Beijing's first garbage composting plant to be upgraded

Nangong Garbage Composting Plant, which opened 11 years ago in 1998 as Beijing's first garbage composting plant, will be reconstructed and expanded to enable its daily garbage disposal capacity to reach 1,000 tons.

The daily garbage disposal capacity will reach 1,000 tons

Garbage composting refers to the process of treating organic garbage such as vegetable and tree leaves, and fruit skins and cores, and converting it into useful compost. Once the garbage is treated about two thirds of it is converted into compost to be reused, greatly reducing the amount of landfill and increasing the rate of converting waste into resources.

The plant's roll-up door and tunnel door system, fermentation and air supply system and pulverization system in the post-maturation zone will be reconstructed and expanded. The head of Beijing Environment Sanitation Engineering Group Co., Ltd's Erqing branch said that after over 10 years of operation, some subsystems within the composting system have become old and therefore some components will be optimized and upgraded.

General Manager Xu Zhongxin said that after the plant was reconstructed in 2005 the daily garbage disposal capacity increased from 400 tons to 600 tons. This time, with the efforts of technicians, the garbage piles in the plant's composting tunnels can be increased by one meter from the current 2.5 meters to 3.5 meters. The composting plant will have a daily disposal capacity of 1,000 tons by the end of 2010 to double its planned capacity.

Space has been reserved in the plant for future extension and renovation so that extensions can be made according to future garbage disposal needs.

The composting plant is "covered" to keep off foul odors

The odors have always troubled residents living in the neighborhood of garbage disposal plants. Once the renovation is completed, areas from which foul odors come such as the composting plant will be surrounded by a sealed tent. This is the equivalent of putting a "cover" over the composting plant, which will contain foul odors before they can circulate in the atmosphere.

"The sealed tent will keep foul odors from escaping. Ventilation systems will blow oxygen-rich fresh air into the plant and a negative pressure system will pump out waste gas generated by the compost." Xu said that after all the compost tunnels have been renovated, waste gas emissions at Nangong Composting Plant will be reduced by 670 tons a year.

The composting process produces waste gases such as hydrogen sulfide, sulfur dioxide and ethers, and aldehyde, most of which are colorless and odorless unless they are mixed together when a consequent chemical reaction makes them unbearably smelly.

Waste gas recycling by "covering" also greatly enhances waste composting efficiency. Composting waste first needs to increase temperature by fermenting and then be kept in a temperature of 50 degrees Celsius for at least five days to kill harmful bacterial such as roundworm ovum and colon bacillus. As temperatures are low in winter, composting requires a long time to raise the temperature, so composting efficiency is very low.

Recycling waste gases and reusing their remaining heat allow the rapid heating of waste newly transported to the plant, accelerating decomposition, shortening the composting time and thus enhancing the efficiency of composting. At present Nangong Composting Plant’s composting time in high temperatures has been reduced from ten days to about seven days, enhancing waste processing capacity by almost 30 percent. In the future, the plant will introduce bacteria from external sources to further enhance the efficiency of waste composting.

140 mu of land has been saved over the 11 years

"Nangong Composting Plant saves 13 mu of land used for landfill every year and has saved a total of 140 mu of land over the 11 years since it opened. This figure will continue to increase in the future." The head of Beijing Environment Sanitation Engineering Group Co., Ltd told reporters that the social benefit of Nangong Compositing Plant is far larger than its economic benefit. Of the household scrap transported from Chaoyang, Xuanwu and Chongwen districts, 68 percent is decomposed as fertilizer and water, and less than one third is sent to landfill to be buried.

Aside from saving land, composting can greatly reduce the pollution of underground water. As some waste such as vegetable leaves and fruit peels contains a lot of water, directly sending it to landfill will lead to excessive leachate, and increases both processing costs and the risk of polluting underground water. During the composting process, water is extracted from the waste using a series of technologies including oxidizing and curing, thus the buried waste is dry and the risk of pollution is eliminated.

Translated by LOTO