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Over the past few decades, bioenergy production from heavy metalcontaminated biomass (HMCB) has been drawing increasing attention from scientists in diverse disciplines and countries owing to their potential roles in addressing both energy crisis and environmental challenges. In this review, bioenergy recovery from HMCBs, i.e. contaminated plants and energy crops, using thermochemical processes (pyrolysis, gasification, combustion, and liquefaction) has been scrutinized. Furthermore, the necessity of the implementation of practical strategies towards sustainable phytoextraction and metalfree biofuels production has been critically discussed. To meet this aim, the paper firstly delivers the fundamental concepts regarding phytoremediation approach, and then, reviews

Recently, dealing with generated heavy metal-contaminated biomasses (HMCBs) harvested from phytoextraction process has drawn increasing attention. In this study, the feasibility of an HMCB (willow) pretreatment using a low-cost ionic liquid (IL), namely, triethylammonium hydrogen sulfate [TEA]­[HSO4], is investigated to remove the high contents of HMs prior to further thermochemical and biological valorization. The operating variables were temperature (75–105 °C), IL:biomass (10:1–30:1) ratio, and time (4–8 h) with constant feedstock particle size (0.35 mm). According to results obtained from response surface methodology–Box Behnken design (RSM–BBD), the optimum conditions of the IL-based pretreatment of HMCB for maximum HMs’ removal are temperature, 93 °C; IL:biomass ratio, 30:1; and time, 7.12 h. Under the optimum conditions, the IL is found to solubilize lignin and hemicellulose respectively about 70.54% and 92.56%; and subsequently, effective removal of HMs from HMCB is obtained (Cu, 100%; Zn, 88.77%; Mn, 79.70%; Fe, 73.11%; Cd, 70.42%; Al, 34.53%; and Cr, 18.17%), while Pb removal is negligible. The average amount of confidence intervals of developed models is ∼95%, and generally, the ratio of IL:biomass shows a higher effect on the efficiency of biomass fractionation and HMs’ removal, compared with temperature and time; however, interactions between the operating parameters are negligible.

Substantial research has been carried out on sustainable waste activated sludge (WAS) management in the last decade. In addition to the traditional approach to reduce its production volume, considering WAS as a feedstock to produce bio-products such as amino acids, proteins, short chain fatty acids, enzymes, bio-pesticides, bio-plastics, bio-flocculants and bio-surfactants represents a key component in the transformation of wastewater treatment plants into biorefineries. The quality of these bio-products is a key factor with respect to the feasibility of non-conventional WAS-based production processes. This review provides a critical assessment of the production process routes of a wide range of value-added products from WAS, their current limitations, and recommendations for future research to help promote more sustainable management of this under-utilised and ever-growing waste stream.