4th International Conference on Sustainable Solid Waste Management Co-digestion of meat-processing by-products, manure and residual glycerin D. Hidalgo*, J. M. Martín-Marroquín, F. Corona (*dolhid@cartif.es) Limassol, 23/25-06-2016
www.lifevalporc.eu VALPORC project Project funded by EC into LIFE + Program (LIFE13 ENV/ES/001115). Aim: To demonstrate a sustainable alternative to the management of pig carcasses and manure. The project includes: The design and construction of a prototype for the treatment of 1t/d of pig carcasses to optimize the meat flour and fat production. Co-digestión of rendering sub-products with pig manure in a two-phase anaerobic plant with sonication pretretment for biogas production. Biodiesel production based on cavitation technology. ADSII
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www.lifevalporc.eu VALPORC project The VALPORC concept proposes the comprehensive treatment and recovery of pig carcasses. The system is designed to optimize, from the energy point of view, the flour and fat production process and to encourage the recovery of these products: Generated fats will enter a process of biodiesel manufacturing Meat flour (with traces of fat), process water and glycerin generated during the manufacture of biodiesel will be co-digested with pig manure in an anaerobic digestion plant for biogas production. The organic matter remaining fraction in the digestate, together with nutrients that have not been transformed in the process and other byproducts of the overall process will be utilized as fertilizer in areas close to the plant, which will result in important savings in chemical fertilizers. ADSII
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www.lifevalporc.eu Introduction
www.lifevalporc.eu Current situation The production of pork is a significant part of meat production in Europe with more than 251 million head of pigs slaughtered in 2014. It is estimated that, annually, remains of pigs corpses in Europe is 5.4 million tons. Over the past 60 years, these remains of slaughterhouse, rich in proteins and lipids, have been treated and used for feed production . in general. Today, due to legal restrictions and consumers increasingly more aware with the environment, treatment of waste and animal by-products has become a major concern not only in the industry of pork, but also in the meat industry in general.
www.lifevalporc.eu Current legislation According to current legislation slaughterhouse waste must be treated by different methods depending on the category of the animal by-product. Community regulations categorize animal by-products into three categories based on the risk: Category 1 is high-risk material (parts of infected animals, international catering, etc.) and it is not allowed to be composted or treated in biogas plants under no circumstance; Category 2 are by-products of animal origin medium risk (sick animals, manure, digestive tract content, etc.) that cannot be used as raw material in composting and biogas plants unless they first have been sterilized at least at 133 °C and 300 kPa for 20 minutes; Category 3 material low risk (catering waste, meat, ready meals, etc.) approved for human consumption, to be treated at least at 70 °C for 1 hour in a closed system.
www.lifevalporc.eu Anerobic digestion Anaerobic digestion is disclosed as a possible method for the treatment of animal subproducts , which in turn allows the production of energy as methane and the use of effluents of digestion as fertilizer for agricultural application (nutrients recovery). However, slaughterhouse wastes are generally considered as difficult substrates for anaerobic digestion, mainly because of their typically high protein and lipid content in rendering processes. A very attractive option is the co-digestion of these animal subproducts with other organic waste, such as manure or wastewater generated in rendering processes.
www.lifevalporc.eu Present study Methanogenic yields in batch digesters of various subproducts proceeding from a rendering plant of pig carcasses , which operate in the mesophilic temperature range (35°C), are analyzed when they are co-digest in different proportions with liquid manure , water process and glycerin generated as a by-product during the production of biodiesel from pig fat.
Experimental assays www.lifevalporc.eu
www.lifevalporc.eu Substrates Five streams generated in the pork industry have been the base of this study: Fats (FA) Meat flour (MF) from a rendering plant. Process water (PW) Pig manure (PM) from a centralized livestock effluents treatment plant. Glycerin (GL), generated as a byproduct during the generation of biodiesel from fat pig in the laboratory. Fats Flour Process water Pig manure Glycerin
www.lifevalporc.eu Methanogenic potential determination Batch experiments were run in glass serum bottles: liquid volume of 300 mL (1000 mL of total volume) experiments carried out at 37±1 ºC in a thermostatic room initial pH 7.2±0.1 continuously stirred on a shaking-table substrate/inoculum (S/X) ratio was maintained at 0.50±0.05 gSVsubstrate / gSVinoculum.
www.lifevalporc.eu Methanogenic potential determination Biogas production was manually measured by using a pressure transmitter located in the head space of each reactor. The ideal gas Law was used to convert pressure differences into biogas volume, by using standard conditions.
www.lifevalporc.eu Selected waste mixtures Content of each stream in the selected mixtures: Mixture 1 (%) Mixture 2 (%) Mixture 3 (%) Mixture 4 (%) Mixture 5 (%) PM 60 50 40 60 80 MF 10 10 10 20 5 PW 20 30 40 10 13 GL 10 10 10 10 2 The proportions have been designed based on the actual availability of each stream, with the manure being the majority element in all the mixtures.
Results and discussion www.lifevalporc.eu
www.lifevalporc.eu Characterization of subproducts and waste streams
www.lifevalporc.eu Streams characterization PM MF PW GL pH 7.4 6.5 6.2 9.8 TS (mg L ‐ 1 ) 93.8 1 30985 16795 792.3 VS (mg L ‐ 1 ) 78.1 1 19698 16513 760.2 COD (mg L ‐ 1 ) 1230 2 54163 67953 15787 TKN (mg/L ‐ 1 ) 103 2 5114 4637 0.03 TP (mg kg ‐ 1 ) 3016 25.5 79.3 <25 C (% dry base) 34.7 49,4 48.3 35.8 H (% dry base) 4.8 7.3 9.7 11.4 N (% dry base) 2.8 9.5 9.4 0.1 Fat (% dry base) ‐ 19.3 3 5.3 3 ‐ Protein (g L ‐ 1 ) 4 11 540 2 24 ‐ 1 percentage; 2g kg -1 ; 3 Soxhlet Method. 4 Protein content has been estimated from the ratio 6.25 g protein per g Norg. A high organic matter content is observed for the four streams analyzed, with different protein proportions depending on the substrate considered. The four streams are suitable as substrate for anaerobic digestion.
www.lifevalporc.eu Anaerobic biodegradability of individual samples
www.lifevalporc.eu Methane production of individual samples Higher biodegradability of WP over the other streams analyzed. Biogas generation begins almost immediately after starting the test for process water, unlike other streams that show longer starting times. The lower biodegradability is shown for MF. This is probably related to its higher protein content and/or the presence of structural proteins (collagen or keratin type), considered highly resistant to anaerobic degradation.
www.lifevalporc.eu Methane production of individual samples The maximum methane production rates were reached by PW, while the minimum are reached by MF. This result is consistent with expectations, because 90% of the organic matter in the PW is in solution and it is easily accessible to the anaerobic microorganisms. On the other hand, MF needs longer periods of operation to be accessible for microbiota. The higher content of methane in the biogas generated corresponds to PW (68.7%), followed by GL (65.7%), PM (62.0%) and, finally, MF (61.0%).
www.lifevalporc.eu Digestates value as fertilizers The analysis of the fraction digested in the biodegradability tests reveals that the four analyzed streams can be, a priori, suitable for agronomic valorization once digested . All digestates have a phytotoxicity lower than 25 Equitox m -3 , which means, that these digestates are considered non-toxic to the environment. Absence of Salmonella and E. Coli and low metal content was found in the four digestates The presence of remaining organic matter and nutrients (N, K and P), increases their potential value as fertilizer.
www.lifevalporc.eu Co-digestion
www.lifevalporc.eu Methane production of individual samples Mixture 4, the one with the higher MF content, reaches the lower net methane production. In all cases, including Mixture 4, co-digestion favors the methanization process. This effect results in a methane generation higher in the mixtures than which would be theoretically obtained if the contributions of each single substrate were added up, considering the stoichiometric composition of each mixture and the methane production of each substrate.
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