Understanding the population dynamics from an industrial wastewater treatment plant and how to use it as an operational tool

Biological treatment technology is commonly used to treat dairy factory processing wastewater in New Zealand at sites where irrigation is inappropriate. When advanced treatment was assessed as appropriate for the Stirling factory site, Membrane Biorector (MBR) technology was proposed – the first MBR plant treating dairy factory wastewater in New Zealand.

Commissioning challenges included the maintenance of nitrification. Dairy factory wastewater has many characteristics that could contribute to nitrification inhibition including high temperatures and fluctuating pH. The influent streams were assessed for inhibition, however no one inhibitory stream was identified. A nitrosomonas growth reactor is proposed for this dairy season to ensure ongoing compliance with ammonia concentrations in the discharge.

Although the plant was not designed to remove additional phosphorus biologically, it was observed that this was occurring intermittently. The causes for this were investigated and attributed to a combination of the operation of the dissolved air flotation (DAF) equipment, the solids capture of the decanter, and the consequent processing of the decanter centrate through the DAF unit.

The mixed liquor from the MBR was regularly observed microscopically and compared with analytical results. The number and types of filamentous bacteria present are a general indication of conditions in the sludge during the last three sludge ages, while the number and type of protozoa indicate current conditions.

There has also been a mixed presence of both Glycogen Accumulating Organisms (GAOs) and Phosphate Accumulating Organisms (PAOs) with relative numbers altering throughout the season.