What are some of the methods that work to process biodegradable waste? How do we choose a method?
The largest portion of waste is biodegradable (~60-70%) or often referred to as “wet” waste. Let’s look at methods to process this chunk of waste!
Processing Wet Waste
We humans rely on mother nature’s agents, bacteria, to do the job. In fact we are only beginning to learn about the many wonders that these organisms have to offer.
These bacteria can process waste either in the presence of air – aerobically, or without air – anaerobically. Aerobic bacteria need air to be healthy. On the other hand, anaerobic bacteria thrive in water and exposure to air impedes their growth and well being. The choice of the bacterial methods largely depends on the moisture in the wet waste.
Our wet waste comes from two sources – plant waste and food waste. The plant waste comes from gardens, trees and bush clippings. While food waste comprises leftover cooked food, canned or bottled food and ingredients. There are some items that fall into both categories such as vegetable peels and fruit.
If we have a large amount of plant clippings, leaves with some amount of vegetable peels, then aerobic bacteria is our choice with the method referred to as composting.
On the other hand, if we have a major portion of over cooked food with a high liquid content such as purees, soups, dal, rice and curry then we need to use anaerobic bacteria with the method referred to as digestion.
An easy way to think about this, is that the food rots and releases water (food is about 90% water). This messes up aerobic bacteria that need air. There are other considerations like the attraction of vermin, etc. Sometimes we need to utilise both methods – composting for plant waste and anaerobic digestion for food waste. The table below will assist you in making a decision.
| Sr | Parameter | Composting | Anaerobic Digestion |
|---|---|---|---|
| 1 | Bacteria | Aerobic | Anaerobic |
| 2 | Air | Yes | No |
| 3 | Moisture / Water | 50% | 900% |
| 4 | Outputs | Compost | Biogas + soil enhancer |
| 5 | Preprocessing | Shredding | Pulping |
| 6 | Processing | Open area | Closed tank |
Conclusions
The largest portion of your waste is “wet” waste and the only way to address this is by working with bacteria. Bacteria are broadly classified as aerobic – that work in air and anaerobic – that work without air. The choice of process and the kind of bacterial we would work with depends on the kind of waste. Both sets of bacteria and processes can also be deployed.
