Initial Biomass Concentration Research Articles

Biotechnological Biosuccinic acid (Bio-SA) production from green microalgae Chlorella sp. hydrolysate: Synergistic effect of agitation and substrate concentration assessment using RSM

This paper evaluates the potential of Chlorella sp. microalgae biomass as a feedstock for biosuccinic acid (bio-SA) production via the fermentation process. In this study, the biomass was pretreated and hydrolyzed using a mild acid before being fermented with Actinobacillus succinogenes. The influence of the initial biomass concentration and agitation rate on bio-SA production during batch fermentation was evaluated using a Response Surface Methodology (RSM) design. The results of the study indicated that Chlorella sp. microalgae biomass contained various types of sugars, with glucose identified as the dominant reducing sugar in the Chlorella sp. hydrolysate. According to the RSM analysis, the study showed that changes in the initial biomass concentration and agitation rate could significantly affect bio-SA production from Chlorella sp. hydrolysate. The highest bio-SA concentration of 14.56 g/L with a yield of 0.62 g/g was achieved when fermentation was performed using 10% (w/v) biomass at 150 rpm. Therefore, this study suggests that Chlorella sp. hydrolysate can be an alternative and renewable feedstock for efficient bio-SA production.

Environmental friendly approach on biosorption of Ag nanoparticles using Aspergillus terreus BIOS PTK 6 biomass: Optimization, kinetics and characterization studies

The present study focused on the biosorption of Aspergillus terreus dead biomass for the removal of silver nanoparticles (AgNPs) from aqueous solution. For the better removal of AgNPs, pH, temperature, incubation time, initial biomass concentration and agitation speed were optimized and AgNPs treated as well as control biosorbents were characterized using Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray spectroscopy (EDX) analyses. In our study, the optimum conditions of pH, temperature, incubation time, initial biomass concentration and agitation speed for the maximum removal of AgNPs was found to be 4, 30 °C, 200 min, 1 mg/mL and 125 rpm, respectively. Interestingly, in our study, Langmuir isotherm model was best correlated with the highest regression coefficient (R2) of 0.992 and the maximum biosorption was found to be 740.63 μg/mL. FTIR results showed that carboxyl, carbonyl and secondary amine groups were involved in the biosorption of AgNPs. FESEM images of AgNPs treated biosorbent depicted rough surface and the presence of AgNPs on the surface of biosorbent was clearly observed. EDX spectrum showed Ag peak, which confirmed the successful uptake of AgNPs by A. terreus dead biomass. Thus, our study shows that A. terreus could be used as a cost-effective eco-friendly biosorbent for AgNPs removal from aqueous solution. Therefore, exploiting the same fungus for both synthesis and removal of AgNPs could be a novel approach in the context of mycoremediation practices.

Establishing a green biodesulfurization process for iron ore concentrates in stirred tank and leaching column bioreactors using Acidithiobacillus thiooxidans.

The presence of sulfur impurities in complex iron ores represents a significant challenge for the iron mining and steel-making industries as their removal often necessitates the use of hazardous chemicals and energy-intensive processes. Here, we examined the microbial and mineralogical composition of both primary and secondary iron concentrates, identifying the presence of Sulfobacillus spp. and Leptospirillum spp., while sulfur-oxidizing bacteria were absent. We also observed that these concentrates displayed up to 85% exposed pyrrhotite. These observations led us to explore the capacity of Acidithiobacillus thiooxidans to remove pyrrhotite-sulfur impurities from iron concentrates. Employing stirred tank bioreactors operating at 30°C and inoculated with 5·106 (At. thiooxidans cellsmL-1), we achieved 45.6% sulfur removal over 16days. Then, we evaluated packed leaching columns operated at 30°C, where the At. thiooxidans enriched system reached 43.5% desulfurization over 60days. Remarkably, sulfur removal increased to 80% within 21days under potassium limitation. We then compared the At. thiooxidans-mediated desulfurization process, with and without air supply, under potassium limitation, varying the initial biomass concentration in 1-m columns. Aerated systems facilitated approximately 70% sulfur removal across the entire column with minimal iron loss. In contrast, non-aerated leaching columns achieved desulfurization levels of only 6% and 26% in the lower and middle sections of the column, respectively. Collectively, we have developed an efficient, scalable biological sulfur-removal technology for processing complex iron ores, aligning with the burgeoning demand for sustainable practices in the mining industry.

Sustainable permeable biobarriers for atrazine removal in packed bed biofilm reactors

The synergy between two supported bacterial biofilms of S. equisimilis and P. putida and a sustainable biocarrier (raw pine) was studied, working both as biobarriers for the treatment of water contaminated with atrazine. Firstly, the effects of ATZ exposure on bacterial growth were evaluated, with Gram-positive S. equisimilis being a more tolerant bacterium to higher amounts of the herbicide. The bioremoval of ATZ by S. equisimilis concentrated biomass was then assessed, reaching around 83.5% after 15 days due to the potential degradation by the biomass and biosorption by the solids, with overlapping of both mechanisms. The optimization of bacterial biofilm attachment onto raw pine prior to bioremoval assays in lab-scale packed bed biofilm reactors was performed by varying initial biomass concentration, inocula growth time and hydrodynamic conditions. Lastly, the optimized biosystems were tested as sustainable remediation designs to treat water contaminated with the selected herbicide. Results reveal an added beneficial effect towards the bioremoval of atrazine using supported biofilms onto raw pine, reaching 90.42% and 79.71% by S. equisimilis and P. putida biofilms, respectively, over 58.31% increase when compared to sorption on fixed bed of pine. The coupling of biosorption/biodegradation favors the bioremoval process significantly.

Influence of light absorption rate on the astaxanthin production by the microalga Haematococcus pluvialis during nitrogen starvation

Large amounts of astaxanthin (about 4% DW) can be produced under nitrogen starvation of Haematococcus pluvialis in photobioreactors (PBRs) exposed to high light conditions to induce a light stress. However, in PBR, the large biomass concentration usually achieved leads to strong light attenuation conditions, which makes complex the analysis of this “light stress”. This study aims to elucidate the role of light transfer in astaxanthin cell content and productivity from the microalga Haematococcus pluvialis during nitrogen starvation. Haematococcus pluvialis was cultivated in a flat-panel PBR in a batch mode with sudden nitrogen starvation conditions and an incident photon flux density (PFD) of 250 µmolhν m−2 s−1. Different initial biomass concentrations ({C}_{{x}_{0}}) were evaluated, 0.21, 0.52, 1.39 and 2.21 kg m−3. As a result, spectral mass absorption cross-sections of Haematococcus pluvialis were measured at different times during nitrogen starvation, and were used to relate the mean rate of photon absorption (MRPA) to the astaxanthin productivity. A minimum initial MRPA of 7000 ± 500 µmolhν kgx−1 s−1 was found necessary to trigger large accumulation of astaxanthin in Haematococcus pluvialis cells (up to 3.21% DW) during nitrogen starvation conditions. The results also demonstrated the link between the MRPA and the daily astaxanthin productivity of Haematococcus pluvialis cultures, introducing then the MRPA as a physical quantity of interest for a rational optimization of the light culture conditions in PBRs.Graphical

Algae in a Drinking Water Reservoir: Development of an Air–Water–Algal Growth Model (AWAM) for Long-Term Prediction

The condition of the water in drinking water source environments is critical for public health. However, in recent years, the rapid growth of algae has become a significant threat to the safety of the drinking water supply. This study investigated the temporal trends and spatial differences in algae in the Nanwan Reservoir during 2022. Regression analysis using the least-squares method demonstrated that water temperature and initial biomass concentration were critical parameters that influenced the rate of algal growth. An air–water–algal growth model (AWAM) for algal growth prediction was developed using a 30-day forecast of air temperature, an air-to-water temperature extrapolating equation, a water temperature–algal growth relationship, and only four monthly measurements of algal concentration. The results demonstrated that the model accurately predicted algal growth in the next 30 days, with an R2 of 0.738, which aligned with the monitored results. Compared to the upstream Wudaohe River inflow point, algal growth in the drinking water intake area near the downstream dam was delayed by at least 30 days. By using the upstream inflow area as a reference point, the prediction period was extended to provide a 60-day early warning. The extended prediction period and the reduced need for monitoring data make the model more convenient for guiding the prevention and control of algal blooms in drinking water reservoirs.

Single-cell mass distributions reveal simple rules for achieving steady-state growth.

Microbiologists have watched clear liquid turn cloudy for over 100 years. While the cloudiness of a culture is proportional to its total biomass, growth rates from optical density measurements are challenging to interpret when cells change size. Many bacteria adjust their size at different steady-state growth rates, but also when shifting between starvation and growth. Optical density cannot disentangle how mass is distributed among cells. Here, we use single-cell mass measurements to demonstrate that a population of cells in batch culture achieves a stable mass distribution for only a short period of time. Achieving steady-state growth in rich medium requires low initial biomass concentrations and enough time for individual cell mass accumulation and cell number increase via cell division to balance out. Steady-state growth is important for reliable cell mass distributions and experimental reproducibility. We discuss how mass variation outside of steady-state can impact physiology, ecology, and evolution experiments.

Kinetic Modeling of Mead Production

This work studies the fermentation kinetics to produce mead using Saccharomyces cerevisiae, selected from three commercial yeasts to generate a product with better organoleptic characteristics and greater acceptance by a group of untrained tasters. The values of the kinetic parameters of the fermentation were obtained from a series of fermentations at laboratory scale, maintaining constant the initial concentration of biomass (1.5 g/L), the operating temperature (33 °C) and the pH (4) and varying the initial soluble solids concentration in four values (10, 16, 22 and 25 °Brix). Based on the experimental results, a mathematical modeling was developed to estimate the variables of interest. Thus, from the application of the Monod model, the saturation constant (Ks) of 336.6 g/L was obtained, with a maximum specific growth rate ( μ max ) of 0.071 h−1. Using the integrated logistic model, the experimental values were adjusted to obtain the average value of μ max of 0.0815 h−1. Finally, the maximum ethanol production rate (rpm) of 0.2621 g/L was obtained through the modified Gompertz model. Therefore, Monod, integrated logistic and modified Gompertz models were ideal mathematical tools to interpret the kinetic behavior of honey fermentations, predict and control this process, both on a laboratory scale and on a subsequent industrial scale. Thus, contributing to the knowledge of the dynamic behavior of mead production and its level of technological development.

Cyanidiales-Based Bioremediation of Heavy Metals.

With growing urbanization and ongoing development activities, the consumption of heavy metals has been increasing globally. Although heavy metals are vital for the survival of living beings, they can become hazardous when they surpass the permissible limit. The effect of heavy metals varies from normal to acute depending on the individual, so it is necessary to treat the heavy metals before releasing them into the environment. Various conventional treatment technologies have been used based on physical, chemical, and biological methods. However, due to technical and economic constraints and poor sustainability towards the environment, the use of these technologies has been limited. Microalgal-based heavy metal removal has been explored for the past few decades and has been seen as an effective, environment-friendly, and inexpensive method compared to conventional treatment technology. Cyanidiales that belong to red algae have the potential for remediation of heavy metals as they can withstand and tolerate extreme stresses of heat, acid salts, and heavy metals. Cyanidiales are the only photosynthetic organisms that can survive and thrive in acidic mine drainage, where heavy metal contamination is often prevalent. This review focuses on the algal species belonging to three genera of Cyanidiales: Cyanidioschyzon, Cyanidium, and Galdieria. Papers published after 2015 were considered in order to examine these species' efficiency in heavy metal removal. The result is summarized as maximum removal efficiency at the optimum experimental conditions and based on the parameters affecting the metal ion removal efficiency. This study finds that pH, initial metal concentration, initial algal biomass concentration, algal strains, and growth temperature are the major parameters that affect the heavy metal removal efficiency of Cyanidiales.

Autofermentation of alkaline cyanobacterial biomass to enable biorefinery approach

BackgroundCarbon capture using alkaliphilic cyanobacteria can be an energy-efficient and environmentally friendly process for producing bioenergy and bioproducts. The inefficiency of current harvesting and downstream processes, however, hinders large-scale feasibility. The high alkalinity of the biomass also introduces extra challenges, such as potential corrosion, inhibitory effects, or contamination of the final products. Thus, it is critical to identify low cost and energy-efficient downstream processes.ResultsAutofermentation was investigated as an energy-efficient and low-cost biomass pre-treatment method to reduce pH to levels suitable for downstream processes, enabling the conversion of cyanobacterial biomass into hydrogen and organic acids using cyanobacteria’s own fermentative pathways. Temperature, initial biomass concentration, and oxygen presence were found to affect yield and distribution of organic acids. Autofermentation of alkaline cyanobacterial biomass was found to be a viable approach to produce hydrogen and organic acids simultaneously, while enabling the successful conversion of biomass to biogas. Between 5.8 and 60% of the initial carbon was converted into organic acids, 8.7–25% was obtained as soluble protein, and 16–72% stayed in the biomass. Interestingly, we found that extensive dewatering is not needed to effectively process the alkaline cyanobacterial biomass. Using natural settling as the only harvesting and dewatering method resulted in a slurry with relatively low biomass concentration. Nevertheless, autofermentation of this slurry led to the maximum total organic acid yield (60% C mol/C mol biomass) and hydrogen yield (326.1 µmol/g AFDM).ConclusionAutofermentation is a simple, but highly effective pretreatment that can play a significant role within a cyanobacterial-based biorefinery platform by enabling the conversion of alkaline cyanobacterial biomass into organic acids, hydrogen, and methane via anaerobic digestion without the addition of energy or chemicals.

Phosphorus uptake and accumulation in Chlamydomonas reinhardtii: Influence of biomass concentration, phosphate concentration, phosphorus depletion time, and light supply

The model microalga Chlamydomonas reinhardtii was cultivated under P depleted and P repleted conditions to test the influence of dissolved P concentration (0–20 mg-P·L−1), initial algal biomass concentration (0.17–0.57 g-DW·L−1), P-depletion time (1 h – 4 days) and light supply (continuous illumination versus darkness) on phosphate uptake rate (mg-P·h−1·L−1) and the cellular P content (as %P of dry cell mass). Dissolved P concentration positively influenced cellular P content, while biomass concentration and P-depletion time did not. Biomass concentration and P-depletion time instead positively influenced P uptake rates. Light supply neither influenced cellular P content nor P assimilation. These findings evidence that depleting the cells at high initial biomass concentration could enhance P removal during wastewater treatment in waste stabilization ponds. Practically, these findings imply that high P removal from wastewater could be achieved by exposing ‘concentrated’ P-depleted biomass to P-laden influent in a relatively short contact-time reactor and subsequently harvesting and removing the resultant P-rich biomass. This stage would be followed by normal biomass growth in larger ponds which depletes the remaining P, with this biomass being harvested and returned to the contact tank for P removal.

Development of a Simple and Robust Kinetic Model for the Production of Succinic Acid from Glucose Depending on Different Operating Conditions

Succinic acid (SA) is one of the main identified biomass-derived chemical building blocks. In this work we approach the study of its production by Actinobacillus succinogenes DSM 22257 from glucose, focusing on the development and application of a simple kinetic model capable of representing the evolution of the process over time for a great diversity of process variables key to the production of this platform bio-based chemical: initial biomass concentration, yeast extract concentration, agitation speed, and carbon dioxide flow rate. All these variables were studied experimentally, determining the values of key fermentation parameters: titer (23.8–39.7 g·L−1), yield (0.59–0.72 gSA·gglu−1), productivity (0.48–0.96 gSA·L−1·h−1), and selectivity (0.61–0.69 gSA·gglu−1). Even with this wide diversity of operational conditions, a non-structured and non-segregated kinetic model was suitable for fitting to experimental data with high accuracy, considering the values of the goodness-of-fit statistical parameters. This model is based on the logistic equation for biomass growth and on potential kinetic equations to describe the evolution of SA and the sum of by-products as production events that are not associated with biomass growth. The application of the kinetic model to diverse operational conditions sheds light on their effect on SA production. It seems that nitrogen stress is a good condition for SA titer and selectivity, there is an optimal inoculum mass for this purpose, and hydrodynamic stress starts at 300 r.p.m. in the experimental set-up employed. Due to its practical importance, and to validate the developed kinetic model, a fed-batch fermentation was also carried out, verifying the goodness of the model proposed via the process simulation (stage or cycle 1) and application to further cycles of the fed-batch operation. The results showed that biomass inactivation started at cycle 3 after a grace period in cycle 2.

Green synthesis of silver nanoparticles through green caviar Caulerpa lentillifera and its phytotoxicity on Allium ascolanicum

Caulerpa lentillifera, one of the edible marine seaweeds, was used to synthesize silver nanoparticles (AgNPs) in this study. According to the results, optimum conditions such as initial biomass concentration, AgNO3 concentration, pH, temperature, agitation rate for the synthesis of AgNPs by using C. lentillifera were 0.01 g/mL, 8 mM AgNO3, pH 10, 85 °C and 0 rpm, respectively. The calculated particle sizes of the synthesized AgNPs were 22.3 nm. The characterizations of synthesized AgNPs were carried out through UV-Vis spectrophotometry, FT-IR and XRD. The development shoot and root of shallot (Allium ascalonicum) experiments were tested to evaluate the phytotoxicity of synthesized C. lentillifera-based AgNPs. The phytotoxic effect of C. lentillifera-based AgNPs was found to be dose dependent. Since the phytotoxicity of the AgNPs synthesized in the study is evaluated, its industrial applications in the food, medicine, pharmacy and agriculture industries can be further considered based on the usage doses.

Synergistic Hydrothermal Conversion of Aqueous Solutions of CO2 and Biomass Waste Liquefaction into Formate.

CO2 utilization by conversion into useful chemicals can contribute to facing the problem of increasing CO2 emissions. Among other alternatives, hydrothermal transformation stands out by the high conversions achieved, just using high-temperature water as the solvent. Previous works have demonstrated that several organic compounds with hydroxyl groups derived from biomass can be used as reductants of NaHCO3 aqueous solutions as inorganic CO2 sources. Formate was obtained as the main product as it was produced by conversion both of the inorganic carbon and of the organic reductants, whose transformation into formate was promoted by the addition of NaHCO3. Based on these results, in this work, the hydrothermal conversion of NaHCO3 is performed together with the liquefaction of lignocellulosic biomass (sugarcane bagasse and pine needles) in a one-pot process. Results show that yields to formate of 10% wt/wt (with respect to the initial concentration of biomass) are achieved by hydrothermal treatment of NaHCO3 and lignocellulosic biomass at 250 °C with a residence time of 180 min. Other products, such as acetic acid and lactic acid, were also obtained. These results demonstrate the feasibility of the hydrothermal reduction of CO2 combined with the hydrothermal liquefaction of residual biomass in a simultaneous process.

Influence of key operational parameters on biohydrogen production from fruit and vegetable waste via lactate-driven dark fermentation

This study aims at investigating the influence of operational parameters on biohydrogen production from fruit-vegetable waste (FVW) via lactate-driven dark fermentation. Mesophilic batch fermentations were conducted at different pH (5.5, 6.0, 6.5, 7.0, and non-controlled), total solids (TS) contents (5, 7, and 9%) and initial cell biomass concentrations (18, 180, and 1800 mg VSS/L). Higher hydrogen yields and rates were attained with more neutral pH values and low TS concentrations, whereas higher biomass densities enabled higher production rates and avoided wide variations in hydrogen production. A marked lactate accumulation (still at neutral pH) in the fermentation broth was closely associated with hydrogen inhibition. In contrast, enhanced hydrogen productions matched with much lower lactate accumulations (even it was negligible in some fermentations) along with the acetate and butyrate co-production but not with carbohydrates removal. At pH 7, 5% TS, and 1800 mg VSS/L, 49.5 NmL-H2/g VSfed and 976.4 NmL-H2/L-h were attained.

Enhancing the bioconversion of ferulic acid from alkaline hydrolysate of corn cobs to vanillin by Amycolatopsis thermoflava under nutrient limitation and reducing sugar control

AbstractBACKGROUNDThe use of commercially available ferulic acid (FA) as a precursor for vanillin production is costly. The utilization of agro‐waste as a starting material provides an alternative to obtain FA at a low cost and establish an economically profitable production system. In this work, optimization of ultrasound‐assisted extraction conditions for releasing FA from corn cobs using alkaline treatment was conducted. Further, bioconversion of FA from the crude hydrolysate of corn cobs to vanillin using Amycolatopsis thermoflava was performed.RESULTSSince autoclaved hydrolysate was unfavorable for cell growth and vanillin formation, pasteurization was proposed. However, the presence of contaminants limited the entire process. Aiming to suppress the growth of contaminants and increase vanillin yield, novel strategies of limiting and controlling the nutrients for the strain were developed. Optimal hydrolysis conditions (NaOH concentration = 0.5 M, solid loading = 10% for 30 min) produced hydrolysate with relatively high titers of FA (715 mg L−1) and p‐coumaric acid (1025 mg L−1). To improve vanillin production from FA, four parameters (including the effects of sterilization method, nutrient limitation, initial biomass concentration, and reducing sugar control) were investigated. By adopting these strategies and performing bioconversion of FA to vanillin with an initial biomass concentration of 1.5 g L−1, the yield of vanillin was significantly increased by 29.5‐fold to 477.4 mg g−1, compared to bioconversion using autoclaved hydrolysate.CONCLUSIONThis approach represents a relatively economical method for vanillin production from agro‐waste because it uses crude hydrolysate, requires minimum nutrients, and involves non‐modified organisms with a relatively short bioconversion time (17 h). © 2022 Society of Chemical Industry (SCI).

Optimizing phosphorus removal for municipal wastewater post-treatment with Chlorella vulgaris

The microalgal species Chlorella vulgaris was cultivated in batch conditions to identify the optimum set of initial conditions for the best biomass growth rate, phosphate removal, polyphosphate accumulation, and protein productivity. To study the effect of phosphorus deficiency caused stress, the microalgal biomass was exposed to phosphorus deficiency conditions for periods varying between 1 and 10 days and inoculated at different initial biomass and phosphate concentrations. A 10-day period of phosphate deficiency, supported by low initial biomass concentration (∼0.25 mg DW L−1), increased the phosphate removal by 62–175% when compared to the reference conditions. A 10-day period of biomass P-deficiency also boosted the polyphosphate accumulation and protein productivity, increasing them up to 40 and 46.8 times, respectively, if compared to reference conditions. At the same time, optimization algorithm model results suggested one-day biomass P-starvation with low initial biomass concentration as the optimum combination to achieve the highest performance while the initial phosphate concentration had less impact. The initial conditions suggested by the optimization model were validated in a sequencing batch photobioreactor, giving 101.7 and 138.0% more phosphate removal and polyphosphate accumulation, compared to the reference conditions. The obtained results present microalgae exposure to phosphorus stress as a supplementary tool for wastewater post-treatment targeted on rapid phosphorus removal.

The Cultivation of Biohydrogen-Producing Tetraselmis subcordiformis Microalgae as the Third Stage of Dairy Wastewater Aerobic Treatment System

The development of wastewater treatment systems, including competitive methods for nitrogen and phosphorus removal, is focused on intensifying final technological effects with due care taken for economic and environmental concerns. Given the possibility of integrating wastewater treatment processes with biofuel production, the prospective seems to be technologies harnessing microalgal biomass. The present study aimed to verify the feasibility of applying T. subcordiformis genus microalgae as the third stage of the dairy wastewater treatment process and to determine microalgae biomass production effectiveness and hydrogen yield in the biophotolysis process. The study proved that microalgae cultivation with dairy wastewater was nearly 35% less effective compared to that with a chemically pure medium. Nitrogen and phosphorus compounds contaminating wastewater were found to represent an available source of nutrients for T. subcordiformis population. The volume of hydrogen produced ranged from 116 ± 7 cm3 to 162 ± 7 cm3, and the percentage of H2 content in the biogas ranged from 55.4 ± 2.2% to 57.2 ± 4.1%. A significantly higher hydrogen yield per initial biomass concentration, reaching 69 ± 4.2 cm3/go.d.m., was determined in the variant with wastewater accounting for 50% of the culture medium. The respective value noted in the control respirometer was 54 ± 2.1 cm3/go.d.m.

Removal process and mechanism of hexavalent chromium by adsorption-coupled reduction with marine-derived Aspergillus niger mycelial pellets

In order to remove hexavalent chromium (Cr(VI)) from solutions efficiently, the mycelial pellets with a marine-derived fungus Aspergillus niger as a biosorbent were prepared. The effects of removal process parameters such as solution pH, initial Cr(VI) concentration and biomass concentration on Cr(VI) removal process were investigated. The results showed that Cr(VI) removal rate up to 100% could be achieved under optimized conditions, which indicated the excellent Cr(VI) removal performance of the Aspergillus niger pellets. As a more important point, the Cr(VI) removal mechanism was studied, and the results revealed that Cr(VI) removal was achieved in the adsorption-coupled reduction process. A little of Cr(VI) was reduced to less toxic trivalent chromium (Cr(III)) in solution, while some was absorbed on the surface of mycelial pellets. Then they may be reduced on the surface or transferred into cells and then be reduced. The marine-derived A. niger mycelial pellets show properties of easy preparation and separation and cost effectiveness, which are potential biosorbent and reductant in the treatment of trace chromate containing wastewater.

Removal of heavy metals from industrial wastewater using microbial fuel cell.

Removal efficiency of gold from a solution of pure tetrachloroaurate ions was investigated using microbial fuel cell (MFC) technology. The effects of type of catholyte solution and initial gold concentration on the removal efficiency were considered. Due to its presence at high levels in the gold wastewater, the effect of copper ions on the removal efficiency of the gold ions was also studied. The effects of pH and initial biomass concentration on the gold removal efficiency was also determined. The results showed that after 5 h contact time, 95% of gold removal efficiency from a wastewater containing 250 ppm of initial gold ions at ambient temperature using 80 g/L yeast concentration was achieved. After 48 h of the cell's operation under the same condition, 98.86% of AuCl4 – ions were successfully removed from the solution. At initial gold concentration in the waste solution of 250 ppm, pH 2, and initial yeast concentration of 80 g/L, 100% removal efficiency of the gold was achieved. On the other hand, the most suitable condition for copper removal was found at a pH of 5.2, where 53% removal efficiency from the waste solution was accomplished.