The Potential of Bioaugmentation-Assisted Phytoremediation Derived Maize Biomass for the Production of Biomethane via Anaerobic Digestion.

Anthropogenic behaviors are causing the severe build-up of heavy metal (HM) pollutants in the environment, particularly in soils. Amongst a diversity of remediation technologies, phytoremediation is an environmentally friendly technology that, when coupling tolerant plants to selected rhizospheric microorganisms, can greatly stimulate HM decontamination of soils. Maize (Zea mays) is a plant with the reported capacity for HM exclusion from contaminated soil but also has energetic importance. In this study, Zea mays was coupled with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), and Cupriavidus sp. strain 1C2, a plant growth-promoting rhizobacteria (PGPR), as a remediation approach to remove Cd and Zn from an industrial contaminated soil (1.2 mg Cd kg-1 and 599 mg Zn kg-1) and generate plant biomass, by contrast to the conservative development of the plant in an agricultural (with no metal pollution) soil. Biomass production and metal accumulation by Z. mays were monitored, and an increase in plant yield of ca. 9% was observed after development in the contaminated soil compared to the soil without metal contamination, while the plants removed ca. 0.77% and 0.13% of the Cd and Zn initially present in the soil. The resulting biomass (roots, stems, and cobs) was used for biogas generation in several biomethane (BMP) assays to evaluate the potential end purpose of the phytoremediation-resulting biomass. It was perceptible that the HMs existent in the industrial soil did not hinder the anaerobic biodegradation of the biomass, being registered biomethane production yields of ca. 183 and 178 mL of CH4 g-1 VS of the complete plant grown in non-contaminated and contaminated soils, respectively. The generation of biomethane from HM-polluted soils' phytoremediation-derived maize biomass represents thus a promising possibility to be a counterpart to biogas production in an increasingly challenging status of renewable energy necessities.

Indoor Air Quality Improvement Using Nature-Based Solutions: Design Proposals to Greener Cities.

Low indoor air quality is an increasingly important problem due to the spread of urbanization. Because people spend most of their time inside, poor indoor air quality causes serious human health issues, resulting in significant economic losses. In this work, the current state of affairs is presented and analyzed, focusing on the current problems and the available solutions to improve the quality of indoor air, and the use of nature-based solutions. These involve the cultivation of microalgae in closed photobioreactors. In these systems, photosynthetic organisms can capture CO2 and other pollutants generated in indoor environments, which they use to grow and develop biomass. Several possible layouts for the implementation of microalgae-based indoor air cleaning systems are presented, taking into account the systems that are currently available at a commercial scale. A critical analysis of the microalgae indoor purification systems is presented, highlighting their advantages and disadvantages, and suggesting potential improvements and future lines of research and development in the area.

Syngas production by bi-reforming methane on an Ni-K-promoted catalyst using hydrotalcites and filamentous carbon as a support material.

Steam reforming of methane (SRM) and dry reforming of methane (DRM) are frequently used in the production of syngas; however, the bi-reforming of methane (BRM) is an interesting and alternative process. In this study, BRM was studied over MgO, a layered double hydroxide (LDH) phase that was destroyed between 600 °C and 900 °C during the reaction. It showed good sorption capacity for CO2 at relatively low temperatures (<500 °C), with CO2 adsorption being a pre-requisite for its catalytic conversion. Among the tested materials, the potassium-promoted LDH showed the highest activity, achieving a maximum CO2 conversion of 75%. The results suggest that at high temperature, the electronic structure of the used materials influences the destabilization of the feed in the order of methane, water and carbon dioxide. K promotes the catalytic activity, compensates the presence of large Ni particle sizes originating from the high metal loading, and favors the formation of Mg-Al-spinel. K is known to be an electronic promoter that releases electrons, which flow to the active metal. This electron flow induces instability on the molecule to be converted, and most probably, also induces size variations on the respective active nickel metal. The influence of the operating conditions in the range of 300 °C to 900 °C on the conversion of the reactants and product distribution was studied. Accordingly, it was concluded that it is only possible to obtain molar ratios of hydrogen-to-carbon monoxide close to two at high temperatures, a pre-requisite for the synthesis of methanol.

Correction: Syngas production by bi-reforming methane on an Ni-K-promoted catalyst using hydrotalcites and filamentous carbon as a support material.

[This corrects the article DOI: 10.1039/D0RA03264F.].

Bio-refinery approach for spent coffee grounds valorization.

Although normally seen as a problem, current policies and strategic plans concur that if adequately managed, waste can be a source of the most interesting and valuable products, among which metals, oils and fats, lignin, cellulose and hemicelluloses, tannins, antioxidants, caffeine, polyphenols, pigments, flavonoids, through recycling, compound recovery or energy valorization, following the waste hierarchy. Besides contributing to more sustainable and circular economies, those products also have high commercial value when compared to the ones obtained by currently used waste treatment methods. In this paper, it is shown how the bio-refinery framework can be used to obtain high value products from organic waste. With spent coffee grounds as a case study, a sequential process is used to obtain first the most valuable, and then other products, allowing proper valorization of residues and increased sustainability of the whole process. Challenges facing full development and implementation of waste based bio-refineries are highlighted.

Sustainability and economic evaluation of microalgae grown in brewery wastewater.

This article evaluates the sustainability and economic potential of microalgae grown in brewery wastewater for biodiesel and biomass production. Three sustainability and two economic indicators were considered in the evaluation within a life cycle perspective. For the production system the most efficient process units were selected. Results show that harvesting and oil separation are the main process bottlenecks. Microalgae with higher lipid content and productivity are desirable for biodiesel production, although comparable to other biofuel's feedstock concerning sustainability. However, improvements are still needed to reach the performance level of fossil diesel. Profitability reaches a limit for larger cultivation areas, being higher when extracted biomass is sold together with microalgae oil, in which case the influence of lipid content and areal productivity is smaller. The values of oil and/or biomass prices calculated to ensure that the process is economically sound are still very high compared with other fuel options, especially biodiesel.

Parametric study of a brewery effluent treatment by microalgae Scenedesmus obliquus.

This work analyses the potential of using microalgae Scenedesmus obliquus (So) for a brewery wastewater treatment and biomass production. The chemical oxygen demand (COD), total nitrogen (TN) and total carbon (TC) was followed in time, and the influence of light exposure, light intensity and culture aeration was studied. Results show that the most adequate conditions for cultivating So in this effluent are the aerated cultures, exposed to a 12h period of daily light, at 12000 Lux intensity. At these conditions it is obtained a maximum of 0.9 g of dry biomass per liter of culture, after 9 days, for a maximum reduction of 57.5% and 20.8% of COD and TN, respectively, after 14 days, and 56.9% of TC, after 13 days, corresponding to the final values of 1692 mg O(2)/L COD, 47 mg N/L TN, and 1mg C/L TC.