EFFECT OF PH ON THE BEHAVIOR OF VOLATILE COMPOUNDS IN ORGANIC MANURESDURING DRY-MATTER DETERMINATION

Dry matter determination by drying at 105 degrees C is one of the most widespread methods used in the characterization of manure. Loss of vo latile compounds during dry-matter determination may lead to considera ble errors in mass balances. Since the behaviour of most volatile comp ounds depends upon pH, these losses may vary from sample to sample. Th e loss of ammonia and volatile fatty acids from pig, cattle and poultr y manure was studied as a function of pH. It was shown that above pH 8 all ammonia was volatilized and below pH 5 all volatile fatty acids e vaporated. Total fixation of ammonia was achieved below pH 4. Above pH 10 all volatile fatty acids were fixed in the residue after drying. T he three types of manure showed only slightly different patterns of lo sses of volatile compounds. The amount of acid or alkali needed to obt ain the desired pH varied strongly between the various kinds of manure .