Estimating a change point in the long memory parameter

We propose an estimator of change point in the long memory parameter d of an ARFIMA(p, d, q) process using the sup Wald test. We derive the consistency and the rate of convergence of the estimator for the time of change. The convergence rate of our change point estimator depends on the magnitude of a shift. Furthermore, we obtain the limiting distribution of our change point estimator without depending on the distribution of the process. Therefore, we can construct confidence intervals for the change point. Simulations show the validity of the asymptotic theory of our estimator if the sample size is large enough. We apply our change point estimator to the yearly Nile river minimum water level.     

Effects of foam composition on the microstructure and piezoelectric properties of macroporous PZT ceramics from ultrastable particle-stabilized foams

Porous lead zirconate titanate (PZT) ceramics could be produced by combining the particle-stabilized foams and the gelcasting technique. In this study, the foaming capacity of particle-stabilized wet foams was tailored by changing the concentration of valeric acid and pH values of suspension. Accordingly, porous PZT ceramics with different porosity, microstructure, dielectric and piezoelectric properties were prepared with the respective wet foam. Increase in the porosity led to a reduction in the relative permittivity (ε_r), a moderate decline in the longitudinal piezoelectric strain coefficient (d₃₃) and a rapid decline in the transverse piezoelectric strain coefficient (d₃₁), which endowed porous PZT ceramics with a high value of hydrostatic strain coefficient (d_h) and hydrostatic figure of merit (HFOM). As a result, the prepared samples possessed a maximal HFOM value of 19,520×10^?15 Pa^?1 with the porosity of 76.3%. The acoustic impedance (Z) of specimens had the lowest value of 1.35 Mrayl, which could match well with those of water or biological tissue; accordingly, the material would be beneficial in underwater sonar detectors or medical ultrasonic imaging.     

Trap level analysis of Ce3+ and Sm3+ in Li6Y(BO3)3

The polycrystalline compounds of Li₆Y(BO₃)₃: Ce³⁺ and Sm³⁺ co-doped polycrystalline samples were prepared by using standard solid state reaction method. The energy levels of the doped lanthanide ions (Ce³⁺ and Sm³⁺) in the borate host materials were investigated by Thermoluminescence (TL) glow peak analysis. The co-doped samples, exhibits the TL peak at higher temperature region around 511?K whereas the Ce³⁺ individually doped sample has peak around 433?K. The X-ray excited emission spectra were carried out for all the prepared samples and found the characteristic emission bands. The trap depths (E) were calculated by using several standard methods, namely peak shape method or chen's (PS), variable heating rate (VHR), initial rise (IR) and computerized glow curve deconvolution (CGCD). The mean activation energy of the co-doped samples found to be 1.21 (0.07±) eV and the frequency factor around 1.38?×?10¹¹ Sec^?1. The calculated trap depths and the predicted energy level values were compared and found in good agreement. This primarily results suggest that the energy level scheme can help in the development of new TL materials suitable in dosimetry.     

Verification of necessity for bioaugmentation—lessons from two batch case studies for bioremediation of diesel‐contaminated soils

BACKGROUND: Two bio‐pile studies undertaken in a controlled laboratory were aimed at deciding optimal strategies to remediate two different artificial diesel‐contaminated soils. Bioaugmentation with various inoculations, biostimulation with various levels of biosurfactant rhamnolipid, and nutrient enhancement were the proposed remediation courses. RESULTS: In Case I, the average of the first‐order kinetic degradation rate constants during the first degradation stage for the bioaugmentation/biostimulation treatments was 0.0195 ± 0.0056 d^?1, which was about 2.6‐fold higher than that of the control batch (0.0075 d^?1). Conversely, in Case II, the rate constants for treatments with amendments and those for the control batch were found to be comparable, 0.0172 ± 0.0015 d^?1 and 0.0158 d^?1, respectively. Microarray results indicated a less diverse indigenous bacterial community in Case I and an abundant indigenous community in Case II, both from the control batches on Day 0. The dynamics of the two microbial communities, revealed by NMS plots, emphasized the similarity among the different treatments during the first degradation stage. CONCLUSIONS: Prior to a remediation project, the usefulness of a bioaugmentation approach can be investigated using an ITS oligonucliotide microarray. Results from the microarray answered why the bioaugmentation approach was useful in Case I, but not in Case II. The abundance of the diesel‐degrading community determined the usefulness of bioaugmentation. Relatively quantified TRFLP results analyzed via the NMS plots demonstrated comparable microbial communities during the first degradation stage, regardless of differences between the two batches. The bacterial community structure might shift with the availability of hydrocarbons. Copyright © 2009 Society of Chemical Industry     

Multiobjective optimization of microalgae (Chlorella sp.) growth in a photobioreactor using Box‐Behnken design approach

This study investigates a parameter optimization approach to maximize the specific growth rate of the Chlorella vulgaris microalgae species, its biomass productivity, and CO₂ capture rate. For this purpose, the Box‐Behnken experimental design technique is applied with temperature, nitrogen to phosphorus ratio, and light‐dark cycle per day, as the growth controlling parameters. For each response, a quadratic model is developed separately describing the algal specific growth rate, biomass productivity, and CO₂ capture rate, respectively. The maximum specific growth rate of 0.84 d^?1 is obtained at 25 °C, with a nitrogen to phosphorus ratio of 3.4:1, and light‐dark cycles of 24/0 h. Maximum biomass productivity of 147.3 mg L^?1 d^?1 is found at 30 °C, with a nitrogen to phosphorus ratio of 3:1, and light‐dark cycles of 12/12 h. In addition, the maximum CO₂ capture rate of 159.5 mg L^?1 d^?1 is also obtained at 30 °C, with a nitrogen to phosphorus ratio of 4:1, and light‐dark cycles of 23/1 h. Finally, a multi‐response optimization method is applied to maximize the specific growth rate, biomass productivity, and CO₂ capture rate, simultaneously. The optimal set of 30 °C, a nitrogen to phosphorus ratio 3:1, and light‐dark cycles 16/8 h, provide the maximum specific growth rate of 0.66 per day, biomass productivity of 147.6 mg L^?1 d^?1, and CO₂ capture rate of 141.7 mg L^?1 d^?1.

     

Thickness dependent growth and ferroelectric/dielectric properties of phase-pure 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thin film derived from a modified sol-gel process

Annealing parameter and thickness are two significant factors affecting microstructure and electrical performance of sol-gel derived 0.65Pb(Mg_1/3Nb_2/3)O₃?0.35PbTiO₃ (0.65PMN-0.35PT) thin film. In this paper, various durations are firstly selected for the investigations on annealing parameter of 0.65PMN-0.35PT thin film. Enhanced insulating and ferroelectric properties can be obtained for the film annealed for 1 min due to its phase-pure and homogeneous perovskite structure. Based on this, a series of 0.65PMN-0.35PT thin films with various thicknesses by modifying deposition layer are synthesized annealed for 1 min and the effects of thickness on crystalline, insulating, ferroelectric and dielectric properties are characterized. It reveals that thickness-dependent behavior can be noticed for 0.65PMN-0.35PT thin film with the results that the 8-layered film possesses a relative large remanent polarization (P_r) of 23.34 μC/cm², and reduced leakage current density of 10^?9 A/cm² with low dissipation factor (tanδ) of 0.03 can be achieved for the 14-layered film.     

Determination of potential methane production capacity of a granular sludge from a pilot‐scale upflow anaerobic sludge blanket reactor using a specific methanogenic activity test

A 450 dm³ pilot‐scale upflow anaerobic sludge blanket (UASB) reactor was used for the treatment of a fermentation‐based pharmaceutical wastewater. The UASB reactor performed well up to an organic loading rate (OLR) of 10.7 kg COD m^?3 d^?1 at which point 94% COD removal efficiency was achieved. This high treatment efficiency did not continue, however and the UASB reactor was then operated at lower OLRs for the remainder of the study. Specific methanogenic activity (SMA) tests were, therefore, carried out to determine the potential loading capacity of the UASB reactor. For this purpose, the SMA tests were carried out at four different initial acetate concentrations, namely 500 mg dm^?3, 1000 mg dm^?3, 1500 mg dm^?3 and 2000 mg dm^?3 so that substrate limitation could not occur. The results showed that the sludge sample taken from the UASB reactor (OLR of 6.1 kg COD m^?3 d^?1) had a potential acetoclastic methane production (PMP) rate of 72 cm³ CH₄ g^?1 VSS d^?1. When the PMP rate was compared with the actual methane production rate (AMP) of 67 cm³ CH₄ g^?1 VSS d^?1 obtained from the UASB reactor, the AMP/PMP ratio was found to be 0.94 which ensured that the UASB reactor was operated using its maximum potential acetoclastic methanogenic capacity. In order to achieve higher OLRs with desired COD removal efficiencies it was recommended that the UASB reactor should be loaded with suitable OLRs pre‐determined by SMA tests. © 2001 Society of Chemical Industry     

Colour removal from textile effluents using hardwood sawdust as an absorbent

Decolourisation of a dilute solution of a basic dyestuff was carried out by using hardwood sawdust as adsorbent. At 80°C 85% decolourisation occurred within 100 min at an initial concentration (C_o) of 200 mg dm^?3. There was a 44% reduction in contact time when the temperature was raised from 25 to 80°C. The rate parameter for different initial dye concentrations was found to follow the equation: k_co=4.20C_o^0.88 and the rate parameter for different mean diameter d_m followed the equation k_dm=4.1 (l/d_m)^0.135. The activation energy of the process was 9.83 kJ mol^?1 which shows that the rate controlling step is intraparticle diffusion.     

Two types of organophosphate pesticides and their combined effects on heterotrophic growth rates in activated sludge process

BACKGROUND: Pesticides are sometimes non‐biodegradable and, moreover, toxic to microorganisms. If pesticides exceed the tolerance of microorganisms, failure of the activated sludge process (ASP) occurs. Therefore the effects of two types of organophosphate pesticides on heterotrophic growth rate constant in sludge from ASP were investigated. Oxygen uptake rate was employed to measure the rate constants. RESULTS: The results indicated that the value of heterotrophic growth rate constant decreased from 3.88 d^?1 to 1.46 d^?1 or by 62% when 0.5 mg L^?1 of glyphosate was added. When adding 0.5 mg L^?1 of malathion, the value of heterotrophic growth rate constant decreased to 1.33 d^?1 or by 66%. The value of heterotrophic growth rate constant decreased to 1.98 d^?1 or by 49% when 0.5 mg L^?1 of pesticide combination (50% for each) was added. CONCLUSIONS: The inhibitory effects of glyphosate and malathion were in good agreement with non‐competitive inhibition kinetics, but pesticide combination did not follow non‐competitive kinetics. The inhibition coefficient values for glyphosate, malathion and their combination were 0.29, 0.29 and 0.58 mg L^?1, respectively. For comparison, linear and exponential types of models were derived by regression. According to non‐competitive kinetics, and linear and exponential models, the inhibitory effects of glyphosate and malathion were almost consistent. Finally, the degree of inhibition was simulated using different types of model. It was found that the toxicity of the two pesticides agreed with the antagonism well. Copyright © 2009 Society of Chemical Industry     

Measurement of the Surface Free Energy of Amorphous Cellulose by Alkane Adsorption: A Critical Evaluation of Inverse Gas Chromatography (IGC)

Surface energies of amorphous cellulose “beads” were measured by IGC at different temperatures (50 to 100°C) using n-alkane probes (pentane to undecane). The equation of Schultz and Lavielle was applied which relates the specific retention volume of the gas probe to the dispersive component of the surface energy of the solid and liquid, γ^d _s and γ^d _l, respectively, and a parameter (“a”) which represents the surface area of the gas probe in contact with the solids. At 50°C, γ^d _s was determined to be 71.5 mJ/m², and its temperature dependence was 0.36 mJ m^?2 K^?1. Compared with measurements obtained by contact angle, IGC results were found to yield higher values, and especially a higher temperature dependence, d(γ^d _s)/dT. Various potential explanations for these elevated values were examined. The surface energy, as determined by the Schultz and Lavielle equation, was found to depend mostly on the parameter “a”. Two experimental conditions are known to affect the values of “a”: the solid surface and the temperature. While the surface effect of the parameter “a” was ignored in this study, the dependence of the surface energy upon temperature and probe phase was demonstrated to be significant. Several optional treatments of the parameter “a” were modeled. It was observed that both experimental imprecision, but mostly the fundamental difference between the liquid-solid vs the gas-solid system (and the associated theoretical weakness of the model used), could explain the differences between γ^d _s and d(γ^d _s)/dT measured by contact angle and IGC. It was concluded that the exaggerated temperature dependence of the IGC results is a consequence of limitations inherent in the definition of parameter “a”.     

Relationship between size of oil droplet generated during chemical dispersion of crude oil and energy dissipation rate: Dimensionless,scaling, and experimental analysis

Droplet formation mechanisms during the chemical dispersion of crude oil were investigated using both theoretical and experimental approaches. Dimensionless and force balance analysis identified four distinct regimes of droplet formations. For d>η, d scales either with (ε^?2/5) or (ε^?1/4) or and for d<η, d scales either with (ε^?1/2) or (ε^?1/4) depending on whether the main restoring force against droplet breakage is provided by surface tension or oil viscosity. The symbols d, η, and ε represent the droplet diameter, the Kolmogorov length scale, and energy dissipation rate, respectively. For d>η and <η, the external force, which tries to deform and break the droplet is provided by the pressure difference across the droplet diameter and viscous shear, respectively. Identification of the relationship d～(ε^?1/4) for d<η is a new contribution of this present study. The validity of this relationship was also proven by our experimental observations over a range of physical properties (dynamic viscosity 0.015–8.6 Pa s; oil–water interfacial tension 0.0001–0.015 N/m) and mixing energies (0.00075–0.16 W/kg), similar to those in real environmental settings (e.g., estuary, surface layer of oceans). All these above findings and observations are vital from the stand point of appropriately scaling droplet formation process, during chemical dispersion of crude oil, and in the development of reliable predictive models.     

A kinetic evaluation of the anaerobic digestion of two‐phase olive mill effluent in batch reactors

A comparative kinetic study was carried out on the anaerobic digestion of two‐phase olive mill effluent (TPOME) using three 1‐dm³ volume stirred tank reactors, one with freely suspended biomass (control), and the other two with biomass supported on polyvinyl chloride (PVC) and bentonite (aluminium silicate), respectively. The reactors were batch fed at mesophilic temperature (35 °C) using volumes of TPOME of between 50 and 600 cm³, corresponding to chemical oxygen demand (COD) loadings in the range of 1.02–14.22 g, respectively. The process followed first‐order kinetics and the specific rate constants, K₀, were calculated. The K₀ values decreased considerably from 2.59 to 0.14 d^?1, from 1.93 to 0.23 d^?1 and from 1.52 to 0.17 d^?1 for the reactors with suspended biomass (control) and biomass immobilized on PVC and bentonite, respectively, when the COD loadings increased from 1.02 to 14.22 g; this showed an inhibition phenomenon in the three reactors studied. The values of the critical inhibitory substrate concentration (S*), theoretical kinetic constant without inhibition (K_A) and the inhibition coefficient or inhibitory parameter for each reactor (n) were determined using the Levenspiel model. Copyright © 2004 Society of Chemical Industry     

Potential fuel oils from the microalga Choricystis minor

BACKGROUND: Continuous culture of the freshwater microalga Choricystis minor was investigated for possible use in producing lipid feedstock for making biofuels. The effects of temperature (10–30 °C) and dilution rate (0.005–0.017 h^?1) on lipid productivity in a nutrient sufficient medium in a 4 L stirred tank bioreactor under continuous illumination at an incident irradiance level of 550 µE · m^?2s^?1 and a controlled pH of 6 under carbon dioxide supplemented conditions are reported. RESULTS: The maximum lipid productivity was 82 mg L^?1 d^?1 at 25 °C and a dilution rate of 0.014 h^?1. Lipid contents of the biomass were 21.3 ± 1.7 g per 100 g of dry biomass, irrespective of the culture temperature and dilution rate. After the biomass had been grown in nutrient sufficient conditions in continuous culture, it was recovered and subjected to various postharvest treatments. With the best postharvest treatment, the neutral lipid contents of the algal biomass were raised ～6‐fold relative to untreated biomass. CONCLUSION: At 82 mg L^?1 d^?1, or 21 000 L ha^?1 year^?1, the lipid productivity of C. minor was nearly four times the lipid productivity of oil palm, a highly productive crop. Therefore, C. minor is potentially a good source of renewable lipid feedstock for biofuels. Copyright © 2009 Society of Chemical Industry     

Simultaneous organic carbon and nitrogen removal in an SBR controlled at low dissolved oxygen concentration

Simultaneous organic carbon and nitrogen removal was studied in a sequencing batch reactor (SBR) fed with synthetic municipal wastewater and controlled at a low dissolved oxygen (DO) level (0.8 mg dm^?3). Experimental results over a long time (120 days) showed that the reactor achieved high treatment capacities (organic and nitrogen loading rates reached as high as 2.4 kg COD m^?3 d^?1 and 0.24 kg NH₃‐N m³ d^?1) and efficiencies (COD, NH₃‐N and total nitrogen removal efficiencies were 95%, 99% and 75%). No filamentous bacteria were found in the sludge even though the reactor had been seeded with filamentous bulking sludge. Instead, granular sludge, which possessed high activity and good settleability, was formed. Furthermore, the sludge production rate under low DO was less than that under high DO. Significant benefits, such as low investment and less operating cost, will be obtained from the new process. © 2001 Society of Chemical Industry     

Mechanism and kinetics of curing of diglycidyl ether of bisphenol a (DGEBA) resin by chitosan

Crosslinking behavior of Diglycidyl Ether of Bisphenol A (DGEBA) resins cured by chitosan was isothermally studied by Fourier Transform Infrared (FTIR) Spectroscopy for various molar ratios of chitosan at different temperatures. Results indicated that oxirane undergoes nucleophilic attack by the primary amine groups in chitosan to form crosslinked structure. Epoxy fractional conversion (α ) was calculated by following the change in area of oxirane peak at 914 cm^?1. Value of α and reaction rate (dα /dt ) increased with increase in curing temperature and chitosan concentration. The maximum epoxy fractional conversion of 70% was obtained for 1:4 molar ratio (Epoxy:Chitosan) at 200°C. A four parameter kinetic model with two rate constants was employed to simulate the experimental data. Overall reaction order and activation energy for all compositions were in the range of 2.5–3 and 25–50 kJ mol^?1, respectively. Results indicated that cure reaction is autocatalytic and does not follow simple n th order cure kinetics. Thermogravimetric analysis (TGA) performed on chitosan cured DGEBA films and compared against neat epoxy and neat chitosan films. Results showed that the degradation of chitosan crosslinked epoxy network occurred in the temperature range of 450–550°C. POLYM. ENG. SCI., 57:865–874, 2017. © 2016 Society of Plastics Engineers     

Start up of biological sequencing batch reactor (SBR) and short‐term biomass acclimation for polyhydroxyalkanoates production

BACKGROUND: The adaptation/selection of mixed microbial cultures under feast/famine conditions is an essential step for polyhydroxyalkanoates (PHA) production. This study investigated the short‐term adaptation of a mixed microbial culture (activated sludge) during the start up of a sequencing batch reactor (SBR). RESULTS: Four different SBR runs were performed starting from different inocula and operated at the same organic load rate (8.5 gCOD L^?1 d^?1) and hydraulic retention time (1 day). At 3–7 days from SBR start up, the selected biomass was able to store PHA at comparable rate and yield with those obtained after long‐term acclimation. Independently from the time passed, a short feast phase was the key parameter to obtain PHA storage at high rate and yield in the following accumulation stage (244 mgCOD g^?1CODnonPolym h^?1 for specific storage rate and 48% COD COD^?1 as PHA content in the biomass). The DGGE profiles showed that the good storage performance and the structure of the microbial community were not fully correlated. CONCLUSIONS: The results suggest a new strategy for operating the PHA accumulation stage directly in the SBR, after very short biomass adaptation, instead of using two separate reactors for biomass enrichment and PHA accumulation, respectively. © 2012 Society of Chemical Industry     

Microstructure and performance studies of (Mo,Ru, Pd,Zr) tetra-doped gadolinium zirconate pyrochlore

Proper disposal of nuclear waste with multi-nuclides and multi-valence is still challenge. A series of (Mo, Ru, Pd, Zr) tetra-doped Gd₂Zr₂O₇ ceramics were studied to understand the microstructure and performance evolution of nuclear waste forms that immobilised simulated waste after trialkyl phosphine oxides (TRPO) process. The structure of as-obtained samples were tested by X-ray diffraction, Raman, scanning electron microscope, electron back-scattered diffraction, and energy-dispersive X-ray spectroscopy, while the mechanical and chemical performance were characterised by Vickers hardness and aqueous leaching method. The results indicate that the mechanical behaviour are closely linked with the phase structure, and the highest Vickers hardness is obtained at the phase turning point. The leaching results show that the normalised leaching rate (LR) of the doped elements decrease in the order of Mo, Ru, Pd, Zr. After reaching equilibrium, their LR are as low as 4.12?×?10^?4?g·m^?2·d^?1, 1.50?×?10^?5?g·m^?2·d^?1, 1.30?×?10^?5?g·m^?2·d^?1, and 2.09?×?10^?7?g·m^?2·d^?1, respectively.     

Continuous methanogenesis of black liquor of pulp and paper mills in an anaerobic baffled reactor using an immobilized cell system

An anaerobic baffled reactor together with an immobilized cell system has been proposed for methanogenesis of the black liquor from pulp and paper mills in a continuous system. A maximum chemical oxygen demand reduction of 50%, and biogas generation of 10 L d^?1, having methane content of 66% (v/v) at an organic loading rate (OLR) of 7 kg m^?3 d^?1 with hydraulic retention time of 2 days, were recorded. OLR values higher than 7 kg m^?3 d^?1 were toxic to methanogenesis and destabilized the reactor system. Copyright © 2006 Society of Chemical Industry     

Specific energy dissipation rate for super‐high‐rate anaerobic bioreactor

BACKGROUND: Specific energy dissipation rate (?) is an important performance parameter of the super‐high‐rate anaerobic bioreactor (SAB) and is closely linked with power matching and operation optimization. The ? value was investigated for a SAB using anaerobic granular sludge and simulating gas production. The ? models for separation, reaction and water distribution units were established. RESULTS: Experimental results showed that the model predictions agreed well with the experimental data and, thus, they may be used for power matching and operation optimization of similar high‐rate anaerobic bioreactors. The ? value for the separation unit was so low as to be neglected. The maximum ? values for the reaction unit during nonfluidization, granular sludge agglomeration, liquid‐solid two‐phase fluidization and gas‐liquid‐solid three‐phase fluidization states were 0.143 W m^?3, 4.449 W m^?3, 2.173 W m^?3 and 11.132 W m^?3, respectively. The maximum ? value for the water distribution unit was 8.37 W m^?3. ? for the reaction unit was significantly influenced by ρ_p, u_l and V_p, u_g and d_p. CONCLUSION: The maximum ? value of 11.132 W m^?3 was the basic parameter for power matching for the SAB. Some measures were introduced to reduce the ? values based on parametric sensitivity analyses. The present investigation will further assist in optimizing the operation and design of SABs. Copyright © 2011 Society of Chemical Industry     

Modeling Kinetics of Anaerobic Co-Digestion of Poultry Litter and Wheat Straw Mixed with Municipal Wastewater in a Continuously Mixed Digester with Biological Solid Recycle Using Batch Experimental Data

The half-saturation rate coefficient and maximum rate constant in the Monod model, yield coefficient defined as the ratio of microbial mass to substrate mass, and endogenous decay coefficient are important kinetic parameters for design of anaerobic digestion. These parameters are usually determined from a continuous stable operation of anaerobic digestion, which is more difficult and complex than batch operation in laboratory scale. In this study, a novel method has been developed to determine those parameters from data of batch experiments. To verify this method, kinetics of batch anaerobic co-digestion of poultry litter and wheat straw mixed with municipal wastewater at three total solid (TS) levels (2, 4, and 8% TS) and 50% volatile solid (VS) of wheat straw (VSWS) were investigated. The results showed that the maximum specific methane volume (209?mL (initial g?VS)^?1)) was reached at 4% TS of 50% VSWS. Using the developed method, the kinetic parameters of endogenous decay coefficient, yield coefficient, maximum rate constant, and half-saturation coefficient were determined to be between 0.57?×?10^?3 and 1.2?×?10^?3?d^?1, 0.00938 and 0.0644?g volatile suspended solid (VSS) (VS)^?1, 1.394 and 13,797?d^?1, and 1.6?×?10^?8 and 99,996?g. The kinetic parameters obtained were used to simulate kinetic behaviors of a continuous mixed digester with biological solid recycle. The simulated results showed that the dilution rate was very significant for methane volume produced, VS and VSS concentrations in digestion operation. The maximum methane volume could be predicted to be 3071 and 4152?mL for 2 and 4% TS, respectively.