Comparison of powdered activated carbon and activated sludge treatment of a kraft pulp mill wastewater.

Abstract

The Powdered Activated Carbon Treatment$\rm\sp{TM}$ (PACT$\rm\sp{TM})$ process consists of powdered activated carbon addition to the activated sludge treatment process. Objectives were (1) to compare treatment of kraft pulp mill wastewater using activated sludge versus PACT$\rm\sp{TM},$ by measuring toxicity, organic load, adsorbable organic halides (AOX) and metals and (2) to assess how three operating conditions: (1) carbon dose; (2) hydraulic retention time; (3) solids retention time, affected performance. Findings were: (1) Lengthy hydraulic retention times are unnecessary. Short hydraulic retention times (4 h) provide adequate treatment. (2) Activated sludge treatment alone removes most biochemical oxygen demand, PACT$\rm\sp{TM}$ offers no improvement. PACT$\rm\sp{TM}$ improves removal of soluble chemical oxygen demand. PACT$\rm\sp{TM}$ improves removal of AOX. Powdered activated carbon dose is the sole determinant of this increased removal. (3) Activated sludge treatment alone removes Microtox$\rm\sp{TM}$ toxicity. PACT$\rm\sp{TM}$ slightly improves treatment of highly toxic wastewaters. Significant chronic toxicity towards Ceriodaphnia remains in effluents from both activated sludge and PACT$\rm\sp{TM}.$ Both treatments remove toxicity to Ceriodaphnia, but PACT$\rm\sp{TM}$ effluents are more toxic. Powdered activated carbon alone exhibits toxicity to Ceriodaphnia. (4) The effect of PACT$\rm\sp{TM}$ on removal of metals is inconclusive. (5) PACT$\rm\sp{TM}$ treatment of kraft mill wastewater would be very expensive. (6) PACT$\rm\sp{TM}$ has limited benefits over activated sludge for the treatment of kraft mill wastewater, therefore PACT$\rm\sp{TM}$ is not recommended for treatment of kraft mill wastewater.