The Effects of Ultrasound on Sludge Digestion

Abstract

Ultrasound treatment, which involves the introduction of high‐intensity sound waves into a sludge medium, is one of several technologies which promote hydrolysis during sludge treatment. It has become well‐established with numerous full‐scale plants in Europe operating for several years. The basic principle involves the release of extra‐cellular material which then catalyses biological reactions and improves bacterial kinetics, resulting in lower sludge quantities and (in the case of anaerobic digestion) increased biogas production. Its use is most suited to plants containing large quantities of refractory material and/or cellular matter, such as waste activated sludge. This paper uses the data from several full‐scale part‐stream ultrasound plants and discusses the influence of the technology on numerous operating conditions, especially with respect to improved digestion and enhanced biogas production.

Mixture of primary and secondary municipal wastewater sludge as a short-term substrate in 2 MW agricultural biogas plant: site-specific sustainability of enzymatic and ultrasound pretreatments

“…An identical increase in methane yields produced at 10% of energy consumption was still insufficient to cover the long‐term installation and maintenance costs of the ultrasound device (BGP Šijanec, internal data). This is in line with the high capital, operational and consumption costs, full stream inhibition due to inhibitory compounds and dependency on incoming WWS sludge characteristics, forming the basis for infrequent ultrasound applications to full scale, despite the −5% to 58% increases in methane yields from activated WWS after ultrasound pretreatment …”

Optimisation of sludge pretreatment by low frequency sonication under pressure

“…thermal, chemical or other mechanical methods, ultrasound (US) has gained interest for such purpose, as it provides efficient sludge disintegration (Pilli et al, 2011;Tyagi et al, 2014) and does not require any chemical additive. Ultrasonic pretreatment was reported to improve biodegradability and bio-solid quality (Khanal et al, 2007;Trzcinski et al, 2015), to enhance biogas/methane production (Barber, 2005;Braguglia et al, 2015;Khanal et al, 2007;Onyeche et al, 2002), to reduce excess sludge (Onyeche et al, 2002) and required sludge retention time (Tiehm et al, 1997).…”

Mesophilic Anaerobic Digestion with High‐Temperature Microwave Pretreatment and Importance of Inoculum Acclimation

“…It was reported that ultrasound is an energy-efficient pretreatment method to enhance anaerobic digestion; however, it does not improve pathogen removal (Barber, 2005;Thiem et al, 2001). The same is true for mechanical pretreatment methods, such as ball milhng, high-pressure homogenizing, and jetting and colliding (MuUer et al, 1998;Nah et al, 2000), Additionally, most physical disintegration methods required more polymer addition after digestion to improve dewaterability.…”