Scientists at the Autonomous University of Madrid used hydrothermal carbonization to convert organic waste into a stable and harmless carbonaceous material with suitable properties for use as a biofuel.
The WASTE2VALUE research group, part of the PROSIAM group of the Faculty of Chemical Engineering of the Autonomous University of Madrid (UMA), specializes in the recycling of materials and energy from biomass waste. The focus is on hydrothermal carbonization (HTC) in the spirit of the principles of a circular economy.
Now, in a paper published in the journal Waste Management, the research team has described the process of producing harmless and stable carbon materials suitable for use as solid biofuels using the hydrocarbonate process, the heat of pig manure and lignocellulosic biomass.
Untreated organic waste is harmful to the environment
Pig manure pollution is a serious environmental problem that can have significant impacts on water, soil and air quality. Manure is a byproduct of pig farming and consists of a mixture of urine, feces and water. They contain large amounts of nutrients such as nitrogen and phosphorus, which can be harmful to the environment if handled improperly.
This pig waste is difficult to recycle and very polluting, which is why control of this waste is mandatory in Spain. Since hydrothermal cocarbonization occurs in the presence of water, the resulting liquid is rich in dissolved organic matter and nutrients, especially phosphorus, allowing the production of methane-rich biogas and inorganic biological fertilizers.
These results open a new method for treating pig manure (manure), which was previously used as fertilizer for crops and caused negative environmental impacts such as eutrophication, nitrification and greenhouse gas emissions.
In addition, the resulting organic fertilizer has little added value. The solid product of CWA treatment improves the properties of the primary waste, increasing its carbon content and calorific value while reducing its nitrogen, sulfur and ash content.
Hydrothermal carbonization
The HTC process, which is carried out at temperatures between 180 °C and 250 °C and for short periods of time (5 to 240 minutes), destroys pathogenic microorganisms and breaks down emerging pollutants such as drugs and hormones. In addition, it facilitates the transfer of phosphorus and other thermally unstable compounds into the liquid fraction, where they can be recovered, creating high added value products such as biofertilizers and energy (biogas).
Anaerobic treatment of the liquid fraction makes it possible to obtain wastewater with a low concentration of organic matter, which can be used as irrigation or filter water in the same pig farms. These results confirm that HTC is a promising technology for recovering valuable products from agro-industrial waste while enabling closed-loop water recovery, reducing greenhouse gas emissions, and thus promoting sustainable processes.
Energetically sustainable process
Therefore, the process of treating these organic wastes is energetically sustainable, reduces dependence on fossil fuels and promotes the production of renewable, clean and environmentally friendly biofuels. In addition, this technology also offers a solution to eliminate pig manure ponds and recover 5-6 times more energy than anaerobic digestion without the need for energy pretreatment.
The resulting biofertilizer is characterized by a high proportion of nutrients necessary for the plants and a low proportion of heavy metals and therefore meets the requirements of EU standards.
WASTE2VALUE, in collaboration with Arquimea Agrotech, has developed a continuous HTC reactor to process pig manure, lignocellulosic biomass and other organic wastes such as sewage sludge and biowaste and convert them into high added value products.
With information from: