By Environment Research Group – Embrapa Swine and Poultry
Brazil is the fourth larger swine producer and exporter of the world. This position was reached through significant changes in the production systems over the last 30 years. Thus, small subsistence models were replaced by larger confined animal feeding operations (10). Nonetheless, confined swine production offers major public concerns in Brazil as result of the higher amounts of waste generated in these operations. Swine manure has the potential to impact soil, air, and water resources requiring proper management, treatment and disposal. Several technologies are currently available for manure management in swine farms. However, the selection of a feasible technology should take into account not only technical and economic challenges but also particular farm characteristics. These include the number of housed animals, the available agricultural land for manure application, and the opportunities for energy and organic fertilizer production for trading or in loco consumption.
Although still mainly concentrated in Southern Brazil, over the last decade there is an increasing trend of expiation to Central-West region of the country (6). This will likely affect farm scales and their characteristics. For instance, a typical swine finishing operation in Southern Brazil holds 750 housed animals in less than 20 ha of the available agricultural land for manure disposal. Moreover, such farms have low manure biomass production required for effective electricity-derived biogas generation and therefore the opportunities for energy trading are scarce or not conceivable. On the other hand, swine finishing farms located at Central-West Brazil has typically 4,500 housed animals with plenty of nearby cropland area that can be used for manure application. These farms often have significant energy production capabilities and offer opportunities for energy trading. Needless to say, the technologies for swine manure treatment and disposal should be designed appropriately to satisfy the needs of these two different farming scenarios.
Liquid manure storage and land application is the main manure management practice in Brazil and other parts of the world due to its simplicity, low cost, and the reduction in crop production costs through the replacement of mineral fertilizers (8). The main disadvantage of such approach resides on the fact that manure transportation is not always economically sound for distances beyond a few kilometers (13). Thus, nearby agricultural land availability is limiting for the farming and productivity scale up. With the constant economic pressure for increasing the number of housed animals, the farmer should consider alternatives manure treatment technologies to make it environmentally sustainable.
Swine manure treatment strategies are based on physical, chemical, and/or biologic processes that are able to reduce manure’s pollution potential and convert them into valuable byproducts such as biomethane (i.e., heat and electricity), organic fertilizers and carbon credits (Certified Emissions Reductions – CERs) (2, 9 and 14). The economic benefits generated can then be used either locally (reducing operational costs) or sold (increasing farm revenue).
The most disseminated manure treatment technology in Brazil consists of biodigestors. The biogas produced can be used to produce energy in form of heat or electricity for in loco consumption or commercialization (1, 11 and 3). Swine producers can obtain additional benefits from biodigestors outcomes as soil fertilizers and diminishing atmospheric methane emissions (and carbon credits) which can be managed through certified broker companies and financial institutions. However, there are limitations in the biodigestors systems. Biodigestors offers only partial solution to manure disposal problem because N and P is not removed from the treated effluent and cropland area is still necessary to spread these nutrients. Considering that land is not limiting to Central-West Brazil, biodigestor technology is widely adopted offering alternative economic opportunities for local agribusiness. Physical-chemical and biological strategies to remove nutrients after anaerobic digestion can be had through the use of technologies such as SISTRATES®. Removing these nutrients from the effluent implies in less cropland area required for disposal. This is particularly important for those farms with area limitations.
Composting is also an alternative that has been promoted in Brazil to manage swine manure (12). During the process water loss through evaporation allows for the formation of solid material (5, 15 and 7). Likewise biodigestion, composting does not reduce the cropland area needed for manure application, nonetheless, it reduces overall volume while increasing nutrients concentration. It makes the handling of manure much easier thus reducing transportation costs and granting it’s trading and exportation to distant regions with higher fertilizer demand. Composting can also potentially increase farm income through the marketing of organic-rich compound with high agronomic value.
Overall, every technology has its own potentials and limitations that must be addressed accordingly to farm characteristics and opportunities for energy or fertilizer production and trading. With this in mind, a simplified model can be used as a tool for decision making.
The user of this guidance should start with the evaluation of the volume of manure produced every year (A) in the swine barns, the available cropland area, and their annual fertilization needs in terms of manure volume (B). If the required cropland fertilization needs is equal or higher than the annual manure production in the farm (A≤B) then manure treatment is not mandatory. In this case, cropland area is not limiting and could be effectively used to recycle manure nutrients for crop production without significant environmental impacts. Alternatively, the use of a biodigestor could be an interesting investment when there are opportunities for energy generation for trading or in loco consumption.
Most of the swine farms located in Southern Brazil have a manure production rate much higher than the soil’s capacity of nutrient recycling in the available cropland area (A>B), thus requiring the use of alternatives remediation strategies mentioned above. For small to medium scale farms it could be interesting consider a combination of cropland application (using either neat or digested manure) assuming soil and crops (A=B) fertilization requirements and the use of composting for the treatment of the exceeding manure volume (A-B). Composting produces valuable fertilizer with interesting marketing opportunities particularly in places with intense fertilization demands.
For larger swine production scales where cropland is limiting, a combination of biodigestor and nutrients removal technology (SISTRATES®) should be considered. Solid-liquid separation prior biodigestor produces low moisture manure enhancing drying processes and increasing its value as a high-quality organic fertilizer. The generated biomethane could be used for energy generation for trading or in loco consumption, minimizing farms demands for heat or electricity. SISTRATES® removes N and P from effluent and produces during the process gaseous inert N2 and a powder CaPO4 which has high agronomical value as a fertilizer, therefore retaining commercial potential. SISTRATES® treated effluents meets Brazilian environmental legislations for water quality (4) and can be disposed directly in water reservoirs or streams.
Overall, the processes and technologies briefly discussed here serve to demonstrate the main swine manure management strategies recommended by Embrapa Swine and Poultry in Brazil. It should be emphasized, however, that the success of these technologies depends critically on its design and implementation focusing on farm´s particular characteristics and needs. The proper manure management should ensure profitability and environmental sustainability for the swine producer and ultimately to the Brazilian society.
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Imagens sources by Embrapa
Edited By Gilberto Silber Schmidt
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