The only reason you can't run a plane jet engine on random crap you pulled from fat trap diluted with some solvent is that a lot of the parts are designed to be

The only reason you can't run a plane jet engine on random crap you pulled from fat trap diluted with some solvent is that a lot of the parts are designed to be lubricated with kerosene, so essentially fuel is also piped for lubrication in many places. The actual burning part tends to work so long as you can 1) push the fuel through the atomizer efficiently enough 2) it will burn "well enough" at the pressure provided (you don't want unburnt fuel fouling up turbine). I believe some turbine engines have been demonstrated to operate with coal dust mixed with ethanol, and similarly with wood dust - engines that normally operate on diesel.