Air stripping and biological treatment of ammonium sulfate wastewater from the caprolactam manufacturing process

The objectives of this study were to determine the optimum operating conditions required for air stripping of ammonium sulfate wastewater from the caprolactam manufacturing process, to determine if biological nitrification is a viable means of treatment, and to identify any compounds present in the ammonium sulfate wastewater that (might) inhibit nitrification. This was accomplished using a combination of air stripping pretreatment, a flow-through conventional activated sludge system, powdered activated carbon (PAC) treatment and batch testing.

Although biological treatment was conducted using conditions to promote nitrifier growth, nitrification was not observed using either conventional or PAC treatment. Air stripping removed fifty per cent of the ammonia-nitrogen at gas-to-liquid ratios greater than 500. However, it had no apparent effect on nitrifier inhibition.

Inhibitor studies of this waste stream focused on two oximes: namely cyclohexanone oxime and methylethyl ketoxime (MEKO), which were both found in the wastewater in concentrations of 50-150 mg/L.

The conclusion of this work is that cyclohexanone oxime is not inhibitory to nitrification .in concentrations less than 100 mg/L; however, MBKO was found to be inhibitory at concentrations as low as 14 mg/L. Furthermore, the inhibitory effect appeared to be pH dependent with increasing inhibition at pH less than eight.

The implications of these findings for the design and operation of a full-scale treatment facility are numerous. The optimum pH range for a full-scale facility would be narrow due to the requirement for a pH high enough to decompose MEKO while maintaining a pH low enough to prevent free ammonia toxicity.