Recent Developments in Process and Reactor Design for Anaerobic Wastewater Treatment

There are a large number of advantages in using microbial anaerobic degradation processes in wastewater pretreatment. However, a disadvantage of this method is the relatively long doubling times of anaerobic microorganisms. Because of the autocatalytic nature of the microbial processes and the low carbon incorporation rate which results in low biomass concentrations in continuously operated systems, decoupling of the residence times for substrate and biomass in necessary. In this way, high volume time yields of biogas can be achieved under anaerobic conditions. From the well known methods for achieving biomass retention, immobilization on inert support media is thought to be an effective alternative. Experiments on anaerobic treatment of sulfite evaporator condensate using immobilized microorganisms were carried out in a 12 1 fixed bed loop reactor. Porous sintered glass with a porosity of about 50% and a mean pore diameter of 60-100 µm served as the media. The reactor was operated for several months under steady state conditions at different residence times. At a residence time of 11 h, 84% of the COD was removed at loading rates up to 100 kg COD.m 3 .day. By optimization of porosity and pore size distribution a further improvement in the volume time yield of biogas was possible. Using reticulated sintered glass with a porosity of 60% and a pore size distribution of 60-300 µm, COD removal rates up to 160 kg/m 3 .d could be obtained. Experiments are currently being carried out with a pilot plant (reactor volume of 1.0 m 3 ). This is necessary to obtain the characteristics necessary for scale up and calculating the economic viability of the process.