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The rapid urbanization that took place in the last 60 years has led to a dramatic increase in the generation of Municipal Solid Waste (MSW). The biodegradable fraction of MSW mainly consists of food waste (FW) and corresponds to about 50% of the total MSW. The disposal of FW in the environment has become a significant challenge. On the other hand, FW is an excellent substrate for anaerobic digestion (AD). This manuscript reviews the different AD technologies for the treatment of FW. Different types of bioreactors and pretreatment methods used to enhance methane production through AD of FW are discussed. The current review gives special emphasis on the methods for biogas upgrading and on technologies for FW digestate valorization. Food waste valorization through anaerobic digestion offers a wide variety of options in all process steps. From the pre-treatment of the feedstock and the selection of the suitable anaerobic digestion technology to the configuration of the process based on the desired products and the valorization of the generated digestate, the design of an integrated anaerobic digestion plant is a challenging task, which necessitates a systematic design. A systematic approach is necessary for FW valorization. The simple single-stage AD process leads to underutilization of the feedstock. There are plenty of available technologies that could be combined for the development of an integrated biorefinery that will be optimized in terms of FW valorization towards the production of biofuels and high-added value products, while introducing a circularity in the nutrients contained in the FW. FW-to-biofuel conversion technologies are high Technology Readiness Level (TRL—9) technologies and anaerobic digestion is applied worldwide at commercial scale.

In the present study, modeling of the anaerobic digestion of food industry waste is examined. A very simple model was developed, assuming that the organic matter (in terms of COD) is composed of a hardly and an easily biodegradable COD fraction, which are consumed through different Monod kinetics towards methane production. Biochemical methane potential tests and continuous stirred tank experiments were carried out and used to estimate the values of the main kinetic parameters. In the sequel, the kinetic model is used to predict the behavior of a periodic anaerobic baffled reactor (PABR), also fed with the same waste. Only a single new parameter, the biomass retention factor is added in order to model the behavior of the high-rate reactor. Despite the structural and operational differences of the two anaerobic digesters, the simple model was able to satisfactorily predict methane production and COD consumption of both bioreactors over a wide range of operating conditions. Thus, the proposed modeling approach can be valuable in describing the behavior of different anaerobic digesters, using a minimal number of kinetic variables and kinetic/stoichiometric parameters.

The challenge for facing highly increasing environmental and health problems of modern society, caused by an ever increasing industrial development and economic growth worldwide, calls for a restructuring of waste management systems , using renewable resources and low-carbon solutions in agreement with the concept of circular economy. The main point of circular economy is the use of natural resource materials in a closed-loop, leading to zero-waste generation and sustainability (Ghisellini et al., 2016; Lieder and Rashid; 2016, Sauvé et al., 2016). The main concept of the HORIZON 2020 Waste4Think project is to introduce and promote 20 eco-innovative solutions that cover the whole waste value chain. These solutions will be applied and assessed in 4 European cities: Zamudio (Basque Country, Spain); Halandri (Greece); Seveso (Italy); and Cascais (Portugal) (Waste4Think, 2015). The eco-innovative solutions will provide: IT tools, apps for citizens, educational materials and serious games, tools for citizen, changes based on economic instruments and social actions, and finally implementation, valorization and reuse of alternatives for the recovery of high-grade materials (Figure 1). &nbsp

Α novel two-phase bioreactor for the microbial removal of Cr(VI) from wastewater with high chromium concentration (up to 1350 ppm) is developed. Among several potential solid-phase adsorbents tested, Cloisite® 30B, a natural montmorillonite modified with a quaternary ammonium salt that absorbs Cr(VI) in a reversible manner proved to be optimal as the solid phase of the bioreactor. Cloisite® 30B has no toxicity to the acclimated biomass and keeps the concentration of Cr(VI) ions at sub-inhibitory levels that ensure the efficient microbial removal of Cr(VI). The microbial removal of Cr(VI) was achieved using an acclimated mixed culture developed from anaerobic sludge. The novel bioreactor was operated as a Sequencing Batch Reactor (SBR) under anaerobic and mesophilic conditions for over 200 cycles, without further addition of the solid adsorbent, and led to even 100% removal of Cr(VI) with high removal rates for concentrations ranging from 900–1350 mg/L Cr(VI). The reduction of Cr(VI) to the less toxic Cr(III) was proved to be mediated by lactate, generated by a lactic acid bacterium, 99% similar to Pediococcus acidilactici as demonstrated by molecular methods The reduction of Cr(VI) took place extracellularly where it reacts with the lactic acid produced during the process of glycolysis.

The challenge for facing highly increasing environmental and health problems of modern society, caused by an ever increasing industrial development and economic growth worldwide, calls for a restructuring of waste management systems , using renewable resources and low-carbon solutions in agreement with the concept of circular economy. The main point of circular economy is the use of natural resource materials in a closed-loop, leading to zero-waste generation and sustainability (Ghisellini et al., 2016; Lieder and Rashid; 2016, Sauvé et al., 2016). The main concept of the HORIZON 2020 Waste4Think project is to introduce and promote 20 eco-innovative solutions that cover the whole waste value chain. These solutions will be applied and assessed in 4 European cities: Zamudio (Basque Country, Spain); Halandri (Greece); Seveso (Italy); and Cascais (Portugal) (Waste4Think, 2015). The eco-innovative solutions will provide: IT tools, apps for citizens, educational materials and serious games, tools for citizen, changes based on economic instruments and social actions, and finally implementation, valorization and reuse of alternatives for the recovery of high-grade materials (Figure 1)., {"references":["http://uest.ntua.gr/athens2017/proceedings/pdfs/Athens2017_Papadopoulou_Lyberatos_Lizarraga_Torre_etal.pdf"]}