Our Research Focus: Breathing Life Back into the Baltic Sea

Patricia Handmann and Anna Canning explain the BOxHy project, designed to sustainably combat coastal deoxygenation by valorising the oxygen from water electrolysis

COVERING over 70% of Earth’s surface, the oceans are vital to regulating our planet’s climate. They capture around a third of our carbon emissions and absorbed a staggering 90% of the heat generated from 1971 to 2010. Yet, this vital buffer is under unprecedented stress. In June 2024, we witnessed the warmest June on record, capping off over a year of alarming global temperatures, according to the US National Oceanic and Atmospheric Administration.

In the urgent global effort to combat climate change, a silent crisis looms large – the deoxygenation of our oceans. Since the 1950s, oxygen levels have steadily declined due to global warming and pollution from sewage, organic matter, and fertilisers, leading to eutrophication. Eutrophication is linked to an excessive richness of nutrients in a body of water, which causes a dense growth of algae, which when degraded by bacteria consume large amounts of the oxygen present in the water. These low oxygen levels can kill fish and seagrass, lead to the production of toxic hydrogen sulfide and significantly reduce the aquatic habitat.

Coastal areas with dangerously low oxygen levels (hypoxia) have surged worldwide. In 1960, there were 45. In 2019, researchers identified over 900 coastal area experiencing eutrofication, of which over 700 were hypoxic.¹ With potentially thousands more unrecorded, it isn’t merely an ecological concern; it jeopardises the livelihoods and food security of billions.

The Baltic Sea serves as a representative example, where nutrient-rich runoff and warming temperatures have triggered toxic algae blooms and expanding areas with low to no oxygen, making it home to seven of the ten largest “dead zones” in the world, according to National Geographic. Since 1990 the Helsinki Commission (HELCOM), the governing body of the Baltic Marine Environment Protection Commission, has limited nutrient input in the Baltic Sea. Unfortunately this effort is not preventing hypoxia (low oxygen levels) and anoxia (no oxygen) from taking hold or spreading.

One economically interesting species profoundly impacted by these low oxygen areas is the Baltic Cod, which faces disruptions in breeding grounds, reduced survival rates of offspring, and limited feeding areas. The latest report from HELCOM highlights that deoxygenation and the Baltic Sea’s poor environmental condition remain serious challenges. These ecological issues have significant economic costs. In 2013, reducing eutrophication – a key cause of low oxygen levels – was estimated to yield annual benefits of €3.8–4bn (US$4–4.3bn). More recent reports indicate that, combined with other pressures, the Baltic Sea’s poor state now results in an annual economic loss of around €5.6bn, due to both direct and indirect losses, including marine resources and biodiversity.

BOxHy: Innovation for marine restoration

The BOxHy (Baltic Sea Oxygenation and the Super-Green Hydrogen Economy) project is designed to address this pressing challenge. Our ultimate long-term goal is to mitigate anoxia and restore and stabilise coastal ecosystems by reoxygenating the affected areas using water electrolysis to produce oxygen from offshore hydrogen production. Our goal is to install our offshore hydrogen production sites close to offshore wind parks. We can use the wind power to split seawater into green hydrogen – for use as a new energy vector to decarbonise the industry and heavy mobility – and its coproduct, oxygen, to reoxygenate marine environments. This oxygen would be piped to a suitable location where it would be dispersed at a certain depth. To prepare for this initiative and aid marine life while improving ecosystem health, a multidisciplinary team is exploring all aspects of the potential project.

Lhyfe, Flexens, and Stockholm University’s Department of Ecology, Environment, and Plant Sciences (DEEP) are working together on adapting existing technologies, evaluating suitable locations for a pilot study, and investigating the integration of green hydrogen production with reoxygenation efforts. Careful consideration is also being given to the implications of these actions.

Launched in October 2023, this feasibility study is among the most comprehensive of its kind. Building on previous research, it focuses on the impacts, potential issues, and methodology of identifying optimal pilot sites to ensure that oxygen injection benefits outweigh potential risks. This marks one of the first attempts in a marine environment to utilise oxygenation, building on successful methods applied in inland waters, while using the process of electrolysis.

BOxHy aims to establish a robust foundation for a pilot project to develop best practices and assess the true impacts of oxygenation in the sea as well as a strategy for monitoring this crucially needed science. A partnership approach is essential for this endeavour and our expert team comprises local environmental and social knowledge, scientific expertise in oceanography, and engineering proficiency in oxygen diffusion, hydrogen production, and distribution.

Previous work in Baltic Sea coastal areas and freshwater applications has provided invaluable insights.

Bringing inland advances to the sea

Since the 1980s, the US has pioneered artificial reoxygenation of freshwater bodies using pure oxygen produced by cryogenic air separation rather than electrolysis. The technologies we are exploring are adapted from successful inland applications, specifically mature linear diffusers used in over 40 US lakes and reservoirs. These diffusers vary in capacity, from less than 10 t/d to as high as 350 t/d.

As we advance with the BOxHy project, several critical areas of ecological engineering require attention. Firstly, the logistics of the oxygenation process are paramount, comprising injection technique, the oxygen flow rate, and the methodology of the results evaluation.

Secondly, practical considerations are significant. Implementing this ambitious project demands meticulous planning to minimise environmental disruption and ensure seamless equipment transport to remote coastal sites as well as social acceptance. Open engagement with local communities will be crucial to address potential concerns, highlight benefits, and gain trust and support.

From a technical perspective, our focus is on efficiency as well as the integration of reoxygenation in hydrogen production projects to maximise impact and sustainability.

Lastly, understanding the economic implications is vital: what are the costs of ongoing deoxygenation versus the investment needed for comprehensive oxygenation across the Baltic Sea?

Offshore green hydrogen for reoxygenation

As more wind turbines are installed at sea, producing green hydrogen becomes increasingly attractive, opening new opportunities for reoxygenation efforts. Lhyfe’s Sealhyfe experiment, conducted 20 km off the French Atlantic coast in 2023, demonstrated the feasibility of future large-scale sites, consistent with ambitious targets set across Europe. Additionally, Lhyfe secured a €20m grant from the European Commission’s Clean Hydrogen Partnership for its planned 10 MW HOPE project in Belgium. This initiative includes a pipeline to transport green hydrogen produced offshore back to shore for compression and delivery.

Producing 1 kg of hydrogen by electrolysis of water also generates 8 kg of oxygen per 1 MW. Therefore, with future sites projected to have a minimum unit capacity of 500 MW, producing around 200 t of hydrogen and yielding 1,600 t of oxygen daily, this presents a significant opportunity for marine oxygenation. By integrating this new oxygen source with established freshwater techniques, there is potential for restoring coastal ecosystems far beyond the Baltic.

Engineering challenges and solutions

During BOxHy our team also worked on potential engineering hurdles. The initial pilot will use oxygen in a small-scale marine system. To ensure a systematic approach, the first pilot will use oxygen injection from oxygen transported to the site. This will allow close monitoring and evaluation of the technical and scientific challenges that come with optimising the reoxygenation process. In the long term, the pilot is the first step towards the integration of reoxygenation in a hydrogen-producing infrastructure. We will then be able to focus on emerging challenges while having a solid science and technology base (see Figure 1).

Along with answering the technical questions, we face the challenge of piping oxygen to the seabed. This includes identifying materials that can withstand seawater pressure, subsea conditions, and prolonged exposure to pure gaseous oxygen, which is critical for the pilot’s success. This coincides with the focus on efficient oxygen deployment through the injection systems and its coupling to hydrogen-producing electrolysers providing pressurised output of oxygen.

Careful planning needs to be implemented to minimise environmental impact during installation and operation. Our pilot test will further assess effectiveness in the marine environment and determine the optimal operating cycles for oxygen release over time. The subsea layout, designed to enhance diffusion rates and dispersion patterns, while minimising impact on the topside design, such as pressure drops, will play a crucial role in optimising the pure oxygen input. To ensure these challenges are effectively managed in the marine environment, rigorous testing and monitoring protocols need to be implemented.

Further comprehensive operations and maintenance procedures are essential for efficient oxygen production, transport, and injection, mitigating downtime risks and environmental impact. Therefore, collaborating with academic and industrial partners is crucial for pooling skills and knowledge to innovate solutions that enhance project performance and sustainability.

Future innovations on the horizon include efficient hydrogen electrolysers capable of producing pressurised oxygen and advancements in subsea diffuser technology to withstand seawater conditions and accommodate intermittent oxygen flows effectively.

UN endorsement and global connections

We’re honoured to have received endorsement from the United Nations Decade of Ocean Science for Sustainable Development (2021–2030), which recognises our work and connects us to a broad network of experts. As part of the Global Ocean Oxygen Decade (GOOD), this affiliation allows us to share knowledge and forge impactful partnerships worldwide. The journey ahead presents challenges, yet with innovation and determination, we can sustainably work our way to breathe new life into our coastal seas.

Reference

1. Denise Breitburg et al, Declining oxygen in the world’s ocean and coastal waters https://pubmed.ncbi.nlm.nih.gov/29301986/