Minimal residuals filter

Soil biofilters are relatively large compared to filters using other media since soil pores are smaller and compounds have low permeability in soil. Soil biofilters also have limited depths due to problems associated with maintaining humidity in soil and minimizing pressure drop. Furthermore, soil sorption capacity is limited and residual contaminants are vented immediately to the atmosphere. 

In order to obtain practically colorless alloxan monohydrate (Note 5), 25 g. of the yellow crystals is dissolved in 37 cc. of hot water, the solution is boiled with Norite, and the hot solution is filtered into a 500-cc. round-bottomed flask. About 15-20 cc. of water is removed by distillation under reduced pressure on a water bath. The colorless crystalline residue is dissolved in the minimal volume of hot water, the solution is cooled somewhat, and to it is added 250 cc. of glacial acetic acid. After the mixture has been kept cold (5-10°) for four to six hours, the alloxan monohydrate is filtered. The yield is 20-21 g. (80-84 per cent recovery) (Note 6) of practically colorless crystals which melt at about 254° (Note 7) with decomposition. 

All the product is dissolved in 40ml of water (previously heated to 80°C) to which one milliliter of pyridine has been added immediately before it is mixed with the solid. When the blue-green substance has dissolved, leaving only a small residue of cream-colored basic nitrite, the hot Hquid is immediately filtered by suction and rapidly cooled in ice. During the cooling process the solution should be continuously agitated to minimize the formation of tenacious crusts on the walls of the vessel these should be removed as needed. 

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