AN APPRAISAL OF THE EFFECT OF BIOLOGICAL TREATMENT ON THE ENVIRONMENTAL-QUALITY OF HIGH-YIELD MECHANICAL PULPING EFFLUENTS

Before biological treatment, the effluents from one CTMP (chemi-thermomechanical pulping) and three TMP (thermomechanical pulping) mills were acutely lethal to fathead minnows (Pimephales promelas) and the water flea Ceriodaphnia with 48-h LC50 values of 2.2 to > 50%. The effluents also caused chronic effects at concentrations of 0.01-5.3%. After biological treatment, effluents from the three TMP mills were not acutely lethal to either test species. Biotreated effluents from the CTMP mill were also not acutely lethal to minnows but were lethal to Ceriodaphnia (48-h LC50: 54-80%). The chronic effects of biotreated effluents occurred at concentrations of 47 to > 100% for fathead minnows and at 5-37% for Ceriodaphnia. Biological treatment also reduced the levels of BOD (> 80%), COD (> 60%) and wood extractives (> 99%).