The type of composting equipment used and the corresponding composting process usually depend on the following factors:
- Types of solid waste;
- Establishing natural conditions of composting plant site (distance from residential area, topography, wind direction, etc.);
- Control level of secondary pollutants (leachate, odor gas) in composting process;
Investment and operation cost of plant construction.
Because of the superiority of geographical location, stacking composting can be widely used in rural areas and small towns. However, in some densely populated rural areas, farms, aquaculture farms, urban suburbs and other areas, the composting process with high efficiency for odor gas and leachate treatment should be chosen first.
Trend of development
The Seattle Solid Waste Utilities Bureau first implemented the Masterminer Program in the United States in 1986, marking the beginning of household composting, which mainly uses composting technology to treat yard waste and food waste. In 1995, 41% of Seattle households implemented household composting, diverting about 8 300 tons of yard waste, 82% of which was used for yard greening. There are studies. In the Mississauga area of Ontario, roadside collection, centralized composting and household composting cost $140 t-1, $190 T-1 and $50 t-1, respectively. Moreover, household composting can reduce the amount of household garbage by 3%-5%. Compared with centralized and large-scale composting systems, household composting has significant advantages: low cost and reduction of solid waste sources. In Seattle, there are two types of household composters for food waste: earthworm boxes and conical buckets. In the past, earthworm boxes were commonly used. Now, conical barrels are popular. The height of conical barrels is about 0.9 M. There is a basket with a height of 0.46 M. It can accommodate food waste produced by a family of three within 6 to 9 months. There are two kinds of household composters for yard waste: 0.34 m3 and 0.59 m3. Wood, recycled polyethylene and stainless steel are used to make household composters.
Composting toilets are suitable for places without or without water, such as large-scale composting toilets for parks, highways, stations, etc., and small-scale composting toilets for ships, etc. The commercial composting toilets are divided into self-contained and centralized ones, which can be operated intermittently or continuously, and are made of glass fibre and polyethylene. The self-contained composter is located next to the toilet, while the centralized composter is located next to the basement or building. Intermittent composting toilets contain more than one compartment. When one compartment is full, they are transferred to another compartment. Its advantage is that there is only one compartment in the composting toilet which can run continuously without contamination by fresh manure. Fresh manure and decomposed quasi-manure are mixed together.
Small Capacity Reactor Suitable for Field Operation
Because of the economic, odor control and site reasons, composting systems with large reactors, forced ventilation static stacking and strip stacking are greatly limited. Therefore, a portable, small-capacity reactor composting system suitable for field operation emerges as the times require. For example, Mulch Co. of County, UK, has built two mobile composting systems (30.584-38.23 m3 in volume) similar to rolling containers, with bucket loaders for feeding and cranes for lifting containers when discharging, and materials poured out from the back door of containers. Temperature and oxygen content are controlled by computer. Although this kind of system has only appeared for a few years, it is receiving more and more attention and application from small sewage treatment plants, food industry, catering industry, communities, schools, hospitals, research institutes and business groups. At present, it is mainly used for food waste treatment. The small capacity reactor composting system on the market includes box system, mixing bin and rotary digester, etc. But at present, the most commonly used one is box composting system. The system can be operated intermittently or continuously. It has the advantages of good process control, low investment and operation cost, simple equipment, easy operation and assembly, etc. But its greatest advantage is that it is easy to operate and assemble. Organic waste treatment technology is provided for groups or units that do not have enough space. Currently, 50 and 25 box composting systems are operating in the United States and Canada, respectively. A typical box-type composting system has a treatment scale of 1-40 t/d-1. It consists of several boxes, two of which are used as biofilters. In order to facilitate field operation, the mixing equipment and reactor are connected with the trailer.
In a word, the source of solid waste is more and more dispersed, and the amount of solid waste is also more and more, so the application scope of composting equipment will gradually expand. For different solid wastes, different composting equipments need to be adopted and developed. With the development of solid waste composting, household composters and small-capacity reactor composting systems emerge as the times require. On the one hand, home composters have been reduced from the source.