A recent upgrade to a sewage treatment plant highlights the long-term benefits investing at the capital stage can offer.


The Mornington Peninsula has long been a favorite holiday destination for residents of Melbourne. It has a permanent population of around 125,000, which can double during summer. The Boneo wastewater treatment plant serves most of the Peninsula and was upgraded by South East Water (SEW) to better handle the peak summer loads.

Due to higher than anticipated growth, SEW predicted that the plant would overload in the summer holiday period of 2015. SEW engaged UGL to design, construct, commission and maintain a major upgrade at the Boneo sewage treatment plant (STP). Duplication of the plant was not practical as the existing plant could cope with the load for 11 months of the year, so the upgrade was tailored specifically to handle the summer peak loads. Capital expenditure had to be minimised and the solution had to be installed without disrupting the existing plant operation.

The first action was to increase the air capacity in the plant. There was an initial preference to duplicate the existing positive displacement blowers as it was straightforward and standardised spare parts and maintenance. However, UGL performed a whole of life cycle cost calculation against HST compressors. The capital investment was higher, but the payback period was calculated at just over one year of operation. In addition to the energy savings, the maintenance requirements, noise levels and footprint of the HSTs were superior to the existing blowers.

The upgrade included two Sulzer HST turbocompressors. The HST20 is an integrated package. The turbocompressor is designed for ease of installation and operation, with an inlet silencer, an outlet silencer and a silenced blow-off valve incorporated into the cabinet. Complexity is reduced, along with the cost of installation. The new HST turbo compressors offer energy savings of approximately 33 per cent compared to the existing positive displacement blowers. Modifications to the system have subsequently been made so that the HSTs can supply the old diffuser system. This allows SEW to benefit from the efficiency gains of the new blowers when the plant is in normal operation.

The second phase was to install additional aeration equipment. Several options were analysed. The existing diffuser system functioned well, but duplication of the system was not possible without taking the bioreactor offline and demolishing some concrete baffle walls. The solution was to install four submerged Sulzer OKI aerators, two in each bioreactor, to cater for the peak periods. The OKI units were ideal for this application as they can be installed, moved and removed for maintenance without taking the bioreactor offline.

Key customer benefits included:

  • Reduced footprint, noise and maintenance costs. Nearly maintenance-free operation.
  • 33 per cent reduction in energy consumption compared to previous blowers, which is real direct LCC savings for SEW.
  • Magnetic bearing technology allows the HST to run alongside PD blowers.
  • Easy installation of the OKI units – no fixing to the floor is required.

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