Perfluorooctane sulphonate (PFOS) and perfluorooctanoic acid (PFOA) are chemicals that have been used for many years as surfactants in a variety of industrial and consumer products. Owing to their persistent, bioaccumulative and toxic (PBT) characteristics, PFOS has been phased out by its principal producer and the use of PFOA has been reduced. This PBT potential and a number of pollution incidents have led in recent years to an increase in studies surveying the concentrations of PFOS and PFOA in environmental waters worldwide. This paper reviews the results of these studies, as well as the monitoring that was conducted after the pollution incidents. The results of surveys suggest that PFOS and PFOA are found in environmental waters worldwide at low levels. In general, these levels are below health-based values set by international authoritative bodies for drinking water. There have been limited measurements of these chemicals in drinking water, but again these are below health-based values, except in some cases following pollution incidents. Monitoring studies suggested that where PFOS and PFOA were detected, they were at similar levels in both source and drinking water, suggesting that drinking water treatment does not remove these chemicals. However, new data show that PFOS and PFOA are effectively removed by granular activated carbon absorbers in practice. Further research is required on the newer perfluorinated chemicals that appear to be safer, but their degradation products have not as yet been fully studied.
Using batch cultures, we determined transformation rate coefficients for microbial transformation of 2,4-dichlorophenoxyacetic acid butoxyethyl ester (2,4-DBE) in periphyton-dominated ecosystems. Rates of 2,4-DBE loss were measured over short periods of time (usually less than 10 h), and first-order transformation rate coefficients ( k 1 ) were determined under the specific conditions of low 2,4-DBE concentrations and no growth. Values for k 1 were divided by total plate counts and by biomass measured as ash-free dry weight to give second-order rate coefficients ( k b and k AFDW , respectively) for use in predictive models. Using periphyton attached to Teflon strips, we also determined second-order rate coefficients based on the ratio of colonized surface area to container volume ( k A ). Mean second-order rate coefficients were used to predict 2,4-DBE transformation rates in microcosms having diverse chemical and biological environments. The observed transformation rates among the microcosms were most accurately predicted by using k A .
The paper describes some water‐treatment processes which have been investigated on a laboratory and pilot‐plant scale for their effectiveness in removing toxic algal cells and the dissolved toxins microcystin‐LR and anatoxin‐a. Oxidation with ozone or potassium permanganate, or treatment by biological activated carbon, were found to be the most effective processes for removal of the dissolved toxins. Chlorination was effective only for the removal of microcystin‐LR. Toxins, contained within algal cells, could be removed effectively by coagulation, clarification and filtration under suitable conditions. Consideration of the structure and properties of micro‐cystin variants suggests that treatments which are suitable for removal of microcystin‐LR and anatoxin‐a should be suitable for removal of other microcystins.
The occurrence of the protozoan parasite Cryptosporidium parvum in water supplies, and the resultant outbreaks of cryptosporidiosis in the UK and USA, have led to concern over the ability of conventional water treatment processes to remove Cryptosporidia from water sources. Large scale pilot plant trials of water treatment have been carried out in the UK to establish the degree of removal that can be achieved by a range of treatment processes, including dissolved air flotation, and to compare the performance of different treatment options. Results from part of these trials are presented in this paper. These results suggest that well operated chemical coagulation based treatment, using either dissolved air flotation or floc blanket clarification, should be capable of achieving removal of Cryptosporidium oocysts of over 99%. There was no evidence of differences in performance between the different types of filter media investigated. The risk of increased Cryptosporidium concentration in the filtered water will increase as filtrate turbidity increases. However, other factors such as high coagulant metal-ion concentration in the filtered water, or a sudden increase in clarified water turbidity, without any increase in filtered water turbidity, may also indicate treatment problems and associated risk from Cryptosporidia. Recycling of backwash waters may also increase the risk.
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