A comparative review of water disinfection methods appropriate for developing countries and their efficacy, cost-efficiency, and usability

Developing countries are heavily burdened by limited access to safe drinking water and subsequent water-related diseases. Numerous water treatment interventions combat this public health crisis, encompassing both traditional and less-common methods. Of these, water disinfection serves as an important means to provide safe drinking water. Existing literature discusses a wide range of traditional treatment options and encourages the use of multi-barrier approaches including coagulation-flocculation, filtration, and disinfection. Most sources do not delve into approaches specifically appropriate for developing countries, nor do they exclusively examine water disinfection methods.^ The objective of this review is to focus on an extensive range of chemical, physio-chemical, and physical water disinfection techniques to provide a compilation, description and evaluation of options available. Such an objective provides further understanding and knowledge to better inform water treatment interventions and explores alternate means of water disinfection appropriate for developing countries. Appropriateness for developing countries corresponds to the effectiveness of an available, easy to use disinfection technique at providing safe drinking water at a low cost.^ Among chemical disinfectants, SWS sodium hypochlorite solution is preferred over sodium hypochlorite bleach due to consistent concentrations. Tablet forms are highly recommended chemical disinfectants because they are effective and very easy to use, but also because they are stable. Examples include sodium dichloroisocyanurate, calcium hypochlorite, and chlorine dioxide, which vary in cost depending on location and availability. Among physio-chemical disinfection options, electrolysis which produces mixed oxidants (MIOX) provides a highly effective disinfection option with a higher upfront cost but very low cost over the long term. Among physical disinfection options, solar disinfection (SODIS) applications are effective, but they treat only a fixed volume of water at a time. They come with higher initial costs but very low on-going costs. Additional effective disinfection techniques may be suitable depending on the location, availability and cost.^

Measurement of isotopic uranium in water for compliance monitoring by liquid scintillation counting with alpha/beta discrimination

A simple and inexpensive method is described for analysis of uranium (U) activity and mass in water by liquid scintillation counting using $\alpha$/$\beta$ discrimination. This method appears to offer a solution to the need for an inexpensive protocol for monitoring U activity and mass simultaneously and an alternative to the potential inaccuracy involved when depending on the mass-to-activity conversion factor or activity screen.^ U is extracted virtually quantitatively into 20 ml extractive scintillator from a 1-$\ell$ aliquot of water acidified to less than pH 2. After phase separation, the sample is counted for a 20-minute screening count with a minimum detection level of 0.27 pCi $\ell\sp{-1}$. $\alpha$-particle emissions from the extracted U are counted with close to 100% efficiency with a Beckman LS6000 LL liquid scintillation counter equipped with pulse-shape discrimination electronics. Samples with activities higher than 10 pCi $\ell\sp-1$ are recounted for 500-1000 minutes for isotopic analysis. Isotopic analysis uses events that are automatically stored in spectral files and transferred to a computer during assay. The data can be transferred to a commercially available spreadsheet and retrieved for examination or data manipulation. Values for three readily observable spectral features can be rapidly identified by data examination and substituted into a simple formula to obtain $\sp{234}$U/$\sp{238}$U ratio for most samples. U mass is calculated by substituting the isotopic ratio value into a simple equation.^ The utility of this method for the proposed compliance monitoring of U in public drinking water supplies was field tested with a survey of drinking water from Texas supplies that had previously been known to contain elevated levels of gross $\alpha$ activity. U concentrations in 32 samples from 27 drinking water supplies ranged from 0.26 to 65.5 pCi $\ell\sp{-1}$, with seven samples exceeding the proposed Maximum Contaminant Level of 20 $\mu$g $\ell\sp{-1}$. Four exceeded the proposed activity screening level of 30 pCi $\ell\sp{-1}$. Isotopic ratios ranged from 0.87 to 41.8, while one sample contained $\sp{234}$U activity of 34.6 pCi $\ell\sp{-1}$ in the complete absence of its parent, $\sp{238}$U. U mass in the samples with elevated activity ranged from 0.0 to 103 $\mu$g $\ell\sp{-1}$. A limited test of screening surface and groundwaters for contamination by U from waste sites and natural processes was also successful. ^