The Optimal Cyanobacterial Sludge Incorporation Balances Nutrient Retention and NH3 Emission Reduction During Composting with Chicken Manure and Wheat Straw

Managing eutrophic waterbodies produced large quantity of cyanobacterial sludge (CS), a biomass rich in nitrogen (N) that can be recycled through composting. However, how this management affects the compost fertility and ammonia (NH3) volatilization is little known. This study used a chicken manure and wheat straw mixture with struvite, as the control composting treatment (CK). Subsequently, 10%, 20%, 30%, and 40% of the chicken manure was substituted with CS at the initiation of composting, which were named CS10%, CS20%, CS30%, and CS40%, respectively. The results showed that compost pH decreased by 0.2–0.5 units, while total N content significantly increased by 10.4–20.8% under all CS amended treatments compared to the CK. Furthermore, cumulative NH3 volatilization in the CS amended treatments increased with higher CS substitution rates, showing a significant increase of 21.3–110.0%. In CS amended treatments, the initial contents of microcystin–RR and –LR were 82.0–328.0 μg kg−1 and 48.0–192.0 μg kg−1, respectively, which were degraded by 35.7–79.5% and 30.2–77.8%, peaking at 30% CS substitution. Notably, the CS40% treatment showed degradation rates dropping to 62.3% and 60.7%, accompanied by a significant increase in microcystin content. Meanwhile, the heavy metals (total arsenic, cadmium, chromium, mercury, and lead) contents of all composts complied with organic fertilizer standard (NY/T 525–2021) of China. Interestingly, the CS10% had significantly lower heavy metal concentrations compared to the CK, thus enhancing compost safety. In conclusion, 10% was an optimal CS incorporating ratio to improve the quality of compost derived from chicken manure, wheat straw and struvite, while reducing NH3 emissions, which provided a feasible technical pathway for recycling the CS.