Dale Foster, Business Development Manager with leading wastewater technology specialists HUBER Technology UK, takes a look at how new build solutions afford the water companies a better opportunity to meet demanding timescales and tough regulatory targets in AMP8 to deliver speedy improvements to CSO infrastructure - and also keep costs down in terms of both time and money.

Dale Foster - The wastewater companies are facing demanding regulatory targets to improve their existing CSO infrastructure within very short timescales in AMP8 – so what factors do they need to take into account when they’re weighing up the benefits of using new build solutions compared to retrofit options?

From our point of view we are always solution-agnostic when it comes to advising our customers – it has to be what is most suitable for the job in hand. However, increasingly we’re finding that a new build approach to fit powered storm screens to CSOs works better than retrofit. And when we outline what both involve, customers are very quick to take on board the considerable advantages new builds offer.

Let’s start with the benefits powered screens offer over static non-powered screens. Firstly, some water companies won’t consider putting static screens on any flows above 150 litres a second. For what reason?

After every stormwater spill operators are supposed to go out and clean the screens because they are only capable of a certain proportion of self-cleansing - and if it's a long duration storm they can frequently get overwhelmed as a result. So then somebody has to go and hose them down and clean them, which in itself involves significant operational expenditure. However, in situations where a decision is made to fit static screens to deal with spill flows of up 400 litres a second, it’s not always clear how these OPEX costs get factored into the process.

When it comes to the whole life cost issue, it can often really be a massive false economy in terms of ongoing costs, maintenance, taking equipment out of action and so on. More importantly, in my opinion it is most definitely not a quick fix, it’s something requiring constant intervention otherwise are we really addressing the issues of aesthetic pollution that the public have quite rightly latched onto?

So for instance, deciding to pursue a policy of upgrading screens in CSOs via retrofits in order to shave a few million pounds off the budget, in reality might result in finding out once investigation work has been done a powered screen simply can’t be fitted into the existing chamber, which means that either some construction work needs to be done to modify the chamber or failing that, a complete new build chamber is needed.

So while a significant proportion of inquiries we are getting might be for retrofits, we always take pains to explain to the customer what this will involve – and how the new build solution might ultimately be the better option.

It might be that previous baseline costings for AMP6 or AMP7 retrofit projects are influencing current thinking on upgrading CSO infrastructure in AMP8?

At the moment we’re finding there appears to be two schools of thought. When you look at the new builds, everybody appreciates that if you can standardise on screen sizes and screen chambers and spill flow volumes, the economies of scale will come. However, there is no understanding of what those economies at scale will look like.

There also appears to be a lack of understanding of how new build can help to accelerate the process needed to deliver and implement the demanding AMP8 programme the water companies are now facing. PR24 included delivery dates set for the end of AMP8 for 93% of storm overflow improvements.

Standardisation around new build solutions offers visibility for both the water companies and the supply chain to plan their activities in a timely manner, enabling the water companies to forward procure and suppliers in turn can schedule their manufacturing timetables to meet those requirements. I think it’s probably true to say that companies who can provide their suppliers with visibility in terms of confirmed forward orders will secure priority in that process. My mantra is no visibility, no plan.

It’s important to bear in mind what fitting a screen as part of a retrofit solution for an existing CSO could entail – not least of which is a longer gestation period, beginning with the enquiry stage through to delivery and construction. Retrofits will take longer - we can't build them in advance, unlike new builds where standardisation facilitates this.

For example, we generally start things off with retrofits by looking at the drawings for the original chamber which may well have been in place for decades. In the meantime, the flow rate may have gone up by a factor of x so we need to first establish whether a screen can actually be fitted in the chamber - This requires hydraulic modelling. So while putting a screen in physically is possible in some of these instances, it would affect the hydraulics of the whole network. The presence of services around chambers or the location may also prevent chamber modifications.

Over the course of looking at the retrofit option and getting to the final design, we may well have gone through several iterations considering different screen sizes before the scheme gets the go-ahead for construction. By the time this is completed, it could be 12 months on from the initial enquiry.

In addition, the benefits standardisation delivers in terms of time and cost savings are generally not available because each screen size has to be individually sized for the requirements of that specific site. You might have another five existing CSO sites all with the same size screen, but the iteration process will still be needed to assess the hydraulics for each individual site.

In contrast, new build chambers have already got some built in resilience because of the way spill flows might be banded – effectively slightly oversizing the chambers to gain economies of scale.

For one client we offer just 3 standard wet side screen solutions. Once a spill flow goes above the threshold of the smaller screen this provides a considerable advantage in terms of future proofing their network in anticipation of growing capacity or increased flows. If the projected demand for screens and chambers is realised I feel sure this approach will positively impact on the art of the possible.

At the end of the day, we will always provide our customers with objective and impartial advice on the best solution and if a retrofit solution is what’s needed then we will always recommend that. But we know what regulatory and financial challenges the water companies are facing in AMP8 – they have to tackle a massive workload in a relatively tight timescale. So over the last couple of years, our approach has been to influence the thinking around new build CSO’s.

It’s also worth bearing in mind that some of the existing CSO chambers may have been in place for decades – sometimes maybe 70 or even 80 years – and even if a new screen could be fitted, they will have degraded over that time and are possibly not in great condition.

So while we are there to advise, we also try to explain the benefits having a new build strategy in place offers the customer. Standardisation of screen sizes is key to this – it also enables standardisation of CSO chambers which gives construction companies a lot more repeatability in terms of pilings, form work and so on. It also introduces the prospect of using different materials like composite plastics in chamber construction.

While there will always be a need for retrofits in certain situations, where the company has the opportunity to choose a new build option we would always explain the benefits very clearly. Any clients who are predominantly focused on retrofits will not get the benefits of standardisation i.e. reduced lead times, cost certainty, repeatability etc. Looking ahead in AMP8, they will also miss the prospect being able to take advantage of forward procurement and supply chain forward manufacturing capabilities.

To sum up, it’s a bit like buying a rackety old house that you think you can renovate – going down that route can end up being a costly and time-consuming exercise. At the end it may be a costly stop-gap which is still not fit for purpose - and you realise you would have been better off knocking it down and replacing it with something completely new that meets all your requirements. 

Click here for more information about CSOs, combined sewage screens for wastewater treatment at sewer overflows and stormwater discharges

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