Optimization of biogas production by co-digesting whey with diluted poultry manure

A series of laboratory experiments were performed in continuously stirred tank reactors at mesophilic conditions, fed semi-continuously with various mixtures of diluted poultry manure and whey. Co-digestion of whey with manure was proved to be possible without any need of chemical addition up to 50% participation of whey (by volume) to the daily feed mixture. Up to this point, specific biogas production (L/kg VS_in) remained roughly unchanged at the various whey fractions added in the feed mixture, mainly due to the lower chemical oxygen demand (COD) of whey compared to that of manure. At whey fractions above 50%, the reactor turned to be unstable, as shown by the considerable decrease in pH and biogas production. The experiments were scaled up to a continuously stirred pilot tank reactor, which had previously been acclimated to poultry manure digestion. Whey was gradually introduced in the feed, at increasing rates, replacing equivalent volumes of manure, in such a way, that total COD of the feed remained constant. For an hydraulic retention time of 18 days at 35 °C and organic loading rate of 4.9 g COD/L_R d, it was found that biogas production increased from 1.5 to 2.2 L/L_R d (almost 40%). This could be mainly attributed to the higher biodegradability of carbohydrates (main constituent of whey) compared to lipids (main constituent of manure) and to the correction (increase) of C:N ratio.     

Physical evaluation of a maize‐based extruded snack with curry powder

Response surface methodology was used to analyze the effect of screw speed (200–280 rpm), feed moisture (13.0–17.0%, wet basis), and curry powder (6.0–9.0%) on the bulk density, lateral expansion, and firmness of maize‐based extruded snack with curry powder. Regression equations describing the effect of each variable on the responses were obtained. Responses were most affected by changes in feed moisture followed by screw speed and curry powder (p < 0.05). Lateral expansion increased linearly as the amount of curry powder added was increased whereas a quadratic increase was obtained in lateral expansion with decreasing feed moisture. The firmness of samples was increased with an increase in feed moisture. The bulk density of samples was increased with increasing feed moisture and screw speeds. Radial expansion was found to be a better index to measure the physical properties of the extruded product indicated by a higher correlation coefficient.     

Design of product specifications and control policies in a single-stage production system

Screening (100%-inspection) is a common practice in quality engineering. Traditional screening procedures seek upper and lower specification limits for a quality characteristic associated with some product, such that the total quality cost per item is minimized. This practice ignores the effect of parts rejection on product lead times, inventory carrying costs, shortage costs, throughput, and, eventually, total profit rate of the system. In this paper, a single-stage production system is considered and two control policies arc determined jointly with the inspection plans. Numerical experiments indicate that such co-ordinated policies achieve a better performance than independently determined quality and production control policies     

Finite modeling of parabolic equations using Galerkin methods and inverse matrix approximations

In this paper we examine order reduction of parabolic systems using modal truncation. The parabolic distributed system is first approximated using the Galerkin method. The system matrices have a special structure that allows us to find the approximate spectrum of the parabolic system. To do this we compute approximate inverses of tridiagonal, diagonally dominant symmetric matrices. The approximation leads to algorithms of orderO(n), as opposed to traditional algorithms of orderO(n), wheren is the order of the system. Finally, an example is presented to illustrate the proposed algorithm.This research was supported by the National Science Foundation under contract NCR-9210408, by the Advanced Research Programs Agency under contract MDA-972-93-1-0032, and by the University of Hawaii Research Council Funds.     

Directed evolution on the cold adapted properties of TAB5 alkaline phosphatase

Psychrophilic alkaline phosphatase (AP) from the Antarctic strain TAB5 was subjected to directed evolution in order to identify the key residues steering the enzyme's cold-adapted activity and stability. A round of random mutagenesis and further recombination yielded three thermostable and six thermolabile variants of the TAB5 AP. All of the isolated variants were characterised by their residual activity after heat treatment, Michaelis-Menten kinetics, activation energy and microcalorimetric parameters of unfolding. In addition, they were modelled into the structure of the TAB5 AP. Mutations which affected the cold-adapted properties of the enzyme were all located close to the active site. The destabilised variants H135E and H135E/G149D had 2- and 3-fold higher kcat, respectively, than the wild-type enzyme. Wild-type AP has a complex heat-induced unfolding pattern while the mutated enzymes loose local unfolding transitions and have large shifts of the Tm values. Comparison of the wild-type and mutated TAB5 APs demonstrates that there is a delicate balance between the enzyme activity and stability and that it is possible to improve the activity and thermostability simultaneously as demonstrated in the case of the H135E/G149D variant compared to H135E.     

Spectroscopic investigations on the depth-dependent degradation gradients of aged triterpenoid varnishes

The depth-profiles of accelerated aged triterpenoid dammar and mastic varnishes, which had been uncovered by optimized KrF excimer laser ablation (248 nm, 25 ns), were examined by ultraviolet-visible (UV/VIS) spectrophotometry and attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy. The results reflect both the optical properties at the bulk (UV/VIS) and the surface (ATR/FT-IR) and establish the presence of degradation gradients across the depth of the degraded natural resin films. It is demonstrated that the UV part of the ambient radiation is absorbed by the deteriorated surface and that the optical densities of the aged varnish decrease as a function of depth. The absorbed UV wavelengths at the surface and the depth-wise reduction of light intensity result in a depth-dependent decrease in carbonyl absorbance and an increase in C-H bending vibration modes of methylene species pointing to structural modification in the triterpenoid mixture across depth.     

NATURAL CONVECTIVE HEAT TRANSFER IN AN ASYMMETRIC GREENHOUSE-TYPE SOLAR STILL--EFFECT OF ANGLE OF INCLINATION

The natural convective flow and heat transfer in air inside an asymmetric, greenhouse-type solar still is studied numerically. The actual configuration consists of two top glass covers, perpendicular to each other and forming angles of 30° and 60° with respect to the horizontal, along with a blackened basin at the bottom where saline water evaporates. The Rayleigh number varies over a wide range of values during a 24-hour cycle of operation, but most of the time the values are high enough so that turbulent flow conditions prevail. Here the interest is in the heat transfer problem and the arising flow structure in the still, and two-dimensional computations are performed using a stream function-vorticity formulation along with a low Reynolds turbulence model. A curvilinear coordinate system is used, with a grid that is made orthogonal to all solid boundaries for most of their length. A multicellular flow pattern arises in the core of the still, depending on the value of the Rayleigh number (here Ra = 10 7 - 10 10 based on the horizontal dimension of the still), with thin boundary layers forming along the top covers and the bottom surface. Alternative configurations are investigated by changing the angle of inclination of the main condensation surface at the top cover. Detailed comparisons are made for a reduced slope of 15° for that surface, and by examining flow patterns and heat transfer rates the relative merits of each of the angles within the chosen range of Ra are examined.     

Conjugate Heat and Mass Transfer from a Drying Rectangular Cylinder in Confined Air Flow

Heat and mass transfer from a porous body subject to convective drying is investigated numerically based on Luikov's equations. The air flow is assumed incompressible, two-dimensional, laminar, confined in a channel, and parallel to the rectangular-shaped solid. The finite-volume method is used and the computed temporal and spatial variations of moisture content, temperature, concentration, and flow parameters for two different flow rates are analyzed. Two flow configurations are studied: with and without a flow divider upstream of the cylinder in an attempt to eliminate the presence of separation zones and study their effect on drying. It was found that such effects may greatly affect the drying process, along with frontal area stagnation and the thickness of the body.     

Application of Inductive Topological Transfer Function Generation for a Cascaded Low-Pass Filter

This work presents applications of an inductive topological approach in the calculation of the transfer function of a cascading network control system. The method provides a very versatile and effective way of counting all the graphs that contribute and of translating them into their algebraic contribution. The contributing graphs are very simple and reflect the morphology of the original control system signal flow graph. Application of the method and results are presented for an n-cell RC network. We derive an analytical formula relating ω(3 dB) to the filter size (n) and R _j C _j (j=1,2,…,n). This formula can be used for designing preset frequency range self-loaded LP filters by varying their size. We also derive general expressions for the sensitivities which we use to observe a sensitivity-insensitivity filter transition for various frequency ranges, relaxation times, and, most importantly, filter sizes.     

Estimation of uncertainties in indirect humidity measurements

The information related to the amount of vapour in the air, can be of critical importance for various processes, such as air-conditioning in buildings, drying or material processing. This information can be provided through different quantities such as the absolute humidity, relative humidity, dew-point temperature or wet-bulb temperature. Quite often, the user is more interested in a secondary quantity, which can be obtained through the use of appropriate relations or charts, rather than the directly measured one. The present work aims at proposing a methodology for the estimation of uncertainty related to the indirect humidity measurements. The analysis concentrates on the usual case which refers to the calculation of the values of derivative quantities, such as relative humidity or the amount of vapour in the air, through the direct measurement of quantities, such as dry-bulb temperature and dew-point temperature.The estimation of uncertainties is based on the propagation of probability distributions which could describe the available state-of-knowledge of the directly measured quantities, through the implementation of the Monte-Carlo simulation, which is consistent with the nonlinear characteristics of the hygrometric equations.