The effects of apple pomace, bentonite and calcium superphosphate on swine manure aerobic composting

• Calcium superphosphate reduced ammonia volatilization and increased TN content.
• Bentonite increased the ammonia volatilization and reduced TN concentration.
• The effect of calcium superphosphate was best, while bentonite was the worst.
• Calcium superphosphate is an effective additive for keeping nitrogen.

The effects of additives such as apple pomace, bentonite and calcium superphosphate on swine manure composting were investigated in a self-built aerated static box (90 L) by assessing their influences on the transformation of nitrogen, carbon, phosphorous and compost maturity. The results showed that additives all prolonged the thermophilic stage in composting compared to control. Nitrogen losses amounted to 34–58% of the initial nitrogen, in which ammonia volatilization accounted for 0.3–4.6%. Calcium superphosphate was helpful in facilitating composting process as it significantly reduced the ammonia volatilization during thermophilic stage and increased the contents of total nitrogen and phosphorous in compost, but bentonite increased the ammonia volatilization and reduced the total nitrogen concentration. It suggested that calcium superphosphate is an effective additive for keeping nitrogen during swine manure composting.