| Occasional excursions of organic nitrogen (ON) and chemical oxygen demand (COD) occurred during activated sludge treatment of wastewater from an organic chemicals plant. The effluent ON typically exceeded the influent levels. The effects of stress conditions possible in the plant on nitrogen and COD metabolism and release were studied to determine the reason(s) for the excursions.; A review of plant data identified major contributing factors as low aeration basin dissolved oxygen (DO), nitrogen and COD shocks and temperature above 30{dollar}spcirc{dollar}C. Initial batch experiments studied nitrogen release from the biomass and its transformations without external substrate. Two continuous flow bench-scale activated sludge units were run using actual plant waste at plant conditions, one as control and the other as excursion system. The waste contained 15-60 mg/l total nitrogen (TN) with ON compounds including dimethyl ethanolamine (DMEA), acrylonitrile (ACN), azo-bis isobutylonitrile (AIBN) and 500-1600 mg/l COD comprising alcohols and ketones. The excursion unit was subjected to 17 transient stresses simulating one or more potential causes stated above. Gas chromatography/mass spectroscopy (GC/MS) were performed to study bio-degradation of specific ON compounds.; Under 72 hour starvation during the batch runs, cells lost 11-16% of their nitrogen, releasing 50-80 mg/l soluble TN. The ON release was higher under anaerobic conditions but lower at lower mixing. A low clarifier DO released 20 mg/l soluble TN to the recycle sludge liquor. A low reactor DO (0.2 mg/l) raised the average soluble TN, ON and COD by 16, 9 and 230 mg/l, and released 6 mg/l soluble ON. The cell nitrogen fell from 10.0% to 8.9%. Settling deteriorated and protozoa and rotifers were eliminated. Shocks of DMEA, ACN, aniline, methanol and a process waste were effectively metabolized at normal DO. Salt shock severely inhibited nitrogen transformations. Bio-degradation of ON compounds fell with DO and increased with temperature.; The major cause for the excursions was low DO which reduced ON breakdown and released biomass nitrogen. Death and lysis of protozoa, rotifers and some bacteria, and partial decay of cell polymers are indicated as the release mechanisms. The excursions did not recur in the plant after raising the bio-basin DO. |
