Rapid Production Biofloc by Inoculating Chlorella pyrenoidosa in a Separate Way

Abstract

Microalgae play an important role in the formation of biofloc. To demonstrate the feasibility of Chlorella pyrenoidosa in biofloc formation, an experiment was performed with a simple random design consisting of five inoculation levels (in triplicate) of C. pyrenoidosa (0, 1 × 108, 1 × 109, 5 × 109, and 1 × 1010 cells·L−1) in the biofloc system. All treatments kept a C:N ratio of approximately 15:1. This study observed the effects of different initial concentrations of C. pyrenoidosa on biofloc formation, water quality and bacterial community in biofloc systems. The results indicated that C. pyrenoidosa had the ability to enhance biofloc development, especially when the C. pyrenoidosa initial concentration reached 5~10 × 109 cells·L−1. Too high or too low a concentration of C. pyrenoidosa will adversely affect the formation of biofloc. The effect of C. pyrenoidosa addition on water quality (TAN, NO2−-N, and NO3−-N) was not significant in the final stage. The inoculation of C. pyrenoidosa decreased the species richness and diversity of the bacterial community but increased the domination of Proteobacteria and Bacteroidota in the biofloc system, especially the order of Rhizobiales. The addition of C. pyrenoidosa could maintain water quality by increasing the proportion of several denitrifying bacteria, including Flavobacterium, Chryseobacterium, Pseudomonas, Brevundimonas, Xanthobacter, etc. These above dominant denitrifying bacteria in the biofloc system could play a major role in reducing the concentration of NO2−-N and NO3−-N. So, we recommended the reasonable concentration is 5~10 × 109 cells·L−1 if C. pyrenoidosa is used to rapidly produce biofloc.