Performance of a combined biofilm-suspended growth system for wastewater treatment

This paper summarizes the results obtained using the hybrid aerated submerg ed fixed-film (HASFF) reactor which utilizes suspended as well as attached biomass for the treatment of wastewater. The HASFF reactor consists of four compartments with an array of fixed ceramic plates maintained under diffus ed aeration to support attached biomass with suspended biomass recycle to p romote suspended growth in the reactor. Wastewater from a municipal treatme nt plant was fed to the reactor and its activated sludge was used for recyc ling in the hybrid system. Four pilot units were operated in the plant at v arious HRTs (2, 4, 6 and 8 hrs) with flow rates in the range of 0.32 to 1.2 m(3)/d, using primary-settled wastewater under organic loading rates up to 0.7 g BOD/g BVS.d. The data obtained showed that the overall BOD removal efficiencies were con sistently above 94.0% at all HRTs, while the COD removal efficiencies range d between 65.7-76%. The effluents' mean filtered BOD concentrations were be tween 4.5-7.5 mg/l whereas the mean filtered COD concentrations ranged betw een 70.0-89.6 mg/l. Increasing the hydraulic loading rate four-fold from 0. 08 to 0.32 m(3)/m(2).d had minor effect on the reactor's BOD and COD remova l efficiencies indicating a robust biological process that is resilient to Row variation, thereby offering a viable treatment option for small plants. The HASFF process achieved organic removal and nitrification in a single r eactor, with minimal sludge production. The organic removal rate was equall y high at all HRTs whereas nitrification was directly proportional to the H RT, being higher at longer HRTs. The suspended biomass activity exceeded th at of the attached biomass at shorter HRTs while the opposite was true at l onger HRTs.