Continuous-stirred Tank Research Articles

The use of co-digested solid fraction as feedstock for biogas plants

A comparative study was set up in order to assess the technical feasibility of the long-term reuse of the mechanically separated co-digested solid fraction as a feedstock for anaerobic digestion plants (ADP). The biogas yields of two feedstock mixtures (A and B) were assessed in mesophilic conditions (40°C±2°C) using 6 lab-scale continuous stirredtank reactors. Feedstock mixture A (control) consisted of pig slurry (70%), farmyard manure (4%), sorghum silage (12%) and maize silage (14%). Feedstock mixture B was the same as the control plus the solid fraction derived from the mechanical separation of the output raw codigestate collected from the reactors. All reactors were fed simultaneously, three times a week, over a period of nine month. According to the study results, the reuse of the co-digested solid fraction as feedstock for ADP could increase the methane yield by approximately 4%. However, ADP efficiency evaluation (<em>e.g.</em>, daily yield of methane per m<sup>3</sup> of digester) suggests limiting this practice to a maximum time period of 120 days.

P241 Évaluation in vitro d’une nouvelle gamme de pompes pour nutrition entérale

The majority of work on chance constrained model predictive control (MPC) for stochastic systems adopts the concept of implicit constraint backoffs for handling state chance constraints. However, implicit backoffs cannot be computed analytically in nonlinear MPC (NMPC), so that they must be approximated and, as a result, chance constraints are not guaranteed by the closed-loop system. This paper proposes a strategy for explicit computation of constraint backoffs that allows tightly guaranteeing chance constraints in NMPC for stochastic systems with arbitrary uncertainty distributions. The proposed method relies on uncertainty propagation through closed-loop system dynamics. Thus, this paper also investigates the use of stochastic surrogate models for constructing the distribution of closed-loop quantities of interest such as state constraint functions or any general performance objectives. To this end, an extension of polynomial chaos that can handle arbitrary probability measures is proposed for a class of disturbance models representing plant-model mismatch. The proposed methods are illustrated on a benchmark continuously-stirred tank reactor problem.

Ostéosynthèse percutanée temporaire et greffe antérieure sélective dans les fractures thoracolombaires

In this preliminary investigation, a so-called Blenke cascade and plate heat exchanger bioreactor configuration were compared in terms of mixing characteristics, contamination free process, operational power costs and overall performance. At room temperature, fermentation was initially started as batch run and switched to continuous operation, when the residual sugars within the reactor were detected to be C ⩽ 1% (g/L). Samples from both configurations were taken and analyzed for ethanol and residual sugar content, as well as for any infection of the fermentation and lactic acid content, respectively. Mixing characteristics were studied by the residence time distribution method. Both geometries behaved as a finite number n of continuous stirred tanks in series, behaving as a plug flow with superimposed axial dispersion. The number of tanks in series n obtained in the plate heat exchanger configuration was 1.5–3 times larger than those in the Blenke cascade. The average ethanol productivity was Qp = 3.07 (g/L h) and Qp = 2.31 (g/L h) for cascade and plate exchanger configuration, respectively. The analysis of operational power costs indicates relevant differences between the two reactors at laboratory scale; however, systems with different types of pumps and viscosities are compared. From an industrial scale point of view, specific operational costs decrease with scale-up, as no mechanical mixing is needed in the fermenters.

Evaluation of Packed-Bed Reactor and Continuous Stirred Tank Reactor for the Production of Colchicine Derivatives

Bioconversion of colchicine into its pharmacologically active derivative 3-demethylated colchicine (3-DMC) mediated by P450BM3 enzyme is an economic and promising strategy for the production of this inexpensive and potent anticancer drug. Continuous stirred tank reactor (CSTR) and packed-bed reactor (PBR) of 3 L and 2 L total volumes were compared for the production of 3-demethylated colchicine (3-DMC) a colchicine derivative using Bacillus megaterium MTCC*420 under aerobic conditions. Statistical optimization technique was utilized with the most significant variables, that is, dissolved oxygen (DO), colchicine concentration, and process time for optimization. The validation of the model was performed by experiments on the predicted values in an individual run, and the optimum parameters were DO (~50%), colchicine concentration (7.5 g/L), and process time (39 h) resulted in a maximum bioconversion of 3-DMC 3.36 g/L. The PBR reactor achieved much higher productivity (6.58 g/L/h) as reported by earlier researchers. This is the first report on the use of PBR for bioconversion of colchicine.

Overview of the Oldest Existing Set of Substrate-optimized Anaerobic Processes: Digestive Tracts

Over millions of years, living organisms have explored and optimized the digestion of a wide variety of substrates. Engineers who develop anaerobic digestion processes for waste treatment and energy production can learn much from this accumulated ‘experience’. The aim of this work is a survey based on the comparison of 190 digestive tracts (vertebrate and insect) considered as ‘reactors’ and their anaerobic processes. Within a digestive tract, each organ is modeled as a type of reactor (continuous stirred-tank, such reactors in series, plug-flow or batch) associated with chemical aspects such as pH or enzymes. Based on this analysis, each complete digestion process has been rebuilt and classified in accordance with basic structures which take into account the relative size of the different reactors. The results show that all animal digestive structures can be grouped within four basic types. Size and/or position in the structure of the different reactors (pre/post treatment and anaerobic microbial digestion) are closely correlated to the degradability of the feed (substrate). Major common features are: (i) grinding, (ii) an extreme pH compartment, and (iii) correlation between the size of the microbial compartment and the degradability of the feed. Thus, shared answers found by animals during their evolution can be a source of inspiration for engineers in designing optimal anaerobic processes.

An evaluation of different bioreactor configurations for continuous bio-ethanol production

In this preliminary investigation, a so-called Blenke cascade and plate heat exchanger bioreactor configuration were compared in terms of mixing characteristics, contamination free process, operational power costs and overall performance. At room temperature, fermentation was initially started as batch run and switched to continuous operation, when the residual sugars within the reactor were detected to be C⩽1% (g/L). Samples from both configurations were taken and analyzed for ethanol and residual sugar content, as well as for any infection of the fermentation and lactic acid content, respectively. Mixing characteristics were studied by the residence time distribution method. Both geometries behaved as a finite number n of continuous stirred tanks in series, behaving as a plug flow with superimposed axial dispersion. The number of tanks in series n obtained in the plate heat exchanger configuration was 1.5–3 times larger than those in the Blenke cascade. The average ethanol productivity was Qp=3.07 (g/Lh) and Qp=2.31 (g/Lh) for cascade and plate exchanger configuration, respectively. The analysis of operational power costs indicates relevant differences between the two reactors at laboratory scale; however, systems with different types of pumps and viscosities are compared. From an industrial scale point of view, specific operational costs decrease with scale-up, as no mechanical mixing is needed in the fermenters.

Effect of temperature and hydraulic retention time on volatile fatty acid production based on bacterial community structure in anaerobic acidogenesis using swine wastewater

To investigate the effect of hydraulic retention time (HRT) and temperature (T) on bacterial community structure and volatile fatty acids (VFAs) production of an acidogenic process, and VFA production and changes in the bacterial community in three identical automated anaerobic continuously-stirred tank reactors were analyzed using response surface analysis (RSA) and nonmetric multidimensional scaling (NMDS). For RSA, 11 trials were conducted to find the combination of T and HRT under which VFA production was greatest; VFA production was affected more by HRT than by T. To identify the bacterial community structure in each trial, DNA from each experimental point of the RSA was analyzed using denaturating gradient gel electrophoresis (DGGE), and eight bacteria species were detected. NMDS was conducted on band intensities obtained using DGGE, and bacterial community structure was affected more by T than by HRT. Taken together, these results suggest that VFA production during acidogenesis was more dependent on the physicochemical properties of acidogens, such as their specific growth rate or contact time with of substrates, than on changes in the microbial community.

Pilot-Scale Removal of Trace Steroid Hormones and Pharmaceuticals and Personal Care Products from Municipal Wastewater Using a Heterogeneous Fenton’s Catalytic Process

The pollution of water sources by endocrine disrupting compounds (EDCs) and pharmaceutical and personal care products (PPCPs) is a growing concern, as conventional municipal wastewater treatment systems are not capable of completely removing these contaminants. A continuous stir tank reactor incorporating a modified polyacrylonitrile (PAN) catalyst and dosed with hydrogen peroxide in a heterogeneous Fenton’s process was used at pilot scale to remove these compounds from wastewater that has undergone previous treatment via a conventional wastewater treatment system. The treatment system was effective at ambient temperature and at the natural pH of the wastewater. High levels of both natural and synthetic hormones (EDCs) and PPCPs were found in the effluent after biological treatment of the wastewater. The treatment system incorporating the modified PAN catalyst/H2O2decomposed >90% of the EDCs and >40% of PPCPs using 200 mgL−1H2O2, 3 hr residence time. The estrogenic potency EE2-EQ was removed by 82.77%, 91.36%, and 96.13% from three different wastewater treatment plants. BOD was completely removed (below detection limits); 30%–40% mineralisation was achieved and turbidity reduced by more than 68%. There was a <4% loss in iron content on the catalyst over the study period, suggesting negligible leaching of the catalyst.

Characterization of Dissolved Organic Matter in Full Scale Continuous Stirred Tank Biogas Reactors Using Ultrahigh Resolution Mass Spectrometry: A Qualitative Overview

Dissolved organic matter (DOM) was characterized in eight full scale continuous stirred tank biogas reactors (CSTBR) using solid-phase extraction and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). An overview of the DOM molecular complexity in the samples from biogas reactors with conventional operational conditions and various substrate profiles is provided by assignments of unambiguous exact molecular formulas for each measured mass peak. Analysis of triplicate samples for each reactor demonstrated the reproducibility of the solid-phase extraction procedure and ESI-FT-ICR-MS which allowed precise evaluation of the DOM molecular differences among the different reactors. Cluster analysis on mass spectrometric data set showed that the biogas reactors treating sewage sludge had distinctly different DOM characteristics compared to the codigesters treating a combination of organic wastes. Furthermore, the samples from thermophilic and mesophilic codigesters had different DOM composition in terms of identified masses and corresponding intensities. Despite the differences, the results demonstrated that compositionally linked organic compounds comprising 28-59% of the total number of assigned formulas for the samples were shared in all the reactors. This suggested that the shared assigned formulas in studied CSTBRs might be related to common biochemical transformation in anaerobic digestion process and therefore, performance of the CSTBRs.

Uraninite oxidation and dissolution induced by manganese oxide: A redox reaction between two insoluble minerals

The longevity of subsurface U(IV) produced by reduction of U(VI) during in situ bioremediation can be limited by reoxidation to more mobile U(VI) species. Coupling of the biogeochemical cycles of U and Mn may affect the fate and transport of uranium. Manganese oxides can act as a powerful oxidant that accelerates the oxidative dissolution of UO2. This study investigated the physical and chemical factors controlling the interaction between UO2 and MnO2, which are both poorly soluble minerals. A multi-chamber reactor with a permeable membrane was used to eliminate direct contact of the two minerals while still allowing transport of aqueous species. The oxidation of UO2 was not significantly enhanced by MnO2 if the two solids were physically separated. Complete mixing of MnO2 with UO2 led to a much greater extent and rate of U oxidation. When direct contact is not possible, the reaction slowly progresses through release of soluble U(IV) with its adsorption and oxidation on MnO2. Continuously-stirred tank reactors (CSTRs) were used to quantify the steady-state rates of UO2 dissolution induced by MnO2. MnO2 dramatically promoted UO2 dissolution, but the degree of promotion leveled off once the MnO2:UO2 ratio exceeded a critical value. Substantial amounts of U(VI) and Mn(II) were retained on MnO2 surfaces. The total production of Mn(II) was less than that of U(VI), indicating that the fate of Mn products and their impact on UO2–MnO2 reaction kinetics were complicated and may involve formation of Mn(III) phases. At higher dissolved inorganic carbon concentrations, UO2 oxidation by MnO2 was faster and less U(VI) was adsorbed to MnO2. Such an inverse relationship suggested that U(VI) may passivate MnO2 surfaces. A conceptual model was developed to describe the oxidation rate of UO2 by MnO2. This model is potentially applicable to a broad range of water chemistry conditions and is relevant to other environmental redox processes involving two poorly soluble minerals.

Kinetics of lead(IV) oxide (PbO2) reductive dissolution: Role of lead(II) adsorption and surface speciation

Lead(IV) oxide (PbO2) is a corrosion product on lead pipes used for drinking water distribution, and its dissolution can control lead release to drinking water. This study evaluated the adsorption of Pb(II) to PbO2 and its impact on the dissolution rate of PbO2. The dissolution rate of PbO2 was determined as a function of pH in the absence and presence of free chlorine using continuously-stirred tank reactors. Pb(II) adsorption was examined as a function of pH and initial Pb(II) concentrations. The dissolution rate of PbO2 increased with decreasing pH. The presence of free chlorine inhibited PbO2 dissolution. The dissolution of PbO2 involves a coupled reduction–detachment process, and a model was developed that accounts for the adsorption of Pb(II) from the reduction. The extent of Pb(II) adsorption to PbO2 increased with increasing pH and Pb(II) concentrations until reaching a plateau. Adsorption was interpreted with a surface complexation model using the diffuse double-layer model and a single surface complex. The dissolution rate of PbO2 was directly related to the distribution of the PbO2 surface species predicted by the surface complexation model. The dissolution rate was predominantly controlled by >Pb(IV)OH2+ for acidic conditions and by>Pb(IV)OH and>Pb(IV)O− at neutral to basic conditions.

Effect of diffusive transport limitations on UO2 dissolution

The effects of diffusive transport limitations on the dissolution of UO2 were investigated using an artificial groundwater prepared to simulate the conditions at the Old Rifle aquifer site in Colorado, USA. Controlled batch, continuously-stirred tank (CSTR), and plug flow reactors were used to study UO2 dissolution in the absence and presence of diffusive limitations exerted by permeable sample cells. The net rate of uranium release following oxidative UO2 dissolution obtained from diffusion-limited batch experiments was ten times lower than that obtained for UO2 dissolution with no permeable sample cells. The release rate of uranium to bulk solution from UO2 contained in permeable sample cells under advective flow conditions was more than 100 times lower than that obtained from CSTR experiments without diffusive limitations. A 1-dimensional transport model was developed that could successfully simulate diffusion-limited release of U following oxidative UO2 dissolution with the dominant rate-limiting process being the transport of U(VI) out of the cells. Scanning electron microscopy, X-ray diffraction, and extended X-ray absorption fine structure spectroscopy (EXAFS) characterization of the UO2 solids recovered from batch experiments suggest that oxidative dissolution was more evident in the absence of diffusive limitations. Ca-EXAFS spectra indicate the presence of Ca in the reacted UO2 solids with a coordination environment similar to that of a Ca–O–Si mineral. The findings from this study advance our overall understanding of the coupling of geochemical and transport processes that can lead to differences in dissolution rates measured in the field and in laboratory experiments.

Methanogenic community dynamics in anaerobic co-digestion of fruit and vegetable waste and food waste

A lab-scale continuously-stirred tank reactor (CSTR), used for anaerobic co-digestion of fruit and vegetable waste (FVW) and food waste (FW) at different mixture ratios, was operated for 178 days at the organic loading rate of 3 kg VS (volatile solids)/(m3·day). The dynamics of the Archaeal community and the correlations between environmental variables and methanogenic community structure were analyzed by polymerase chain reactions – denaturing gradient gel electrophoresis (PCR-DGGE) and redundancy analysis (RDA), respectively. PCR-DGGE results demonstrated that the mixture ratio of FVW to FW altered the community composition of Archaea. As the FVW/FW ratio increased, Methanoculleus, Methanosaeta and Methanosarcina became the predominant methanogens in the community. Redundancy analysis results indicated that the shift of the methanogenic community was significantly correlated with the composition of acidogenic products and methane production yield. Different mixture ratios of substrates led to different compositions of intermediate metabolites, which may affect the methanogenic community. These results suggested that the analysis of microbial communities could be used to diagnose anaerobic processes.

Mitigating ammonia inhibition of thermophilic anaerobic treatment of digested piggery wastewater: Use of pH reduction, zeolite, biomass and humic acid

High free ammonia released during anaerobic digestion of livestock wastes is widely known to inhibit methanogenic microorganisms and result in low methane production. This was encountered during our earlier thermophilic semi-continuously fed continuously-stirred tank reactor (CSTR) treatment of piggery wastewater. This study explored chemical and biological means to mitigate ammonia inhibition on thermophilic anaerobic treatment of piggery wastewater with the aim to increase organic volatile carbon reduction and methane production. A series of thermophilic anaerobic batch experiments were conducted on the digested piggery effluent to investigate the effects of pH reduction (pH 8.3 to 7.5, 7.0 and 6.5) and additions of biomass (10% v/v and 19% v/v anaerobic digested piggery biomass and aerobic-anaerobic digested municipal biomass), natural zeolite (10, 15 and 20 g/L) and humic acid (1, 5 and 10 g/L) on methane production at 55 °C for 9–11 days. Reduction of the wastewater pH from its initial pH of 8.3 to 6.5 produced the greatest stimulation of methane production (3.4 fold) coupled with reductions in free ammonia (38 fold) and total volatile fatty acids (58% TVFA), particularly acetate and propionate. Addition of 10–20 g/L zeolite to piggery wastewater with and without pH reduction to 6.5 further enhanced total VFA reduction and methane production over their respective controls, with 20 g/L zeolite producing the highest enhancement effect despite the ammonia-nitrogen concentrations of the treated wastewaters remaining high. Without pH reduction, zeolite concentration up to 20 g/L was required to achieve comparable methane enhancement as the pH-reduced wastewater at pH 6.5. Although biomass (10% v/v piggery and municipal wastes) and low humic acid (1 and 5 g/L) additions enhanced total VFA reduction and methane production, they elevated the residual effluent total COD concentrations over the control wastewaters (pH-unadjusted and pH-reduced) unlike zeolite treatment. The outcomes from these batch experiments support the use of pH reduction to 6.5 and zeolite treatment (10–20 g/L) as effective strategies to mitigate ammonia inhibition of the thermophilic anaerobic treatment of piggery wastewater.

Fermentative hydrogen production from wastewaters: A review and prognosis

Biohydrogen is a promising candidate which can replace a part of our fossil fuels need in day-to-day life due its perceived environmental benefits and availability through dark fermentation of organic substrates. Moreover, advances in biohydrogen production technologies based on organic wastewater conversion could solve the issues related to food security, climate change, energy security and clean development in the future. An evaluation of studies reported on biohydrogen production from different wastewaters will be of immense importance in economizing production technologies. Here we have reviewed biohydrogen production yields and rates from different wastewaters using sludges and microbial consortiums and evaluated the feasibility of biohydrogen production from unexplored wastewaters and development of integrated bioenergy process. Biohydrogen production has been observed in the range of substrate concentration 0.25–160 g COD/L, pH 4–8, temperature 23–60 °C, HRT 0.5–72 h with various types of reactor configuration. The most efficient hydrogen production has been obtained at an organic loading rate (OLR) 320 g COD/L/d, substrate concentration 40 g COD/L, HRT 3 h, pH 5.5–6.0, temperature 35 °C in a continuously-stirred tank reactor system using mixed cultures and fed with condensed molasses fermentation soluble wastewater. The net energy efficiency analysis showed vinasse wastewater has the highest positive net energy gain followed by glycerin wastewater and domestic sewage as 140.39, 68.65, 51.84 kJ/g COD feedstock with the hydrogen yield (HY) of 10 mmol/g COD respectively.

Alternative Approach to Evaluate Sedimentation Performance of Stormwater Detention Basins Using a Nondimensionalized Time Scale

AbstractTo evaluate sediment removal in dry detention basins, one of the most frequently used Best Management Practices (BMPs), a particle pathline model using plug flow assumption was proposed in a previous study. The model requires numerical integration, thus it may not be convenient for quick evaluation and design of detention basins. To overcome the difficulty a simpler continuous stirring tank reactor (CSTR) model is proposed and used to compare outflow Suspended Sediment Concentrations (SSCs) from different size storms using a nondimensionalized time scale. The CSTR model satisfactorily predicts sediment removal and outflow SSC measured using a physical model. The paper presents the time nondimensionalization and CSTR model application processes and discusses the critical characteristics of the proposed models.

The FM01-LC reactor modeling using axial dispersion model with a reaction term coupled with a continuous stirred tank (CST)

This work is aimed at modeling the operation of the FM01-LC reactor coupled with a continuous stirred tank (CST) in recirculation mode. The parametric flow dispersion model with an electrochemical reaction limited by mass transfer coupled with Poisson (tertiary potential distribution) and CST equations are used to describe the performance of a FM01-LC reactor with 3D electrodes. Theoretical predictions for dispersion reaction coupled with CST showed a good agreement with the experimental data on depletion of electroactive species as a function of time and potential distribution, whereas these data have not been adequately described by the plug-flow model. Fluid dispersion obtained in the reaction zone (depending on the fluid flow velocities and geometric configuration), plays an important role in tertiary potential distribution.

Thermophilic fermentative hydrogen production from various carbon sources by anaerobic mixed cultures

In the present work, various carbon sources, xylose, glucose, galactose, sucrose, cellobiose, and starch were tested for thermophilic (60 °C) fermentative hydrogen production (FHP) by using the anaerobic mixed culture. An inoculum was obtained from a continuously-stirred tank reactor (CSTR) operated at pH 5.5 and HRT 12 h, and fed with tofu processing waste. The dominant species in the CSTR were found to be Thermoanaerobacterium thermosaccharolyticum and Clostridium thermosaccharolyticum, which are well known thermophilic H2-producers in anaerobic-state, and have the ability to utilize a wide range of carbohydrates. When initial pH was adjusted to 6.8 ± 0.1 but not controlled during fermentation, vigorous pH drop began within 5 h, and finally reached 4.0–4.5 in all carbon sources. Although over 90% of substrate removal was achieved for all carbon sources except cellobiose (71.7%), the fermentation performances were profoundly different with each other. Glucose, galactose, and sucrose exhibited relatively higher H2 yields whereas lower H2 yields were observed for xylose, cellobiose, and starch. On the other hand, when pH was controlled (pH ≥ 5.5), the fermentation performance was enhanced in all carbon sources but to a different extent. A substantial increase in H2 production was observed for cellobiose, a 1.9-fold increase of H2 yield along with a substrate removal increase to 93.8%, but a negligible increase for xylose. H2 production capabilities of all carbon sources tested were as follows: sucrose > galactose > glucose > cellobiose > starch > xylose. The maximum H2 yield of 3.17 mol H2/mol hexoseadded achieved from sucrose is equivalent to a 26.5% conversion of energy content in sucrose to H2. Acetic and butyric acids were the main liquid-state metabolites of all carbon sources while lactic acid was detected only in cellobiose, starch and xylose exhibiting relatively lower H2 yields.

Fermentative Hydrogen Production from Soybean Protein Processing Wastewater in an Anaerobic Baffled Reactor (ABR) Using Anaerobic Mixed Consortia

Fermentative H(2) production from soybean protein processing wastewater (SPPW) was investigated in a four-compartment anaerobic baffled reactor (ABR) using anaerobic mixed cultures under continuous flow condition in the present study. After being inoculated with aerobic activated sludge and operated at the inoculants of 5.98 gVSS L(-1), COD of 5000 mg L(-1), HRT of 16 h and temperature of (35 ± 1) °C for 22 days, the ABR achieved stable ethanol-type fermentation. The specific hydrogen production rate of anaerobic activated sludge was 165 LH(2)kg MLVSS(-1) day(-1), the substrate conversion rate was 600.83 LH(2)kg COD(-1)and the COD removal efficiency was 44.73% at the stable operation status. The ABR system exhibited a better stability and higher hydrogen yields than continuous stirring tank reactor under the same operational condition. The experimental data documented the feasibility of substrate degradation along with molecular H(2) generation utilizing SPPW as primary carbon source in the ABR system.

Concentration Control of CSTR using NNAPC

This paper presents a new advanced control algorithm for Concentration tracking of a continuous stirring tank reactor (CSTR). This algorithm called: Neural Network Approximate Generalized Predictive Control (NNAPC) that uses a combination of Artificial Neural Network (ANN) with Approximate Generalized Predictive Control technique (APC). This algorithm is based on the use of ANN as a nonlinear predictio n model of the CSTR. This modeling technique is done by using the data from the system input/output information without requiring the knowledge about CSTR parameters. The outputs of the neural predictor are the future values of the controlled variables nee ded by the optimization algorithm. Simulation results show the effectiveness of the proposed control method.