Incineration Ash of Food Wastes

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Incineration is the most popular method of disposing of combustible solid wastes in Japan, especially for MSW from restaurants, hotels, and supermarkets. For a long time incineration was perceived as a progressive method and the percentage of incineration of MSW was near 80%.

Table 9 Percentages of Raw Materials of Various Kinds of Cement

Portland cement Portland cement Eco-original__recent__cement

Table 9 Percentages of Raw Materials of Various Kinds of Cement

Portland cement Portland cement Eco-original__recent__cement

Lime stone

78

76.5

52

Qay

16

1

Silicate

4

7.5

Iron source

2

2

1

Pretreated ash of MSW

1

39

Others (coal ash, sludge,

12

8

plastics)

Total

100

100

100

However, the evaluation of this method has changed with the discovery of dioxins (DXNs). After incineration, ash containing DXNs is inevitably generated, resulting in another type of hazardous wastes derived from food products. Recently, it has become popular in Japan to recycle the ash to cement raw material. Table 8 illustrates two methods for this type of recycling: (a) eco-cement which uses MSW ash at 39% of total amount of raw material, (b) ordinary cement, which uses pretreated ash at 0.5-0.7% of raw material, as shown in Fig. 4. In Yamaguchi Prefecture 50,000 tons of MSW ash can be recycled by this second method.

This method is considered to be tentative as the final means of recycling. Essentially the goal should be to recycle back to farmland not only major nutrients like N and P but also various minor nutrients like Ca, Mg, Fe, Mn, Cu, Zn, Mo, and B. This means mineral resources derived from food are contaminated by heavy metals through incinaration of garbage together with various other wastes.

Figure 4 Ash recycling for Portland cement feedstock.

27.6 RECENT TECHNOLOGIES ON FOOD WASTES TREATMENT

27.6.1 Waste Management in Fermentation Industries

Fermentation industries cover a wide range of food processing from the traditional industries of breweries, soy source, miso, pickles, to yeast, alcohol, amino acids, nucleic acids, antibiotics, enzyme, and other bio-active fine chemicals. Usually, the harvest rate of these products is not high except for traditional fermentation, which typically has a large pollutant load. However, the possibility of resources recovery is also high because hazardous chemicals are rarely used.

The wastewater comes from (a) the mother liquid after harvesting the products, (b) cleaning water of cells or reactors, (c) condensates from the evaporator, (d) spent eluting solution in purifying processes, and (e) ammonium sulfate, used in salt crystallization of enzymes, and others.

The following information is cited mainly from a thesis [25] published in 1983. While details may have changed since then, the fundamental structures remain largely the same.

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