INFERRED METAL TOXICITY DURING THE BIOTREATMENT OF HIGH AMMONIA LANDFILL LEACHATE

Two nitrification-denitrification systems were used to determine the possible inhibitory and/or toxic effects of supplemental metals addition to the nitrification-denitrification process in the treatment of a relatively high ammonia, low biodegradable carbon, municipal landfill leachate. The addition of metals likely resulted in the precipitation of phosphorus which caused the nitrification-denitrification process to be inhibited due to the deficiency of bioavailable phosphorus. Even though the phosphorus concentrations in mixed liquor and system effluent samples filtered through Whatman No. 4 filters or glass-fiber filters appeared to be adequate, it was discovered that they were considerably lower when filtered through 0.45-mum membrane filters. This seemed to indicate that although some of the precipitated phosphorus passed through the Whatman No. 4 filter, it was not available as a nutrient for microbial metabolism. Therefore, only the phosphorus that will pass through a 0.45-mum membrane filter, and is defined as soluble in Standard Methods (1985) is readily available to the microorganisms. This should be monitored to ensure sufficient nutrient availability in nitrification-denitrification treatment systems potentially exposed to metals capable of precipitating phosphorus. It is recommended that a minimum soluble phosphorus concentration of 0.5 mg/L be maintained to ensure adequate phosphorus for nitfification and denitrification; in addition, when conducting activated sludge metal toxicity studies, total or Whatman No. 4-filtered samples should not be used to determine the presence of adequate phosphorus.