Influence of biomilking on methanotrophs cultivation during biogas conversion into ectoines

Ectoine is one of the most profitable value chains for biogas valorisation. This study assessed the long-term effects of biomilking for ectoine (Ect) and hydroxyectoine (Hy) extraction on upstream methane bioconversion into ectoines using a halotolerant methanotrophic consortium cultivated in a Taylor-Flow bioreactor. After a control stage (S-I), fractions of the culture broth volume of 10 %, 50 %, 30 % and 60 % (S-II to S-VI) were subjected to biomilking before a final control (S-VII). No adverse effects were observed at 10 %, while higher fractions led to salt depletion, a ∼10 % reduction in CH₄ bioconversion efficiency, and a loss of dominant ectoine producers, mainly Methylomicrobium. A decrease in intracellular Ect was also observed. Restoring salt levels (S-VI) recovered Methylomicrobium dominance and Ect content in the culture broth. Enhanced biomilking yielded up to 27.2 g-Ect + Hy per inlet kg of CH₄, supporting its feasibility for sustainable biogas valorisation at a commercial scale.