Lowest Specific Energy Consumption Research Articles

Comparison of efficiency between liquefied petroleum gas (LPG) and electric hot air dryer: case study of dried pork slice

ABSTRACT To reduce the foods spoilage in remote areas of Thailand where electricity is inaccessible, drying processes must be applied. This research developed an LPG hot air dryer under insufficient electricity supply and investigated its performance on dried pork slice under different air velocities (1, 1.5 and 2 m/s) and temperatures (50, 55 and 60°C). The results were compared with those of an electric hot air dryer, under the same conditions, to determine the optimal device. The drying rate from both dryers increased with an increase in temperature and air velocity. This mostly fitted with Avhad and Marchetti model. However, the lowest specific energy consumption was found in LPG hot air dryer. The moisture in dried pork slices was lower than 30%, regardless of different dryers. This agreed with Thai community product standard. Therefore, the LPG hot air dryer could be used as an alternative instrument for drying pork slice.

Electrodialysis with Bipolar Membranes for the Sustainable Production of Chemicals from Seawater Brines at Pilot Plant Scale.

Environmental concerns regarding the disposal of seawater reverse osmosis brines require the development of new valorization strategies. Electrodialysis with bipolar membrane (EDBM) technology enables the production of acid and base from a salty waste stream. In this study, an EDBM pilot plant with a membrane area of 19.2 m2 was tested. This total membrane area results much larger (i.e., more than 16 times larger) than those reported in the literature so far for the production of HCl and NaOH aqueous solutions, starting from NaCl brines. The pilot unit was tested both in continuous and discontinuous operation modes, at different current densities (200-500 A m-2). Particularly, three different process configurations were evaluated, namely, closed-loop, feed and bleed, and fed-batch. At lower applied current density (200 A m-2), the closed-loop had a lower specific energy consumption (SEC) (1.4 kWh kg-1) and a higher current efficiency (CE) (80%). When the current density was increased (300-500 A m-2), the feed and bleed mode was more appropriate due to its low values of SEC (1.9-2.6 kWh kg-1) as well as high values of specific production (SP) (0.82-1.3 ton year-1 m-2) and current efficiency (63-67%). These results showed the effect of various process configurations on the performance of the EDBM, thereby guiding the selection of the most suitable process configuration when varying the operating conditions and representing a first important step toward the implementation of this technology at industrial scale.

Thermodynamic analysis of single and multi-effect freeze desalination

Freezing desalination technology can be used to treat hypersaline brine more. It requires less energy than conventional desalination. A refrigeration CO2 system is used for cooling required in freeze desalination (FD). The suggested CO2 system has a greater COP than traditional systems because it uses two condensers in the place of a gas cooler to chill CO2 and a low-pressure condenser to melt ice. In multi-effect freeze desalination plants, the brine of previous effect is used as feed water for next effect. Analysis was performed for one-effect freeze desalination (1EFD), two-effect freeze desalination (2EFD), and three-effect freeze desalination (3EFD) with different ice ratio fraction (Fs) for each effect, and 14 configurations with the lowest specific energy consumption (SEC), and highest recovery were selected and the effects of temperature and salinity of feed water and Fs are studied. Multi-effect freeze desalination is more energy efficient than single-effect freeze desalination based on a thermodynamic study of two processes. Compared to a 1EFD, a 2EFD used 39 % less energy to function at a recovery of 68 %. Furthermore, the SEC of 3EFD system at the recovery of 76.11 % is 11.63 kJ/kg of product water.

Comparing economic model predictive control to basic and advanced regulatory control on a simulated high-pressure grinding rolls, ball mill, and flotation circuit

Mineral processing plants remain nowadays infamous for their low energy efficiency. Economic model predictive control (EMPC), by directly considering the energy costs, could possibly help reduce their footprint, but its environmental benefits are yet to be clearly quantified. In an attempt to cast some light on this topic, this paper compares the response to a given ore feed size and hardness disturbance sequence of an EMPC to that of basic and advanced regulatory control systems using the profits and the specific energy (power draw/ore feed rate) as metrics. The simulated circuit comprises a high-pressure grinding rolls (HPGR), a ball mill, and a flotation circuit. It is based on population balance modeling and is an extension of previous works. The basic regulatory control (BRC) system comprises only single-input–single-output control loops with proportional–integral (PI) controllers and operates at a fixed feed rate. The advanced regulatory control (ARC) system consists of PI controllers maximizing the plant feed rate with override constraint handling. The results show that (1) ARC generates more revenue and maintains a lower circuit specific energy consumption than BRC, (2) ARC can produce the same economic performance as EMPC because the constraints of the system define the economic optimum, and (3) EMPC can trade revenues for a lower circuit specific energy with a hybrid criterion that penalizes power draw.

Microwave-assisted vacuum frying of durian chips: Impact of ripening level on the drying rate, physio-chemical characteristics, and acceptability

The microwave assisted vacuum frying (MWVF) of Durian cv. Monthong was performed to investigate the effect of microwave power levels (400, 480, and 560 W) and ripening stages (1 Day, 2 Days, 3 Days, and 4 Days after harvesting) on the kinetics of the durian chips. The physio-chemical properties, the specific energy consumption (SEC) and product acceptability using sensory evaluation were also determined at 110 °C and absolute pressure of 8 kPa. At the higher microwave power, the frying time was reduced leading to a lower SEC. Moreover, it also resulted in decreasing oil absorption, decreasing shrinkage, and increasing porosity. In addition, more ripeness in durians led to longer frying time, increased oil uptake, but also produced a more porous structure and higher crispiness. Furthermore, using the 7-point hedonic scale test, the sensory evaluation revealed that the chips from the more ripened durian had the higher overall acceptability score.

Modular desalination concept with low-pressure reverse osmosis and capacitive deionization: Performance study of a pilot plant in Vietnam in comparison to seawater reverse osmosis

Membrane capacitive deionization (MCDI) has shown many advances, however, its performance in combination with other treatment technologies has not been widely reported. In this study, a pilot-scale low-pressure reverse osmosis (LPRO) (FilmTec™ XLE-2540) with MCDI (CapDI© C17, Voltea) was developed and tested as a promising modular desalination system. The systems were evaluated individually at different salinities and tested together as a modular system. The study focused in the comparison to conventional seawater reverse osmosis (SWRO) (FilmTec™ SW30-2540) at pilot-scale and in theory using the software Water Application Value Engine (WAVE, DuPont™), including a cost evaluation of the systems. Pilot tests were carried out in Can Gio, a riverine estuary region in South Vietnam, which is affected by progressive salinization (TDS ≈ 1–25 g/L). Drinking water quality (TDS < 600 mg/L) was achieved with a specific energy consumption (SEC) of 5.2 kWh/m³. Additionally, fouling mitigation was investigated for the ultrafiltration (UF) pre-treatment by periodic hydraulic and chemical enhanced backwashing. While the SWRO had a slightly lower SEC of 5.0 kWh/m³, WAVE calculations showed that lowering the SEC to 3.6 kWh/m³ is possible by improving the LPRO pump design and an optimization of the MCDI operation.

Thermodynamic Simulation in Eco-Friendly Aquadest Production Through Compression System Method Combined with Steam Power Plant as Heat Source

Access to clean water and sanitation is one of the Sustainable Development Goals (SDGs), a global action plan agreed upon by world leaders. Water demand is increasing every year. As much as 97% of the water on earth is seawater, which requires desalination technology to convert seawater into freshwater that will be used to meet daily human needs. It is necessary to continue to develop environmentally friendly clean water treatment technology to overcome the problem of freshwater crisis. Research related to clean water treatment technology needs improvement in order to have a high effectiveness value to be applied and developed in areas with clean water crisis. Therefore, this study aims to produce distilled water by utilizing heat from the condenser of a steam power plant. The cooling water from the condenser must first be throttled to allow the vapor and liquid extraction to occur. Next, the steam is compressed to raise the temperature. After the compression process, the steam must be condensed using a water-cooled condenser to produce the distilled water in order to get maximum distilled water yields and low energy consumption. In this study, the lowest SEC (Specific Energy Consumption) was -1194.02kJ/kg of distilled water with the mass flow rate of 0.996 kg/s. To overcome the environmental problems, the condenser temperature was lowered to 41.5°C, and the PPTD (Pinch Point Temperature Difference) by 10 made the temperature discharge to seawater drop to 31.5°C. The lowest energy consumption can be obtained by setting the temperature in the cyclone separator to 22°C and the mass of water discharged to the sea by 99%, which lowers compressor energy consumption.

Electrodialysis with Bipolar Membranes for the Generation of NaOH and HCl Solutions from Brines: An Inter-Laboratory Evaluation of Thin and Ultrathin Non-Woven Cloth-Based Ion-Exchange Membranes.

The SEArcularMINE project aims to recover critical raw materials (CRMs) from brines from saltworks, thus facing a CRM shortage within Europe. To promote a fully circular scheme, the project valorises concentrated brines using electrodialysis with bipolar membranes (EDBM) to generate the required amounts of reactants (i.e., acids and bases). Regarding the performances of new non-woven cloth ion-exchange membranes (Suez): (i) an ultra-thin non-woven polyester cloth and (ii) a thin polypropylene cloth acting as the support structures were assessed. Additionally, the anion layer includes a catalyst to promote the water dissociation reaction. The effect of current density (100, 200, and 300 A m-2) on the performance of two combinations of membranes in an inter-laboratory exercise using 2 M NaCl was evaluated. According to statistical analysis ANOVA, there was an agreement on the results obtained in both laboratories. NaOH/HCl solutions up to 0.8 M were generated working at 300 A m-2 using both combinations of membranes. Regarding the performance parameters, stack set-ups incorporating thin polypropylene membranes showed lower specific energy consumption (SEC) and higher specific productivity (SP) than ultra-thin polypropylene ones. Hence, for ultra-thin polypropylene membranes, SEC was reported to be between 2.18 and 1.69 kWh kg-1NaOH and SP between 974 and 314 kg m-2 y-1.

Experimental investigation on maximizing conveying efficiency of belt conveyors used in series application and estimation of power consumption through statistical analysis

AbstractIn this research work, different parameters have been studied which affect the energy consumption of belt conveyors. The effect of conveying distance and vertical lift on energy consumption was studied in detail by collecting energy consumption and other associated data of belt conveyors from different cement plants and analyzed with the help of different statistical analysis. The highest specific energy consumption was found to be 0.0011 kWh/Ton‐m in the smallest belt conveyor of 15 m and the lowest specific energy consumption was found to be 0.0007 kWh/Ton‐m in the longest belt conveyor of 100 m. Specific energy consumption is reduced up to 36% per ton‐meter of material conveying in the longest belt conveyor compared with the smallest belt conveyor. On the contrary, the specific energy consumption for different vertical lifts is found almost the same. Hence, it can be suggested that for horizontal conveying, the series of belt conveyors should be replaced with a single long conveyor to achieve maximum conveying efficiency and to lower specific energy consumption. The above study will be helpful for heavy industries such as cement plants, steel plants, and so forth to reduce their energy consumption on belt conveyors and achieve the environmental sustainability goals. At the last part of the study an equation is derived for estimating energy consumption in belt conveyors by applying multiple regression analysis. The proposed equation will be helpful for estimation of energy consumption of belt conveyors according to which the decision for conveyor length can be taken.

Lead Electrorefining Process from Exhausted Lead Acid Batteries by Using Acidic and Alkaline Electrolytes

The recycling of lead acid batteries (LABs) comprises relevant concerns on the suitable methodologies to recover lead. In this investigation, two electrorefining processes, by using acidic and alkaline electrolytes, have been compared to determine the most significant results of both methodologies. Acidic electrolytes used 200 g/L HBF4, 1.2 g/L H3PO4, 10 g/L H3BO3, and 100 g/L PbO, while the alkaline ones employed 120 g/L NaOH, 75 g/L PbO, 50–92 g/L glycerol, and 2 g/L gelatin. All the solutions were studied by varying temperature and current density (CD) to determine remarkable changes on current efficiency (CE), cell voltage (CV), specific energy consumption (SEC), and on the deposit quality. The results highlighted that by using the acidic electrolyte containing dextrin it is possible to obtain a compact deposit even using high CDs. Acidic solution without dextrin addition allows to obtain good quality deposits by working at 40 °C and 100 A/m2 CD. After testing the behavior of different alkaline electrolytes, it is possible to observe that the solution containing the highest glycerol concentration allows to obtain, for intermediate valued of CD, CE higher than 97% with a SEC of about 0.37 kWh/kg. By comparing the results it is evident that the acidic electrolyte is the one that allows to reach higher productivity with lower SEC. In the selected conditions, lead deposits appear pure and compact.Graphical

Improved production process with new spheroidization machine with high efficiency and low energy consumption for rounding natural graphite for Li-ion battery applications

The demand for rounded graphite for lithium-ion batteries will increase rapidly in the next years, mainly driven by the growing number of electric vehicles. Due to the different particle morphology, synthetic and natural graphite materials have different processing requirements to produce battery-grade materials. However, similar rounding processes with batch-wise operating classifier mills or continuously running classifier mill cascades are used today. For natural graphite in particular, these processes are not very efficient due to their low yield and high energy demand. In this paper, we present a newly developed rounding process for natural graphite, with lower specific energy consumption and higher yield compared to the existing processes. These advantages make the proposed process more economical especially in periods of time with high energy prices. The quality of the material produced by the new process was investigated and compared with the material produced by the existing process, by showing similar graphite properties. Furthermore, the scalability of the new spheroidization process is demonstrated in this paper. Finally, the good cycling performance of the rounded natural graphite material produced by the new process is demonstrated in stacked pouch cells assembled with double side coated anodes. The tested pouch cells still had a capacity retention of over 88% after more than 1000 charge and discharge cycles.

Hybrid semi-batch/batch reverse osmosis (HSBRO) for use in zero liquid discharge (ZLD) applications

Hybrid semi-batch/batch reverse osmosis (HSBRO) is a new method of high-recovery desalination that provides low Specific Energy Consumption (SEC) in a compact design. In this first experimental study on HSBRO, we report SEC over a range of operating parameters using brackish feed water. For example, at 500–1500 mg/L feed concentration, and recovery of 0.94, we measured hydraulic and electrical SEC of 0.20–0.31 kWh/m3 and 0.42–0.54 kWh/m3 respectively, using a flux of 18.9 L/m2/h and obtaining an output of 17.5 m3/day. Second law efficiency was 7.8–17.8 % thus improving on available multistage and semi-batch RO systems. A model of the system, that includes the effect of finite salt rejection, predicts SEC with accuracy of 1–3 %. With improvements in membrane permeability, valves, and pump efficiency, we predict electrical SEC lowered to 0.14–0.28 kWh/m3 and second law efficiency elevated to 22.8–34.5 %. Though simple batch RO can achieve comparable SEC to HSBRO, for recovery as high as 0.94 it would require an impractically large work exchanger. The model shows that feed of salinity up to 6000 mg/L may be treated with recovery of 0.95 and peak system pressure < 120 bar, indicating great potential in ZLD and MLD applications.

Spray Drying of Chokeberry Juice—Antioxidant Phytochemicals Retention in the Obtained Powders versus Energy Consumption of the Process

The production of chokeberry powder, an important functional additive in food, should exhibit both maximization of bioactive properties retention and minimization of energy consumption. The process of spray drying chokeberry juice on a maltodextrin carrier was tested on a semi-technical scale. The research scope included the variability of the inlet air temperature in the range of T = 150–185 °C and concentration of the feed solution in the range of Ud.m = 15–45% d.m. The powder yield, energy consumption and bioactive properties of the obtained powders were determined. The highest levels of bioactive properties retention were expressed in total polyphenol content (TPC) and anthocyanin content (AC) and obtained at T = 150 °C and Ud.m = 25–30% d.m. However, the most advantageous process parameters in terms of specific energy consumption (SEC) minimization were T = 160–170 °C and Ud.m = 30–35% d.m. Analysis of the dependence on SEC versus TPC and SEC versus AC showed that the most favorable drying parameters for chokeberry juice were as follows: inlet air temperature T = 170 °C and feed solution concentration Ud.m = 35%. Hence, under such process conditions, chokeberry powders were produced with approx. 3% lower bioactive properties retention (in relation to the maximum values), but with 20.5% lower SEC.

Study of an Ejector Water Intake and Treatment Plant with a Pressure-Vacuum Hydrocyclone

The intake of natural water or waste water from a depth exceeding the suction height of centrifugal pumps is mainly carried out due to additional water supply at the suction of the pump. However, this process becomes more complicated if it is necessary to purify water from mechanical impurities. The purpose of the presented work is to consider this issue based on the development and study of the parameters of an ejector water intake treatment plant equipped with a pressure-vacuum hydrocyclone. The main contribution of the ongoing research is the establishment of the technological parameters of the installation, and their features in the pressure-vacuum mode of operation, in contrast to the known pressure and vacuum hydrocyclones separately. In terms of methodology, the main parameters of the developed installation were established during the testing of its prototype on a specially built stand using well-known regulatory guidelines in the hydraulic research system. As a result of the study, the nature of the change in pressure inside a cylindrical–conical hydrocyclone, with established design dimensions and the patterns of formation of vacuum and pressure-vacuum modes depending on the initial parameters, was revealed. The data obtained to determine the effect of technological parameters of ejection and the characteristics of the supplied water with impurities on the operating mode of the hydrocyclone confirm the efficiency of water intake and purification. A rational mode of joint operation of the elements of a closed system is achieved at the maximum value of the installation efficiency and ensuring low specific energy consumption per 1 m3 of treated water.

Experimental investigation of membrane distillation with bubble column dehumidifier system for water desalination

The performance of a new integrated system of single-stage sweeping gas membrane distillation module and a bubble column dehumidifier (SGMD-BCD) was experimentally investigated. The productivity and energy consumption of the system is evaluated under different operating conditions. The SGMD module acts as a humidifier to produce high-quality distilled and the bubble column dehumidifier is an effective condenser for improved performance. The sweeping air stream is created in two different ways; using a vacuum pump and compressed air. Results showed that the integrated system yields higher permeate flux, better gained output ratio (GOR), and lower specific thermal energy consumption (SEC) when the vacuum pump is used. Increasing the feed temperature from 50 to 80 °C increased the flux by 175%, on average. Doubling the sweeping air flow rate from 1 to 2 SCFM resulted in flux enhancement of 49% and 25% for the vacuum pump and the compressed air supply, respectively. Operating the system with the vacuum pump and without cooling the bubble column dehumidifier showed a marginal reduction in flux but resulted in significant improvements in GOR and SEC values of 0.76 and 909 kWh/m3, respectively, at an optimum dehumidifier water column height of 9.5 cm.

Feasibility analysis of a thermo-hydraulic process for reverse osmosis desalination: Experimental approach

Reverse osmosis is a widely used desalination technique, mainly because of its low specific energy consumption. Autonomous reverse osmosis processes are increasingly developed because of their energy efficiency and the decentralization of numerous water stress areas. In this context, a reverse osmosis process powered by an innovative thermo-hydraulic desalination system using heat has been developed. This new process aims to autonomously produce fresh water from a brackish water source, compatible with the needs of a small remote village. This new reverse osmosis desalination process exploits a low temperature heat source (60–80 °C) such as the one delivered by solar flat-plate collectors. The heat is then converted into hydraulic energy by a thermodynamic engine cycle in which the expansion of the working fluid directly pressurizes the brackish water by means of hydro-pneumatic tanks, while energy from high pressure brine is recovered by an innovative hydraulic cylinder. Since previous numerical work on this process shown a specific energy consumption about 12 kWh m−3 for a 4 g L−1 brackish water, which is close to performances of relatable processes, an experimental full scale prototype has been built. The work presented here shows the results of the experiments conducted on this prototype, its behavior and performances. Numerical and experimental results are compared and discussed, and confirm the feasibility of the process. These tests show a promising cyclic functioning as the numerical results suggested. The freshwater production and salinity is remaining under the drinkability limit and the experimental specific energy consumption has been calculated to 25 kWh m−3. In order to reach better performances, transfer tanks needs to be improved to avoid heat transfer between working fluid and saltwater which leads to condensation issues, and another hydraulic cylinder design needs to be consider to avoid gasket abrasion.

Ion transport channels in redox flow deionization enable ultra-high desalination performance

Redox flow deionization (RFD) is an emerging derivative of redox flow cell technology that desalinizes salt water while simultaneously storing energy. However, conventional RFDs are limited by high specific energy consumption and low salt removal rates caused by low ionic conductivity in low-salinity ranges (especially < 3000 mg L–1). This study investigates the potential of ion transport channels composed of ion exchangers to enhance ionic conductivity in low-salinity ranges. The RFD cell with ion exchangers (IE-RFD) exhibited significantly lower resistance and specific energy consumption than conventional RFD cells when processing low salinity feeds. A finite element analysis demonstrated that the current density in the ion exchangers, especially where the ion exchangers were in contact, was much higher than that of the surrounding solution, indicating effective ion transport in low-salinity ranges. The IE-RFD cell showed excellent desalination performance (99.4% at 10 000 mg L–1) and low energy consumption (0.99 Wh L–1). We did not observe any deterioration in performance over 10 d of continuous desalination. Compared with other electrochemical desalination technologies, e.g., membrane capacitive deionization, flow capacitive deionization, and traditional RFD, the IE-RFD is superior in terms of energy consumption, salt removal ability, and stability. This study described an efficient strategy to enhance the desalination performance of RFDs through ion transport channels. With further optimization, this technology could help to alleviate the critical global demand for fresh water using minimal energy.

Vacuum-Assisted Multistage Membrane Distillation With Bubble Column Dehumidifier for Efficient Water Production

Abstract An experimental investigation of a novel integrated system of a multistage sweeping gas (air) membrane distillation module and a bubble column dehumidifier (BCD) is presented for an energy-efficient high production water desalination system. The sweeping air stream is created using a vacuum pump installed between the membrane distillation unit and the BCD to apply a degree of vacuum behind the membrane in the air channel of the membrane cell to reduce the vapor mass transfer resistance through the membrane pores. Performance metrics of the system include the measurement of permeate flux and the calculations of energy consumption at various operating conditions in a comprehensive manner. The system performance is mainly controlled by feed temperature and flowrate and the sweeping air flowrate. The dehumidifier water level and its temperature have moderate impacts in the tested ranges. A permeate flux of 18 kg/m2 . h was measured with a relatively high gained output ratio of 0.62, low specific energy consumption of 1120 kWh/m3 when the feed temperature is 80 °C, and the dehumidifier column height of 4.5 cm. The study results revealed an enhanced system’s performance compared to other sweeping gas membrane distillation systems in the literature, which is very promising.

Design of an integrated membrane system to produce dairy by‐product from waste processing

SummaryMembrane technology is used in different applications. In this work, a whey‐based product with a final protein content of 16% has been formulated from Scotta – the last waste of the dairy industry – by cross‐flow ultrafiltration (UF) membrane followed by vacuum evaporation (EV). Until now, Scotta was only revalorized in conjunction with whey and into the biogas production process. It was never revalorized as food in the food supply chain. UF and EV processes led to an overall water amount removed from the whey of 84.9%. A vertical configuration of the polyethersulfone (PES) hollow‐fibre membrane was used in the OUT‐to‐IN structure. At 1.50 bar of pressure with 120 min of time interval, higher permeate flow decay has been obtained with a further reduction of the microbiological environments. A combination of intermediate and standard blocking seems to happen in all membranes, but concentration polarisation (CP) may be neglected for membranes with high fibres. The best EV operating conditions have been obtained at ten bars, with 37°C of the heating bath and 2.5 h of time, further preventing microorganism formation and protein denaturation. For future applications of Scotta revalorized in a food, it would be interesting to investigate the use of the multistage methods of membrane and evaporators to obtain a low specific energy consumption and to reduce costs further.

Cu-mediated optimization of PbO2 anodes for electrochemical treatment of electroless nickel plating wastewater

Effective removal of Ni(Ⅱ)-organic complexes from electroless nickel plating wastewater remains a challenge by conventional industrial effluent treatment processes. In this study, electrochemical oxidation using a PbO2 anode is proposed for effective decomplexation of Ni-organic complexes. The electrode quality and electrocatalytic capability of the PbO2 anode is shown to be greatly affected by the nature of the PbO2 active layer that is formed during the electrodeposition process with the current density, cathode material and electrolyte constitutions all exerting an influence on the Pb deposition behavior. Our investigations reveal that the presence of Cu2+ in the electrolyte can precisely control the amount of elemental Pb formed with Pb cathodic reduction and deposition prevented as a result of preferential Cu0 deposition. The doping of PbO2 with Cu significantly improved the morphology and electrocatalytic performance of the PbO2 deposit. Ni-citrate and TOC removal percentages of 83 % and 55 % respectively were achieved with the optimal Cu-doped PbO2 anode with 73 % of the Ni recovered at the cathode at a relatively low specific energy consumption of 12.7 kWh m−3. A possible mineralization pathway of Ni-citrate by the PbO2 anodic oxidation process is proposed.