Sono-thermal pre-treatment of waste activated sludge before anaerobic digestion

Abstract

Sonication and thermalization can be applied successfully to disrupt the complex waste activated sludge (WAS) floc structure and to release extra and intra cellular polymeric substances into soluble phase along with solubilization of particulate organic matters, before sludge digestion. In this study, sonication has been combined with thermalization to improve its disintegration efficiency. It was aimed that rise in temperature occurring during the sonication of sludge was used to be as an advantage for the following thermalization in the combined pre-treatment. Thus, the effects of sonication, thermalization and sono-thermalization on physical and chemical properties of sludge were investigated separately under different pre-treatment conditions. The disintegration efficiencies of these methods were in the following descending order: sono-thermalization > sonication > thermalization. The optimum operating conditions for sono-thermalization were determined as the combination of 1-min sonication at 1.0 W/mL and thermalization at 80 °C for 1h. The influences of sludge pre-treatment on biodegradability of WAS were experienced with biochemical methane potential assay in batch anaerobic reactors. Relative to the control reactor, total methane production in the sono-thermalized reactor increased by 13.6% and it was more than the sum of relative increases achieved in the sonicated and thermalized reactors. Besides, the volatile solids and total chemical oxygen demand reductions in the sono-thermalized reactor were enhanced as well. However, it was determined that sludge pre-treatment techniques applied in this study was not feasible due to their high energy requirements.

Combined thermo-chemo-sonic disintegration of waste activated sludge for biogas production

“…To facilitate the sludge liquefaction, various sole and combined disintegration methods (e.g., thermal, thermochemical, ultrasonic, microwave, and biological disintegrations) have been applied to pretreat Waste activated sludge (WAS), as reported in the literature (Uma et al, 2012a;Gayathri et al, 2015;Ebenezer et al, 2015;Kavitha et al, 2013Kavitha et al, , 2015b. Several researchers have reported affirmative synergistic upshots of the combined pretreatment methods on subsequent anaerobic digestibility (Tyagi and Lo, 2012;Zhen et al, 2014;Sahinkaya and Sevimli, 2013). Among the combinative pretreatment methods, thermochemical was widely applied to disintegrate the sludge (Tyagi and Lo, 2012;Sahinkaya and Sevimli, 2013).…”

Enhancing the functional and economical efficiency of a novel combined thermo chemical disperser disintegration of waste activated sludge for biogas production

“…Surplus sludge produced by various treatment plants are of an immense ecological peril due to the presence of unprocessed solids, pathogens and other organic pollutants (Sahinkaya and Sevimli, 2013;Kavitha et al, 2013 Conversely, the management of sludge is one of the most tedious and costly processes in the treatment plants. The treatment and disposal of these unprocessed sludge accounts up to 60% of the total functioning cost of the wastewater treatment plants (WWTPs) (Appels et al, 2008).…”

Sono-Oxidative Pre-Treatment of Waste Activated Sludge Before Anaerobic Biodegradation

“…The sludge flocs were rapidly disrupted and the exposed cells were disintegrated in the rapid sludge disintegration stage, while additional cells were exposed and damaged by sonication in the following slow disintegration stage (Huan et al, 2009). Similarly, Huan et al (2009), Şahinkaya and Sevimli (2013a), Yan et al (2010) and Zhang et al (2007) also reported that the ultrasonic sludge disintegration occurred in two stages. The reason for this rapid disintegration obtained in the first 10 min was the rapid cavitational effect arising from the collapse of powerful transient bubbles created in fractions of microseconds close to microbial cells (Show et al, 2007).…”

“…Inevitably, the formation of large amounts of excess biomass (called "waste activated sludge, WAS") is the most important disadvantage of the activated sludge process. Prior to final disposal of the WAS, it must be treated, because its improper disposal brings about a significant threat for ecological systems due to its highly putrescible nature and its pathogen content (Şahinkaya and Sevimli, 2013a). However, the treatment and disposal of the waste sludge are among the most difficult and expensive problems in the treatment plants.…”

“…However, its most important disadvantage is its consumption of high amounts of electrical energy. In order to reduce its capital and operating costs, sonication can be combined with acidification (Şahinkaya, 2015), alkalization (Şahinkaya and Sevimli, 2013b), the Fenton process (Şahinkaya et al, 2015) and thermal pretreatment (Şahinkaya and Sevimli, 2013a). The present work presents a new approach combining sonication with an advanced oxidation method using potassium ferrate (K2FeO4).…”