Pretreatment of Sludge with Microwaves for Pathogen Destruction and Improved Anaerobic Digestion Performance

Abstract

A new way of generating Class A sludge using microwaves was evaluated through a series of laboratory‐scale experiments. Microwaves provide rapid and uniform heating throughout the material. Other benefits of microwave treatment include instant and accurate control and selective and concentrated heating on materials, such as sludge, that have a high dielectric loss factor. Sludge was irradiated with 2450‐MHz microwaves, and fecal coliforms were counted. Fecal coliforms were not detected at 65°C for primary sludge and anaerobic digester sludge and at 85°C for waste activated sludge when sludge was irradiated with 2450‐MHz microwaves. During the bench‐scale anaerobic digester operation, the highest average log reduction of fecal coliforms was achieved by the anaerobic digester fed with microwave‐pretreated sludge (≥2.66 log removal). The anaerobic digester fed with microwave‐irradiated sludge was more efficient in inactivation of fecal coliforms than the other two digesters fed with raw sludge and externally heated sludge, respectively. It took more than three hydraulic retention times for a bench‐scale mesophilic anaerobic digester to meet Class A sludge requirements after feeding microwave‐irradiated sludge. Class A sludge can be produced consistently with a continuously fed mesophilic anaerobic digester if sludge is pretreated with microwaves to reach 65°C.

Application of physico-chemical pretreatment methods to enhance the sludge disintegration and subsequent anaerobic digestion: an up to date review

“…Above 68°C, bacterial activity was almost ceased. Hong et al (2006) studied the application of MW treatment (specific energy 2,450 MHz and temperature 85°C) in pathogen removal in terms of fecal coliforms. They reported that Class A sludge can be produced constantly with continuously fed mesophilic anaerobic digester using MW pretreated sludge at 65°C.…”

Microwave Enhanced Advanced Oxidation Process Application to Treatment of Dairy Manure

“…Moreover, both DNA and bacterial cellular membranes can be damaged by microwave irradiation. Such an effect on the treatment process, besides heating, is referred to as the athermal effect (Hong et al 2006). Microwave heating has been applied in various processes and manufacturing industries, such as food process, wood drying and waste treatment process (Jones, et al, 2002).…”

“…Microwave heating has been applied in various processes and manufacturing industries, such as food process, wood drying and waste treatment process (Jones, et al, 2002). For the sewage wastewater treatment industry, there are many applications of microwave heating on sludge treatment for reducing volume, improving dewaterability, enhancing digestibility, enhancing nutrient release, pathogen destruction, and stabilizing heavy metal (Menendez, et al, 2002;Liao, et al, 2005;Wojciechowaska 2005;Hong et al, 2006;Eskicioglu et al, 2007;Hsieh et al, 2007;Yu, et al, 2010). It has also been reported that the overall treatment efficiency could be increased with a combination of microwave heating with chemicals (thermo-chemical) for the treatment of sludge (Chan, et al, 2007;Qiao, et al, 2008).…”

Value-Added Products Derived from Waste Activated Sludge: A Biorefinery Perspective

“…Microwave radiation can lead to a combination of thermal and non-thermal effects on cell disruption, and possible release of cellular organic matter [40,41]. Intracellular liquid heating to boiling point leads to the thermal effect, increasing kinetic energy as molecular rotation [42], while the non-thermal effect causes the disruption of hydrogen bonds due to the polarisation of macromolecule chains aligning with electromagnetic poles [43]. The addition of hydrogen peroxide and acids during this treatment can further help solubilize WAS solids, and release ammonia and phosphorus.…”