Supercritical water oxidation (SCWO): a process for the treatment of industrial waste effluents

Abstract

SuperCtical Water Oxidation (SCWO) process is investigated at the Institut of Technical Chemistry, ITC-CPV. The objectives were to determine destruction efficiencies of model compounds and industrial waste effluents and to study the feasability of the SCWO process.

Two continuous SCWO bench scale plants are operated a pipe reactor and a transpiring wall reactor system (design data: T= 630°C, P = 32MPa, feed rate waste water =10 and 50kg/h, air feed rate = 20kglh, transpiring and quench water feed rate = 50 kg/h). Suspensions containing up to 5%wt solid material can be fed to the reactor using a membrane pump.

With the pipe reactor, efficiencies of up to 99.99% were achieved for the oxidation of model compounds (ethanol, toluene, phenol) as well as real waste effluents (paper, chemical, pharmaceutical industry, sewage works). The use of the pipe reactor is limited to feeds without salt to avoid plugging.

Salty feeds are processed using the transpiring wall reactor, which is consisting of a pressure bearing tube outside and a porous tube as reactor inside. Water is steadily running through the porous reactor preventing the formation of deposits on the wall.

SCWO has a high potential at least for the destruction of halogented organic compounds using the transpiring wall reactor system and is seen to be competitive to other processes for waste destruction.     

A Lattice of Varieties of Completely Regular Semigroups

In a previous communication, we defined a countably infinite sequence of varieties of completely regular semigroups, termed canonical. Finite intersections of these varieties constitute the upper ends of the intervals which are the classes of the congruence induced by the complete homomorphism 𝒱 → 𝒱 ∩ ?, where ? is the variety of all bands. We construct here the lattice generated by the first few of these varieties in some detail. In particular, we determine their bases and illustrate our findings by three diagrams.     

On Some Monogenic Semigroups with an Associate Subgroup

Let S be any semigroup and a, s ∈ S. If a = asa, then s is an associate of a. A subgroup G of S is an associate subgroup of S if every a ∈ S has a unique associate a* in G. It turns out that G = H _z for some idempotent z, the zenith of S. The mapping a → a* is a unary operation on S. We say that S is monogenic if S is generated, as a unary semigroup, by a single element.

We embark upon the problem of the structure of monogenic semigroups in this sense by characterizing monogenic ones belonging to completely simple semigroups, normal cryptogroups, orthogroups, combinatorial semigroups, cryptic medial semigroups, cryptic orthodox semigroups, and orthodox monoids. In each of these cases, except one, we construct a free object. The general problem remains open.     

The Malcev product of quasivarieties of normal bands

Research supported by N.S.E.R.C. of Canada.     

Multidimensional reaction coordinate for the excited-state H-atom transfer in perylene quinones: importance of the 7-membered ring in hypocrellins A and B

The excited-state intramolecular H-atom transfer reactions of hypocrellins B and A are compared by using time-resolved absorption and fluorescence upconversion techniques. The hypocrellin B photophysics are well described by a simple model involving one ground-state species and excited-state forward and reverse H-atom transfer with a nonfluorescent excited state. We suggest that excited-state conformational changes are coupled to the H-atom transfer in hypocrellin B just as gauche/anti changes are coupled to the H-atom transfer in hypocrellin A.     

Picosecond dynamics of a peptide from the acetylcholine receptor interacting with a neurotoxin probed by tailored tryptophan fluorescence

A tryptophan analog, dehydro-N-acetyl-L-tryptophanamide (delta-NATA), which is produced enzymatically via L-tryptophan 2',3'-oxidase from Chromobacterium violaceum, is newly used for time-resolved fluorescence. The absorption and emission maxima of delta-NATA at 332 and 417 nm, respectively, in 20% dimethylformamide-water are significantly shifted to the red with respect to those of tryptophan in water, permitting us to measure its fluorescence in the presence of tryptophan residues. We demonstrate that the steady-state spectra and the fluorescence decay of delta-NATA are very sensitive to environment, changing dramatically with solvent as the chromophore is localized within a protein and when this tagged protein binds to a peptide. The tryptophan oxidase was also used to modify the single Trp of a neurotoxin from snake (Naja nigricollis) venom. Modification of the toxin alpha (dehydrotryptophan-toxin alpha) permitted its investigation in complex with a synthetic 15-amino acid peptide corresponding to a loop of the agonist-binding site of acetylcholine receptor (AchR) from Torpedo marmorata species. The peptide alpha-185 possesses a single Trp at the third position (Trp187 of AchR) and a disulfide bridge between Cys192 and Cys193. A single-exponential rotational diffusion time with a constant of 1.65 ns is measured for the isolated 15-amino acid peptide. This suggests that Trp motion in the peptide in solution is strongly correlated with the residues downstream the peptide sequence, which may in part be attributed to long-range order imposed by the disulfide bond. The dynamics of the bound peptide are very different: the presence of two correlation times indicates that the Trp187 of the peptide has a fast motion (taur1 = 140 ps and r(0)1 = 0.14) relative to the overall rotation of the complex (taur2 = 3.4 ns and r(0)2 = 0.04). The correlation of the Trp residue with its neighboring amino acid residues and with the overall motion of the peptide is lost, giving rise to its rapid restricted motion. Thus, the internal dynamics of interacting peptides change on binding.     

Tumor cell toxicity of hypericin and related analogs

A series of hypericin analogs were found to differ in their cytotoxic activity induced by ambient light levels. These analogs vary in their ability to partition into cells, to generate singlet oxygen as well as in other photophysical properties. The data suggest that the biological activity of hypericin is due to a combination of factors whose roles may vary under different circumstances.     

Bands of groups with universal properties

For a nonempty setX, a bandB, and a mapping :XB, we construct a band of groups, here called a cryptogroup,F(X,,B) which exhibits some remarkable properties. The first of these is a universal property relative to the classCG of all cryptogroups. In fact,CG is a variety with the operations of multiplication and inversion. For a varietyV of bands, we find a varietyV ⁰ of cryptogroups such that wheneverB is a band free inV ⁰ on the setX with embedding :XB, F(X,,B) is free inV ⁰. IfB is a normal band given as a strong semilattice of rectangular bands, we construct an isomorphic copy ofF(X,, B) which is a strong semilattice of completely simple semigroups. The objectsX, , B) admit the structure of a category, which is then related to the category of cryptogroups and their homomorphisms.This research was supported, in part by, NSERC Grant A4044.