Effect of C/N shock variation on the performances of a moving bed membrane bioreactor

•A MB-MBR pilot plant subject to C/N shock variation was investigated.•Respirometry showed that nitrification was significantly affected by C/N and ammonia.•Nitrite oxidizing bacteria (NOB) highly suffered the C/N shock variations.•Extracellular polymeric substances (EPSs) strongly influenced membrane fouling.

The effect of a sharp variation of C/N ratio in a moving bed membrane bioreactor (MB-MBR) pilot plant treating high strength wastewater has been investigated. The experimental campaign was divided into two periods, each characterized by a different C/N ratio (namely, 2.5 and 15, Period 1 and Period 2, respectively). The MB-MBR system was analyzed in terms of organic carbon removal, nitrification efficiency, biokinetic activity and fouling behavior. The results showed that the nitrification process was severely affected by lower C/N value and by high concentration of ammonia. It was noticed an extensive stress effect on the autotrophic bacteria. Furthermore, it was observed an increase of the resistance related to particle deposition into membrane pores, likely due to a worsening of the cake layer features, with a reduction of the “pre-filter” effect, also related to the increase of the total Extracellular Polymeric Substances production with the C/N ratio.