Tertiary treatment for wastewater reuse based on the Daphnia magna filtration – comparison with conventional tertiary treatments

Abstract

Tertiary treatments are required to permit safe reuse of wastewater. The performance of a new biological tertiary treatment based on the filtration by a population of Daphnia magna was studied and compared with the performance of other conventional tertiary treatments such as coagulation-flocculation, settling tank, disc filtration, sand filtering and ultraviolet (UV) light. The analysis was based on the efficiency in the particle removal and Escherichia coli inactivation. The Daphnia magna treatment reduced the concentration of particles with diameters below 30 μm by 35%, depending on abiotic parameters such as water temperature and the hydraulic retention time (HRT). The Daphnia magna filtration increased with water temperature for water temperatures >20 °C, while it remained constant for water temperatures <20 °C. Lower HRTs induced the growth of the Daphnia magna population, maintaining the same water quality. Furthermore, the Daphnia magna treatment inactivated E. coli in 1.2 log units. This inactivation was six times larger than that obtained by the conventional macrofiltration systems analyzed, although lower than the inactivation attained by UV light, which ranged between 1.5 and 4 log units.

The hydraulic retention time on the particle removal efficiency by Daphnia magna filtration on treated wastewater

“…Schalau et al (2008) found that water temperatures above 6°C guaranteed Daphnia development. Serra et al (2014) found an increase in the Daphnia filtration rate for temperatures above 20°C, which also coincided with a greater food concentration in warmer periods. As mentioned by Burns (1969), in warmer environments Daphnia start to grow earlier than in colder environments (Berger et al 2006).…”

“…In the experiments of both Serra et al (2014) and Pau et al (2013), Daphnia preyed directly on the suspended sludge particles. Serra et al (2014) did not found any relationship between the removal of E. coli and the particle retention by conventional treatments, in the range of particle sizes from 2.5 to 500 lm. However, they did find that the Daphnia filtration method was more efficient in inactivating E. coli than the conventional particle retention methods, but less efficient than the inactivation attained by UV light.…”

“…Daphnia is therefore considered the most powerful grazer among the zooplankton filter-feeders in lakes (Knisley and Geller 1986). Shiny et al (2005) and Serra et al (2014) from laboratory and mesocosm experiments, respectively, demonstrated that Daphnia magna are promising organisms in the area of water disinfection, preying directly on suspended sludge particles. Kim et al (2003) used an artificial food web technology based on phytoplankton and Daphnia magna chambers to remove nutrients from domestic wastewaters.…”

“…The artificial food web system was composed of bacteria, Chlorella and Daphnia magna working in sequential chambers. Serra et al (2014) and Pau et al (2013) studied the wastewater filtration by Daphnia magna in both laboratory and mesocosm experiments. In the experiments of both Serra et al (2014) and Pau et al (2013), Daphnia preyed directly on the suspended sludge particles.…”

“…Serra et al (2014) and Pau et al (2013) studied the wastewater filtration by Daphnia magna in both laboratory and mesocosm experiments. In the experiments of both Serra et al (2014) and Pau et al (2013), Daphnia preyed directly on the suspended sludge particles. Serra et al (2014) did not found any relationship between the removal of E. coli and the particle retention by conventional treatments, in the range of particle sizes from 2.5 to 500 lm.…”