Info

Fig. 11.13 PAH breakdown pattern during steady-state treatment of sediment by the SDP process: A slurry mill, O DITS reactor, ISB reactor, Q press cake.

PAH degradation level was about 92% for an overall residence time of 16 d. No significant evaporation was measured in the off-gas. In this sediment, the degradation of mineral oil showed a similar pattern (Fig. 11.14); however, an overall degradation level of only 65% was achieved. Final concentrations after dewatering were around 3000 mg kg-1. In this sediment, mineral oil seems to be less available for microbial breakdown than the PAH. Recycling standards for PAH could be achieved, but levels of oil contamination remained too high.

A contaminated soil treated by the slurry process showed a steady-state breakdown pattern (Fig. 11.15). Starting at moderate contamination levels of 1200-1300 mg kg-1 mineral oil, final concentrations of <50 mg kg-1 were achieved, which is well below the recycling standards.

Comparing the steady-state continuous results (Fig. 11.14) with the batch results (Fig. 11.6b) for the same sediment and contaminant, we can clearly see that the continuous mode results in much better conversion (final concentration in continuous mode is ±3000 mg kg-1 vs. 7000 mg kg-1 in batch mode). This improvement due to continuity is in accordance with observations on cascade breakdown (Apitz et al., 1994). However, despite the improvement shown in Figure 11.14, the Dutch recycling standard (mineral oil = 500 mg kg-1) for this specific sediment was not met.

For a less contaminated solid waste (Fig. 11.15), the recycling standard was met without difficulty: a mineral oil starting concentration of900 mg kg-1 was decreased to an output concentration <50 mg kg-1. If this oil conversion is compared with the results in Figure 11.14 (8000 mg kg-1 of mineral oil input was decreased to 3000 mg kg-1 output), we can see that, at higher concentrations, limited bioavailabil-ity seriously hinders microbial breakdown. As a consequence, it is often difficult to

14000

12000 -

-D 10000

E 8000

2000

12000 -

-D 10000

E 8000

2000

final filling slurry mill

operation period [d]

Fig. 11.14 Mineral oil breakdown pattern during steady-state treatment of sediment by the SDP process: E slurry mill, O DITS reactor, ISB reactor, Q press cake.

1400

1200

-a 1000

2 400

1200

-a 1000

2 400

final filling slurry mill

"/ K\ J vX

Zl \ - Jw~

□————~^

operation period [d]

Fig. 11.15 Mineral oil breakdown pattern during steady-state treatment of soil by the SDP process: E slurry mill, O DITS reactor, cascade, Q press cake.

achieve complete conversion and achieve low end concentrations when starting with high input concentrations.

We should note that analytical difficulties (especially for oil) in the handling of wet samples can easily lead to incorrect data. For example, in addition to a standard deviation of 20% within one laboratory, sample-exchange assays between various laboratories led to results that had a variation of more than 75% (Warbout and Oubot-er, 1988). Bearing in mind these variations, analytical results should be regarded with care. This holds even more when samples of processed solids are compared to recycling standards.

Was this article helpful?

0 0
Organic Gardeners Composting

Organic Gardeners Composting

Have you always wanted to grow your own vegetables but didn't know what to do? Here are the best tips on how to become a true and envied organic gardner.

Get My Free Ebook


Post a comment