Soil balls containing the so-called effective microorganisms (EM) have been applied to improve water quality of small ponds, lakes, and streams worldwide. However, neither the physical conditions facilitating their proper application nor the diversity of microbial community in such soil balls have been investigated. In this study, the application of 0.75% of hardener to the soil balls exerted almost neutral pH (pH 7.3) which caused up to a fourfold increased hardness of the soil ball. Moreover, the 0.75% of hardener in the soil ball also improved the water quality due to a significant reduction in dissolved oxygen, total phosphorus, and total nitrogen contents. Metagenomic analysis of the microbial community in the soil ball with 0.75% hardener was compared with control (traditional soil ball) through next-generation sequencing. The traditional soil ball microbial community comprised 96.1% bacteria, 2.7% eukaryota, and 1% archaea, whereas the soil ball with 0.75% hardener comprised 71.4% bacteria, 27.9% eukaryota, and 0.2% viruses. Additionally, metagenomic profiles for both traditional and improved soil balls revealed that the various xenobiotic biodegradation, such as those for caprolactam, atrazine, xylene, toluene, styrene, bisphenol, and chlorocyclohexane might be responsible for organic waste cleanup.
Keywords: Biodegradation; Effective microorganisms; Metagenome; Microbial community; Soil ball; Water quality.