Biofilm photobioreactors for the treatment of industrial wastewaters

A flat plate and a tubular packed-bed photobioreactor with an algal-bacterial biofilm attached onto Poraver® beads carriers, a flat plate and a tubular photobioreactor with the biofilm attached onto the reactor walls, and an algal-turf reactor were compared in terms of BOD removal efficiencies, elimination capacities, and stability. A control column photobioreactor with suspended algal-bacterial biomass was also tested to compare the performance of biofilm photobioreactors with conventional algal-based processes. When the algal-bacterial biomass was immobilized onto Poraver® the process never reached a steady state due to a poor homogenization in the bioreactor. When the biofilm was formed onto the reactor wall (or reactor base) the process was stable. A maximum degradation rate of 295 mg BOD l−1 h−1 was achieved in the algal-turf reactor although control experiments performed in the dark showed atmospheric O2 diffusion represented 55% of the oxygenation capacity in this system. BOD removal rates of 108, and 92 mg BOD l−1 h−1 were achieved in the tubular and flat plate biofilm reactors, respectively, compared to 77 mg BOD l−1 h−1 in the control suspended bioreactor. In addition, all biofilm photobioreactors produced an easily settleable biomass. Evidence was found that biomass attachment to the reactor's wall improved stability.