Bug hunting beyond chlorine

Chlorine has saved countless millions of lives and it continues to perform humane miracles to this day. But it is effective because it is indeed a killer. Not only can chlorine create carcinogens after reacting with organic compounds in water, as anybody who has dipped into a municipal swimming pool will know it does not taste or smell that nice either. Many people do not like the taste of heavily chlorinated water, making household filters and even bottled water increasingly attractive in markets such as the USA. In the background are a body of data assembled by institutions such as the US Environmental Protection Agency suggesting that too much exposure to chlorinated water is potentially harmful to for example, pregnant women. This has been grabbed with aplomb by lobbyists for every cause, but it leaves us with one great question – how do we deliver water that people can enjoy drinking and can trust, at a fair and attractive price?

Going forwards to a post chlorine drinking water takes us back to water treatment’s roots. Sand filtration is a great way of cleaning up a water stream before using UV. Slow sand filters have been used for treating water since the days of the Egyptians, with small plants used across the medieval world and for a town for the first time in Paisley in 1804. In 1829, the first large scale facility opened, serving the Chelsea waterworks company (now part of Thames Water) in 1829. During much of this time, it was assumed that diseases were transmitted by ‘miasmas’ in foul air and the sand was simply making the water more pleasant to drink.

Sometimes water engineering is a triumph of hope over reality. Leafing through the water treatment literature, you are assured that each technique will blast all bugs into oblivion, with clear sterile water coming out the other end. For example, while Ultra Violet disinfection is a powerful way of finishing off water or wastewater treatment it is only as good as the fluid that you treat and when suspended solids remain, they create a shadow behind which pathogens can survive.

Today, with our fuller understanding of infections and impurities and how to deal with them, sand filtration has much to offer when it comes to removing particulates from treated water. But sand filtration was not called ‘slow sand’ without reason. Even in modern ‘rapid sand’ units the flow rate can be low and the maintenance needs can be high.

BlueWater Bio acquired Filter Clear in 2011 to expand its range of offerings in water and wastewater treatment. Filter Clear’s forte is to minimise contaminant build up so that the units operative life is maximised, while being able to maintain a flow rate which is appreciably higher than seen in slower sand filters. Unlike sand based filtration systems, an internal self-cleaning backwash system cuts back on the downtime needed for cleaning. Even so, the system can retain particles down to 0.5 to 1.0 microns compared with 3.0-10.0 in competing technologies, which minimises the size and concentration of suspended solids remaining in the filtrate.

So, using a Filter Clear unit as a pre-treatment for UV, micro-organisms can run through the water, but they cannot hide. The process removes particulates from the water, giving the UV a free run to eliminate all the contaminants and minimising or removing the need for any post treatment chloride.

Wastewater mining

The nutrient crunch is not a headline grabber, but it ought to be and it is something we are going to learn to get pretty concerned about.

Wastewater used to be seen simply as a waste, something to be treated and disposed of. It is nothing of the sort – it is a vital and under-appreciated resource. Apart from the water that can be recovered, it is a source of increasingly scarce nutrients and contains significant amounts of embedded energy.

From 1450 to 1850, London’s dung was carted to sewage farms, where it was spread, untreated on the ground. It was a brutal job (the carters were well paid, but tended to die young) which provided fertiliser for farms supplying the city. In the 1850s the Guano trade blasted the sewage farms out of use, which was probably a good thing at the time. It meant on the one side a safe source of nutrients and that sewage treatment was taken seriously as an alternative to dumping raw effluent on farmland.

At its peak, the Guano trade saw 100,000 dry tonnes of fertiliser being imported to Britain every year. It has been taken over in turn by other sources of phosphorous, nitrogen and potassium, but none of these sources are likely to last for much longer given the rising demand for food worldwide.

The real problem is that when nutrients are washed out into rivers and seas not only do they harm these habitats but they cannot be beneficially recovered. The nutrient cycle is different to the water cycle – there is no vast sea of nutrients that can be mobilised each year and replaced on the ground. For example, the natural rate of airborne nutrient deposition on a cleared site such as a former clay pit is such that it takes approximately 100 years before there is a nutrient build up enough to support ‘non-leguminous woody shrubs’ as I was taught as a young Environmental Biologist at university thirty years ago. Clearly, it is a fact that has stuck in my mind and it shows just how dependent we are on securing nutrient supplies to optimise agricultural productivity.

The more intensive the agriculture is the more nutrients are needed, even is genetically modified crops become more broadly socially and politically acceptable. Whichever way agriculture evolves, it faces the task not only of feeding the currently hungry, and meeting the challenges of affluence and dietary change, there will also be a further two billion mouths to feed by 2050.

So it is time to take a modern look at nutrient recovery from wastewater. This means going as long way beyond applying post treatment sludge to land, let along the sewage farms of old.

Properly applied, recovering nutrients from sewage can account for a significant amount of what is needed for crop growing. Most of the nutrients are in fact in urine, rather than the sewage sludge so you need to be able to get all of those nutrients out of the combined stream in a recoverable form.

Bluewater Bio’s Hybacs plays its part in realising the potential benefits wastewater has to offer us. As part of its high BOD removal rate, the SMART system is geared towards nitrogen and / or phosphorous removal, creating a post treatment sludge which is well suited for recovering these nutrients as well as ensuring more efficient water and energy recovery.

Written by Dr David Lloyd Owen – Senior Advisor at Bluewater Bio