Effects of ammonia and phosphate limitation on the activated sludge treatment of calcium-containing chemical waste

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Abstract
Laboratory‐scale biotreaters were used to study the effects of NH3‐N and PO4‐P nutrients on the activated sludge treatment of a chemical waste containing soluble calcium (1300 mg/L). Units receiving high or low levels of NH3‐N and PO4‐P were similar in their ability to remove organic compounds from the waste. Adaptation of sludges to low PO4‐P levels (3 in the biosolids, whereas those receiving high PO4‐P (2–4 mg/L effluent) had little CaCO3. Microscopic observations of CaCO3 containing sludges showed substantial amounts of CaCO3 crystals imbedded in the biomass. These flocs also appeared to be enriched with nonfilamentous bacterial species in contrast to flocs devoid of CaCO3 which had a floc structure of filamentous and nonfilamentous organisms. Scanning electron micrographs of flocs grown under low NH3‐N showed a microbial fibrillar network of exocellular material interconnecting cells in the floc matrix. The sludges adapted to low NH3‐N also produced higher amounts of extractable polysaccharide. CaCO3 containing biosolids were more dense, larger, and settled better (low SVI, high ISV) than flocs devoid of the precipitates. It is not known from our experiments whether PO4‐P or some inorganic or organic polymer produced by the floc bacteria are involved in inhibiting CaCO3 precipitation in the activated sludge treatment of calcium‐containing wastes.