Pig slurry and agricultural by-products - perfect pair for biogas production
A team of Spanish researchers has developed a new way of optimising biogas production - by combining pig slurry and agricultural by-products. The scientists, from the Institute for Animal Science and Technology of the Universitat Politècnica de València in Spain, hope their research will mean excess slurry from farms will now have added value and by-products from the fruit and vegetable processing industry can have a sustainable 'afterlife'. The team of agronomy experts - scientists who specialise in the science of producing and using plants for food, fuel, feed, fibre and reclamation - wanted to investigate the large amounts of excess slurry, consisting mainly of animal excreta, cleaning water and feed residues, generated on pig farms. Normal practice is for this surplus to be stored in pools before being used as fertiliser. Yet this practice poses some severe environmental problems. Due to the high levels of nitrogen and phosphorus in nutrient-rich manure, the soil, water and atmosphere can become polluted as a result of excessive accumulation of these nutrients and the emission of greenhouse gases and ammonia. María Cambra-López, one of the lead researchers on the project, explains how some areas of Spain with high concentrations of pig farms don't have enough agricultural land to absorb the levels of slurry produced. And transporting it elsewhere can be pricey for the farmer as well as for the environment. Now the València team hope that their research into combining these surplus by-products to make biogas will prove to be a sustainable and cost-effective solution for this tricky problem. Slurry on its own does not produce much energy, and therefore a biogas plant is not a profitable business for farmers. However, by combining it with certain fruits and vegetables from their local region that are not good enough to sell, methane levels can be increased and this way biogas can be produced more cost effectively. The researchers tested in vitro the combination of pig slurry with peppers, tomatoes, peaches and kaki to study their potential to produce biogas and the optimal combination of both substrates. The findings showed that peppers increased methane production by 44 % compared with slurry only, tomatoes by 41 %, peaches by 28 %, and kaki made no difference to methane production. Based on these findings the team will now carry out trials in large-scale digesters and simulate the real biogas production process using peppers, tomatoes and peaches. The long-term aim is to use this technology in full-scale biogas plants. The team will also now look at the effects of adding agricultural by-products such as rapeseed oil, orange pulp or rice husk in pig feed on methane emissions from manure that could in turn increase biogas production. If this solution is eventually implemented on a large sale it would both reduce emissions of the highly polluting gas methane during slurry storage, and provide farmers with a cost effective and profitable alternative use for pig slurry.For more information, please visit:Universitat Politècnica de València:http://www.upv.es/index-en.html
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Spain