Mixed Bacterial Culture Research Articles

Bioengineering for multiple PAHs degradation for contaminated sediments: Response surface methodology (RSM) and artificial neural network (ANN)

Scientific community around the globe have major focus on designing bioremediation strategies for persistent, recalcitrant, highly toxic and carcinogen/mutagen polycyclic aromatic hydrocarbons (PAHs) present in marine environment. For the bioremediation strategy, components of growth medium are a key factor, which enhance degradation of the PAHs through simulating the microbial growth. Thus, present study involves bioengineering of growth medium (ONR7a) using response surface methodology (RSM) and artificial neural network (ANN) for enhanced multiple PAHs biodegradation. Microbes were isolated from contaminated sediments of Alang Sosiya Ship Breaking Yard (ASSBRY), Gulf of Khambhat, Gujarat, India. RSM - a process centric approach has resulted in an increase in PAHs degradation from 69% (Unoptimized) to 90.03% with 1.29 folds increase on 5th day with R2 value of 0.98. Moreover, use of Artificial Neural Network (ANN) – a data centric approach resulted in better prediction of PAHs degradation of 93.36% compared to the CCD-RSM predicted PAHs degradation of 90.03% with R2 value of 0.98. Based on various error functions such as mean absolute deviation (MAD), mean squared error (MSE), root mean squared error (RMSE) and mean absolute percentage error (MAPE), the predictive ability of the constructed ANN models was found to be higher compared to RSM. As this is the first ever report on PAHs degradation by bacterial mixed culture using data centric approach, this study bridges the gap between fundamental research and its application for policymakers and stakeholders which would be helpful in designing appropriate bioremediation technologies.

Bioremediation treatment improves water quality for Nile tilapia (Oreochromis niloticus) under crude oil pollution.

Despite favorable publicity of bioremediation as an affordable technology for cleanup of crude oil, public concerns on ecological safety in the presence of residual oil remain a global challenge. In this study, effects of crude oil exposure at sublethal concentration (0.25% v/v) and bioremediation treatment were investigated on histology and biochemical parameters of organs (gills, liver, kidney, and brain) of juvenile Nile tilapia (Oreochromis niloticus). Ten percent (10%) of mixed bacterial culture was used for bioaugmentation treatment. Ninety juvenile fish were used for study, and experiments were carried out in triplicates for three different groups. Malondialdehyde (MDA), an index of lipid peroxidation, was assayed as biomarker for oxidative stress. Activities of antioxidant enzymes (superoxide dismutase (SOD) and catalase (CAT)), level of non-enzymatic antioxidant (reduced glutathione (GSH)), and activity of brain acetylcholinesterase (AChE) were assayed in selected fish organs as markers for environmental stressor. Histological examination of fish organs was done for all groups. Results of treated groups were compared with those of the control. Levels of MDA significantly increased with significant inhibition of antioxidant enzyme activities in the polluted group. Activities of SOD, CAT, and AChE and levels of GSH in fish organs in the bioaugmentation group were similar to results obtained in the control. Remarkably, the bioaugmentation group showed minimal or no lesions which suggested the efficacy of bioremediation technique in alleviating crude oil toxicity and preserving normal physiology of fish. This study provides deeper insights into the ecosafety of bioremediation treatment and can be extrapolated to other species of fish.

TLR4-MyD88 signaling pathway is responsible for acute lung inflammation induced by reclaimed water

Previous research found that inhalation exposure of reclaimed water could cause severe pulmonary inflammation, and the endotoxin was proposed to be the key risk factor. To further support this view, the toxic effects of different reclaimed water induced by acute inhalation exposure were compared between wildtype C57BL/6J and TLR4 signaling pathway defect mice. It was found that reclaimed water with high levels of endotoxin could induce strong inflammation in wildtype mice, but not in Tlr4−/− and MyD88−/− mutants. The mixed bacterial culture from the reclaimed water showed very weak response in wildtype mice and no response in TLR4-signaling pathway deficient mice, which further suggested that the cell-bound endotoxins contribute little in the inflammation induced by reclaimed water. In addition, conditional knockout of the Tlr4 gene in myeloid cells resulted in a significant reduction of sensitivity to the reclaimed water in mutants, which indicates that myeloid cells play the most important role in the defensive immune system against the pollutants in the water. In general, this study demonstrated that the TLR4-MyD88 signaling pathway is responsible for the acute lung inflammation induced by reclaimed water, which excludes the possibility of other signaling pathway dependent inflammation inducers in reclaimed water.

Enhancing the degradation of mixed polycyclic aromatic hydrocarbon and medium-chain-length polyhydroxyalkanoate production by mixed bacterial cultures using modified repeated batch fermentation.

To increase the biodegradation of phenanthrene (PHE), pyrene (PYR) and fluoranthene (FLU) through mixed cultures of polycyclic aromatic hydrocarbon (PAH)-degrading bacteria, using modified repeated batch fermentation. Novel bacterial strains of Pseudomonas putida, Pseudomonas sp. and Ralstonia eutropha were cultivated and the biodegradation and conversion of mixed PAH to medium-chain-length polyhydroxyalkanoates (MCL-PHA) was determined. The highest degradation of PAH (100%) and PHA production (50·0%) was obtained in medium containing 30mmoll-1 of mixed PAH after three cycles of repeated batch fermentation. The concentration of PAH in the reactor was increased from 30 to 90mmoll-1 with repeated additions of PAH, and bacteria were able to produce PHA at 40% of cell dry mass. The MCL-PHA were identified by gas chromatography/mass spectroscopy, with the 3-hydroxydecanoate (3-HD) monomer higher than 75mol.%. This study demonstrated that the biodegradation of PHE, PYR and FLU was enhanced by modified repeated batch fermentation using a mixed culture of bacteria. In addition, this fermentation strategy also increased the production of PHA, with an increase in monomer composition. This was the first study to describe the enhancement of the degradation of mixed solutions of PHE, PYR and FLU, and PHA production, using novel mixed bacterial cultures and modified repeated batch fermentation. The MCL-PHA formed had uniquely high 3-HD content.

USE OF LACTIC ACID BACTERIA IN PEANUT SEED TREATMENT

Three lactic acid bacteria (LAB) strains, Lactobacillus sp. L5, Lactobacillus sp. L3, Lactobacillus sp. L2N, isolated from Vietnamese traditional Nem chua grew well in cabbage broth supplemented with 12 g/L glucose and 15 g/L peptone and showed inhibitory activity ranging from 40% to 44% against Aspergillus sp. CDP isolated from mould contaminated peanuts, while Daconil 75WP – a fungicide compounds – as a positive control showed only 26.9%. LAB strains also displayed Indole-acetic acid (IAA) production, P-solubilization and biofilm formation. Soaking seeds in separate cabbage based culture broth of three LAB strains with/without heat treatment and mixed culture broths at the ratio 1:1:1 with the total bacterial count 108cfu/mL exhibited the antifungal activity of mixed cultures in both cases with or without bacterial culture heat treatment. Soaking seeds in the same mixed bacterial cultures without heat treatment increased seed germination and vigor index, compared to the control seeds without any treatment and those treated with fungicide compounds. After 75 days of sowing the length and total fresh weight of LAB-treated peanut plants increased by 22.4 % and 99.6%, higher than that of Daconil treated ones with only 15.9% and 59.7% increment. Moreover, the fresh yield of peanut pegs increased 2.5 times, compared to those of untreated and Daconil treated seeds. This study suggested that seed treatment with LAB is a novel technology towards organic farming to replace fungicide used in conventional agriculture.

Optimization of Methylene blue removal by mixed bacterial culture isolated from dye contaminated site

Optimization of Methylene blue removal by mixed bacterial culture isolated from dye contaminated site

Microbial Decolorization of Triazo Dye, Direct Blue 71: An Optimization Approach Using Response Surface Methodology (RSM) and Artificial Neural Network (ANN).

The release of wastewater from textile dyeing industrial sectors is a huge concern with regard to pollution as the treatment of these waters is truly a challenging process. Hence, this study investigates the triazo bond Direct Blue 71 (DB71) dye decolorization and degradation dye by a mixed bacterial culture in the deficiency source of carbon and nitrogen. The metagenomics analysis found that the microbial community consists of a major bacterial group of Acinetobacter (30%), Comamonas (11%), Aeromonadaceae (10%), Pseudomonas (10%), Flavobacterium (8%), Porphyromonadaceae (6%), and Enterobacteriaceae (4%). The richest phylum includes Proteobacteria (78.61%), followed by Bacteroidetes (14.48%) and Firmicutes (3.08%). The decolorization process optimization was effectively done by using response surface methodology (RSM) and artificial neural network (ANN). The experimental variables of dye concentration, yeast extract, and pH show a significant effect on DB71 dye decolorization percentage. Over a comparative scale, the ANN model has higher prediction and accuracy in the fitness compared to the RSM model proven by approximated R2 and AAD values. The results acquired signify an efficient decolorization of DB71 dye by a mixed bacterial culture.

Identification and Characterization of Natural Habitats of Electrochemically Active Bacteria

Aims: This study aims to define criteria for the main physical and chemical characteristics of the environmental niches populated with electrochemically active microorganisms, capable to perform anaerobic respiration and potentially used in Bio-electrochemical systems such as Microbial Fuel Cells. 
 Study Design: In this study, specific parameters of the environment in water bodies (such as lakes, streams etc.) and their bottom layers are analyzed. The main parameters of interest include the concentration of dissolved oxygen in the water column, the organic matter content in the sediments and the presence of alternative electron acceptors (such as iron and manganese ions) to support anaerobic respiration. Sediment microorganisms are characterized for their electrochemical and biodegradation activity.
 Place and Duration of Study: The tested sediment and water samples were collected from "Poda" Protected Site located on the outfall of Lake “Uzungeren”, south of City of Burgas, Bulgaria.
 Methodology: The samples were analyzed employing TGA, ICP and microbiological methods focusing on chemical, physical and biological conditions available for anaerobic respiration in this ecological niche.
 Results: The results show very low concentrations of dissolved oxygen (from 1.4 to 2.2 mg/dm3 in the various locations). The conductivity and the pH values ​​measured were relatively high and the mean values obtained are 5230 μS/cm and 8.2 respectively. The sediment samples demonstrated very high organic matter content (22.5% of the dry mass) and relatively high levels of iron and manganese.
 Microbial fuel cell powered by mixed bacterial culture isolated from the tested sediment samples demonstrated stable performance reaching power density of 3.5 W/m2 and the COD removal rate of 42 mgO2/dm3 per day.
 Conclusion: The result confirms the initial hypothesis that electrochemically active microorganisms are available in environments with high concentration of organic matter, iron and manganese in combination with low availability of dissolved oxygen. Mixed culture of anaerobic bacteria isolated from the tested sediment sample was successfully implemented to power Microbial Fuel Cell.

Fed-Batch Decolourization of Mixture of Brilliant Green and Evans Blue by Bacteria Species Applied as Pure and Mixed Cultures: Influence of Growth Conditions

Synthetic dyes, generally resistant, toxic and carcinogenic presents a substantial risk to the environment and health of human. The present study was aimed to decolourize a dye mixture (Evans blue and brilliant green) by selected bacterial strains cultivated at different growth conditions (e.g. unmodified, correction of pH value and supplementation with nutrients). The bacterial strains used as pure and mixed cultures include facultative anaerobes Aeromonas hydrophila (Abs37), Citrobacter sp. (Cbs50) and obligatory aerobe Pseudomonas putida (Pzr3). The efficiency of removal of all successive doses of dye mixture (4–5 doses, total load 170–200 mg/l) was tested in static conditions in fed-batch bioreactors. The modification of bacteria growth conditions influenced on decolourization efficiency: most advantageous was pH value correction combined with nutrient supplementation then pH correction alone and nutrient supplementation (final removal results 95.6–100%, 92.9–100% and 89.1–97.2%, respectively). The mixed bacterial cultures removed the total load of dyes with higher efficiency than pure strains (final removal 95.2–100% and 84.0–98.2%, respectively). The best results were obtained for the mixture of facultative anaerobe Citrobacter sp. and obligatory aerobe Pseudomonas putida which removed the highest load of dye mixture (200 mg/l introduced at five doses) in the shortest time (288 h), while the others pure and mixed cultures needed 425–529 h for removal four doses of dye mixture (total load 170 mg/l). The zoo- and phytotoxicity decreased after these processes (from V class of toxicity (extremely toxic) even to II class (low toxicity)). The main mechanisms of decolourization was biotransformation/biodegradation, supported by sorption.

Reverse engineering directed gene regulatory networks from transcriptomics and proteomics data of biomining bacterial communities with approximate Bayesian computation and steady-state signalling simulations

BackgroundNetwork inference is an important aim of systems biology. It enables the transformation of OMICs datasets into biological knowledge. It consists of reverse engineering gene regulatory networks from OMICs data, such as RNAseq or mass spectrometry-based proteomics data, through computational methods. This approach allows to identify signalling pathways involved in specific biological functions. The ability to infer causality in gene regulatory networks, in addition to correlation, is crucial for several modelling approaches and allows targeted control in biotechnology applications.MethodsWe performed simulations according to the approximate Bayesian computation method, where the core model consisted of a steady-state simulation algorithm used to study gene regulatory networks in systems for which a limited level of details is available. The simulations outcome was compared to experimentally measured transcriptomics and proteomics data through approximate Bayesian computation.ResultsThe structure of small gene regulatory networks responsible for the regulation of biological functions involved in biomining were inferred from multi OMICs data of mixed bacterial cultures. Several causal inter- and intraspecies interactions were inferred between genes coding for proteins involved in the biomining process, such as heavy metal transport, DNA damage, replication and repair, and membrane biogenesis. The method also provided indications for the role of several uncharacterized proteins by the inferred connection in their network context.ConclusionsThe combination of fast algorithms with high-performance computing allowed the simulation of a multitude of gene regulatory networks and their comparison to experimentally measured OMICs data through approximate Bayesian computation, enabling the probabilistic inference of causality in gene regulatory networks of a multispecies bacterial system involved in biomining without need of single-cell or multiple perturbation experiments. This information can be used to influence biological functions and control specific processes in biotechnology applications.

Nutrient (sulphate) removal from wastewater in inverse fluidized bed biofilm reactor

Sulphate is one of the inorganic nutrient pollutants present in wastewater which needs to be treated due to present day global stringent emission norms. Among the several available biological means to treat industrial wastewaters, the use of inverse fluidized bed biofilm reactors (IFBBRs) has gained much attention in recent years over other fluidized bed reactors. In this work, the feasibility of removal of sulphate from synthetic wastewater having initial concentrations of 13.096, 32.74, and 65.48 mg/l was studied using mixed bacterial culture. Spherical polypropylene balls were taken as biomass support particles having density of 920 kg/m3 and diameter of 5.63 mm. Three different bed-volume to reactor-volume (Vb/Vr) ratios i.e., 0.304, 0.380, & 0.445 and three different superficial air velocities i.e., 0.0065, 0.0085, & 0.0106 m/s were considered for experimental runs. The reactor inoculum was prepared from the sludge collected from local steel industry’s wastewater treatment plant. The effects of different input parameters such as Vb/Vr ratio, superficial air velocities, and initial concentration of sulphate in synthetic wastewater on the output sulphate concentration were studied. Temperature of 30–32 °C and pH of 8.3–8.8 were maintained throughout the degradation studies. The reactor was operated in semi-batch recirculation mode with superficial water velocity of 0.0021 m/s. Sulphate concentration was measured by turbidity method using UV spectrophotometer at 420 nm which is as per APHA standards. The maximum removal efficiency of sulphate was found to be 72–75% which was achieved at a Vb/Vr ratio of 0.380 and the superficial gas velocity of 0.0085 m/s observed at a time of 40 h. Higher sulphate reduction was not achieved due to presence of more inorganic salts in the synthetic wastewater. At higher initial sulphate concentration, reactor operational difficulties were observed.

Synergy of Granular Activated Carbon and Anaerobic Mixed Culture in Phenol Bioremediation of Aqueous Solution

The present study focused on the synergistic effects bioremediation of phenol in aqueous solution using combination of anaerobic mixed culture and Granular Activated Carbon (GAC) as a biological GAC (BGAC). Meanwhile, the effect of contact time and various phenol concentrations on adsorption and biosorption process investigated. The phenol concentration was analyzed using UV/Vis spectrophotometer. The morphology and structure of two adsorbents (GAC and BGAC) were characterized by FESEM and BET specific surface area analysis. The batch experiments using mixed bacterial culture, isolated from wood and paper factory wastewater, were adapted to high concentrations of phenol and employed in order to evaluate the tolerance and biosorption capability of microorganisms for phenol biodegradation. The synergetic effect of phenol removal using combination of GAC with an anaerobic biofilm indicated that the removal efficiency for concentration of 700, 800, and 1000 mg/l at initial stages increased to 4, 10, and 12%, respectively and while by increment of the retention time did not shown significant impact on the removal efficiency. These results conducted both desorption of adsorbates due to biotransformation in the aqueous solution and direct assimilation of adsorbates on GAC by the microorganism’s biofilm. The adsorption data were fitted with pseudo-first-order and pseudo-second-order models and it was found that the pseudo-second-order model explains the adsorption kinetics more efficiently. The compatibility of the Freundlich and Langmuir adsorption models to equilibrium data were investigated. In fact, the Langmuir isotherm was found to be the best fitting isotherm.

Bovine Mastitis in Oman is Mainly Associated with Environmental Bacteria that Show High Resistance to Commonly Used Antibiotics

In Oman, mastitis is an important disease that affects the dairy animals, especially cows. In this study, bacteria and fungi from subclinical and clinical mastitis were identified using 16S rDNA and 18S rDNA, respectively, in 76 milk samples from 30 cows. The frequency of subclinical mastitis (75%) was higher than clinical mastitis (25%). Bacterial isolates were detected in 82% of the samples, out of which 12% showed mixed bacterial cultures. The most predominant isolated bacteria were environmental bacteria rather than minor and contagious bacteria from subclinical (53.6%, 42.8% and 3.6%, respectively) and clinical mastitis (62.5%, 25% and 12.5%, respectively). Antibiotic resistance profiles of the isolated bacteria for six commonly used antibiotics showed an increase in resistance compared to a previous study in 1991. Most isolated bacteria were resistance to AMP, while they were more sensitive for SXT and TE. Eleven percent of the isolated bacteria were resistance to four of the antibiotics tested or more. About half of the samples (47%) were positive for fungal growth. Most of those samples were positive for bacteria, which suggested that detected fungi may be opportunistic. However, 3% of the investigated samples were negative for bacterial growth, which may indicate pathogenic involvement in mastitis. In conclusion, the major association of mastitis with environmental bacteria and the detected multi-antibiotics resistance emphasized the need for using appropriate control protocols by allowing to investigate each case and determine whether antibiotic treatment is necessary and which antibiotics to be used.

The potential bio-conversion of Palm Oil Mill Effluent (POME) as Bioethanol by steady-state anaerobic processes

Biomass is a central issue as new material that can be used as a substrate to produce biofuels, it has become global research to replace liquid fossil fuels with alternative renewable and sustainable fossils. Palm oil mill effluent (POME) is the potential of Agri-industrial waste to be used as alternative energy with anaerobic digestion of high concentration organic wastewater can be used for bioethanol production to replace food as raw material. Bioethanol can be produced in acidogenic steps in the organic degradation process. In this research, bacterial mixed cultures sourced from bovine rumen as biomass and the substrate used was palm oil mill effluent (POME) with a characteristic COD concentration of 25,600 mg/L, The operation of the reactor is set at pH 5; 6; 7 for 72 hours with the type of anaerobic circulating batch reactor (CBR), measurement of bioethanol products and acidogenesis of samples is carried out every 6 hours. The results showed that the reactor with variations in pH conditions 5 gave the highest efficiency of bioethanol formation in the 12 hour running process, result is 102,94 mg/L with a maximum formation rate of 9,98 mg/L/hour.

Oregano powder reduces Streptococcus and increases SCFA concentration in a mixed bacterial culture assay.

Food borne illnesses have a world-wide economic impact and industries are continuously developing technologies to reduce the spread of disease caused by microorganisms. Antimicrobial growth promoters (AGPs) have been used to decrease microbiological infections in animals and their potential transfer to humans. In recent years there has been a global trend to remove AGPs from animal feed in an attempt to reduce the spread of antimicrobial resistant genes into the human population. Phytobiotics, such as oregano powder, are one of the potential replacements for AGPs due to their well-established antimicrobial components. 16S rRNA gene amplicons were used to determine the effect of oregano powder (1% w/v) on the microbiota of mixed bacterial cell cultures, which were obtained from the ceca of traditionally grown meat chickens (broilers). Oregano powder had a mild effect on the microbial cell cultures increasing Enterococcus faecium, rearranging ratios of members in the genus Lactobacillus and significantly reducing the genus Streptococcus (p = 1.6e-3). Beneficial short chain fatty acids (SCFA), acetic and butyric acid, were also significantly increased in oregano powder supplemented cultures. These results suggest that oregano powder at a concentration of 1% (w/v) may have beneficial influences on mixed microbial communities and SCFA production.

Biodegradation of LLDPE plastic by mixed bacteria culture of Pseudomonas aeruginosa and Brevibacterium sp.

Plastics take more than 400 years to naturally degrade. This study therefore aims to degrade Linear Low Density Polyethylene (LLDPE) plastic using a mixture of culture bacteria Pseudomonas aeruginosa and Brevibacterium sp. Pieces of LLDPE plastic measuring 1 x 1 cm2, weighing 10 grams are put into containers containing Nutrient Broth (NB) growth media. The biodegradation process is carried out for 30 days with the test parameters being temperature (°C) and acidity (pH). The Gravimetric method was used to determine weight, while Fourier Transform Infrared (FTIR) analysis was used to actuate the morphology, changes in structure and surface of polyethylene. The results showed that mixed bacterial culture has the potential to degrade LLDPE plastic with a removal percentage of 2-7%, which is based on gravimetric analysis at 25°C, acidity value (pH) 7 for 30 days. Therefore, this study proves that mixed bacterial cultures degrades LLDPE plastic by using it as a carbon source.

The effect of pH-temperature on plastic allowance for Low-Density Polyethylene (LDPE) by Thiobacillus sp. and Clostridium sp.

LDPE are plastic polymers, widely used because they are affordable, waterproof, and flexible, hence difficult to degrade naturally. This study aim therefore is to degrade LDPE plastic using a biotechnology approach with a mixture of Thiobacillus sp. and Clostridium sp. at a variety of pH and temperatures. Mixed bacterial cultures were grown on Stone Mineral Salt Solution (SMSs) with a batch system, thereafter, gravimetric method was used to determine the difference in weight and Fourier Transformer Infrared Spectroscopy (FTIR) was used to determine changes in functional groups. To obtain the optimum condition that produces the highest degradation, researchers conducted the experiment at temperature varied from 25, 30, 35o C and pH 5, 7, 9. The highest removal of LDPE occurred at 30oC with pH 7. Gravimetrically, mixed cultures of Thiobacillus sp. and Clostridium sp. was capable of degrading LDPE plastic with an allowance of 2-7% for 30 days. Considering that this research produces a relatively small allowance, further research is needed to exploit the potential of using both bacteria in degrading LDPE plastic.

Volatile fatty acid production from semi-synthetic milk processing wastewater under alkali pH: The pearls and pitfalls of microbial culture.

Volatile fatty acids (VFA) are one of the most promising sustainable and environmentally friendly bioproduct owing to their wide usage area and high market demand. For this reason, in this study, the evaluation of VFA production from pure and mixed bacterial cultures was aimed. Three different mixed cultures with C. aceticum, C. butyricum and P. acidipropionici as pure cultures were used for inoculation of milk processing wastewater fermentation under pH 10 for 15days. The mixed culture fermentation had the highest VFA production efficiency whereas the highest amount of acetic, butyric and propionic acid productions were obtained by C. aceticum, C. butyricum and P. acidipropionici, respectively. Also, the mixed cultures demonstrated faster pH regulation and acclimation than the pure cultures tested. Therefore, development of synthetic cultures may offer a useful approach to produce VFA mixtures with one-dominant acid type and with high production efficiency.

Biological attenuation of arsenic and nitrate in a suspended growth denitrifying-sulphidogenic bioreactor and stability check of arsenic-laden biosolids

ABSTRACT Co-occurrence of arsenic and nitrate in groundwater sources at a wide range of concentrations is reported. In this work, performance of suspended growth semi-batch reactor was assessed for co-removal of arsenic and nitrate from simulated groundwater to meet the drinking water standards in the absence of iron. The bioreactor was inoculated with mixed bacterial culture and operated in the absence of oxygen for more than 450 days under varying influent arsenate (200–800 µg/L), nitrate concentrations (50–250 mg/L), and hydraulic retention time of 3–6 days. Complete nitrate removal was observed at all tested concentrations. Arsenic removal was found to meet drinking water standards from initial concentrations and up to 600 µg/L. The extended toxicity characteristic leaching procedure leaching experiments indicated that arsenic-laden biosolids would not constitute a hazardous waste. The arsenic leaching was found to increase with an increase in dissolved oxygen and the final leachate concentrations of arsenic were below 150 µg/L. The leaching experiments suggested maintaining non-alkaline conditions for minimum arsenic release from arsenic biosolids formed under sulphidogenic conditions. This study is the first to report that nitrate and arsenic can be simultaneously removed to meet drinking standards in a suspended growth bioreactor.

Areca nut (Areca catechu) husks and Luffa (Luffa cylindrica) sponge as microbial immobilization matrices for efficient phenol degradation

Immobilization of microorganisms is a widely adopted strategy for the efficient degradation of hazardous organic compounds like phenol. Microorganisms can be immobilized in synthetic or natural matrices. In this work dried areca nut (Areca catechu) husks and luffa (Luffa cylindrica) sponge fibers were used as alternative and inexpensive natural matrices for microbial cell immobilization. The potential of these immobilization systems for the effective bioremediation of phenolic wastewater was explored. A bacterial consortium was isolated by enriching a sludge sample from a petroleum refinery in high phenol concentrations. The mixed bacterial culture was capable of degrading 1000 mg L−1 of phenol in suspension cultures. The bacterial consortium was immobilized on the lignocellulosic matrices. Phenol degradation studies were performed in batches to optimize the physicochemical parameters. Optimum pH and temperature for phenol degradation was found to be 8.0 and 37 °C. At an optimum pH and temperature, the areca nut husk and luffa sponge systems immobilized with the mixed culture could degrade 1000 mg L−1 phenol in 28 h and 30 h respectively. The highest experimental degradation rates in areca nut husk and luffa sponge systems were 0.37 h−1 and 0.21 h−1 respectively at 200 mg L−1 phenol. Degradation kinetic studies were carried out using several inhibition models. Further studies revealed that both matrices with immobilized microbes could be reused for several successive batch degradation experiments and stored at 4 °C for several weeks without any noticeable loss in degradation efficiency.