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Sustainable wastewater option

Across Europe, Veolia Water is pioneering many exciting innovations in wastewater treatment. Municipaloperations director Nigel Earnshaw explains how it plans to bring them to the UK as a sustainable bio-refinery

The bio-refineryThe bio-refinery

Historically, wastewater has been viewed as the poor relation of the water industry. However, I believe this is about to change, because Veolia Water (VW) is pioneering a revolutionary concept: the bio-refinery. So what exactly is a bio-refinery?

The bio-refinery brings together the latest wastewater treatment thinking on the following areas: energy generation, energy management, bio-plastics, nutrient recovery and effluent reuse. Building on innovations already successfully implemented in Europe, my team and I are working hard to bring these to the UK. Here I will outline these exciting bio-refinery developments.

VW is a global water and wastewater services provider, serving 71 million customers in more than 50 countries. It operates more than 3,300 wastewater treatment plants (WwTPs) worldwide and invests around £50M each year in research and development.

Much of that research budget is ploughed into the field of wastewater treatment and the investment is certainly bearing fruit, with several VW businesses across Europe having recently developed and implemented new ways to extract maximum value from wastewater. Over the last decade, the price of energy has more than doubled and it is showing no sign of coming back down, which is why energy production from wastewater is such an attractive proposition.

By introducing enhanced digestion processes, wastewater treatment plants can ensure that they convert as much volatile matter as possible into biogas, which can then be converted to electricity through optimised combined heat and power (CHP) engines.

Thermal hydrolysis (TH) offers a very effective way to release and capture the energy in sludge. The technology involved is like a big pressure cooker: the sludge is heated to around 150-190ºC at 6-15 bar pressure, which ‘cracks’ the long chain sludge molecules. This process releases a substantial amount of gas as well as reducing and pasteurising the sludge.

It is a very sustainable solution: some of the off-gas fuels the ‘pressure cooker’ and the rest is used to generate electricity; and the pasteurised sludge is used as a fertiliser. A number of UK water companies have already implemented TH technology at their treatment plants, and many more are moving in this direction. VW is currently investing £14M in a new TH plant at Seafield, Edinburgh, which will generate 80% of the site’s electricity needs.

Co-digestion

Co-digestion is another way of increasing on-site gas yield, thereby enabling large amounts of electricity to be generated. Co-digestion involves adding imported organic wastes to municipal sludge. It has been implemented by Veolia Water’s South Pest treatment works in Budapest, Hungary, which treats wastewater for 300,000 people.

Under the new process, the South Pest plant now receives industrial and commercial food wastes, which it co-digests with sewage sludge. Revenue is being generated from gate fees and existing revenue streams have been enhanced: biogas production is up by 400% and subsequent energy generation is up by 300%.

At Braunschweig, Germany, the Veolia Water plant treats the wastewater generated by 250,000 people. It blends sludge with fats, oils and greases (FOG) collected from local businesses, to improve the plant’s biogas yield. The biogas produced by co-digestion, together with gas extracted from nearby landfill and green waste fermentation, is then used to co-generate 14GWh/a of electricity.

This impressive output means that the site is actually 100% energy self-sufficient. In addition to the energy potential of sludge, the wastewater contains significant amounts of low-grade heat. This heat can be recovered and then put to good use. For example, in Berlin, VW supplies a large IKEA furniture store with heating and cooling from wastewater. The installation consists of a bypass from the sewerage network, a heat exchanger and a heating pump.

The heat recovered from the wastewater through this process provides 70% of the energy needed for heating the premises and 100% of the energy needed for cooling. The installation has also reduced the store’s annual greenhouse gas emissions by 770t of carbon equivalent.

Micro hydropower

If there is a sufficient outlet flow from the WwTP, it is possible to recover the water energy and then use it to produce electricity. VW uses conventional low-head hydro turbines to generate electricity at several of its wastewater treatment works around the world, including three in Europe. The following outputs have been achieved:

Energy management

Real- time measurement of power consumption on key pieces of process equipment is being carried out on Veolia Water’s private finance initiative (PFI) contract at Hatton, near Dundee.

This has three main purposes: by close monitoring of the power used means, process equipment operation can be optimised. For example, it has already been possible to change the operation of the aeration blowers leading to significant cost savings.

Fault diagnosis – for example, high power usage can be an indicator that a pump is about to fail for example. A regular check on electricity consumption is now part of the maintenance regime for the pumps.

Overall process optimisation – a small team of Veolia process experts is building up knowledge bank of the amount of power that different sizes of wastewater treatment plants should theoretically use. By comparing theoretical usage with actual usage it will be possible to spot where a works is using more power than expected. A targeted investigation can then take place.

Bio-polymers

Bio-polymers are the base material for, amongst other things, shopping bags and injection plastic mouldings. VW’s European research and innovation team has been working to develop new methods for producing and then extracting bio-polymers from wastewater.

Having proven the concept, the team is now working with global chemical companies to commercialise the process. This is an exciting new potential revenue stream for wastewater, because it is anticipated that bio-polymers will offer a sustainable and economically viable alternative to petroleum-based plastics.

Nutrient recovery

Wastewater contains many potentially valuable nutrients. Phosphate, for example, can be extracted from wastewater and then sold on for use by other areas of industry, providing a great way to reduce the use of scarce raw materials.

As part of its Berliner WasserBetriebe (BWB) at Waβmannsdorf WwTP, near Berlin, Veolia Water has been operating a phosphate recovery plant  for a number of years. The phosphate produced has been sold to the local farming community since 2008.

Veolia is developing further technologies to help remove phosphate in the form of struvite and is currently developing two pilot plants for application across a number of their sites.

Within the current operation, Veolia Organic Recycling focuses on maximising the benefits of organic waste streams for land based projects including farming and land restoration. Veolia Water Organics Recycling is expanding this operation, looking at ways where it can move waste streams up the value chain by maximising the nutrient benefits of these materials.

In the UK, we may well have to look more seriously at water reuse, especially in South-east England, where climate change and population growth are putting ever increasing pressures on water supply.

UK public opinion may not be ready for direct feed from wastewater treatment works outlets into water treatment inlets, but feeds from wastewater works into an aquifer may be more acceptable.

At a time of growing concern about global warming and the state of the global economy, water companies are also having to comply with environmental legislation that is more stringent than ever. This is while they are coming under pressure to reduce operating costs and minimise investment.

But the smart money is on the companies that continue to invest in new, more efficient ways of working. VW is bringing these innovations to its’ PFI sites in the UK under the banner of ‘bio-refinery’.

It is a concept that is sure to transform wastewater from a necessary evil to a valuable new revenue stream.

Nigel Earnshaw will present a paper on the bio-refinery concept at Water NI, which is being held in Belfast on 26 February 2012 www.wwt-ni.net

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