Energy generation by methanation of persistent wastes

A 15-L anaerobic fixed-film reactor (AFFR) was evaluated for treating a trade effluent containing inhibitory concentrations of persistent branched-chain fatty acids, namely 2-ethylhexanoic acid (2-EHA) and neopentanoic acid (NPA), at a total of 17,000 mg COD/L. The AFFR was packed with fire-expanded clay spheres, and start-up was accomplished in 60 d. The organic load was increased in steps from 1.1 to 8.5 g COD/L/d. Total COD, 2-EHA, and NPA removal efficiencies were maintained above 70, 98, and 75%, respectively. The reactor could recover from a shock load of 150% increase in organic load. Combined mechanisms of organic adsorption and biodegradation rendered the AFFR more stable with shock loads. Mathane gas produced from the process could be used for preheating the effluent.     

Mixed- and plug-flow performances of an anaerobic biofilter treating 2-ethylhexanoic acid

The performance of a 20-L anaerobic biofilter treating 2-ethyl-hexanoic acid (2-EHA) operating with the effluent recirculated was compared with that of the same biofilter operated without any recirculation. The recirculation of effluent was at a rate of 60 L/h through the biofilter. Tracer experiments were carried out to study the hydrodynamics in the biofilter under different modes of operation. The dispersion number (D/UL) obtained from these tracer experiments for the biofilter operated with and without effluent recirculation were 0.65 and 0.06, respectively. These values show that the recirculation was effective in achieving a mixed-flow pattern in the biofilter, whereas the biofilter operated without recirculation was essentially a plug-flow column with a moderate level of axial dispersion. The feed consisted of 2-EHA at a concentration of 8200 mg/L, which is equivalent to a COD of 20,000 mg/L. The optimal performance of the mixed-flow biofilter was at a hydraulic retention time (HRT) of 1.1 d, with a COD removal efficiency of 92.8% and a biogas production rate of 6.44 L/L biofilter vol/d. The biofilter failed at 0.83 d HRT, as a result of washout of biomass at this high hydraulic loading rate. By comparison, the optimal performance achieved for the plug-flow system was at 2 d HRT. The COD removal efficiency was 74.1%, and biogas production rate was 2.13 L/L biofilter vol/d. When the HRT was lowered to 1.5 d, failure occurred owing to inhibition as indicated by the low methane yield of 0.192 L/g COD removed. The superior performance of the mixed-flow mode can be attributed to the presence of the recycle stream, which diluted and evenly distributed the feed.     

Performance of fibrous bed bioreactor for treating odorous gas

A fibrous bed bioreactor was used for treatment of odorous volatile fatty acid (VFA). The effect of gaseous VFA (acetic, propionic, and butyric acids) mass loading on the bioreactor performance was investigated. The VFA degrading microbial culture was selected from activated sludge by the three VFAs using a shake-flask culture. The selected microorganisms were then immobilized in a biofilter using cotton fabric as packing material. In the biofiltration experiment, the inlet gas flow rates ranged from 1 to 4 L/min, the total VFA concentrations ranged from 0.10 to 0.43 g/m³, and the resulting total mass loadings of VFA studied ranged from 9.7 to 104.3 g/m³/h. At total mass loading of 104.3 g/m³/h, the VFA removal efficiency was 87.7%. Higher removal efficiencies (>90%) were achieved at mass loadings below 50.3 g/m³/h.     

Analyticity of weighted central paths and error bounds for semidefinite programming

The purpose of this paper is two-fold. Firstly, we show that every Cholesky-based weighted central path for semidefinite programming is analytic under strict complementarity. This result is applied to homogeneous cone programming to show that the central paths defined by the known class of optimal self-concordant barriers are analytic in the presence of strictly complementary solutions. Secondly, we consider a sequence of primal–dual solutions that lies within a prescribed neighborhood of the central path of a pair of primal–dual semidefinite programming problems, and converges to the respective optimal faces. Under the additional assumption of strict complementarity, we derive two necessary and sufficient conditions for the sequence of primal–dual solutions to converge linearly with their duality gaps. This research was supported by a grant from the Faculty of Mathematics, University of Waterloo and by a Discovery Grant from NSERC.     

A recyclable non-immobilized siloxy serine organocatalyst for the asymmetric direct aldol reaction

A recyclable siloxy-l-serine organocatalyst has been developed to catalyze asymmetric direct aldol reactions in [bmim][BF₄], furnishing the β-hydroxy carbonyl scaffold in high enantio- and diastereoselectivities using a selection of aromatic aldehydes and cycloalkanes. The siloxy serine organocatalyst in the ionic liquid can be reused for up to four successive cycles with comparable enantioselectivities.     

Self-improving properties of inequalities of Poincaré type on measure spaces and applications

We show that the self-improving nature of Poincaré estimates persists for domains in rather general measure spaces. We consider both weak type and strong type inequalities, extending techniques of B. Franchi, C. Pérez and R. Wheeden. As an application in spaces of homogeneous type, we derive global Poincaré estimates for a class of domains with rough boundaries that we call ?-John domains, and we show that such domains have the requisite properties. This class includes John (or Boman) domains as well as s-John domains. Further applications appear in a companion paper.     

Visualization of flows behind the lobed forced mixers using the smoke-wire technique

Flow visualization studies have been conducted using the smoke-wire technique to examine the flows behind lobed forced mixers of different trailing edge configurations (namely a square wave, semi-circular wave and a triangular wave) at a velocity ratio 1:1 across the lobe. The wake region shed by a lobe is found to be the largest with lobe geometry consisting of straight parallel sidewalls. Streamwise vortices are formed within the first four wavelengths downstream of the trailing edge in the square and semi-circular lobed mixers. These vortices are largely responsible for intense mixing at downstream locations. However, similar observation is not found in the case of triangular lobed mixer. The present visualization tests agree qualitatively with the velocity measurements obtained by authors using a laser-Doppler anemometer.     

Investigation of pupil-fill factors as process window indicators for dry optical lithography

This work presents two pupil-fill factors as process window indicators for optical projection lithography when resolution enhancement techniques are employed. The formulations of these two pupil-fill factors are based on two different concepts of the correlation between the process window and the diffraction orders captured at the pupil of the imaging lens. One pupil-fill factor considers the amplitude of the diffracted orders. The other pupil-fill factor considers the extent of overlap between the 0th and the 1st diffraction orders at the pupil. This work investigates how accurately the variation of the two pupil-fill factors indicates the influences of source configuration and mask features on the process window. The Chromeless Phase Shift Lithography (CPL™) technology, in the context of dry optical lithography, is used as a case study. The results suggest that the pupil-fill factor, which considers the amplitude of the diffraction spectrum, is a better process window indicator than the other.