Influences of operating parameters and membrane characteristics on the net energy production in dense, porous, and composite hollow fiber membrane contactors for dissolved biomethane recovery

A membrane contactor has been considered as one of the most effective tools for biomethane (CH₄) recovery from anaerobic effluents owing to its several strengths. However, without thoroughly understanding various factors ranging from operating parameters (e.g., liquid or gas flow rate) to membrane characteristics (e.g., porosity, pore size, hydrophobicity, inner diameter, membrane area, and fiber length), a membrane contactor could just break even, or even worse, may be operated at a loss before turning a profit. Much of the groundwork is required to make sure to gain net benefits while avoiding those sorts of pitfalls. Herein, we attempted to screen several factors ranging from operation-to membrane-related parameters to ensure whether they meet essential criteria. To be specific, this study covers the following aspects: i) the optimal gas-liquid flow rate (G/L) ratio to minimize both the gas-phase resistance and the dilution of the final sweep gas, ii) the combined effects of G/L ratio and mass transfer area (AM) on the energy recovery performance, iii) the influences of an inner diameter (dᵢ) and AM on the CH₄ recovery (RECH₄) and the net energy production, iv) the influences of the L, porous structure, AM, and hydrophobicity on the RECH₄ and the energy output from the microturbine, v) the minimum criterion for the dᵢ to minimize the energy required for the liquid pump, and vi) correlation between the pore structure and pore clogging. Through the thorough studies, we drew nine useful and meaningful conclusions including the best G/L ratio (0.0425 at the AM of 1 m²), necessary requisites (porous structure, larger AM, and more hydrophobicity) for higher RECH₄, the lower limit of a dᵢ (190 μm) to minimize the energy required for the liquid pump, and so on. We expect that this comprehensive study can help researchers and engineers opt for operation- and membrane-related parameters leading to the desirable performance of a membrane contactor for energy recovery from anaerobic effluents.