Abstract
The management of residual flows from swine farms, such as slurry and hydrolyzate, is a serious environmental problem in Portugal, so the search for new solutions is important, especially if they can be implemented in production sites, avoiding the transport of waste. Anaerobic co-digestion can configure a sustainable method of management and valorization of these flows in swine farms, resulting in biogas to produce energy and a digestate with agronomic value. The swine hydrolyzate is the product from the elimination of swine carcasses on the farms, through a hydrolysis process. Its use in the anaerobic process wasn’t found in the literature, identifying the need to evaluate its potential. Thus, anaerobic co-digestion of swine slurry and hydrolyzate was carried out and the main purpose of this research was to find the best feeding ratio between the two substrates in batch test, focusing on biogas production. The study was developed in two phases, both under mesophilic conditions. In the first one, using 100 ml syringes, the effect of the relative proportion of substrates on the anaerobic co-digestion potential was investigated and the effect of pressure sterilization of the substrates on biogas production was verified. In the second phase, a larger scale study was carried out in a 4,500 ml digestor, ran under the conditions identified as the most favorable in the preliminary tests. The results obtained allowed us to conclude that the largest volume of accumulated biogas was obtained with the proportion of 90.9% swine slurry: 9.1% swine hydrolyzate (v/v); and that the sterilization of the substrates doesn’t constitute an effective thermal pre-treatment. The larger scale test revealed an inefficient anaerobic process due to the inhibitory effect caused by the accumulation of ammonia and volatile organic acids. However, the production yield was 606.8 LBiogas/kgVS and 431.6 LMethane/kgVS, indicating that process allowed a production of biogas and methane higher than the values cited in literature for anaerobic digestion of swine slurry. This result showed that the use of swine hydrolyzate as a co-substrate results in a better balance of nutrients, promoting a better development of microorganisms.
Highlights
The growing demand for food, namely meat and dairy products, has intensified livestock production in recent decades
The preliminary tests in different swine slurry (SS):swine hydrolyzate (SH) proportions (% v/v), whether using a feed volume of the digesters of 22 ml or 11 ml, resulted in an identical evolution of biogas production with the highest volume of accumulated biogas obtained in the Anaerobic co-Digestion (AcoD) tests 90.9% SS:9.1% SH (v/v)
The accumulated biogas obtained in the AcoD test of 90.9% SS: 9.1% SH (v/v) after 31 days, was higher than that obtained in the anaerobic digestion (AD) test of SS (85 ± 3 ml vs. 41 ± 3 ml, respectively)
Summary
The growing demand for food, namely meat and dairy products, has intensified livestock production in recent decades. Ferreira (2014) mentions a value of 5 dm3/animal.day to estimate the SS production in Portugal Considering this value for the number of swine in 2019, an annual availability of approximately 3.9 million m3 can be estimated. SH originates from fetuses, oocytes, embryos, semen, blood, placentas and swine that die on the farm due to natural causes and are not suitable for human consumption. It results from the implementation of a plan to eliminate these materials on the farms, through a hydrolysis process. With about 200000 breeding-female swine stock, an annual SH production potential of approximately 20.000 m3 can be estimated
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
