Influence of biomilking on methanotrophs cultivation during biogas conversion into ectoines

• The effect of long-term ectoines extraction on bioreactor performance was assessed. • Ectoines extraction resulted in limited decreases in CH 4 bioconversion (∼10 %). • Extraction resulted in slight decreases in Ect (∼2.5 %) and Hy (∼0.5 %) content. • Salt level control favoured Methylomicrobium dominance. • Salt level control guaranteed process stability and bioconversion efficiency. 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 CH 4 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 CH 4 , supporting its feasibility for sustainable biogas valorisation at a commercial scale.