Dry anaerobic digestion of organic residues on-farm - a feasibility study

Objectives The feasibility study shall answer the following questions: Are there economical and ecological advantages of on-farm dry digestion biogas plants? How the construction and operation parameters of a dry digestion biogas plant influence environment, profit, and sustainability of on-farm biogas production? The aim of the feasibility study is to provide facts and figures for decision makers in Finland to support the development of the economically and environmentally most promising biogas technology on-farm. The results may encourage on-farm biogas plant manufacturers to develop and market dry anaerobic digestion technology as a complementary technology. This technology may be a competitive alternative for farms using a dry manure chain or even for stockless farms. Results Up to now farm scale dry digestion technology does not offer competitive advantages in biogas production compared to slurry based technology as far as only energy production is concerned. However, the results give an over-view of existing technical solutions of farm-scale dry digestion plants. The results also show that the ideal technical solution is not invented yet. This may be a challenge for farmers and entrepreneurs interested in planning and developing future dry digestion biogas plants on-farm. Development of new dry digestion prototype plants requires appropriate compensation for environmental benefits like closed energy and nutrient circles to improve the economy of biogas production. The prototype in Järna meets the objectives of the project since beside energy a new compost product from the solid fraction was generated. On the other hand the two-phase process consumes much energy and the investment costs are high (>2000 € m-3 reactor volume). Dry digestion on-farm offers the following advantages: Good process stability and reliability, no problems like foam or sedimentation, cheap modules for batch reactors, less reactor capacity, reduced transport costs due to reduced mass transfer in respect of the produced biogas quantity per mass unit, compost of solid digestion residues suitable as fertiliser also outside the farm gate, use of on-farm available technology for filling and discharging the reactor, less process energy for heating because of reduced reactor size, no process energy for stirring, reduced odour emissions, reduced nutrient run off during storage and distribution of residues because there is no liquid mass transfer, suitable for farms using deep litter systems. These advantages are compensated by following constraints: Up to 50% of digestion residues are needed as inoculation material (cattle manure does not need inoculation) requiring more reactor capacity and mixing facilities. Retention time of dry digestion is up to three times longer compared to wet digestion requiring more reactor capacity and more process energy, filling and discharging batch reactors is time and energy consuming. We conclude that only farm specific conditions may be in favour for dry digestion technology. Generally, four factors decide about the economy of biogas production on-farm: Income from waste disposal services, compensation for reduction of greenhouse gas emission, compensation for energy production and - most important for sustainable agriculture - nutrient recycling benefits. Evaluation of the results We did not find any refereed scientific paper that includes a documentation of an on-farm dry digestion biogas plant. It seems that we tried first. We also could not find any results about the biogas potential of oat husks, so we may have found these results first. Farm scale production of anaerobically treated solid manure for composting is new. Dry fermentation biogas plants offer the possibility to design solid manure compost by variation of fermentation process parameters. From different scientific publication databases we found about 10 000 references concerning biogas research during the past 10 years. Less than ten are dealing with biogas reactors for non-liquid substrates on-farm. Recent research mainly concentrates on basic research, biogas process research for communal waste, large-scale biogas plants, and research on laboratory level. This mirrors the fact, that production of research papers is rather financed than product development on site. Our conclusion is that it seems worldwide to be very difficult or even impossible to find financial support for on site research, especially for on-farm prototype biogas reactors. We suppose the following reasons for this fact: biogas plant research requires proficiency in many different scientific disciplines, lack of co-operation between engineering and life sciences, high development costs to transfer basic research results into practical technical solutions, low interest of researchers because on site and on-farm research enjoys low appreciation in terms of scientific credits, portability of farm specific design and process solutions is difficult. Our conclusion is that on site and on-farm research has to be supported by funding agencies if integration of biogas and bio energy into the farm organism is considered as an important target within the agricultural policy framework. Future research on both dry fermentation technique and biogas yield of solid organic residues may close present knowledge gaps. Prototype research may offer competitive alternatives to wet fermentation for farms using a solid manure chain and/or energy crops for biogas production. To encourage farmers and entrepreneurs to foster the development of dry fermentation technology support in terms of education and advisory services is also necessary

Nutrient balance of a two-phase solid manure biogas plant

So called "dry fermentation" prototype plants for anaerobic digestion of organic material containing 15-50 % total solids show added advantages compared to slurry digestion plants (Hoffman 2001): Less reactor volume, less process energy, less transport capacity, less odour emissions. However on-farm dry fermentation plants are not common and rarely commercially available. Recent on-farm research (Kusch & Oechsner 2004) and prototype research (Linke 2004) show promising technical solutions for dry fermentation batch reactors on-farm. The Biodynamic Research Institute in Järna developed a two-phase on-farm biogas plant. The plant digests manure of dairy cattle and organic residues originating from the farm and the surrounding food processing units containing 17.7-19.6 % total solids. A new technology for continuously filling and discharging the hydrolysis reactor was developed and implemented. The output of the hydrolysis reactor is separated into a solid and liquid fraction. The solid fraction is composted. The liquid fraction is further digested in a methane reactor and the effluent used as liquid fertiliser. Initial results show that anaerobic digestion followed by aerobic composting of the solid fraction improves the nutrient balance of the farm compared to mere aerobic composting. Composted solid fraction and effluent together contain about 70 % of total input nitrogen and 94 % of input NH4. The manure that was merely aerobic digested contained about 51 % of total input nitrogen and 3.9 % of input NH4. Additionally anaerobic digestion improves the energy balance of the farm producing up to 269 l biogas kg-1 volatile solids or 1,7 kWh heat kg-1 volatile solids

Ownership and Control in the Netherlands

This paper analyses ownership and control structures of Dutch listed companies. Legislation effective since 1992 mandates all shareholders with holdings of 5 percent or more in Dutch companies to disclose their holdings. Our analysis shows that the average ownership stakes of the largest and the three largest shareholders are 27% and 41%, respectively. The average ownership stakes of banks, insurance companies and other financial institutions are relatively low. We observe that voting rights are more concentrated than ownership rights; the use of a supervisory board representing interests of different stakeholders is ubiquitous; and listed companies use different forms of antitakeover defence measures.Ownership, Control, Corporate governance

Two phase continuous digestion of solid manure on-farm: design, mass and nutrient balance

During the last decade some so called ‘dry fermentation’ prototype plants were developed for anaerobic digestion of organic material containing 15-50 % total solids. These plants show added advantages com-pared to slurry digestion plants: Less reactor volume, less process energy, less transport capacity, less odour emissions. However on-farm dry fermentation plants are not common and rarely commercially available. This paper reports about an innovative two phase prototype biogas plant designed for continuous digestion of solid dairy cattle manure

Segmenting the cruise market: an application of multiple correspondence analysis

The cruise line industry is one of the fastest growing travel sectors, and an industry with a high rate of repeat business. This study contributes to the understanding of potential repeat visitors by segmenting cruise tourists based upon their intent to cruise in the future. The purpose of this research note is to reflect on the segmentation method applied. Respondents were asked to respond to questions about their intentions to cruise in the future, and were able to answer yes, no, or not sure, thus making a traditional factor-cluster approach using principal components analysis (or similar) not feasible. This study uses a two step method that combines Multiple Correspondence Analysis (MCA) with a k-means cluster analysis, to segment the sample based on responses to five questions about future cruising intentions.</jats:p

Biogas from manure – a new technology to close the nutrient and energy circuit on-farm

The Biodynamic Research Institute in Järna developed a two-phase on-farm biogas plant. The plant digests manure of dairy cattle and organic residues originating from the farm and the surrounding food processing units containing 17.7-19.6 % total solids. A new technology for continuously filling and discharging the hydrolysis reactor was developed and implemented. The output of the hydrolysis reactor is separated into a solid and liquid fraction. The solid fraction is composted. The liquid fraction is further digested in a methane reactor and the effluent used as liquid fertiliser. Initial results show that anaerobic digestion followed by aerobic composting of the solid fraction improves the nutrient balance of the farm compared to mere aerobic composting. Composted solid fraction and effluent together contain about 70.8 % of total input nitrogen and 93.3 % of input NH4. The manure that was merely aerobic digested contained about 51.3 % of total input nitrogen and 3.9 % of input NH4. Additionally anaerobic digestion improves the energy balance of the farm producing up to 269 l biogas kg-1 volatile solids or 1.7 kWh heat kg-1 volatile solids