Assessment of leaching tests on construction material made of incinerator ash (sewage sludge): investigations in Japan and Germany

Abstract

Heavy metal release from bricks or blocks made of sewage sludge considerably decreases by sintering or cement consolidation. With such treatment, the enviromnental compatibility of recycled material can be ensured. In the framework of joint German-Japanese research, two types of leaching tests were introduced to develop a standardized test for construction material made of sewage sludge. One type is considered as a worst-case-test with low pH-values of 4-5 which describes the leaching availability under strong natural conditions (e.g. acid rain). The other type is a standardized test without pH-control. Both types of tests are investigated by using crushed samples of blocks. Generally, there are two different ways for a sustainable assessment of the enviromnental compatibility. One way is to use a test with a low pH-value like the worst-case-tests. The other way is to crush the sample in small particles to produce large surfaces when using a standardized test. The smaller the particle size is, the higher is the concentration of heavy metals in the eluate. From the Japanese point of view, blocks are usually utilized in original shape, small particles are not appropriate as samples. That is why medium-sized particles are used for the leaching tests. But using “bigger” particles, lower pH-values can be used. Therefore, a modified Swiss method is assumed to be suitable as a new standardized test for the effect of acid rain. This method is discussed from the point of view of sample diameter. From the German point of view, crushed samples with diameter <10 mm are used in combination with a standardized test. The heavy metal release from Japanese re-products is very low, and it has a close relationship with the release of the alkaline and alkaline earth metals. This effect can be shown on ash bricks from Germany also. Considering recommended limits in Germany, higher firing temperatures of >1100°C should be used.