Social life cycle assessment of low-tech digesters for biogas and biofertiliser production in small-scale farms

This study aimed to assess the social performance of a low-tech digester implemented in a small-scale farm in Colombia. To this aim, a Social Life Cycle Assessment framework was developed to evaluate two scenarios: i) previous (baseline) scenario where manure was stored in a manure pit, liquefied petroleum gas was used for cooking and synthetic fertiliser was applied to crops; ii) current scenario where a low-tech digester treats manure and produces biogas and biofertiliser (digestate). The biogas is used for cooking replacing the liquefied petroleum gas while the digestate replaces the synthetic fertiliser. The stakeholder groups considered were: farmers/digester users (i.e. workers), local community, value chain actors, society and consumers. The impact categories were: cultural heritage, health and safety, working conditions, education, human rights, socio-economic repercussions, and consumer vs. user relationships. Results showed that low-tech digester implementation had a better social performance than piling up organic waste (with a final score of 36 and 10, respectively). This was mainly due to: i) education improvement and poverty alleviation for farmers; ii) improvement of community engagement, access to material resources (fuels, fertiliser, food) and education for the local community; iii) enhancement of social responsibility and supplier vs. user relationships for value chain actors; and iv) improvement of transparency and feedback mechanisms for consumers. Implementing low-tech digesters in the frame of a wider programme led by local entities and aiming at training and empowering farmers is a key issue for achieving the aforementioned social benefits and deep and long-term social change. More efforts should be made to reduce potential health and safety risks for all the stakeholders by i) training users to perform daily maintenance checks, and ii) setting up strategies to improve digestate quality for its safe reuse in agriculture.