In-vessel co-composting of horse stable bedding waste and blood meal at different C/N ratios: process evaluation.

This study explores the potential of using blood meal, a nitrogen-rich byproduct from slaughterhouses, in co-composting with horse stable bedding waste. The results show that a carbon-to-nitrogen (C/N) ratio of 32 is ideal, enabling faster, odour-free composting, without significant loss of nutrients.

Methodology

• The study was conducted using a 10-tonne per day in-vessel composter, which allowed for the controlled composting of the mix of horse stable bedding and abattoir blood meal.
• Two C/N ratios, specifically 32 (called “LBM” or “low blood meal”) and 16 (“HBM” or “high blood meal”), were used to evaluate the effects of nitrogen availability on the composting process.
• After initial in-vessel composting for one week, the mix was further cured aerobically.

Results

• After 56 days of composting, the LBM and HBM mixtures were within the guideline values for ammoniacal-N, CO2 production, and C/N ratio.
• There was a significant 84% loss of initial ammoniacal-N in the high blood meal (HBM) mix, indicative of excessive nitrogen loss.
• Both the LBM and HBM mixtures showed similar organic decompositions (about 62% and 60% respectively), suggesting that the amount of blood meal did not severely impact overall decomposition.
• However, decomposition in the HBM mix was delayed, as >8 weeks were required for stabilisation compared to 6-7 weeks for the LBM mix.
• Seed germination index, an indicator of compost maturity, was lower for the HBM mix, indicating a lesser quality of the final composting product.

Conclusions

• A C/N ratio of 32 appeared to be the most favourable for co-composting horse stable bedding waste with blood meal.
• This ratio resulted in faster, odour-free composting that did not significantly compromise the nutrient content of the final compost.
• In comparison, a C/N ratio of 16 resulted in prolonged composting time and lower quality of final compost, making it less suitable for the co-composting of these materials.