Sewage Treatment

Proven technologies

  • Least whole of life cost treatment solution on the market
  • > 50% lower energy than other technologies
  • Excellent ability to manage peak flow conditions
  • High quality effluent outcomes
  • Ability to integrate reuse application

When it comes to sewage treatment, the technologies provided by The Water and Carbon Group draws upon many decades of national and international experience.  Our team includes partners from several international leaders in specific technologies, including Enexio 2H Water Technologies GmbH (Germany) for Trickling Filters, VA Teknik (Sweden) for distributers and clarifiers, Orbicon (Denmark) for Sludge Treatment Reed Beds, and EPUR Nature (France) for decentralised reed beds.

Whilst our approach is not locked into a specific process solution our core specialisation is modern plastic media trickling filters and various forms of constructed wetland.  These have been successfully employed around the world both on a regional scale and for very large applications.  For example, Trickling Filter at Malmo WWTP (Sweden) processes wastewater from 300,000EP; and the Nimr constructed wetland in Oman is a 750ha in size and treats 115ML/day of oil and gas wastewater.

The simplicity of operation of Trickling Filters and Constructed Wetlands are often incorrectly  believed to be a “lesser” solutions than mechanical processes which have complex control instrumentation, pumps, blowers, membranes and chemical adjustments and require skilled operator to ensure reliability. By using Trickling Filters and Constructed Wetlands we are able to deliver robust secondary and tertiary treatment that are simple to operate with very low energy requirements.

Narrigon WWTP

Peak flow management advantage

One of the key advantages of constructed wetlands and Trickling Filters is that they are able to hydraulically accept much larger peak flows than their formal treatment design capacity.    The benefit is that some level of treatment will be provided for the majority of peak flows through the WWTP, without having to bypass the main treatment plant.

Five applications where the Water and Carbon Group solutions can be considered

Economic Upgrades of Existing Sewage Treatment Plants

Water and Carbon Group
All sewage treatment plants will at some point in time require an upgrade; be it due to aging infrastructure, capacity limitations, or process inadequacies.

The reality of most upgrade situations is the whole sewage plant does not “fail” at once, rather particular modules within the overall process train gradually come under pressure, affecting the how the plant performs. Plastic Media Trickling Filters and engineered wetlands can offer very practical solutions to improving capacity and performance for long-term solutions, without having to rebuild the entire plant from scratch.

Plastic Media Trickling Filters are especially appropriate for any aerobic process with a treatment train, e.g. activated sludge, aerated pond and old trickling filters. They can be designed to handle from several hundred kL/day to many ML/day, with some international systems being designed to handle over 500,000EP of flow. Treatment areas where Plastic Media Trickling Filters are particularly used are in the following processes:

A. Primary aerobic roughing filter (provided screening is <3mm)
B. Secondary BOD filter
C. Nitrification filter

Another low energy technology that can be utilised for WWTP enhancements is constructed wetlands. They are especially well suited to provide effective tertiary treatment and enhanced polishing of effluent prior to discharge or reuse. Wetlands can be designed to achieve very stringent water quality for nutrients, BOD or suspended solids, and can be easily incorporated to the end of the WWTP with minimal impact on existing operational activities while being constructed; an important feature where no redundancy in the treatment train is available to take modules off-line.

An example where the Water and Carbon Group has brought innovative thinking to sewage treatment plant upgrades is Water Corporation’s Narrogin WWTP. The Water and Carbon Group was able to utilise existing primary ponds and secondary clarifiers, whilst replacing the secondary treatment with a BOD removal / nitrification Plastic Media Trickling Filter. A tertiary treatment constructed wetland was also incorporated into the upgrade to remove nutrients prior to discharge to the local watercourse. The Water and Carbon Group approach to upgrading the Narrogin WWTP, saved Water Corporation several million dollars compared to alternative technology upgrades that were also considered.

Read more on our Case Study

Effluent Disposal Schemes

Land based effluent disposal schemes are generally a prefered environmental approach to managing the final treated effluent from a WWTP compared to discharging to natural watercourses.

Where opportunities for land disposal exist, it is important to ensure that the irrigation rates of the effluent are sustainably matched to the soil/climate conditions of a site.

The Water and Carbon Group has horticultural and agronomic expertise that is able to provide the necessary technical assessment and design to support effluent reuse schemes.

A recent project was for the detailed design of a 13ha irrigation forest and 3ha polishing wetland for UnityWater’s 1ML/day MBR sewage treatment plant at Maleny.  That scheme provided a sustainable solution to managing the treated effluent from the sewage plant as well as providing an opportunity to rehabilitate degraded land with a biodiverse rainforest, create a new environmental corridor to connect to the wider ecosystems, and providing a place for community engagement with pathways developed throughout the scheme.

Some of the areas where we can support effluent disposal solutions include:

  • Water balance characterization;
  • Agronomic modelling to determine fate of water, nitrogen, phosphorus and salts (e.g. MEDLI);
  • Wet weather management strategies;
  • On-site soil characterisation for effluent application;
  • Habitat and ecosystem assessment of regional constraints that may affect effluent disposal solutions;
  • Plant selection of suitable species for treated water characteristics;
  • Irrigation design and installation;
  • Development of multi-value opportunities for irrigation schemes: using effluent to rehabilitate and restore natural ecosystems, provide safe community access areas;
  • Regulatory support, and;
  • Integration of disposal solution with treatment design.

Refurbishment of Waste Stabilisation Ponds

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Waste Stabilisation Ponds (WSP) are the most common form of technology in Australia for sewage treatment.

Although lagoon based systems are simple to operate due to their minimal mechanical components, they often have variable performance (largely due to lack of maintenance) and habour high concentrations of algae that subsequently cause elevated suspended solids and high pH’s in the final effluent.

Constructed wetlands are an effective solution that can be easily retrofitted to existing WSPs to provide a final secondary/tertiary treatment and improve performance.  Queensland Urban Utilities selected this solution at their Heldion and Aratula sewage WSPs where Surface Flow Wetlands were built at the end of the two stage ponds to bring them into consistent license compliance for BOD, SS and pH.  Details about the economic benefits of why Queensland Urban Utilities selected a wetland solution for these upgrades over other technologies were presented in a joint paper by The Water and Carbon Group and Queensland Urban Utilities at the regional AWA conference in Mackay in July 2014.

For some situations, sub-surface flow wetlands (e.g. gravel reed beds) will be better suited for a particular Waste Stabilisation Pond arrangement over Surface Flow systems. Sub-Surface Wetlands generally require a smaller footprint and have less establishment times over Surface Flow Wetlands, however there is a higher risk of blockage if they are not managed correctly and gravel supply can be prohibitively expensive in very remote situations.

The decision on which solution is best suited is determined on a site by site basis considering economic, process performance and logistical arrangements.

Refurbishment of Stone Media Trickling Filters

stone media replacement
Many regional water utilities have poor performing stone media trickling filters over 40 years old. Common issues include overloading, blocking, filter flies, and subsequent poor effluent quality.

A cost effective solution to improving the performance of those systems without having to build an entirely new treatment plant is to replace the stone media with modern high performance structured plastic media.

Replacing the media with structured plastic media will increase the performance capacity by 2-3 times and addresses many of the limitations that are commonplace with stone trickling filters due to the increase in biofilm surface area and air voids within the media that promote aerobic reactions.

Structured plastic media also is self supporting and does not rely on the integrity of the tank to contain the media.

Reuse Opportunities


The ability to reuse effluent for different applications (e.g. watering gardens, parks etc), is largely influenced by the choice of final disinfection used in the WWTP.

It is often wrongly thought that treatment technologies such as Membrane Bioreactors (MBR) are the only processes that can achieve Class A effluent quality. Effluent from a low energy trickling filter/wetland solution can therefore be easily transformed into a Class A+ sewage treatment plant with a suitable final disinfection added at the end of the process train (e.g. sand filter/chlorination/UV).

The benefit of using a trickling filter/wetland solution with an added “disinfection” module is that it is able to achieve the organic and nutrient outcomes for a substantially lower power/operational cost than an MBR or other Activated Sludge based processes, whilst providing the flexibility to treat either all or part of the effluent stream to a quality that meets reuse requirements (e.g. log 6 reduction in virus).