Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 143

separate composting for each test substance. Municipal biowaste was used
as starting material. The application of each of the test substances to the
biowaste was carried out individually and took place prior to composting.
The thermophilic phase was simulated for 29 days, reaching temperatures
of ~70

C and the maturation phase was
simulated for another 49 days. The long-term fate of the test substances
was monitored for 6 months at temperatures of 30

° C. The material was cooled to 30 °

C and a water content of
40%. Samples were taken after the thermophilic phase, after the maturation
phase and after 120 and 200 days during the long-term study.

°

Analytical procedure

The characterization of the test substances involved both analysing the
compost matrix and examination of the reactor exhaust gas.
A sequential fractionation was carried out with the compost matrix,
differentiating the 14 C-radioactivity between extractable fractions and
non-extractable residues. The extraction was performed by shaking with
water and acetonitrile, by Soxhlet with toluene, and by shaking with sodium
hydroxide. The 14 C-radioactivity in the extracts was determined by liquid
scintillation counting (LSC; Packard). The identity of 14 C-radioactivity in
the extracts was analysed via 14 C-HPLC (RP18 hypersil with gradient elu-
tion acetonitrile/water). NERs were transformed into 14 CO 2 by incineration
using a Packard oxidizer and the radioactivity was determined by LSC.
For quantification of the mineralization rate, the exhaust air was passed
through PUF plugs to trap organic volatiles and subsequently passed
through NaOH traps where CO 2 was absorbed. The 14 C-radioactivity
trapped in the sodium hydroxide was determined daily by LSC.

Results and Discussion

Mineralization

Degradation of [ 14 C]DEHP to 14 CO 2 occurred rapidly during the
thermophilic phase. After 200 days, 70% of the initial [ 14 C]DEHP was
mineralized (Fig. 3.6.1). The degradation of [ 14 C]simazine to 14 CO 2
was minor, leading to a mineralization rate of only 8% altogether. The
degradation of pyrene was intermediate between these values. After a low
mineralization rate during the thermophilic phase, the degradation to
14 CO 2 increased rapidly and reached 56% of the initial [ 14 C]pyrene after
6 months. This delayed mineralization was also observed by Martens
(1982), who found that in fresh composts only minor amounts of four-ring
polycyclic aromatic hydrocarbons (PAHs) could be degraded. However,