It is cost effective to treat high-strength wastewater effluents with a combination of anaerobic-aerobic processes. This was recently shown by Eckenfelder et al. [27], whose economic analysis pointed out that if the wastewater has a BODin excess of 1000 m combined anaerobic- aerobic process can be advantageous. This approach has been used in different applications, including a recent one involving the combined use of powered activated carbon and both anaerobic (first) and aerobic (second) stages 128.29]. These applications were developed primarily to treat high-strength wastewater. In all these case the reactors used for each stage were of the type described above for each class of organisms.