Effect of temperature and dissolved oxygen on biological nitrification at high ammonia concentrations.

Effect of temperature and dissolved oxygen concentration on nitrification rate were investigated with enrichment cultures of nitrifying bacteria. Values of specific nitrite oxidation rate in the absence of ammonia were 2.9-12 times higher than maximum specific ammonia oxidation rates at the same temperatures. The presence of high ammonia levels reversed this relationship, causing maximum specific nitrite oxidation rates to fall to 19 to 45% as high as maximum specific ammonia oxidation rates. This result suggests that nitrification at high ammonia levels will invariably result in nitrite accumulation. The K(O2) for nitrite oxidation in the presence of high ammonia levels was higher than the K(O2) for ammonia oxidation when temperature exceeded 18 degrees C, whereas the opposite was true at lower temperatures. These results indicate that low oxygen tensions will exacerbate nitrite accumulation when water temperature is high.

Effects of toxicants on nitrifying biomass in flocs vs. carriers.

Effects of chemical toxicants on nitrifying bacteria in flocs and porous carriers were compared. Mean inhibitory concentrations (IC50s) of toxicants were invariably higher in carrier suspensions than floc suspensions. The greatest differences were seen with cyanide, nickel and copper, whereas small differences were observed for the organic toxicants Methomyl and thiourea. Decreasing the size of the carriers lessened their protective effect. The results suggest that carriers would be advantageous for nitrification systems subjected to short-term inputs of heavy metals or cyanide but not helpful for systems subjected to transient inputs of organic chemicals.

Removal of nitrogen and phosphate from wastewater by addition of bittern.

Removal of nitrogen and phosphate through crystallization of struvite (MgNH(4)PO(4).6H(2)O) has gained increasing interest. Since wastewaters tend to be low in magnesium relative to ammonia and phosphates, addition of this mineral is usually required to effect the struvite crystallization process. The present study evaluated the feasibility of using bittern, a byproduct of salt manufacture, as a low-cost source of magnesium ions. High reaction rates were observed; the extent of nitrogen and phosphorus removals did not change beyond 10 min. Phosphorus removals from pure solutions with bittern added were equivalent to those obtained with MgCl(2) or seawater. Nitrogen removals with bittern were somewhat lower than with the alternate Mg(2+) sources, however. Application of bittern to biologically treated wastewater from a swine farm achieved high phosphate removal, but ammonia removals were limited by imbalance in the nitrogen:phosphorus ratio.