Removal kinetic of Escherichia coli and enterococci in a laboratory pilot scale wastewater maturation pond

Abstract

During the last 15 years several authors studied the disinfection in waste stabilisation pond (WSP) and several empirical models were developed. There are huge differences between the models describing this process and there is really a need to improve the design of ponds for better disinfection. This paper addresses the Escherichia coli and enterococci disinfection in a laboratory pilot scale maturation pond (1.5 l) with light intensity (0, 12 and 25 W/m(2)) under controlled pH, temperature and dissolved oxygen (DO) conditions. The aim of this study is to improve modelling for a better design of disinfection in maturation ponds (MP) and to identify the key parameters influencing the process. It was found that kinetic coefficients K values for E. coli and enterococci are closely dependent on physicochemical parameters. K values increase with increasing pH, I, T and DO. E. coli disinfection depends closely on the pH and the DO and increases strongly when the pH is above 8.5. The enterococci disinfection depends essentially on DO. Two equations are suggested to calculate the kinetic coefficient K related to the environmental average state variables.

Effects of Environmental Factors on the Disinfection Performance of a Wastewater Stabilization Pond Operated in a Temperate Climate

“…In this four-year full-scale WSP study, the removal efficiencies of E. coli may increase with increasing temperature. This observation is consistent with a number of studies that have reported increased removal efficiencies of fecal coliforms with increasing temperature [25,[34][35][36][37][38]. It should be noted that effects of hydraulic retention [39,40], hydraulic efficiency [39,40], sunlight [3], attachment/sedimentation [9], predation and nutrient availability may all contribute to It should be noted that effects of hydraulic retention [39,40], hydraulic efficiency [39,40], sunlight [3], attachment/sedimentation [9], predation and nutrient availability may all contribute to disinfection in WSPs.…”

“…In this four-year full-scale WSP study, the removal efficiencies of E. coli may increase with increasing temperature. This observation is consistent with a number of studies that have reported increased removal efficiencies of fecal coliforms with increasing temperature [25,[34][35][36][37][38].…”

“…Hence, these observations would suggest that pH levels higher than 8 could be considered effective in E. coli inactivation under these temperate climatic conditions. The observed correlation between E. coli removal and pH is consistent with other studies, which reported increased E. coli inactivation with increases in pH [24,25]. A neutral to slightly acidic pH has been reported as optimal for fecal bacteria growth [26], while pH levels higher than 9 have been reported to be effective in pathogen removal [9,[26][27][28].…”

“…Figure 7 shows the relationship between E. coli concentrations and DO levels. Light inactivation of E. coli and enterococci increased with increasing levels of DO [25]. As previously noted, oxygen is produced as a by-product of algal photosynthesis, which is also a source of oxygen in WSP systems.…”

“…A number of studies have reported that light inactivation of E. coli is dependent on pH [24,25,29]. Under elevated pH conditions (pH > 8.5), E. coli would be inactivated by exogenous mechanisms, while endogenous mechanisms would inactivate E. coli more slowly under more moderate pH conditions [24,29].…”