Study of geometry and operational conditions on mixing time, gas hold up, mass transfer, flow regime and biomass production from natural gas in a horizontal tubular loop bioreactor

A horizontal tubular loop bioreactor (HTLB) was used for production of biomass from natural gas. Hydrodynamic characterizations (mixing time and gas hold up) and mass transfer coefficients were considered in the HTLB (L=2.2 m, H=0.4 m and D=0.03 m) as functions of design parameters, i.e., horizontal length to diameter ratio (L/D) and volume of gas–liquid separator (S) as well as operational parameters, i.e., superficial gas and liquid velocities (UsG, UsL). In addition, flow regime in different gas and liquid flow rates was investigated. It was observed from experimental results that UsL has remarkable effects on gas hold up and kLa   due to its influence on mixing time. The volumetric mass transfer coefficients for oxygen (kLaO2)(kLaO2) and methane (kLaCH4)(kLaCH4) were determined at different geometrical and operational factors. In average, the amount of oxygen consumption for metabolism is approximately 1.4 times higher than that of methane. In bubble flow regime, the HTLB was used for biomass production, too. A gas mixture of 50% methane and 50% oxygen (based on results of dry cell weight, optical density and doubling time) was the best gas mixture inlet for biomass production. The empirical correlations for mixing time, gas hold up and kLa in terms of UsG, UsL, L/D and volume of gas–liquid separator were obtained and expressed separately.