Influence of carbon source supplementation on the development of autotrophic nitrification and microbial community composition in biofloc technology systems

Abstract

Biofloc technology (BFT) is an eco-friendly water management strategy in intensive aquaculture that uses carbon sources to enhance ammonia assimilation by heterotrophic bacteria (HBA). However, the effect of these carbon sources on chemoautotrophic nitrification (CAN) in BFT systems is unclear, hindering efficient practice development. We conducted a 110-day experiment to evaluate the effects of two types of carbon sources: glucose (soluble) and polyhydroxy butyrate-hydroxy valerate (PHBV, slow-release), compared to a control group without carbon source addition. The results indicated that CAN was established in all reactors. However, the peak nitrate concentration occurred later in the glucose-supplemented group on day 45, compared to day 24 in the control group and day 28 in the PHBV group. The findings align with the observation that glucose addition led to reduced abundances of bacterial amoA and nxrB genes. The treatment with PHBV supplementation closely resembled the control in terms of inorganic nitrogen and microbial profiles. However, the addition of substrate and glucose apparently altered the microbial community. Microbial samples were clustered into three distinct groups, with biomarkers identified at the order level: Flavobacteriales & Enterobacterales for cluster I, Myxococcales for cluster II, and Rhodobacterales & Micrococcales for cluster III. These clusters and biomarkers were closely associated with environmental factors. The Sloan neutral community model indicated that deterministic processes governed microbial community assembly. Notably, the relative contribution of the deterministic process increased with the addition of substrate and carbon sources. These findings provide valuable guidance for enhancing and maintaining BFT systems in aquaculture wastewater treatment.