Traditional and new trend strategies to enhance pigment contents in microalgae.

Microalgae are a source of a wide variety of commodities, including particularly valuable pigments. The typical pigments present in microalgae are the chlorophylls, carotenoids, and phycobiliproteins. However, other types of pigments, of the family of water-soluble polyphenols, usually encountered in terrestrial plants, have been recently reported in microalgae. Among such microalgal polyphenols, many flavonoids have a yellowish hue, and are used as natural textile dyes. Besides being used as natural colorants, for example in the food or cosmetic industry, microalgal pigments also possess many bioactive properties, making them functional as nutraceutical or pharmaceutical agents. Each type of pigment, with its own chemical structure, fulfills particular biological functions. Considering both eukaryotes and prokaryotes, some species within the four most promising microalgae groups (Cyanobacteria, Rhodophyta, Chlorophyta and Heterokontophyta) are distinguished by their high contents of specific added-value pigments. To further enhance microalgae pigment contents during autotrophic cultivation, a review is made of the main related strategies adopted during the last decade, including light adjustments (quantity and quality, and the duration of the photoperiod cycle), and regard to mineral medium characteristics (salinity, nutrients concentrations, presence of inductive chemicals). In contrast to what is usually observed for growth-related pigments, accumulation of non-photosynthetic pigments (polyphenols and secondary carotenoids) requires particularly stressful conditions. Finally, pigment enrichment is also made possible with two new cutting-edge technologies, via the application of metallic nanoparticles or magnetic fields.

Short-term tuning of microalgal composition by exposition to different irradiance and small doses of sulfide.

Suitability of microalgae valorization mainly depends on its biochemical composition. Overall, among all microalgal derivatives, pigments currently stand out as the major added-value component. While it is well recognized that microalgal growth conditions strongly affect biomass composition, final tuning of already grown microalgae has been scarcely studied. Herein, pigment crude extract and debris biomass composition of an already grown microalgal consortium was evaluated after a short-term exposure (90 min) to different levels of irradiance (15, 50, 120 µmol m-2 s-1) and sulfide concentrations (0, 3.2, 16 mg L-1). Although lipid, protein, and carbohydrate contents of debris biomass were not decisively modified by the short-term exposures, pigments content of the crude extracts were strongly modified after 90-min exposure at given sulfide and irradiance conditions. Particularly, a higher content of chlorophyll a, chlorophyll b, and total carotenoids was estimated at an optimal sulfide concentration of 5 mg L-1, and the higher irradiance of 120 µmol m-2 s-1. Contrarily, the average irradiation level of 50 µmol m-2 s-1 and the absence of sulfide stimulated the production of phycoerythrin and phycocyanin which could be increased by 65 and 50%, respectively. Thus, a final qualitative and quantitative tuning of pigment content is plainly achievable on grown microalgal biomass, in a reduced exposure time, at given irradiance or sulfide conditions.

Reduced graphene oxide decorated with magnetite nanoparticles enhance biomethane enrichment.

The addition of magnetite nanoparticles (MNPs), reduced graphene oxide (rGO), and reduced graphene oxide decorated with magnetite nanoparticles (rGO-MNPs) was evaluated during biomethane enrichment process. rGO-MNPs presented the highest beneficial impact on the hydrogenotrophic assays with an improvement of 47 % in CH4 production. The improvement was linked to the increase of the electron shuttling capacity (ESC) by rGO-MNPs addition, which boosted the hydrogenotrophic activity of microorganisms, to the rGO and rGO-MNPs, which served as reservoirs of hydrogen, improving H⁠2 transport from the gas to the liquid phase, and to the iron ions released, which acted as a dietary supply for microorganisms. Raman and XRD confirmed a greater disorder and lower crystallinity of rGO-MNPs after the hydrogenotrophic assays, with a lower effect at a nanoparticle concentration of 50 mg/L. Moreover, FTIR analysis indicated that rGO-MNPs were oxidized during the hydrogenotrophic tests. This study highlights the advantages of adding rGO-MNPs as a magnetic nanocomposite. Furthermore, rGO-MNPs can be easily recovered, minimizing their release to the environment.

Evaluation of bioaerosols by flow cytometry and removal performance in a biofilter treating toluene/ethyl acetate vapors.

The removal efficiency (RE) and bioaerosol emission of a perlite biofilter treating vapors of toluene (T) and/or ethyl acetate (EA) were assessed, under different operating conditions, during 171 days. Under the first stages of operation, a mixture of EA and T was treated, with equivalent inlet loads (ILs) of each compound (ranging from 26 to 84 g m-3 h-1), achieving a 100% RE of EA, and a maximum elimination capacity (EC) of T of 58.7 g m-3 h-1. An inhibition of T removal was noted in presence of EA, as T was treated subsequently to EA, along biofilter depth. A 17 days starvation period induced no global deterioration of performance regarding EA removal, but a 50% lower RE of T. Suspension of one contaminant, with interspersed feeding of only one component of the mixture, caused a permanent drop of the RE of EA (to 87.3%), after a T only feeding of 41 days. Flow cytometry (FC) was applied for quantification of bioaerosols, allowing for differentiation between viable, dead and damaged cells. During the overall biofilter operation, bioaerosol emission was not statistically different from bioaerosol retention. However, the biofilter significantly emitted bioaerosols (mostly viable cells) during start-up and IL increase, whereas a global retention of dead cells was observed during the interspersed feeding of one contaminant. Bioaerosols measured by FC (107 Cells m-3) were three orders of magnitude greater than with plate counting dishes, indicating that FC does not underestimate bioaerosols as culture dependent techniques.

Microbial contamination in methanol biofilters inoculated with a pure strain of Pichia pastoris: A potential limitation for waste revalorization.

Novel biotechnologies to valorize waste emissions are based on the use of specialized microbial groups that produce different compounds of industrial interest. On this scenario, the retention of such specific microorganisms in the system is of critical interest; however, the potential limitations of working with simplified cultures in a competitive open environment are neither fully explored nor well understood. In this work, a series of biofilters treating methanol vapors coupled with heterologous endochitinase production were used to evaluate the performance of a specialized microbial population during a typical open-to-environment operation. The biofilters were inoculated with a transformed strain of Pichia pastoris and were operated identically for about 90 days. The results showed that the biofiltration performance became diverse with time in terms of the elimination capacity (EC) shifting from a variation coefficient of 1.5% (EC = 274 ± 24, 279 ± 5, and 281.9 ± 25 g/[m3 h]) at the beginning of the operation to 33% (EC = 297 ± 9, 338 ± 7, and 341 ± 2 g/[m3 h]) at the end of operation. Epifluorescence analysis and cloning-sequencing suggested that P. pastoris remained as the dominant microorganism of methanol degradation, whereas diverse airborne bacteria, including Ochrobactrum spp. and Klebsiella oxytoca, played a secondary role possibly associated with the consumption of intermediates. Overall, this study found that low diversity systems operated under non-sterile conditions could be susceptible to contamination with external microorganisms causing a diversifying behavior at the performance and microbial community levels. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2715, 2019.

Temporal and longitudinal biofilm matrix analysis of a biofilter treating ethyl acetate during ozonation.

The present paper focuses on the biofilm composition and pattern of biomass in gas biofiltration of ethyl acetate working under continuous addition of ozone (O3). Two biofilters were operated for 230 days, one under continuous addition of O3 (90 ppbv) and another one without. Throughout the operation time, the extracellular polymeric substances (EPS), the main components in the extracellular matrix (ECM), were extracted from the biofilm and characterized qualitatively using Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and quantitatively by analyzing its main constituents: carbohydrates, proteins, and glucuronic acid. To date, EPS characterization has been attempted mainly with biofilm aggregates related to water treatment, not air biofiltration. The results of this study may be helpful and provide more information about EPS structure when O3 was added. O3 addition only affected the amount of EPS and not its composition. The greater effect was observed on carbohydrate content since it is the main component in EPS. The EPS/biomass ratio measured was twice lower with O3 addition. Higher removal efficiency (RE) and mineralization rates were obtained with the biofilter subjected to O3 addition, and a smaller volume of a reactor would be necessary to treat all contaminant under this condition. EPS content is only quantitatively reduced by O3 addition, and at the low O3 concentration applied, no structural alteration is noted regarding the composition of the EPS.

A state-of-the-art review on nitrous oxide control from waste treatment and industrial sources.

This review aims at holistically analyzing the environmental problems associated with nitrous oxide (N2O) emissions by evaluating the most important sources of N2O and its environmental impacts. Emissions from wastewater treatment processes and the industrial production of nitric and adipic acid represent nowadays the most important anthropogenic point sources of N2O. Therefore, state-of-the-art strategies to mitigate the generation and release to the atmosphere of this greenhouse and O3-depleting gas in the waste treatment and industrial sectors are also reviewed. An updated review of the end-of-the-pipe technologies for N2O abatement, both in the waste treatment and industrial sectors, is herein presented and critically discussed for the first time. Despite the consistent efforts recently conducted in the development of cost-efficient and eco-friendly N2O abatement technologies, physical/chemical technologies still constitute the most popular treatments for the control of industrial N2O emissions at commercial scale. The recent advances achieved on biological N2O abatement based on heterotrophic denitrification have opened new opportunities for the development of eco-friendly alternatives for the treatment of N2O emissions. Finally, the main limitations and challenges faced by these novel N2O abatement biotechnologies are identified in order to pave the way for market implementation.

Effect of extended and daily short-term starvation/shut-down events on the performance of a biofilter treating toluene vapors.

Industrial emissions of Volatile Organic Compounds are usually discontinuous. To assess the impact of interruptions in pollutant supply on the performance of biological treatment systems, two identical biofilters previously operated under continuous toluene loadings were subjected for 110 days to extended (12, 24, 36, 48, 60, 72, 84 and 96 h) and for a week to daily (8 h on, 16 h off) toluene starvation/shutdown events. One biofilter was operated under complete shutdowns (both air and toluene supply were interrupted), while the other maintained the air supply under toluene starvation. The biofilter operated under complete shutdowns was able to withstand both the extended and daily pollutant interruptions, while starvation periods >24 h severely impacted the performance of the other biofilter, with a removal efficiency decrease from 97.7 ± 0.1% to 45.4 ± 6.7% at the end of the extended starvation periods. This deterioration was likely due to a reduction in liquid lixiviation (from a total volume of 2380 mL to 1800 mL) mediated by the countercurrent airflow during the starvation periods. The presence of air under toluene starvation also favored the accumulation of inactive biomass, thus increasing the pressure drop from 337 to 700 mm H2O.m-1, while decreasing the wash out of acidic by-products with a significantly higher pH of leachates (Student paired t-test <0.05). This study confirmed the need to prevent the accumulation of inhibitory compounds produced during process perturbation in order to increase biofiltration robustness. Process operation with sufficient drainage in the packing material and the absence of countercurrent airflow are highly recommended during toluene deprivation periods.

Effect of the continuous addition of ozone on biomass clogging control in a biofilter treating ethyl acetate vapors.

Biofiltration systems have been recognized as a cost-effective and environmentally friendly control technique for volatile organic compounds (VOC) removal. However, the long-term operation of biofilters causes biomass accumulation, and thus the occurrence of bed clogging, leading to a major decrease in biofilter performance. Control methods have been carried out in order to solve clogging problems, including backwashing, bed stirring, modification of flow patterns, predation, starvation and others. Ozone (O3) has been used in biofiltration systems at low concentrations to control the excess of biomass. It is worth mentioning that all these biofiltration studies involving O3 treated recalcitrant pollutants such as chlorobenzene, formaldehyde and toluene, which do not produce enough biomass to effectively prove clogging prevention. Thus, this study evaluated the effect of the continuous addition of O3 as a chemical oxidant at a very low concentration (90ppbv) as a practical solution to overcoming clogging in a process of biofiltration of ethyl acetate (EA), a readily degradable molecule. The maximum elimination capacities achieved ranged from 200 to 120gm-3h-1, with and without O3, respectively. The biomass concentrations in these systems ranged from 23.3-180.1 to 43.31-288.46mgbiomassgperlite-1 with and without O3 addition, respectively. Based on the results, it was concluded that the continuous addition of O3 could be an attractive solution to improving biofilter performance and extending the lifetime of the filter bed.

Assessing biofiltration repeatability: statistical comparison of two identical toluene removal systems.

Biofiltration of volatile organic compounds is still considered an emerging technology. Its reliability remains questionable as no data is available regarding process intrinsic repeatability. Herein, two identically operated toluene biofiltration systems are comprehensively compared, during long-term operation (129 days). Globally, reactors responded very similarly, even during transient conditions, with, for example, strong biological activities from the first days of operation, and comparable periods of lower removal efficiency (81.2%) after exposure to high inlet loads (140 g m(-3) h(-1)). Regarding steady states, very similar maximum elimination capacities up to 99 g m(-3) h(-1) were attained. Estimation of the process repeatability, with the paired samples Student's t-test, indicated no statistically significant difference between elimination capacities. Repeatability was also established for several descriptors of the process such as the carbon dioxide and biomass production, the pH and organic content of the leachates, and the moisture content of the packing material. While some parameters, such as the pH, presented a remarkably low divergence between biofilters (coefficient of variability of 1.4%), others, such as the organic content of the leachates, presented higher variability (30.6%) due to an uneven biomass lixiviation associated with stochastic hydrodynamics and biomass repartitions. Regarding process efficiency, it was established that less than 10% of fluctuation is to be expected between the elimination capacities of identical biofilter set-ups. A further statistical comparison between the first halves of the biofilter columns indicated very similar coefficients of variability, confirming the repeatability of the process, for different biofilter lengths.

By-passing acidification limitations during the biofiltration of high formaldehyde loads via the application of ozone pulses.

A formaldehyde airstream was treated in a biofilter for an extended period of time. During the first 133 days, the reactor was operated without ozone, whereas over the following 82 days ozone was intermittently implemented. The maximum stable elimination capacity obtained without ozone was around 57 g m(-3) h(-1). A greater load could not be treated under these conditions, and no significant formaldehyde removal was maintained for inlet loads greater than 65 g m(-3) h(-1); the activity of microorganisms was then inhibited by the presence of acidic byproducts, and the media acidified (pH<4). The implementation of ozone pulses allowed a stable elimination capacity to be obtained, even at greater loads (74 g m(-3) h(-1)). The effect of ozone on the extra cellular polymeric substances detachment from the biofilm could not be confirmed due to the too low biofilter biomass content. Thus, the results suggest that ozone acted as an in situ pH regulator, preventing acidic byproducts accumulation, and allowing the treatment of high loads of formaldehyde.