Bacillus-Chlorella consortium improves water quality and reduces GHG emissions from aquaculture

Abstract

Aquaculture has developed as an alternative industry to meet the growing demand for food worldwide. However, intensive aquaculture causes negative effects on water quality and increases greenhouse gas (GHG) emissions. This study investigated the effects of Bacillus spp. (BA), Chlorella pyrenoidosa (CH) and their consortium on water quality, GHG emissions and bacterial diversity in aquaculture ponds. Four ponds were treated as follows: a control (with no microbial agent), 1.5 g/m 2 BA, 3 g/m 2 CH and a consortium mixture of BA + CH at the same levels. Water quality, GHG and microbial diversity were measured for five days. The results showed the BA + CH consortium had effective removal efficiencies for total phosphorus and organic matter (as measured by chemical oxygen demand). The BA had higher removal rates for ammonium and total nitrogen up to 45.02% and 61.96%, respectively compared to the control. Moreover, the BA + CH consortium mitigated carbon dioxide (CO 2 ) and methane (CH 4 ) emissions, while the use of BA or CH alone reduced CH 4 emissions without affecting nitrogen oxide (N 2 O) emission. Furthermore, both the BA or CH treatments altered the microbial diversity and composition in water and sediment. The sediment bacteria-driven carbon cycle was the dominant contributor to the reduction of CO 2 and CH 4 emissions. Nitrification and denitrification processes facilitated by aquatic and sedimentary bacteria affected nitrogen cycling. Our findings suggest that the application of a Bacillus - Chlorella consortium offers a simple and effective way to decrease CO 2 and CH 4 emissions from aquaculture ponds. • The Bacillus - Chlorella consortium mitigated CO 2 and CH 4 emissions from aquaculture ponds. • The application of Bacillus spp. and Chlorella pyrenoidosa has demonstrably improved water quality. • The bacterial-driven carbon cycle ( cbbM , pmoA ) in sediment mitigates CO 2 and CH 4 emissions. • Denitrification driven by sediment bacteria ( napA , narG , nirS , nosZ ) accelerates the nitrogen cycle.