Research theme:
Carbon, nitrogen and phosphorus recovery at sewage treatment plants
A wastewater treatment process that recovers carbon, nitrogen and phosphorus at sewage plants
Sewage treatment is estimated to account for around 1% of global electricity consumption. Aeration takes much of the energy, and nitrogen removal also generates N₂O. A scaled-up Bloomo aims to replace part of this treatment cost with resource recovery through four layers: lower aeration, CO₂ uptake, nitrogen and phosphorus recovery, and N₂O suppression. Its application to sewage is currently at the research and small-scale validation stage.
Context, product, outlook
Context
Sewage treatment is estimated to account for around 1% of global electricity consumption. In the activated sludge process, aeration takes 50–60% of the energy, and nitrogen removal generates N₂O, with a GWP of 273.
Product
Bloomo for Sewage is being developed to fit into existing treatment processes. It combines oxygen supply through photosynthesis, CO₂ uptake and the assimilation of NH₄⁺ into amino acids, with a target of above 90% removal for both nitrogen and phosphorus (targets, not yet validated).
Outlook
We will start with joint research with sewerage operators and maintenance companies in Japan, and assess the technology as a complement to existing treatment, on the premise of meeting discharge standards. We will also study how CO₂ uptake could be shown as environmental value.
Users and product
USER
Municipalities and infrastructure companies
- High energy consumption in sewage treatment
- Requirements to quantify and suppress N₂O and CH₄ emissions
- Recovering nitrogen and phosphorus as resources
- Decarbonisation during the renewal of ageing plants
PRODUCT
Bloomo for Sewage
An integrated algal process designed to fit into existing plants (research stage)
- Photosynthesis partly substituting for aeration energy
- Uptake of CO₂ from flue gas
- Nitrogen recovered by assimilating NH₄⁺ into amino acids
- N₂O suppression through biochar addition (under study)
Core technology and features
Lower aeration energy
Photosynthetic oxygen partly replaces the O₂ supplied to aerobic bacteria (the net energy balance, including mixing and harvesting, will be assessed in demonstration)
CO₂ uptake
Uses CO₂ from plant flue gas. About 1.83 t CO₂ per tonne of biomass is the theoretical uptake, not a net reduction
N and P recovery
NH₄⁺ assimilated into amino acids and protein. Studies with PBR+MPBR report removal above 90%
N₂O suppression
Studies report lower N₂O emissions from microbial denitrification with biochar addition (under study at Novelgen)
Turning sewage treatment from a cost into resource recovery
Sewage treatment is indispensable infrastructure for public health, yet it is estimated to account for around 1% of global electricity consumption[1]. In the activated sludge process, aeration takes 50–60% of the energy[2], and nitrogen removal generates N₂O (GWP 273)[3][4]. Here we outline a process concept, based on a scaled-up Bloomo, that aims to replace part of this cost with resource recovery (research stage).
PROBLEMStructural problems of conventional sewage treatment
High energy consumption and CO₂ emissions
Aeration takes 50–60% of the electricity consumed by the activated sludge process. The global sewage treatment sector accounts for around 1% of electricity consumption and is expected to grow 20% by 2030.
References: [2][5]
N₂O emissions
Incomplete nitrification and denitrification generate N₂O as a by-product. N₂O is an extremely potent greenhouse gas with a 100-year GWP of 273, and its emission factor varies widely between facilities.
References: [3][4][6]
Recovering nitrogen and phosphorus
Nitrification and denitrification release much of the nitrogen to the atmosphere as N₂. Efforts to recover phosphorus from sludge are already under way. Recovery by algae is being studied as a complement to existing sludge recovery.
References: [7]
SOLUTIONA four-layer concept with Bloomo
Reducing aeration energy
Photosynthetic oxygen partly replaces the oxygen supplied to aerobic bacteria. Removal of nitrogen, phosphorus and COD has been reported in systems that co-culture algae with activated sludge. Photosynthetic oxygen is only produced in daylight, however, and the net energy balance, including mixing and harvesting, will be assessed in demonstration.
References: [8]
CO₂ uptake
Microalgae take CO₂ into their biomass through photosynthesis. Assuming carbon makes up 50% of dry weight, the theoretical uptake is about 1.83 t CO₂ per tonne of biomass (a gross figure, not a net reduction). High-concentration CO₂ can be supplied from flue gas, and some studies use flue gas containing NOx/SOx, but its effects also need to be assessed.
References: [9]
Recovering nitrogen and phosphorus
NH₄⁺ is assimilated by the algae into amino acids and protein. Studies combining a PBR with membrane separation (MPBR) and similar set-ups have reported removal above 90% for nitrogen and phosphorus. We aim to recover most of the nitrogen as biomass, but the nitrogen balance, including N₂O produced by the algae themselves and ammonia volatilisation, will be checked in demonstration. Sewage-derived biomass is not intended for feed; we expect to use it for fertilizer, biochar and similar uses (subject to analyses such as heavy metals and pathogens, and to compliance with the relevant laws).
References: [10][11][14]
Using the recovered biomassSuppressing N₂O emissions
Lower N₂O emissions have been reported in constructed wetlands with biochar added. We are studying how biochar made from the biomass Bloomo recovers could be returned to the treatment system (the effect has not been validated).
References: [12][13]
System architecture comparison
BENCHMARKPerformance indicators (targets, under validation)
| Metric | Conventional process | Bloomo integrated (target) |
|---|---|---|
| Nitrogen removal | Depends on the treatment process | > 90% (target) |
| Phosphorus removal | Depends on the treatment process | > 90% (target) |
| Share of energy from aeration | 50–60% of the total | Partly replaced by photosynthesis (net to be assessed) |
| N₂O emission factor | 1.01% kg N₂O-N/kg TN (median) | Aiming to suppress (including N₂O from algae) |
Note: the Bloomo integrated column shows targets that have not yet been validated (the sources are the studies the targets are based on). Application to sewage is at the research and small-scale validation stage, with no track record of large-scale implementation.
BUSINESSHow it would be offered (concept)
Bloomo for Sewage is expected to be offered through collaboration and licensing with infrastructure companies and municipalities. Specific terms are discussed within joint research.
- ▸ The Algal Bloom Capture technology package (strain library, cultivation protocols, AI control know-how)
- ▸ Bloomo Cloud Service (remote monitoring and optimisation)
- ▸ Collaboration models with partner companies (infrastructure companies, municipalities)
ROADMAPDevelopment roadmap
- 1.Demonstration in aquaculture: confirming the performance of the units and cultivation control through Bloomo for aquaculture operators and seedling production facilities
- 2.Validation with wastewater and sewage (current): application to sewage is at the research and small-scale validation stage; after demonstration with real wastewater, we aim for operational readiness
- 3.Deployment: offering through licences or as a service, confirming conformity with Japanese discharge standards, and studying how to calculate environmental value
References
- Maktabifard M., et al. Achieving energy neutrality in wastewater treatment plants. Rev. Environ. Sci. Bio/Technol., 2018, 17, 655–689. DOI →
- Pathways to a net-zero-carbon water sector through energy-extracting wastewater technologies. npj Clean Water, 2022, 5, 49. DOI →
- Kampschreur M.J., Temmink H., Kleerebezem R., Jetten M.S.M., van Loosdrecht M.C.M. Nitrous oxide emission during wastewater treatment. Water Research, 2009, 43(17), 4093–4103. DOI →
- Stylianou M., et al. Factors Affecting N₂O Emissions from Activated Sludge WWTP — A Review. Resources, 2023, 12(10), 114. DOI →
- Mizuta K., Shimada M. Benchmarking energy consumption in municipal WWTPs in Japan. Water Science and Technology, 2010, 62(10), 2256–2262. DOI →
- Song C., et al. Oversimplification and misestimation of nitrous oxide emissions from WWTPs. Nature Sustainability, 2024, 7, 1348–1358. DOI →
- Mayer B.K., et al. Total Value of Phosphorus Recovery. Environ. Sci. Technol., 2016, 50(13), 6606–6620. DOI →
- Abdelfattah A., et al. Microalgae-based wastewater treatment: Mechanisms, challenges, recent advances, and future prospects. Environmental Science and Ecotechnology, 2022, 13, 100205. DOI →
- Cheah W.Y., Show P.L., Chang J.-S., Ling T.C., Juan J.C. Biosequestration of atmospheric CO₂ and flue gas-containing CO₂ by microalgae. Bioresource Technology, 2015, 184, 190–201. DOI →
- Goh P.S., et al. Microalgae-Enabled Wastewater Remediation and Nutrient Recovery through Membrane Photobioreactors: Recent Achievements and Future Perspective. Membranes, 2022, 12(11), 1094. DOI →
- Bezerra S.S., Fontana L., Arantes C.C., de Jesus T.A. Phosphorus removal from wastewater by microalgal cultivation in photobioreactors: a systematic literature review and multivariate analysis. Environ. Monit. Assess., 2025, 197(11), 1182. DOI →
- Huang L., Xiong H., Jiang C., He J., Lyu W., Chen Y. Pathways and biological mechanisms of N₂O emission reduction by adding biochar in the constructed wetland based on ¹⁵N stable isotope tracing. J. Environ. Manage., 2023, 342, 118359. DOI →
- Zhang Y., Zhang Z., Chen Y. Biochar Mitigates N₂O Emission of Microbial Denitrification. Environ. Sci. Technol., 2021, 55(12), 8068–8078. DOI →
- Plouviez M., et al. The biosynthesis of nitrous oxide in the green alga Chlamydomonas reinhardtii. The Plant Journal, 2017, 91(1), 45–56. DOI →
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