Effect of Activated Sludge Retention Time, Operating Temperature, and Influent Phosphorus Deficiency on Floc Physicochemical Characteristics and UV Disinfection

Abstract

Pilot-scale sequencing batch reactors (SBRs) were used to assess the effects of sludge retention time, temperature, and influent phosphorus level on floc physicochemical characteristics, effluent quality, and UV disinfection kinetics. Increasing the operating temperature from 12 to 22 °C caused an increase in the activated sludge flocs fractal dimension from 0.1 to 0.2, and improved the UV disinfection of final effluent. Influent phosphorus limitation, i.e., COD:N:P of 100:10:0.3, caused the formation of more spherical flocs with higher resistance to UV disinfection (by 1 log). However, influent phosphorus starvation, i.e., COD:N:P of 100:10:0.03, decreased the average floc size and sphericity, increased the final effluent turbidity, and lowered effluent UV dose demand. The findings provide useful information in terms of modifying wastewater treatment processes in the context of water reuse and improving UV disinfection efficiency.

The use of moving bed bio-reactor to laundry wastewater treatment

“…Biological bed's microorganisms had assured, constant delivery of raw wastewater with stable composition and optimal for them temperature (25-35C) which can reduce demand for a phosphorus compounds. At the same time weak excess sludge sedimentation ability has been observed [21].…”

Comparative study of chemical and physical methods for distinguishing between passive and metabolically active mechanisms of water contaminant removal by biofilms

“…UV treatment is a proven, environmentally friendly technology used for effluent disinfection in wastewater systems (Azimi et al, 2014). With this, UV light is absorbed by the nucleic acids (DNA and RNA) of exposed microbial cells, altering DNA structure and thus preventing metabolic activity and any further cell division.…”

Understanding the stability of cyclic aerobic-anoxic conditioned sludge flocs under deflocculative stresses

“…This led to bigger and stronger but more open-structured flocs. The increased filamentous growth with increasing temperatures is observed to be a common theme with the deterioration of the sludge floc properties in the reported studies [29,48,49].…”

“…The differences in EPS composition and the filamentous bacterial content were reported to be possible reasons for the differing bioflocculation behavior of the two sludges [48]. Azimi, Allen [49] also observed increased filamentous bacterial growth with a temperature shift from 12 to 22°C. This led to bigger and stronger but more open-structured flocs.…”

“…Scott, Liss [161] reported that EPS composition (protein, carbohydrate, and DNA content) of flocs were not significantly affected by varying the SRT from 4 to 20 days. Azimi, Allen [49] reported that the mechanical strength of the flocs, in terms of median shear stress value, turbidity and effluent suspended solids concentration was not significantly different between flocs cultivated at an SRT of 7 and an SRT of 20 days. In their study, they reported the temperature at which the reactors were operated had a more profound influence on the flocs than the SRT.…”