Microwave irradiation: A sustainable way for sludge treatment and resource recovery

In recent years, microwave (MW) irradiation has gained widespread popularity as an effective thermal method for sludge treatment, mainly due to its rapid and selective heating, energy efficiency, capacity to enhance the yield and quality of product and diminished hazardous product formation and emissions (thus rendering the technique environmentally friendly). The present review aspires to advance understanding of the versatile uses of the MW irradiation technique in sludge treatment, including sludge pretreatment and enhancement in the anaerobic biodegradability of waste sludge and sludge sanitisation, resources (bio-gas, bio-oil, nutrients and heavy metals) recovery and, heavy metals stabilisation. It also summarises future research directions for the better use of MW energy in sludge treatment, process optimisation and developments for industrial-scale implementation of the MW technique and, safety and health related issues.