It is not often that the arts section of a newspaper finds itself concerned with the aesthetic merits of a sewage works. But then there are few facilities designed with the finesse of the new €139m (£117m) wastewater treatment plant in Arklow, which stands like a pair of minty green pagodas on the edge of the Irish Sea. Nor are there many architectural firms who have thought so deeply about the poetics of effluent as Clancy Moore.

“There’s a wonderful passage in Ulysses,” says practice co-founder, Andrew Clancy, summoning James Joyce as we tiptoe along a metal gantry above a gigantic vat of bubbling brown sludge. “The narrator turns on the tap to fill a kettle, sparking a lengthy rumination on where the water comes from, how it flows from reservoirs, through aqueducts and pipes, describing each step in minute detail, from the volume of the tanks to the dimensions and cost of the plumbing.”

There can’t be many sewage works designers quoting Joyce (despite the Irish author’s scatological inclinations). But Clancy’s point is that there is an entire universe of water treatment, storage and distribution that is rarely celebrated, or even much thought about. It takes place beneath our feet and out of sight, in a world hidden below ground and squirrelled away in anonymous sheds behind tall fences, far from town.

Not in Arklow. For generations, sewage has been at the forefront of the place’s mind – and unavoidable on the beach – because it had no water treatment plant at all. Since time immemorial, this town – 45 miles south of Dublin in County Wicklow, on Ireland’s south-east coast – has pumped the waste produced by its 13,500 inhabitants into the Avoca river which takes it straight out to sea. The European Commission took note. Successive rulings by the European court of justice over the last two decades have found Ireland in continual breach of its wastewater treatment directives, and slapped with hefty fines for its repeated failure to remedy the situation. The lack of waterworks has also been a brake on the town’s development: without a treatment plant, no new homes could be built. Something had to be done.

A sewage works was first proposed for Arklow in 1988, but it became mired in a generation-long dispute over its location, one of the longest planning battles in the county’s history. It was originally going to be built in the north docks, then an area known as Seabank, which bitterly divided the town. Some argued the site was prone to erosion, others that it was home to a rare species of horsehair worm. The well-resourced owners of a nearby caravan park decided to take the council to the supreme court. Twelve years on, in 2011, they finally lost the case. But they ultimately won the battle: by then, the plant’s 10-year planning permission had expired.

“We had to start from scratch,” says Michael Tinsley, project manager at Irish Water, or Uisce Éireann, the state-owned water company founded in 2013, which took on the contentious project. “This time around, we made a point of talking to absolutely everybody.” After considering numerous options, they hit on a location close to where the plant had originally been proposed, on the site of a former wallboard factory in Ferrybank, on Arklow’s north quay. It was a topographical low point, and therefore required the least pumping. Unusually, the national planning board insisted that an architect be involved, given the visual prominence of the site, on a key promontory overlooked by the whole town, where future development is planned. In Clancy’s eyes, that’s exactly where such a monument of civic infrastructure should be.

“Think of the Sydney Opera House,” he says, drawing a comparison to the world’s most famous waterfront building. “It occupies the most prominent site in the city. But not many people actually go to the opera. If you were building a town, you would probably think of the poo before you thought of the opera.”

He’s got a point. Rather than trying to beckon the Bilbao effect by building a palace of culture, Arklow has elevated the prosaic, with a cathedral of crap, like many a grand Victorian pumping station before it. It is an earthy hymn to the fact that locals may finally be able to swim without fear of floaters.

Even on a drizzly grey day, the complex is an elegant thing to encounter. The two vast processing sheds stand like ocean-liners on the horizon, their profiles serrated with angled louvres, giving them the look of concertina paper lanterns, gently glowing by night. A single Cyclopean window punctures each building – one looking out to sea, one looking back to the town – while the louvres are inverted and enlarged at the top, forming a cornice-like crown. They have an almost cartoonish presence from afar, their oversized gills a caricature of ventilation, while also providing habitats for bats and birds.

Close up, they take on another character. The long horizontal louvres (made of fibre cement panels, bolted to a demountable steel frame) are corrugated, recalling the fluted pantiles of a Chinese temple. Their celadon green hue reinforces that allusion, although here the colour references local sports teams, as well as sea thistle and the hulls of Arklow Shipping boats. A third laboratory building – scaled like a Dinky Toy in comparison – looks like a cheeky creature, keeping a beady eye on proceedings. Its facade greets you with a wink at the entrance to the site, a single eye-like window above a protruding nose-like canopy, and a butterfly roof forming two perky ears.

Compositional games are played with form and scale. The walls of the smaller building are clad with smooth panels of the same minty colour as its big siblings, each layer tilting out at an angle to echo their louvres. Both the lab building and the treatment sheds sit on chunky triangular buttress-like supports, the concrete power-washed to reveal its gritty aggregate, giving a rusticated heft in contrast to the paper-thin louvres above. The attention to detail is remarkable for an industrial complex, with even the corners of the sheds carefully cut and folded inwards where the louvres meet, as if sliced with a scalpel. It all has a model-like quality, wrought more with the precision of one of the German artist Thomas Demand’s beguiling paper sculptures than your usual wastewater sheds.

The process of protecting these design details – which are so often lost on projects of this scale – was unusual. “There are no drawings in the tender package for a water treatment works,” says Clancy, whose firm is more used to designing private houses. “Because it rightfully assumes that technological developments are outpacing the speed of public procurement.” As a result, the architects had to translate their design into precise passages of text, enshrining the ratios and proportions of their facades in exacting legalese, making the design contractually binding.

“We also made sure the architecture was the cheapest thing,” he adds, “so it would be the last to be cut on the ‘value engineering’ list.” Tinsley estimates the architecture amounts to about 3% of the total project cost. “At one point, we had some internal debates at Irish Water, with colleagues thinking we were lavishing money on a big, fancy building,” he says. “But it’s within the margin of error – the architecture cost was dwarfed by the cost of inflation.”

Besides, the architects brought more than just a pleasing wrapper. Working as mediators, negotiators and catalysts within a team of specialist engineers – from odour control to tunnelling, marine ecology to highways – they were the glue that bound it all together. They also brought fresh innovation. While a conventional plant pumps wastewater multiple times from tank to tank, in Arklow the system is stacked, meaning the water is only pumped once, with the rest of the process happening by gravity, reducing energy consumption. Roofing the whole structure (which is usually open air) also allowed gantry cranes to be installed for future maintenance and servicing, along with a solar farm that generates about a third of the total energy requirements.

It has been a long time coming, and the people of Arklow are rightfully relieved. As Tinsley puts it plainly: “No one wants to be the biggest town in Ireland with shite going into the river.”

On the British mainland, we can only dream of such civilisation. Since the UK’s water industry was privatised in 1989, it has seen a race to the bottom, with infrastructure left to crumble while shareholders profit from bumper dividends. Leaving the EU has only accelerated the decline, fuelling a rampant increase in raw sewage being dumped into our waterways. As Ireland has shown, nationalisation is the only way to clean up the mess – and it may even bring things of beauty in the process.