Determination and applicability of ASM model parameters for nitrogen removal in submerged membrane bioreactors
Submerged membrane bioreactors (SMBRs) processes can significantly improve effluent quality in a wastewater treatment plant when strict effluent standards are required. They are operated at high biomass concentration (8 - 20 gMLSS/L). High SRT and biosolids concentration changes the microbial community and its nutrient removal kinetic behaviour. The main objective of this thesis was to determine the biokinetic parameters to predict the biological nitrogen removal from domestic wastewater by SMBR based on the activated sludge model 1 (ASM 1). A combination of batch tests using respirometric techniques and pilot plat tests were used to determine the kinetic and stoichiometric parameters for nitrogen removal by SMBRs. Effects of solids retention time (SRT) on nutrient removal performance by SMBR, as well as the dynamic response to a shock load of nutrients were examined. Three different configurations were tested on a SMBR pilot plant to determine their effect on biological nutrient removal performance. Hydraulic retention time (HRT) and SRT were varied to obtain the concentration of mixed liquor suspended solids (MLSS) up to 16 gMLSS/L. All of the tested configurations achieved nitrification-denitrification with over 90% ammonia and COD removal but total nitrogen removal was only 70%. Aerobic conditions in the SMBR enable nitrification to occur, thus causing the release of nitrate in the permeate. Organic carbon, ammonia and nitrate measurements in each reactor zone were used for model calibration. From the dynamic calibration, a set of values for the kinetic and stoichiometric parameters was determined to describe the nitrification and denitrification processes in SMBR systems. A comparison between the biokinetic parameters used for conventional activated sludge and the proposed for SMBR in this work showed differences in the nitrogen removal performance at high SRT. The yield and the endogenous decay coefficient for heterotrophic biomass were in the range of 0.15-0.46 gCOD/gCOD, and 0.14-0.38 day-1, respectively. The different between the CAS and SMBR parameters are related to changes in activated sludge biocenosis. Response of SMBRs to shock load of nutrients could not be predicted by calibrated ASM 1 because changes in biomass structure and composition induced by the sudden increase in influent nutrients.