Aerobic Batch Research Articles

Removal of nutrients from synthetic wastewater by different Brazilian chlorophyte strains in batch bioreactors under various light regimes.

With the increase in pollution and improper waste disposal, aquatic ecosystems are experiencing escalating degradation leading to various detrimental effects, including eutrophication and adverse impacts on the health of the population reliant on these water resources. Consequently, microalgae have demonstrated efficacy in nutrient removal, minimal environmental disruption, and superior cost-effectiveness in comparison to traditional treatment methods. Thus, this study aimed to investigate wastewater treatment in an aerobic batch system, using two strains of non-axenic mixotrophic chlorophytes, Chlorella sp. and Desmodesmus sp., across distinct light regimes: continuous light exposure for 24h, a photoperiod of 12h light and 12h darkness, and complete absence of light for 24h. The Desmodesmus sp. strain exhibited superior efficiency in the proposed biological treatment, yielding more favorable nutrient removal results across all conditions, except for total nitrogen removal under the 24-h continuous light condition in which Chlorella sp. removed 0.199 ± 0.02% by biomass. In other parameters, Desmodesmus sp., remediated by biomass 0.408 ± 0.013% of inorganic phosphorus in 24h light, 0.372 ± 0.011% of COD and 0.416 ± 0.004% of carbohydrate in 24h dark. While Chlorella sp. removed 0.221 ± 0.01% of inorganic phosphorus in 24h light, 0.164 ± 0.02% of COD in 24h light and 0.214 ± 0.002% of carbohydrates in 24h dark. Nevertheless, both strains displayed potential as viable alternatives for wastewater biological treatment, indicating that nutrient removal is achievable across all tested light conditions, albeit with variations in efficiency depending on the specific nutrient type.

Efficient Bio-Oxidation of Cellobiose with Engineered Gluconobacter oxydans to Provide Highly Concentrated Cellobionic Acid

Cellobionic acid (CBA) can be obtained through the oxidation of cellobiose, the monomer of cellulose. CBA serves as a plant-based alternative to its stereoisomer lactobionic acid, which is used in the pharmaceutical, cosmetic, and food industries. Gluconobacter oxydans is a well-established whole-cell biocatalyst with membrane-bound dehydrogenases (mDH) for regio-specific oxidations. As G. oxydans wildtype cells show low cellobiose oxidation activities, the glucose mDH from Pseudomonas taetrolens was overexpressed in G. oxydans BP9, a multi mDH deletion strain. Whole-cell biotransformation studies were performed with resting cells of the engineered G. oxydans in stirred tank bioreactors. Initial biomass specific cellobionate formation rates increased with increasing cellobiose concentrations up to 190 g L−1, and were constant until the solubility limit. The maximal volumetric CBA formation rates and the oxygen uptake rates increased linearly with the concentration of engineered G. oxydans. This enables the estimation of the maximum biocatalyst concentration limited by the maximum oxygen transfer rate of any bioreactor. Thus, 5.2 g L−1 G. oxydans was sufficient to produce 502 g L−1 CBA with >99% yield in a simple aerobic batch process. The highly concentrated CBA will reduce downstream processing costs considerably after cell separation.

Production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Bacillus megaterium LVN01 Using Biogas Digestate

The Bacillus megaterium LVN01 species native to Colombia has demonstrated the ability to metabolize different coproducts or industrial waste (such as fique juice, cane molasses, and residual glycerol) and accumulate polyhydroxybutyrate (PHB), giving it potential in the bioplastics industry. In this research, the potential of liquid digestate as a carbon source for the production of PHA polymers in fermentation processes with this bacterial strain was evaluated. Favorably, it was found that B. megaterium utilizes the nutrients from this residual substrate to multiply appropriately and efficiently synthesize poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Bench-scale aerobic batch fermentation, under the operational conditions of this research [volume: 3 L; temperature: 30.8 °C; agitation: 400 rpm; pH: 7.0 ± 0.2; dissolved oxygen: 100% saturation; antifoam: 10% (v/v)], generated maximum values of dry cell weight (DCW) (0.56 g cell L−1) at 60 h, while the maximum PHBV yield (360 mg PHBV L−1) occurred at 16 h, which is very favorable for sustainable degradable bioplastics production. Additionally, GC–MS and NMR analyses confirmed that the PHBV copolymer synthesized by B. megaterium is made up of the monomers 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV). Furthermore, the thermal properties determined by TGA (Tonset = 283.1 °C; Tendset = 296.98 °C; Td = 290.114 °C) and DSC (Tm = °C 155.7 °C; ΔHf = 19.80 J g−1; Xcr = 18.17%) indicate that it is a thermally stable biopolymer with low percentages of crystallinity, providing flexibility that facilitates molding, adaptation, and application in various industrial sectors.

Extracellular Self-DNA Effects on Yeast Cell Cycle and Transcriptome during Batch Growth.

The cell cycle and the transcriptome dynamics of yeast exposed to extracellular self-DNA during an aerobic batch culture on glucose have been investigated using cytofluorimetric and RNA-seq analyses. In parallel, the same study was conducted on yeast cells growing in the presence of (heterologous) nonself-DNA. The self-DNA treatment determined a reduction in the growth rate and a major elongation of the diauxic lag phase, as well as a significant delay in the achievement of the stationary phase. This was associated with significant changes in the cell cycle dynamics, with slower exit from the G0 phase, followed by an increased level of cell percentage in the S phase, during the cultivation. Comparatively, the exposure to heterologous DNA did not affect the growth curve and the cell cycle dynamics. The transcriptomic analysis showed that self-DNA exposure produced a generalized downregulation of transmembrane transport and an upregulation of genes associated with sulfur compounds and the pentose phosphate pathway. Instead, in the case of the nonself treatment, a clear response to nutrient deprivation was detected. Overall, the presented findings represent further insights into the complex functional mechanisms of self-DNA inhibition.

Complementary Field and Laboratory Batch Studies to Quantify Generation Rates of Perfluoroalkyl Acids in a Contaminated Agricultural Topsoil with Unknown Precursors

AbstractSoil microbiome changes and generation rates of per‐ and polyfluoroalkyl substances (PFAS) precursors were studied in a contaminated agricultural field using a combination of field and laboratory batch microcosm studies. 16S rRNA gene amplicon sequencing was used to track how microbial community composition changed over time, while perfluoroalkyl acids (PFAA) generation rates were quantified using a combination of field and batch incubations combined with the direct total oxidizable precursor (dTOP) assay. The study site in Brilon‐Scharfenberg, North Rhine‐Westphalia, Germany, has PFAS contamination in the topsoil (0 to 30 cm) originating from compost. Generation rate constants of these short‐chain PFAA estimated from batch incubations (0.12 to 0.75 1/year) were higher but similar to rate constants from the fields (0.05 to 0.22 1/year). Long‐term field mass discharge data (2009 to 2023) suggest that at least 60 years are needed to remove 99.99% of short‐chain PFAA and their precursors. 16S rRNA gene amplicon sequencing data revealed a major impact of PFAA on the biodiversity of soil microorganisms, with batch‐incubated contaminated soils showing higher richness and diversity indexes than field control soils. However, most of these impacts occurred at lower taxonomical ranks and did not seem to have a prominent impact on the overall structure of the autochtonous microbial communities of the soils where PFAA were produced and accumulated. Overall, our findings demonstrate that well‐controlled aerobic batch test combined with the results of dTOP assay are a suitable approach for estimating short‐chain PFAA generation rates. Additionally, our research suggests that the complete removal of PFAA precursors from topsoil will take decades.

Influence of the composition of the culture medium on the growth and sporulation of the probiotic strain Bacillus amyloliquefaciens M

Bacillus amyloliquefaciens M is a non-pathogenic microorganism with probiotic properties isolated from mineral waters in the village of Yabаlkovo, Haskovo region, for inclusion in the composition of probiotics and probiotic foods. It has high antimicrobial activity against pathogenic bacteria, causing food toxic infections and intoxications, as well as against saprophytic microorganisms - bacteria and fungi, which makes it suitable as a biological preparation for plant protection. In order to perform these functions, it is necessary to obtain a spore concentrate. The composition of the nutrient medium for the cultivation and sporulation of the strain has been determined: MP nutrient broth with the addition of salts, in which the strain grew well and a high sporulation rate of 99% was achieved. Cultivation in a bioreactor has been carried out and the time to achieve a high degree of sporulation has been determined. The kinetic parameters of growth and sporulation of Bacillus amyloliquefaciens M in aerobic batch cultivation with a high concentration of spore forms have also been determined. It has been shown that the sporulation process in this strain starts after 12 h from the cultivation start.

Valorisation of Pineapple Cannery Waste as a Cost Effective Carbon Source for Poly 3-hydroxyabutyrate (P3HB) Production.

Pineapple is one of the most important agro-industrial sugar-based fruits in Thailand. In this study, the waste stream from pineapple cannery processing was utilised and evaluated for potential use in the production of a main biopolymer group widely known as polyhydroxyalkanoates (PHAs) through aerobic batch fermentation. Firstly, pineapple cannery waste (PCW) collected from three processing sources, pineapple juice (PAJ), peel and core juice (PCJ), and pulp-washing water (PWW), was used as a carbon source. Secondly, it was characterised and pretreated. Then, batch fermentation was performed by using the optimal condition (200 rpm agitation rate, 37 °C, and fermentation time of 72 h) under two different nutrient conditions in each type of carbon source. The results revealed that PHAs were produced during 24-72 h of fermentation without any interference. The PHAs product obtained was characterised by their properties. Interestingly, GC-MS showed homopolymer of poly 3-hydroxybutyrate (P3HB) group characteristics, such as OH, CH, and C=O; meanwhile, H1 NMR analysis showed signals corresponding to CH3, CH2, and CH, respectively. Remarkably, utilising the PCW showed a high-potential cheap carbon source for the production of PHAs as well as for the treatment of wastewater from the fruit industry.

Effect of temperature during the hydrothermal carbonization of sewage sludge on the aerobic treatment of the produced process waters

The treatment of the highly contaminated process water produced during the hydrothermal carbonization (HTC) of waste activated sludge is of major concern for the full-scale implementation of the HTC process. So far, no satisfying treatment strategies have been elaborated and the biodegradability under aerobic conditions has hardly been studied. To fill these gaps, aerobic tests were first carried out in batches with HTC process waters produced at 190 °C, 218 °C and 249 °C, and two parallel sequencing batch reactors (SBR) were operated to treat process waters produced at 190 °C and 217 °C. Both experiments show that the HTC temperature has only a little effect on the elimination of dissolved organic carbon (DOC). In the aerobic batch tests, DOC removal were 80.5–81.9 %. In the SBR, 28 % of the initial DOC was found to be recalcitrant, and 25–28 % of the initial nitrogen. In the SBR experiments, the nitrification was also monitored, and nitrification inhibition test were conducted on both process waters obtained at 190 °C and 217 °C. Nitrification the initial SBR reactors was only possible after dilution of the process waters, which indicates the presence of inhibiting substances. The inhibition tests validated those observations, and showed that process waters derived at 217 °C had a higher inhibition potential. This study demonstrates that aerobically treated HTC process waters are still too polluted to be discharged in a wastewater treatment plant: model calculations showed an increase in effluent DOC of 8.3 mg C/L.

Biological treatment of high strength monoethanolamine (MEA)-containing wastewater from printed circuit board manufacturing industry

Develop-etch-strip (DES) process in printed circuit board (PCB) manufacturing industries produces wastewater containing high organic nitrogen, in which monoethanolamine (MEA) is the main COD and nitrogen source. This study evaluated feasibility of biological treatment of high concentration MEA-containing acidified DES wastewater collected from a full-scale PCB industry. Batch test results indicated that aerobic conditions attained the highest specific COD degradation rates (6.5–14.6 mgCOD/gVSS/h), anoxic conditions attained second (4.81 mgCOD/gVSS/h), and anaerobic conditions was the lowest (1.3–3 mgCOD/gVSS/h). The anoxic/oxic (A/O) sequencing batch reactor (SBR) with porous polyurethanes carriers, BioNET, was able to treat MEA-containing acidified DES wastewater with 80 % COD removal and 23 % TN removal at influent COD of 300 mg/L, while the A/O continuous stirred tank reactor (CSTR) with BioNET at 8 h of HRT achieved above 96 % COD removal and 78 % TN removal at influent COD of 630 mg/L. The aerobic batch test results indicated that specific COD degradation rates followed a Haldane-type model, suggesting that MEA acts as an inhibitory substrate, especially at concentrations above 2000 mg/L. In addition, MEA inhibited the onset of nitrification, but not specific nitrate production rate, suggesting that MEA may inhibit nitrification by inhibiting expression of amoA gene, based on amoA gene expression results. Finally, the contribution for COD degradation, denitrification and nitrification by BioNET (< 20 %) was lower than that for suspended sludge in the A/O CSTR, suggesting that the role of BioNET carriers could retain microorganisms and served as the habitats for microorganisms to avoid washout at a shorten HRT situation.

Kinetic modelling of high concentration 4-Nitrophenol biodegradation by an isolated bacterial consortium and post-treatment ecotoxicity analysis

The present study documents the kinetics of aerobic batch growth and biodegradation of 4-Nitrophenol (4-NP) by an isolated bacterial consortium capable of utilizing 700 mg l−1 of 4-NP as the sole source of carbon and energy, the highest reported concentration to be biodegraded till date. The results of the batch biodegradation studies suggested that the consortium exhibited substrate inhibition kinetics and the Haldane model fitted the experimental data well. The estimated biokinetic parameters applied to biomass growth were maximum specific growth rate, μmax = 0.1532 h−1, half saturation coefficient, Ks = 4.717 mg l−1, and inhibition coefficient, Ki = 77.34 mg l−1. The specific degradation rate, q, was fitted to the model, and the kinetic parameters obtained were: qmax = 0.1700 g g−1 h−1, K's = 5.871 mg l−1, and K'i = 171.9 mg l−1. The yield coefficient (YX/S) varied in the range of 0.93–0.23 g g−1 for 12–700 mg l−1 4-NP concentration. The maintenance coefficient (m) and true yield (YG) were calculated to be 0.04491 h−1 and 0.9496 g g−1, respectively, based on the Pirt's equation. Furthermore, cytotoxicity and phytotoxicity assessment involving the animal cell line HEK293 and different seed variants, respectively, confirmed the detoxification of the biodegraded product, emphasizing the biocatalytic efficiency of the consortium in the bioremediation of 4-NP contaminated wastewater and suitability of its environmental discharge.

Coupling of endogenous/exogenous nitrification and denitrification in an aerobic granular sequencing batch reactor

ABSTRACT The performance of endogenous/exogenous nitrification and denitrification in an aerobic granular sequencing batch reactor was investigated for treating inorganic wastewater with ammonia nitrogen of 250 mg/L. The sequencing batch reactor with an effective volume of 120.5 L was started by seeding autotrophic nitrifying granular sludge (ANGS) and operated under oxic (110 min)/anoxic (120 min)/oxic (110 min) aeration mode. The total inorganic nitrogen (TIN) removal efficiency of ANGS was between 60% and 70% without external carbon sources in days 1–25. However, the operation mode was unsustainable as endogenous nitrification and denitrification would lead to an obvious decrease of sludge concentration. After sodium acetate (the contributed chemical oxygen demand in the reactor was 250–300 mg/L) was added at the beginning of the anaerobic/anoxic stage from day 26, aerobic granules were inadaptable in a few days, which resulted in particle disintegration and SVI increase. As microbes gradually acclimated to the new environment, the aerobic granular sludge became smoother and denser, the relative abundance of denitrifying bacteria increased to 66.07%, and the removal efficiency of TIN gradually increased to more than 90% from day 89. Contributions of endogenous/exogenous nitrification and denitrification to TIN removal were 54.09% and 46.01%, respectively. The coupling of endogenous/exogenous nitrification and denitrification could reduce the aeration consumption, save the external carbon source dosage and decrease the alkalinity consumption, which provided another option for treating wastewater from ionic rare earth mine.

Adaptive modeling of nonnegative environmental systems based on projectional Differential Neural Networks observer

A new design of a non-parametric adaptive approximate model based on Differential Neural Networks (DNNs) applied for a class of non-negative environmental systems with an uncertain mathematical model is the primary outcome of this study. The approximate model uses an extended state formulation that gathers the dynamics of the DNN and a state projector (pDNN). Implementing a non-differentiable projection operator ensures the positiveness of the identifier states. The extended form allows producing continuous dynamics for the projected model. The design of the learning laws for the weight adjustment of the continuous projected DNN considered the application of a controlled Lyapunov-like function. The stability analysis based on the proposed Lyapunov-like function leads to the characterization of the ultimate boundedness property for the identification error. Applying the Attractive Ellipsoid Method (AEM) yields to analyze the convergence quality of the designed approximate model. The solution to the specific optimization problem using the AEM with matrix inequalities constraints allows us to find the parameters of the considered DNN that minimizes the ultimate bound. The evaluation of two numerical examples confirmed the ability of the proposed pDNN to approximate the positive model in the presence of bounded noises and perturbations in the measured data. The first example corresponds to a catalytic ozonation system that can be used to decompose toxic and recalcitrant contaminants. The second one describes the bacteria growth in aerobic batch regime biodegrading simple organic matter mixture.

Enhanced biological phosphorus removal in low-temperature sewage with iron-carbon SBR system

ABSTRACT This study proposed an AO-SBR (Anaerobic Aerobic Sequencing Batch Reactor) combined with iron-carbon micro-electrolysis (ICME) particles system for sewage treatment at low temperature and explored the dephosphorisation mechanism and microbial community structure. The experimental results illustrated that ICME particles contributed to phosphorus removal, metabolic mechanism of poly-phosphorus accumulating organism (PAO) and microbial community structure in the AO-SBR system. The optimal treatment effect was achieved under the conditions of pH 7, DO 3.0 mg/L and particle dosage of 2.6 g Fe-C/g MLSS, and the removal rates of COD, TP, NH4 +-N and TN reached 80.56%, 91.46%, 69.42% and 57.57%. The proportion of phosphorus accumulating organisms (PAOs) increased from 4.54% in the SBR system to 10.89% in the ICME-SBR system at 10°C. Additionally, the metabolic rate of PAOs was promoted, and the activities of DHA and ETS both reached the maximum value of 13.34 and 102.88 μg·mg−1VSS·h−1. These results suggest that the ICME particles could improve the performance of activated sludge under low-temperature conditions. This technology provides a new way for upgrading the performance of sewage treatment in the cold area.

Effect of Carbon Source on Biological Nutrient Removal in an Anaerobic, Hypoxic, Anoxic, or Aerobic Sequencing Batch Reactor

AbstractA sequencing batch reactor was constructed to realize simultaneous nitrification and denitrification (SND) and denitrifying phosphorus removal (DPR). The influence of different carbon sourc...

Towards a Capture and Reuse Model for Aquaculture Effluent as a Hydroponic Nutrient Solution Using Aerobic Microbial Reactors

Controlled environment agriculture (CEA) technologies are required to meet current and future food production demand as the global population rises, arable land decreases, and minerals for fertilizer production are depleted. Hydroponics and recirculating aquaculture systems (RAS) are intensive production methods that can provide season-independent vegetables and seafood in urban settings but are limited by a reliance on fertilizing solutions made from finite mineral reserves and the treatment and disposal costs of nutrient rich effluent, respectively. The development of a capture and reuse system where RAS effluent is solubilized to become plant-available and utilized as a hydroponic nutrient solution would aid both industries and increase food security in urban food deserts. Aerobic mineralization is used in domestic wastewater treatment to reduce solid content and solubilize particulate-bound nutrients. Preliminary studies have also shown that aerobic mineralization can be an effective method for RAS effluent treatment. Aerobic batch reactors were used to mineralize RAS effluent in this study. Suspended solids reduction achieved in the reactors was measured throughout the experiment and the plant-availability of twelve nutrients was determined before and after treatment. It was shown that aerobic mineralization can effectively reduce particulate-bound solids and solubilize nutrients to increase plant utilization in RAS effluent.

Biosynthesis and profiling of single cell carotenoids of Phaf ia rhodozyma in waste-based cultivation media

In order to investigate the feasibility of low-cost media for producing well- characterized single-cell carotenoid, the study on biosynthesis and profiling carotenoid in the yeast of Phaf ia rhodozyma was carried out. We have successfully identified the profiles of single-cell carotenoids of P. rhodozyma, which was cultivated in glucose-based medium (MG), molasses-based medium (MM), and coconut water-based medium (MC). Cells were separately cultured in those media under aerobic batch culture system to obtain the carotenoid profiles based on high performance liquid chromatography (HPLC) analysis. The results showed that medium composition strongly affects the profiles of P. rhodozyma carotenoids represented by ratio of astaxanthin and beta-carotene (ratio A/B). Astaxanthin was highly synthesized in cells cultivated in MG with ratio A/B as much of 20:1. On the other hand, MM and MC produced a lower ratio A/B than MG as much of 0.4:1 and 0.2:1, respectively. In addition, carotenoids profiles were detected more diverse when this yeast species was cultivated in two waste-based media. This study provided a basic physiological knowledge of P. rhodozyma cells for carotenoid biosynthesis using potential low cost cultivation m

Performance Evaluation of Selenite (SeO32−) Reduction by Enterococcus spp.

Lactic acid bacteria (LAB) such as Enterococcus spp. have an advantage over several bacteria because of their ability to easily adapt to extreme conditions which include high temperatures, highly acidic or alkaline conditions and toxic metals. Although many microorganisms have been shown to reduce selenite (SeO32−) to elemental selenium (Se0), not much work has been done on the combined effect of Enterococcus spp. In this study, aerobic batch reduction of different selenite concentrations (1, 3 and 5 mM) was conducted using Enterococcus hermanniensis sp. and Enterococcus gallinarum sp. (3.5 h, 35 ± 2 °C, starting pH &gt; 8.5). Results from the experiments showed that the average reductions rates were 0.608, 1.921 and 3.238 mmol·(L·h)−1, for the 1, 3 and 5 mM SeO32− concentrations respectively. In addition, more selenite was reduced for the 5 mM concentration compared to the 1 and 3 mM concentrations albeit constant biomass being used for all experiments. Other parameters which were monitored were the glucose consumption rate, protein variation, pH and ORP (oxidation reduction potential). TEM analysis was also conducted and it showed the location of electron-dense selenium nanoparticles (SeNPs). From the results obtained in this study, the authors concluded that Enterococcus species’s high adaptability makes it suitable for rapid selenium reduction and biosynthesis of elemental selenium.

Aerobic growth physiology of Saccharomyces cerevisiae on sucrose is strain-dependent.

Present knowledge on the quantitative aerobic physiology of the yeast Saccharomyces cerevisiae during growth on sucrose as sole carbon and energy source is limited to either adapted cells or to the model laboratory strain CEN.PK113-7D. To broaden our understanding of this matter and open novel opportunities for sucrose-based biotechnological processes, we characterized three strains, with distinct backgrounds, during aerobic batch bioreactor cultivations. Our results reveal that sucrose metabolism in S. cerevisiae is a strain-specific trait. Each strain displayed distinct extracellular hexose concentrations and invertase activity profiles. Especially, the inferior maximum specific growth rate (0.21 h-1) of the CEN.PK113-7D strain, with respect to that of strains UFMG-CM-Y259 (0.37 h-1) and JP1 (0.32 h-1), could be associated to its low invertase activity (0.04-0.09U/mgDM). Moreover, comparative experiments with glucose or fructose alone, or in combination, suggest mixed mechanisms of sucrose utilization by the industrial strain JP1, and points out the remarkable ability of the wild isolate UFMG-CM-259 to grow faster on sucrose than on glucose in a well-controlled cultivation system. This work hints to a series of metabolic traits that can be exploited to increase sucrose catabolic rates and bioprocess efficiency.

Nitrite build-up effect on nitrous oxide emissions in a laboratory-scale anaerobic/aerobic/anoxic/aerobic sequencing batch reactor

Biological wastewater treatment processes with biological nitrogen removal are potential sources of nitrous oxide (N2O) emissions. It is important to expand knowledge on the controlling factors associated with N2O production, in order to propose emission mitigation strategies. This study therefore sought to identify the parameters that favor nitrite (NO2-) accumulation and its influence on N2O production and emission in an anaerobic/aerobic/anoxic/aerobic sequencing batch reactor with biological nitrogen removal. Even with controlled dissolved oxygen concentrations and oxidation reduction potential, the first aerobic phase promoted only partial nitrification, resulting in NO2- build-up (ranging from 29 to 57%) and consequent N2O generation. The NO2- was not fully consumed in the subsequent anoxic phase, leading to even greater N2O production through partial denitrification. A direct relationship was observed between NO2- accumulation in these phases and N2O production. In the first aerobic phase, the N2O/NO2- ratio varied between 0.5 to 8.5%, while in the anoxic one values ranged between 8.3 and 22.7%. Higher N2O production was therefore noted during the anoxic phase compared to the first aerobic phase. As a result, the highest N2O fluxes occurred in the second aerobic phase, ranging from 706 to 2416 mg N m-2 h-1, as soon as aeration was triggered. Complete nitrification and denitrification promotion in this system was proven to be the key factor to avoid NO2- build-up and, consequently, N2O emissions.

Sustainable generation of bioethanol from sugarcane wastes by Streptomyces coelicolor strain COB KF977550 isolated from a tropical estuary

The damaging effect and challenges associated with the use of fossil fuel is enormous and very costly. Biofuels could be obtained from plant biomass wastes which are known to be sources of environmental pollution and breeding grounds for vectors of diseases. Sugarcane bagasse was exploited as a renewable substrate for obtaining bioethanol using Streptomyces strain COB KF977550 as inoculum. Submerged aerobic batch fermentation was performed in flasks containing mineral salts medium supplemented with 5.0 g (w/v) sugarcane bagasse. Incubation was done in a shaker (150 rpm) at 30 °C for 21 days. Microbial growth was assessed by measurement of the optical density (O.D 600nm) at 3-day intervals. Fractional distillation was carried out in batch mode using a simple fractional distillation setup. Metabolic products were determined using GC-FID. Further analyses were performed using FTIR and GC-MS. The optical density of S.coelicolor strain COB KF977550 increased from 0.9 to 1.41. The GC-FID showed that 43.08 g/L ethanol was generated. Interestingly, the results showed the presence of diverse biochemicals released into the medium in addition to the main product ethanol. Ten carboxylic acids including formic acid, glycolic acid, tartaric acid, acetic acid, citric acid, oxalic acid, malic acid, lactic acid, n-valeric acid, and 3-hydroxybutyric acid were identified as biochemical organic acids by-products.