Biofloc technology plays an important role in maintaining the quality of rearing water and provides extra food for aquaculture species. This technology could solve the adverse effects of nitrogen discharge.
As a microbe-based system, biofloc is considered to contain 29% microalgae, 35% bacteria, 24% fungi, and 12% zooplankton. Microalgae, as one of the main components, are involved in the formation of biofloc.
In this sense, the researchers from Huzhou University evaluated what is the initial concentration of Chlorella pyrenoidosa that could be adequate for the formation of biofloc, and reveal the mechanisms of promotion of C. pyrenoidosa in the biofloc through water quality and the bacterial community.
Microalgae and biofloc
Chlorophyceae, Bacillariophyceae, and Cyanophyceae are the main species in the initial stages of the biofloc system. Furthermore, Chlorella, Acutodesmus, and Chlamydomonas are regularly found in the composition of a stable biofloc.
These microalgae not only participate in the formation of the biofloc, but also play an important role in removing nitrates, providing oxygen to heterotrophic bacteria, and increasing the aggregation of microorganisms in the water through their excretions.
Researchers have reported that the addition of Chlorella vulgaris, Chlorella sorokiniana, Scenedesmus dimorphus, and Neochloris oleoabundans can form the biofloc; and that the addition of Chlorella sp., Grammatophora sp., and Navicula sp. can increase the amount of proteins and lipids in biofloc.
Compared to C. vulgaris, Chlorella pyrenoidosa (C. pyrenoidosa) produces higher biomass. This microalga is widely distributed and cultivated as feed for aquaculture animals.
Influence of Chlorella pyrenoidosa on biofloc development
When the concentration of phytoplankton in the biofloc system increases, the amount of biofloc also increases.
“Our results indicate that C. pyrenoidosa can promote biofloc formation. We found that there is no significant effect on biofloc formation when the initial addition of C. pyrenoidosa was less than 1 × 108 cells·L−1”, they report.
When the initial addition of C. pyrenoidosa exceeds 1 × 108 cells·L−1, this could significantly promote biofloc formation. However, a biofloc system with the addition of C. pyrenoidosa (1 × 1010 cells L−1) resulted in lower production during the final phase.
Influence of C. pyrenoidosa on the bacterial community
“We have found that Pseudomonadales, Caulobacterales, and Sphingomonadales belonging to the Proteobacteria phylum were the four main orders that played a role in the above metabolic process,” the study highlights.
They also reported that Pseudomonas, Brevundimonas, and Xanthobacter were the dominant genera in the Proteobacteria phylum. Pseudomonadales (Pseudomonas) had the characteristics of heterotrophic nitrification and aerobic denitrification simultaneously.
“The present investigation clearly demonstrated that the addition of C. pyrenoidosa could promote the production efficiency of the biofloc. Especially when the initial concentrations were in the range of 5~10 × 109 cells·L-1, it was the best-inoculated level for rapid biofloc formation and stability,” they concluded.
Too low a concentration could not produce a macroscopically visible effect, while too high a concentration would inhibit the yield of biofloc production.
“We also show that the addition of C. pyrenoidosa could lead to reduced species richness and diversity. At the same time, the inoculation of this microalga could make Proteobacteria and Bacteroidota dominant in the biofloc system, while the Rhizobiales order could be a main biological factor promoting biofloc formation,” they described.
Finally, C. pyrenoidosa inoculation could maintain water quality by increasing the proportion of various denitrifying bacteria (such as Flavobacterium, Chryseobacterium, Pseudomonas, Brevundimonas, Xanthobacter, etc.).
The research was financially supported by the Public Welfare Research Key Project of Huzhou City, the Basic Public Welfare Research Project of Zhejiang Province, the Natural Science Foundation of Zhejiang Province, and the Innovation and Entrepreneurship Training Project for College Students.
Reference (open access)
Chen, Yang, Zhichao Fu, Zhenyi Shen, Rongfei Zhang, Jianhua Zhao, Yixiang Zhang, and Qiyou Xu. 2023. “Rapid Production Biofloc by Inoculating Chlorella pyrenoidosa in a Separate Way” Water 15, no. 3:536. https://doi.org/10.3390/w15030536