Lets not waste an opportunity: Nature-based solutions to our wastewater woes – thejournal.ie

WE DONT REALLY like to think about issues involving our wastewater. Yet, these issues are more regularly coming up to the surface in both a political sense and, more unfortunately, a literal one.

Globally, over four billion people use sanitation facilities that lack adequate wastewater treatment, which results in the contamination of the environment and a severe risk to public health. Ireland is no exception.

We have recently suffered a wave of swimming bans following summer heavy rains. This is a result of ageing wastewater infrastructure such as sewers and treatment plants incapable of supporting population growth and the impacts of climate change.

Irelands means of treating wastewater can be divided into two main types. The first is a centralised system in large urban areas such as Dublin where wastewater mostly flows by gravity across the city and ultimately arrives in facilities like Ringsend where it is stored and treated to remove harmful pathogens, using a lot of energy in the process.

A major concern is the collection systems where rainfall runoff from urban environments end up in the sewer, akin to safety releases, during high rainfall events. When this happens, diluted untreated sewage is released into rivers and bays due to rainwater drains overflowing into the sewers.

Sludge from household septic tank being emptied Source: KaliAntye via Shutterstock

Septic tanks across the island

The second form of treatment for wastewater is on-site or decentralised systems. Due to our sparsely-populated rural areas, we have one of the highest proportions of households around 489,000 in Europe using on-site domestic wastewater treatment systems.

The most common system is a septic tank, which separates wastewater of heavier solids and fats. Following this separation, wastewater is dosed underground into the soil along specially made trenches filled with gravel. Bacteria attached to the gravel and soil naturally treat wastewater as it percolates down to the underlying groundwater.

In my professional experience, if these systems are built according to the EPA code of practice, they should be considered an effective nature-based solution to on-site wastewater treatment. The key issue, however, is that much of the function takes place underground, so it is hard to know if these systems are functioning adequately.

Local authorities do inspect these systems, but with so many systems, and an average inspection rate of 1,000 per year, it will take nearly half a millennium to look at the systems currently in operation.

Aerial view of Ringsend Wastewater Treatment Plant, August 2020 Source: 4H4 Photography

Solutions to our sewage problem

One thing you come to understand when working in this area, is that there is more than one solution to the sewage problem.

Centralised systems such as those in Dublin are crucial as they treat high volumes of sewage on relatively little land but they do use a great deal of energy to do so.

These facilities could be aided by improvements in rainwater capture reducing the impact of climate change on our drainage network and improving our overall water supply.

On-site wastewater systems, if installed adequately, can also offer a low cost and low-energy alternative to smaller populations currently relying on septic tank systems. A good example is the integrated constructed wetland system at Castle Archdale in Co Fermanagh.

The system consists of a series of artificial wetland ponds over a three acre site, using natural processes with plants and bacteria to clean the wastewater. This system has a treatment capacity of 1,000 people and has resulted in a 100% reduction in electricity usage compared to the now decommissioned wastewater treatment plant.

These systems require little maintenance or technical labour in the long-term. They also have a natural aesthetic value with an abundance of plant life that starkly contrasts the typical austere or brutal facades of wastewater treatment plants.

Aeriel photo of Castle Archdale Treatment System Source: NI Water

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There are already examples of such systems in the Republic of Ireland, including Dunhill in Co Waterford, Glaslough in Co Monaghan, Clonaslee in Co Laois and Lixnaw in Co Kerry. Archdale Castle should inspire us to further develop more systems in the south.

The treatment capacity of a system like Archdale Castle could satisfy the needs of 569 of our 846 population centres accounting for nearly 250,000 people. It may not always be cost effective to replace an existing system with these natural process alternatives, but with 32 sites still pumping raw sewage into the environment daily, there is good reason to examine their potential.

Systems like Archdale would have the capacity to treat 15 of these sites, with minimal need for technical staff and energy to run them. These systems could also be adapted to more densely populated urban areas to passively treat wastewater before arriving at Ringsend and relieve some of the strain on the facility.

If we dont want to drown in our own misfortune, it is crucial that we collectivise our waste management, with the added bonus of diversifying our treatment methods and incorporating nature-based processes with minimal impact on the environment.

Alejandro Javier Criado Monleon is a doctoral candidate at the Department of Civil Structural and Environmental Engineering at Trinity College Dublin. His background is in public health, disease surveillance, water, wastewater, and microbiology. His current work focuses on the soil microbiology in on-site wastewater systems.

EMPTY THE TANK INVESTIGATION

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Lets not waste an opportunity: Nature-based solutions to our wastewater woes - thejournal.ie