Effect Of Recycle Ratio Research Articles

Effect of hydraulic retention time and effluent recycle ratio on biogas production from POME using UASB-HCPB fermentor assisted with ultrafiltration membrane at mesophilic condition

Biogas is renewable energy produced through anaerobic digestion based on palm oil mill effluent. Biogas production is overgrowing and is carried out in various bioreactors, such as the Upflow Anaerobic Sludge Blanket - Hollow Centered Packed Bed fermentor. Even though this process is considered successful in producing biogas, it has not adopted a recycling system. Therefore, the remaining sludge (effluent) after the processing process is generally not reused and is thrown into the environment, which still has the opportunity to produce biogas. The combination of the performance of the the Upflow Anaerobic Sludge Blanket - Hollow Centered Packed Bed fermentor with an ultrafiltration membrane is one of the latest innovations to reduce the volume of effluent wasted through recycling the effluent (retentate) into the feed tank. This research aims to produce biogas from liquid waste from palm oil mills using an Up-flow Anaerobic Sludge Blanket-Hollow Centered Packed Bed fermentor combined with ultrafiltration membranes under mesophilic conditions. In this research examines the effect of hydraulic retention time and the effluent recycling ratio on the pH profile, alkalinity, production, biogas composition, and kinetics of biogas production. The research began with loading up by varying the hydraulic retention time, namely 40, 25, and 10, until reaching the target hydraulic retention time of 6 days in a 5.4 L fermentor with a pH of 7 ± 0.2 under mesophilic conditions. Next, the effect of the recycling ratio was studied by varying the effluent (retentate) recycling ratio, namely 0, 15, and 25 %. The parameters analyzed are pH, M-Alkalinity, total solids, volatile solids, total suspended solids, volatile suspended solids, chemical oxygen demand, volume, and biogas composition. The organic content in the substrate is used as a kinetic parameter for biogas production using the modified Gompertz, Logistic, and Monod kinetic equation. The research results show that in mesophilic conditions, a recycling ratio of 25 % shows better results compared to ratios of 0 and 15 % where biogas production is 20×10-5 L/mgVS.day, with a best composition of methane, carbon dioxide and hydrogen sulfide each of 88.2; 10.8; and 0.07 % (v/v), with ΔVS decomposition at 15 % and 25 % recycle ratio of 42.50 and 45.83 % (w/v). The equation for the biogas production rate constant as a function of temperature obtained is the biogas production rate constant: M=299.81+exp(14.28299.8(0.39−t)+2) for logistic model, M=27.2xs2.46+s for monod model, M=250.1×exp{−exp[1.85.e250.1(0.42−t)+1]} for Gompertz modified kinetic model. Based on the scanning electron microscope results, it can be seen that the membrane used is an ultrafiltration membrane type, with a characteristic thickness of 7-8 µm and a pore size of 100–300 nm. The scanning electron microscope results also show that effluent contaminants deposition in the inner layer (spinger membrane) and deformation of the spinger structure are driven by forces during the effluent recycling process. The results obtained in this research show that this condition provides a clean, effective, and low-energy biogas production system that can be optimistically applied to the national palm oil industry power generation system.

New insight into continuous recirculation-process for treating arsenate using bacterial biosorbent

In this study, a new recirculation column reactor system for arsenate removal using a polyethylenimine coated bacterial biosorbent was developed. Solution pH was the most important factor in process design and operation. In order to control and optimize solution pH favorable for arsenate removal, a pH control and recirculation system was added to a column reactor. The effects of recycle ratio, initial arsenate concentration, and flow rate on the arsenate removal performance of the developed process were examined. Thomas and Yoon-Nelson models were used to interpret the breakthrough curve of arsenate removal. The maximum arsenate adsorption amount of the new reactor was determined to be 50.86 mg/g by the Thomas model. Importantly, the new reactor showed unimpeded adsorption performance compared with that in the batch experiments. The desorption study also showed excellent reusability. The results indicated that the newly developed process could be a promising application prospect for removing arsenate.

Effect of recycle ratio on methanogenic anaerobic digestion of palm oil mill effluent (POME) in a stirred tank reactor assisted by ultrafiltration membrane into biogas in transition conditions

The purpose of this study is to increase the conversion of biogas production using digester type CSTR by recycling the effluent through ultrafiltration membrane at transition conditions (45°C). In this research was investigated the effect of recycle ratio on the pH profile, alkalinity, production, and biogas composition produced. Initially, the suitable loading up was determined by varying HRT at 25, 15, 10, and 6 days in 2 L CSTR with agitation rate 250 rpm, pH 7 ± 0.2, and at temperature of 45°C. Furthermore, the effect of the recycle ratio was determined by varying the recycle ratio, i.e. 0, 15, and 25%. Analysis of total solids (TS), volatile solids (VS), total suspended solids (TSS), volatile suspended solids (VSS), and chemical oxygen demand (COD) were carried out to study the changes of organic compounds that were converted into biogas. Gas analysis is also carried out by measuring the volume and composition of the biogas produced. The highest total biogas production was achieved at 25% recycle ratio of 33.15 x 10-2 L/g.VS.day, with the composition of methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S) were 79; 19; and 0.006% respectively.

Parametric study of heat transfer enhancement on cross-flow heat exchangers

Energy crisis is increasingly serious all over the world, therefore, energy saving and efficiency enhancement is on the focus. Technology in heat transfer enhancement, which can improve efficiency of heat exchangers, is always attached importance to by scientists and engineers. Heat exchangers with recycle means a part of worked fluid is delivered by a pump to the inlet port and mixed with incoming working fluid to achieve larger convective heat transfer coefficient.In this research, cross-flow heat exchangers with external and internal recycles were investigated in the laminar regime respectively. Mathematical models of heat exchangers were established to study its thermo-hydraulic performances. The effects of recycle ratio, capacitance rate ratio and heat transfer area were investigated. The results demonstrate that the dimensionless heat transfer rate rises with the increase of recycle ratio R or capacitance rate ratio C2/C1, or with the decrease of heat transfer area A. The maximum increase of efficiency reached up to 28% and 21% for internal and external recycles, respectively.

Modeling and simulation of CO methanation process for renewable electricity storage

In this paper, a new approach of converting renewable electricity into methane via syngas (a mixture of CO and H2) and CO methanation is presented. Surplus of electricity is used to electrolyze H2O and CO2 to H2 and CO by using a SOEC (Solid Oxide Electrolysis Cell). Syngas produced is then converted into methane. When high consumption peaks appear, methane is used to produce electricity. The main conversion step in this process is CO methanation. A modeling of catalytic fixed bed methanation reactor and a design of methanation unit composed of multistage adiabatic reactors are carried out using Aspen plus™ software. The model was validated by comparing the simulated results of gas composition (CH4, CO, CO2 and H2) with industrial data. In addition, the effects of recycle ratio on adiabatic reactor stages, outlet temperature, and H2 and CO conversions are carefully investigated. It is found that for storing 10 MW of renewable electricity, methanation unit is composed of three adiabatic reactors with recycle loop and intermediate cooling at 553 K and 1.5 MPa. The methanation unit generates 3778.6 kg/h of steam at 523.2 K and 1 MPa (13.67 MW).

Effect of recycle ratio on the cost of natural gas processing in countercurrent hollow fiber membrane system

The separation of the countercurrent hollow fiber membrane module has been characterized adapting a “Multi-component Progressive Cell Balance” approach and incorporated within the Aspen HYSYS process simulator. The simulated data is found to exhibit good accordance with published experimental result. The study of the double staged membrane module with permeate recycle system, which was proposed to be the optimum configuration in previous works, has been extended by altering the recycle ratio of the permeate stream to study the process economics. Parameter sensitivities of typical membrane selectivity and CO2 feed concentration adapted in industrial application have been conducted. The study of high CO2 content is highlighted since it represents the future expansion of natural gas extraction considering that most of the remaining fields contain high concentration. It is observed that the recycle ratio is an important parameter to be considered in the industrial design process since it affects the gas processing cost significantly. Increasing the recycle ratio is proposed to increase the membrane area and compressor power while improving the hydrocarbon recovery, with substantial impact observed at low selectivity membrane and high CO2 feed concentration. A tradeoff must be determined among these parameters for determination of the optimal recycle ratio configuration.

Bifurcation analysis of two continuous bioreactors operated in series with recycle

In this paper, bifurcation analysis has been carried out for two continuous bioreactors operated in series with recycle from the second reactor. The existence of multiplicity of steady states is analyzed by considering Contois growth kinetics in the process model. It was observed that there exist two possible steady states of which one is trivial (wash out condition). Stability analysis is carried out to determine the stability of these steady states and it was observed that both these steady states are unstable in nature. Bifurcation analysis has been carried out for substrate and biomass concentration with dilution rate as the bifurcation parameter. Effect of recycle ratio, substrate separation factor and biomass separation factor is studied and analyzed. It was observed that Hopf bifurcation occurs at a dilution rate of 1.0208 with purely imaginary Eigen values which showed that sustained oscillatory behavior exists in the substrate concentration of the second reactor. The significance of different bifurcation points and the operating conditions by considering biomass and substrate concentrations in each reactor is studied and it was observed that the bioreactors need to be operated at intermediate dilution rates to obtain improved conversion and yield.

Simultaneous C and N removal from saline salmon effluents in filter reactors comprising anoxic-anaerobic-aerobic processes: Effect of recycle ratio

Salmon processing generates saline effluents with high protein load. To treat these effluents, three compact tubular filter reactors were installed and an integrated anoxic/anaerobic/aerobic process was developed with recycling flow from the reactor's exit to the inlet stream in order to save organic matter (OM) for denitrification. The reactors were aerated in the upper section with recycle ratios (RR) of 0, 2, and 10, respectively, at 30°C. A tubular reactor behave as a plug flow reactor when RR = 0, and as a mixed flow reactor when recycle increases, thus, different RR values were used to evaluate how it affects the product distribution and the global performance. Diluted salmon process effluent was prepared as substrate. Using loads of 1.0 kg COD m−3d−1 and 0.15 kg total Kjeldahl nitrogen (TKN) m−3d−1 at HRT of 2 d, 100% removal efficiencies for nitrite and nitrate were achieved in the anoxic-denitrifying section without effect of the dissolved oxygen in the recycled flow on denitrification. Removals >98% for total organic carbon (TOC) was achieved in the three reactors. The RR had no effect on the TOC removal; nevertheless a higher efficiency in total nitrogen removal in the reactor with the highest recycle ratio was observed: 94.3% for RR = 10 and 46.6% for RR = 2. Results showed that the proposed layout with an alternative distribution in a compact reactor can efficiently treat high organic carbon and nitrogen concentrations from a saline fish effluent with OM savings in denitrification.

Effect of recycle ratio on performance of pre-denitrification moving bed biofilm reactors in treating coal gasification wastewater

AbstractA lab-scale sequential anoxic moving bed biofilm reactor (ANMBBR) and aerobic moving bed biofilm reactor (AEMBBR) for pre-denitrification system were used to treat real coal gasification wastewater. Removal efficiencies of COD, phenols, thiocyanate (SCN−), ammonium (–N), and total nitrogen (TN) were investigated at different recycle ratios, and then NaHCO3 was added into the inlet of the AEMBBR to promote nitrification. Maximal removal efficiencies of COD, phenols, and SCN− were 84.2, 88, and 99.9% at a recycle ratio of 3.0, respectively. –N and TN removal efficiencies could achieve 97.4 and 78.2% with the addition of NaHCO3 (3 g NaHCO3 per day). Concentrations of –N and –N were always below 0.2 mg/L in the effluent of the ANMBBR. –N accumulation could be observed in the effluent of the AEMBBR after adding NaHCO3.

Effect of Recycle Ratio and Hydraulic Retention Time on the Performance of Extended Aeration Activated Sludge

Three laboratory scale units are designed and constructed in order to perform the present work. These units are capable of working under different hydraulic retention time (HRT) (16-32hrs), recycle ratio (0.25–1.5), and temperature (20 -35 ̊C). The results show that BOD5, COD, NO3-1, PO4-3 removal is increased with increasing HRT and recycle ratio under different temperatures. The maximum removal efficiency of COD and BOD5 is 97.16 % and 97.99 % respectively under 24 hrs retention time, 1.5 recycle ratio and 20 ̊C. However, the maximum removal efficiency of NO3-1 (83 %) was obtained under the same mentioned condition except temperature which was 35 ̊C. The maximum removal efficiency of PO4-3 (76.59 %) is obtained at 32hrs HRT, 1.25 recycle ratio, and 20 ̊C. It is obvious from the results of the present work that BOD5, COD, and NO3-1 removal increased with increasing temperature while; PO4-3 removal is decreased with increasing temperature.

Performance improvement of wire mesh packed double-pass solar air heaters with external recycle

The device performance of the new design of wire mesh packed double-pass solar air heaters with attaching wire mesh under external recycle was investigated experimentally and theoretically. The improvement of device performance of wire mesh packed solar air heaters with different flow patterns is represented graphically and compared, including the single-pass, flat-plate double-pass with recycle and wire mesh packed double-pass with recycle. Heat transfer improvement is considerably obtained by employing such a recyclic double-pass with wire mesh packed, instead of using the flat-plate single-pass operation. The wire mesh packed double-pass device introduced in this study was proposed for aiming to strengthen the convective heat transfer coefficient for air flowing through the wire mesh packed bed, and to determine the optimal design on an economic consideration in terms of both heat transfer efficiency improvement and power consumption increment. The effect of recycle ratio on the heat transfer efficiency enhancement as well as the power consumption increment has been also delineated.

Heterogeneous Modeling, Identification and Simulation of Activated Sludge Processes

Problem statement: The activated sludge system is a complex dynamic process and must account for a large number of reactions between large numbers of components. There is necessity for simulation models which describe the dynamic behavior of the activated sludge process. The application of the models in most treatment plants is limited due to lack of appropriate data acquisition and parameters identification studies. To realize this, an improvement of the operating strategies of Waste-Water Treatment Plants (WWTP) is required. The objectives of this study were to: (i) To build a process model considering mass transfer limitations and simulate an existing plant (Helwan WWTP) and validate the results using data from another existing plant with (Zenine WWTP). (ii) To adjust the model kinetic parameters of the biochemical reactions under the effect of mass transfer conditions to be prepared for simulation purposes. (iii) Study the effect of the operating conditions on the removal efficiency of both substrate and ammonia. Approach: A process model of the process was built considering mass transfer limitations and the three growth processes: Carbon oxidation, nitrification and denitrification. Helwan WWTP was used in order to extract the suitable stoichiometric and kinetic parameters to be used for the simulation. Helwan WWTP was used through the simulation results of the substrate (BOD) and ammonia. Egyptian Zenine WWTP was used for the testing and validation of the process model through predicting the response of substrate. Results: The average error of the removal efficiency in Helwan WWTP reached 3.3% for the substrate and 12.5% for the ammonia while the average error of the removal efficiency in Zenine WWTP of substrate reached 4.6%. The effects of recycle ratio, flow rate and influent substrate concentrations on the removal efficiency of the aeration tank were studied. It was found that the removal efficiency of substrate and ammonia was increased by increasing the recycle ratio, influent substrate concentrations and also increased by decreasing influent flow rates. It was found also that the sludge age increased by increasing the recycle ratio and decreased by decreasing the influent flow rates. Conclusion: The heterogeneous process model was able to describe the characteristics and reflects the real phenomena existing in activated sludge processes.

Effect of internal recycle on the nitrogen removal efficiency of an anaerobic/anoxic/oxic (A 2/O) wastewater treatment plant (WWTP)

Internal recycle ratio is an important parameter in anaerobic/anoxic/oxic (A 2/O) wastewater treatment plant (WWTP) operation. An increase in this ratio decreases nitrate and nitrite concentration in the effluent and hence improves the nitrogen removal efficiency, even though the economical cost increases simultaneously. Determining the most favourable recycle ratio taking into account both considerations is an important item in A 2/O WWTP operational optimisation. In this work, the effect of recycle ratio on nitrogen removal when using different influent nitrogen loads was tested in a pilot A 2/O WWTP. Experimental results obtained show how increasing the internal recycle ratio from 0 to 5 produced a 12% increase in nitrogen removal. This increase was achieved by improving N–NO x removal by 9% with an increase in N–NH 4 + removal of 3%.

The effect of recycle ratio on nitrogen removal in the combined pre‐denitrification/nitrification biofilter system

The effect of recycle ratio on nitrogen removal in the combined pre‐denitrification/nitrification biofilter system

Studies on Cephalosporin-C production using immobilised cells of Cephalosporium acremonium in a packed bed reactor

The production of the β-lactam antibiotic, Cephalosporin-C in a packed bed bioreactor was studied using Cephalosporium acremonium immobilised in calcium alginate, bagasse, and silk sachets. The specific β-lactam antibiotic production rate of immobilised cells was about 120%, 125% and 133% at 100 h (free cells 100%) for calcium alginate, bagasse and silk sachets, respectively. A cells-to-carrier ratio of 3:2 was found to be optimum throughout these studies. The effect of recycle ratio indicated diffusion barriers to substrate transport.

Modeling of Axial and Recycle Backmixing Effects in a Biological Packed Bed Loop Reactor

A theoretical model for a packed bed biological loop reactor is presented by considering both external and internal resistances for the general case of Monod kinetics. Numerical solutions have been obtained by the method of orthogonal collocation for a wide range of saturation parameters to cover the two limiting cases of zero-order and first-order kinetics. The numerical solutions for the limiting cases were found to show good agreement with the analytical solutions. The effects of recycle ratio and axial dispersion on the performance of the reactor were studied parametrically. The results show that for low recycle ratios the conversion increases with decrease in Peclet number for first-order and Monod type kinetics; for zero-order kinetics, however, the conversion is independent of both Peclet number and recycle ratio. The effectiveness factor profiles along the length of the reactor were compared for Monod kinetics. It was found that an increase in recycle ratio tends to flatten the profile. The effect of axial dispersion on the concentration profiles at higher recycle ratio was found to be negligible. The dynamics of how steady state conditions are achieved in the reactor is also presented.

Oscillations during CO oxidation over supported metal catalysts: II. Effects of reactor operating conditions on oscillatory behavior for a [formula omitted] catalyst

The oscillatory behavior occurring during CO oxidation over a (PtPd) γ-Al 2O 3 catalyst was studied in an isothermal recycle reactor. The effects of recycle ratio (0–50), gas phase temperature (373–423 K), feed composition (0.053–0.43 mole% CO, 50–99% O 2), feed flow rate (78–445 μmol/s), and reactor pressure (0.1–0.2 MPa) were examined. Care was taken to ensure that the catalytic activity remained constant throughout the investigation. The results indicate that oscillations are caused by changes in the rate controlling step coupled with heating of the metal crystallites to temperatures above those of the support and gas phase. It is proposed that the rate controlling step changes from oxygen adsorption to surface reaction followed by rapid burn-off (ignition) of adsorbed CO and oxygen.