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Waste water cycle


 
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Dr Stephen Woodcock, from the School of Mathematical and Physical Sciences at the University of Technology Sydney, sums up how waste water management and treatment can be improved by environmental engineering. Mathematical models can improve the quality of water and environmental cost of waste water management. These mathematical models use applied probability, trying to put boundaries on things which are inherently unpredictable. This is a traditional area of finance pricing (derivatives, options, investment portfolios) to minimise risk but is also applicable to handling volatile systems of waste

 
The City of Toronto’s benchmarking project under the Green Energy Act shows for energy requirements, three of the five exceptionally large ones are related to the water treatment and supply. They completely dwarf many of the city’s major public services in terms of energy demand. http://www.toatmosphericfund.ca/2013/11/06/first-annual-benchmarking-report-on-city-facilities/    

 
One of the by products of waste water is ammonia which has to be removed by a biological process. This process actually encourages the bacterial groups that oxidise ammonia, ultimately getting rid of it. So sewage treatment plants use an amazing mix of physics, chemistry and biology to treat the water, making it is safe enough to use as tap water. There are many variables in such a system. Temperatures change and different substances (influent) get flushed into the system, all of which have to be managed at a micro level. Such complex molecular methods need lab-intensive procedures done by microbiologists. Such bio augmentation is reflected in humans. Some people want to change the bacterial communities inside their bodies by eating products such as certain types of yoghurt in order to improve digestion. The idea is that good bacteria will help aid that process.
Water treatment can work in the same way by getting the right community of bacteria to remove pollutants. The challenge in waste water is to get the balance right in such complex molecular communities. We now have the microbiological tools to really investigate waste water, something which has come about in the last 3-4 decades. About 50 years ago samples of waste water were taken and grown as cultures in lab dishes in order to see these bacterial communities. Then it was realised that this was a biased picture as it was only a small subset of a much larger microbiological community. Ten years ago samples of waste water that yielded 200 individual bacteria were used to characterise that waste water. Now tens of thousands and even millions of individual bacteria can be identified in samples, resulting in huge datasets (gigabytes) that have to be handled by mathematicians and statisticians. More recently, scientists have been able to remove DNA to profile what is actually living in those communities. They can be tracked through time to see changes in the influent like domestic and industrial waste or salinity.

 

    
Chesapeake Bay Program illustrates the sheer scale of sewage treatment plants in the developed world. Creative Commons Licence) use credit: Chesapeake Bay Program

 
The entire world uses some 3-4% of its energy on water treatment, a massive amount. In the US, 45 million tons of greenhouse gases are produced in terms of the energy generated to be used in waste water systems. The energy is used to move the waste water around and to bubble oxygen into it, an expensive process. A better understanding of microbiology could reduce this costly use of electricity. Currently waste water systems are 10% more efficient than they were a decade ago but they are still beyond the reach of many countries because they need infrastructure and do not run in a sustainable way given their high energy use. Dr Woodcock sees the future of waste water management as a downsized one that does not rely on expensive infrastructure, one based on the benefits of really understanding complex biological processes. It will be the waste water cycle of the future.

Dr Stephen Woodcock was interviewed for A Question of Balance by Ruby Vincent. Images from Dr Woodcock. Summary text by Victor Barry, 2015.

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