Production of drinking water from rainwater in the Mekong delta: Pilot plant project Nuoc Mua

The Mekong Delta in Vietnam has multiple water-related problems. These include salinization of fresh resources due to sea level rise induced by climate change and over-exploitation of groundwater, soil-subsidence from over-abstracted groundwater resources, and severe pollution of all available water sources by pathogens and pesticides. These water-related pressures are severely affecting human and animal health since 80% of all diseases are water-borne. Agricultural production (e.g. livestock) is also under severe pressure due to these water stresses. We therefore propose an innovative technology to treat harvested rainwater, through a gravity based purification system, especially for dangerous pollutants like pathogens and pesticides. The system is a combination of a biofilter and an UF module. To our knowledge, such technology is not yet available in Vietnam and the previously conducted feasibility study showed a positive outcome. This technology was tested in a project focused on providing drinking water with good quality (WHO Guidelines) for both human and agricultural (livestock rearing) purposes. This project was set up with Water Innovation Consulting (WIC), WUR (WEnR and WFBR), Your Filter Factory, Mekong Institute of Can Tho University and STEPSVN (a water treatment company). The project was granted by Partners for Water in the Netherlands and ran from June 2023 to January 2026. In this pilot project we installed four rainwater harvesting treatment facilities of which two in urban areas and two in rural areas. The urban pilots included a large building at DONRE (local government) at Ca Mau. The second urban pilot was the building of the Mekong Institute on the campus of Can Tho University. One rural pilot plant was installed at the Abavina demonstration farm near Can Tho. The second pilot plant was much larger (storage capacity of 40 m3 water and a production capacity of 400 m3/year). It was installed at a chicken farm in Soc Trang. This farm is located in an area with highly salinized groundwater. The plants comprised biofilters filled with Acticarbon BGP granules from Chemviron (0.6 – 2 mm) in small nylon bags and sand from old slow sand filters, with an empty bed hydraulic residence time of 2.8-2.9 minutes, and UF modules with multibore PES hollow fibers with a 0.02 μm / 100–150 kDa cut-off. Moreover, smooth operation was also possible using a coarse filter with 150 to 300 μm pores to remove debris in the run-off water from the roof. From August 2024 to August 2025 samples were taken and analysed on chemical and microbiological composition and physical properties. Main findings The four plants had a start-up phase in 2024 in which removal efficiencies were low and bacteria were still present in the effluent, but we changed the bags (smaller) for the activated carbon and we disinfected the effluent pipelines in 2025, and in June - August 2025 the plant worked very well with sufficient removal of coliforms, E.coli, Pseudomonas aeruginosa, pesticides and suspended solids. With respect to these parameters, the effluents complied with the WHO, EU and Dutch standards for drinking water. Our main challenge and target, to remove pesticides, was fulfilled. Removal was at least 97% and no sign of activated carbon saturation was found. The numbers of total aerobic microorganisms in the effluent were acceptable, an indication that the plants were operated properly. The ammonia concentrations in all four effluents were lower than the EU drinking water standard. At least in two plants a clear ammonia removal has been observed which may be caused by biological nitrification. The effluents of all four plants still contained dissolved oxygen, which was positive to prevent production of odorous compounds. The concentrations of heavy metals tested (Zn, Ni, Pb and Cu) were lower than the WHO, EU and Dutch drinking water standards. All plants worked well at all locations with respect to the production of acceptable drinking water, rural or urban, near to the coast or far away. The effluents of all four pilot plants are most probably potable (100 mL samples are required to really proof that in a follow up project). The number of pumps required depends on the height difference between the gutter and the UF module. We have used 1 or 2 pumps in most of our pilot plants, and we demonstrated in one plant that free hydraulic flow (no pumps) was possible. Investment costs for a Nuoc Mua plant are estimated at € 13,700 (418 million VND) and the total costs to produce drinking water € 0.004/L (VND 131/L) in case the investment is depreciated in 40 years or € 0.008/L (VND 247/L) using a depreciation period of 10 years. This is well below the 20 L water bottle price of € 0.491 /20 L (VND 10,000), which equals € 0.025/L (VND 750/L). Recommendations A demonstration plant would be welcome to make a longer run e.g. one year. This plant should be located at a place where rainwater is sufficiently polluted. Larger samples should be taken to prove the removal of micro-organisms. Dedicated tests should be carried out to reveal if the removal of pesticides occurs by biodegradation, adsorption or a combined action. Knowledge of the mechanism can be helpful in trouble shooting and to predict lifetime of the biofilter packing. The same is true for knowledge on the development of biofilms in the biofilter and UF module. We should gain more knowledge on timing and method for UF membrane cleaning. We have to find out if a certificate for this type of plant is required by the Vietnamese Government and what does it take to get a certificate e.g. run a demo and carry out sufficient analyses. The results of the current project can be presented at conferences, on websites and in journals. These results may also be used in other countries or even for other types of water.