Effects of scale-up on a hybrid moving bed biofilm reactor – membrane bioreactor for treating urban wastewater

Abstract A hybrid moving bed biofilm reactor–membrane bioreactor (hybrid MBBR–MBR) system has been tested in this study at two scales to analyse the scale-up effect. Two municipal wastewater treatment plants were used, one at laboratory scale (hybrid MBBR–MBR L ) with a reactor working volume of 24 l and one at pilot scale (hybrid MBBR–MBR P ) with a reactor working volume of 358 l. Hybrid MBBR–MBR L and hybrid MBBR–MBR P showed that the hybrid MBBR–MBR systems used in this research were reliable for organic matter removal with COD removal percentages of 90.97±2.55% and 95.56±2.01% for hybrid MBBR–MBR L and hybrid MBBR–MBR P , respectively. In hybrid MBBR–MBR L , the sludge retention time was higher but the biofilm density was lower due to the wall effect, so the two effects cancelled one another out and the COD removal efficiencies were found to be similar. The study identified the most influential variables and their effects on the process. Hybrid MBBR–MBR L and hybrid MBBR–MBR P were influenced by the attached and suspended biomass and temperature, while the influent loading rate only affected hybrid MBBR–MBR P . On the whole, hybrid MBBR–MBR P showed a better performance from the point of view of the kinetics of the heterotrophic biomass, with values of Y H =0.6130 mg VSS mg COD −1 , μ m,H =0.0146 h −1 , K S =9.8852 mg O 2  L −1 , and b H =0.0031 h −1 .