Turning Wastewater Ammonia Into Hydrogen

Every wastewater treatment plant spends money getting rid of ammonia. At Severn Trent Water alone, aeration to oxidise ammonia to nitrate costs around £1 million a year, burning through 10 GWh of electricity and generating roughly 5,000 tonnes of CO2 in the process. That ammonia isn’t waste, it’s about 3,000 tonnes a year of nitrogen sitting in the wastewater stream and it can be converted into hydrogen instead of just being destroyed.

That’s the problem we’re working on as part of REsilient WAter Innovation for Smart Economy (REWAISE) an EU Horizon 2020 project (Grant Agreement 869496) that runs until 2026. It’s coordinated by FCC Aqualia, with a 25-strong consortium spanning water utilities, universities and SMEs across nine countries, including Severn Trent Water, Coventry University and Organics. The project’s aim is to build a network of nine “living labs” across Europe, grouped into three regional hubs, demonstrating technologies and governance models that cut freshwater and energy use and recover value, nutrients, materials and energy from water that would otherwise just be treated and discharged.

Our piece of it, alongside Severn Trent Water (STW) and Coventry University, is turning ammonia recovered from wastewater into green hydrogen and we’re doing it by running two competing recovery technologies side by side to see which one actually works at scale.

Two approaches in parallel

The project didn’t commit to one ammonia recovery method up front. Instead, it’s running a direct comparison at two UK sites, both at 5 m³/day scale:

• Bioflex, trialled at the STW Spernal Living Lab
• OTAR (Organics Thermal Ammonia Removal), our own thermal stripping technology, trialled at Southern Water

Running both in parallel, rather than picking one on paper, is deliberate. It means the project ends up with real operating data, energy use, ammonia recovery rate and electrolyte purity, instead of a vendor comparison based on datasheets. Whichever technology comes out ahead gets carried into the technical-economic assessment we deliver jointly with STW and Coventry.

The design envelope

How OTAR fits into the process

The OTAR unit is a skid-mounted filtration and packed tower system, built with transfer pumps, a control panel and instrumentation. It strips ammonia from the wastewater stream thermally and produces a purified ammonia electrolyte.

That electrolyte doesn’t stop at Organics. It gets fed to a skid-mounted electrolyser, also designed and built by us. Where ammonia electro-oxidation happens and hydrogen comes off the other end. Coventry University runs the lab-scale characterisation (electrode stability, membrane performance, cell voltage) on a 100 cm² stacked cell before the process gets scaled up. STW, Coventry and Organics then jointly assess electrolyser performance using the electrolyte from both the OTAR and Bioflex streams, so the comparison is apples-to-apples on the same electrolyser hardware.

A HAZOP study is built into the workplan too, ahead of scale-up, flagging risks to personnel and equipment before the unit goes into wider deployment.

What it saves

The economics only make sense if the energy numbers hold up and the project’s figures give a sense of scale. Capturing 3,000 tonnes of ammonia a year avoids the equivalent artificial fertiliser production via the Haber-Bosch process (which needs at least 10 kWh/kg), saving around 30 GWh of electrical energy about £3 million and cutting roughly 15,000 tonnes of CO2 a year.

Converting that recovered ammonia to hydrogen adds a second value stream. At the volumes modelled, it could generate around 400 tonnes of hydrogen a year, enough to give vehicles a combined range of 40 million km, displacing about 3 million litres of diesel and its 8,000 tonnes of associated CO2. At roughly £9,000/tonne for hydrogen as a diesel replacement, that’s a meaningful income line on top of the emissions saving. Though it depends on hydrogen pricing holding up, which is the part least in anyone’s control.

What’s in our scope and what isn’t

Our budget line for REWAISE is €195,484, broken down roughly as:

• Design and build of the OTAR ammonia recovery skid, plus the electrolyser skid: bought-in components (~€136,000), logistics (~€12,000), engineering services (~€15,000)
• Laboratory time on WP2 electrolyte characterisation (~€20,000)
• Travel to the Midlands Living Lab and General Assembly meetings (~€12,500)

What’s not in our scope: the sewer mining and desalination work in other hubs, the smart-network leakage detection under WP6 and the biopolymer and struvite recovery streams. Those sit with other consortium partners (STW, CETIM, UNIPA and others). Organics role is specifically the thermal stripping and electrolyser hardware and the technical-economic comparison against Bioflex.

Timeline reality

The task itself runs Month 10 to Month 56, which sounds tight against a Month 60 deliverable, but it’s worth knowing that the whole project has already moved once. A 2025 amendment extended REWAISE by 10 months from 60 to 70 months overall with WP6 (and our tasks within it) rearranged accordingly, along with the deliverable dates and reporting periods. Multi-partner EU projects rarely land exactly on the original schedule and REWAISE is no exception. The extension mostly reflects the reality of coordinating hardware builds and lab testing across five countries rather than any one partner falling behind.

Why we’re the ones building this

Organics has been doing thermal ammonia stripping since 1999, when we commissioned our first plant for Swire SITA at the NENT landfill site in Hong Kong. Twelve more thermal ammonia stripping plants have followed since. We’re a 28-person SME based in the UK, part of a wider group with global operations and about £4.9 million in combined turnover. That track record is the reason our role in REWAISE isn’t just supplying a technology, it’s providing the operational knowledge of what actually goes wrong when you try to scale ammonia stripping past the lab bench.