The effect of mixing intensity on the performance and microbial dynamics of a single vertical reactor integrating acidogenic and methanogenic phases in lignocellulosic biomass digestion

A comprehensive review on the production and enhancement techniques of gaseous biofuels and their applications in IC engines with special reference to the associated performance and emission characteristics

The increasing global demand for energy, coupled with environmental concerns associated with fossil fuels, has led to the exploration of alternative fuel sources. Gaseous biofuels, derived from organic matter, have gained attention due to their renewable nature and clean combustion characteristics. The paper extensively explores production pathways for gaseous biofuels, including biogas, syngas, and hydrogen, providing insightful discussions on various sources and processes. The energy content, physical, and chemical properties of gaseous biofuels have been analysed, highlighting their potential as viable alternatives to conventional fuels. Distinctive properties of biogas, producer gas, and hydrogen that impact combustion characteristics and engine efficiency in IC engines are underscored. Furthermore, the review systematically reviews enhancement techniques for gaseous biofuels, encompassing strategies to augment quality, purity, and combustion efficiency. Various methods, ranging from substrate pretreatment for biogas to membrane separation for hydrogen, illustrate effective means of enhancing fuel performance. Rigorous examination of performance parameters such as brake thermal efficiency, specific fuel consumption and emissions characteristics such as NOx, CO, CO2, HC of gaseous biofuels in dual-fuel mode emphasizes efficiency and environmental impact, offering valuable insights into their feasibility as engine fuels. The findings of this review will serve as a valuable resource for researchers, engineers, and policymakers involved in alternative fuels and sustainable transportation, while also highlighting the need for further research and development to fully unlock the potential of gaseous biofuels in IC engines.

Enhanced wastewater treatment with an AnF-AAO system for improved internal carbon source utilization

The main challenge in removing nutrients from municipal wastewater in China is the lack of available carbon sources. While hydrolysis acidification tanks can improve wastewater biodegradability by effectively utilizing internal carbon sources, high sludge concentrations are difficult to control in traditional tank variants. In this study, an innovative anaerobic filter (AnF) hydrolysis acidification reactor composed of a continuously stirred tank reactor (CSTR) and cloth media filter was designed to regulate and maintain high sludge concentrations in the hydrolysis acidifier. The reactor was used as a pretreatment unit for the anaerobic/anoxic/oxic (AAO) units and combined into an AnF-AAO system to explore the effectiveness of internal carbon source utilization in wastewater. The results indicate that as the sludge concentration in the hydrolysis acidifier increased, the hydrolysis and acidification processes became more efficient. The optimal sludge concentration was 40 g/L, which significantly increased the production of soluble chemical oxygen demand and volatile fatty acids. Above this concentration, the efficiency decreased. Compared to traditional AAO processes, the AnF-AAO system achieved superior total nitrogen and phosphorus removal with shorter hydraulic retention times and reduced sludge production by a significant amount of 35%. Due to its capacity for enhancing internal carbon source utilization, the AnF-AAO system constitutes a promising approach for sustainable urban wastewater treatment.

Effect of mixing intensity on volatile fatty acids production in sludge alkaline fermentation: Insights from dissolved organic matter characteristics and functional microorganisms

Alkaline fermentation for volatile fatty acids (VFAs) production has shown potential as a viable approach to treat sewage sludge. The hydrolysis and acidogenesis of sludge are greatly influenced by mixing. However, the effects of mixing intensity on VFAs production in sludge alkaline fermentation (SAF) remain poorly understood. This study investigated the impacts of mixing intensity (30, 90 and 150 rpm continuous mixing, and 150 rpm intermittent mixing) on VFAs production, dissolved organic matter (DOM) characteristics, phospholipid fatty acid profiles and microbial population distribution in SAF. Results showed that 150 rpm continuous and intermittent mixing enhanced the hydrolysis of sludge, while 150 rpm intermittent mixing resulted in the highest VFAs production (3886 ± 266.1 mg COD/L). Analysis of fluorescent and molecular characteristics of DOM revealed that 150 rpm intermittent mixing facilitated the conversion of released DOM, especially proteins-like substances, into VFAs. The abundance of unsaturated and branched fatty acids of microbes increased under 150 rpm intermittent mixing, which could aid in DOM degradation and VFAs production. Firmicutes and Tissierella were enriched at 150 rpm intermittent mixing, which favored the maximum VFAs yield. Moreover, Firmicutes were found to be the key functional microorganisms influencing the yield of VFAs during SAF. This study provides an understanding about the mixing intensity effects on VFAs production during SAF, which could be helpful to improve the yield of VFAs.

High-rate anaerobic digestion of sewage sludge using anaerobic dynamic membrane bioreactor under various sludge composition and organic loading rates

This study investigates the effects of sludge compositions and organic loading rates (OLRs) on stable biomethane production during sludge digestion. Batch digestion experiments evaluate the effects of alkaline-thermal pretreatment and waste activated sludge (WAS) fractions on the biochemical methane potential (BMP) of sludge. A lab-scale anaerobic dynamic membrane bioreactor (AnDMBR) is fed with a mixture of primary sludge and pretreated WAS. Monitoring of volatile fatty acid to total alkalinity (FOS/TAC) helps maintain operational stability. The highest average biomethane production rate of 0.7 L/L·d is achieved when the OLR, hydraulic retention time, WAS volume fraction, and FOS/TAC ratio are 5.0 g COD/L·d, 12 days, 0.75, and 0.32, respectively. This study finds functional redundancy in two pathways: hydrogenotrophic and acetolactic. An increase in OLR promotes bacterial and archaeal abundance and specific methanogenic activity. These results can be applied to the design and operation of sludge digestion for stable, high-rate biomethane recovery.

Adaptive Pathways of Microorganisms to Cope With the Shift From P- to N-Limitation in Subtropical Plantations

Ecological stoichiometry is increasingly acknowledged as one of the main control factors for microbial activity and diversity. Soil carbon/nitrogen (C/N) and carbon/phosphorus (C/P) ratios are usually much higher than microbial nutrient requirements and vary with planting density and stand age in forestlands. However, how microorganisms cope with such stoichiometric imbalances and how they regulate nutrient cycling remain unclear. Here, 5- and 35-year-old experimental Cunninghamia lanceolata [Lamb.] Hook plantations with five planting densities (1,667, 3,333, 5,000, 6,667, and 10,000 stems ha⁻¹) were used to explore the underlying mechanism of the response of microorganisms to stoichiometric imbalances. We found that (i) enzyme activity and microbial biomass and diversity increased with planting density at age 5 but decreased at age 35; (ii) soil microorganisms were P-limited at age 5, but gradually shifted from P- to N-limitation during the development of plantations from 5 to 35 years; and (iii) significantly negative relationships between microbial biomass stoichiometry and enzymatic stoichiometry were observed. The adaptive pathways of soil microorganisms to cope with stoichiometric imbalances include (i) adjusting the stoichiometry of microorganisms and enzymes; (ii) changing the relative abundance of the dominant microbial phyla; and (iii) increasing the ratio of fungal to bacterial diversity. These results highlight how to use the ecological stoichiometry method to identify soil microbial nutrient limitations with planting density during the development of plantations. By underlining the important role of stoichiometry on microbial growth and activity, these findings furthermore emphasize the dependency of organic matter transformation and nutrient cycling on the microbial community.

Current development and perspectives of anaerobic bioconversion of crop stalks to Biogas: A review

As one of the most abundant biomass resources, crop stalks are great potential feedstock available for anaerobic digestion (AD) to produce biogas. However, the specific physical properties and complex chemical structures of crop stalks form strong barriers to efficient AD bioconversion. To overcome these problems, many efforts have been made over the past few years. This paper reviewed recent research in the evolving field of anaerobic bioconversion of crop stalks and was focused on three critical aspects affecting AD performance: various pretreatment methods and their effects on the improvement of crop stalk biodegradability, determination of specific AD operation parameters for crop stalks, and development of AD technologies. Finally, recommendations on the future development of crop stalk AD were proposed.

Performance and microbial community evaluation of full-scale two-phase anaerobic digestion of waste activated sludge

"Temperature Staging and Biological Phasing" (TSBP) is an improved two-phase anaerobic digestion (AD) technology. This technology hydrolyzes waste activated sludge (WAS) at 45 °C and converts methane at mesophilic temperature (35-38 °C), with hydraulic retention times of 3-5 d and 14-17 d, respectively. In this study, the performance and microbial community dynamics of full-scale TSBP-based sludge anaerobic digestion system were studied, and the technology was evaluated by energy balance and ecological benefit analysis. The stable operation for 390 d showed that the cumulative biogas yield was about 349,041 m³, the maximum biogas yield rate was 563.68 L/kg VS, and the VS degradation rate of organic matters in the sludge was 47.19%. Proteobacteria and Firmicutes were found to be the dominant bacteria in both thermophilic and mesophilic reactors. Methanobacterium and Methanosarcina were the two most abundant methanogenic genera in the AD samples. The aceticlastic methanogenesis was likely the predominant production pathway of methane in AD processes based on metagenomics. The TSBP system operated stably, and the recovered energy could achieve energy self-sufficiency, which provided technical reference for the anaerobic treatment of sludge.

Strategy of optimizing anaerobic digestion of cassava distiller wastewater using a novel automatic biological incubation system

Due to the drawbacks of using fossil fuels and the need to mitigate global warming caused by increasing greenhouse gas emissions, agricultural biomass for bioenergy production is gaining great interest around the world. This work presented a study at a biochemical plant in Lianyungang, Jiangsu Province, China to maximize methane production from cassava distiller wastewater. The plant's annual production of cassava distiller wastewater is more than 3 million tons and currently was treated using a series of 5000 m³ Internal Circulation (IC) reactors. Modification was applied at No.19 IC reactor by connecting it to two 1 m³ automatic biological incubators called Information Bio-Booster (IBB). The effluent of the IC reactor was fed into the IBBs and iron, cobalt and nickel were added directly in the IBBs. The function of the IBBs was to regulate the microbial community. Afterwards, the microorganisms in the IBBs were pumped back into the IC reactor to participate in the methane production reaction. Daily net increase of methane content and COD removal reached 8.02% and 33% respectively in No.19 IC reactor comparing to the unadjusted reactors. Preliminary lab experiments found that improvements of biogas production, enhanced COD removal and VS removal was closely related to the enhancement of anaerobic microbial communities' diversity and the promotion of enzyme activity through the addition of the metal salts. Daily economic value could be estimated to be $218 which indicated the application potential of using the proposed system to enhance anaerobic digestion at industrial plants for bioenergy production.

Effect of low-thermal pretreatment on the methanogenic performance and microbiome population of continuous high-solid anaerobic digester treating dewatered sludge

Undigested and dewatered sludge at 10% total solids was pretreated at 60 °C for 3 h and fed to a lab-scale horizontal anaerobic bioreactor for 130 days with solids retention time (SRTs) from 25 to 16 d. The low-thermal pretreatment enabled higher net energy production, improved sludge treatment efficiency, and enhanced digestion stability. The highest average biomethane yield and production rate were 138.5 mL/g VS and 0.43 L/L.d, respectively, and the economic benefit was expected to be the maximum at SRT 16 d. Pretreatment did not increase the specific methanogenic activity per unit methanogen, but resulted in higher abundance of methanogenic archaea and hydrolytic bacteria. Methanogenic population shifted from hydrogenotrophic to acetoclastic, consistent with predicted gene expression at SRT equal or below 20 d. Anaerobic digestion along with low-thermal could be a feasible management strategy for undigested dewatered sludge from small WWTPs.

Exogenous N-acyl-homoserine lactones promote the degradation of refractory organics in oligotrophic anaerobic granular sludge

For refractory industrial wastewaters, anaerobic granular sludge technology cannot be widely used because of its limited treatment capacity, so strengthening the anaerobic degradation of refractory organics should be discussed. In this paper, the feasibility of adding exogenous N-acyl-homoserine lactones (AHLs) to promote the degradation of refractory organics in oligotrophic anaerobic granular sludge was addressed. The results showed that, after easily-degradable organics were completely metabolized, exogenous AHLs strengthened the further degradation of refractory organics and improved the methanogenic activity of anaerobic granular sludge. In addition, adding AHLs could promote the secretion of more extracellular polysaccharides and proteins by anaerobic microorganisms to resist the oligotrophic environment. Microbiological analysis showed that adding AHLs significantly optimized the microbial community in oligotrophic anaerobic granular sludge. With the regulation of AHLs, the abundance proportion of hydrolytic acidifying bacteria for refractory organics in bacterial community and the abundance proportion of acetotrophic methanogens in methanogens community increased obviously. Exogenous AHLs showed concentration-related effects on the optimization of bacteria and methanogens, and AHLs of higher concentration were beneficial to the succession of community structure in a better direction. Exogenous regulation of AHLs-mediated QS provided an attractive strategy for enhancing the anaerobic degradation of refractory organics, and proposed a technical idea for the application of anaerobic granular sludge technology in refractory industrial wastewaters.

A comparison and evaluation of the effects of biochar on the anaerobic digestion of excess and anaerobic sludge

The mechanisms and enhancing effects of different biochar loadings on the digesters receiving low and high excess (or anaerobic) sludge loadings were thoroughly examined in the present study. This was done to explore an efficient method for converting excess sludge to anaerobic sludge. Biochar had an obvious effect on the anaerobic digestion of excess sludge but not on the anaerobic sludge. When the amount of biochar added was equivalent to 100% of the sludge TS, the cumulative methane yields of anaerobic digestion inoculated with small and large amounts of excess sludge were respectively 30.2 and 1.7 times that of those without biochar. The number of methanogens in the digesters that received small and large inoculations of excess sludge with 100% biochar, were respectively 105.4% and 20.6% higher than those without biochar. The biochar enhanced the systems performance because it selectively enriched the Trichococcus and Methanomicrobiales tightly attach to it. This enhanced the synergy and overall activity of the system by promoting biofilm development. Ultimately, the integration of 100% biochar and excess sludge can be used as a substitute for anaerobic sludge as an inoculum by giving similar overall performance.

Investigation of the interaction between lighting and mixing applied during the photo-fermentation biohydrogen production process from agricultural waste

To better clarify the effect of lighting and mixing on the hydrogen production from agricultural waste, experiments under diverse constant and dynamic light intensities and mixing speeds were conducted. Cumulative hydrogen yield, hydrogen production rate, OD₆₆₀, pH, reducing sugar concentration were monitored. Results showed that mixing had positive effects on high substrate concentration. The interaction between lighting and mixing was drawn. Higher light intensity (7000 Lux) was suitable for hydrogen production under mixing. Higher light intensity with higher mixing speed (150 RPM) showed the highest cumulative hydrogen yield of 78.1 mL/g TS. Different periods of hydrogen production process required distinct lighting and mixing. Combined with Gompertz model, dynamic lighting and mixing strategies were discussed. Dynamic light intensity (4000-7000-4000 Lux) accompanied with dynamic mixing speed (50-150-50 RPM) was the optimal condition for PFHP. Highest hydrogen yield of 84.7 mL/g TS and highest light conversion efficiency of 36.32% were obtained.

Accelerated biomethane production from lignocellulosic biomass: Pretreated by mixed enzymes secreted by Trichoderma viride and Aspergillus sp

Biological pretreatment is a promising technology to increase biogas yield. The methane yield and microbial community resulting from anaerobic digestion of maize straw after pretreatment of enzymes [extracted from Trichoderma viride (ETv) and Aspergillus sp. (EAs)] at different mixing ratios [5/0, 4/1, 3/2, 2/3, 1/4, 0/5] were evaluated. The methane yields from mixed enzymes pretreatment were higher than single enzymes pretreatments of ETv and EAs. The optimal enzymes mixing ratio of ETv and EAs was found to be 2/3, with the cumulative methane yield 512.64 mL/g TS_added, which was 31.74% higher than the control. Enzymatic pretreatment promoted an increase in the abundance of bacteria and archaea associated with cellulose decomposition. The majority of bacteria and archaea were assigned to Bacteroidetes, Firmicutes and Methanosaeta.

Regulatory relationship between quality variation and environment of Cistanche deserticola in three ecotypes based on soil microbiome analysis

The environment affects the composition and function of soil microbiome, which indirectly influences the quality of plants. In this study, 16S amplicon sequencing was used to reveal the differences in soil microbial community composition of Cistanche deserticola in three ecotypes (saline-alkali land, grassland and sandy land). Through the correlation analysis of microbial community abundance, phenylethanoid glycoside contents and ecological factors, the regulatory relationship between microbial community and the quality variation of C. deserticola was expounded. The metabolic function profile of soil microbiome was predicted using Tax4Fun. Data showed that the soil microbial communities of the three ecotypes were significantly different (AMOVA, P < 0.001), and the alpha diversity of grassland soil microbial community was the highest. Core microbiome analysis demonstrated that the soil microbial communities of C. deserticola were mostly have drought, salt tolerance, alkali resistance and stress resistance, such as Micrococcales and Bacillales. The biomarkers, namely, Oceanospirillales (saline-alkali land), Sphingomonadales (grassland) and Propionibacteriales (sandy land), which can distinguish three ecotype microbial communities, were excavated through LEfSe and random forest. Correlation analysis results demonstrated that 2'-acetylacteoside is positively correlated with Oceanospirillales in saline-alkali land soil. The metabolic function profiles displayed highly enriched metabolism (carbohydrate and amino acid metabolisms) and environmental information processing (membrane transport and signal transduction) pathways. Overall, the composition and function of soil microbiomes were found to be important factors to the quality variation of C. deserticola in different ecotypes. This work provided new insight into the regulatory relationship amongst the environment, soil microbial community and plant quality variation.

Effects of adding EDTA and Fe2+ on the performance of reactor and microbial community structure in two simulated phases of anaerobic digestion

The uptake of trace elements can be impeded by precipitation in the presence of carbonates and sulfates. The objective of this study was to investigate whether ethylenediaminetetraacetic acid (EDTA) enhances the performance of anaerobic digestion by forming dissolved complexes with Fe²⁺. Batch experiments were performed in this study and acidogenic and methanogenic phases were artificially simulated. EDTA was added to both of phases to examine its effects on Fe bioavailability, metabolic parameters and microbial community structure. The results showed that EDTA significantly accelerated the digestion process in both phases because its addition changed the Fe sorption law and increased Fe-bioavailability. The microbial community structure changed following by the change of Fe-fractions which was determined by EDTA. This study demonstrated that EDTA as ligand could increase the Fe-bioavailability and then reduced or replaced the addition of Fe.

Effect of mixing intensity on hydrolysis and acidification of sewage sludge in two-stage anaerobic digestion: Characteristics of dissolved organic matter and the key microorganisms

Mixing should be optimized in anaerobic digestion (AD) systems to achieve excellent biomaterials production in the sewage sludge (SS) management in wastewater treatment plant. AD depends on the coordinated activity of hydrolysis, acidification and methanogenesis. However, the effect of mixing intensity on characteristics of hydrolysis and acidification in AD of SS is still poorly understood. This study focused on the mixing intensity (30, 60, 90 and 120 rpm) effect on the characteristics of dissolved organic matter (DOM) and the key microorganisms in the hydrolysis and acidification of SS. Results showed that enhanced hydrolysis and acidification efficiency was obtained at mixing of 90 and 120 rpm (p < 0.05), while the maximum acetic acid (388 ± 21 mg/L) was produced at 90 rpm. Mixing at 90 rpm enhanced the release of protein and polysaccharide as well as humic acid. Further analyses of DOM molecular features revealed that 90 rpm led to the highest molecular diversity and easily biodegradable molecules (lipid and proteins/amino sugars), which contributed to the maximum hydrolysis and acidification efficiency. Firmicutes and Actinobacteria significantly increased with mixing intensity (p<0.05), and Chloroflexi and Fusobacteria were enriched at mixing of 90 rpm, which favored the hydrolysis of SS. The enrichment of Clostridium XI and Clostridium sensu stricto contributed to the acidification of DOM at 90 and 120 rpm. The results of this study can advance our knowledge about mixing intensity effects on the AD systems of SS. This research also showed how increasing mixing intensity to a relatively high speed can enhance the hydrolysis and acidification efficiency of SS.

A new perspective of using sequential extraction: To predict the deficiency of trace elements during anaerobic digestion

Trace elements were commonly used as additives to facilitate anaerobic digestion. However, their addition is often blind because of the complexity of reaction conditions, which has impeded their widespread application. Therefore, this study was conducted to evaluate deficiencies in trace elements during anaerobic digestion by establishing relationships between changes in trace element bioavailability (the degree to which elements are available for interaction with biological systems) and digestion performance. To accomplish this, two batch experiments were conducted. In the first, sequential extraction was used to detect changes in trace element fractions and then to evaluate trace element bioavailability in the whole digestion cycle. In the second batch experiment, trace elements (Co, Fe, Cu, Zn, Mn, Mo and Se) were added to the reaction system at three concentrations (low, medium and high) and their effects were monitored. The results showed that sequential extraction was a suitable method for assessment of the bioavailability of trace elements (appropriate coefficient of variation and recovery rate). The results revealed that Se had the highest (44.2%-70.9%) bioavailability, while Fe had the lowest (1.7%-3.0%). A lack of trace elements was not directly related to their absolute bioavailability, but was instead associated with changes in their bioavailability throughout the digestion cycle. Trace elements were insufficient when their bioavailability was steady or increased over the digestion cycle. These results indicate that changes in trace element bioavailability during the digestion cycle can be used to predict their deficiency.

Evaluation of phase separation in a single-stage vertical anaerobic reactor: Performance and microbial composition analysis

In order to explore whether the acidogenic phase and methanogenic phase could be separated vertically into a single-stage anaerobic reactor, a controlled double circulation (CDC) anaerobic reactor was proposed for treating traditional Chinese medicine (TCM) wastewater in this study. The results showed that most of the organic pollutants and refractory were removed in the first reaction area where most of the amount of sludge existed. The organic acids were accumulated in the first reaction area, and larger specific methanogenic activity (SMA) and coenzyme F₄₂₀ values were found in the second reaction area. Bacterial and archaeal community structures in the two reaction areas of the CDC reactor were analyzed by Illumina MiSeq Sequencing, which revealed that the archaeal community showed larger difference compared with the bacterial community. Differences in the performance and microbial composition of the two reaction areas confirmed that phase separation was implemented in the CDC reactor.

Simulation and Analysis of Flow Field in Sludge Anaerobic Digestion Reactor based on Computational Fluid Dynamics

Because of the complexity of flow and the opacity of sludge, usually we can’t gain a precise and comprehensive sight of sludge flow type and its associated flow characteristics in the anaerobic digestion (AD) reactor. In the present study, we focused on the sludge rheological properties as well as the flow behavior in the digester. The viscosity decreased with the increase of shear rate, and sludge as a kind of pseudo-plastic fluid was proved. Based on computational fluid dynamics (CFD), taking sludge rheological index and rotational speed into consideration, then the flow field distribution in the digester was obtained. The fluid velocity raised with increase in rotational speed, moreover, fluid near blades had higher velocity while it was almost stagnant in the areas near reactor bottom and top as well as reactor wall and stirring shaft. The effect of rheological index on improving the velocity of fluid farther from impeller exceeded the influence on fluid at the impeller installation height. Regarding dead zone fraction as an indicator of the mixing effect, it was recommended that the suitable rotational speed for AD of 96 % moisture content sludge is 40 r/min. Finally, the reactor performance was optimized respectively from impeller form and reactor configuration, the results showed that both combined impellers and oval reactor can reduce dead zone volumes and produce a better mixing effect.

Aerobic deterioration of corn stalk silage and its effect on methane production and microbial community dynamics in anaerobic digestion

Ensilage is a commonly used method of preserving energy crops for biogas production. However, aerobic deterioration of silage is an inevitable problem. This study investigated the effect of aerobic deterioration on methane production and microbial community dynamics through anaerobic digestion (AD) of maize stalk silage, following 9days air exposure of silage. After air exposure, hydrolytic activity and methanogenic archaea amount in AD were reduced, decreasing the specific methane yield (SMY); whereas lignocellulose decomposition during exposure improved the degradability of silage in AD and enhanced SMY, partially compensating the dry matter (DM) loss. 29.3% of the DM and 40.7% of methane yield were lost following 0-9days exposure. Metagenomic analysis showed a shift from Clostridia to Bacteroidia and Anaerolineae in AD after silage deterioration; Methanosaetaceae was the dominant methanogenic archaea.

Oxygen mass transfer and shear stress effects on Pseudomonas putida BCRC 14365 growth to improve bioreactor design and performance

In this work, the experimental evidence is presented for two basic issues including oxygen mass transfer and shear analysis on the microorganism containing medium on the most prominent sections of the bioreactor. Computational fluid dynamics (CFD) methodology reproduces shear rate values for specific impeller designs using the commercial code (Fluent 6.2). CFD calculates volumetric mass transfer coefficient based on the Higbie's penetration theory. Four types of impeller are used. The spherical probe is used to measure flow hydrodynamic parameters to obtain shear rate by electro-diffusion (ED) method. The obtained results are validated experimentally and it is shown that a fully axial pattern impeller represents more enhanced results than partially axial and radial. In this regard, experimental results for volumetric oxygen mass transfer coefficient (k _l a) confirm CFD predictions by acceptable deviations of 2.65, 8.90, and 9.20 for 0.15, 0.2, and 0.3 VVM, respectively. These results collaboratively indicate that LIGHTNIN-C 200 type operates more efficiently by reflecting the flow to the bottom corner stagnation areas with the minimum tolerable shear and the most velocity distribution uniformity. Furthermore, the values of k _l a improve by aeration rate. Conversely, increasing the rotational speed of impeller creates difficulties for cell growth due to the generated harsh shear condition. CFD provide a better understanding of how operational and geometrical variables may be manipulated to achieve a moderate shear rate and acceptable level of mass transfer.