Designing and developing an integrated water treatment process
Treatment of water from desalination plant and wastewater treatment of discharge containing polyethyleneimine and dissolved salts
Project overview
Client: Sirona Technologies Location: Sultanate of Oman Industry: Technology
Key results
Water production unit designed
A reverse osmosis system producing demineralised water at 76.2% recovery rate, covering the full make-up water demand of the DAC process at a total operational cost of 6.12 €/m³.
Wastewater treatment process defined
Four technologies evaluated across three techno-economic models, with nanofiltration identified as the preferred solution for removing polyethyleneimine to below the 0.5 mg/L discharge limit.
Investment and operating costs quantified
Capital investment for the water production unit estimated at 25 to 60 k€, with a clear trade-off analysis between manual and fully automated configurations.
The Challenge
A Direct Air Capture system in a remote arid location, where water is both essential to the process and scarce that requires treatment on both the supply and discharge side.
Sirona Technologies develops and manufactures Direct Air Capture (DAC) systems designed to remove CO₂ from the atmosphere for permanent underground storage. Water plays a critical role in the DAC process: it is used as both a heat carrier and a chemical medium through a steam and condensate cycle. A porous sorbent captures CO₂ from the air, then releases it when heated with steam during regeneration. Most steam returns to the system as condensate, but losses are inevitable, requiring a continuous supply of high-purity make-up water.
The planned deployment site is located in a remote area of the Sultanate of Oman, near the coastline. No suitable water source is available on site: feedwater must be sourced from a nearby desalination plant, supplied either by pipeline or by truck. This water must be treated to demineralised quality before it can safely feed the boiler, as scaling and corrosion would compromise both process efficiency and equipment lifespan.
On the discharge side, the condensates produced during CO₂ desorption cycles contain traces of polyethyleneimine (PEI), a sorbent chemical used in the capture process. PEI must not accumulate in the boiler and cannot be discharged above 0.5 mg/L. Dissolved salts from boiler blowdowns add a second treatment challenge, with a discharge limit of 3,000 mg/L. Both streams require treatment before any effluent can be safely released.
Sirona mandated Revalio to design an integrated water management strategy covering both the supply and discharge sides of the DAC process, and to provide the techno-economic basis for investment decisions.
What Revalio delivered
The study was structured in two parts, each following a methodology of quality mapping, technology selection, treatment design, and techno-economic analysis.
Part A: Water Production Unit
The feedwater supplied by the desalination plant was found to be of relatively high quality, close to drinking water standards. However, to protect the boiler from scaling and corrosion and to allow more than 200 concentration cycles, a conductivity below 30 μS/cm is required, which the feedwater alone cannot meet.
Reverse osmosis (RO) was identified as the most reliable and cost-effective technology to bridge this quality gap. A pretreatment sequence was designed upstream of the RO membrane, including microfiltration, activated carbon, softening, and UV disinfection, to protect the membrane and extend its lifespan.
The RO unit was dimensioned at a nominal flow rate of 400 L/h to cover the DAC's design demand of 157 L/h, with margin for operating variability. Under a conservative 15°C scenario, the system produces permeate at approximately 8 μS/cm at 76.2% recovery. Total water draw from the desalination supply is projected at 1,731 m³/year to produce 1,319 m³/year of demineralised water. Capital investment is estimated at 25 to 60 k€ depending on the level of instrumentation and automation, with operating costs at 4.9 €/m³ driven primarily by feedwater purchase price.
Part B: Wastewater Treatment Unit
Two discharge streams require treatment: condensates from CO₂ desorption cycles containing PEI, and boiler blowdown water containing dissolved salts. Four technologies were evaluated: activated carbon (AC), nanofiltration (NF), and combinations of both.
Treatment scenario | PEI removal | Blowdown volume | Complexity |
Activated carbon alone | ~90% | High | Low |
AC combined with NF | ~100% | Max 40 L/h | Medium |
Nanofiltration alone | ~100% | Max 10 L/h | Higher |
Nanofiltration alone emerged as the most attractive option: it achieves close to 100% PEI removal, generates the lowest liquid waste volume, requires no dry waste disposal, and avoids PEI entering the boiler altogether. The addition of an open-air passive evaporation basin, requiring 100 to 140 m² of surface area, can further reduce liquid waste volumes and minimise operating costs. Activated carbon was retained as a backup option for maintenance periods or system failures.
How the study works
Revalio's engineering study follows a structured approach designed to de-risk technology investment before capital is committed.
The process begins with quality mapping: defining exactly what each water stream contains at entry and what it must meet at exit, whether for process use or discharge compliance. Technologies are then reviewed and shortlisted against these quality targets, and detailed models are built to compare performance, water consumption, waste generation, and cost across scenarios.
For Sirona, this meant working simultaneously across two very different treatment problems: producing ultrapure water from a desalination supply in a remote desert environment, and treating a chemically specific wastewater stream containing a sorbent compound with strict regulatory discharge limits. Resolving both within a single integrated study allowed Revalio to identify synergies, size equipment consistently, and deliver a coherent basis of design for the full water management system.
Study results
✓ Reverse osmosis selected and dimensioned as the preferred water production technology, with a full pretreatment sequence defined and simulated under conservative operating conditions.
✓ Water production unit sized at 400 L/h nominal capacity, producing demineralised water at 8 μS/cm and 76.2% recovery, comfortably meeting the DAC's 157 L/h make-up demand.
✓ Four wastewater treatment technologies evaluated across three techno-economic models, with nanofiltration identified as the preferred solution for PEI removal to below 0.5 mg/L.
✓ Capital investment quantified at 25 to 60 k€ for the water production unit, with operating cost at 4.9 €/m³, providing a robust basis for investment decision-making.
✓ Passive evaporation identified as a cost-effective option for liquid waste minimisation, requiring 100 to 140 m² of open-air basin area to process 10 L/h of PEI-contaminated blowdown.
✓ A clear set of recommendations and next steps delivered, including pilot-scale nanofiltration testing, feedwater variability sampling, and detailed engineering for the preferred treatment concept.
Need to study your process water or wastewater treatment challenges?
When water is both a critical process input and a regulated discharge, getting the treatment strategy right before construction begins is not optional. Revalio designs and delivers engineering studies that give you the technical and economic clarity to make confident investment decisions.
Talk to our experts.