Fuel gases from organic wastes using membrane bioreactors

One way to produce fuel gases is using bioreactors producing CH4/CO2, H2/CO2 and CH4/H2/CO2 gas mixtures. This method has many advantages; for example, low energy consumption, high ecological efficiency, utilization of organic wastes, accessibility and simplicity of hardware implementation. The results of organic waste bioconversion into methane and hydrogen by using an active membrane system integrated with aerobic and anaerobic bioreactors are presented. The suggested biomembrane system includes three types of fermenters: an aerobic phototrophic biomass producing reactor for CO2 consumption and O2 production from Anabaena variabilis, an anaerobic methane bioreactor for biomass transformation into biogas by using the methanogenic community, and Rhodobacter capsulatus immobilized in a polymeric matrix. The latter system was used for lactate or other low organics decomposition. The combination of the biosystem with membrane contactors and a selective membrane valve achieves a continuous process for energy production and total removal of CO2 from microbial gas mixtures, which can be fed back into the first aerobic productive reactor. In total, the developed system obtains energy from sunlight in the form of combustive gases (CH4 and H2) with a net CO2 consumption.

A solar-powered membrane bioreactor for fuel gas production is currently under development. It was shown that a combination of aerobic and anaerobic bioreactors with active membrane systems allows for the construction of a closed loop for the CO2 and liquid phases. Two types of active membrane systems are suggested for binary gas mixture separation. An active membrane system with a moving liquid carrier (without compressor) combined into one block: the membrane and absorption methods operating in the recirculating mode were integrated with laboratory-scale bioreactors. It was shown that MC based on non-porous polyvinyltrimethylsilane membranes provide effective recovery of methane (at >95% purity) and hydrogen (>90% purity). Non-porous polymeric membranes provide molecular diffusion fluxes and sterile compartments. These membranes remain stable and have good selectivity in relation to the number of gases, which make them attractive for industrial microbiology. The suggested type of membrane bioreactor can be a good example for ecologically clean renewable energy sources in the form of combustive gases for local supply. One way to improve performance of the system is to select a more productive producer from algae or cyanobacteria, but it should be borne in mind that the growth medium for the first reactor should be 100% compatible with the one in the anaerobic digester. Otherwise, the two reactors will be unbalanced after a short time. Another advantage of the developed scheme is the possibility of using organic waste feed for the second anaerobic bioreactor for digestion and obtaining methane (biogas); the resulting CO2 after CH4 separation can be fed back into the photobioreactor as an additional source of carbon for the whole system. However, after UF separation, the resulting biomass can be used as fertilizer. The anaerobic photobioreactor can be used independently from the entire system for decomposing local dairy plant wastes, containing lactate as the main low-weight organic acid. The suggested membrane bioreactor could be a good example for ecologically clean renewable energy sources in the form of combustive gases for local supply.