Pilot scale testing of a new configuration of the membrane aerated biofilm reactor (MABR) to treat high-strength industrial sewage.

An alternative design of the membrane aerated biofilm reactor (MABR) was developed to overcome some of the current technical and economical limitations preventing full scale applications of the process. The ZeeLung system uses a new dense hollow-fibre membrane with an unprecedented thin diameter. Two pilot units treating a synthetic high-strength industrial wastewater (4700 mgCOD/L, 145 mgTKN/L) operated successfully for 16 months. They performed simultaneous COD removal, nitrification and denitrification. The very high specific surface area (810 m2/m3) allowed the surface loading rate to be kept low enough (3.6 gCOD/(m2.d)) to maintain a relatively thin biofilm (200 to 350 microm) and use low-pressure air (41 kPa) instead of high-pressure pure oxygen. Intermittent air and liquid mixing at high frequency and low shear were compared: they were equally effective in enhancing substrate transfer, but failed to stabilize biofilm accumulation. Air sparging additionally prevented the acidification of the bulk by stripping CO2.

Effects of fluctuating iron dosage on nitrification in integrated fixed film and conventional activated sludge processes.

An integrated fixed-film activated sludge (IFFAS) process with four media cells is operating in parallel with a conventional activated sludge (CAS) train at Lakeview Wastewater Treatment Plant (Ontario, Canada). During winter 2007, an intensive sampling campaign was conducted to monitor the temporal and spatial variations of the nitrification capacity within the two plug-flow reactors. At the beginning of the six-week study, the CAS train was partially nitrifying, whereas the IFFAS train was nitrifying completely using the first two IFFAS cells only. Within one week, the CAS train lost nitrification because of a drop in solids retention time and pH caused by the onset of iron overdosing. When the IFFAS train received an iron spike, the carriers at the injection point (first cell) became iron-coated and lost 80% of their nitrification capacity. However, this train maintained its total nitrification capacity using the reserve capacity in the three remaining cells.

Updated activated sludge model number 1 parameter values for improved prediction of nitrogen removal in activated sludge processes: validation at 13 full-scale plants.

The Activated Sludge Model number 1 (ASM1) is the main model used in simulation projects focusing on nitrogen removal. Recent laboratory-scale studies have found that the default values given 20 years ago for the decay rate of nitrifiers and for the heterotrophic biomass yield in anoxic conditions were inadequate. To verify the relevance of the revised parameter values at full scale, a series of simulations were carried out with ASM1 using the original and updated set of parameters at 20 degrees C and 10 degrees C. The simulation results were compared with data collected at 13 full-scale nitrifying-denitrifying municipal treatment plants. This work shows that simulations using the original ASM1 default parameters tend to overpredict the nitrification rate and underpredict the denitrification rate. The updated set of parameters allows more realistic predictions over a wide range of operating conditions.

Comparison of performance and operation of side-by-side integrated fixed-film and conventional activated sludge processes at demonstration scale.

A full-scale demonstration of an integrated fixed-film activated sludge (IFFAS) process with floating carriers has been conducted in Ontario, Canada, since August 2003. In this study, data collected on-site from July 2005 to December 2006 are analyzed and compared with the performance of a conventional activated sludge train operated in parallel. Both trains received similar loadings and maintained comparable mixed liquor concentrations; however, the IFFAS had 50% more biomass when the attached growth was considered. In the winter, the conventional train operated at the critical solids retention time (SRT) and had fluctuating partial nitrification. The IFFAS nitrified more consistently and had a doubled average capacity. In the summer, the suspended SRT was less limiting, and the benefit of IFFAS for nitrification was marginal. The lessons learned from the operational requirements and challenges of the IFFAS process (air flow, carrier management, and seasonal foaming) are discussed, and design recommendations are proposed for whole plant retrofit.