• Energy Research

The tannery industry is one of the economic sectors that contributes to the development of different countries. Globally, Europe and Asia are the main producers of this industry, although Latin America and Africa have been growing considerably in recent years. With this growth, the negative environmental impacts towards different ecosystem resources as a result of the discharges of recalcitrated pollutants, have led to different investigations to generate alternative solutions. Worldwide, different technologies have been studied to address this problem, biological and physicochemical processes have been widely studied, presenting drawbacks with some recalcitrant compounds. This review provides a context on the different existing technologies for the treatment of tannery wastewater, analyzing the physicochemical composition of this liquid waste, the impact it generates on human health and ecosystems and the advances in the different existing technologies, focusing on advanced oxidation processes and the use of microalgae. The coupling of advanced oxidation processes with biological processes, mainly microalgae, is seen as a viable biotechnological strategy, not only for the removal of pollutants, but also to obtain value-added products with potential use in the biorefining of the biomass.

Microalgae have been studied in recent years for various reasons, one among them being their potential in the production of biofuels. Biofuels are considered as a renewable source that does not compete with the food industry, and their production results in a reduced environmental footprint. The objective of the present study was to evaluate the different culture conditions that influence the productivity of the microalgae Chlorella vulgaris and Scenedesmus obliquus as a potential source for the production of biodiesel. Bold, Bristol, and modified Algal Assay Procedure (AAP) culture media were evaluated to determine which of them can provide the best conditions that favor biomass production and lipid deposition. The results indicated that S. obliquus cultivated in Bold medium exhibited a higher production of biomass after 30 days (1.730 g/l), while C. vulgaris showed a higher production in the modified AAP medium (1.880 g/l). Although the cultures grown in the AAP medium showed a more significant percentage of biomass comprising lipids than those in the other two media, between the two microalgae, the highest final lipid production was obtained by growing S. obliquus in Bold medium (0.685 g/l, 39.60% of biomass). N, P, Fe, and Mo were the elements added to the growth media, and depending on their concentration in the media, there were differences in the production of lipids. Thus, it can be concluded that S. obliquus cultivated in Bold medium has the highest potential in the production of lipids for biodiesel, but it is necessary to further optimize the cultivation of biomass to obtain a greater quantity of lipids, while interfering as little as possible in its synthesis capacity.

Se analizó la producción de biodiesel por medios químicos y enzimáticos, a partir de aceite de cocina usado (ACU), evaluandola calidad y rendimiento del producto obtenido en cada método. Para el proceso químico se desarrolló una esterificación ácida seguida de unatransesterificación básica (temperatura de reacción: 60 °C, relación molar aceite:metanol 1:6, concentración de catalizador KOH: 1% p/p),tiempos de reacción: 55 y 70 min; y la transesterificación enzimática (temperatura: 38 °C, relación molar aceite:metanol 1:3, concentración decatalizador enzima lipasa XX 25 split liquida: 5%), tiempos de reacción: 3 y 6 horas. Se determinó propiedades fisicoquímicas (i.e. densidad,viscosidad cinemática, contenido de humedad, perfil de ácidos grasos, índice de acidez, peróxidos y saponificación) de la materia prima,registrando presencia de ácido oleico (42.45%) y ácido palmítico (33.52%). El mejor rendimiento obtenido fue a partir de la transesterificaciónquímica bajo las condiciones de 60 °C, 1% KOH y 70 minutos, evidenciando un porcentaje de conversión del 96.15% y un número ácido de1.33 mmKOH/g, en comparación con la transesterificación enzimática que registró un alto número ácido de 6.91 mmKOH/g y porcentaje deconversión de 48.8% bajo las condiciones de 38 °C, 5% de enzima lipasa y 3 horas

The present research evaluates the simulation of a system for transforming inland-fisheries wastewater into sustainable fish feed using Designer® software. The data required were obtained from the experimental cultivation of Chlorella sp. in wastewater supplemented with N and P. According to the results, it is possible to produce up to 11,875 kg/year (31.3 kg/d) with a production cost of up to 18 (USD/kg) for dry biomass and 0.19 (USD/bottle) for concentrated biomass. Similarly, it was possible to establish the kinetics of growth of substrate-dependent biomass with a maximum production of 1.25 g/L after 15 days and 98% removal of available N coupled with 20% of P. It is essential to note the final production efficiency may vary depending on uncontrollable variables such as climate and quality of wastewater, among others.

The search for innovation and biotechnological strategies in the biodiesel production chain have become a topic of interest for scientific community owing the importance of renewable energy sources. This work aimed to implement an enzymatic transesterification process to obtain biodiesel from waste frying oil (WFO). The transesterification was performed by varying reaction times (8 h, 12 h and 16 h), enzyme concentrations of lipase XX 25 split (14%, 16% and 18%), pH of reaction media (6, 7 and 8) and reaction temperature (35, 38 and 40 °C) with a fixed alcohol–oil molar ratio of 3:1. The optimum operating conditions were selected to quantify the amount of fatty acid methyl esters (FAMEs) generated. The highest biodiesel production was reached with an enzyme concentration of 14%, reaction time of 8 h, pH of 7 and temperature of 38 °C. It was estimated a FAMEs production of 42.86% for the selected experiment; however, best physicochemical characteristics of biodiesel were achieved with an enzyme concentration of 16% and reaction time of 8 h. Results suggested that enzymatic transesterification process was favorable because the amount of methyl esters obtained was similar to the content of fatty acids in the WFO.

Today, the world is increasingly concerned about energy and environmental challenges, and the search for renewable energy sources has become an unavoidable priority. In this context, Elaeis guineensis (better known as the African oil palm) has been placed in the spotlight due to its great potential and specific characteristics for the production of alternative fuels in the search for sustainable energy solutions. In the present study, bibliometric and co-occurrence analyses are proposed to identify trends, gaps, future directions, and challenges related to the production of bioethanol and hydrogen from oil palm rachis, using VOSviewer v.1.6.20 as a tool to analyze data obtained from SCOPUS. A mapping of several topics related to bioethanol and hydrogen production from oil palm bagasse or rachis is provided, resulting in contributions to the topic under review. It is shown that research is trending towards the use of oil palm rachis as a raw material for hydrogen production, consolidating its position as a promising renewable energy source. The field of hydrogen production from renewable sources has undergone constant evolution, and it is expected to continue growing and playing a significant role in the transition towards cleaner and more sustainable energy sources, potentially involving the adoption of innovative technologies such as solar-powered steam generation. From an economic point of view, developing a circular economy approach to bioethanol and hydrogen production from oil palm rachis and waste management will require innovations in material design, recycling technologies, and the development of effective life cycle strategies that can be evaluated through computer-assisted process simulation. Additionally, the extraction and purification of other gases during the dark fermentation method contribute to reducing greenhouse gas emissions and minimizing energy consumption. Ultimately, the sustainability assessment of bioethanol production processes is crucial, employing various methodologies such as life cycle assessment (LCA), techno-economic analysis, techno-economic resilience, and environmental risk assessment (ERA). This research is original in that it evaluates not only the behavior of the scientific community on these topics over the past 20 years but also examines a less-studied biofuel, namely bioethanol.

This study investigates the influence of photoperiod and wastewater concentration on the growth of microalgae and cyanobacteria for the removal of environmentally significant parameters (COD, BOD, Cr, Fe, color, chlorides, nitrogen compounds, and phosphates) from dyeing wastewater. A two-factor central composite design with surface response was employed, involving two algae species (Chlorella and Scenedesmus sp.) and two cyanobacteria species (Hapalosiphon and Oscillatoria sp.). The findings indicated that extended photoperiods (>13 h) and higher wastewater concentrations (70–80% v/v) enhanced biomass production across all strains. However, Hapalosiphon and Chlorella sp. (1.6 and 0.45 g/L) exhibited better tolerance to the wastewater’s high toxicity, resulting in higher biomass concentrations and improved COD and BOD removal by Hapalosiphon sp. (75% and 80%, respectively). Further analysis of the obtained biomass revealed their potential applications. Among the cyanobacteria, Hapalosiphon sp. synthesized the highest concentrations of total proteins and lipids (38% and 28% w/w, respectively), while Oscillatoria sp. displayed a high protein content (42% w/w). In contrast, the algae demonstrated a strong propensity for storing substantial quantities of total carbohydrates (65% and 57% w/w for Scenedesmus and Chlorella sp., respectively). These results signify the feasibility of cultivating photosynthetic microorganisms in industrial dyeing wastewater as a sustainable source of nutrients for targeted metabolite production.

Activated sludge processes are often inhibited by nickel, cadmium, and cobalt. The inhibitory effect of these heavy metals on a synthetic wastewater treatment process was tested through pulse microrespirometry; i.e., pulse of substrate injected in a microreactor system. The inhibitory effect was tested under different conditions including the heavy metals, substrate and biomass concentrations, and exposure time. The inhibitory effect was quantified by the percentage of inhibition, half saturation constant (KS), inhibition constant (KI), and maximum oxygen uptake rate (OURmax). The results indicated that, in a range of concentration from 0 to 40 mg L-1, the three heavy metals exerted an uncompetitive and incomplete inhibitory effect, with a maximum inhibition of 67, 57, and 53% for Ni, Co, and Cd, respectively. An increase of the biomass concentration by 620% resulted in a decrease of the inhibition by 47 and 69% for Co and Cd, respectively, while no effect was observed on Ni inhibition. An increase of the substrate concentration by 87% resulted in an increase of the inhibition by 24, 70, and 47% for Ni, Co and Cd, respectively. In the case of nickel and cadmium, an increase in the exposure time to the heavy metals also increased the inhibition.