A comparative study of the effects of microbial agents and anaerobic sludge on microalgal biotransformation into organic fertilizer

Abstract

The effects of Lactobacillus bulgaricus, Rhodopseudomonas palustris, Issatchenkia orientalis and anaerobic sludge on anaerobic digestion of microalgae to organic fertilizer were studied. High-throughput sequencing was used to analyze characteristics of microbial community structure during anaerobic digestion of microalgae using different inocula. Lactobacillales and Saccharomycetales were more likely to become dominant bacteria and eukaryotes. The relative abundance of Lactobacillales was 98.15%, 88.61% and 81.73% of total bacteria at the beginning, middle and end of the experiment, respectively. Meanwhile, the relative abundance of Saccharomycetales was 90.91%, 98.41% and 98.8% of eukaryotes at the beginning, middle and end of the experiment, respectively. At the end of digestion, the microcystin content in the reactor inoculated with Issatchenkia orientalis decreased to 0.71 μg/kg, which met drinking water standards. Rhodopseudomonas palustris did not become a dominant microorganism and had the most negative impact on the atmosphere. Volatile organic compounds were 11.92 mg/kg while the odor concentration reached 97,724 ou/m3. The organic matter content in reactors inoculated with specific groups of microbial agents, which was higher than the standard required for bio-organic fertilizer, occupying over 96% dry weight. In addition, the effective microorganism counts of Issatchenkia orientalis and Lactobacillus bulgaricus in fermentation products reached 1.8E+09 colony-forming units (cfu)/g and 1.6E+09 cfu/g, respectively, which are suitable values for microbial fertilizer.