Sludge Rheology and Non-Newtonian Pipeline Hydraulics

Wastewater sludge with solids concentrations above about 2% exhibit non-Newtonian behavior, i.e., the sludge apparent viscosity changes with the shear rate (flow velocity). To determine pipeline head loss for sludge streams to and from anaerobic digesters, samples of primary, secondary and digested sludge were collected from Orange County Sanitation District Plant No. 1 and analyzed to determine their rheological parameters. The results were used in non-Newtonian hydraulic calculation procedures to estimate head loss under future operating conditions with sludge streams containing high solids concentration. This paper presents the basic sludge rheology theory, provides some details on the sludge sampling and viscosity measurements, and describes the non-Newtonian hydraulic theory and calculation procedures used to estimate head loss for sludge streams having high solids concentrations.