PROJECT DESCRIPTION
BACKGROUND
Combustion of biogas for energy production is increasing in the European Union because of the lower cost and reduced greenhouse gas emissions compared to fossil fuels. However, the use of biogas as fuel requires the removal of hydrogen sulphide (H2S), a gas that causes a variety of problems: corrosion, damage to equipment and emissions of sulphur dioxide (SO2) from biogas combustion. Desulphurisation of biogas used for energy production is needed to minimise the problems caused by H2S, but current desulphurisation technologies have harmful environmental impacts with high energy consumption and use of chemicals reagents.
OBJECTIVES
The BIOGASNET project demonstrated cost-efficient, low-carbon-footprint technologies that reduced the H2S concentration in biogas (500 ppmv (parts per million by volume) being considered the highest concentration accepted for internal combustion engine). The project designed, implemented and operated a prototype for the period of one year in a landfill in Spain and another year in a municipal solid waste treatment plant in Greece.
The project aimed at boosting the use of biogas as a sustainable energy source and at reducing the carbon footprint of the biogas desulphurisation process. The project also showed how secondary raw materials (including elemental sulphur and ammonium sulphate) can be produced from the desulphurisation process, thus demonstrating a method to reduce waste in line with circular economy best practices. The project thus contributed to the implementation of the European Union strategy Closing the loop - An EU action plan for the Circular Economy (COM(2015) 614 final).
RESULTS
LIFE BIOGASNET demonstrated the technical reliability of a new, cost-effective and environmentally friendly process for the desulphurisation of biogas through an entirely biological process. This led to the production of high-quality biogas and valuable chemical by-products. All this also brought to a significant boost in the use of biogas as sustainable energy source, to a reduction of the carbon footprint of the energy cycle and to a promotion of the circular economy.
The technology was tested through the operation of a prototype in two different sites. Initially installed at a landfill located in Cádiz (Spain), the prototype consisted of a nitrifying reactor coupled to a bio-scrubber operated in anoxic conditions to favour the autotrophic denitrification-partial sulphur oxidation process. The landfill leachate was used as nitrogen source for the nitrite production. The prototype operated for 14 months. Then, the prototype was moved to a municipal solid waste treatment plant in Athens (Greece) where it was operating for 11 months with biogas of different characteristics, as well as a different source of nitrogen (gaseous ammonia) obtained from composting exhaust gases. The prototype was completed with an absorption column for ammonia scrubbing previous to the nitrification reactor. The principal advantage of this innovative anoxic alternative is the coupling of biogas desulphurisation and ammonia-containing wastewater or waste gases denitrification in a single system.
A total of 414 986 Nm3 of sour biogas were treated during the project (264 986 Nm3 in Cádiz and 150 000 Nm3 in Athens).
The main innovation of the project has been the development of a new technology for biogas desulphurisation based on the use of sulphur-oxidising nitrate-reducing bacteria. This is a clear benefit to the environment thanks to the application of a new system promoting the reduction in reagents consumption and in carbon footprint. Another innovative aspect of the developed technology is the recovery of secondary raw material from the desulphurisation process, and the use of waste (gas and liquid) effluents as nitrogen source for microbial activity. Therefore, in addition to desulphurisation, LIFE BIOGASNET acts secondarily as a waste pretreatment that eliminates/reduces pollutants content of other processes waste effluents.
The LIFE BIOGASNET desulphurisation process has been proven to be an advantageous alternative compared to chemical systems. A comparative analysis with chemical scrubbing technology revealed that LIFE BIOGASNET technology presented a significantly better economic and environmental performance. The annual biogas desulphurisation cost of LIFE BIOGASNET technology was around 80% lower than the chemical scrubbing. This enabled a very competitive Levelised Cost of Electricity (LCOE) value: 0.029 €/kWh in cogeneration.
Regarding its environmental performance, the technology developed presents environmental advantages compared to current practices as it reduces, compared with chemical scrubbing, chemicals consumption, environmental footprint (from 50 to 95%, depending on the assessed impact category) and waste generation. It also brought to valuable byproducts at times, such as elemental sulphur and ammonium sulphate, which can be valorised by different industrials sectors.
