Mechanisms involved in Escherichia coli and Serratia marcescens removal during activated sludge wastewater treatment

Abstract

Wastewater treatment reduces environmental contamination by removing gross solids and mitigating the effects of pollution. Treatment also reduces the number of indicator organisms and pathogens. In this work, the fates of two coliform bacteria, Escherichia coli and Serratia marcescens, were analyzed in an activated sludge process to determine the main mechanisms involved in the reduction of pathogenic microorganisms during wastewater treatment. These bacteria, modified to express green fluorescent protein, were inoculated in an activated sludge unit and in batch systems containing wastewater. The results suggested that, among the different biological factors implied in bacterial removal, bacterivorous protozoa play a key role. Moreover, a representative number of bacteria persisted in the system as free-living or embedded cells, but their distribution into liquid or solid fractions varied depending on the bacterium tested, questioning the real value of bacterial indicators for the control of wastewater treatment process. Additionally, viable but nonculturable cells constituted an important part of the bacterial population adhered to solid fractions, what can be derived from the competition relationships with native bacteria, present in high densities in this environment. These facts, taken together, emphasize the need for reliable quantitative and qualitative analysis tools for the evaluation of pathogenic microbial composition in sludge, which could represent an undefined risk to public health and ecosystem functions when considering its recycling.

Achilles heel of environmental risk from recycling of sludge to soil as amendment: A summary in recent ten years (2007–2016)

“…It is attributed to some tenacious bacterias with strong vitality. Therefore, amendment of sludge to soil as organic fertilizer needs to be cautiously considered because of possible risk to public health and ecosystem function (Orruno et al, 2014). And periodic monitoring, analysis and evaluation to pathogenic microbial survival in amended soil and its epidemic risk triggered by possible body contact are necessary and deserved (Harder et al, 2016).…”

Reduction of Microbial Contamination of Outlet Waste in Urban Wastewater Treatment Plants

“…Removal performances for bacteria and several chemical compnents were more exterior during the primary year contrasted to the second year of action, offering concern for long-term performance and consistency of such wastewaters (Orruño et al, 2014). Microalgae increase the elimination of nutrients, organic pollutants, heavy metals and pathogens from domestic effluent and furnish an interesting raw substance for the generation of high-value chemicals (algae metabolites) or biogas.…”

Comparative study on two different waste-water treatment plants in El-Menofeyia Province, Egypt

“…Wastewater is a mixture of domestic, industrial, agricultural and rainwater. The development of wastewater treatment was driven by the need to recycle, retrieve and reduce the environmental contaminations brought about by the uncontrolled discharge of polluted effluents such as organic matter, nitrogenous, phosphorus compounds and pathogens into rivers and streams (Orrun et al, 2014). Biological wastewater treatment includes mainly two methods; trickling filters and the suspended growth reactors using the activated sludge (Curds and Hawk, 1975).…”