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Bauxite residue (BR) is the main by-product of the alkaline production of alumina from bauxite containing significant amounts of valuable metals such as scandium that belongs to rare-earth elements (REEs), classified by the European Community as critical raw materials (CRMs). BR is considered a hazardous waste due to its huge volume and high alkalinity making its disposal a serious universal environmental problem. The recovery of scandium from Greek BR can be an excellent approach for waste management and resource efficiency of the waste using environmentally friendly biometallurgical methods. In this work, bioleaching of scandium from bauxite residue using the fungus Aspergillus niger was studied. Bioleaching experiments were performed using the Taguchi experimental design, in batch cultures with BR at various pulp densities (1, 5 and 10%, w/v), sucrose concentrations (40, 90 and 140 g/L) and fungus suspension of 2, 4, and 6% v/v under one-step bioleaching condition and subculturing. The highest Sc recovery equal to 46%, was achieved in 20 days at 1% pulp density. Biosorption phenomena were observed during the leaching process. Lactic, acetic, oxalic and citric were the main organic acids identified. Graphical Abstract

Purpose: The acquisition of reliable data on Municipal Solid Waste (MSW) composition is very important for the development of environmentally sound, sustainable and economically viable integrated waste management systems. However, no standardized universally accepted waste characterization protocol has been developed, as there are various methodologies described in the relevant literature. In this study, a generic and easy-to-apply MSW sampling and sorting protocol is developed and presented. Methods: The MSW composition characterization was used for the development of an innovative waste management strategy in the Municipality of Halandri (Attica region, Greece). The methodology was applied four times, to study the repeatability of the results, as well as the potential impact of seasonality. In each sampling point one collection bin for each waste stream was employed (mixed waste, recyclables, paper/cardboard and food waste in the region where food waste was separately collected at the source) in order to collect all the separate streams and account for the entire MSW production profile. The sampling points were selected in strictly residential areas (no shops, companies nearby). For 7 consecutive days the content of the bins was collected on a daily basis and transported to a sorting facility, where the content was sorted and weighed. Results: The results repeatedly indicated source separation rates of up to 79% and a level of impurities in the recycling waste source separation and collection streams (recyclables and paper/cardboard) not exceeding 20%. Conclusion: The applied methodology proved to generate accurate results, offering a detailed picture of the Municipal Solid Waste management performance.

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.

The combination of anaerobic digestion and composting is examined as an integrated valorization process of the livestock waste generated in rural areas. Both biogas and high quality compost may be produced by such a combined process. Six different kinds of waste (pig manure, cow manure, cattle manure, poultry manure, sheep manure and whey) were mixed considering the annual waste production of Metsovo region, Greece, in a representative way. The feed was subjected to a solids/liquid separation step. The bioreactor was operated in different phases with different organic loadings of the liquid fraction of the waste. During phase #1, the Periodic Anaerobic Baffled Reactor (PABR) was fed with a hydraulic retention time (HRT) of 10.65 days, (an organic loading rate of 0.83 g-COD Lreactor−1 day−1) and the biogas production rate was 0.2 Lbiogas Lreactor−1 day−1. During phase #2, the organic loading rate was increased to 1.9 g-COD Lreactor−1 day−1. The biogas production rate was 0.41 Lbiogas Lreactor−1 day−1. During phase #3, the organic loading rate was increased to 2.69 g-COD Lreactor−1 day−1 by decreasing the HRT to 6 days, resulting in the kinetic limitation of the process. The biogas production rate increased to 0.68 Lbiogas Lreactor−1 day−1 with an average methane composition of 65%. The experimental results obtained were used as a basis for the development of an ADM1 model (Batstone et al. in Anaerobic digestion model no. 1 (ADM1). IWA Task Group for Mathematical Modelling of Anaerobic Digestion Processes Report no 1, vol 1(1), 2002) that was able to adequately simulate the operation of the bioreactor. The solid fraction of the pretreatment step was mixed with sawdust and fed to a closed-vessel composter. The highest temperature (56.2 °C) was reached in 2 days. The germination index (GI) of the compost produced was 77.8%, meaning that it was free of phytotoxic substances.

The objective of this work is the evaluation of two alternative ways of valorizing the liquid fraction of a mixture of different kinds of livestock waste and cheese whey, namely (a) biogas production through the anaerobic co-digestion of in a Periodic Anaerobic Baffled Reactor (PABR) and (b) electrical energy generation in a Microbial Fuel Cell (MFC). The different kinds of livestock manure (pig manure, cow manure, poultry manure, sheep manure and cheese whey) were collected from the region of Metsovo, Greece. The mixture was passed through a pretreatment process producing a liquid fraction that was treated (a) in a pilot-scale Periodic Anaerobic Baffled Reactor (PABR) for methane production and (b) in a lab-scale two-chamber Microbial Fuel Cell for electricity production. In the present study, the experimental data obtained from a previous study [1] were used for the evaluation of a simple mathematical model, based on Monod kinetics, for the PABR using Aquasim 2.1 [2]. The simple model was able to satisfactorily describe the behavior of the PABR in terms of soluble COD consumption. In addition, the same liquid waste, filtered (0.70 μm) and diluted at different initial concentrations, was used as feedstock for electricity production, using a two-chamber microbial fuel cell (MFC). The experiments showed that the MFC performance was not limited by the wastewater strength, since the substrate removal efficiency and the maximum power density were not affected by an increase of the initial concentration. The required time showed a linear relationship with the initial concentration of the substrate.

This study concerns the production of hydrogen and methane from a Food Residue Biomass (FORBI) product (Papanikola et al. in 5th international conference on sustainable waste management systems, Athens, 2017), generated from pre-sorted HFW in a CSTR and in a PABR respectively. FORBI is generated by drying and shredding the fermentable fraction of household food waste collected door-to-door in the Municipality of Halandri, Greece. Hydrogen production from FORBI through anaerobic fermentation under acidogenic mesophilic conditions was carried out using a 4 L CSTR, operated at 12 h HRT under an organic loading of 15 g TS L−1. The H2-CSTR was operated for 40 days. During the operation of H2-CSTR the production of biogas reached up to 0.1026 Lbiogas gFORBI−1 and the percentage of hydrogen in the gas up to 48.2%. The conversion of FORBI into methane was carried out through the operation of a 77 L PABR operated under mesophilic methanogenic conditions at various operating parameters (OLR, HRT, T). Two different approaches were adopted for the pre-treatment of the feedstock. For the two first phases of the experimental procedure, a liquid extraction step was carried out before feeding the bioreactor with the separated liquid fraction, while in the subsequent three phases, a whole suspension of FORBI was used as feed. The mean biogas production rate was 0.158 ± 0.02 Lbiogas gFORBI−1 and the mean methane percentage in the biogas was 67.5 ± 2.1%, in the first two phases. The mean biogas production rate was 0.519 ± 0.03 Lbiogas gFORBI−1 and the mean methane percentage in the biogas was 66 ± 2.8%, when a whole suspension of FORBI was fed to the PABR.

Aim Lignocellulosic biomass, mostly by agricultural and forestry sources, mainly consists of cellulose, hemicelluloses, and lignin. White rot fungi are known to be efficient degraders of cellulose due to their ligninolytic enzyme system. The use of Pleurotus ostreatus AMRL 141 as a biological treatment of wheat straw (WS) was explored to determine the most significant variables affecting the cultivation of fungus. Methods Two experimental designs were applied: firstly, a 2-level factorial design (screening) with 7 variables and 3 responses and a central composite design with 4 variables and 3 responses. The optima of the statistically adequate models obtained for a 2 weeks cultivation period were then found. The solid state medium used was sandy soil mixed with agricultural residue (milled WS). Results Overall, the results of many previous studies of our research group have proved that Pleurotus ostreatus is an efficient lignocellulosic decomposer. In this study, design of experiments methodologies were successfully used and the optimum values of responses found for the two weeks cultivation period were lag time (2 days), extent of colonization (46 mm), and propagation velocity (3 mm d−1). © 2015 American Institute of Chemical Engineers Environ Prog, 2015

Dyes released by the textile industries pose a threat to environmental quality. Ligninolytic white-rot fungi can effectively decolorize colored effluents and conventional dyes. The present study investigates the ability of eleven strains belonging to Pleurotus, Ganoderma and Lentinula mushroom genera in the decolorization of eight textile azo and anthraquinone dyes added in solid-plate cultures. Pleurotus pulmonarius AMRL 177, showing the greatest decolorization ability, was further investigated for Remazol Brilliant Blue R (RBBR) decolorization using response surface methodology (RSM). RSM involved Box-Behnken design matrix for three design factors: dye concentration, nitrogen concentration and copper concentration were successfully employed for the optimization of four responses: lag time, mycelium extension rate, decolorization rate and laccase activity. Optimum values of responses obtained were: lag time 3 days, mycelium extension rate 2.8 mm d−1, decolorization rate 2.7 mm d−1 and laccase activity 480 U ml−1.

Mixtures of a sandy soil and wheat straw were doped with the organochlorine insecticide lindane in glass tubes and were inoculated with the polypore fungus, Ganoderma australe. An evaluation of bioremediation process effectiveness was searched and five parameters identified for the solid-state system. Fungi growth is a function of temperature and requires moisture for a proper colonization. These microorganisms need inorganic nutrients such nitrogen and phosphorus to support cell growth and it is also appropriate to know the range of concentration and toxicity of the used insecticide. Thus, an orthogonal central composite design (CCD) of experiments was used to construct second order response surfaces. Five design factors, namely temperature, moisture, straw, lindane content and nitrogen content and seven optimization parameters (responses), namely lag time, propagation velocity, biomass growth rate, biodegradation rate, biodegradation/biomass, biomass/propagation and biomass content were analyzed. The optima of the responses of the adequate models were found to be the following: propagation velocity 4.25mm/day, biomass growth rate 408mg/day, biodegradation/biomass 56.9microg/g, biomass/propagation 250mg/mm and fungal biomass content in solid mixture 260mg/cm(3). The most important response for bioremediation purposes is biodegradation/biomass which is maximized at the factors levels: temperature 17.3 degrees C, moisture 58%, straw content 45%, lindane content 13ppm and nitrogen content 8.2ppm.