The feasibility of dry stacking wastewater treatment (WWT) sludges is examined. The results indicate that dry stacking has the potential to dramatically improve the performance of WWT sludge drying pans.
Drying pans are used during wastewater treatment (WWT) to store, stabilise, and dry residual solids. The pans are filled with sludge that dries via exposure to sunshine and wind.
Here Australian researchers propose that drying pans are operated based on dry stacking principles, a technique with proven success in the mineral processing industry.
The implementation of the dry stacking technique requires very little in the way of additional engineering, beyond a conventional drying pan. By applying the sludge in thin layers, the sludge naturally forms its own stack, with an angle that depends on the consistency of the material.
The benefits of dry stacking are that the slope allows instantaneous runoff of rainfall and supernatant, allowing operation throughout the year rather than seasonally. The layering approach also maximises the evaporation achieved in the available deposition area, compared to filling the pans sequentially.
A series of laboratory tests were carried out on samples from Melbourne Water's Western Treatment Plant in Werribee, Australia, to provide validation of the dry stacking concept for WWT sludges.
Rheological tests showed that samples had appropriate flow properties to form stacks. Drying and re-wetting tests on the samples indicated that a sloped, partially dry sludge sheds rainfall, depending on the slope, cake dryness, and amount of rainfall.
Local rainfall data were used to estimate a potential increase in pan throughput of 65% to 140% due to dry stacking. The greatest improvements were predicted to occur during wetter years.
In combination, the results indicate that dry stacking has the potential to dramatically improve the performance of WWT sludge drying pans.
