Optimizing intermittent rotary aeration to enhance efficiency and reduce greenhouse gas and ammonia emissions during fish manure composting.

The treatment of fish manure from industrial recirculating aquaculture systems (IRAS) is challenging due to its low carbon-to-nitrogen (C/N) ratio and poor separability. This study investigated the optimization of composting efficiency and greenhouse gas mitigation for such manure using a rotating-bin system. A self-developed concentration technique was employed to obtain the feedstock, which was composted under varying rotational aeration frequencies. We comprehensively assessed the process by analyzing physicochemical parameters, product maturity, gas emissions (N2O, CH4, NH3, CO2), and microbial community metagenomics. Results identified an intermittent aeration regime of 5-min rotation followed by a 45-min rest (Treatment D) as optimal. Only Treatment D produced mature compost, achieving a seed germination index of 83.76 %. Critically, this regime reduced cumulative emissions of N2O, CH4, and NH3 by 47.6 %, 56.5 %, and 47.9 %, respectively, compared to continuous aeration, with a 44.2 % reduction in total CO2-equivalent emissions. Metagenomic analysis linked this improvement to a 23.5-31.2 % higher relative abundance of key nitrogen-cycle genes (amoA, hao), enhancing organic nitrogen assimilation and humification. This work demonstrates that optimized intermittent aeration in rotating bins significantly advances the sustainable, low-emission composting of fish manure from IRAS.