Five modes of waste disposal are :
- Incineration - it includes burning of waste
- Sewage Treatment- it includes treating the waste material and then discarding it in rivers or using treated water for irrigation etc.
- Preparation of compost- Biodegradable waste can be converted in compost which can be then used as manure in the fields.
- Landfill - The waste material is dumped under the ground.
You can refer to the answer of your friend for details.
@ Shivangi : Good work. Keep posting!!