ASHS 2024 Conference

Food and farm waste processed by anaerobic digestion (AD) generates a nutrient-rich digestate suitable for use as a biofertilizer. Small-scale AD systems production of biofertilizer offer an on-site solution accessible to individual households and small horticultural producers. Unlike common and more complex AD solutions, small-scale systems do not require extensive management or infrastructure investments. In 2022, we investigated the nutrient content and usability of digestate from two small-scale biodigester models: A commercially built digester with a 1,200 L digester tank, and a prototype we designed with a 114 L capacity. Locally sourced fresh raw cow milk served as inoculum. Over a span of 16 weeks, 12 randomly selected households in Bozeman, Montana, tested the two digester models, feeding them with the food waste they generated. Six of the households received the commercial model, and six tested the prototype. Digestate samples were collected biweekly to analyze their chemical properties and potential as a biofertilizer. After 16 weeks, we blended all digestate, taking equal parts from all household samples, and tested it in a greenhouse study as a fertilizer for red cabbage (Brassica oleracea L. Capitata Group) seedlings. In addition to a control treatment where no biofertilizer was used, we applied 40 ml of biofertilizer per plant in a “high dose treatment” and 20 ml biofertilizer per plant in a “low dose treatment.” Each treatment involved 50 cabbage plants growing individually in trays of 10 cm diameter. On a weekly interval, the biofertilizer was sprayed on the substrate, with amounts varying by treatment. The substrate consisted of loam soil, washed sand, Canadian sphagnum peat moss, perlite, vermiculite, and dolomitic lime. Seedlings were irrigated manually every second day. To ensure sufficient nitrogen supply, all three treatments received an initial application of 40 mL of fish emulsion per cabbage plant. No pest or disease management practices were implemented. After 30 days, all plants were harvested, and their aboveground dry biomass was measured. A trend towards higher aboveground dry biomass in the "high biofertilizer dose" treatment compared to the "low biofertilizer dose" and control treatments was observed. Additionally, the aboveground biomass underwent nutrient content analysis, revealing a tendency towards the highest potassium content in the "high dose treatment." This study showed that household food waste processed through small-scale AD systems generates valuable biofertilizer that can help manage crops’ nutrient needs.