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Recovery of organic matter and nutrients from biogas plants wastewater to optimise its efficiency and productivity

Development of a high yield fermentation where residual flows are no longer a by-product but more raw materials for other industries. Valuable minerals such as potassium and phosphate are recovered. Organic remains are converted into biomass for incinerators to produce green electricity.

Starting from the early 1980s, a new regulation was enacted in Europe which stated that the electricity produced from biogas plants had to be purchased at a fixed price. As a result, in 2005, the EU used 20 million toes (tonne of oil equivalent) of agricultural wastewater and produced 5 millions toe of methane gas, and the generated electric volume of biogas was up to 14,600 GW-h. Recent increasing crude oil prices and gaining popularity in renewable energy have further increased the need for alternative energy sources. Biogas is one of the most popular choices in providing a sustainable solution. Biomass, which commonly consists of energy crops, manure, and other organic matters, produces methane gas by biomethanisation in the anaerobic digester which is then used for generating electricity. A typical biogas plant is operated with animal manures and other organic matters. Only 50% of the organic matter is used for biomethanisation the rest remains into the digester effluent. The anaerobic digester effluent from the biomethanisation process up until now is still commonly land-applied as organic fertilizer. In countries with large farmland areas, the fertilizer can be used without any special restrictions. However, countries with small farmlands can not accept the excessive amount of fertilizer; therefore it needs to be treated as wastewater. Furthermore, land-applying anaerobic digester effluent often creates serious environmental problems. For instance, the limitation of farm lands can cause excessive accumulation of nutrients and the odour often bothers neighbouring residents as people expending into rural areas from crowed cities. Additionally, runoff after heavy rain falls or storms can cause eutrophication and pollution when these nutrients are carried to the surface or ground water. A biomass recovery unit (BRU) can optimise the fermentation process up till 30% more methane gas (energy) production with the same amount of organic matter. Therefore the digester effluent will be separated into different components. Since methane production in anaerobic digesters is based on biomethanisation of organic matter these organic parts together with the bacteria should be separated from the digester effluent so they can be fed back into the process. By doing this the gas production will rise, the process will be stable and you do not use more organic matter. When organic matter is fed back to the process it is possible that some excessive amount of nutrients will kill the bacteria so they need to be separated from the process. Membrane filtration would be a good candidate for such task; however, conventional membrane systems will almost be fouled immediately once the digester effluent is introduced due to its high-fouling characteristics. FMX, the vortex-generating membrane filtration system, can provide an economical and effective process for the anaerobic digester effluent treatment. It is capable to separate and concentrate the small organic parts and bacteria from the nutrients witch are no longer useful for the anaerobic digester. This concentrate is ideal for the biogas production because the small organic parts are converted rapidly into biogas and the bacteria load of the digester will rise so it can convert even more organic matter into biogas. The effluent from the FMX module contains most of the nutrients but has also a high percentage of water content, causing high shipping expenses and results in an excessive amount of fertilizer. To minimise the volume, this FMX effluent will be treated with a 3 stage reverse osmoses system whereby the nutrients are concentrated and the system produces clean water that meads the strict regulations from the EU. After these processes the only residues are non digestible and the concentrate from the RO system. These residue still contain a lot of water therefore, the volume of sludge must be minimised as much as possible. Superheated Steam drying (SHS) is the most advanced and eco-friendly process because it uses the exhaust heat from the CHP (Combined Heat and Power). SHS can economically and effectively dewater the sludge and turn it into dry matter for ease of transportation as soil conditioner or other energy sources. It produces almost clean steam witch can be used for different processes ore we could recover the latent heat of the steam to use in the process. SHS drying is done in a total closed chamber under high temperatures so no odour will occur.
Acronym: 
wasteless BGP
Project ID: 
5 419
Start date: 
01-02-2010
Project Duration: 
44months
Project costs: 
2 500 000.00€
Technological Area: 
Unconventional and Alternative Energies
Market Area: 
Other alternative energy (including nuclear energy and uranium mining)

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.