A systematic review of synergistic effects of additives on organic waste composting

Abstract

Mounting volumes of biomass waste globally necessitate valorization strategies that recover energy and nutrients while mitigating greenhouse gas emissions. Composting is an essential method

however, most optimization efforts have focused on single additives, and as a result, the potential benefits of combined additive strategies remain largely underexplored. In this review we fill this critical gap, by systematically analyzing 84 studies (2015–2025) across diverse waste substrates to evaluate how combinations of physical, chemical, biological, and conductive additives affect composting performance beyond individual additive effects. We found that strategic multi-additive combinations significantly accelerated decomposition, enhanced humification, improved nutrient (NPK) retention by ∼30-46 %, and reduced gaseous gas emission relative to single-additive approaches. Combined additive strategies such as co-applying biochar with wood vinegar reduced methane and ammonia emissions by ∼63 % and ∼36 %, respectively, compared to biochar alone, while adding zeolite (10 %) further shortened the thermophilic phase and curtailed emissions by over 50 %. Integrating nitrification inhibitors with acidifying amendments or introducing microbial inoculants alongside structural additives achieved 81–88 % reductions in nitrous oxide emissions. These synergistic effects are attributed to complementary mechanisms, including improved electron transfer capacity (15–28 % increase), enhanced substrate bioavailability (20–35 % faster degradation), pH buffering, increased aeration, and microbial niche diversification. Future research priorities include field-scale validation across climate zones, long-term soil health assessment, mechanistic modeling integrating multi-omics data, and techno-economic feasibility under uncertainty. Overall, rational additive combinations can make composting faster, lower-emission, and resource-efficient, supporting circular economy goals and climate mitigation commitments under SDG 12 and the Paris Agreement. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.