A 630 m3/d pilot plant was installed at Subiaco WRRF to determine design and operational parameters of a hybrid Modified Ludzack-Ettinger – Membrane Aerated Biofilm Reactor (MLE-MABR) configuration. Two commercial ZeeLung MABR cassettes were installed in series in the anoxic zone and the pilot was fed with primary effluent (averaging COD 601 mg/L, TKN 68.5 mg/L and 17–29 °C). A nitrifying biofilm was developed within 3 weeks and the nitrous oxide (N2O) gas emissions from the MABR exhaust gas proved to be a reliable parameter to assess biofilm development. Both MABRs achieved the average nitrification rate (NR) of 3.7 gNH4-N/m2.d when air flow was 8.6 and 11.2 Nm3/h to MABR1 and MABR2 respectively, which reached a maximum oxygen transfer rate of 17.4 gO2/m2.d. Biofilm thickness was controlled via air scouring and intermittent coarse bubble mixing (90 s on/90 s off). This paper discusses the startup strategy, minimum requirements for process monitoring, impact of different air flow conditions, ORP and mixing patterns on performance efficiency over a 22-week period.

Wastewater management is continually evolving with the development and implementation of new, more efficient technologies. One of these is the Membrane Bioreactor (MBR). Although a relatively new technology in Australia, MBR wastewater treatment has been widely used elsewhere for over 20 years, with thousands of MBRs now in operation worldwide. Over the past 5 years, MBR technology has been enthusiastically embraced in Australia as a potential treatment upgrade option, and via retrofit typically offers two major benefits: (1) more capacity using mostly existing facilities, and (2) very high quality treated effluent. However, infrastructure optimisation via MBR retrofit is not a simple or low-cost solution and there are many factors which should be carefully evaluated before deciding on this method of plant upgrade. The paper reviews a range of design parameters which should be carefully evaluated when considering an MBR retrofit solution. Several actual and conceptual case studies are considered to demonstrate both advantages and disadvantages. Whilst optimising existing facilities and production of high quality water for reuse are powerful drivers, it is suggested that MBRs are perhaps not always the most sustainable Whole-of-Life solution for a wastewater treatment plant upgrade, especially by way of a retrofit.

Achieving and maintaining good biomass settling characteristics is a critical process design objective for any activated sludge wastewater treatment plant (WWTP), whether intermittent or continuous technology. One way of ensuring good sludge settleability in intermittent WWTPs is the incorporation of bioselectors in the process. A bioselector is essentially a small discrete reactor volume designed primarily for carbon absorption, in which activated sludge organisms are exposed to a high substrate concentration for a relatively short time. It is normally very much smaller than an anoxic zone and the activated sludge recycle is only a fraction of that typically adopted in continuous plants. With proper conditioning, recycled biomass rapidly absorbs and stores soluble organic wastewater components before transfer to the main treatment basin. This absorption and storage mechanism, and careful management of aeration throughout the intermittent treatment cycle, plays a crucial role in many subsequent growth and treatment processes, including sludge floc formation, denitrification and biological phosphorus removal. This paper examines some design considerations, and reviews the benefits of bioselectors by reference to the commissioning and initial operation of the new 160ML/d Woodman Point Sequencing Batch Reactor in Perth, Western Australia. The applicability of bioselectors in continuous plants is discussed.

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