Surfactin as an ingredient in cosmetic industry: Benefits and trends.

Surfactin is a natural surfactant almost exclusively produced by Bacillus species with excellent physical-chemical, and biological properties. Among innovative applications, surfactin has been recently used as an ingredient in formulations. The antibacterial and anti-acne activities, as well as the anti-wrinkle, moisturizing, and cleansing features, are some of the reasons this lipopeptide is used in cosmetics. Considering the importance of biosurfactants in the world economy and sustainability, their potential properties for cosmetic and dermatological products, and the importance of patents for technological advancement in a circular bioeconomy system, the present study aims to review all patents involving surfactin as an ingredient in cosmetic formulas. This review was conducted through Espacenet, wherein patents containing the terms "cosmetic" and "surfactin" in their titles, abstracts, or claims were examined. Those patents that detailed a specific surfactin dosage within their formulations were selected for analysis. All patents, irrespective of their publication date, from October 1989 to December 2022, were considered. Additionally, a comprehensive search was performed in the MEDLINE and EMBASE databases, spanning from their inception until the year 2023. This complementary search aimed to enrich the understanding derived from patents, with a specific emphasis on surfactin, encompassing its associated advantages, efficacy, mechanisms of action on the skin, as well as aspects related to sustainability and its merits in cosmetic formulations. From the 105 patents analysed, 75% belong to Japan (54), China (14), and Korea (9). Most of them were submitted by Asian companies such as Showa Denko (15), Kaneka (11) and Kao Corporation (5). The formulations described are mainly emulsions, skincare, cleansing, and haircare, and the surfactin dose does not exceed 5%. Surfactin appears in different types of formulas worldwide and has a high tendency to be used. Surfactin and other biosurfactants are a promising alternative to chemical ingredients in cosmetic formulations, guaranteeing skin health benefits and minimizing the impact on the environment.

OBJECTIF: La surfactine est un agent tensioactif naturel presque exclusivement produit par les espèces de Bacillus, qui présente d'excellentes propriétés physico­chimiques et biologiques. Parmi les applications innovantes, la surfactine a été récemment utilisée comme ingrédient dans les formulations. Les activités antibactériennes et anti­acnéiques, ainsi que les propriétés antirides, hydratantes et nettoyantes, sont quelques­unes des raisons pour lesquelles ce lipopeptide est utilisé dans les cosmétiques. Compte tenu de l'importance des biosurfactants pour l'économie mondiale et la durabilité, de leurs propriétés potentielles pour les produits cosmétiques et dermatologiques, et de l'importance des brevets pour les progrès technologiques dans un système de bioéconomie circulaire, la présente étude vise à passer en revue tous les brevets impliquant la surfactine en tant qu'ingrédient dans les formules cosmétiques. MÉTHODES: Cet examen a été mené en utilisant Espacenet, dans lequel les brevets contenant les termes « cosmétique ¼ et « surfactine ¼ dans leurs titres, résumés ou revendications ont été examinés. Les brevets détaillant un dosage spécifique de surfactine dans leurs formulations ont été sélectionnés pour l'analyse. Tous les brevets, quelle que soit leur date de publication, d'octobre 1989 à décembre 2022, ont été pris en compte. En outre, une recherche complète a été effectuée dans les bases de données MEDLINE et EMBASE, depuis leur création jusqu'à l'année 2023. Cette recherche complémentaire visait à enrichir la compréhension dérivée de brevets, en mettant l'accent sur la surfactine, ses avantages associés, son efficacité, ses mécanismes d'action sur la peau, ainsi que les aspects liés à la durabilité et ses mérites dans les formulations cosmétiques. RÉSULTATS: Sur les 105 brevets analysés, 75 % appartiennent au Japon (54), à la Chine (14) et à la Corée (9). La plupart d'entre eux ont été soumis par des sociétés asiatiques telles que Showa Denko (15), Kaneka (11) et Kao Corporation (5). Les formulations décrites sont principalement des émulsions, des soins de la peau, des nettoyants et des soins capillaires, et la dose de surfactine n'excède pas 5 %. CONCLUSIONS: La surfactine apparaît dans différents types de formules dans le monde et conserve une forte tendance à l'utilisation. La surfactine et d'autres biosurfactants sont une alternative prometteuse aux ingrédients chimiques dans les formulations cosmétiques, garantissant des bénéfices pour la santé de la peau et minimisant l'impact sur l'environnement.

Conidia production of the entomopathogenic fungus Beauveria bassiana using packed-bed bioreactor: Effect of substrate biodegradability on conidia virulence.

This work presents the scale-up of the conidia production of the entomopathogenic fungus Beauveria bassiana using two different wastes, coupled with concentration and virulence tests of the produced conidia against the pest Tenebrio molitor. Beauveria bassiana CECT 20374 was used in solid state fermentation (SSF) operating under batch strategy. Two substrates with different biodegradability (rice husk and beer draff) were tested, successfully scaling from 1.5 L to 22 L bioreactors. Higher conidia production was reached using beer draff as substrate (2.5 × 109 and 6.0 × 108 conidia g-1 dry matter in 1.5 and 22 L reactors respectively) highlighting air free porosity relevance as scale-up parameter. Concentration and dose-response tests against larvae and adult Tenebrio molitor were performed to compare strain CECT 20374 with control strain KVL 13-39 (a B. bassiana strain previously tested against T. molitor). Virulence effect of the 22 L fermentation product of strain CECT using rice husk or beer draff was tested against T. molitor adult stage. However, quality loses between conidia produced in agar plates and fermented products were observed (from 75 to 80% mortality in plates to 40% in rice husk and 50-60% in beer draff fermented products respectively). The differences between plate and fermented samples also indicated fermentation process, extraction and conservation steps as possible causes for quality losses, highlighting the need to optimize them to maximize virulence maintenance.

Scanning agro-industrial wastes as substrates for fungal biopesticide production: Use of Beauveria bassiana and Trichoderma harzianum in solid-state fermentation.

As a waste valorisation option, agro-industrial residues (rice husk, apple pomace, whisky draff, soy fiber, rice fiber, wheat straw, beer draff, orange peel and potato peel) were tested as feasible substrates for fungal conidia production. Solid-state fermentation tests were conducted at laboratory scale (100 g) with Beauveria bassiana or Trichoderma harzianum which conidia are reported to have biopesticide properties. Conidia concentrations with all substrates were at least two orders of magnitude above inoculum except for both fibers, thus demonstrating the possibilities of the proposed waste recovery option. Highest productions were at least 1 × 109 conidia g-1 dry matter for Beauveria bassiana using rice husk or potato peel and higher than 5 × 109 conidia g-1 dry matter for Trichoderma harzianum using beer draff, potato peel or orange pomace. Principal component analysis has been used to understand which parameters affect the most fungal conidia production for an easier evaluation of other similar wastes, being air-filled porosity and initial pH for Beauveria bassiana and cumulative oxygen consumption, initial moisture and total sugar content for Trichoderma harzianum.

Bioproduction of 2-phenylethanol and 2-phenethyl acetate by Kluyveromyces marxianus through the solid-state fermentation of sugarcane bagasse.

2-Phenylethanol (2-PE) and 2-phenethyl acetate (2-PEA) are important aroma compounds widely used in food and cosmetic industries due to their rose-like odor. Nowadays, due to the growing demand for natural products, the development of bioprocesses for obtaining value-added compounds has become of great significance. 2-PE and 2-PEA can be produced through the biotransformation of L-phenylalanine using the generally recognized as safe strain Kluyveromyces marxianus. L-phenylalanine bioconversion systems have been typically focused on submerged fermentation processes (SmF), but there is no information about other alternative productive approaches. Here, the solid-state fermentation (SSF) of sugarcane bagasse supplemented with L-phenylalanine was investigated as a sustainable alternative for producing 2-PE and 2-PEA in a residue-based system using Kluyveromyces marxianus as inoculum. An initial screening of the operational variables indicated that air supply, temperature, and initial moisture content significantly affect the product yield. Besides, it was found that the feeding strategy also affects the production and the efficiency of the process. While a basic batch system produced 16 mgproducts per gram of residue (dry basis), by using split feeding strategies (fed-batch) of only sugarcane bagasse, a maximum of 18.4 mgProducts g-1residue were achieved. Increase in product yield was also accompanied by an increase in the consumption efficiency of nutrients and precursor. The suggested system results as effective as other more complex SmF systems to obtain 2-PE and 2-PEA, showing the feasibility of SSF as an alternative for producing these compounds through the valorization of an agro-industrial residue.

Bioprocesses for 2-phenylethanol and 2-phenylethyl acetate production: current state and perspectives.

2-Phenylethanol (2-PE) and 2-phenethyl acetate (2-PEA) are valuable generally recognized as safe flavoring agents widely used in industry. Perfumes, pharmaceuticals, polishes, and personal care products, are some of the final products using these compounds as additives due to their rose-like odor. Also, 2-PE is used in disinfectants, pest control, and cleaning products due to its biocide capability. Although most of these additives production are derived from chemical synthesis, the current trend of consumers to prefer natural products has contributed to the development of biotechnological approaches as an alternative way to obtain natural 2-PE and 2-PEA. The most efficient route to bioproduce these compounds is through the bioconversion of L-phenylalanine via the Ehrlich pathway, and most of the advances have been focused on the development of this process. This review compiles the most recent developments in the biotechnological production of 2-PE and 2-PEA, indicating the most studied strains producing 2-PE and 2-PEA, the current advances in the in situ product recovery in liquid systems, an overview of the strain developments, and the progress in the use of residue-based systems. Future research should address the need for more sustainable and economic systems such as those using wastes as raw materials, as well as the scale-up of the proposed technologies.

Valorization of soy waste through SSF for the production of compost enriched with Bacillus thuringiensis with biopesticide properties.

There is a growing generation of biodegradable wastes from different human activities from industrial to agricultural including home and recreational activities. On the other hand, agricultural and horticultural activities require significant amounts of organic amendments and pesticides. In this framework, the present study evaluates the viability of soy fiber residue valorization as organic soil amendment with biopesticide properties through aerobic solid-state fermentation (SSF) in the presence of Bacillus thuringiensis (Bt). The experiments were performed first under sterile and non-sterile conditions at lab scale using 115 g of sample and controlled temperature (30 °C). Bt growth was successful in sterile conditions, obtaining 6.2 × 10(11) CFU g(-1) DM and 8.6 × 10(10) spores g(-1) DM after 6 days. Bt survived on solid culture under non-sterile conditions (3.8 × 10(9) CFU g(-1) DM and 1.3 × 10(8) spores g(-1) DM). Further, the valorization process was scaled-up to 10 L reactors (2300 g) under non-sterile conditions obtaining a final stabilized material with viable Bt cells and spores (9.5 × 10(7) CFU g(-1) DM and 1.1 × 10(8) spores g(-1) DM in average) after 9 days of SSF. These results confirm the possibility of managing biodegradable wastes by their transformation to a waste derived soil amendment with enhanced biopesticide effect, in comparison to traditional compost using a valuable and low-cost technique (SSF).

Valorisation of biodiesel production wastes: Anaerobic digestion of residual Tetraselmis suecica biomass and co-digestion with glycerol.

One of the principal opportunity areas in the development of the microalgal biodiesel industry is the energy recovery from the solid microalgal biomass residues to optimise the fuel production. This work reports the cumulative methane yields reached from the anaerobic digestion of the solid microalgal biomass residues using different types of inocula, reporting also the improvement of biogas production using the co-digestion of microalgal biomass with glycerol. Results demonstrate that the solid microalgal biomass residues showed better biogas production using a mesophilic inoculum, reaching almost two-fold higher methane production than under thermophilic conditions. Furthermore, the solid microalgal biomass residues methane production rate showed an increase from 173.78 ± 9.57 to 438.46 ± 40.50 mL of methane per gram of volatile solids, when the co-digestion with glycerol was performed. These results are crucial to improve the energy balance of the biodiesel production from Tetraselmis suecica, as well as proposing an alternative way to treat the wastes derived from the microalgae biodiesel production.

Programmed iron oxide nanoparticles disintegration in anaerobic digesters boosts biogas production.

A novel concept of dosing iron ions using Fe3O4 engineered nanoparticles is used to improve biogas production in anaerobic digestion processes. Since small nanoparticles are unstable, they can be designed to provide ions in a controlled manner, and the highest ever reported improvement of biogas production is obtained. The nanoparticles evolution during operation is followed by an array of spectroscopic techniques.

Addressing the gaseous and odour emissions gap in decentralised biowaste community composting.

Composting has demonstrated to be an effective and sustainable technology to valorise organic waste in the framework of circular economy, especially for biowaste. Composting can be performed in various technological options, from full-scale plants to community or even individual composters. However, there is scarce scientific information about the potential impact of community composting referred to gaseous emissions. This work examines the emissions of methane and nitrous oxide as main GHG, ammonia, VOC and odours from different active community composting sites placed in Spain, treating kitchen, leftovers and household biowaste. Expectedly, the gaseous emissions have an evident relation with the composting progress, represented mainly by its decrease as temperature or biological activity decreases. GHG and odour emission rates ranged from 5.3 to 815.2 mg CO2eq d-1 kg-1VS and from 69.8 to 1088.5 ou d-1 kg-1VS, respectively, generally being lower than those find in open-air full-scale composting. VOC characterization from the community composting gaseous emissions showed a higher VOC families' distribution in the emissions from initial composting phases, even though terpenes such as limonene, α-pinene and ß-pinene were the most abundant VOC along the composting process occurring in the different sites studied. The results presented in this study can be the basis to evaluate systematically and scientifically the numerous current projects for a worldwide community composting implementation in decentralised biowaste management schemes.

Using green waste as substrate to produce biostimulant and biopesticide products through solid-state fermentation.

Although the use of green waste as a substrate in different types of microbial bioprocessing has a major impact on improving green waste valorization, very little information has been provided on this issue. The purpose of this paper is to study the feasibility of using green waste to produce a biostimulant (Indole-3-acetic acid (IAA)) and biopesticide (conidial spore) through solid-state fermentation. Trichoderma harzianum was selected as the inoculum of the process and the green waste was a mixture of grass clippings and pruning waste. An experiment was designed to study the effect of tryptophan concentration, proportion of grass and pruning waste, and substrate moisture on IAA and spore production. The results show that washing and using phosphate buffer has a beneficial effect on green waste quality in terms of bioproduction. The maximum IAA and spore productions reported in the current study were 101.46 µg g-1 dry matter and 3.03 × 109 spore g-1 dry matter, respectively. According to the results, IAA production increases with a higher amount of tryptophan and grass. However, the number of spores increased with lower amounts of tryptophan and grass. The model suggested the following optimized parameters for the production of spores and IAA: tryptophan 0.45 %, grass 61 %, and moisture 74 %. The effect of fermentation time was also studied, and the results show that the maximum IAA and spore production was obtained on days 3 and 7, respectively.

Magnetite-based nanoparticles and nanocomposites for recovery of overloaded anaerobic digesters.

The effect of magnetite nanoparticles and nanocomposites (magnetite nanoparticles impregnated into graphene oxide) supplement on the recovery of overloaded laboratory batch anaerobic reactors was assessed using two types of starting inoculum: anaerobic granular sludge (GS) and flocculent sludge (FS). Both nanomaterials recovered methane production at a dose of 0.27 g/L within 40 days in GS. Four doses of magnetite nanoparticles from 0.075 to 1 g/L recovered the process in FS systems between 30 and 50 days relaying on the dose. The presence of nanomaterials helped to reverse the effect of volatile fatty acids inhibition and enabled microbial communities to recover but also favoured the development of certain microorganisms over others. In GS reactors, the methanogenic population changed from being mostly acetoclastic (Methanothrix soehngenii) to being dominated by hydrogenotrophic species (Methanobacterium beijingense). Nanomaterial amendment may serve as a preventative measure or provide an effective remedial solution for system recovery following overloading.

A plant-like battery: a biodegradable power source ecodesigned for precision agriculture.

The natural environment has always been a source of inspiration for the research community. Nature has evolved over thousands of years to create the most complex living systems, with the ability to leverage inner and outside energetic interactions in the most efficient way. This work presents a flow battery profoundly inspired by nature, which mimics the fluid transport in plants to generate electric power. The battery was ecodesigned to meet a life cycle for precision agriculture (PA) applications; from raw material selection to disposability considerations, the battery is conceived to minimize its environmental impact while meeting PA power requirements. The paper-based fluidic system relies on evaporation as the main pumping force to pull the reactants through a pair of porous carbon electrodes where the electrochemical reaction takes place. This naturally occurring transpiration effect enables to significantly expand the operational lifespan of the battery, overcoming the time-limitation of current capillary-based power sources. Most relevant parameters affecting the battery performance, such as evaporation flow and redox species degradation, are thoroughly studied to carry out device optimization. Flow rates and power outputs comparable to those of capillary-based power sources are achieved. The prototype practicality has been demonstrated by powering a wireless plant-caring device. Standardized biodegradability and phytotoxicity assessments show that the battery is harmless to the environment at the end of its operational lifetime. Placing sustainability as the main driver leads to the generation of a disruptive battery concept that aims to address societal needs within the planetary environmental boundaries.

Valorization of agro-industrial wastes by producing 2-phenylethanol via solid-state fermentation: Influence of substrate selection on the process.

2-phenylethanol (2-PE) is a value-added compound widely used in industry due to its rose-like odor and antibacterial properties that can be bioproduced using wastes as raw materials. This study presents the valorization of nine agro-industrial wastes as potential substrates for 2-PE production using an isolated 2-PE producer Pichia kudriavzevii, and the solid-state fermentation (SSF) technology as an alternative approach. The assessed substrates comprised wastes of varied traits such that each of them provided different characteristics to the fermentation. Thus, by using a principal component analysis (PCA), it was possible to identify the most significant characteristics associated with the substrates affecting the 2-PE production. Results show that L-phenylalanine biotransformation was more efficient than de novo synthesis for producing 2-PE. Besides, from the evaluated set, the maximum 2-PE production was achieved with red apple pomace, reaching 1.7 and 25.2 mg2PE per gram of used waste through de novo and L-phenylalanine biotransformation, respectively. In that scenario, volumetric productivity and precursor yield were 39.6 mg2PE L-1h-1 and 0.69 g2PE per gram of L-phenylalanine added, respectively. From the PCA, it was identified that the reducing sugars content of the substrate, the air-filled porosity of the bed and the L-phenylalanine availability were the most critical parameters (associated with the substrates) influencing the microbial activity and 2-PE production. These results suggest that the desirable traits a solid media needs for promoting 2-PE production via SSF could be reached by using a combination of wastes in a synergistic approach.

Sustained effect of zero-valent iron nanoparticles under semi-continuous anaerobic digestion of sewage sludge: Evolution of nanoparticles and microbial community dynamics.

The effects of adding zero-valent iron nanoparticles (nZVI) on the physicochemical, biological and biochemical responses of a semi-continuous anaerobic digestion of sewage sludge have been assessed. Two sets of consecutive experiments of 103 and 116 days, respectively, were carried out in triplicate. nZVI were magnetically retained in the reactors, and the effect of punctual doses (from 0.27 to 4.33 g L-1) over time was studied. Among the different parameters monitored, only methane content in the biogas was significantly higher when nZVI was added. However, this effect was progressively lost after the addition, and in 5-7 days, the methane content returned to initial values. The increase in the oxidation state of nanoparticles seems to be related to the loss of effect over time. Higher dose (4.33 g L-1) sustained positive effects for a longer time along with higher methane content, but this fact seems to be related to microbiome acclimation. Changes in microbial community structure could also play a role in the mechanisms involved in methane enhancement. In this sense, the microbial consortium analysis reported a shift in the balance among acetogenic eubacterial communities, and a marked increase in the relative abundance of members assigned to Methanothrix genus, recognized as acetoclastic species showing high affinity for acetate, which explain the rise in methane content in the biogas. This research demonstrates that biogas methane enrichment in semicontinuous anaerobic digesters can be achieved by using nZVI nanoparticles, thus increasing energy production or reducing costs of a later biogas upgrading process.

Rice husk as a source for fungal biopesticide production by solid-state fermentation using B. bassiana and T. harzianum.

Solid-state fermentation using rice husk as substrate with either Beauveria bassiana or Trichoderma harzianum was conducted on batch reactors at laboratory scale to establish optimal conditions for spore production. Time course tests were performed to determine maximum spore production time, which was 7.7 days for Beauveria bassiana and 5.7 days for Trichoderma harzianum. The effect of moisture, inoculum concentration, airflow rate, temperature and C/N ratio on spore production was evaluated by two Box-Behnken experimental designs. Final spore concentrations ranged from 2.0 × 108 to 2.0 × 109 spores g-1 dry matter. Main factors influencing spore production were moisture (optimum values of 55-60% for Trichoderma harzianum and 65-70 for Beauveria bassiana) and temperature (25 °C). The effect of mixing enhanced Trichoderma harzianum spore production while influencing negatively in the case of Beauveria bassiana. Robustness of the process has been demonstrated through statistical analysis using box-plots.

Adding value to home compost: Biopesticide properties through Bacillus thuringiensis inoculation.

Home and community composting are considered potential tools for the self-management of organic waste. The production of added value products from biowaste is an encouraging step further to valorise this waste stream. To increase the profits of homemade compost, this paper presents a strategy to produce enriched home compost with biopesticide properties through a simple and low-cost process. Bacillus thuringiensis (Bt) was inoculated in a home composter bin through a solid inoculum previously prepared using the same waste as substrate. The process was monitored and compared with a home composting control process without inoculation. Final composts were analysed and compared in terms of physicochemical and microbiological properties, respiration and germination indices, indicating the suitability of both to be used as organic amendments. Also, a standardized toxicity test proved that Bt-enriched compost can be safely applied to the soil. Microbiological analysis revealed highly diverse communities in both cases, with limited differences at phylum taxonomic level, but dissimilar relative abundances of species within phylum. Bacteroidetes and Proteobacteria were dominant, with the presence of species able to transform organic matter from vegetal origin, but not usually related to compost. Bt-cristal toxin was clearly present in Bt-enriched compost, indicating the coexistence of Bt with the different microbial populations till the end of the composting process. Although Bt has been widely investigated due to its biopesticide properties, the incorporation of this microorganism to home composting level has not been previously reported.

The use of composting for the treatment of animal by-products: Experiments at lab scale.

Animal by-products (ABP), containing mainly rabbit and chicken carcasses were composted at laboratory scale. Results indicate that if proper conditions are used, wastes can be successfully composted and stabilised meeting current European hygienisation standards regarding the disposal of this type of wastes. During the process, temperatures above 60 degrees C were easily reached and maintained for 2 days at least, due to the high energy potential of these materials. However, care must be taken to ensure that these temperatures are reached in the entire reactor to guarantee proper hygienisation of the material. These high temperatures may bring about operational problems such as moisture losses due to very high airflows required for their control. Biological activity indices, such as respiration index (RI) and oxygen uptake rate (OUR) used for the monitoring of the process, were able to indicate potential and actual conditions within the composting reactor, respectively.

In search of a reliable technique for the determination of the biological stability of the organic matter in the mechanical-biological treated waste.

The biological stability determines the extent to which readily biodegradable organic matter has decomposed. In this work, a massive estimation of indices suitable for the measurement of biological stability of the organic matter content in solid waste samples has been carried out. Samples from different stages in a mechanical-biological treatment (MBT) plant treating municipal solid wastes (MSW) were selected as examples of different stages of organic matter stability in waste biological treatment. Aerobic indices based on respiration techniques properly reflected the process of organic matter biodegradation. Static and dynamic respirometry showed similar values in terms of aerobic biological activity (expressed as oxygen uptake rate, OUR), whereas cumulative oxygen consumption was a reliable method to express the biological stability of organic matter in solid samples. Methods based on OUR and cumulative oxygen consumption were positively correlated. Anaerobic methods based on biogas production (BP) tests also reflected well the degree of biological stability, although significant differences were found in solid and liquid BP assays. A significant correlation was found between cumulative oxygen consumption and ultimate biogas production. The results obtained in this study can be a basis for the quantitative measurement of the efficiency in the stabilization of organic matter in waste treatment plants, including MBT plants, anaerobic digestion of MSW and composting plants.

Fed-Batch and Sequential-Batch Approaches To Enhance the Bioproduction of 2-Phenylethanol and 2-Phenethyl Acetate in Solid-State Fermentation Residue-Based Systems.

This study describes the use of alternative operational strategies in the solid-state fermentation of the agro-industrial leftover sugar cane bagasse (SCB) supplemented with l-phenylalanine, for bioproducing natural 2-phenylethanol (2-PE) and 2-phenethyl acetate (2-PEA) using K. marxianus. Here, fed-batch and sequential-batch have been assessed at two scales (1.6 and 22 L) as tools to increase the production, as well as to enhance the sustainability of this residue-based process. While in the reference batch strategy a maximum of 17 mg of 2-PE+2-PEA per gram of added SCB was reached at both scales, the implementation of fed-batch mode induced a production increase of 11.6% and 12.5%, respectively. Also, the production was increased by 16.9% and 2.4% as compared to the batch when a sequential-batch mode was used. Furthermore, the use of these strategies was accompanied by lower consumption of key resources like the inoculum, air, and time, promoting savings between 22% and 76% at both scales.

Dehydrogenase activity as a method for monitoring the composting process.

Dehydrogenase enzymatic activity was determined to monitor the biological activity in a composting process of organic fraction of municipal solid waste. Dehydrogenase activity is proposed as a method to describe the biological activity of the thermophilic and mesophilic stages of composting. The maximum dehydrogenase activity was detected at the end of the thermophilic stage of composting, with values within 0.5-0.7mgg dry matter(-1)h(-1). Also, dehydrogenase activity can be correlated to static respiration index during the maturation mesophilic stage.