Before water temperatures drop, you should increase MLSS concentrations. More biomass means lower F/M for when organism metabolism slows. This is also the same as increasing MCRT.
Other engineering solutions in areas with prolonged low temperatures is to use deeper basins with less surface area. Aeration via diffusers (no surface aerators). Using attached growth (MBBR or RBC) and MBR systems also allow for higher biological solids concentrations and can be used to retrofit existing systems.
For occasions where biomass has not had time to increase/adapt and low temperatures slow growth, you can use bioaugmentation. This works by increasing the number of active microorganisms, especially those organisms that function well below 15 Deg C. Over the years, we have found wastewater heterotrophic organisms with growth down to 3 – 5 Deg C.