Selecting for polyhydroxybutyrate-accumulating consortium via supplementation of Type II methanotroph along with waste-activated sludge

Abstract

Wastewater treatment plants contributed approximately 6% of anthropogenic methane sources. Methanotrophs, capable of converting methane into polyhydroxybutyrate (PHB), provide a viable solution for utilizing methane as a carbon source and activated sludge as seed culture for PHB production. However, maintaining and enriching PHB-accumulating methanotrophic enrichment is challenging. This research investigated the potential of Methylosinus trichosporium OB3b in bioaugmenting PHB accumulating methanotrophic enrichment within activated sludge to enhance PHB production. Waste-activated sludges with varying ratios of M. trichosporium OB3b (1:0, 1:1, 1:4, and 0:1) were cultivated. This result revealed substantial growth and methane consumption in waste-activated sludge with M. trichosporim OB3b-amended cultures, particularly in a 1:1 ratio. Enhanced PHB accumulation, reaching 37.1% in the same ratio culture, indicated the dominance of type II methanotrophs. Quantification of methanotrophs by digital polymerase chain reaction showed gradual increases in type II methanotrophs, correlating with increased PHB production. However, while initial bioaugmentation of M. trichosporium OB3b was observed, its presence decreased in subsequent cycles, indicating the dominance of other type II methanotrophs. Microbial community highlighted the successful enrichment of type II methanotrophs-dominated cultures due to the addition of M. trichosporium OB3b, outcompeting type I methanotrophs. Methylocystis and Methylophilus were the most abundant in M. trichosporium OB3b-amended cultures. Therefore, the bioaugmentation strategies, leveraging M. trichosporium OB3b, could significantly enhance PHB production and foster enrichments of PHB accumulating methanotrophs in activated sludge. These findings could be dedicated to integrating PHB production in wastewater treatment plants, providing a sustainable solution for resource recovery.