Sanihub - Case studies - The Saniforce, a Solar Thermal Pasteurizer, for wastewater disinfection and cholera prevention in humanitarian settings

The Saniforce, a Solar Thermal Pasteurizer, for wastewater disinfection and cholera prevention in humanitarian settings

OCTOPUS Case Study
Implemented by: International Organization for Migration, Veolia Foundation
22 December 2025
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Description of the emergency context

The Rohingya, an ethnic minority from Myanmar, have faced decades of discrimination, restricted rights, and violent crackdowns, particularly after the 1962 military coup. The latest escalation in August 2017 forced nearly one million Rohingya to flee to Bangladesh. The Government of Bangladesh established large refugee settlements across the hilly areas of Cox’s Bazar (Ukhia and Teknaf), which by June 2023 hosted over 1.1 million people. In such mass-displacement settings, effective faecal sludge management (FSM) is essential to protect public health and reduce environmental contamination.
Numerous national and international organisations are responsible for faecal sludge management (FSM) in the camps. As of 2023, the Cox’s Bazar WASH Cluster reported approximately 49,530 latrines, serving an average of 21 people per latrine. This results in an estimated sludge generation of 1.1 L/person/day—equivalent to roughly 1,025 m³ of faecal sludge per day (1.5–2% solids). In parallel, 164 faecal sludge treatment plants operate in the camps with a combined treatment capacity of 879 m³/day, which remains insufficient to treat the total daily sludge production (data sourced from the FSM Strategy for Cox’s Bazar, August 2023, available at: https://rohingyaresponse.org/wp-content/uploads/2023/08/FSM-strategy-Final-Version-CXB-August-2023.pdf).
Extreme population density, limited land availability, constrained technical capacity, and exposure to climate hazards (including frequent flooding and landslides) make WASH service provision exceptionally challenging in the Rohingya camps. These vulnerabilities can lead to cholera outbreaks, which continue to pose a persistent threat to the local community. In this context, robust, resilient and easy-to-operate technologies are needed to safeguard public health. The solar thermal pasteuriser (STP) Saniforce, developed by the Veolia Foundation, offers a promising solution that utilises solar energy to inactivate pathogens without the use of chemicals.
A pilot unit was deployed at the decentralised wastewater treatment system (DEWATS) in Camp 12 to assess its ability to fully inactivate pathogens as a post‑treatment step. The objective is to generate evidence on treatment effectiveness and evaluate its suitability for replication in other humanitarian contexts. By ensuring complete pathogen inactivation, the STP contributes to cholera prevention and reinforces infection‑prevention and control measures in a setting highly vulnerable to rapid disease transmission.

Description of the treatment process
The core concept of the system is to inactivate pathogens through heat, with solar thermal energy serving as the primary source of that heat. To achieve this, the system uses three rows of five solar thermal collectors, each with a surface area of 2.28 m², giving a total collection area of 34.2 m². These collectors heat water, which then acts as the thermal medium for raising the temperature of the wastewater or faecal sludge.
Pasteurisation takes place in a 500 L mechanically stirred, thermally insulated tank equipped with a double jacket. Operating in batch mode, the process gradually increases the temperature of the sludge until it reaches the pasteurisation setpoint. Once this temperature is achieved, active heating stops and the sludge is held at that temperature for the required retention time to ensure pathogen inactivation.
To stabilise performance and optimise the use of solar energy, the system includes two interconnected 800 L thermally insulated buffer tanks for storing excess heat. One of these tanks is equipped with a 3 kW electric resistance heater, which provides backup heating during periods of low solar radiation, such as cloudy days. The hot water circulation is flexible: it can flow from the solar collectors to the pasteurisation tank, from the collectors to the buffer tanks, and from the buffer tanks to the pasteurisation tank.
The solar pasteurisation system is modular and can be adjusted to match the required treatment capacity in different contexts. It can be upscaled by adding more solar thermal collectors and increasing the number and/or volume of the buffer and pasteurisation tanks. Conversely, it can be downscaled by using fewer collectors, and smaller buffer and pasteurization tanks.
Assessment & design feasibility
The solar pasteuriser was installed in Camp 12 next to one of the 40 DEWATS plants operating in the camp. The feedstock consists of faecal sludge from pit latrines serving approximately 5,000 people. The DEWATS treats around 3,000 L/day of faecal sludge, reducing organic, nutrient and pathogen loads to a level that permits infiltration into the soil through an infiltration bed (for more information, see: https://octopus.solidarites.org/2023-01-iom-decentralized-wastewater-treatment-system-dewatsin-rohingya-refugee-camps-coxs-bazar). However, pathogen concentration remains too high for discharge into surface water or for safe irrigation.
The prototype itself was installed on flat, compacted soil adjacent to the DEWATS plant. For performance assessment, the DEWATS effluent was directed to the solar pasteuriser prototype. This stream had the appearance of a low-viscosity liquid (similar to water), with a strong odour, notable turbidity and visible suspended particles..
While the design and construction of the system require engineering skills, the unit is built in a workshop and delivered to site almost ready to use. Some expertise is still needed to install the solar thermal collectors and connect them to the pasteuriser. In contrast,, its day-to-day operation and maintenance are straightforward and do not demand specialised expertise. In case of technical issues, support from a local plumber or electrician is generally sufficient to restore functionality.
The site is exposed to heavy monsoon rains and flooding risks, but the technology has proven resilient thanks to its robust construction, corrosion-resistant materials, and heavy structural weight, which provide stability and protection under challenging weather conditions.
Construction
All major components of the system were supplied through the Veolia Foundation. The pasteurisation tank was fabricated by a mechanical workshop subcontracted by the Foundation, while the solar equipment, hydraulic components, and electrical elements were sourced from suppliers in France. Minor items—such as plumbing fittings, electrical consumables, and installation accessories—were procured locally in Bangladesh. Several components – including solar thermal collectors, buffer tanks, hydraulic material and some electric supplies – can also be sourced on the local market for future deployments, offering significant potential for cost reduction and easier procurement.The equipment was shipped from France to Bangladesh and the on-site installation for this prototype required approximately two weeks. All components were assembled directly at the Camp 12 site. New design iterations now include the option of pre-assembled modules, enabling plug-and-play installation upon arrival and further reducing installation time to a few days.
Operation & Maintenance
(i) OperationBefore starting the system, the hydraulic circuits must be filled with water and pressurised to approximately 2–2.5 bar, ensuring that all air is properly purged. Several operational modes were tested during field assessment:– Mode 1: heating the pasteurisation tank directly from the solar collectors;– Mode 2: heating the buffer tanks using solar energy;– Mode 3: heating the pasteurisation tank using stored thermal energy from the buffer tanks;– Combined Mode 2 and 3: heating the buffer tanks from the solar thermal collectors while heating the solar pasteuriser from the tanks Switching between modes requires activating or deactivating the corresponding pumps and opening or closing the relevant valves. When required, the electric resistance installed in one of the buffer tanks can be activated to boost the temperature of the stored water and ensure sufficient thermal energy for pasteurisation. Different pasteurisation temperatures and holding times were also trialled.For each batch, the pasteuriser is filled with sludge, heated to the target temperature, held for the required exposure time, and then emptied. During operation, the operator must verify correct functioning by checking the water flow in the circuits through the flowmeter and temperature readings in different locations of the system.(ii) MaintenanceRoutine maintenance is simple and does not require specialised skills. The solar collector surfaces must remain clean—free of dust, sand, and grease. They should be rinsed only with water or specialised products, but no detergents as they may leave residues that reduce efficiency. It should be verified that there is sufficient water in the tank connected to the pressure booster, which keeps the system pressure above 2 bar. Also, it is important to check regularly that the pressure booster is working properly to keep the system pressure above 2 bar. The pasteurisation tank should be cleaned daily with water after use; a water pressure gun can facilitate this task. Detergents are not required.
Lessons learned
• Higher pasteurisation temperatures result in more efficient pathogen inactivation, but they also reduce overall treatment capacity due to longer heating times.• A pasteurisation temperature of 60 °C with a holding time of ~15 minutes was found sufficient to achieve safe inactivation levels (including E. coli and V. cholerae) while maintaining a reasonable treatment capacity.• Optimal operation requires strategic use of stored thermal energy and backup electric heating in the early morning and late afternoon, while direct solar heating is most effective during midday. • To improve the system to reduce the operating costs, the most viable improvements include:– Using a photovoltaic system instead a diesel generator to electricity for the electric equipment; – Increasing the number of solar thermal collectors;– Using an LPG boiler instead of a diesel generator for backup heating;– Integrating a heat exchanger for energy recovery (more suitable for long-term deployments)• The technology is replicable in other geographical contexts, where even better performance may be achieved—South Sudan is a promising example due to higher average solar radiation.• The solar pasteuriser is particularly suited for treating effluents from cholera treatment units/centres, potentially becoming an integral part of infection prevention and control (IPC) protocols to limit the spread of cholera. It can also be applied to the treatment of highly pathogen-loaded wastewater or sludge from hospitals, clinics, public health laboratories, and similar facilities.• Important areas of R&D to further improve the process include: real-time monitoring and control; integration of the solar pasteuriser with an incinerator used for solid waste treatment to recover waste heat for pasteurisation; incorporation of a heat-recovery unit to pre-heat the incoming stream using the thermal energy of the hot pasteurised effluent; and the development of safe reuse pathways for the pasteurised effluent.
Strengths
• Efficient pathogen reduction without the need for chemicals
• Scalable technology (can be expanded or downsized depending on demand)
• Climate-resilient, with durable materials able to withstand extreme weather and a system capable of maintaining operation through stored thermal energy or backup power
• Low carbon footprint thanks to primary reliance on solar thermal energy
• Sustainable and energy-efficient system requiring minimal to low external power
• Replicable and adaptable to other humanitarian or low-resource settings
• Simple to operate and maintain, without the need for highly specialised skills
• Reduces health risks linked to contaminated effluent, especially during cholera outbreaks
Weaknesses
• No reduction of solids, organic matter, or nutrient load
• Requires sufficient space for installing the solar thermal collectors
• Limited performance during overcast or rainy conditions when relying solely on solar energy, making backup power necessary
• Challenging to reach and maintain temperatures above 70 °C’
• Unable to operate well with too viscous sludges
Sharable project files

Final-report_Solar-Pasteuriser

pdf

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Project Details

Geographic Location
Ukhia, Bangladesh
Main treatment objectives
Pathogen reduction
Resources needed for operation
Electricity
Engine
Water
Technologies employed
Disinfection
Design population
500 - 2000 people
Design input flow
0.5 - 2 m2/day
Source of sludge
Lined pit latrines
Final outputs
Effluent
Skills level
Design and Engineering Specialist
FSM specialist for construction
Local NGO for operation and maintenance

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