Harting sewage spills
Harting Wastewater Treatment Works (HWTW) has a long history of being the sewage works with the greatest number of hours of spillage of untreated wastewater (including sewage) in our area (Buriton did head up that infamous league table one year but their sewage is now pumped to Petersfield for treatment). From November 2024 we have all been able to see when and where these spills are happening on Southern Water’s Rivers and Seas Watch Map, so this last winter we knew that HWTW started spilling in January and kept going (with a couple of short pauses) til late March.
HWTW discharges into Elsted Stream which then joins the Rother in Trotton. ERA contacted both Harting and Trotton Parish Councils to suggest they contact Southern Water and request an explanation of these spills. In short, too much ground water was finding its way into the pipes feeding into HWTW, resulting in more wastewater reaching the site than the site could cope with, but more importantly, more than their permit dictates they have to treat. That made the spills legitimate – as long as the site is treating the amount their permit says that they must then any excess will sit in a storm tank, allowing some settlement to occur, and the residual liquid can then be discharged into the tiny Harting Stream. Neither Parish Council felt this made the situation acceptable and asked for more information. As a result, representatives of both Parish Councils were invited to a site visit at HWTW.
Meanwhile, Barry and I attended the River Rother Partnership Summit, hosted by the Western Sussex Rivers Trust where three representatives of Southern Water were among the speakers. In the Q&A after their presentation I questioned them at some length about the Harting spills last winter, resulting in ERA being offered the opportunity to send some representatives to the planned site visit.
We learnt far more than those initial responses from Southern Water to the parish councils had told us.
The recent development work at HWTW was designed to increase their Flow to Full Treatment (FFT) rate, increasing it more than two-fold from 12 to 27l/s. This is the first of three actions they are planning to reduce their spills rate from this site. When the next heavy and persistent rains come our way they will know if this first action will prove enough to sort the sites ongoing problem with groundwater ingression into the pipework that brings effluent to the site. If not, the second course of action will be to reline the pipes as has been done effectively in the Pan Parishes and the Lavant valley. This would be like a modern and greatly upgraded version of using a sealant akin to Radweld to stop the radiator in your car from leaking. If those first 2 options still do not prove to be enough their 3rd option is to design and create a managed wetland so that what is currently spilled directly into the Harting Stream can be redirected into this wetland which will process the effluent using natural processes. Such wetland is currently the subject of DEFRA trials.
The second option, relining pipework, is complicated by the fact that Southern Water does not own all of that pipework and tracking down the relevant owners and getting their permission can be a protracted process.
We walked the site following the route that the effluent takes during the various stages of its treatment. Follow this link to read more about this. If you are on mains drainage and have flushed a toilet today, or turned on a washing machine, I am sure you will want to know what happens next to all that wastewater.
This article is a follow-up to the one below from 29 July:
Site visit to Harting Wastewater Treatment Works
The recent development work at Harting Wastewater Treatment Works (HWTW) was designed to increase their Flow to Full Treatment (FFT) rate, increasing it more than two-fold from 12 to 27l/s. This is the first of three actions they are planning to reduce their spills rate from this site. When the next heavy and persistent rains come our way they will know if this first action will prove enough to sort the sites ongoing problem with groundwater ingression into the pipework that brings effluent to the site. If not, the second course of action will be to reline the pipes as has been done effectively in the Pan Parishes and the Lavant valley. This would be like a modern and greatly upgraded version of using a sealant akin to Radweld to stop the radiator in your car from leaking. If those first two options still do not prove to be enough their third option is to design and create a managed wetland so that what is currently spilled into the Harting Stream can be redirected into this wetland which will process the effluent using natural processes. Such wetland is currently the subject of DEFRA trials.
The second option, relining pipework, is complicated by the fact that Southern Water does not own all of that pipework and tracking down the relevant owners and getting their permission can be a protracted process.
We walked the site following the route that the effluent takes during the various stages of its treatment.
On entry to the site the effluent passes through inlet screens to remove ‘rag’, that being tissue, wet wipes (which we all know almost always contain a plastic skeleton) etc. At this point consolidated fat is also scooped out – cooking oil should never go down the plug hole! If we all only flushed away the 3Ps, poo, pee, paper, there would be much less work for the inlet screening process, reducing Southern Water’s processing costs and with the potential to even reduce our bills. These solids are then compressed to remove liquid and collected in a skip for later removal from the site.
As the effluent leaves the inlet screen the Flow to Full Treatment rate is measured. Should this ever reach 27l/s then the excess flow (above 27 l/s) gets diverted to the two storm tanks as that is the maximum FFT that the site can now process. Since the new higher FFT rate of 27 l/s came online this has not yet happened, due to very little rain, but as we generally now get heavier more prolonged periods of rain due to climate change, this is the eventuality that they wish to test out to see if further measures will be needed. When the storm tanks are full, and the treatment works is processing its maximum capacity (as defined by the sites Permit) discharging of untreated effluent, ‘spills’, occur. The Event Duration Monitors (EDMs) record the occurrence and duration of these spills. Sometimes these recorded spills prove to be ‘not genuine’. The EDMs use a sonic scanning system which can be fooled by something like a spider’s web covered in dew, giving a false reading that later gets classified as not genuine.
Treating effluent that is heavily diluted by rainwater is a longer process as the bugs that do some of the work are less effective on this diluted liquid, preferring the more concentrated wastewater.
As an aside we learnt that pre-privatisation most of the coastal sewage was not treated at all, but simply released into the sea. One of the reasons for going private was to access the funding to bring wastewater treatment works online along the coast.
Ferric dosing is the next step for effluent on its journey through the treatment works. This is a method for reducing the phosphate levels in the sewage. Compulsory target levels for phosphates in the final affluent leaving the treatment works are set for each site by the Environment Agency (EA) with target levels recently being reduced for some sites, including Harting. Levels of 0.1ppm in a waterway are enough to have the potential to cause environmental damage. The Southern Water (SW) staff were clearly proud to tell us that they have been compliant with the new, lower target of 0.7 mg/l (annual average) since it came in. All of these targets are laid out in the site’s permit and we were told that the SW culture is very much ‘Not just meeting the permit, but beating the permit’. The EA is increasing the number of checks they make on such sites and Harting had an audit this last May.
The effluent then sits in settlement tanks, allowing sludge to amass at the bottom of the tank. Part of the recent development at Harting was to increase the number of settlement tanks. Currently the sludge from these tanks is tankered away to an offsite SW facility to be dried and processed so that it can be sold to farmers for use on agricultural land, although not on land being used to grow food for people. There are strict regulations around its use. It is, however, used for growing crops, presumably predominantly for animal feed. Around 87% of treated sludge in the UK is recycled to agricultural land as a soil improver. Strong opinions were expressed by some of those on the tour that this practice is not good for the soil given that the sludge contains microplastics (not to mention nanoplastics) and PFAS (‘forever chemicals’). The Independent Water Commission, chaired by Sir Jon Cunliffe, is reviewing the water sector regulatory system in England and Wales, with their Full Report due out summer 2025, and is expected to comment on both sludge management and water abstraction, both have significant impacts on the water environment. If the sludge did not go to agriculture an alternative use/destination needs to be found for it. We were told that there is research ongoing to find an alternative solution to the sludge issue, but that the infrastructure to bring this online could easily take a decade to become a reality.
The whole process we were being shown is driven by regulations imposed by government. SW would not be allowed to spend a small fortune on any innovation that addressed an area where they had not been given a clear directive to reduce/change some outcome of the process. If we want SW to stop selling sludge to farmers we have to exert pressure on government to bring in regulations to that effect.
After time in the settlement tank the effluent is moved on to other tanks for biological treatment. These tanks contain clinker and are where the bugs mentioned earlier are at work removing the ammonia from the urine in the effluent. These are the circular beds with rotating arms spilling the effluent on to the clinker bed. Air is provided through ventilation through these beds to introduce oxygen to aid the process. At Harting the recent development work increased the sites capacity at this part of the process too.
Some treatment works now use activated sludge tanks to achieve the same thing with these being smaller but more expensive, in these systems air is pumped into the treatment process.
The next part of the process is the humus tank, involving more settlement and removal of residual solids, which then are returned to an earlier stage of the process to go round again.
A final treatment involved moving, aerated sand filters, designed to remove any final solids to EA regulation levels. This piece of equipment was gurgling in the background throughout our visit.
Before the effluent can be discharged into Harting Stream it is passed through copa sacks which provide the regulated 6mm x 6mm filtering that is required before discharge. These sacks are replaced weekly. Even releases of untreated effluent from the storm tanks must go through copa sacks. This is why any sighting of ‘rag’ (tissue, wet wipes, visible sewage solids etc.) in any waterway must be a significant pollution incident as it should never routinely occur and require immediate reporting to the EA, even spills of untreated sewage following significant rain should never include rag. We discussed with the SW staff how the permit levels are set up by the EA and being based on the dilution capacity of the receiving river. If the river levels are low then the discharge will, of course, not be so diluted. With climate change, drought conditions may cause rivers to be more polluted even when permits are not breached.
Anything caught in the copa sacks is taken from the site in skips along with the initial screenings. Sludge from the settlement tanks leaves the site via a tanker.
Some other wastewater treatment works use UV light to kill pathogens.
Before the fully treated effluent leaves the site, levels of iron, phosphorus and ammonia are checked. A continuous record of these readings is automatically kept and will be checked periodically by the EA. For iron and ammonia there is a top limit (upper tier) that must never be bridged and another ‘look up table limit’ which has to be passed on a 95%ile compliance basis, if a site is sampled 12 times a year two failures of any LUT limits are allowed. However, with phosphorus the target is an annual average target, meaning that high levels are permitted as long as they average out OK with lower levels at other times.
The EA has set a target that by 2050 a maximum of 10 spills (storm overflow discharges of untreated effluent) per year will be allowed, but that seems rather far distant. The number is calculated using a ‘12/24’ algorithm. If an outflow takes longer than 24 hours then each 24 hour part of the outflow counts as a separate spill. Conversely, if multiple brief outflows occur in a 12 hour period then they only count as one with respect to the annual total. So, if more than 10 days in total of outflows occur in a year then the annual target will definitely be breached.
South Harting has a flow meter installed which allows them to know how many litres of untreated sewage have been released. Not all waste water treatment plants have such a meter. However, the volume of untreated outflows is not published, just the number and duration of outflows.
If an event duration monitor (EDM) is not working then it does not record any spills, whether there has been any or not. We were told that ‘the current system for making spills data publicly available requires Southern Water to record when an EDM is not working’.
We questioned why there was one incident last winter which had been self-reported by SW to the EA, as it sounded a bit concerning. This particular case was when there was a pump failure, and consequent spillage, from one of the sand filter tanks. SW explained that they are actually incentivised to self-report issues by the EA, to improve public trust.
One of the attendees from Harting Parish council was concerned that the newly expanded site would have sufficient capacity to handle the added load from Uppark, and from newly built houses. SW said that Uppark is now being included and there have been no untreated outflows yet. Water companies have a statutory duty to accept domestic flows from new developments.
This site visit took place because both Harting and Trotton parish councils had written to SW when ERA made them aware of the near continuous release of untreated sewage from HWTW from January to March this year. The PCs had received replies that they felt to be unsatisfactory and a site visit was then offered. If those initial responses had included an outline of the development work at Harting and its expected impact then I suspect that their concerns would have been assuaged . . . but then we would not have had such an interesting and informative site visit!