Greenhouse gas emission during composting of different mixing combinations of natural resource by-products

Abstract

Utilizing locally available natural resource by-products from forestry (wood shavings ⎯ WS, wood ash ⎯ WA, biochar ⎯ BC, and paper sludge ⎯ PS) and animal husbandry sectors (poultry manure ⎯ PM) to produce compost, may be an alternative for heavily using synthetic fertilizer and may help to improve soil physicochemical and biological characteristics. During composting, greenhouse gas (GHG) emissions are unavoidable due to microbial activities. The objectives of this research study were to: i) determine the best mixing ratio of PS with WS, and PM to reduce GHG (nitrous oxide ⎯ N₂O, carbon dioxide ⎯ CO₂, methane ⎯ CH₄) emissions during the composting process, ii) detect the impact of BC on GHG emission during composting of PS, WS, and PM, and iii) find out the effect of BC on quality of final compost product. There were four treatments with two mixing ratios; T1 ⎯ PS: WS: PM – 6:2:1 and T3 ⎯ PS: WS: PM – 1:2:1. In addition, T2 and T4 had 4% biochar added to T1 and T3, respectively. The high sludge mixing ratio showed higher GHG emissions than the low sludge mixing ratio for CO₂ and CH₄, but not for N₂O. The addition of 4% biochar did not show any significant difference among treatments for GHG emissions or the quality of the final compost although biochar showed some effects in reducing CH₄ and N₂O emissions. According to the final C/N, the compost did not reach its maturity within the 90 day period. However, all treatments reached a Germination Index of over 80%, indicating a reduction in phytotoxicity. Except for zinc and magnesium, all other micronutrients in all the treatments were within maximum acceptable limits for land application. Further studies are required to monitor GHG and NH₃ emissions in large-scale outdoor experiments using these treatments. Additionally, field trials are required to test the effect of compost on plant growth, which may help to further improve the final compost product.