The role of restaurant wastewater for producing bioenergy towards a circular bioeconomy: A review on composition, environmental impacts, and sustainable integrated management

Population inflation has led to the unprecedented increase in urbanization, thus causing negative impacts on environmental sustainability. Recently, there is an upsurge in the number of restaurants due to the changing lifestyles of the people round the globe. For instance, there were 167,490 food and beverage establishments in 2015, representing an annual growth rate of 5.1% since 2010 in Malaysia. The rapid growth of restaurants has implicated a negative impact due to the generation of highly polluted restaurant wastewater (RWW). RWW is mainly generated during the cooking, washing, and cleaning operations. RWW typically contain fat, oil, and grease (FOG) resulting from residues of meat, deep-fried food, baked items and butter, and has caused serious blockages of sewer due to clogging and eventually sewage backup. This has increased the required frequency of cleaning and sanitary sewer overflows (SSOs). Results from the previous studies have shown that FOG can be treated using physical, chemical, and biological processes. Different technologies have been applied for the treatment of FOG and other pollutants (COD, BOD, SS and NH4–N) present in RWW. Therefore, this review aims to provide an in-depth understanding of the characteristics of RWW, chemical and physical characteristics of FOG with the mechanism of its formation and utilization for biocomposites, biogas and biodiesel productions for circular bioeconomy. Besides, this review has discussed the potential treatment technologies comprehensively for RWW which is currently remain understudied. Integrated sustainable management of FOG with technoeconomic analysis of bioproducts, sustainable management with international initiatives and previous studies are also summarized. Hence, this review aims towards providing better alternatives in managing RWW at sources, including its treatment and potential of its biorefinery, therefore eventually contributing towards environmental sustainability.