Recycling of sludge 2001.04(84)

  According to the "Industrial Waste Discharge and Disposal Situation (FY1997 Results)" released by the Ministry of Health, Labor and Welfare in June 2000, the total amount of industrial waste discharged nationwide in FY1997 was approximately 415 million tons (down 2.6% from the previous year), of which sludge, which accounted for 47.3% of the total, came in first at 196.17 million tons (down 0.4% from the previous year). Only 5% of this sludge is recycled, while the remaining 13% remains untouched, and 82% is landfilled after being dried or incinerated to reduce its volume.

The effective utilization of sewage sludge is approximately 640,000 tons (based on dried weight at the time of sludge generation), of which 430,000 tons are used for construction materials and 210,000 tons are used for green agricultural land. Given the current situation, an important issue is how to utilize the sludge and reduce the amount for final disposal.

Brick and Block Conversion

Municipalities with a high sewerage system penetration rate are recycling large amounts of sewage sludge by pressing the sludge incinerator ash and then firing it into bricks or blocks. For example, "Metro Bricks" produced at the Tokyo Metropolitan Government's Bureau of Sewerage's Nanbu Sludge Plant (Jonanjima, Ota-ku, Tokyo) and "Hama Bricks" produced in Yokohama City are typical examples. However, the energy costs involved in pretreatment and calcination have made profitability an issue.

1 Carbonization

Kawasaki Heavy Industries, Ltd. has developed a device that produces activated carbon by steaming sludge generated from sewage and general wastewater. This technology converts the organic components in the sludge into activated carbon, which can be used as an adsorbent or soil conditioner. However, the carbonization business has profitability issues.

2 Conversion to raw material for cement

Almost any waste or by-product can be used as raw fuel for cement, and sludge is no exception. However, the production cost of eco-cement is slightly higher, and user acceptance is an issue. On the other hand, Obayashi Corporation has developed a technology to reuse sludge generated during the concrete manufacturing process and when washing concrete from ready-mixed concrete trucks.

3 Biogas Utilization

Sludge from sewage sludge and food factories, which contains a large amount of organic matter and water, is attracting attention as a method of converting it into energy through methane fermentation. The Ministry of Health, Labour, and Welfare (MHLW) also provides subsidies for new human waste treatment facilities, but only for recycling-type facilities. In addition, the Tokyo Metropolitan Government's Bureau of Sewerage is planning to build a power generation facility using methane gas generated from the sewage sludge treatment process.

4 Sludge Fertilizer and Compost

The use of sludge fertilizers and compost made from sewage sludge is increasing. This is due to soaring final disposal costs and the revision of the Fertilizer Control Law, which has promoted recycling projects. However, the sewage sludge composting business has low barriers to entry, and competition is intense.