A partnership between Bega Cheese and Hydro Innovations resulted in a 50 per cent fall in chemical oxygen demand and increasing dissolved oxygen levels at its Strathmerton plant in Victoria. This article was first published in Food & Drink Business September/October 2020.
The existing wastewater system consisted of a DAF unit, which flowed into an aerated lagoon. The effluent was then stored in two non-aerated lagoons during winter, before irrigation in summer. Surface aerators were needed to keep the chemical oxygen demand (COD) down and reduce odours in the aerated and downstream non-aerated lagoons.
As the ageing aerators failed, cranes and/or boats would have to be deployed to access them. It was an expensive process that also caused damage to the dam liner.
Bega contacted Hydro Innovations about its “bank-mounted” Venturi-Aeration systems. Mounted on the banks of lagoons, these use a self-priming pump to draw water from the lagoon. The pump discharges water under pressure through the Venturi-Aerator.
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.
Hydro Innovations showed that with the right pump, oxygen transfer efficiency (OTE) for Venturi-Aeration units can be as high or higher than 1.86kgO2/kWh, making them as at least as efficient as surface (floating) technologies.
The aerated lagoon contained 45ML of effluent, with in-flows from 80-120ML per year. This required a 150mm Venturi-Aeration unit, paired with a Gorman-Rupp V6A60-B self-priming pump, which has 70 per cent hydraulic efficiency.
Since installation, Bega has seen a continued increase in the dissolved oxygen (DO) level, and COD fall by 50 per cent even though the higher level of mixing was re-suspending settled solids, which became more “bioavailable” to the CFUs.
Bega is happy with the results and its odour free lagoon. Maintenance can also be done safely, without the use of cranes, boats or winches.