Performance of semi-continuous membrane bioreactor in biogas production from toxic feedstock containing d-Limonene

•Addition of 1g/L limonene did not affect methane production in MBR.•A lag phase was observed in MBR with addition of 5g/L of limonene.•Addition of 10g/L reduced methane production by 50% and no recovery was observed.•The MBR worked well with addition of limonene between 5 and 10g/L in the medium. A novel membrane bioreactor configuration containing both free and encased cells in a single reactor was proposed in this work. The reactor consisted of 120g/L of free cells and 120g/L of encased cells in a polyvinylidene fluoride membrane. Microcrystalline cellulose (Avicel) and d-Limonene were used as the models of substrate and inhibitor for biogas production, respectively. Different concentrations of d-Limonene i.e., 1, 5, and 10g/L were tested, and an experiment without the addition of d-Limonene was prepared as control. The digestion was performed in a semi-continuous thermophilic reactor for 75days. The result showed that daily methane production in the reactor with the addition of 1g/L d-Limonene was similar to that of control. A lag phase was observed in the presence of 5g/L d-Limonene; however, after 10days, the methane production increased and reached a similar production to that of the control after 15days.