Life cycle assessment of poultry slaughterhouse by-product treatment methods

Abstract

With population growth, rises the topic of resource scarcity and food security, therefore high-lighting the issue of efficient utilization of resources within the food industry. This issue can be seen in the meat industry, where increasing consumption of meat, especially poultry meat, leads to increasing slaughterhouse by-products, and if not dealt with sustainably, can lead to drastic environmental impacts such as greenhouse gas emissions and environmental contami-nation. Currently, many different treatment methods of slaughterhouse by-products exist, some of these methods contribute to environmental degradation more than others, therefore the com-parison of these methods help to allow for informed decisions on what treatment methods to choose. The treatment methods include, uncontrolled landfilling, low temperature wet rendering (LTWR) and low temperature wet rendering with enzymatic hydrolysis (LTWR+EH). This study aims to understand the environmental impacts of these treatment methods where a life cycle assessment (LCA) was conducted to study the cradle-to-gate life cycle, with the assumption that the slaughterhouse by-product has no carbon footprint due to it being a side stream of an-other process. The rendering process is a method used to convert animal by-products into usable materials by breaking them down under high heat and pressure. This process efficiently recycles by-products from the meat industry into valuable products such as fats and proteins, minimizing waste. The high heat and pressure requirement contributes to the carbon emissions, with dif-ferent fuel types being more harmful such as peat. Low temperature wet rendering produces two end products, protein meal and fat, which can be used to produce animal feed, pet food, fertilisers, and biofuel. A new solution enhancing current wet rendering methods involve utilizing enzymatic hydrolysis to further improve the qualities and increase the yield of the end-product. Landfilling is a common solution to treating the waste when there is lack of incentives and sup-porting infrastructures. The result of this study shows that uncontrolled landfilling of slaughterhouse by-products is the least environmentally viable option as it is estimated to emits approximate 746-2356 kgCO2e per ton of slaughterhouse by-product, based on data for landfilling of biowaste and bio-chemical methane potential of poultry by-products. LTWR was the second least environmentally viable treatment option with the parameters based on Honkajoki’s case, which showed that it emits approximately 242-258 kgCO2e per ton of slaughterhouse by-product. The most envi-ronmentally viable treatment option would be the LTWR+EH method, with the addition of steam generation heat pumps to upgrade waste heat into steam. This treatment method is estimated to emit 175-191 kgCO2e per ton of slaughterhouse by-product. In addition, a sensitivity analysis was conducted to assess the impact of emission factors for electricity and fuel ratio for steam production on total greenhouse gas (GHG) emissions. The emission factor sensitivity analysis saw a 24% increase for LTWR and 30% increase in LTWR+EH total emissions. The steam pro-duction fuel ratio sensitivity analysis, which reduced peat consumption and increased biogas consumption by 10%, saw a 3% decrease for LTWR and 5% decrease for LTWR+EH total emissions. Overall, this study found that low temperature wet rendering with enzymatic hydroly-sis is the best option for slaughterhouse by-products. It also highlighted the impact of energy consumption in rendering processes and the importance of emission factors in conducting LCAs, as using the inaccurate emission factors can impact the calculations.