Scientists from Spain’s University of Huelva, have used 3D printing to create a spiral structure capable of removing eighteen disinfection by-products (DBPs) from drinking water.
Chronic exposure to such chemicals has been demonstrated to increase health risks, including the threat of cancer, and the team’s research project aims to make the purification process more efficient at removing them. The scientists’ novel approach could have applications at water treatment facilities, to identify and separate the most dangerous chemicals, and make water safer to drink.
Disinfection by-products in drinking water
While water disinfection is essential to public health, toxic substances can be formed as a consequence of the process. These include a particularly volatile non-regulated group of chemicals called Haloketones (HKs), Trihalomethanes (THMs) and Nitrogenous disinfection by-products (N-DBPs), which are formed after several treatment processes. Many different methods exist for removing HKs, but even though the first technique was devised in 1995, research is ongoing in order to streamline the process. Researchers from the University of Cordoba for instance, developed a method of removing 14 HKs from treated water in 2015, which provided lower limits of detection than previous studies.
According to the Huelva researchers, the Cordoba method presented drawbacks, such as poor reproducibility and a low capacity of the extraction due to the small absorbent area. The Huelva scientists opted to build upon an existing technique called hollow-fibre liquid phase microextraction (HF-LPME) instead.
Using 3D printing to create the assembly made it easy to operate, more robust and available at a lower cost than previous iterations, according to the researchers. In addition, the structure displayed a higher superficial area for the extraction, and the disposable nature of the fiber reduced the risk of cross-contamination or carryover effect. Additive manufacturing also enabled the scientists to overcome shortcomings identified in previous projects, such as difficulty miniaturizing the assembly and producing commercial prototypes.
The 3D printed support structure and new methodology
Designed using CAM software, the device was 3D printed using Wuppertal polypropylene hollow-fibre materials, in a Prusa i3 open source 3D printer. The final device featured an internal diameter of 600 μm, a wall thickness of 200 μm, and 0.2 μm pores. Composed of five pieces: the cap septum, septum, stopper piece, hollow fibre positioner and closure piece, the design was connected by a syringe needle leading through all the components.
Once these parts had been combined, the device’s hollow fiber positioner was then entered into the acceptor phase. This involved the application of 20 μL of octanol for 2 minutes to open its pores, in addition to making it more flexible. A mixture of sodium sulphate and pH adjusted water were then added to increase the extraction efficiency of the DBPs, before it was introduced to 20ml of sample drinking water.
The extraction of the target chemicals took place over a period of 30 minutes, with the solution being heated to a temperature of 45oC. Effervescence was applied to the process in the form of CO2 gas bubbles which caused volatile analytes to move from the donor phase (liquid) to the acceptor phase (gas). This prevented the sample water from being heated, favouring selectivity, as only volatile compounds can be recovered at low temperature. Moreover, the turbulence produced in the liquid by the formation of the bubbles favoured natural agitation, which then minimized the extraction time.
The 3D printed device was pivotal to the process, with its simple fibre handling, reproducibility and extraction efficiency representing important improvements on other needle-based techniques. The structure also allowed for an increased fibre surface even with a low sample volume, which significantly facilitated the extraction.
Test results showed detection limits ranging from 10 to 35 THMs and 10 to 16 HKs, well within the 80-100 μg and 20-70 μg recommended for safe drinking water by the World Health Organization (WHO). The applicability of the method was assessed in 6 local water distribution systems. Although the concentration of THMs in the reservoirs were higher than that in the treated water of their source plant, the researchers suggest that this is because of possible degradation along the distribution system.
The Huelva scientists deemed the method to be reproducible, and able to facilitate existing purification operations, opening up opportunities for further investigations using miniaturized instruments in future.
Additive manufacturing in water purification
3D printing has been utilized in a similar way by hobbyists and business groups, with the intention of making different water supplies safer to drink.
In July 2017, a hobbyist 3D printing project from a multidisciplinary team at the University of Bath created a plastic ‘slab.’ Designed to provide clean drinking water to communities in parts of Asia, Africa, and Latin America, its maze-like design harnessed the heat and ultraviolet light from the sun, to kill harmful microbes living in contaminated liquids.
Researchers used 3D printed advanced spacer mesh in November 2016, to enable the more productive use of reverse-osmosis to produce water that was safe to drink. The material was found to reduce the cost, time and risk of the process, and the team aimed to develop a strategy for reverse-osmosis membranes on the Pacific Coast of Mexico.
The first Additive Manufacturing Consortium (Conmad) in Latin America, was hosted in Mexico in 2018, with more than $13m invested in 3D printing projects. Mexican government agency Conacyt attended the event, pledging to help provide clean drinking water to communities on the Pacific Coast of Mexico.
The researchers’ findings are detailed in their paper titled “Effervescence-assisted spiral hollow-fibre liquid-phase microextraction of trihalomethanes, halonitromethanes, haloacetonitriles, and haloketones in drinking water” which was published in volume 397 of the Journal of Hazardous Materials. It was co-authored by A. Dominguez-Tello, A.Dominguez-Alfaro J.L. Gómez-Ariza, A. Arias-Borrego and T. García-Barrera.
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Featured image shows the researchers’ five part spiral design being connected by a syringe needle, alongside its 3D printed support device. Photo via Hazardous Materials.