Solar rainwater reactorWATERSPOUTT will develop new reactors for the solar disinfection of harvested rainwater. These will provide up to 125 liters/day of drinking water to communities in South Africa and Uganda.
Harvesting rainwater is a sustainable means for reducing water demand, increasing the regional water security and providing economic benefits to the community, however harvested and storage water can be heavily contaminated by a variety of pathogenic organisms.
Research on low-cost solar reactors to enhance the efficacy of solar water disinfection has been carried out in the last decade. Flow reactors have focused on increasing the optical inactivation component of sunlight using solar mirrors, while others have focused on increasing the thermal component of the solar spectrum. The use of either compound parabolic collectors (CPC) or other low-cost reflectors increases the solar light collection. CPCs are known to speed up the inactivation process and to increase the radiation exposure. To increase the output of treated water, new SODIS photo-reactors should achieve efficient collection of sunlight for large volumes of water.Automatic sequential bath reactor concept (Polo-Lopez et al., J. Haz. Mat., 196 (2011) 16-21)100L- flow solar reactors with add-on CPC mirrors (Plataforma Solar del Almeria, CIEMAT, Spain)
Water turbidity is also critical for reactor design. If the water is sufficiently transparent the optical reactor path length (diameter) can be increased up to 10 cm. Several works have demonstrated the use of solar CPC aluminum mirrors to enhance the disinfection performance for several waterborne pathogens (E. coli, Enterococci, fungi spores, and C. parvum oocysts). There are limitations in scaling-up these systems for using large batch volumes or continuous flow recirculation reactors.Twenty-five litre static batch Solar Water disinfection system with low turbidity (left) and high turbidity water (right). (Ubomba-Jaswa et al. J. Chem. Tech. Biotech 85, 2010)
Solar JerrycanWATERSPOUTT will develop, pilot and commercialize a 20L transparent jerrycan suitable for solar disinfection. In 2015 RCSI, NUIM and CIEMAT-PSA researchers demonstrated that 20L transparent polycarbonate water dispenser bottles, identical to the water cooler bottles found in many office environments, were just as effective for SODIS as 2L PET plastic bottles. The 20 L bottles have been already introduced into primary schools in the Lwengo District of Uganda
In Sub-Saharan Africa, the plastic jerrycan is the most commonly used container for water collection and transport. Those jerrycans are easily contaminated, and therefore are at risk of rendering the water they are carrying unsafe for consumption. Standard jerrycans are typically made of opaque polycarbonate plastic, but their shape is particularly suited for SODIS applications.Typical plastic jerrycan used for water transportPlastic bottle (20 L) undergoing SODIS
A 20 L jerrycan can be specifically designed to maximize solar disinfection. For example, the optical path length should not be too long, so that solar energy is not scattered out of the bulk by suspended particulates or absorbed by humic acids in the water. Ideally, a transparent jerrycan can be laid on its side to receive maximum incident solar radiation.
Rather than proceed with a standard jerrycan design and just change the container material from opaque to transparent, the WATERSPOUTT design team will liaise with the community leaders and potential users in Ethiopia (Tigray) to ensure that the prototype meets the needs of the people it is designed for.
Solar-ceramic filtrationWATERSPOUTT will design, develop and prototype a technology which combines the basic principles of SODIS with ceramic water filtration.
Ceramic water filtration is a technique used in many low-income countries to obtain safe drinking water. The water percolates through the ceramic filter, which blocks pathogens. Ceramic filters can typically be expected to reduce bacterial populations by 99%-99.9%, but while they are good at removing turbidity, in general ceramic filters are not effective against viral pathogens, and require regular maintenance to be kept in good working condition.
Despite the limitations in efficacy and long term viability, ceramic filtration is widely accepted in many low-income communities. Part of the appeal is associated with a “technology bias” in that the ceramic filter has the appearance of a modern technology and there is social prestige associated with owning one.
Although SODIS is a more effective method to obtain safe drinking water, it is adversely affected by technology bias since the SODIS apparatus usually consists of 2L plastic bottles which are not perceived as being of a high technological value. It would be ideal to combine the effectiveness of SODIS with the acceptance of ceramic water filtration.
Most commercially available ceramic filtration units use a 10-20L transparent container to collect and store the filtered water. Such transparent containers have been shown by RCSI and CIEMAT researchers to be suitable for SODIS. Variations on the possible design can include transparent source water containers with the ceramic filter unit inserted into the bottom of the assembly. Such a design allows SODIS treatment of the source water while it resides in the upper reservoir.Ceramic water filtration units being examined for solar-ceramic filtration potential in Almeria