Effect of coagulation and sonication on the dissolved air flotation (DAF) process for thickening of biological sludge in wastewater treatment

Abstract

Background: Dissolved air floatation (DAF) is one of the methods has been used for the sludge thickening in wastewater treatment plants. This study aimed to investigate the effects of coagulation and sonication processes as additional configurations on the efficiency of a lab-scale DAF process for thickening of the biological sludge of an industrial wastewater treatment plant in Kashan, Iran. Methods: The required amounts of sludge samples were collected from a wastewater treatment plant and kept at temperature of 4°C. Variables, such as pressure (3, 5, and 7 atm), flotation time (5 and 10 minutes), ultrasonic irradiation power (0, 75, and 150 W), and presence/absence of Fe-based coagulant were considered on a sequencing batch reactor (SBR) included coagulation, flotation, and sonication processes, respectively. Results: The use of ultrasonic waves led to an insignificant increase in the DAF efficiency (P > 0.05), however, the application of coagulant significantly increased the thickening efficiency (P < 0.05). The maximum efficiency of the process was achieved at flotation time of 5 min, pressure of 3 atm, and sonication power of 75 W. Conclusion: According to the results, DAF has a proper efficiency for thickening of biological sludge. Coagulation compared to sonication has a greater effect on the efficiency of the process.

Evaluation of different polymeric coagulants for the treatment of oil refinery wastewater

“…DAF being a separation process works on the following principles: (i) air bubbles encapsulating the insoluble particles, (ii) agglomeration of air bubble-insoluble particles to form flocculent structures and (iii) chemical adsorption of the air bubbles to the insoluble particles (Atamaleki et al, 2020;. In this case, attachment of the air bubbles to the oil droplet caused the specific gravity to be less than that of water.…”

“…Biological methods require large area, long treatment time, and low efficiency when applied as a single treatment system, likewise with physiochemical systems such as dissolved air flotation (DAF) (Bahrekazemi & Hekmatzadeh, 2017;. The DAF is a promising technology, which is gaining prominence to enhance chemical pretreatment processes in various wastewater settings (Atamaleki et al, 2020;.…”

“…Wang et al, 2017). Integration of coagulation-dissolved air floatation (CDAF) technology has gained much interest in the industrial applications as a clarification technology for separating low-density particles such as oil droplets from oily waste (Atamaleki et al, 2020). The CDAF configuration usually applied in the WWTPs involves a coagulation-flocculation step followed by the DAF (Aliff Radzuan et al, 2016;Diya'Uddeen et al, 2011;Karhu et al, 2014;Kyzas & Matis, 2016).…”

“…The CDAF configuration usually applied in the WWTPs involves a coagulation-flocculation step followed by the DAF (Aliff Radzuan et al, 2016;Diya'Uddeen et al, 2011;Karhu et al, 2014;Kyzas & Matis, 2016). In the CDAF process, the addition of the coagulants enhanced the agglomeration of the flocs, while inducing micro-bubbles to promote buoyancy by decreasing the oil droplet weight to enhance the separation efficiency (Aliff Radzuan et al, 2016;Atamaleki et al, 2020).…”

“…The application and selection of coagulants (coagulation) depend on the hydrodynamic interaction and the surface chemistry with the oil droplets which varies with ORW source, composition, and density, which may significantly affect the subsequent treatment process (Atamaleki et al, 2020;Tetteh & Rathilal, 2019). Iron and aluminium-based coagulants have been the most widely used coagulants with active charge ions on their surface (Boaventura et al, 2000;Ukiwe et al, 2014).…”