellulose, hemicellulose and lignin) to be processed into a spectrum of products and bioenergy. Since lignocellulosic biomass from LCMW has less competition with food and energy crops, it is expected to become an important future source of biomass available at moderate costs as the feedstock for Bio-Refineries. Usually, lignocellulosic biomass is given mechanical, thermal and/or chemical pre-treatments e.g. with acid or alkaline agents to release cellulose, hemicellulose and lignin from the cell structure. Cellulose and hemicellulose are further converted with enzymatic-hydrolysis into mainly glucose, mannose (C6 sugar) and xylose (C5 sugar). Currently, C6 and sometimes C5 sugars are predominantly used as feedstock for fermentation to produce biofuels such as ethanol, butanol, hydrogen and/or added-value chemicals. Lignin is utilized in production of combined heat and power which fulfils internal energy demands of the units or marketed, if in surplus (de Jong and Jungmeier, 2015). Not only separated woody and herbaceous biomass but mixed LCMW from olive pruning, tree and hedge-rows, roadside and riverside maintenance could be well utilized within the concept of biochemical Bio-Refinery.