Sludge Degradation Study

Objective

To measure the decomposition rate of sludges from ANC, MW, and SLP as a function of waste type, soil type, temperature, and rates/frequency of application.

Experimental Design

  • 3 sludges  (ANC, MW, SLP)
  • 3 temperatures (5°C,15°C and 25°C)
  • 6 rates/frequencies of sludge additions (once at 0, 2.5, 5, and 10 cm; and twice at 2.5 and 5 cm)
  • 6 sampling times (0, 1, 3, 6, 12, and 24 weeks)
  • 2 soils (coarse and medium texture)
  • 3 replicates

Measurements

  • CO2 evolved and O2 consumed (every week)
  • Soil C, and N (every sampling event)
  • Soil pH, CEC, oil and grease (first and last sampling times)
  • GC-MS of oil and grease extract and Microtox (first and last sampling times)

Results

  • Higher degradation rates were observed for the coarse textured soil.
  • Degradation (for all 3 sludges) increased with both temperature and rate of application.
  • Rates of degradation (24 weeks incubation) ranged from 10 to 40% of added sludge, and increased with temperature.
  • Differences were observed for sludge source (SLPC>MW>=ANC).
  • Soil pH and oil and grease content increased with sludge additions; the increase depended on sludge rate, type and incubation temperature.
  • Microtox (EC50) of the soil water soluble fraction increased with time of incubation, indicating a detoxification of the sludge material through degradation
  • GC-MS analysis of oil and grease fraction from the 3 sludges showed the presence of fatty acids, plant sterols, and phthalate (a likely industrial contaminant)
  • Sludge incubation (24 weeks) led to a significant decrease in the above organic compounds for all sludges