Respiration Of Microorganisms Research Articles

Enhancing the microbial advanced oxidation of P-nitrophenol in sediment through accelerating extracellular respiration with electrical stimulation

Microbial advanced oxidation, a fundamental process for pollutant degradation in nature, is limited in efficiency by the weak respiration of indigenous microorganisms. In this study, an electric field was employed to enhance microbial respiration and facilitate the microbial advanced oxidation of p-nitrophenol (PNP) in simulated wetlands with alternation of anaerobic and aerobic conditions. With intermittent air aeration, an electric field of 0.8 V promoted extracellular electron transfer to increase Fe2+ generation through dissimilatory iron reduction and the production of hydroxyl radicals (•OH) through Fenton-like reactions. As a result, the PNP removal rate of the electrically-stimulated group was higher than that of the control (72.15 % vs 46.88 %). Multiple lines of evidence demonstrated that the electrically-induced polarization of respiratory enzymes expedited proton-coupled electron transfer within the respiratory chain to accelerate microbial advanced oxidation of PNP. The polarization of respiratory enzymes with the electric field hastened proton outflow to increase cell membrane potential for adenosine triphosphate (ATP) generation, which enhanced intracellular electron transportation to benefit reactive oxygen species generation. This study provided a new method to enhance microelectrochemical remediation of the contaminant in wetlands via the combination of intermittent air aeration.

Modelling and optimizing hydraulic retention time in the biological aeration unit: Application of artificial neural network and particle swarm optimization

The biological aeration unit (BAU) is essential for removing organic and inorganic matter in the wastewater. Microorganisms present in the wastewater are able to remove organic and inorganic matter. The challenge is that the BAU consumes large quantities of energy during the process, due to the constant supply of air for the respiration of microorganisms. The standard hydraulic retention time (HRT) in the BAU is between 4 and 12 h per treatment cycle which is extensive, hence the high levels of energy consumption. The purpose of this study is to optimize the HRT in the BAU, by reducing the operation time of the air pumps/blowers, resulting in less energy consumption per treatment cycle. Particle swarm optimization (PSO) algorithm optimizes the HRT in the BAU. Variables in the optimization model are verified using the sensitivity analysis method. The results of the study show a reduction in HRT from 4 to 2.4954 h, which is a 37.6 % energy saving in the BAU. The biggest drivers in the HRT optimization model are energy consumption (61.3 %), airflow rate (36.8 %), and temperature (1.2 %). Therefore, decreasing airflow rate and increasing wastewater temperature reduces HRT in BAU.

Isotope effects of O2 consumption in a deep lake as means for understanding partitioning of O2 demand among microorganisms, particles, and sediment

AbstractThe isotopic ratio 18O/16O of dissolved O2 in aquatic systems is affected by the preferential biological uptake of 16O (ε). Studies over the past six decades reveal that during incubation experiments, the isotopic effect of microorganism respiration (εorganism) varies in the range of −18‰ to −22‰. In contrast, natural variations in the deep‐ocean O2 concentration and δ18O levels show a considerably weaker effect (~ −10‰). The differences between these observations have been explained to result from either O2 uptake by sediments or organic particles that, due to diffusion‐limited respiration, are expected to weakly fractionate oxygen isotopes, by mixing processes or by weak fractionation at low temperatures. To gain better insight, we studied oxygen demand and δ18O in the deep, cold hypolimnion of Lake Stechlin between 2018 and 2021 as well as in various laboratory incubations. Our incubation results demonstrate an εorganism of about −24‰. Simple model calculations demonstrate a sediment O2 demand isotope effect (εSOD) of about −8.4‰, and a variated water‐column O2 demand isotope effect (εWOD) which is lower than εorganism, ranging from −13.9‰ in 2019 to −23‰ in 2021. Accompanying experiments indicate that the lower magnitude of εWOD may be related to respiration at organic particles lending to a weaker fractionation effect. Thus, variations in εWOD may reflect a changing partitioning of hypolimnion oxygen uptake between suspended particles and their containing microorganisms. Based on own incubation experiments with Daphnia carcasses, we discuss how possible changes of particle rigidity might influence εWOD.

Soil environment, carbon and nitrogen cycle functional genes in response to freeze-thaw cycles and biochar

Freeze-thaw cycles (FTCs) are a common phenomenon in seasonal frozen soil areas, which can significantly affect the changes in the soil environment and functional genes of microorganisms. To explore the effect of biochar application on soil carbon and nitrogen cycling under FTCs, an indoor soil column simulation test was used in this study. The experimental setup included different application rates of biochar (0%, 1%, 2%), with the carbon and nitrogen cycle functional genes serving as indicator genes. Real-time fluorescence quantitative PCR technology was employed for analysis. Based on the correlation heat map and redundancy analysis (RDA), the response mechanism of soil environment changes and carbon and nitrogen cycle functional genes before and after FTCs was analyzed. The results revealed that the application of biochar significantly increased soil's water-holding capacity held available nutrients in soil, and increased the ability of environmental change. Due to the influence of soil moisture and aeration, biochar reduced the variation of soil carbon sequestration gene cbbL, cbbM, and nitrogen fixation gene nifH abundance after FTCs. The application of 2 % biochar significantly increased the abundance of the nitrification gene amoA and denitrification gene nirK and enhanced the respiration of soil microorganisms. Soil moisture (SM) is the main environmental factor that determines the abundance changes of the soil carbon sequestration genes cbbL and cbbM. Soil organic matter (SOM), pH, nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N) were the main environmental factors determining the abundance of soil nitrogen fixation gene nifH, nitrification gene amoA, and denitrification gene nirK. This study can provide new insights into the internal mechanism of the soil carbon and nitrogen cycle in seasonal frozen soil areas, and provide some reference for the rational application of biochar and the efficient utilization of water and soil resources in seasonal frozen soil areas in the future.

The influence of the hydrometeorological factors on the CO2 fluxes from the oligotrophic bog surface.

The influence of the hydrometeorological factors on the CO2 fluxes from the oligotrophic bog surface.

Microplastics and microorganisms in sediments from stormwater drain system

Research has already confirmed the occurrence of microplastics (MPs) in sediments of stormwater drain system (SDS). However, the microplastic pollution remains to be elucidated well in sediments, especially the spatio-temporal distribution and the impacts of MPs on microorganisms. In this study, the averaged abundance of MPs in SDS sediments was 479 ± 688 items·kg−1 for spring, 257 ± 93 items·kg−1 for summer, 306 ± 227 items·kg−1 for autumn and 652 ± 413 items·kg−1 for winter. As expected, the abundance of MPs was the lowest in summer due to runoff scouring, while the highest in winter attributed to infrequent low-intensity rainfall. The major polymers of MPs were polyethylene terephthalate and polypropylene plastics, occupying 76 % to 98 % of the total number. Fiber MPs were the most regardless of season (41 % to 58 %). MPs with size of 250–1000 μm accounted for over 50 %, which is in accordance with the previous study that MPs of <1000 μm were the major. High-throughput sequencing of analysis shows that MPs provided an ecological niche for bacterial communities different from that of SDS sediments. Actinomycetes and bacteria with chemoheterotrophic genes tended to be enriched on the surfaces of MPs. In addition, Acidobacteria and bacteria with nitrification genes would not like to present in microplastisphere. A strong positive correlation (R from 0.74 to 0.83, P < 0.01) was found between the abundance of MPs in sediments and the abundance of functional genes for denitrification and nitrogen respiration of microorganisms on the surfaces of MPs. It indicates that MPs may influence the nitrogen transformation processes in SDS sediments via the occurrence of denitrification processes on the surfaces of MPs. The abundance of MPs had no significant relationship with the various functional genes of microorganisms in the sediments (P > 0.05), which means that MPs could not profoundly influence the expression of microbial functional genes in SDS sediments.

Multivariate Statistical Analysis of the Spatial Variability of Hydrochemical Evolution during Riverbank Infiltration

Riverbank filtration (RBF) is increasingly being used as a relatively cheap and sustainable means to improve the quality of surface water. Due to the obvious differences in physical, chemical, and biological characteristics between river water and groundwater, there are strong and complex physical, chemical, and biogeochemical effects in the process of bank filtration. In this paper, multivariate statistical analysis was used to identify the spatial variation of hydrogeochemical groundwater in the process of bank filtration. Firstly, the evolution process of groundwater hydrochemistry during the filtration process was identified through factor analysis. According to the results, the evolution of groundwater hydrochemistry in this area is attributable to four main types of reactions: (1) Leaching; (2) Regional groundwater influence; (3) Aerobic respiration and denitrification; and (4) Mn (IV)/Fe (III)/SO42− reduction. According to the similarity of the geochemistry, the flow path could be divided into four different hydrochemical zones through cluster analysis, revealing the evolution law of groundwater hydrochemistry and its main influencing factors during riverbank infiltration. Large hydraulic gradient in The Zone Strongly Influenced by River Water (The first group) resulted in a weak effect of leaching on groundwater chemistry. Reoxygenation and microorganism respiration occurred in The Zone Moderately Influenced by River Water (The second group), The Zone Weakly Influenced by River Water (The third group), and The Zone Strongly Influenced by Regional Groundwater (The fourth group), resulting in fluctuations in Eh and pH values of groundwater. As a result, sulfate reduction and Mn (IV) and Fe (III) reduction alternated along the flow path. The Zone Strongly Influenced by Regional Groundwater (The fourth group) groundwater chemistry was mainly affected by regional groundwater.

Ecological toxicity (ECx) of Pb and its prediction models in Chinese soils with different physiochemical properties

The lack of toxicological data becomes the main bottleneck of ecological risk assessment of lead (Pb) in Chinese soils. The present study assessed Pb toxicity on three underground test endpoints (barley root elongation, earthworm avoidance response, and substrate-induced respiration (SIR) of microorganism) in 10 different soils. Hormetic dose-response induced by Pb was >118 % for earthworm avoidance response. EC10 and EC50 (the effective concentrations of Pb that inhibit 10 % or 50 % of endpoint bioactivity and also represents the toxicity threshold of Pb) after leaching increased by 0.32–8.73 times, and 1.02–3.75 times, respectively. Leaching factor (LF) prediction models indicated pH and cation exchange capacity (CEC) were the vital predictors for LF10 and LF50, explaining 60.6 % and 73.1 % of variations, respectively. SIR was one sensitive test endpoint for Pb toxicity, with the lowest of EC10 and EC50 values (from 373.7 to 1008.5 mg·kg−1, and from 837.1 to 2869.0 mg·kg−1, respectively). The best prediction models between ECx and soil properties is LogEC50 = 1.324Log(pH) + 0.423Log(CEC) + 1.742 (R2 = 0.761, p < 0.01). The results displayed significant implications for deriving ECx of Pb, and provided a scientific basis for soil ecological risk assessment of Pb.

In situ carbon dioxide capture to co-produce 1,3-propanediol, biohydrogen and micro-nano calcium carbonate from crude glycerol by Clostridium butyricum

BackgroundClimate change caused by greenhouse gas emission has become a global hot topic. Although biotechnology is considered as an environmentally friendly method to produce chemicals, almost all biochemicals face carbon dioxide emission from inevitable respiration and energy metabolism of most microorganisms. To cater for the broad prospect of biochemicals, bioprocess optimization of diverse valuable products is becoming increasingly important for environmental sustainability and cleaner production. Based on Ca(OH)2 as a CO2 capture agent and pH regulator, a bioprocess was proposed for co-production of 1,3-propanediol (1,3-PDO), biohydrogen and micro-nano CaCO3 by Clostridium butyricum DL07.ResultsIn fed-batch fermentation, the maximum concentration of 1,3-PDO reached up to 88.6 g/L with an overall productivity of 5.54 g/L/h. This productivity is 31.9% higher than the highest value previously reports (4.20 g/L/h). In addition, the ratio of H2 to CO2 in exhaust gas showed a remarkable 152-fold increase in the 5 M Ca(OH)2 group compared to 5 M NaOH as the CO2 capture agent. Green hydrogen in exhaust gas ranged between 17.2% and 20.2%, with the remainder being N2 with negligible CO2 emissions. During CO2 capture in situ, micro-nano calcite particles of CaCO3 with sizes in the range of 300 nm to 20 µm were formed simultaneously. Moreover, when compared with 5M NaOH group, the concentrations of soluble salts and proteins in the fermentation broth of 5 M Ca(OH)2 group were notably reduced by 53.6% and 44.1%, respectively. The remarkable reduction of soluble salts and proteins would contribute to the separation of 1,3-PDO.ConclusionsCa(OH)2 was used as a CO2 capture agent and pH regulator in this study to promote the production of 1,3-PDO. Meanwhile, micro-nano CaCO3 and green H2 were co-produced. In addition, the soluble salts and proteins in the fermentation broth were significantly reduced.Graphical

Weak isotopic fractionation of dissolved O2 during community respiration

AbstractThe isotopic composition of dissolved O2 (δ18O) in aquatic environments is strongly affected by the preferential uptake of the lighter isotopologue during biological consumption processes. Numerous studies have shown that during incubation experiments, the isotopic effect of microorganism respiration (εorganism) is on the order of −20‰. However, studies of the co‐variations of O2 and δ18O in natural environments show considerably weaker in situ fractionation (εapp). A possible explanation for this discrepancy is that a significant fraction of the O2 consumption is diffusion‐limited. Although this is a generally accepted mechanism in sediments, it cannot explain the weak fractionations observed in mid‐ocean sites. Here, we analyze a time series of O2, δ18O, and auxiliary data from the northern Gulf of Aqaba (Red Sea). Although an incubation experiment showed strong fractionation against the heavy isotopologue (εorganism = −24.5‰), the in situ εapp was only −14‰ in deep water isolated from the photic zone. We show that this result requires an additional O2 consumption mechanism with weak fractionation, rather than mixing, and suggest that this mechanism is diffusion‐limited respiration into aggregates of organic material. We estimate that this mechanism could be responsible for 30% of the O2 consumption in the Gulf and suggest that it may also constitute a major O2 consumption pathway in the world's oceans.

Fresh chicken manure fumigation reduces the inhibition time of chloropicrin on soil bacteria and fungi and increases beneficial microorganisms

Chloropicrin (CP) controls soil-borne plant diseases caused by pathogenic microbes, increases crop yield, but has a long-term inhibitory effect on beneficial soil microorganisms. Therefore, we evaluated the effects of biofumigation material fresh chicken manure (FCM) on soil microorganisms, and the duration of those effects in this experiment. Our results showed that in the laboratory, FCM significantly increased substrate-induced respiration (SIR) of soil microorganisms by 2.2–3.2 times at 80 d compared to the control, however, CP significantly inhibited the SIR of soil microorganisms. FCM and CP increased NH4+-N concentration within 40 days which then returned to the control level. FCM increased NO3--N by 2.82–5.78 times by 80 days, compared with the control, while the concentration of NO3--N in the CP treatment was not significantly different from the control at the 80 day. Although in the laboratory FCM inhibited the relative abundance of 16 S rRNA and the nitrogen cycle functional genes AOA amoA, AOB amoA, nirK and nosZ over a 40-day period, the taxonomic diversity of soil bacteria and fungi in the FCM treatment were restored to unfumigated level within 90 days in the field. However, CP treatment has a strong inhibitory effect on soil microorganisms after 90 days. Importantly, the relative abundance of some beneficial microorganisms that control soil-borne pathogenic microbes or degrade pollutants increased significantly in FCM, including Bacillus, Pseudomonas and Streptomyces bacterial genera and Chaetomium and Mycothermus fungal genera. Noteworthy, like CP, FCM still had a strong inhibitory effect on Fusarium at 90 d. Our results indicated that FCM not only increased the content of inorganic nitrogen and improved the respiration rate of soil microorganisms, but it also shortened the recovery time of beneficial soil microorganisms and increased taxonomic diversity. Our previous reports showed that FCM and CP treatments had the same effect in disease control and crop growth. Combined with the results of this experiment, we believe that FCM has the potential to replace CP, which would eliminate CP's detrimental environmental impact, improve farmer safety and promote sustainable crop production.

Review on Microphotosynthetic Power Cells—A Low‐Power Energy‐Harvesting Bioelectrochemical Cell: From Fundamentals to Applications

Biophotoelectrochemical cells are gaining prominence in recent years due to the necessity of sustainable power generation at both micro‐ and macroscale. Toward this direction, microphotosynthetic power cells (μ‐PSC) play a vital role in generating clean energy. The μ‐PSC generates sustainable power under light and in the dark through the photosynthesis and respiration of photosynthetic microorganisms or cells, such as cyanobacteria and green algae. Herein, particulars on μ‐PSCs from fundamentals to real‐time applications are provided. The state of the art of μ‐PSCs, in terms of the principle of operation, design, and materials is presented. μ‐PSCs reported to date are classified based on design, operating parameters, and photosynthetic organisms. In addition, details on the metrics and factors influencing the performance of μ‐PSCs are also discussed. The need for the development of mathematical and electrical equivalent models of μ‐PSCs and the progress in these areas are briefed. Current challenges for μ‐PSCs’ commercialization are identified as high cost and low power densities, and the factors that are leading to low power density and high cost are explored and are also discussed. In addition, the potential solutions to overcome these challenges are investigated.

Study on chemical and biological properties of paddy soils in Nagari Taram, Harau District, Lima Puluh Kota Regency

Intensive cultivation of paddy soil without giving rest to the soil for years will affect the chemical properties and the presence of microorganisms in the soil. This study aims to examine some of the chemical properties of paddy soil such as pH, CEC, Total organic carbon, exchangeable bases, Total N, Available P, silica content and calculating the population and respiration of microorganisms at various slopes. This research is located in Nagari Taram, Harau District, Limapuluh Kota Regency. The study used a survey method in four stages, namely preparation, pre-survey, main survey and sampling, laboratory analysis and data processing. Samples were taken on rice fields that have been cultivated for approximately 100 years at a depth of 0-20 cm at 5 slopes those are 0-3%, 3-8%, 8-15%, 15-25% and 25-45%. Based on the results of the data analysis it is known that differences in slope affect the chemical and biological properties of the soil. The higher the slope, the decreased several soil chemical properties such as pH, C-organic, P-available, total N, CEC and silica. Soil microorganism populations varied for each slope. The highest bacterial and fungal populations were found on land with a slope of 0-3%, while the highest respiration of soil microorganisms occurred on lands with a slope of 3-8% that is 13.8 mg / kg / day.

The role of beneficial microorganisms in an anoxic-oxic (AO) process for treatment of ammonium-rich landfill leachates: Nitrogen removal and excess sludge reduction

This study comprehensively investigated the performances of the anoxic-oxic processes with (AO-M) and without the beneficial microorganisms (AO-N) for the treatment of the ammonium-rich landfill leachates. Although the AO-M had the lower concentrations of the mixed liquor suspended solids (MLSS, 3230 mg L−1) and mixed liquor volatile suspended solids (MLVSS, 2480 mg L−1) compared to the AO-N process (MLSS = 7790 mg L−1; MLVSS = 5260 mg L−1), dissolved organic compounds and nitrogen species could be more effectively removed using the AO-M process (removal efficiency of dissolved organic carbon (DOC) = 99.0%; removal efficiency of total nitrogen (TN) = 79.2%) than the AO-N process (removal efficiency of DOC = 98.6%; removal efficiency of TN = 75.1%). Moreover, the excess sludge production was also less pronounced for the AO-M process than the AO-N process since the enhanced endogenous respiration and relative enzyme activity of microorganisms in the oxic bioreactor of the AO-M process via the inoculation of the beneficial microorganisms reduced the excess sludge production significantly. These observations suggest that the variations in the relative abundances of microorganisms through the inoculation of the beneficial microorganisms into the sludge digestion tank might enhance the removal of nitrogen species and the reduction of the excess sludge production during the during the treatment of the ammonium-rich landfill leachates.

Aqueous Systems of Dissolved Oxygen in Reservoir

Oxygen plays a crucial role in aquatic ecosystem particularly for supporting aquaculture and hydropower. In freshwater, importance of oxygen is for metabolic respiration and balance for heterotrophic organisms. Oxygen is also involved in various chemical equations in which compounds influence each other. To prevent oxygen depletion, understanding the changes in DO and all interactions with other water qualities been reviewed with purposed to know aqueous systems work. Photosynthesis by phytoplankton is the main production of dissolved oxygen. Carbon dioxide as output from respiration of microorganisms and degradation of organic inputs and light as energy transformation of photosynthesis is needed in the process. The temperature level is involved as a determinant of gas solubility. There is also gas exchange from atmosphere to water as oxygen diffusion that move toward an equilibrium. However, dissolved oxygen absorption occurs in high demand in case an oxidizer in the degradation of organic matter which come into the reservoir. In eutrophic condition, the abundance of phytoplankton also requires oxygen for respiration, especially at night. The consumption of dissolved oxygen often spurs reservoir managers to monitor the input into the reservoir to build an aerator as a form of ensuring adequate dissolved oxygen circulation.

Enhancing methane production of synthetic brewery water with granular activated carbon modified with nanoscale zero-valent iron (NZVI) in anaerobic system

Anaerobic digestion is an effective treatment technology for wastewater. However, long HRT and low CH4 production limit the application of anaerobic treatment. Iron-based materials, carbon-based materials and Fe-C composite particles have been used in anaerobic processes. However, the strengthening effect of Fe-C composite particles on anaerobic systems requires further research. In this study, granular activated carbon (GAC) loaded with nanoscale zero-valent iron (NZVI) was prepared by a co-precipitation method and its morphology was characterized. Different concentrations of GAC-NZVI particles were used in the batch experiment to study the enhancing effect of the anaerobic biological treatment process. The water quality, sludge properties and microbial community were analyzed. The degradation rate of COD and total CH4 production increased by 9.38% and 14.29% with particles at a concentration of 1000 mg/L, respectively. The average methane yield was 169.86 mL CH4/g-COD removed, which was 9.39% higher than that of the control. The measurement results of extracellular polymeric substance (EPS), conductivity, cyclic voltammetry (CV) and Fe concentration indicated that the composite particles showed excellent electrical conductivity and promoted microorganism metabolism, which accelerated the use of substrates and methane generation. The 3-dimensional excitation (Ex) – emission (Em) matrix (3D-EEM) fluorescence spectroscopy of soluble microbial product (SMP) and EPS indicated that the particles could affect the endogenous respiration of microorganisms. Microbial community analysis revealed that the dominant genus Methanothrix (acetoclastic methanogens) increased by 13.32%, which could strengthen acetoclastic methanogenesis and lead to higher CH4 production. The abundance of hydrogenotrophic archaea decreased after the addition of GAC-NZVI. These results provide an alternate method for enhancing anaerobic wastewater treatment using conductive particles.

Photosynthetic microorganisms (Algae) mediated bioelectricity generation in microbial fuel cell: Concise review

Abstract Since the last century, the search for clean and renewable energy is going on. This process will continue until there is a stable solution available as an alternative to fossil fuels. Several energy-producing products arise from photosynthetic-organisms like biofuel, bioelectricity, and there are various methods also available for the extraction of these products. Microbial fuel cells (MFCs) are energy transducers which convert organic matter directly into electricity, through the process of anaerobic respiration of microorganisms. Now a day’s researchers have taken as a challenge to use algae along with the bacterial communities to provide an organic carbon fuel source for the MFCs. This paper describes the potential application of algal biomass in the field of bioelectricity. Till now, many scientific experiments conducted all around the world to demonstrate how well efficient is this green photosynthetic organism capable of producing electricity along with its other applications like biofuel, demand in the food industry, and much more. The present manuscript aimed to provide an overview of the potential use of algae as a biocatalyst in MFCs. Further, this article also provides the current status of numerous countries which are excelled in the field of bioelectricity generation.

The Effect of Antibiotics on the Respiration of Microorganism in Northern Ohio Rivers

This experiment was conducted for the purpose of inquiring how the concentration of antibiotics, specifically Amoxicillin and Cephalexin, would affect the productivity of aquatic microorganisms within Northeastern Ohio rivers. In acknowledgment of the growing concerns over agricultural pollution, the study was devised to increase current knowledge of how the presence of antibiotics could affect aquatic microorganisms other the well-documented creation of antibiotic-resistant bacteria. In order to achieve the research goal, water was collected from a Northeastern Ohio river and then tested with various amounts of antibiotics. Over the following five days, the concentration of dissolved oxygen was measured which was used to calculate the overall rate of respiration of the sample. The overall respiration rates of the samples with Amoxicillin were 0.0369 mg/L·hr (milligram per liter per hour) with no antibiotics, 0.835 mg/L·hr with 250 mg, 1.16 mg/L·hr with 500 mg, and 0.951 mg/L·hr with 750 mg. The samples with Cephalexin yielded rates of 0.963 mg/L·hr with 250 mg, 0. mg/L·hr with 500 mg, mg/L·hr with 750 mg. These yielded R-values of 0.694 and 0.788 respectively.. This means that the null hypothesis was rejected, thus showing a statistically significant correlation. However, the alternate hypothesis was not supported as a positive correlation between the respiration rate and antibiotic concentration was shown.

A live bio-cathode to enhance power output steered by bacteria-microalgae synergistic metabolism in microbial fuel cell

Microbial fuel cells (MFCs) are energy transducers that convert organic matter into electricity via anaerobic respiration of electro-active microorganisms. An avenue of research in this field is to utilize microalgal biomass for electricity generation in the MFCs. Here, Chlorella sp. is used as substrate in anode and as live-culture to constitute a bio-cathode. Addition of flue-gas (10 ± 2% CO2, v/v) in the biocathode leads to increase in biomass production (1.34 gL-1) and CO2 sequestration (190.9 mgL−1d−1). The performance of microalgae-driven green MFC (MFC-2) is compared with control MFC (MFC-1) which receives tap water and synthetic wastewater in its cathodic and anodic compartment, respectively. With the increase in biomass concentration from 0.08 (t = 0) to 1.34 gL-1 a maximum increase of 55% in power density is obtained in MFC-2 than MFC-1. Chronoamperometric curves obtained in this study shows enhanced current production (3.1 mA) in biocathode. Along with a stable voltage of 0.852 ± 01 V and cathodic dissolved oxygen concentration of 11.2 mgL−1, the removal of chemical oxygen demand (75 ± 5%) is also found to be better in MFC-2. The results demonstrate the novelty and efficacy of bacterial-algal synergistic metabolism in producing bio-electricity using inorganic and organic wastes.

Chemical attributes and microbial activity of soil cultivated with cassava under different cover crops

ABSTRACT Conservationist systems of crop management increases the amount of substrate, alters fertility and increases soil biological activity. The objective of this study was to evaluate the influence of soil management systems on the chemical attributes and microbial activity of soil under cassava crop. The experiment was set as completely randomized design in a factorial scheme of 2 x 3 x 2, being two systems of cultivation (minimum with only mown; minimum with mown and incorporation), three types of soil coverage (fallow; Crotalaria juncea L.; Canavalia ensiformis L.) and two soil depths (0-0.10 and 0.10-0.20 m), with four repetitions. The production of dry mass from cover crops, the soil chemical attributes and the soil microbial activity were evaluated. There were no differences between management systems, and the C. juncea cover crop presented superior dry mass production among the soil coverages. The concentrations of soil Ca and K were greater in the fallow coverage and C. juncea areas in the 0-0.10 m soil layer; however, these nutrients differ in the soil layer below (0.10-0.20 m). There were no differences for the basal respiration of soil microorganisms in both soil depths or among soil coverage, but the carbon from microbial biomass was superior in the most superficial soil layer where more substrate is available to soil microorganisms.