The present study determines the endotoxin removal efficiency of drinking water treatment plants (DWTPs) in Egypt, as examples of conventional treatment methods used in developing countries. The total endotoxin in source water (Nile River) of these DWTPs ranged from 57 to 187 EU-mL-1, depending on the location of treatment plants. Coagulation/flocculation/sedimentation (C/F/S) after chlorine pre-oxidation removed bound endotoxins by 76.1-85.5%, but caused cell lysis and increased free endotoxins by 28.2-33.3% of those detected in raw waters. Rapid sand filtration had not significant effect on free endotoxins, but reduced bound endotoxins by 23-33.3%. Final chlorine disinfection also reduced bound endotoxins to levels around 1 EU/mL, accompanied by an increase in free endotoxins (37-112 EU-mL-1) in finished waters. Simultaneously, final chlorine disinfection removed all heterotrophic bacteria, with low cyanobacterial cell numbers (348-2 450 cells-mL-1) detected in finished waters. Overall, conventional treatment processes at these DWTPs could removal substantial amounts of bound endotoxins and bacterial cells, but increase free endotoxins through cell lysis induced by pre-oxidation and final chlorine disinfection. The study suggests that conventional processes at DWTPs should be optimized and upgraded to improve their performance in endotoxin removal and ensure safe distribution of treated water to consumers.

Resumo Objetivo Nosso estudo visou determinar quais espécies de fitoplâncton, como alimento natural, podem ser ingeridas e digeridas pela tilápia do Nilo (Oreochromis niloticus L.). Métodos Durante o estudo, coletamos e analisamos o fitoplâncton nos intestinos de tilápia do Nilo cultivadas em três viveiros de peixes no sul do Egito, durante o período de outubro de 2012 a setembro. 2013. Indivíduos de tilápias foram colocados em aquários contendo água filtrada para detectar espécies de fitoplâncton não digeridas nas fezes. Resultados A maioria do fitoplâncton encontrado no intestino de tilápia do Nilo foi cianobactérias (36-50%) e clorofíceas (27-38%). Outros grupos, como Diatomáceas, Euglenophyta e Dinophyta, também foram encontrados em menores quantidades (<19%). As espécies fitoplanctônicas mais importantes e dominantes encontradas no intestino de tilápia foram as cianobactérias potencialmente tóxicas, Anabaena, Anabaenopsis, Cylindrospermopsis, Microcystis e Planktothrix. Apenas as diatomáceas foram registradas nas fezes, indicando a capacidade da tilápia de digerir todo o fitoplâncton, exceto espécies deste grupo. Conclusão Os dados deste estudo podem ser úteis para a biomanipulação de proliferação de fitoplâncton em ambientes aquicolas eutróficos.

Abstract Aim This study was carried out to determine which phytoplankton species, as a natural food, can be ingested and digested by Nile tilapia (Oreochromis niloticus L.). Methods During this study, phytoplankton in the gut contents of Nile tilapia collected from three fishponds in southern Egypt were investigated during the period Oct. 2012-Sep. 2013. Samples of tilapia fish were grown in aquarium containing filtered pond water to detect undigested phytoplankton species in the feces. Results The majority of the phytoplankton found in the gut of Nile tilapia was Cyanobacteria (36-50%) and Chlorophyta (27-38%). Other groups such Diatoms, Euglenophyta and Dinophyta were also found but with lower percentages (<19%). The most important and dominant phytoplankton species found in Tilapia gut were the potentially toxic cyanobacteria, Anabaena, Anabaenopsis, Cylindrospermopsis, Microcystis and Planktothrix. Only diatoms were recorded in the feces, indicating the ability of Tilapia to digest all phytoplankton except diatoms. Conclusions The data of this study could be useful for biomanipulation of nuisance phytoplankton blooms in eutrophic aquacultures.

The presence of cyanobacteria and their toxins (cyanotoxins) in processed drinking water may pose a health risk to humans and animals. The efficiency of conventional drinking water treatment processes (coagulation, flocculation, rapid sand filtration and disinfection) in removing cyanobacteria and cyanotoxins varies across different countries and depends on the composition of cyanobacteria and cyanotoxins prevailing in the water source. Most treatment studies have primarily been on the removal efficiency for unicellular Microcystis spp., with little information about the removal efficiency for filamentous cyanobacteria. This study investigates the efficiency of conventional drinking water treatment processes for the removal of the filamentous cyanobacterium, Oscillatoria limnetica, dominating the source water (Nile River) phytoplankton in seven Egyptian drinking water treatment plants (DWTPs). The study was conducted in May 2013. The filamentous O. limnetica was present at high cell densities (660-1 877 cells/mL) and produced microcystin (MC) cyanotoxin concentrations of up to 877 μg·g-1, as determined by enzyme-linked immunosorbent assay (ELISA). Results also showed that conventional treatment methods removed most phytoplankton cells, but were ineffective for complete removal of O. limnetica. Furthermore, coagulation led to cell lysis and subsequent microcystin release. Microcystins were not effectively removed and remained at high concentrations (0.37-3.8 μg·L -1) in final treated water, exceeding the WHO limit of 1 μg·L-1. This study recommends regular monitoring and proper treatment optimization for removing cyanobacteria and their cyanotoxins in DWTPs using conventional methods.