A bioreactor arrangement for growing a biomass has a source of feedstock, a biomass growth surface, and a feedstock transfer arrangement that delivers the feedstock to the biomass growth surface. A biomass harvester removes the biomass from the biomass growth surface. The source of feedstock is in the form of a pool, and includes a pan for the feedstock. The biomass growth surface is configured as an absorbent belt or as a ribbed belt. A semi-permeable membrane has a porosity of approximately 30 microns, and prevents viral and sewage contamination of the biomass. The biomass growth surface is either open or closed to the atmosphere. When closed, a CO2 enhanced and temperature controlled environment is provided. Growth illumination is enhanced by a light enhancing lens or a mirror. A tracking arrangement reorients the mirror to maintain enhanced illumination on the biomass growth surface.