Vitamin B12 bioaccumulation in Chlorella vulgaris grown on food waste-derived anaerobic digestate

Anaerobic digestion plays a pivotal role in the modern circular economy, as it offers a sustainable solution for converting organic waste into biogas (methane). It also results in a nutrient-rich liquid stream, referred to as digestate. This digestate is extensively applied to agricultural land as fertilizer due to its high macronutrient (N, P) content, but the bioactive micronutrients it contains and their significance for downstream applications remain largely unknown. Here, we investigate whether digestate generated from a vitamin B-12-deficient substrate (fruit and vegetable waste) can be enriched in this vitamin through anaerobic digestion, and explore the capability of the microalga Chlorella vulgaris to grow in this medium and bioaccumulate B-12. Our findings uncover, for the first time, that substantial amounts of B-12 are synthesized during anaerobic digestion, and that C. vulgaris can effectively be enriched with this vitamin when grown in the digestate (10.6 mu g B-12.g(-1) dry weight). Additionally, we identified that pH-induced ammonia toxicity was the main inhibitor when growing microalgae in the digestate, which allowed us to significantly enhance productivity at lab- and pilot-scale through pH control. The case of B-12 synthesis in digestate and accumulation in microalgae highlights the potential for enhancing the value of these waste streams through the identification and utilization of bioactive compounds.

Automated summary

Anaerobic digestion is a sustainable solution for converting organic waste into biogas, and it can also generate nutrient-rich digestate that can be used as fertilizer. This study found that substantial amounts of vitamin B-12 can be synthesized during anaerobic digestion, and a microalgae called Chlorella vulgaris can effectively accumulate B-12 when grown in the digestate. The study also identified pH-induced ammonia toxicity as the main inhibitor for microalgae growth in the digestate, and productivity can be significantly enhanced through pH control.