Drinking water treatment using upflow slow sand filtration systems in high density Cylindrospermopsis raciborskii cyanobacteria water

Abstract

a b s t r a c tCyanobacterium Cylindrospermopsis raciborskii may cause problems in drinking water treatment plants if specific attention is not focused on removing the cyanobacteria. Slow sand filtration possesses a good capacity for cyanobacteria removal and is a simple alternative to more expensive treatments. However, high cyanobacteria concentrations can correspond to an operational problem for slow sand filters by reducing the filter running time, and therefore rough filtration is necessary. In this study, two similar upflow slow sand filters were used to evaluate C. raciborskii removal. Water with 9.1 × 10 5 cells/mL was used and an average of 99% of cells were removed. Nevertheless, average concentrations of 1.4 × 10 4 and 2.1 × 10 4 cells/mL were observed after filtration, and this could continue to act as a problem for water treatment. The system also indicated good results in terms of removing total coliforms, colour and turbidity. The average turbidity was below 1.0 NTU, which is the maximum value permitted by Brazilian regulations and WHO recommendations. The major advantage of the upflow slow sand filter involved the high removal of C. raciborskii without compromising the running time of the filter with the filters operating for almost 80 days without the use of rough filters. However, it is necessary to use a complementary treatment process to achieve better water quality results.

Influence of slow sand filter cleaning process type on filter media biomass: backwashing versus scraping

“…A. ambigua, other diatoms, and filamentous cyanobacteria were the most common microorganisms present (Figure 3, 3 and 8). These microorganisms appearance is not surprising since they are common on the Lagoa do Peri water and were previously reported as filter clogging phytoplankton (de Souza et al, 2017;Saavedra del Aguila and Di Bernardo, 2003;Saupe and Mosimann, 2003). Cyanobacteria are highlighted in this study because of their abundance in the raw water, especially the genera Cylindrospermopsis and Pseudanabaena.…”

“…Previous studies suggested backwashing for SSF cleaning as an alternative to scraping (de Souza et al, 2017Souza et al, , 2016Michelan et al, 2011;Pizzolatti et al, 2014). The application of backwashing is particularly recommended for medium and small-scale filters (<1m²) that can be easily applied in small and isolated communities or in small agroindustry (FUNASA, 2019;Michelan et al, 2011;Pizzolatti et al, 2014).…”

“…Cyanobacteria are highlighted in this study because of their abundance in the raw water, especially the genera Cylindrospermopsis and Pseudanabaena. They are related to filter clogging, are usually removed by SSF, and explain filtration runs of 15 days on average (de Souza et al, 2017;Mondardo, 2009;Pereira et al, 2012;Pizzolatti et al, 2014;Schöntag et al, 2015). Both the Cylindrospermopsis (0.00%-0.18%) and Pseudanabaena (0.00%-2.10%) genera were identified in both ScSF and BSF, being more abundant in the schmutzdecke (0.88%-12.67%), and were visible at microscope (Figure 3 and 4).…”

Applying Bio-Slow Sand Filtration for Water Treatment

“…SSF is a well-known process for drinking water treatment and is widely used for the production of biologically stable drinking water and particle removal [4]. After two centuries of improvement and perfection, the SSF has been characterized by the following advantages: 1) good removal efficiency of bacteria, viruses, and organic material; 2) simple structure that is easy to construct; 3) independence from the gravitydriven automatic inflow as only one mechanical piece of equipment, a water pump, is necessary -no other automatic or electronic equipment is required, making it easy to operate; and 4) it is not necessary to add any chemical agent, which avoids the risk of transportation and storage of chemical agents and avoids the production of by-products due to chemical disinfection (e.g., the production of chloramines due to the addition of chlorine for disinfection) [5][6].…”

Physico‐Chemical Processes

“…The reduction started at Week 6 and total elimination was reached in Week 9 and later. It suggested that slow sand filtration could remove other plant pathogenic viruses.deSouza et al (2017) investigated the removal of cyanobacteria Cylindrospermopsis raciborskii using upflow slow sand filtration process. High concentration of cyanobacteria was tested with removal efficiency of 99%, but the resultant concentration warranted complementary treatment for better water quality Sabiri et al (2017).…”