Question

why is municipal sewage first seperated into degradable and non degardable waste

Answer 1

so that the degradable waste can be dumped separately and be degraded while non degradable waste are dumped separately so that it can't stop other wastes to degrade

HOPE IT'S CLEAR

Answer 2

Municipal sewage is seperated into degradable and non-degradable wastes as because degradable wastes can be biologiacally degraded or decomposed or dump into pits or yards so that it can help increasing the fertility of the soil and used by the plants.