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Bio-electrochemical systems (BESs) enable microbial catalysis of electrochemical reactions. Plain electrical power production combined with wastewater treatment by microbial fuel cells (MFCs) has been the primary application purpose for BESs. However, large-scale power production and a high chemical oxygen demand conversion rates must be achieved at a benchmark cost to make MFCs economical competitive in this context. Recently, a number of valuable oxidation or reduction reactions demonstrating the versatility of BESs have been described. Indeed, BESs can produce hydrogen, bring about denitrification, or reductive dehalogenation. Moreover, BESs also appear to be promising in the field of online biosensors. To effectively apply BESs in practice, both biological and electrochemical losses need to be further minimized. At present, the costs of reactor materials have to be decreased, and the volumetric biocatalyst activity in the systems has to be increased substantially. Furthermore, both the ohmic cell resistance and the pH gradients need to be minimized. In this review, these losses and constraints are discussed from an electrochemical viewpoint. Finally, an overview of potential applications and innovative research lines is given for BESs.

Bio-electrochemical systems (BESs) enable microbial catalysis of electrochemical reactions. Plain electrical power production combined with wastewater treatment by microbial fuel cells (MFCs) has been the primary application purpose for BESs. However, large-scale power production and a high chemical oxygen demand conversion rates must be achieved at a benchmark cost to make MFCs economical competitive in this context. Recently, a number of valuable oxidation or reduction reactions demonstrating the versatility of BESs have been described. Indeed, BESs can produce hydrogen, bring about denitrification, or reductive dehalogenation. Moreover, BESs also appear to be promising in the field of online biosensors. To effectively apply BESs in practice, both biological and electrochemical losses need to be further minimized. At present, the costs of reactor materials have to be decreased, and the volumetric biocatalyst activity in the systems has to be increased substantially. Furthermore, both the ohmic cell resistance and the pH gradients need to be minimized. In this review, these losses and constraints are discussed from an electrochemical viewpoint. Finally, an overview of potential applications and innovative research lines is given for BESs.

Agricultural application of sewage sludge has been emotionally discussed in the last decades, because the latter contains organic micropollutants with unknown fate and risk potential. In this work, the reuse of anaerobically digested sludge in agriculture is evaluated from an environmental point of view by using Life Cycle Assessment methodology. More specifically, the potential impacts of emerging micropollutants, such as pharmaceuticals and personal care products, present in the sludge have been quantified. Four scenarios were considered according to the temperature of the anaerobic digestion (mesophilic or thermophilic) and the sludge retention time (20 or 10d), and they have been compared with the non-treated sludge. From an environmental point of view, the disposal of undigested sludge is not the most suitable alternative, except for global warming due to the dominance (65-85%) of the indirect emissions associated to the electricity use. Nutrient-related direct emissions dominate the eutrophication category impact in all the scenarios (>71.4%), although a beneficial impact related to the avoidance of industrial fertilisers production is also quantified (up to 6.7%). In terms of human and terrestrial toxicity, the direct emissions of heavy metals to soil dominate these two impact categories (>70%), and the contribution of other micropollutants is minimal. Moreover, only six (Galaxolide, Tonalide, Diazepam, Ibuprofen, Sulfamethoxazole and 17alpha-ethinyloestradiol) out of the 13 substances considered are really significant since they account for more than 95% of the overall micropollutants impact.

Agricultural application of sewage sludge has been emotionally discussed in the last decades, because the latter contains organic micropollutants with unknown fate and risk potential. In this work, the reuse of anaerobically digested sludge in agriculture is evaluated from an environmental point of view by using Life Cycle Assessment methodology. More specifically, the potential impacts of emerging micropollutants, such as pharmaceuticals and personal care products, present in the sludge have been quantified. Four scenarios were considered according to the temperature of the anaerobic digestion (mesophilic or thermophilic) and the sludge retention time (20 or 10d), and they have been compared with the non-treated sludge. From an environmental point of view, the disposal of undigested sludge is not the most suitable alternative, except for global warming due to the dominance (65-85%) of the indirect emissions associated to the electricity use. Nutrient-related direct emissions dominate the eutrophication category impact in all the scenarios (>71.4%), although a beneficial impact related to the avoidance of industrial fertilisers production is also quantified (up to 6.7%). In terms of human and terrestrial toxicity, the direct emissions of heavy metals to soil dominate these two impact categories (>70%), and the contribution of other micropollutants is minimal. Moreover, only six (Galaxolide, Tonalide, Diazepam, Ibuprofen, Sulfamethoxazole and 17alpha-ethinyloestradiol) out of the 13 substances considered are really significant since they account for more than 95% of the overall micropollutants impact.

Production of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. Although several norms and guidelines for BMP tests exist, inter-laboratory tests regularly show high variability of BMPs for the same substrate. A workshop was held in June 2015, in Leysin, Switzerland, with over 40 attendees from 30 laboratories around the world, to agree on common solutions to the conundrum of inconsistent BMP test results. This paper presents the consensus of the intense roundtable discussions and cross-comparison of methodologies used in respective laboratories. Compulsory elements for the validation of BMP results were defined. They include the minimal number of replicates, the request to carry out blank and positive control assays, a criterion for the test duration, details on BMP calculation, and last but not least criteria for rejection of the BMP tests. Finally, recommendations on items that strongly influence the outcome of BMP tests such as inoculum characteristics, substrate preparation, test setup, and data analysis are presented to increase the probability of obtaining validated and reproducible results.

Production of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. Although several norms and guidelines for BMP tests exist, inter-laboratory tests regularly show high variability of BMPs for the same substrate. A workshop was held in June 2015, in Leysin, Switzerland, with over 40 attendees from 30 laboratories around the world, to agree on common solutions to the conundrum of inconsistent BMP test results. This paper presents the consensus of the intense roundtable discussions and cross-comparison of methodologies used in respective laboratories. Compulsory elements for the validation of BMP results were defined. They include the minimal number of replicates, the request to carry out blank and positive control assays, a criterion for the test duration, details on BMP calculation, and last but not least criteria for rejection of the BMP tests. Finally, recommendations on items that strongly influence the outcome of BMP tests such as inoculum characteristics, substrate preparation, test setup, and data analysis are presented to increase the probability of obtaining validated and reproducible results.