Periodic Reporting for period 1 - Treat2ReUse (Treatment of Animal Waste to Reduce Gaseous Emissions and Promote Nutrient Reuse)
Reporting period: 2019-02-18 to 2021-02-17
There is an increasing concern about the impacts that agriculture has on the environment and on public health. Agriculture is responsible for a significant proportion of the global gaseous emissions, being livestock production the largest contributor to ammonia (NH3) emissions of increased concern in the EU. During last decades, livestock production has been intensified in response to a greater demand for food from a more populated world. These intensified operations produce large amount of animal slurries with the consequent impact on the environment, and therefore proper manure management technologies to reduce gaseous emissions are needed. However, less than 8% of the livestock manure produced in Europe is processed, with large variations within regions. Furthermore, properly treated manure could serve as a valuable source of organic matter and nutrients for fertilizing crops and for energy production, replacing current fossil-based products.
Acidification of slurries is one of the treatments that is currently being implemented at farm scale in different countries in Europe to reduce ammonia and methane volatilization. However, there are drawbacks associated to the use of sulfuric acid in this practice. In one hand, even if sulfuric acid is one of the cheapest inorganic acids in the market, the treatment is still a cost for the farmer and the use of such a strong acid is hazardous. Additionally, acidified slurry using sulfuric acid can not be used as fertilizer in organic farming. Organic farms under current EU organic certification schemes are not allowed to use synthetic acids, and these farms also need to reduce their ammonia emissions and increase slurry fertilizer value. Furthermore, the use of acidified slurries with sulfuric acid for biogas production prohibits their extensive use due to the high content in sulphur.
Therefore, there is a need for an alternative to the current acidification technology to facilitate proper slurry treatment and reuse of acidified slurries.
The current project aimed to develop a new and efficient treatment technology to reduce environmental impacts from animal manure. This technology would have a substantial contribution for a more sustainable and environmental friendly agriculture practice, with an added economic value from the reuse of treated manures to replace mineral fertilizer, contributing to a biobased and circular economy.
Acidification of slurries is one of the treatments that is currently being implemented at farm scale in different countries in Europe to reduce ammonia and methane volatilization. However, there are drawbacks associated to the use of sulfuric acid in this practice. In one hand, even if sulfuric acid is one of the cheapest inorganic acids in the market, the treatment is still a cost for the farmer and the use of such a strong acid is hazardous. Additionally, acidified slurry using sulfuric acid can not be used as fertilizer in organic farming. Organic farms under current EU organic certification schemes are not allowed to use synthetic acids, and these farms also need to reduce their ammonia emissions and increase slurry fertilizer value. Furthermore, the use of acidified slurries with sulfuric acid for biogas production prohibits their extensive use due to the high content in sulphur.
Therefore, there is a need for an alternative to the current acidification technology to facilitate proper slurry treatment and reuse of acidified slurries.
The current project aimed to develop a new and efficient treatment technology to reduce environmental impacts from animal manure. This technology would have a substantial contribution for a more sustainable and environmental friendly agriculture practice, with an added economic value from the reuse of treated manures to replace mineral fertilizer, contributing to a biobased and circular economy.
Bio-acidification of animal slurry is a microbially mediated process that occurs under anaerobic conditions, where the slurry is acidified to organic acids produced by the microorganisms present in the slurry. This bio-acidification can be induced by adding easily degradable organic substrates, which are metabolized in a fermentation process by the microorganisms present in the slurry. Among the organic acids produced, lactic acid is one of the main ones, which is capable of decreasing the slurry pH. To favor lactic acid production over other weaker organic acids, desirable conditions for lactic acid bacteria should be established. The organic substrates to induce the fermentation would ideally be residues from agriculture with a high content of easily fermentable sugars.
To reach this main goal, it was necessary to understand first the main mechanisms happening during different acidification treatments. Manure composition is affected during acidification and there is no clear understanding of the chemical and microbial changes occurring when different substrates or acids are applied to different slurries. Therefore, several manures were characterized prior, during and after acidification and different treatments were performed. Treatments were carried out with sulphuric acid as the traditional inorganic acid used in farms, and with glucose as a carbohydrate source model and brown juice - a residue obtained during the extraction of protein from grass - as a carbohydrate source and acidifying agent to promote the bio-acidification treatment. The mechanisms happening during the storage of treatments were studied, by weekly following pH, glucose consumed and lactic acid produced, as well as by-products formation such as volatile fatty acids. This allowed us to determine the most efficient bio-acidification treatment where pH is maintained stable by lactic acid production and by-products avoidance.
Next experiment was carried out to find out the lowest substrate addition for the bio-acidification treatment able to maintain a long term stable pH, at which NH3 and GHGs emissions are minimized. Several treatments were performed to find out the best bio-acidification approach in terms of pH stability, reduction in substrate needs as well as effects on gaseous emissions reduction. The two best performing acidification and bio-acidification treatments maintaining a low and stable pH were selected to be applied to liquid fraction digestates from a biogas plant before the two pilot scale filtration units, ultrafiltration (UF) and forward osmosis (FO). We concluded that the bio-acidification treatment applied before UF increased the recoveries and acidification had a positive effect of the membrane permeability. Treatments promoted a higher N retention in the UF concentrate and increased P solubilisation. A higher fertilizer value could be obtained from treated digestates before filtration units, with the UF concentrate containing higher N and the FO permeate higher soluble P.
Finally, to study the effects of the treatments on main nutrients, plant fertilizer value and soil characteristics, pot experiments were carried out where we analysed the water extractability of P, N and P uptake and the plant biomass yield. We concluded that acidification increased the water-extractable P fraction of slurries and the plant P uptake.
To reach this main goal, it was necessary to understand first the main mechanisms happening during different acidification treatments. Manure composition is affected during acidification and there is no clear understanding of the chemical and microbial changes occurring when different substrates or acids are applied to different slurries. Therefore, several manures were characterized prior, during and after acidification and different treatments were performed. Treatments were carried out with sulphuric acid as the traditional inorganic acid used in farms, and with glucose as a carbohydrate source model and brown juice - a residue obtained during the extraction of protein from grass - as a carbohydrate source and acidifying agent to promote the bio-acidification treatment. The mechanisms happening during the storage of treatments were studied, by weekly following pH, glucose consumed and lactic acid produced, as well as by-products formation such as volatile fatty acids. This allowed us to determine the most efficient bio-acidification treatment where pH is maintained stable by lactic acid production and by-products avoidance.
Next experiment was carried out to find out the lowest substrate addition for the bio-acidification treatment able to maintain a long term stable pH, at which NH3 and GHGs emissions are minimized. Several treatments were performed to find out the best bio-acidification approach in terms of pH stability, reduction in substrate needs as well as effects on gaseous emissions reduction. The two best performing acidification and bio-acidification treatments maintaining a low and stable pH were selected to be applied to liquid fraction digestates from a biogas plant before the two pilot scale filtration units, ultrafiltration (UF) and forward osmosis (FO). We concluded that the bio-acidification treatment applied before UF increased the recoveries and acidification had a positive effect of the membrane permeability. Treatments promoted a higher N retention in the UF concentrate and increased P solubilisation. A higher fertilizer value could be obtained from treated digestates before filtration units, with the UF concentrate containing higher N and the FO permeate higher soluble P.
Finally, to study the effects of the treatments on main nutrients, plant fertilizer value and soil characteristics, pot experiments were carried out where we analysed the water extractability of P, N and P uptake and the plant biomass yield. We concluded that acidification increased the water-extractable P fraction of slurries and the plant P uptake.
Main project outcomes were: i) understanding of the main mechanisms happening during the acidification treatments and development of a novel bio-acidification treatment ii) minimization of gaseous emissions with safer practice on farms and iii) a gained value from reused products, limiting the dependence on mineral fertilizers.
Therefore, the results of this project contribute towards a background knowledge through understanding of fundamental mechanisms needed to develop a proper slurry treatment, as well as a gained value from reused slurries which limits the dependency on finite resources like mineral fertilizers, contributing to a more sustainable agricultural practice and a bio-based circular economy.
Therefore, the results of this project contribute towards a background knowledge through understanding of fundamental mechanisms needed to develop a proper slurry treatment, as well as a gained value from reused slurries which limits the dependency on finite resources like mineral fertilizers, contributing to a more sustainable agricultural practice and a bio-based circular economy.