Siemens has recently invented a new biodrying process that can convert sewage sludge into usable elements – all of this while saving a great deal of energy. Thus, their “mechanically enhanced biodrying” doesn’t require any external heat source, but produces its own with the help of the microbes in the sludge, which costs about 30 percent less than in the case of a classic thermal drying process.
A one of its kind test plant has already been set up in Shenyang, China, and will dry 1,000 tons of wet sludge a day, becoming the world’s largest sewage sludge treatment plant using a non-thermal technique.
Usually, sewage treatment plants use pressing to separate solid matter from liquids, but the process is mostly inefficient, as it can only yield 20 percent solid waste (that can be used as fertilizer, for example). New laws in China require that at least 60 percent of the sludge be obtained from treatment plants, and the only way it can be done is through drying.
Solar heat would be one answer to the problem, but it can take up to two months for that to happen. Siemens’s solution rose the percentage of recycled solids from 20 to 65 percent, with a total processing time of only about 22 days, with the heat produced by biological processes.
The plant will need electricity for only one thing: the aeration and mixing of the sludge to keep the bacteria alive. A pilot test carried out at a composting plant in Merrimack, New Hampshire, demonstrated that the process works at temperatures as low as minus 10 degrees Celsius.
This system’s only drawback is that it needs a lot of space compared to traditional sewage treatment plants, but that’s also not a problem in developing countries, where there’s plenty of room if there are energy (and money) savings at stake.