| Title | Arsenic removal by discontinuous ZVI two steps system for drinking water production at household scale |
| Abstract | Different countries in Europe still suffer of elevated arsenic (As) concentration in groundwaters used for human consumption. In the case of households not connected to the distribution system, decentralized water supply systems, such as Point of Use (POU) and Point of Entry (POE), offer a direct benefit for the consumers. Field scale ex-situ treatment systems based on metallic iron (ZVI) are already available for the production of reduced volumes of drinking water in remote areas (village scale). To address drinking water needs at larger scale, we designed a pilot unit able to produce an elevated daily volume of water for human consumption. We tested the long-term As removal efficiency of a two steps ZVI treatment unit for the production of 400 L/day clean water based on the combination of ZVI corrosion process with sedimentation and retention of freshly formed Fe precipitates. The system treated 100 mu g/L As(V)-contaminated oxic groundwater in a discontinuous operation mode at a flow rate of 1 L/min for 31 days. Final removal was 77-96% and the most performing step was aeration/sedimentation (A/S) tank with a 60-94% efficiency. Arsenic in the outflow slightly exceeded the drinking water limit of 10 mu g/L only after 6000 L treated and Fe concentration was always below 0.2 mg/L. Under proposed operating conditions ZVI passivation readily occurred and, as a consequence, Fe production sharply decreased. Arsenic mobility attached to particulate was 13-60% after ZVI column and 37-100% after A/S tank. Uniform amorphous cluster of Fe nanoparticles (100 nm) formed during aeration drove As removal process with an adsorption capacity corresponding to 20.5 mgAs/gFe. Research studies often focus only on chemico-physical aspects disregarding the importance of biological processes that may co-occur and interfere with ZVI corrosion, As removal and safe water production. We explored the microbial transport dynamics by flow cytometry, proved as a suitable tool to monitor the fate of both single cells and bioactive particles along the treatment train of the pilot unit. A net release of bioactive particles, representing on average 26.5% of flow cytometric events, was promoted by the ZVI filter, with densities 10 times higher than those found in the inflow. In conclusion, the proposed system was efficient to treat large daily volumes of As contaminated groundwater. However, filter design and operating conditions should be carefully adapted to specific situation, since several key factors affect As removal efficiency. An effort in the optimization of ZVI filter design should be made to reduce fast observed ZVI passivation and low As adsorption capacity of the whole filter: More attention to biomass retention and bioactive particles travelling within the unit should be given in order to elucidate bacteria influences on As removal efficiency and related sanitary risks on long term basis. (C) 2016 Elsevier Ltd. All rights reserved. |
| Source | Water research (Oxf.) 106, pp. 135–145 |
| Keywords | ArsenicZero valent ironIron precipitationFlow cytometryDrinking waterAdsorption |
| Journal | Water research (Oxf.) |
| Editor | Pergamon Press., New York, Regno Unito |
| Year | 2016 |
| Type | Articolo in rivista |
| DOI | 10.1016/j.watres.2016.09.057 |
| Authors | Casentini, Barbara; Falcione, Fabiano Teo; Amalfitano, Stefano; Fazi, Stefano; Rossetti, Simona |
| Text | 364001 2016 10.1016/j.watres.2016.09.057 ISI Web of Science WOS 000388047500014 Scopus 2 s2.0 84989315295 Arsenic Zero valent iron Iron precipitation Flow cytometry Drinking water Adsorption Arsenic removal by discontinuous ZVI two steps system for drinking water production at household scale Casentini, Barbara; Falcione, Fabiano Teo; Amalfitano, Stefano; Fazi, Stefano; Rossetti, Simona Istituto di Ricerca sulle Acque Consiglio Nazionale della Ricerca Different countries in Europe still suffer of elevated arsenic As concentration in groundwaters used for human consumption. In the case of households not connected to the distribution system, decentralized water supply systems, such as Point of Use POU and Point of Entry POE , offer a direct benefit for the consumers. Field scale ex situ treatment systems based on metallic iron ZVI are already available for the production of reduced volumes of drinking water in remote areas village scale . To address drinking water needs at larger scale, we designed a pilot unit able to produce an elevated daily volume of water for human consumption. We tested the long term As removal efficiency of a two steps ZVI treatment unit for the production of 400 L/day clean water based on the combination of ZVI corrosion process with sedimentation and retention of freshly formed Fe precipitates. The system treated 100 mu g/L As V contaminated oxic groundwater in a discontinuous operation mode at a flow rate of 1 L/min for 31 days. Final removal was 77 96% and the most performing step was aeration/sedimentation A/S tank with a 60 94% efficiency. Arsenic in the outflow slightly exceeded the drinking water limit of 10 mu g/L only after 6000 L treated and Fe concentration was always below 0.2 mg/L. Under proposed operating conditions ZVI passivation readily occurred and, as a consequence, Fe production sharply decreased. Arsenic mobility attached to particulate was 13 60% after ZVI column and 37 100% after A/S tank. Uniform amorphous cluster of Fe nanoparticles 100 nm formed during aeration drove As removal process with an adsorption capacity corresponding to 20.5 mgAs/gFe. Research studies often focus only on chemico physical aspects disregarding the importance of biological processes that may co occur and interfere with ZVI corrosion, As removal and safe water production. We explored the microbial transport dynamics by flow cytometry, proved as a suitable tool to monitor the fate of both single cells and bioactive particles along the treatment train of the pilot unit. A net release of bioactive particles, representing on average 26.5% of flow cytometric events, was promoted by the ZVI filter, with densities 10 times higher than those found in the inflow. In conclusion, the proposed system was efficient to treat large daily volumes of As contaminated groundwater. However, filter design and operating conditions should be carefully adapted to specific situation, since several key factors affect As removal efficiency. An effort in the optimization of ZVI filter design should be made to reduce fast observed ZVI passivation and low As adsorption capacity of the whole filter More attention to biomass retention and bioactive particles travelling within the unit should be given in order to elucidate bacteria influences on As removal efficiency and related sanitary risks on long term basis. C 2016 Elsevier Ltd. All rights reserved. 106 Published version Arsenic removal by discontinuous ZVI two steps system for drinking water production at household scale Casentini_Water Research_2016.pdf Articolo in rivista Pergamon Press. 0043 1354 Water research Oxf. Water research Oxf. Water res. Oxf. Water research. Oxf. simona.rossetti ROSSETTI SIMONA stefano.fazi FAZI STEFANO stefano.amalfitano AMALFITANO STEFANO barbara.casentini CASENTINI BARBARA |
