THE MAGAZINE FOR THE DRAINAGE, WATER & WASTEWATER INDUSTRIES
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considerable investment that was already being made to develop the future for effectively cleansing sewers.
This raised a very important question: “Will localised reactive High Pressure low volume mains water Sewer Jetting provide a sustainable solution for the future?” The findings that lead to this question are outlined below:
Carefully considered trials were designed to allow the build up a head of water and to release the attenuated flow as rapidly as possible triggering a surge flow. This “Tsunami” passed down from the upper extents or intermediate points of a catchment, flushing all in its path. Multiple flushing was undertaken to enable us to consider the benefits of performing this on a repeating basis with the objective of achieving a sustainably clean sewer.
It became apparent very quickly, that this technique delivered capabilities and benefits that far exceeded any other solution being used or considered at the time. On the very first release of flow, conducted within a large sewer with a smaller diameter outlet, which provided a perfect opportunity to observe the resulting surge, this removed literally tons of Fats Oils and Greases. Also, sedimentation which although less visible at the time, became apparent during subsequent investigations. The benefits downstream were also considerable with results of the discharge observed many miles downstream when the FOG’s reached the ultimate Sewage Treatment Plant. Subsequent surcharge and flush cycles continued to deliver outstanding results but with each flush visibly removing less and less. This demonstrated a need for these operations to be performed regularly to prevent the significant accumulation and resultant load if these methods were only conducted periodically.
But let’s be honest, there were clear limitations!
It was clear to all that the mechanism used to perform these surge releases of flow were far from ideal. Manually operated Penstock Valves. These are only sporadically located around any catchment. They are typically poorly maintained and as a result difficult to operate. We were fortunate that we were able to use air powered wrenches, to open and close these substantial gate valves more effectively than would normally be possible. But even so, the speed of closure and more importantly of release was extremely slow, reducing the initial wave effect of any surge release. The upstream catchment also had to be observed carefully to ensure that surcharge levels were effectively monitored, and no localised flooding occurred. This was a labour intensive, high risk and clearly an unsustainable future model for use within the sewer network generally. However, it demonstrated a clear need for an alternate
FOLLOW US
method to be considered which delivered automated and repeating Flushing releases of high volume, low-pressure effluent.
Short term disappointment, followed by…?
The cleansing review commission was concluded, the subsequent report submitted and surprisingly no follow up effort was given to invest in looking for a potential solution. Investment was however made on mobile robotic systems, which were extensively trialled but eventually failed. Thereafter a significant increased investment was made in Operational Expenditure as more and more outsourced reactive cleansing was performed using Pressurised Water Jetting. The increasing prevalence and awareness of Fatbergs once again was dealt with by high cost, labour intensive and highly dangerous manned-entry removal.
Health and Safety risks but were they disregarded?
We had during the trials notified our clients about the considerable danger that manual removal methods and the risks to those who perform the work can encounter. Not only is it potentially harmful to health as a result of inadequate PPE and the digestion of water vapours and the release of harmful gases trapped with the FOG and sedimentation. But also, where total obstructions occur, a head of effluent can accumulate behind the obstruction. On one particular occasion, the partial removal of the significant Fatberg in
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