by Ross Tieman
In March this year, Jim Service, the chairman of water supply company Actew Corporation, and councillors from the Australian city of Canberra dutifully drank bottlesof purified sewage water as they unveiled plans to recycle part of the city's wastewaterinto tapwater.Within days, Professor Peter Collignon, director of infectious diseases and microbiologyat the Canberra Hospital, wrote an open letter laying out his concerns about the healthimplications of the scheme.What assurance could there be, he asked, that treatment would remove all disease-causingbacteria and viruses, as well as hormones and pharmaceutical compounds present insewage?It is a good question. As Antoine Frerot, chief executive of Paris-based global waterchampion Veolia Water, observes: "Louis Pasteur said 150 years ago that we drink 90 percent of our illnesses. That is why water treatment was created."Around the world, water companies and their equipment suppliers insist we have thetechnology to render sewage safe to drink but they don't all guarantee they can pick uphormones or unexpected compounds. "This is an area in which we and others are doing alot of research," says Roger Radke, chief executive of Warrendale, Pennsylvania-basedSiemens Water Technologies.Microfiltration through polymer membranes, followed by reverse osmosis throughmembranes can remove even viruses if a small enough pore size is specified, says MrRadke, though to drink the water, you had better then pass it under ultra-violet light to besure to kill microscopic parasites such as cryptosporidium and giardia.But this adds expense. In reality, the level of treatment is dictated by standards that havebeen deemed necessary by regulators for the intended use. And when deployed, ittypically comes at the back-end of the traditional waste-water treatment process.In the case of Canberra, waste water would be treated in the conventional way withchemical and bacteriological processes to remove solids and create water of the quality that is typically released back into rivers around the world.Actew says it is still investigating exactly which processes the water would then undergobefore being pumped into the supply reservoir. It says it would expect to use acombination of micro-filtration and ultra-filtration to remove microscopic particles,contaminants and pathogens; reverse osmosis to remove salts, organic compounds andviruses; and ultra-violet disinfection/oxidation to additionally ensure any trace of organicmaterial is destroyed. A final option is to let the water flow through an artificialmarshland before joining the reservoir.After that, the reservoir water would pass through an existing treatment plant beforeentering the tapwater distribution system.Canberra, like many Australian towns, is short of water because of a drought that hasproved longer, and more severe, than anyone forecast. Last year, residents ofToowoomba, Queensland, rejected proposals for a similar waste water-to-tapwaterscheme in a referendum in which health concerns played a key role. The Canberraproposals could prove equally contentious.Veolia's Mr Frerot says: "To my knowledge, there are only two places in the world wheretreated waste water is gradually mixed into tapwater: the town of Windhoek, in Namibia,and Singapore."In Windhoek, that is because the river is more polluted than the waste water, he says. InSingapore, it is a political choice designed to reduce dependence on supplies fromneighbouring Malaysia and accounts for less than 1 per cent of water consumed.Yet all around the world, city populations consume treated water drawn from rivers thatreceive treated wastewater from communities further upstream. Just as the citizens ofRouen, in France, drink the waste water of Parisians, the same is true in the RiverThames in the UK, the Colorado in the US, and the Rhine in Germany and its neighbours.Without wastewater, these rivers would almost run dry.Treatment prior to drinking is imperative: a 2003 study found the level of hormones inthe River Seine sufficient to change the gender of some of its fish. And a study by theNetherlands government found that using Dutch rainwater even to flush toilets wouldpose a health risk.If we are going to drink treated wastewater, says Mr Frerot, the best strategy, wheregeological conditions permit, is to reinject it into aquifers as happens in Berlin andAdelaide. The soil acts as a natural filter, and the time-lag provides additional water forabstraction in periods of peak summer demand. Man is merely shortening the naturalcycle.Otherwise the most obvious and economically viable solution, he suggests, is to usetreated waste water for industry and irrigation. Orange County, in California, adopted Siemens' micro-filtration and reverse osmosis to treat waste water a decade ago, initiallyreinjecting it into aquifers, and subsequently selling additional supplies to farmers andindustry which covers the cost of the additional treatment, says Mr Radke.In Australia and elsewhere, some towns have a second distribution system for"reticulated" water used by householders for garden watering and washing cars.Meantime, treated sewage water is widely used to supply industry, farms and golfcourses, freeing up "natural" supplies for tapwater. Veolia alone has 100 such facilities inFrance, and others scattered from Honolulu to Durban in South Africa.Degremont, a Suez Environment subsidiary, cleans wastewater from Grasse, France'sperfume capital, to bathing standards, says Degremont chief operating officer RemiLantier, providing water quality guarantees for fish farms downstream.Pumping treated waste water into marshlands and reed beds, where sunlight and plantscomplete the purification, is an option too. But the outfall from even a small town wouldrequire a vast swamp to be effective.The simplest solution for small communities, says Mr Radke, is to buy a Siemens skidmountedmodular unit the size of a small car for a few thousand, or tens of thousands ofdollars, and turn waste water into irrigation quality water by passing it throughmembranes.Degremont's Mr Lantier says companies like his can produce ultra-pure water in whichthe only molecules are H20. He likens the safety issue to that in the nuclear industry,standards are that stringent.Globally, says Mr Lantier, only 45 per cent of the world's collected waste water istreated. The most urgent priority is to treat the 55 per cent released untreated. Of thattreated, 20m m3 a day is recycled about 2 per cent. He expects that proportion to triple incoming decades.Ultimately, says Mr Frerot, the most cost-effective solution to water shortages developingin many towns and cities must surely be to supply such treated waste water for use inindustry and irrigation, in place of the tapwater used today. "That would halve thedemand for natural water," he says. "That is what we should do, before talking aboutdrinking waste water."Case study: Ross Tieman: Ironies stack up in sludge plantThe huge Seine Amont sewage treatment plant, on the south-western outskirts of Paris, isabout as modern as any in the world.It processes the waste water from the homes and offices of 2.4m Parisians, as well as therainwater run-off from a quarter of the city and its outskirts, and is operated through a public-private partnership. The public arm, SIAAP, regroups the sewage treatmentfacilities of the Paris agglomeration: the private arm, Sequaris, involves two SuezEnvironment water companies, Degremont and Lyonnaise des Eaux. The latest expansionand upgrade was completed, at a cost of 500m, only 9 months ago.The plant draws 80 per cent of its energy from the 60,000 tonnes of sludge it extractseach year from the inflows. Much of the energy used helps make the remaining sludge,30,000 tonnes a year into granules resembling instant coffee, or pellets that look likeanimal feed. These have a calorific content on a par with coal, and most are trucked to acement works where they help fire the kilns.Yet for all the modernity and efficiency of the stainless steel and concrete hardwarespread across its 80 hectare site, you wouldn't want to swim in, let alone drink, the waterit releases into the Seine.The quality of that water, says Sequaris plant director Jean-Luc Ventura, pulling out hisweekly testing reports, amply exceeds the standards laid down by European regulationsand the Seine river authority. But the outflow can contain Coliform bacteria and othermicro-pollutants.But there are two other challenges that concern neighbours: smell, and sludge.The Seine Amont plant at Valenton has been designed to resolve both issues. The nearesthuman neighbours, are half a kilometer away.The plant receives its inputs of human waste water and storm run-off via pipes 30 metresbelow the surface. This water can total 600,000 m3 (cubic metres) a day of householdand office waste, and 1.5m m3 of rain run-off. The household waste water contains up to216 tonnes of solid matter each day, the run-off up to 317 tonnes after a dry spell,including dust and dog faeces.The human waste enters sealed pre-treatment tanks, where biological activatorsencourage breakdown of the organic matter. Methane gas produced is collected. Theresidue is fed into covered sludge tanks, where the sediment collects. In the third phase,nitrate is added or removed, as necessary, to complete the biological breakdown of solids.Powerful extractor fans draw off air and pump it through three chemicals baths to removeany smell, leaving nitrogen to be released into the atmosphere.Does Seine Amont smell? Sporadically, as you walk round the site, you catch an odour.The inside of the sludge-drying plant smells like a cow-shed, without the acrid urineedge. If you poke your nose into one of the covered sludge concentration tanks, the smellis pretty overpowering.Before the modernisation, says Mr Ventura, smells from the plant had become "a bigissue for nearby residents". Since, he says with a broad smile: "We haven't had a single complaint for six months."Most sludge is pumped into a new drying plant, where it is heated in revolving drumsusing the methane drawn off earlier, together with previously dried sludge, as fuel. Theresulting product can be burned as fuel or spread dry on fields as fertiliser."Bringing together all the individual operations that are used elsewhere into a single plantis a world first," says Mr Ventura with a hint of pride.Yet there is an irony. Existing regulations regard this treated sludge as a waste product.Suez sees it as a biofuel, but it doesn't attract any financial aid or benefit from inclusionin regimes that would qualify it as a renewable power source.So the cement manufacturer that uses much of it declines to pay, saying it is doing Suezand the municipality a favour by getting rid of it. Mr Ventura and SIAPP site director MrRenard reckon its calorific content alone merits a price of at least 20 a tonne.
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