Bega Cheese upgrades wastewater system with new aerator

In 2018, Bega Cheese Environmental Manager for Northern Victoria Sean Trebley was given the task of upgrading the wastewater aeration system at Bega’s Strathmerton Plant.

The existing wastewater system consisted of a dissolved air floatation (DAF) unit, which flowed into an aerated lagoon. The resulting effluent was stored in two non-aerated lagoons during winter, with irrigation occurring in summer.

Aerators reduce chemical oxygen demand (COD) in wastewater as well as odours in the aerated and downstream non-aerated lagoons. Bega had an ageing system of surface aerators in the aerated lagoon, consisting of two 22 kW units and six 8 kW units, but generally only one or two of these units were operated at any time.

Over several years the ageing surface aerators had progressively failed. Repairs involved the deployment of cranes and/or boats to gain access — an expensive process that had resulted in damage to the dam liner. Eventually it became uneconomical to keep repairing the aerators.

Bega Cheese installed the aeration unit in early 2019. This image shows the condition of the lagoon at this point, after the previous system had been decommissioned for several months.

Bega decided to look for a solution that was safer for operators and easier to maintain. Trebley contacted Hydro Innovations to discuss the use of the company’s bank-mounted Venturi Aeration system. This solution is mounted on the banks of lagoons, using a self-priming pump to draw water from the lagoon. The unit draws in atmospheric air using the Venturi effect, mixes it with the water being pumped, and discharges it back into the lagoon, charged with dissolved oxygen.

Trebley and his team liked the idea of bank mounting because it gave operators easy access to equipment for monitoring and/or repair, making it safer and more cost-effective to maintain. Bega’s only concern was whether the units were as efficient as surface-mounted technologies. Hydro Innovations was able to provide information indicating that, with the use of the right pump, oxygen transfer efficiency for Venturi Aeration units can be as high or higher than 1.86 kg O₂/kWh, making them at least as efficient as surface (floating) technologies.

The aerated lagoon contained 45 ML of effluent, with in-flows from 80–120 ML per year. This required a 150 mm Venturi Aeration unit, which was paired with a Gorman-Rupp V6A60-B self-priming pump, with a hydraulic efficiency of 70%.

Since installation, operators have observed a continued increase in the dissolved oxygen level and have seen COD fall by 50%, even though the higher level of mixing was re-suspending settled solids, which became more bioavailable to colony-forming units.

Trebley and the Bega Cheese crew are happy with the ever-increasing levels of dissolved oxygen, the reduction in COD and their odour-free lagoon. The wastewater and maintenance teams are also pleased that monitoring and maintenance can be done safely, without the use of cranes, boats or winches.

Above: the lagoon two weeks after the installation of the Venturi Aerator. Ripples from the aerator that radiate to all parts of the lagoon ensure a good level of mixing.