High Mixing Intensity Research Articles

Oil in food waste to methane by anaerobic digestion: Co-effects of mixing intensity and long chain fatty acid loading

Oil in the food waste can contribute improved energy yield by anaerobic digestion, and also poses an inhibition risk from the intermediate long chain fatty acids (LCFAs). The digestion performance partly depends on the solubility of oil/LCFAs concerned recently, while mixing intensity control can disturb the solubility characteristics. Combined with oil loading such a fundamental control parameter, co-effects of mixing intensity and oil loading on methanogenic characteristics were illuminated. A series of mixing intensities 0–240 rpm and oil/inoculum (F/I) ratios 0.2–1.2 were set to conduct a batch experiment, and relevant affecting mechanisms were further disclosed as well. It turned out that variation of mixing intensity could have effects on methanogenesis from oil in food waste. Increasing mixing intensity prolonged lag phase. Mixing intensity at 120 rpm was proved as a starting point to disturb LCFA inhibition. Methanogenic rates climbed to the top at F/I 0.4, and further increase loading resulted in the rate decline. Methanogenic potential release was also reduced with both mixing intensity and loading at higher values. Hereinto, oleic acid (C18:1) as a key LCFA in oil played an important role in inhibition, while higher mixing intensity and loading could promote degradation and conversion of another critical LCFA palmitic acid (C16:0). The study favors achieving a cost-effective strategy controlled by mixing intensity to promote safe energy improvement.

Investigation of an Industrially Scalable Production of Sulfur‐Polyacrylonitrile Based Cathodes

AbstractSulfur‐polyacrylonitrile (SPAN) is a sulfur‐based active material for next‐generation lithium‐sulfur battery cathodes. Due to the covalent bonding between sulfur chains and the polymeric backbone, the shuttle effect degrading classical sulfur‐based cathodes can be suppressed while also achieving a high active material content in the cathode. In this paper, we investigate the processability of an industrially scalable SPAN active material with 38 wt.‐% of sulfur in a water‐based and scalable process route. The potential of the SPAN material for industrial adoption and the impact of the process route on the cell performance are discussed. We show that when processed correctly, the SPAN material delivers exceptional cycling stability and good C‐rate performance with ether‐based electrolytes. However, the performance of the SPAN cathode is influenced by the mixing characteristic. Using higher mixing intensities during the slurry preparation leads to deterioration of the electrochemical performance. This can be attributed to a decreasing carbon black percolation with increasing tip speed in combination with the kinetic limitation of sulfur cathodes during Li2S2 and Li2S oxidation.

Екологічні характеристики, біомаса, чисельність і домінуючі комплекси фітопланктону різнотипних водойм та водотоків пониззя Дунаю

In the context of modern environmental challenges, being under constant anthropogenic pressure, systematic study of the spatial and temporal dynamics of phytoplankton distribution, its quantitative and qualitative indicators, biomass and abundance, and determination of the dominant complex are indicative factors of biodiversity and water productivity. In the context of constant anthropogenic pressure, such research and monitoring of biodiversity and water quality are essential for the functioning of biocenosis. It was found that the diversity of phytoplankton in different hydroecosystems of the lower Danube River is represented by a wide floristic spectrum and amounts to 156 species (158 species) belonging to 8 divisions: Cyanobacteria, Bacillariophyta, Cryptophyta, Miozoa, Ochrophyta, Charophyta, Chlorophyta, Euglenozoa. The research of phytoplankton ecological characteristics showed that planktonic and planktonic-benthic forms are the most common in terms of biotopic habitat. Analyzing the phytoplankton by habitat, indifferent species dominate in all studied hydroecosystems. In relation to pH, most of the representatives belong to indifers, and fewer to alkalifers. The number of phytoplankton cells ranged from 375 thousand cells/m2 to 1320 thousand cells/m2, with Cyanobacteria being the most numerous. The main role in the formation of the biomass of water bodies in summer in the studied areas belongs to the divisions Chlorophyta, Miozoa, and Bacillariophyta and ranges from 0.3361 mg/dm3 to 0.944205 mg/dm3. The analysis of the dynamics of phytoplankton abundance and biomass showed that these indicators vary depending on the location of the algosampling stations. The structure of phytoplankton biomass in the lower Danube is unevenly represented, according to the hydroecosystem, and is formed mainly by the Bacillariophyta-Chlorophyta complex, but in some samples, representatives of the Mioza order dominate in terms of biomass. At the same time, summarizing the values of phytoplankton abundance, it was found that the leading role belongs to Cyanobacteria, with Chlorophyta and Bacillariophyta also widespread. It was noted that in shallow waters and in areas with high dynamics of hydrological processes, namely river-sea transition zones, there is a predominance of the diatom complex, formed mainly by planktonic-benthic and benthic forms. This spatial distribution is typical for areas with high intensity of water mass mixing.

Chaos and mixing in NETmix

AbstractNETmix is a network of mixing chambers interconnected by channels, in which the most efficient mixing occurs under chaotic flow regimes. Chaos is highly influenced by the topology, particularly by the ratio chamber diameter/channel width, D/d. In this work, micromixing in NETmix is characterized through Lagrangian Mixing Simulation (LMS), which enables to establish the relation between the degree of mixing and the topology, D/d. The degree of mixing is then related with the Eulerian chaoticity from hydrodynamics and spectral analysis. The best mixing is obtained at D/d = 6.65 and is associated to a thin 8 shaped strange attractor. The spectral analysis shows a principal oscillation frequency at St = 0.13. Since the quasi‐periodic regime is alternated with chaotic behavior, NETmix has an intermittent bifurcation. For the NETmix system, orderly flows in the quasi‐periodic regime have higher mixing intensity than less orderly flows in the weak or strong chaotic regimes.

Revealing the influence of additional structure on the flow field characteristics and flocculation performance in thickener feedwell through PIV experiments

Cemented paste backfill (CPB) is a widely used method for resource utilization of tailings. The thickener feedwell is the key equipment for CPB to realize solid-liquid separation. Flocculation is a significant process in treating slurry thickening and dehydration. To reveal the flow field variation in the flocculation process, a range of feedwells with additional structures were devised, containing the guide chute feedwell, guide shelf feedwell, and no-additional structure feedwell. The effects of hydrodynamics on flocculation performance were investigated with particle image velocimetry. The velocity and energy distribution were used to describe the variation of the flow field. The size and fractal dimension of aggregates for the flocculation reaction were studied. Furthermore, the turbidity was compared to evaluate the flocculation performance. The results indicated that additional structure can improve flocculation performance, ultimately achieving efficient solid-liquid separation. The flocculation process in feedwell incorporates the mixing-collision section and settling-growth section along the flow direction, with bounding by additional structure. The ideal high-efficiency feedwell should produce a symmetrical and uniform flow field, providing matched shear strength for two sections. The guide chute feedwell exhibited superior performance, resulting in significantly larger aggregate sizes while also experiencing remarkable compactness compared to the alternative additional structure. The reason is that tailings slurry and flocculant obtain high mixing intensity and residence time in the mixing-collision section, causing the effective collision of micro aggregates, further increasing their size and compactness in the settling-growth section. Meanwhile, gradually decaying energy distribution avoids fragmentation of aggregates. This work is expected to provide theoretical and technical support for the design and optimization of feedwells, finally achieving deep dewatering of tailings slurry, and reducing solid waste pollution in mines.

Predicting phosphorus accumulation and proposing conditions needed for an algal-based phosphorus uptake process

ABSTRACT Algal-based waste stabilisation ponds (WSP) are a common wastewater treatment system for small communities but have poor phosphorus removal. Under certain conditions algae in WSPs will perform ‘luxury uptake’ increasing their phosphorus content to over 3% (gP/gSS) by storing polyphosphate. For the first time in the literature this paper presents a systematic study which determines the conditions needed to maximise phosphorus accumulation within WSP biomass taking into account the interactions between key variables. The key variables of temperature, phosphorus concentration, light intensity, mixing intensity, organic load, and pH were evaluated in 40 batch factorial experiments using a WSP algal culture. All six variables examined had significant main effects or interactions on the phosphorus content of the biomass. These were incorporated into a regression equation which was successfully validated against independent data sets from the literature. The conditions required to maximise the phosphorus content of the biomass were predicted for both summer (high light and high temperature) and winter (low light and low temperature) scenarios. The required conditions were revealed to be high phosphorus concentration, high mixing intensity, no supplementary CO2 addition, and low organic load. Interestingly, these conditions were consistent for both summer and winter suggesting that year-round treatment is possible. Practical methods of achieving these conditions were proposed. While further work will be needed to evaluate the effect of growth and potential influence of algal species, the findings presented provide a vital step towards developing a new phosphorus removal treatment process based on an enhanced understanding of environmental biotechnology.

Correlation between kinetic parameters, reactor performance, and biogas and methane potential of co-digestion and mono-digestion of active sludge and olive mill wastewater

Abstract Anaerobic co-digestion(AcoD) of active sludge (AS) and olive mill wastewater (OMW) is becoming an increasingly recognized alternative to manage waste and generate renewable energy. A kinetic study of the performance of biochemical methane potential (BMP) and continuous stirred tank reactors (CSTR) bioreactors was conducted to identify critical parameters influencing. Substrates of 100%OMW, 100%AS, 25:75%, 75:25%, and 50:50 were utilized in the BMP and CSTR digesters. To identify the optimum mixing, BMP tests were conducted under three different operating conditions: no mixing (NM), low-continuous mixing intensity (LM) of 25 rpm, and high continuous mixing intensity (HM) of 60 rpm. CSTR with an optimum mixing regime is utilized to identify the optimum substrate. In particular, the removal efficiency of volatile solids (VSs), total chemical oxygen demand (TCOD), and the production of biogas and methane (CH4) were investigated to specify the performance of the anaerobic digestion (AD) process. The results revealed that the optimum mixing regime is LM with BMP tests. Also, the maximum performance in CSTR-ML was achieved by 75:25 AS:OMW, 0.339 Nm3/kg VS of biogas, 69.89% of CH4, and a removal efficiency of 87.12% of VS and 79.23% of TCOD. For BMP tests, the biogas and CH4 yield production kinetics were best fitted by the modified Gompertz models: mono-digestion and co-digestion 75:25 and 50:50 of AS:OMW, while the best-fit model for co-digestion 25:75 was achieved by the transfer model. The production kinetics were well described by modified Gompertz models in CSTR tests. These results point to the possibility of optimizing digester systems on a wide scale using the outputs that have been observed. Novelty statement. This research work provides novel insights into the performance of the digester under diverse mixing conditions and varying co-substrate concentrations of AS:OMW and presents the best model to predicate the biogas and CH4 at various operation conditions.

A 3D homogeneous microreactor with high mixing intensity at wide Re range for MOF preparation and POCT application

Most microreactors can only work under high Re or extremely low Re conditions to obtain enough mixing efficiency, the inefficient reaction intensity undoubtedly limits its application scenarios. In this study, a novel 3D homogeneous microreactor (3D-HM) was reported that demonstrate a strong mixing intensity over a wide range of Re conditions. The 3D geometries of shunt and lateral secondary flow structure were optimized in details, and then were added to the Zigzag mixing channel to promote mixing index (MI) (over 94 % from Re = 0–10, and more than 98 % for Re > 10). Compared with the traditional T-shaped, Split and Recombine micromixer, a shorter mixing distance (Lmix) and mixing time (τmix) were needed to realize fully mixing. The 3D-HM was used for the preparation of Zeolitic imidazolate framework (ZIF-8), the particle size, yield and drug loading capacity of ZIF-8 prepared using the 3D-HM under a milder Re conditions were better than those prepared by traditional and existing microfluidic methods under a harsh Re conditions. The promotion to diffusion mixing with 3D-HM channel was then verified using the enzymatic catalytic reaction driven by syringe pump at low Re and capillary pump, respectively. Enzyme and substrates in the laminar flow in the 3D-HM are more likely to bind each other than that in the T-shaped diffusion mixing. In addition, the laminar diffusion mixing process was scaled up by microfluidic channel design, so that the results of enzymic catalytic reaction was visualized for Point-of-care Testing (POCT) application. The MI, Lmix and τmix directly determine the homogeneous microreaction intensity. The proposal of the 3D-HM may provide more possibilities for the application of micromixing-based reactors.

The flame structure and combustion dynamics in a steam diluted H2/Air micromix flame

The OH* chemiluminescence is used to investigate experimentally the effects of nozzle diameter (d), steam dilution ratio (D) and equivalence ratio (φ) on flame structure and combustion dynamics in a steam diluted H2/air micromix burner. Two flame types, anchored and lifted, are found. The OH* signal for the anchored flame primarily presents in flame shear layer zone (SLZ), while that for the lifted flame mainly appears in the flame central recirculation zone (CRZ) and flame tail zone (FTZ). The increase of the velocity of hydrogen (as the D decreasing or the φ increasing) would change anchored flame to lifted flame. The Power Spectral Density (PSD) analysis shows that changing from anchored to lifted flame would result a high OH* fluctuation frequency, which shows the same trend as the decrease of d. The Dynamic Mode Decomposition (DMD) analysis shows that the distribution of dominant mode is similar to the distribution of OH* signal. The SLZ is the primary oscillation zone for anchored flame and the CRZ for lifted flame. The anchored flame is more stabler comparing to the lifted one, and the lifted flame should be avoided in practical burners. Besides, the high mixing intensity of fuel and oxidizer is beneficial to the stability of micromix flame.

Process intensification using a semi-continuous mini-blender to support continuous direct compression processing

The production of pharmaceutical tablets is shifting towards continuous manufacturing. Therefore, individual unit operations such as powder blending need to be re-designed. Continuous powder blending has been implemented successfully, but for low-dose formulations this is challenging due to difficulties with continuously dosing small amounts of powder. To overcome such challenges, a semi-continuous mini-blending operation combined with batch-wise dosing can be introduced in a continuous process. The objective of this study is to investigate key factors that affect blending performance of a novel, semi-continuous mini-blending process. A design of experiments is performed, varying both process settings and blend formulations. This reveals that blending performance of the mini-blending process is largely controlled by process settings. These results show that the mini-blender design, with high mixing intensity and short mixing times, supports process intensification of powder blending. The results obtained can be used for Quality by Design-based formulation development for continuous direct compression.

Kaoline-based catalyst for a high stability desulfurization of sour heavy naphtha in a three-phase oscillatory baffled reactor

To meet the rapidly increasing demand for energy and the dramatic depletion of conventional crude oil, it is imperative to utilize sour naphtha. With no coke being produced, oxidative desulfurization (ODS) of naphtha lowers its sulfur content and average molecular weight. In this article, we outline a method for heavy naphtha non-extractive ODS using a very stable catalyst. The technique involves the use of a solid catalyst with oxygen gas as the oxidant. This necessitated relatively high mixing intensities; hence a three-phase Oscillatory Baffled Reactor (OBR) was used. The catalyst was based on the zeolite ZSM-5, prepared from natural kaolin by a series of delamination and activation steps and impregnated with Fe. A TiO2 nanolayer was applied, using the sol-gel method, to prevent rapid deactivation. The reactor performance was evaluated to minimize the sulfur content in the naphtha fuel. Due to the protective coating, the sulfur conversion stabilized at 90%. The results of this work establish the use of natural clay-based catalysts in a continuous, three-phase ODS, particularly with regard to proving long-term stability. It also showed that modest ODS can be achieved using an environmentally friendly oxidant, at mild operating conditions, whilst maintaining stability.

ИССЛЕДОВАНИЯ ВЛИЯНИЯ СКОРОСТИ ПЕРЕМЕШИВАНИЯ ОТХОДОВ АГРОПРОМЫШЛЕННОГО КОМПЛЕКСА НА КОЛИЧЕСТВО ПРОИЗВОДИМОГО БИОГАЗА

At the enterprises of the agro-industrial complex there is a large amount of waste, most of which is not recycled. This leads to a number of environmental problems, such as soil acidification and the greenhouse effect caused by methane emissions into the atmosphere. Meanwhile, waste from the agro-industrial complex (AIC) is an excellent raw material for the production of biogas, an environmentally friendly fuel that agribusiness enterprises can use for their own generation of heat and electricity, thus reducing the volume of energy purchases from generating companies. In addition to heat and electricity, biogas technologies make it possible to obtain high-quality fertilizers, which agricultural enterprises can later use, for example, for growing greenhouse cropsIn this paper, we studied the effect of the waste mixing rate in a bioreactor on the amount of biogas produced. The studies were carried out at the following mixing speeds: 40, 70 and 100 rpm. The research results showed that at a speed of 70 rpm, the most efficient mixing of the biomass in the reactor is observed. At a stirrer speed of 40 rpm, the presence of dead zones was observed in the reactor, which indicates a low efficiency of biomass mixing. In addition, at a stirrer speed of 70 rpm, the maximum daily production of biogas is observed, namely 1100 l. At a stirrer speed of 100 rpm, a noticeable reduction in the amount of biogas produced was observed due to the high mixing intensity. In general, in the studied time period (17 days), at mixing speeds of 40, 70 and 100 rpm, 9800, 10400 and 8000 liters of gas are produced, respectively. Thus, the highest performance of the bioreactor is achieved at a biomass stirring speed of 70 rpm.

Scalable Synthesis of (R,R)-N,N-Dibenzyl-2-fluorocyclohexan-1-amine with CsF under Hydrogen Bonding Phase-Transfer Catalysis

Hydrogen bonding phase-transfer catalysis offers a convenient solution to activate safe and economical metal alkali fluorides for enantioselective nucleophilic fluorination. Herein, we demonstrate the scalability of this protocol with the fluorination of 200 g of racemic trans-N,N-dibenzyl-2-bromocyclohexan-1-amine in a mechanically stirred 1 L glass reactor using 0.5 mol % of a bis-urea organocatalyst. In these experiments, full conversions were obtained for high mixing intensities (impeller average shear rate >10 000 s–1; maximum energy dissipation per unit of mass >300 W/kg). The thermal safety of the reaction was assessed by differential scanning calorimetry and reaction calorimetry, assigning the reaction to Stoessel’s critical class 3.

Optimization of the Structural Design of the Process of Fertilizer Mixing and Biomodification of Solid Mineral Fertilizers

A rational structural construction of the general process of fertilizer mixing and biomodification of solid mineral fertilizers is proposed. It covers all the process steps starting from the receipt of individual mixing components at the enterprise fertilizer mixing section through to the shipment of the finished biomodified fertilizer mixture to the finished product warehouse. The condition of synchronous operation of units and assemblies of a fertilizer mixing line is substantiated, where its maximum productivity, high mixing intensity and good quality of the mixture are achieved.

Development and Research of New Media Jet Aeration Scheme in a Loop Bioreactor Producing Microbiological Products

Abstract Jet aeration loop reactors are widely used in the chemical industry due to their high mixing intensity, possibility of significant saturation of medium with gases, and simplicity of scaling the processes when passing from laboratory equipment to industrial designs. However, to ensure the necessary amount of air in standard jet aeration schemes with ejectors, high pressure of the medium (up to 6 bars) is required in the reactor loop. This paper presents a newly developed scheme of jet aeration, based on mixing the pressure flows of medium and air supplied to the ejector by individual blowers. Experiment results of the new water aeration scheme showed that, for the formation of suspended matter in the ejector with an air content of 2–20 l per 1 l of water, a pressure of 0.3 bar in the reactor loop at an air pressure of 1 bar is sufficient. This allows usage of low-pressure pump and compressor, which form the basis for the energy consumption reduction and creates prerequisites for lowering the shear loads on a crop. The medium aeration rate during experiments was 0.220–0.266 vvm. It was found that, for each mode of joint operation of pump and compressor, it is possible to maintain a constant aeration rate, which is not significantly affected by the flowrate regulation of medium in loop.

Influence of mixing on the generation of nanoparticles in cement systems

In this work, we study the effect of mixing intensity on the size and concentration of nanoparticles in quartz and cement systems. We vary the local shear rate in the studied suspensions induced by mixing by either changing solid volume fraction or mixing speed. Our results obtained on quartz, cement and quartz-cement suspensions provide a master curve relating the concentration of nanoparticles in the pore solution as a function of the local shearing conditions computed at a micromechanical level. Our results suggest, in accordance with literature, that high mixing intensity is at the origin of a detachment of nano-hydrates from the surface of cement particles. These nanoparticles can be stabilized and therefore detected in the pore-solution only in the presence of superplasticizers, which inhibit their agglomeration to other particles.

The Dynamics of Globally Unstable Air-Helium Jets and Its Impact on Jet Mixing Intensity

The paper presents experimental investigations of the low-density air-helium jets. The paper is aimed at the analysis of the flow conditions promoting the local absolute instability leading to global flow oscillations. A number of the test cases are analysed with a wide range of the shear layer thickness showing conditions favorable for the global modes and also mixing intensity triggered by such a regime. It is shown that high mixing intensity is determined not only by the global regime but also by the vortex pairing process. The results are compared with a recently proposed universal scaling law for an onset into the global mode. The results turn out to be far from this scaling law and the reasons for such discrepancies are discussed. The measurements show also that if the shear layer at the nozzle exit is thin enough the global modes are suppressed. The mechanism leading to the global mode suppression under such conditions is carefully analysed.

Evaluation of mass and photon transfer enhancement by an impinging jet atomization photoreactor for photocatalytic degradation of p-nitrophenol

In this study, the photocatalytic degradation of p-nitrophenol (PNP) was investigated in a slurry impinging jet atomization reactor and TiO2 nanoparticles have been applied as the photo-catalyst. Formation of the thin leaf-like liquid sheet with high mixing and turbulence intensity due to the collision of two jets, brings a perfect mass transfer. Moreover, the low thickness of the sheet will enhance photon transfer which is an integral factor in UV/TiO2 processes. The impact of different parameters consisting of initial PNP concentration (30−70 mg/L), catalyst loading (0.2−0.8 gr/L) and Reynolds number (15000–31000) on the PNP conversion were investigated in the operating time of 180 min. Based on the results, the optimum experimental condition for the PNP initial concentration of 50 mg/L was 0.5 g/L catalyst loading and Reynolds number of 31,000 with the removal percentage of 55.78 % during 180 min that has been enhanced to 71.91 % by increasing the operation time to 360 min. DLS**Dynamic light scattering analysis has also been conducted for investigation of TiO2 loading effect on particles agglomeration. A pseudo-first-order kinetic model, which is the modified form of Langmuir-Hinshelwood kinetic model, was applied for prediction of p-nitrophenol photocatalytic degradation. A good compatibility between the predicted and experimental data has been observed.

Groundwater Flow and Moisture Dynamics in the Swash Zone: Effects of Heterogeneous Hydraulic Conductivity and Capillarity

AbstractA density‐dependent, variably saturated groundwater flow and solute transport model was used to investigate the influence of swash motions on subsurface flow and moisture dynamics in beach aquifers with heterogeneous distributions of hydraulic conductivity (K) and capillarity. The numerical simulations were performed within a Monte Carlo framework using field measurements conducted in the swash zone of a sandy beach. Our results show that heterogeneous capillarity causes spatially variable capillary rise above the groundwater table. In response to swash motions, heterogeneity creates capillary barriers that result in pockets of elevated moisture content beneath the swash zone. These moisture hotspots persist within the unsaturated zone even at ebb tide when the swash motions recede seaward. Heterogeneous capillarity also results in highly tortuous preferential flow paths and alters the flow rates from the sand surface to the water table. Heterogeneous K greatly enhances the seawater infiltration into the swash zone and modulates its spatial distribution along the beach surface. Due to heterogeneous K and capillarity, complex mixing patterns emerge. Both strain‐dominated and vorticity‐dominated flow regions develop and dissipate as tides and waves move across the beach surface. Complex mixing patterns of seawater percolating from the swash zone surface to the water table, with localized areas of high and low mixing intensities, are further demonstrated by analysis of dilution index. Our findings reveal the influence of geologic heterogeneity on swash zone moisture and flow dynamics, which may have important implications for sediment transport and chemical processing in beach aquifers.

Effect of the shear rate and supersaturation on the nucleation and growth of struvite in batch stirred tank reactors

Controlled struvite precipitation is a promising solution for phosphorus recovery in wastewater treatment plants. Particle size distribution of recovered struvite affects its efficacy as a fertilizer, so should be considered in the design and operation of struvite recovery reactors. This contribution analyzes the effect of varying the average shear rate (between 150 s−1 and 876 s−1) and saturation index (between 0.76 and 2.96) in two different experimental set-ups. Solution pH and particle number and size measurements using an electric zone sensing method are used to monitor the process. In addition, photomicrographs are used to observe the shape of the precipitated particles. Interestingly, for identical thermochemical conditions, a higher mixing intensity, associated with the shear rate, leads to shorter induction times, faster precipitation and a greater particle density. On the other hand, for similar mixing conditions, a higher saturation index is also linked with shorter induction times, faster precipitation and a greater particle density. From the experimental data it is concluded that the effect of the fluid shear rate cannot be ignored and should be further studied in the precipitation process.