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SMART-Plant points way to circular economy

European wastewater experts have worked together to open seven pilot plants which demonstrate technologies which could help make the circular economy a reality

The Resources

Sewage contains a lot of material that can potentially be recycled. It is estimated that each year, the wastewater from a single person in Europe could provide 6kg of cellulose, 3.3kg of biopolymers, 0.9kg of phosphorus, 4.6kg of nitrogen, 12.8kg of methane, 9.1kg of organic fertiliser and 91 cubic metres of reusable water.

- Most of the cellulose present in wastewater comes from toilet paper, which is 80% cellulose. Removing it from the wastewater stream at the first opportunity improves the efficiency of the rest of the wastewater treatment process, as well as giving a product which can be sold to make plastics, construction materials such as asphalt.

- Phosphorus is one of the nutrients that can be recovered using the new technologies, and can be used to make fertiliser. European utilities are under pressure to remove phosphorus from wastewater to help meet stricter environmental water quality standards in watercourses resulting from the Water Framework Directive. However, there is also an ecological imperative to recover P, which is a finite and diminishing resource.

- Biopolymers, or polyhydroxyalkanoates (PHA) are linear polyesters created in nature by bacterial fermentation, and are valuable as alternatives to using petroleum in the production of plastic. Bioplastics created in this way have the big advantage of being biodegradable, as well as being less carbon-intensive, meaning they are in demand for a host of eco-friendly products. One of the UK-based partners in the SMART-Plant project is EcoDek, which makes environmentally-friendly composite decking boards.

- Methane extracted from sewage as a result of anaerobic processes (biogas) can be used to generate energy, making the entire treatment process cheaper and using less fossil fuels

by James Brockett

Wastewater treatment innovators from across Europe are jointly helping the sector take steps towards the circular economy in the EU-funded SMART-Plant research programme.

The 4-year project, which is funded by the Horizon 2020 EU innovation fund, is a collaboration between 25 partner organisations in 9 countries, including Severn Trent Water, Cranfield University and Brunel University in the UK. It is exploring how technologies that recover valuable materials from wastewater can be retrofitted into existing sewage treatment plants and optimised so they perform well at scale. The recovered materials – which include cellulose, nutrients and the biopolymer PHA – are then being formed into marketable products such as bioplastic and fertiliser.

One year into the project, it has made significant progress, with seven pilot plants featuring different technologies either operational or about to open. These plants – situated in the Netherlands, Israel, Spain, the UK, Italy and Greece – will provide ample evidence for how utilities might convert their wastewater treatment sites to become resource recovery plants, with outputs which benefit agriculture and the chemical and construction industries, as well as generating energy and decreasing the cost of their own operations.

This is in keeping with the vision of the circular economy, making the most of resources which will become scarce over time, explains Pete Vale, Technical Innovation Lead at Severn Trent, which is one of the partner organisations in the project.

“The linear economic model where we ‘take, make and dispose’ of things is not sustainable – it relies on large quantities of cheap, easily accessible materials and energy,” says Vale. “In contrast, a circular economy is one that keeps resources in use for as long as possible, then recovers and regenerates products and materials at the end of each service life. In the water industry, we can play an important role in the emerging circular economy - we receive huge amounts of ‘waste’ water that is full of material that can be recovered and regenerated.”

All the technologies in the project are proven, but the large pilot scale installations will reveal a great deal of useful information about how they can best be deployed and combined in order to give the best value, he adds.

Many of the technologies also have multiple benefits. For example, upstream cellulose recovery reduces the load experienced in the main activated sludge plant, so it not only gives you usable cellulose, but makes the whole wastewater treatment process more efficient. Tertiary nutrient removal helps meet effluent discharge standards as well as giving nutrients that can be used for commercial fertiliser; and the anaerobic treatment of sewage makes for a cheaper treatment process at smaller plants while also providing energy-producing biogas.

While European utilities may initially adopt individual technologies involved in the project, the thinking behind the programme is that in time they will want to use them in concert, with operations that make the most of multiple resources.

The Processes

The SMART-Plant project involves seven material recovery techniques which can be applied to existing wastewater treatment plants, each of which is being demonstrated through a pilot system which is either fully operational or about to launch at a live sewage treatment site.

SMART Tech 1 is cellulose recovery, through upstream dynamic fine-screen and post-processing of cellulosic sludge. Cellulose is a key ingredient of toilet paper, so is present in large quantities in sewage; the cellulose recovered can be used to make bioplastics and construction materials such as asphalt. Suitable for cellulose harvesting at medium or large wastewater treatment plants, the process works using a fine dynamic sieve called a Salsnes Filter, which separates cellulosic sludge from raw sewage; the cellulose is then refined and cleaned by post-processing. It is being demonstrated at Geestmerambacht in the Netherlands.

SMART Tech 2a is the mainstream anaerobic treatment of sewage with secondary biogas recovery, using a polyurethane-based anaerobic biofilter. This process allows for the recovery of biogas from small and medium sized wastewater treatment works which have irregular organic-load peaks, and would not therefore be considered suitable for anaerobic digestion. It works using a biofilter with an innovative polymeric-based immobilisation matrix, which is applied in the activated sludge process. As well as biogas recovery, which can be used to generate energy, the technology results in high COD and TSS removal so the treated effluent can be reused in agriculture. It is being demonstrated at Karmiel in Israel.

SMART Tech 2b is a novel type of biological nutrient removal known as SCEPPHAR (Short-cut Enhanced Phosphorus and PHA Recovery), which is being applied to the mainstream sewage treatment process. It allows for the enhanced recovery of phosphorus and the chemical PHA, which can be used to make bioplastics. The system works via two sequencing batch reactors (SBRs) one for heterotrophic bacterial growth and one for the growth of autotrophic nitrifiers; there is also an interchange vessel and a chemical system for the recovery of P as struvite. The pilot-scale system is being demonstrated at Manresa in Spain.

SMART Tech 3 is the tertiary recovery of nitrogen and phosphorus based on ion exchange. This process, applied to secondary treated effluent, results in the extraction of nutrients which can be used in agricultural fertiliser. It uses two different ion exchange media, with the process optimised to the ideal regeneration cycle to keep the media working. The system has been developed by UK project partner Cranfield University, and is being demonstrated at Cranfield’s own wastewater treatment plant.

SMART Tech 4a is a novel configuration of sludge treatment known as SCENA which allows for enhanced biological phosphorus removal in combination with conventional AD and biogas recovery. In the SCENA (Short-cut Enhanced Nutrient Abatement) set-up, nitrogen is removed through the processes of nitritation/denitritation, and enhanced P removal is achieved through the alternation of anaerobic and aerobic conditions. The output is P-rich sludge and VFA. It is being demonstrated at Carbonera in Italy.

SMART Tech 4b is the same SCENA configuration but used in combination with enhanced AD, which uses thermal hydrolysis pre-treatment. This allows for even greater recovery of P-rich sludge. This is being demonstrated at Psyttalia in Greece (pictured, above left).

SMART Tech 5 is the same SCEPPHAR technology used in 2b but applied to the sidestream sludge treatment process. It enables the integration of conventional biogas recovery from sewage sludge with energy-efficient nitrogen removal from sludge reject water and the recovery of PHA and phosphorus in the form of struvite. It is being demonstrated at Carbonera in Italy.

● Downstream Processes: The resources that are extracted by the seven main SMART technologies (whether they are cellulose, nutrients, PHA or VFA) are then able to be transformed into marketable products by two ‘Downstream SMART Techs’. The first of these (developed by Brunel University in London) uses cellulosic and PHA materials to make biocomposite plastic which can be used in industry, construction or for consumer goods. The second (at Manresa in Spain) consists of dynamic composting which allows the cellulosic and P-rich sludges to be formed into commercial fertiliser or to be enabled to be used as fuel at biomass plants.

Water Company View: "Our mindset is that we are open to recovering as much from the treatment process as we can.”

Severn Trent is one of the UK partners in the SMART-Plant project, and recently hosted the regular update meeting for the 25 partners in the project at its headquarters in Coventry.

Speaking at this event, Bob Stear, Severn Trent’s Head of Innovation, explained why resource recovery is an exciting field for the utility:

“Predicting the future is hard work, but we put concrete in the ground that lasts for 50, 60 or 70 years, so as a company we have got to be good at it. Five years ago, we went on a journey with our innovation strategy where we aimed to focus our efforts on those approaches that made sense whatever happens in the future - plotting a course that would work for the maximum number of possible worlds. We decided then that our strategy was to really go after the circular economy.

“Many of our 1000 wastewater treatment works are small and located in rural areas, but we also have a number of large urban works, and it is here that the ‘conveyor belt’ of the circular economy, recovering resources which can be re-used, really makes sense. We already recycle energy: we have been operating anaerobic digestion plants for more than 40 years, and today, 35% of our total power comes from renewable sources. So the obvious next step is to see what else we can recover. That fits in with our innovation needs document, which contains eight priorities, with protecting the environment being one of those eight.

“Some of the technologies and techniques in the SMART-Plant project are those that we are already know about - we have done a lot of interesting work on phosphorus recovery, for example – but others, such as cellulose recovery, are newer. Our mindset is that we are open to recovering as much from the wastewater treatment process as we can. As an innovation team, with a limited budget, we are only able to invest in a limited number of initiatives at any one time, which is why the consortium approach adopted by SMART-Plant is such a good thing. It’s a great way for us to keep in touch with all the latest technologies that are on the conveyor belt. Some of them will be ready for adoption quickly and some might take longer, but over time this collaborative approach is likely to pay off and we will be in the best position to take advantage.”

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