An electrical- and chemical-free approach using microfilter and Ag-based catalysts for emergency drinking water treatment

In emergency cases such as disasters, supplying enough safe drinking water is one of the most urgent needs for human life. This research aimed to develop a chemical- and electricity-free drinking water treatment system based on microfiltration and catalysts of Ag and Ag-TiO2-SiO2 coated on glass spheres in both dark and sunlight conditions. The system was applied to treat raw water samples taken from five rivers in Vietnam, simulated floodwater samples with high turbidity and E. coli concentration, and real flooding water samples. The results showed the filtration unit fed with simulated floodwater generated lower fluxes and shorter working durations before chemical cleaning than that fed with normal river water. However, filtrate quality was not significantly different for these five water samples with very low values of turbidity (0-0.66 NTU), total coliform (5-19 CFU (100 mL)-1), and E. coli (0-17 CFU (100 mL)-1). The catalyst units using glass spheres coated with either Ag in dark and sunlight or Ag-TiO2-SiO2 under sunlight can completely remove E. coli and coliform as well as additionally mitigate natural organic matters. This study hence suggests the combination of microfiltration and Ag-based catalytic treatment for safe drinking water supply in emergencies, especially for flooding conditions.

Morphological and elemental properties of urban aerosols among PM events and different traffic systems

Morphology and elemental composition of individual fine ambient particles varied among types of PM events and between two different urban environments having different major transportation systems (gasoline/diesel vehicles versus motorcycles). Carbonaceous particles were the most dominant in PM events, whereas S-rich particles were the highest in non-events at urban Gwangju in Korea. The aged soot, semi-volatile organic (SVO), and non-volatile organic (NVO) particles were more abundant in the polluted-long range transport (LTP) event than those in the dust-LTP event and non-event. In the dust-LTP event, the aged mineral dust particles outnumbered the fresh ones, suggesting the mineral dust particles were aged during their long-range transport. At HoChiMinh (HCM) in Vietnam, the fraction of carbonaceous particles was much higher than Gwangju (66% versus 30%) possibly due to more abundant two-stroke motor vehicles at HCM. Of the carbonaceous particles, combustion soot (19%) was the highest, followed by NVO (18%), SVO (17%), and biological particles (11%) at HCM, whereas SVO (11%) and NVO (10%) particles were the highest, followed by combustion soot particles (8%) at Gwangju. The higher fraction of mineral dust particles was also observed at HCM, indicating the sampling site was influenced by dust from unpaved roads and construction sites.

Oxidation and coagulation of humic substances by potassium ferrate

Ferrate (FeO₄²⁻) is believed to have a dual role in water treatment, both as oxidant and coagulant. Few studies have considered the coagulation effect in detail, mainly because of the difficulty of separating the oxidation and coagulation effects. This paper summarises some preliminary results from laboratory-based experiments that are investigating the coagulation reaction dynamically via a PDA instrument, between ferrate and humic acid (HA) at different doses and pH values, and comparing the observations with the use of ferric chloride. The PDA output gives a comparative measure of the rate of floc growth and the magnitude of floc formation. The results of the tests show some significant differences in the pattern of behaviour between ferrate and ferric chloride. At pH 5 the chemical dose range (as Fe) corresponding to HA coagulation was much broader for ferrate than ferric chloride, and the optimal Fe dose was greater. Ferrate oxidation appears to increase the hydrophilic and electronegative nature of the HA leading to an extended region of charge neutralisation. A consequence of the ferrate oxidation is that the extent of HA removal was slightly lower ( approximately 5%) than with ferric chloride. At pH 7, in the sweep flocculation domain, ferrate achieved much greater floc formation than ferric chloride, but a substantially lower degree of HA removal.