Arsenic removal from geothermal influenced groundwater with low pressure NF pilot plant for drinking water production in Nicaraguan rural communities

This research evaluated the effect of different fluxes (16, 23 & 30 L/m(2) h) and temperatures (31,35 & 43 degrees C) on the rejection of As(V) during nanofiltration (NF) of natural geothermal influenced groundwater in Nicaragua. A NF pilot plant powered by solar panels was built and operated in rural community Telica, exposed to As-rich chinking water sources due to geothermal influences. The results showed that even at high temperatures it is possible to obtain high rejection of As(V) (0.87-0.9) during NF filtration (recovery 10%; flux 16 L/m(2) h) of geothermal influenced groundwater, with the additional advantage of requiring low operating pressures (1.2 bar similar to 12mwc).The permeate concentration (similar to 5 mu g/L) complied with the WHO guideline for drinking water and the concentrate (similar to 55 mu g/L) could be used by local villagers for daily activities (e.g., laundry and bathing). For all investigated fluxes and temperatures the order of rejection of As(V) (as HAsO42-), compared with the other anions, could be interpreted on the basis of its charge, hydrated radius and hydration free energy. At lower temperatures (31 and 35 degrees C) permeate quality improved slightly (similar to 3 mu g/L), but although an increased temperature had a negative effect on the As rejection, As concentrations in the permeate never exceeded 5 mu g/L, while the required TMP dropped - depending on the flux - with 0.5 to 1 bar. This decrease in required pressure might be of huge benefit in deserted, rural locations where electricity is scarce, as with an overhead tank of 10-15 m a gravity fed NF system would be feasible. (C) 2019 Elsevier B.V. All rights reserved.