The effect of temperature and overwater dissolved oxygen concentration on benthal feedback from pulp and paper mill sludges

Abstract

Settleable solids accumulate (benthal layer) in stabilization lagoons, reducing volume for treatment and providing a source of oxygen demand and nutrients (feedback). The objective of this research was to define the impact of overwater dissolved oxygen (DO) and temperature upon these benthal properties. Batch benthal deposits (2:1, vol/vol, primary clarifier underflow and waste activated sludge) under a continuous-flow overwater layer were subject to variable temperature and DO. Experiment conditions simulated a facultative lagoon. Over 124 days, DO uptake was measured and effluent was sampled for chemical oxygen demand (COD), ammonia-N, and ortho-phosphate. Nearly all phosphorus feedback occurred in the first 31 days, and ammonia-N feedback was most constant for the duration. COD feedback was greatly reduced and DO uptake increased slightly with increasing DO. All feedbacks increased more from 15°C to 20°C than from 20°C to 26°C. Residual sludge analyses indicated that phosphorus was limiting to benthal stabilization. Temperature dependent reactions caused a linear decrease in total and volatile suspended solids.