Compost collection can be commenced 2-3 months after starting the bin. The time taken for composting depends on the material added to the bin and maintenance practices that are followed. Removed compost must heap up outside (1-2 weeks) for maturation. This reduces the phytotoxic compounds in the compost. In order to obtain a uniform product, this compost is sent through a 4 mm mesh. Oversize particles can be sent back to the bin for further decomposition.
The quality of the compost
The following features are visible when the compositing is completed in a proper manner. Good quality control program is required if it is intended to market or commercialize the product, targeting the large scale agricultural systems (especially for organic farming).
- Dark brown to black in color.
- Practically insoluble in water.
- Has a C/N Ratio ranging from 10 to 20.
- Has a beneficial effect both on the soil and the growing crops.
- Free from weed seeds and pathogens.
But precaution is necessary when using compost produced from mixed garbage. This compost may be contaminated with,
- Heavy metals of Arsenic, Lead, Cadmium and mercury are extremely harmful to both humans and domestic animals.
- Pathogens of diseases of Enteritis, Tuberculosis etc. Pathogens could be found in city wastes since their thermal death points are specific, care should be taken to allow the heating up of heaps.
Use of made compost
Compost is more important as a soil conditioner rather than a nutrient supplier. It improves the soil chemical, physical and biological parameters so that it provides a better environment for plant growth. This compost can be used as;
- Mulch: spread a layer of compost 1-3 inches thick around the plants and over bare soil to prevent soil erosion, conserve water and control weed growth.
- Soil conditioner: mix about 4-5 inches of compost into soil when start a nursery, vegetable garden or plant new trees.
- Potting mixture: screen the compost through a ¼ inch mesh. Mix 2 parts of compost with 1 part of sand and 1 part of top soil and use as a potting mixture for plants.
Recommendation for design improvement
A) Material of the bin
Metal composting bins are not suitable due to high corroding problems. The economic
benefit of the concrete composting bin is higher than the metal bin due to longer life span. Plastic bins are convenient to use but cost is high compared to other designs and it does not give a good protection especially against the rodents.
B) Design modification in concrete bin
Design modifications were done with considering the scientific requirement of the composting process and practical problems experienced by the users.
When bin designs were identified at the beginning, it did not include aeration holes in the bottom ring. Aeration is a critical factor for composting process and as a result, delayed composting and bad odor problems were identified.