Life cycle assessment for the production of MSWI fly-ash based porous glass-ceramics: Scenarios based on the contribution of silica sources, methane aided, and energy recoveries.

Municipal solid waste (MSW) production in the world has increased by 60 % in recent years. Incineration of MSW reduces their volume in conjunction with energy recovery. Incineration produces two residues, namely bottom ash (BA) and fly ash (FA), with high concentration of heavy metals and organic pollutants, especially for FA, making them an environmental concern. Vitrification is a costly, highly safe high temperature treatment, ensuring encapsulation of heavy metals. FA vitrification requires a source of silica to be able to get vitrified. In this study, we have proposed valorizing treated (vitrified) FA through the production of porous glass-ceramics, subsequently to MSWI. The entire process, from incineration to glass-ceramics production, was evaluated for several scenarios by Life Cycle Assessment (LCA) using Sima Pro 9.0. Three main scenarios were analysed; each one considering a different silica source: bottom ash (BA), glass cullet (G) and silica sand (S), and for each scenario, three thermal recovery subscenarios were assumed: no thermal recovery used to heat FA prior to vitrification (N), heating FA prior to vitrification using incineration gases thermal recovery (T) and methane-combustion-aided thermal recovery, which exploits methane combustion to further increase the gases temperature (M). Results proved that vitrification was a technically feasible and environmentally-energetically sustainable technology. The result indicates that the most eco-sustainable scenario was using bottom ashes as a silica source together with methane-combustion-aided recovery: 0.467 kgCO2,eq, 5.83 × 10-8 carcinogenic-CTUh and 9.26 MJ required per kg of glass-ceramics produced.

Simultaneous CO2 reduction and NADH regeneration using formate and glycerol dehydrogenase enzymes co-immobilized on modified natural zeolite.

In this work, the co-immobilization of formate dehydrogenase (FDH) and glycerol dehydrogenase (GlyDH) enzymes is proposed to reduce CO2 into formic acid, an important chemical intermediate. The reduction of carbon dioxide is carried out by FDH to obtain formic acid, simultaneously, the GlyDH regenerated the nicotinamide cofactor in the reduced form (NADH) by the oxidation of glycerol into dihydroxyacetone. Natural zeolite was selected as immobilization support given its good properties and low cost. The natural zeolite was modified with subsequent acid-alkaline attacks to obtain a mesostructurization of the clinoptilolite. The two enzymes were co-immobilized on clinoptilolite, previously hetero-functionalized with amino and glyoxyl groups. The distribution of the enzymes was confirmed by fluorescence microscopy analysis. Furthermore, a great increase in the retained activity for the formate dehydrogenase enzyme was noted, passing from 18% to 89%, when the mesostructured clinoptilolite was used as support. The immobilization yield of formate dehydrogenase and glycerol dehydrogenase is around 100% with all the supports studied. The promising results suggest a possible development of this procedure in enzyme immobilization and biocatalysis. The biocatalysts were characterized to find the optimal pH and temperature. Furthermore, a thermal stability test at 50 °C was carried out on both enzymes, in free and immobilized forms. Finally, it was shown that the biocatalyst is effective in reducing CO2, both by using the cofactor in the reduced form (NADH) or the oxidized form (NAD+), obtaining NADH through the regeneration with glycerol in this latter case.

A practical method for gas changing time estimation using a simple gas-liquid mass transfer model.

The present work explains a practical and simple method to calculate the gas changing time of anaerobic systems. It is substantiated under the physics of gas-liquid transfer theory and allows researchers to obtain an approximate value of gas changing time with few measurements of the gas composition in the outlet of the reactor. The only analytical equipment required is a gas analyzer, and calculations can be done using a spreadsheet. Along with the validation of the model, a short guide for its application in the laboratory is introduced. The model fit the experimental data with less than 1% error in the composition of the out-gas when no carbon dioxide is involved. This method will allow savings in valuable resources such as time and gases while providing greater comprehension of the characteristics of the gas-liquid transfer of the studied system.

Covalent Immobilization of Dehydrogenases on Carbon Felt for Reusable Anodes with Effective Electrochemical Cofactor Regeneration.

This study presents the immobilization with aldehyde groups (glyoxyl carbon felt) of alcohol dehydrogenase (ADH) and formate dehydrogenase (FDH) on carbon-felt-based electrodes. The compatibility of the immobilization method with the electrochemical application was studied with the ADH bioelectrode. The electrochemical regeneration process of nicotinamide adenine dinucleotide in its oxidized form (NAD+ ), on a carbon felt surface, has been deeply studied with tests performed at different electrical potentials. By applying a potential of 0.4 V versus Ag/AgCl electrode, a good compromise between NAD+ regeneration and energy consumption was observed. The effectiveness of the regeneration of NAD+ was confirmed by electrochemical oxidation of ethanol catalyzed by ADH in the presence of NADH, which is the no active form of the cofactor for this reaction. Good reusability was observed by using ADH immobilized on glyoxyl functionalized carbon felt with a residual activity higher than 60 % after 3 batches.

Synthesis and characterization of ordered mesoporous silicas for the immobilization of formate dehydrogenase (FDH).

This work studied the influence of the pore size and morphology of the mesoporous silica as support for formate dehydrogenase (FDH), the first enzyme of a multi-enzymatic cascade system to produce methanol, which catalyzes the reduction of carbon dioxide to formic acid. Specifically, a set of mesoporous silicas was modified with glyoxyl groups to immobilize covalently the FDH obtained from Candida boidinii. Three types of mesoporous silicas with different textural properties were synthesized and used as supports: i) SBA-15 (DP = 4 nm); ii) MCF with 0.5 wt% mesitylene/pluronic ratio (DP = 20 nm) and iii) MCF with 0.75 wt% mesitylene/pluronic ratio (DP = 25 nm). As a whole, the immobilized FDH on MCF0.75 exhibited higher thermal stability than the free enzyme, with 75% of residual activity after 24 h at 50 °C. FDH/MCF0.5 exhibited the best immobilization yields: 69.4% of the enzyme supplied was covalently bound to the support. Interestingly, the specific activity increased as a function of the pore size of support and then the FDH/MCF0.75 exhibited the highest specific activity (namely, 1.05 IU/gMCF0.75) with an immobilization yield of 52.1%. Furthermore, it was noted that the immobilization yield and the specific activity of the FDH/MCF0.75 varied as a function of the supported enzyme: as the enzyme loading increased the immobilization yield decreased while the specific activity increased. Finally, the reuse test has been carried out, and a residual activity greater than 70% was found after 5 cycles of reaction.

Recovery of humic acids from anaerobic sewage sludge: Extraction, characterization and encapsulation in alginate beads.

Wastewater production is rising all over the world and one of the most difficult problems is the disposal of sewage sludge (SS). It is known that SS contains certain quantities of added-value compounds, such as humic acids (HA) which in turn have beneficial effects on soil quality and plant growth. On the other hand, SS can retain many pollutants, such as heavy metals. The present work aimed to implement an HA alkaline extraction protocol from anaerobic sewage sludge (ASS). Subsequently, the HA were quantified in ASS, in HA extract and in commercial HA, used as a benchmark, which gave results of 12.53%, 26.87% and 77.87% (on dry matter basis), respectively. FESEM and EDX analyses on lyophilized HA extract confirmed that no heavy metals had passed into the extract. Afterwards, in order to allow controlled release of the HA in soils, alginate beads containing the HA extract were created. Finally, a pot experiment in a greenhouse was performed using Chilean lettuce plants (Lactuca sativa L.) treated with alginate-HA extract beads. At the end of the greenhouse experiments, the hypogean dry biomass of the treated plants was significantly higher than for non-treated plants. The relevance of this study relies not only on the exploitation of green chemistry principles, by converting a waste stream into a high-value product, but also on the application of an approach following a circular economy model.

Anaerobic digestates from sewage sludge used as fertilizer on a poor alkaline sandy soil and on a peat substrate: Effects on tomato plants growth and on soil properties.

Anaerobic digestates from sewage sludge (SSADs) are a by-product of the wastewater treatment process that still preserves a certain agronomic interest for its richness in plant nutrients and organic matter. Fertilizing properties of two liquid and two dewatered SSADs were tested on tomato plants (Solanum lycopersicum L.). Pot experiments were performed on sandy soil and peat substrate under greenhouse conditions with a SSADs application rate of 170 kg N/ha over a period of three months. Beneficial effects of SSADs were reported on different growth parameters, revealing an increase in biomass and height up to 37.5 and 6-folds over untreated control. No phytotoxic effect occurred on SSAD-exposed plants. Chemical analysis of soils treated with SSADs showed enrichment of macro- and micro-nutrients as well as organic matter. In some cases, the chemical characterization of leaves revealed an enhancement of uptaken macronutrients. This study contributed in general to deepen the knowledge on the short-term growing season fertilizing effects of SSAD. Despite the treatment dosage was calculated only on nitrogen requirements, the study highlighted the importance of the other nutrients and organic matter on plant growth.

Evaluation of anaerobic digestates from sewage sludge as a potential solution for improvement of soil fertility.

Sewage sludge production in European countries has widely raised in the last decade and its fate is currently landfilling, incinerators, composting or land application. To explore its agronomic potential, the main target of this work is to understand the effects of anaerobic digestates from sewage sludge (SSAD). To this aim, four different SSADs (two liquids and two dewatered) were characterized. On the liquid ones, Germination Index was evaluated through a plate bioassay with Lepidium sativum L. seeds; low concentrations of SSAD (2.5%) improved GI in one case, while at higher concentrations phytotoxic effects occurred in both. Then, pot experiments were set in climate chamber with Cucumis sativus L. grown for 30 days on two different substrates: a sandy, alkaline and poor soil, and peat substrate. All SSADs and a mineral fertilizer were used at three increasing dosages: 85, 170, 255 kg of nitrogen per hectare (kg N/ha). Results in terms of germination, dry biomass, chlorophyll content, net photosynthesis, stomatal conductance, CO2 concentration in substomatal cavity and root development were compared to a not treated control. All treatments gave results significantly higher or similar to control on all the parameters evaluated. Moreover, the intermediate nitrogen dosage (170 kg N/ha) generally showed the highest results compared to other dosages, especially for dewatered SSADs. All these results were much more evident for cucumber plants grown on an the alkaline, sandy and poor soil than on peat substrate, such demonstrating that SSADs have a fertilizing effect for plants growing on this kind of soil.

Life Cycle Assessment of waste disposal from olive oil production: Anaerobic digestion and conventional disposal on soil.

Extra virgin olive-oil (EVO) production is an important economic activity for several countries, especially in the Mediterranean area such as Spain, Italy, Greece and Tunisia. The two major by-products from olive oil production, solid-liquid Olive Pomace (OP) and the Olive Mill Waste Waters (OMWW), are still mainly disposed on soil, in spite of the existence of legislation which already limits this practice. The present study compares the environmental impacts associated with two different scenarios for the management of waste from olive oil production through a comparative Life Cycle Assessment (LCA). The two alternative scenarios are: (I) Anaerobic Digestion and (II) Disposal on soil. The analysis was performed through SimaPro software and the assessment of the impact categories was based on International Life Cycle Data and Cumulative Energy Demand methods. Both the scenarios are mostly related to the cultivation and harvesting phase and are highly dependent on the irrigation practice and related energy demand. Results from the present study clearly show that the waste disposal on soil causes the worst environmental performance of all the impact categories considered here. Important environmental benefits have been identified when anaerobic digestion is chosen as the final treatment. It was consequently demonstrated that anaerobic digestion should be a feasible alternative for olive mills, to produce biogas from common olive oil residues, reducing the environmental burden and adding value to the olive oil production chain.

Anodic microbial community analysis of microbial fuel cells based on enriched inoculum from freshwater sediment.

The characterization of anodic microbial communities is of great importance in the study of microbial fuel cells (MFCs). These kinds of devices mainly require a high abundance of anode respiring bacteria (ARB) in the anode chamber for optimal performance. This study evaluated the effect of different enrichments of environmental freshwater sediment samples used as inocula on microbial community structures in MFCs. Two enrichment media were compared: ferric citrate (FeC) enrichment, with the purpose of increasing the ARB percentage, and general enrichment (Gen). The microbial community dynamics were evaluated by polymerase chain reaction followed by denaturing gradient gel electrophoresis (PCR-DGGE) and real time polymerase chain reaction (qPCR). The enrichment effect was visible on the microbial community composition both during precultures and in anode MFCs. Both enrichment approaches affected microbial communities. Shannon diversity as well as ß-Proteobacteria and γ-Proteobacteria percentages decreased during the enrichment steps, especially for FeC (p < 0.01). Our data suggest that FeC enrichment excessively reduced the diversity of the anode community, rather than promoting the proliferation of ARB, causing a condition that did not produce advantages in terms of system performance.

Ureteral double-J stents performances toward encrustation after long-term indwelling in a dynamic in vitro model.

Three different single-lumen double-J ureteral stents of different materials were studied and compared after the insertion into a dynamic in vitro model with sterile artificial urine up to 6 months. The aim was to evaluate, at selected time steps of 1, 3, and 6 months, the material performances of the stents in preventing the formation of inorganic encrustations. Morphological, compositional, and qualitative analyses were carried out both before stent insertion and after stent permanence for the different time steps, showing an increasing level of encrustation which remains particularly low in the case of two polyurethane stents. Mechanical tests show that both the polyurethane stents and the chitosan one do not decrease the tensile strength after 6 months of indwelling. Evaluation of the wetting behavior of the stent outer surfaces indicates a hydrophilic behavior in most of the cases, which is generally preserved after immersion in artificial urine for the different time steps. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2244-2253, 2017.

New insights in Microbial Fuel Cells: novel solid phase anolyte.

For the development of long lasting portable microbial fuel cells (MFCs) new strategies are necessary to overcome critical issues such as hydraulic pump system and the biochemical substrate retrieval overtime to sustain bacteria metabolism. The present work proposes the use of a synthetic solid anolyte (SSA), constituted by agar, carbonaceous and nitrogen sources dissolved into diluted seawater. Results of a month-test showed the potential of the new SSA-MFC as a long lasting low energy consuming system.

Pyrolytic carbon-coated stainless steel felt as a high-performance anode for bioelectrochemical systems.

Scale up of bioelectrochemical systems (BESs) requires highly conductive, biocompatible and stable electrodes. Here we present pyrolytic carbon-coated stainless steel felt (C-SS felt) as a high-performance and scalable anode. The electrode is created by generating a carbon layer on stainless steel felt (SS felt) via a multi-step deposition process involving α-d-glucose impregnation, caramelization, and pyrolysis. Physicochemical characterizations of the surface elucidate that a thin (20±5µm) and homogenous layer of polycrystalline graphitic carbon was obtained on SS felt surface after modification. The carbon coating significantly increases the biocompatibility, enabling robust electroactive biofilm formation. The C-SS felt electrodes reach current densities (jmax) of 3.65±0.14mA/cm(2) within 7days of operation, which is 11 times higher than plain SS felt electrodes (0.30±0.04mA/cm(2)). The excellent biocompatibility, high specific surface area, high conductivity, good mechanical strength, and low cost make C-SS felt a promising electrode for BESs.

Additive Manufacturing of a Microbial Fuel Cell--A detailed study.

In contemporary society we observe an everlasting permeation of electron devices, smartphones, portable computing tools. The tiniest living organisms on Earth could become the key to address this challenge: energy generation by bacterial processes from renewable stocks/waste through devices such as microbial fuel cells (MFCs). However, the application of this solution was limited by a moderately low efficiency. We explored the limits, if any, of additive manufacturing (AM) technology to fabricate a fully AM-based powering device, exploiting low density, open porosities able to host the microbes, systems easy to fuel continuously and to run safely. We obtained an optimal energy recovery close to 3 kWh m(-3) per day that can power sensors and low-power appliances, allowing data processing and transmission from remote/harsh environments.