Biomass effects on membrane bioreactor operations

Diverse operating parameters were investigated for their effects on biomass characteristics, membrane fouling and aeration efficiency in submerged membrane bioreactors (MBRS). The characteristics of the solid phase of the biomass were affected by the biomass state (unstabilised, stabilising and stabilised) and by the SRT and HRT, whereas the characteristics of the liquid phase appeared to be more dependent on inuent composition and strength. Under operating conditions at constant SRT and HRT, the biomass characteristics reached their stabilised state aer 1.0±0.3 SRT. The impact of membrane aeration, permeate flux and biomass characteristics was determined for biomass at unstabilised state and at stabilised state. A transitional permeate flux was observed between 16.5 and 22 l.m2.hl, below which no significant fouling was observed regardless of the permeate flux, membrane airflow velocity and biomass characteristics. Above transitional flux, membrane fouling increased and was affected by the permeate flux, the membrane aeration velocity and parameters either characterising the liquid or the solid phase of the biomass depending on the carbohydrate concentration of the liquid phase. A comparison of ne and coarse bubble aeration efficiency for biomass at unstabilised state and at several airflow rates established that ne bubble aeration was more efficient in tem of oxygen transfer rate, but led to similar values to coarse bubble aeration for ot-factor. The effects of airflow rate and biomass characteristics on oxygen transfer coefficient and ot-factor were determined for biomass coming from pilot and full scale submerged MBRS treating municipal and industrial wastewaters. Solids concentrations (correlated to viscosity), COD concentration of the liquid phase, carbohydrate concentration of the EPS and volumetric airflow rate were found to affect the aeration efficiency parameters. A transitional solids concentration existed around 15 g.L", above which low or no oxygen transfer occurred.