Based on the above results, the OCF has achieved the design performance requirements with I 00% compliance for H 2S and odour. For mercaptans and DMS, sampling methods were not sufficiently accurate to quantify removal efficiencies specified, although all measured outlet concentrations were less than design levels.
Key Features One of the benefits of the OCF is its compact modular des ign having been co nstructed to allow easy upgrade to a future maximum capacity of 72,000 m3/hr (additional area has been currently reserved for this upgrade) through che addition of bioscrubbers, carbon fil ters and fans. The other benefit relates to the ease of media replacement for any of the vessels. Activated carbon is very effective at adsorb ing contaminants and has been designed for a minimum media life of 12 months. By having four units operating in parallel for the bioscrubbers and carbon filters, media replacement can be carried out relatively easily by caking one unit off line at a time whilst keeping the overall facility operating at the required performance. Another design feature was the dual bed arrangement of the carbon filters which is effectively two filters in one resulting in a substantially reduced footprint compared to traditional single deep bed fil ters. T he bioscrubbers were designed to operate on recycled water (Class B) in addition to potable water. Using recycled water brought rhe obvious benefits of conserving rhe co mmunity's valuable potable water supplies, however it also co ntained enough nutrients for the bacteria within the bioscrubber to function effectively with out the need for external nutrient dosing which is required when potable water is used. Although a dedicated nutrient dosing facility has been incorporated, it is not currently used as pare of normal operation. A furth er consideration of the modular design, and one of the design features that helped guarantee a low WOLC for this plant, was the consideration of future maintenance and renewal activities within the OCF. Considerable discussion centred on optimisi ng design such char almost all of the major process units and ductwork can be removed from site and replaced without having to unbolt anything more than just the adjacent process component. All walkways were constructed of marine grade al uminium and featu red bolted sections char are easily demountable if a vessel beneath needs to be excracred for maintenance or renewal, although most have clear vertical access and can be removed through the use of cranes. One of rhe major reasons for adopting marine grade aluminium for stairs and landings, apart from the obvious corrosion resistance, was the "man-handle-ability" of the removable sections. Attention to chis derail also means that expected rimes for major component replacement is considerably reduced, potentially saving thousands of dollars in environmental costs and fines. T he plant has also been set up such that any process unit can be isolated and/or bypassed while the plant is still on line ensuring compliance with rhe plant's operating license.
procedures implemented resulted in no lost time injuries over the 370,000 manhours worked.
Conclusions The OCF implemented as part of the upgraded Merrimac WWTP represents an environmentally sustainable approach to odour control. This has been achieved through the use of bacteria for the primary odour treatment stage rather than hazardous chemicals, as has been the case for most other large wastewater treatment plants around Australia. Through the use of an integrated design approach by all members of che Alliance, and the implementation of a proven technology, the OCF has successfully achieved the project objectives under budget for che benefit of Gold Coast Water and the co mmunity.
The Authors Gary Finke is Managing Director of Aromatrix Australia Pry Led specialising in the design and supply of odour treatment systems. Email gary.finke@aromatrix.com.au. Peter R Oliver was Mechanical T echn ical Specialist in Gold Coast Water's Asset C reation Department th roughou t this project. He has recently left Gold Coast Water after 18 years and has now joined Aromarrix Australia. Email perer.oliver@aro macrix.com.au. Mark Thomas is a Commissioning Manager with John Holland Water Pry Ltd. Email MA.Thomas@jhg.com.au. Dr Ian Evanson is Principal Process Engineer (Technical Leader, Odour Management) with MWH Australia Pry Ltd. Email Ian.Evanson@au.mwhglobal.com.
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Significant attention had to be given to the disposal of waste fluid (blowdown) fro m the bioscrubbers. Since this waste stream has a low pH, it couldn't just be discharged to the nearest waste stream within the plant as it could potentially interrupt the wastewater creatment process. To address this issue, a new pump station was built with a dedicated delivery pipe to the centre of rhe secondary anoxic stage of rhe bioreactor. This location presented rhe most cost effective discharge point for suitable flow mixing and dilution so as nor to adversely impact the treatment process. Lastly, occupational health and safety (OH&S) was an important issue for all Alliance partners during the project. The OH&S Journal of the Australian Water Association
Water
MARCH 2008 153