I haven't any direct ...

I haven't any direct knowledge of nitrification and denitrification of wastewater with high TDS using an MBBR  process, but I have encountered the situation of high TDS with a MBR and a conventional activated sludge process.  In both these cases full nitrification and denitrification was adversely impacted resulting in nitrification to nitrite only, and virtually no denitrification.  The MBR process was part of a water reclamation and reuse system with the recycle ratio greater than 50 percent, resulting in the accumulation of nitrite to over 300 mg/L,  identified by an extremely high disinfection chlorine demand.  This suggested that ammonia-oxidizing bacteria were unaffected by high TDS levels but nitrite-oxidizing bacteria (NOB) and denitrifying bacteria were affected by high TDS concentrations. 

Eliminating the unintentional source of seawater inflow to the sewer feeding the treatment plant resolved the problem in both cases.  

Based on this experience, I concluded that nitrification and denitrification were inhibited by high TDS concentrations but I later learned through a literature search that both complete nitrification and denitrification can be accomplished under high TDS concentrations in the order of 3 to 5 percent salt (30,000 - 50,000 ppm) if the TDS is gradually increased to allow the bacteria to acclimatize.   I expect this would be the same for a MBBR process.