Column Leaching Study

One of the approaches for contaminants to reach groundwater and eventually surface water is their movement or migration in soil profiles. Factors which affect the transport of pollutants in soil profiles include:

  • chemical characteristics of the substances being transported
  • the properties of the receiving soil
  • the level of water addition (precipitation) to the soil mix

Objective

To study the leachability of pulp and paper sludge components added to soil, and to evaluate the rate of sludge application and level of water addition of these components in soil columns.

Methods

  • Silt loam soil from Fox Creek, Alberta, were packed into polypropylene columns.
  • Sludge was added and mixed with soil to a depth of 15 cm in the column.
  • Water was added at the equivalent of one and two times average annual precipitation at the Whitecourt area. 
  • Leachate was collected bi-weekly and samples were collected for organic C and elemental analysis.
  • At time intervals of 1, 3, and 6 months during the leaching process, soil columns were sectioned in 5 cm intervals and submitted for analysis.  
  • The collected soils were analyzed for saturated paste extracts, total elements, total-N, organic C and cation exchange capacity.

Results

Leachate Characteristics

  • Maximum ↑ in EC was 2.5 dS/m.
  • During the leaching process EC initially ↑ and ↓ with ↑ water addition.
  • Temporary ↓ in pH however the long-term effect was negligible.
  • Sludge application ↑ organic C and cation levels.

Soil Characteristics

  • Sludge addition ↓ pH and ↑ alkalinity, EC, base cations, anions and trace elements of water saturated paste extracts to various levels, but the effects diminished with ↑ water additions during the leaching process.
  • Total nitrogen, total carbon contents  and CEC were ↑ by sludge amendment.
  • Total N remaining in the column ↑ as leaching ↓.
  • Total C and CEC were not affected by leaching.
  • Total trace metals were not significantly affected by sludge amendment rate and water addition level.