Transcription
Marisa Buyers-Basso:
Something that you hear wastewater treatment engineers or professors say, 'wastewater treatment saved more lives than doctors.' Not actively saved lives, but passively saved for sure very, very many lives because diseases from waste were huge.
For much of humanity, for as long as we have lived in cities, life was short..
Diseases like cholera, typhoid and dysentery tore through city populations, spread by untreated waste.
Until Sir John Snow removed the handle from a water pump in Broad Street, London. A pump located at the very centre of a cholera outbreak.
This simple step helped prove the disease was spread through water, not air.
It led to a new approach to wastewater, and the eventual building of modern sewage systems, like London’s, designed by Joseph Bazalgette.
From there evolved a system of wastewater treatment so efficient, we can afford not to think about it.
We flush and forget. But that means that these systems are often overlooked.
Marisa Buyers-Basso:
One of the other really big challenges for wastewater treatment is that people, the public, let's say, isn't always aware of it. And there's not a lot of buy-in. So funding is always a challenge.
Marisa Buyers-Basso:
People understand, you know, why they need to spend money on healthcare and hospitals and things like that and politicians also understand that easily, and it's easy to sell.
Marisa Buyers-Basso:
But why you need to spend money on wastewater treatment, what happens to your waste when you flush it down the toilet—there's not a lot of knowledge around that.
Marisa Buyers-Basso:
It's really unfortunate because it is quite an interesting process when you get down into it as well. And I think that it's something that people are open to knowing about, but for a long time it just hasn't been paid attention to.
Welcome to Engineering Matters. I’m Alex Conacher, and I’m Tim Sheahan. For this episode, we’ve partnered with Egis, to explore how the treatment of wastewater is evolving, with new technologies that combine biology and engineering, and will allow growing cities to handle increasing amounts of waste, within tighter environmental regulations.
Marisa Buyers-Basso is Associate Director of Design and Engineering for Water Technology Products at Dutch consultancy Haskoning. Her career started as a process engineer at the Ringsend Wastewater Treatment Plant in Dublin.
Through her career, she has seen the regulations covering wastewater get tighter and tighter.
Marisa Buyers-Basso:
So really across the board you see that the effluent standards, the requirements for what comes out at the end of the treatment process are becoming stricter and stricter. Environmental agencies are regulating them. They're looking for lower and lower limits. So that's always a challenge and that's kind of going on.
Technology adds to the challenge. New materials like PFAs, used widely in industry, now need to be removed from wastewater, as do pharmaceuticals. This means more treatment processes are needed, on sites with tight constraints.
And bigger cities, with more people, need more clean water and produce more waste.
Marcus Fagan is a chartered engineer, working for Egis in Ireland.
Egis are part of a 3JV [3 party joint venture] with TJOC and Haskoning responsible for design, planning, procurement, and project management to increase capacity from 1.64 M to 2.4 M Population Equivalent (PE) of Ringsend Wastewater Treatment Plant.
Marcus Fagan:
I think in 2024, the figures for water consumption, daily water consumption, I think there are 630 million litres per day. It's the highest on record. I think it's up 40 million liters per day based on Irish Water's figures over last year.
Marcus Fagan:
That's an unsustainable solution at the moment—that's roughly 40% of the flow of the Liffey is used for water consumption. So that's a huge challenge for growth and for housing.
And the same growth is seen downstream, at the Ringsend treatment plant at the mouth of Dublin’s River Liffey, where Marcus and Marisa have been working to increase Dublin’s waster water treatment capacity,
Marcus Fagan:
What we're doing in Ringsend, it's a case of “water in, water out” so we've more water coming out our taps, we're consuming more water so that has to be treated. So you can't have one without the other. The water supply needs water treatment on the other end.
Marcus Fagan:
The wastewater capacity at the site is a constraint and it's a constraint in terms of growing population and increased economic activity.
And while Ringsend has already seen one upgrade this century, many sites are much older.
Marisa Buyers-Basso:
Aging assets is always a challenge for water utilities. I mean a lot of the kind of original biological treatment systems around the world went in the seventies.
So what are we talking about, when we talk about wastewater treatment?
Marisa Buyers-Basso:
Wastewater itself is essentially water that's generated by municipal or industrial sources. That has contaminants in it, which will negatively affect the environment if it's discharged into the receiving waters like lakes or oceans. And wastewater treatment itself is essentially the engineered removal of those contaminants.
Wastewater contains a myriad of contaminants.
Marisa Buyers-Basso:
One of which is really just solids or particulate matter. And that can really cause discoloration or reduced light transmissivity in receiving waters. Also, sometimes they can break down into other contaminant types.
Marisa Buyers-Basso:
We have organic material, so essentially this is stuff that will break down in the receiving waters and require oxygen, which then depletes the oxygen in the receiving waters, which can cause environmental issues like fish kills and things like that.
Marisa Buyers-Basso:
There are then nutrients, namely phosphorus and nitrogen, that when they're discharged into water bodies lead to eutrophication, which is basically algae growth. And when that algae breaks down again it can deplete the oxygen in that environment.
Marisa Buyers-Basso:
There are pathogens, so things that can cause disease, of course, as well.
A wastewater treatment plant processes each of these contaminants in stages.
Marisa Buyers-Basso:
The first thing that you would encounter coming into the plant is the preliminary treatment. So that is kind of mechanical removal of solids and debris, so large grit, rags. Fats, oils, and grease also are removed during preliminary treatment. This is done with screens, classifiers, fog tanks, etc. It does reproduce some waste streams itself that need off-site disposal.
Marisa Buyers-Basso:
Then you go into primary treatment, which is the mechanical removal of the suspended solids.
Marisa Buyers-Basso:
Again, more of these solids that need to be removed. This is the heavier solids, the stuff that you can actually see in the wastewater. There's inert material in there, but there's also some of the biological organic waste that needs to be reduced, and that's settled out mechanically.
Wastewater passes from primary to secondary treatment, from a mechanical to a biological process.
Marisa Buyers-Basso:
This is where we use actual bacteria to break down the organic material and the nutrients that come in in the wastewater.
Marisa Buyers-Basso:
We do this through essentially a controlled environment where we give them air or do not have air with different zones, to allow the bacteria to consume the organic material or to assimilate the nutrients or to convert ammonia into eventually nitrogen gas that leaves the process that way.
Later steps then eliminate other contaminants.
Marisa Buyers-Basso:
And then after biological treatment, um there are downstream processes like tertiary treatment, which um can be either further settling um or things like disinfection which would be um like ozone or UV or chemical disinfection to remove any kind of remaining pathogens that could cause disease
Marisa Buyers-Basso:
And now with the let's say emergence of micropollutants, there's even talk about quaternary and quinary treatment steps.
Egis, Haskoning, and the contractors working to upgrade Ringsend needed to keep the plant working, while adding massively to its capacity.
Marcus Fagan:
It's located on the south bank of the river Liffey adjacent to Dublin Bay, so right in the middle of Dublin really. A lot of constraints there: we've a special area of conservation to the south of the site; we've industry there surrounding.
Marcus Fagan:
It's about a, I'd say, an area of about 10 hectares the site itself. All of that is used. We had a small area of about 0.8 of a hectare available to us to do works on.
Marcus Fagan:
The equipment and the structures themselves are over 20 years old.
Marcus Fagan:
The site itself is made-up ground that was reclaimed land effectively from the bay.
The current work is being performed for Uisce Eireann [Pron: Ishka Air-ann], known in English as ‘Irish Water’. But it has been planned for a long time.
Marisa Buyers-Basso:
Interestingly, the project actually started before Uisce Eireann even existed.
Marisa Buyers-Basso:
The wastewater treatment plant that was built in 2003 was owned by Dublin City Council. And they identified the need to expand that. That treatment plant was built for 1.6 million population equivalent.
We’ll be measuring site capacity ‘population equivalent’, or PE. It’s the key metric used in the sector.
Marisa Buyers-Basso:
And they need to expand that to about 2.4 million. That's basically the most that they think they can treat on that site.
Marcus Fagan:
The original design capacity, when it was upgraded, was 1.64 million population equivalent. The figures were prepared for it and given the growth in the area and population increase the target figure was 2.4 million population equivalent. Now that's not a straight increase because we also the urban wastewater treatment directives imposed a higher effluent quality on it.
Marisa Buyers-Basso :
There are a lot of constraints because essentially they not only need to treat now to 2.4 million people equivalents, but also the Urban Wastewater Treatment Directive from the EU came in and that said that that because they discharged the lower Liffey estuary, which is a nutrient-sensitive water body, they now have to meet stricter effluent requirements.
Water had been discharged into the biodiverse Liffey Estuary. As Marisa explained earlier, this can block light or cause algae blooms, which suffocate marine wildlife.
Marcus Fagan:
Initially the thought process on this, and it had received planning for a long sea outfall, a nine-kilometer long sea outfall that would have brought the final effluent out beyond the sensitive area.
Marisa Buyers-Basso:
When Uisce Eireann took over, they re-looked at that project and they revisited all of the different technologies that had been kind of considered in that selection process. And emerging technologies, including at the time, which you know this is about 2014, Aerobic Granular Sludge, which had just kind of hit the full-scale market as Nereda.
Nereda would work well on this site, as it had already been fitted with suitable batch reactors.
Marisa Buyers-Basso:
And it was really considered a lot of potential for this site because they have existing sequencing batch reactors. That's a type of biological treatment process, where you actually treat, you do, all of the treatment steps in one tank. So you feed wastewater in, you then aerate it for the biological treatment process, and then you allow it to settle within the tank itself.
Traditionally, wastewater treatment was a continuous process. But many newer or upgraded plants like Ringsend have a sequential batch process.
Marisa Buyers-Basso:
In a batch reactor, it works a little bit differently. You have wastewater come in and then it goes, then it stops, and then you aerate what's in that tank separately. And then you stop and then you allow it to settle. And then you discharge effluent and then you do it all over again.
Marisa Buyers-Basso:
And the Nereda process is also a batch process. So there was the ability to retrofit into the existing tanks with Nereda and also to get more out of the very limited space that was available.
Nereda goes beyond basic biological engineering, to create an environment that encourages bacteria to grow in a way that allows for a more efficient process.
Marisa Buyers-Basso:
The conditions in the operation of a Nereda reactor force the bacteria to grow not as flock or flocculent biomass, but in kind of granular aggregates of bacteria. And the difference between these is that the granular aggregates of bacteria, well it's the same type of bacteria, but when it grows—when we force it to grow—as granules, it can settle a lot faster.
Typically, bacteria grows as strands or fluffy foams. This is lighter, and sits on top of the wastewater.
The heavier Nereda granules sink to the bottom of the sequential batch reactor.
Marisa Buyers-Basso:
So then we also are saving time on that settlement phase, right? Instead of an hour, or an hour and a half, we can do it in 20 minutes.
Marisa Buyers-Basso:
That means there's a lot more time available for that aeration step, that biological step, that time to treat and treat to low limits.
As the granules are more solid, wastewater undergoes different processes at different points within them. Some with lots of oxygen, some with less, some with none at all.
Marisa Buyers-Basso:
The granular structure also allows for multiple biological processes to happen at one time.
Marisa Buyers-Basso:
I've talked a lot about aeration, but realistically you also use anaerobic conditions, conditions without oxygen, and anoxic conditions, conditions where you only have nitrate present, to achieve your nutrient removal.And we can actually have all of that happening within the granule, because there are diffusion gradients within the—so the oxygen doesn't get all the way to the center. So you actually have an aerobic zone, an oxygen-rich zone, you have an anoxic zone, and you have an anaerobic zone all within the granule.
Marisa Buyers-Basso:
So you actually are doing multiple things at once while you're treating biologically. So that allows you also to use the time really effectively to remove organic material and nutrients.
There’s no genetic engineering here. Instead, it’s about creating a Darwinistic environment, where the bacteria most fitted to the process you want, survive the best.
Marisa Buyers-Basso:
It's about natural selection. So we're basically creating environment in which bacteria that grows as granules lives, and if it doesn't grow as granules, it doesn't get fed and it doesn't stay in.
Marisa Buyers-Basso:
It's just the conditions that we create through the treatment of wastewater that cause the bacteria to grow as granules.
Haskoning developed Nereda, and they advise engineering firms like Egis—and their contractor partners—on how to build plants that use it.
Marisa Buyers-Basso:
What we do is we size the process, so we say how big the tank need to be, what the flow rates in and out should be, how you waste the sludge, again how you remove the surplus sludge, how you feed the tank, what the inside of the tank looks like in order to create the conditions that stimulate granule growth.
And these are complex projects, with multiple companies working together.
Marisa Buyers-Basso:
Ringsend is a huge and very complex plant in a very, very small amount of space. And you have to keep the plant running. You have to keep treating wastewater. It doesn't stop showing up at the gate.
Marisa Buyers-Basso:
It's such a huge project that you couldn't actually do it all with one contractor, because the work, the scope of the packages, would be too large financially for any one contractor that's working in Ireland to handle.
The task for Egis, and Marcus, was to ensure that the upgrades could be built, without stopping Dubliners being able to flush their toilets.
Marcus Fagan:
They're a very, very constrained site and it's an operational site. We've a limited window in terms of, say, the number of hours we can shut down the plant for on any given day.
Marcus Fagan:
The average flow, I think, into the plant is five meters cubed per second, but that's five tons of water effectively coming at you every second. So trying to hold that back or hold it somewhere, you know, is a massive, massive challenge.
The site had been designed with these constraints in mind, with the opportunity to stack reactors on top of each other.
Marcus Fagan:
Unfortunately with most wastewater treatment plants are they're in a built-up area or land is a precious commodity so back in the early 2000s when the original plant was being designed or upgraded the designer looked at constructing a two-tier reactor—so one reactor sitting on top of another, two stories—just because of the constraints around land. So as part of our upgrade we first constructed a new capacity upgrade, we called it, that gave us an additional 400,000 population equivalent.
Marcus Fagan:
And that was constructed on an 0.8 hectare site, again using that two-tier construction. So it allowed us to get that within that footprint. That upgrade then allowed us to look at the existing reactors that were there and to retrofit some of those as Nereda reactors. And then that allowed us to increase the capacity over and beyond what the existing capacity was..
Working step-by-step, Egis added capacity to one reactor, and made space for the next.
Marcus Fagan:
We had to do a number of steps in order to get there. We initially did a pilot plant, a small plant—I think it was about maybe about a thousand population—just to prove that the technology worked on the influent, because every influent is different. But that showed that it worked. And you got the Nereda effect as we call it, you're getting the granules.
As they did this, they proved Nereda would work on the site.
Marcus Fagan:
That was our pilot plant and then we went into a full-scale pilot um in one of the reactors—now the reactors are quite large, they're 55 meters by 35 by nearly eight meters deep, so they're significant tanks, they're huge. So we did a full-scale pilot on that and proved again that this works in a large-scale scenario—it's obviously been proven internationally but we wanted to prove it in Ireland as well and that demonstrated to the client, Uisce Eireann, that this technology works and it could be implemented on a larger scale.
The work of all the contractors had to be carefully sequenced
Marcus Fagan:
So managing all that, that probably was one of the biggest of those interfaces, trying to keep the plant operational at the same time as taking out reactors to upgrade them. That's why the 400 000 population equivalent, that upgrade, gave us the headspace to take out reactors and allowed us to do the upgrade.
Marcus Fagan:
We also had numerous contracts operating side by side
Marcus Fagan:
You had maybe three contractors side by side, operating within a very confined space, and trying to manage those interfaces between the two of them—one contractor would go so far and another contractor would have to meet them at an interface point—and then these were big interfaces.
Egis’s talent for digital design was vital to the project’s delivery.
Marcus Fagan:
So a lot of that was done through the use of BIM and Revit models: so the models are shared collaboratively between the contractors you know to say this is where your tie-in point is.
The plant is now operational. As the bacteria in the Nereda granules do their work, Haskoning is using its own digital tools to optimise their behaviour.
Marisa Buyers-Basso:
One of the other things that we provide as part of a Nereda package is the Nereda controller, which is an advanced control system.
Marisa Buyers-Basso:
We use real-time information about what's happening in the process to make decisions about the process.
This is very different from standard approaches to wastewater treatment.
Marisa Buyers-Basso:
In a conventional, let's say, non-advanced controlled plant, you would feed for the same amount of time in every batch, you'd aerate for the same amount of time, at the same intensity for every batch, you'd settle for the same amount of time at the same intensity every batch.
Marisa Buyers-Basso:
What we do with advanced control is we actually monitor what's the oxygen concentration, what's the ammonia concentration. What's the phosphorus concentration? And we adjust how much air we put in, what flow rates we use, things like that, based on the real-time information, essentially to prevent using energy unnecessarily.
And the results prove the success of the Nereda technology
Marisa Buyers-Basso:
The project is is still just towards the end of its implementation. So the first thing that we did was we built six brand new reactors called what we call the capacity upgrade, which allowed us to take other reactors out of service in order to retrofit them.
Marisa Buyers-Basso:
It was designed for a certain amount of wastewater to hit the nutrient removal requirements, the future ones. But what's actually been—we've been putting even more wastewater through it in order to facilitate the retrofit. And it's performed extremely well during that, even achieving some of the requirements that it needs to do, even though it's receiving maybe 150% of its design loading.
