Biokinetics study on the effects of salinity and soluble microbial product (SMP)

Abstract

The increasing use of membrane bioreactors (MBR) for treatment of wastewater has led to concerns for the contents of wastewater, quality of permeate and reduction of carbon foot prints. This study monitors the activity and performance of microorganisms in a forward osmosis membrane bioreactor (FOMBR) under high salinity and investigates the possible influence of soluble microbial products (SMP) on the system. Batch test were carried out on three conditions, namely fresh water, SMP and salt conditions with microorganisms from the FOMBR and a bioreactor without saline condition. The SMP was collected from the supernatant of the FOMBR. It is observed that salt and SMP did show inhibition effects in term of substrate removal efficiency, growth rates, floc size and specific oxygen uptake rate. With fresh water conditions, the substrate removal efficiency of 86.1% and initial specific growth rate of 6.84d-1 was reported with Source, a bioreactor without saline condition whereas the FOMBR achieved only 51.9% with specific growth rate of 1.53d-1. The substrate removal efficiency and specific growth rate decrease with SMP and salt conditions for Source despite acclimation with salt to a concentration of about 10-15g/L. Floc size was monitored to have small changes with time in all conditions however the changes were not significant. The specific oxygen uptake rate can be correlated to the removal efficiency and specific growth rate for Source but not with FOMBR. It is suspected that microorganisms do have feedback mechanisms and ‘recognizes’ its own SMP.