Using sound to predict flow rate of leaks in pipes

It's not surprising that leakages in water distribution systems is a worldwide issue with many consequences. These include the money required to fix leaks, the potential for contaminants to enter the water distribution systems, and the environmental impact of wastewater pipe leaks. Leaks can be found through a method called leak noise correlation, where sensors are placed to record and analyse the sound emissions from the leak. This method is widely used to find locations of leaks already, but the sensors record data that could potentially be used to find out the leak’s flow rate. Being able to predict flow rate could help those managing these systems to prioritise repairs based on flow rate. However, no reliable method has been found to predict the flow rate of a leak in distribution pipes using sound emissions. 

Joseph Butterfield, a STREAM researcher, set out to find a way to predict leak flow rate using leak noise correlation. The study aimed to predict the leak flow rate in medium-density polyethylene pipes using sound emission signals. The novel method involved four circular holes of different sizes being tested at several leak flow rates. 

The study was able to accurately predict the leak flow rate, regardless of the area and with no prior knowledge of the area. This shows the potential of this technique being used to assess and prioritise leak repair. As this was the first study, there would need to be much more testing, but now there is a first base case in leak flow rate prediction through sound emissions.

There were also attempts to predict leak area using this model. When contaminants enter water distribution systems through leaks, the leak area influences the level of contamination, and therefore development of this method could prove useful in judging the risk of contamination and therefore the threat to public health. Even further development of the use of leak noise correlation could include using it for detecting locations, flow rate, and leak area simultaneously.

Full article: Prediction of leak flow rate in plastic water distribution pipes using vibro-acoustic measurements, JD Butterfield, V Meruane, RP Collins, G Meyers, SBM Beck, Structural Health Monitoring 17 (4), 959-970

Full-scale Metaldehyde removal via biodegradation

It is a well-established fact in the water treatment industry that polar, low molecular weight pesticides are very difficult to remove from water using conventional methods. One of the main examples of this is metaldehyde, used frequently in slug pellets. It often seeps into water supplies after rain, so contamination is hard to avoid. As a result, metaldehyde is responsible for most of the pesticide-related drinking water failures in the UK. Whilst biological treatment is often effective against micropollutants, only some operational biofilters have be able to remove metaldehyde. Due to the minor role of the other methods used, biodegradation is likely to be the main removal pathway for metaldehyde. 

STREAM researcher Catherine Rolph monitored and assessed the biodegradation in an operational slow sand filter. The long-term data showed that the degradation of metaldehyde did improve when the inlet concentrations increased. Active and inactive sand batch reactors were compared, and that showed that metaldehyde removal happened mainly through biodegradation. 

The removal rates were greater if the biofilm was acclimated through high metaldehyde concentrations – there was a 40% increase in metaldehyde removal in acclimated columns compared to non-acclimated. This suggested that metaldehyde removal was reliant on enrichment, which means the process could be engineered to decrease the treatment times from days to hours. It is also important to note that this increase was sustained for more than 40 days, with an average of 80% removal, reducing metaldehyde concentration to be compliant with the approved levels. The study also looked into the microbial makeup of the acclimated and non-acclimated biofilms, and the microbial communities were found to be slightly different. This implies that as biofilms become acclimated, the bacteria present changes to be more appropriate for breaking down metaldehyde. 

This study provides a new basis for faster, chemical free, low cost, biological treatment of metaldehyde, as well as other polar pollutants, in drinking water.  Whilst this is a first study into this method, the results imply that this is a promising option after further investigation, especially since it was done at full scale and for more than 40 days.

Full article: From full-scale biofilters to bioreactors: Engineering biological metaldehyde removal, C Rolph, R Villa, B Jefferson, A Brookes, A Choya, G Iceton, F Hassard, Science of the Total Environment