A.A. Van Haute

Denitrification with methanol: Fundamental study of the growth and denitrification capacity of Hyphomicrobium sp

Abstract Hyphomicrobrium spp was found as dominant organism in a two-sludge nitrifying-denitrifying wastewater treatment system with methanol as external carbon source. The optimal pH for growth was found to be 8.3 and the organism seemed to be rather temperature sensitive (Q10 = 3.3). The denitrification rate was expressed as a function of pH and temperature since it was almost independent on the concentrations of methanol and nitrate-nitrogen. Identical growth rates are found when using either nitrate- or nitrite-nitrogen; the nitrite consumption rate, however, is twice the nitrate reduction rate. Nitrate to nitrite reduction is the rate limiting step in denitrification reaction and some inhibition by high concentrations of nitrite on the nitrate reduction is measured. The methanol/nitrate-N ratio is 2.55 and increasing to 3.5 at extreme pH values. The endogenous denitrification rate is only 10% of the normal denitrification rate measured.

Use of the multi-allelic self-incompatibility gene in apple to assess homozygocity in shoots obtained through haploid induction

Abstract To obtain homozygous genotypes of apple, we have induced haploid development of either the female or the male gametes by parthenogenesis in situ and anther culture, respectively. Of the shoots obtained, which were mainly of a non-haploid nature, some could be derived from fertilised egg cells or from sporophytic anther tissue. In order to select the shoots having a true haploid origin, and thus homozygotes, we decided to use the single multi-allelic self-incompatibility gene as a molecular marker to discriminate homozygous from heterozygous individuals. The rationale behind this approach was that diploid apple cultivars contain 2 different alleles of the S-gene and therefore the haploid induced shoots obtained from them should have only one of the alleles of the single parent. The parental cultivars used were ‘Idared’ (parthenogenesis in situ) and ‘Braeburn’ (androgenesis), and their S-genotypes were known, except for 1 of the ‘Braeburn’S-alleles. To stimulate parthenogenetic development ‘Idared’ styles were pollinated with irradiated ‘Baskatong’ pollen, the S-alleles of the latter (2n) cultivar were also unknown. The cloning and sequence analysis of these 3 unidentified S-alleles, 1 from ‘Braeburn’ and 2 from ‘Baskatong’ is described, and we show that they correspond to the S24-, S26- and S27-alleles. We have optimised a method for analysis of the S-alleles of ‘Idared/Baskatong’- or ‘Braeburn’-derived in vitro plant tissues and have shown that this approach can be applied for the screening of the in vitro shoots for their haploid origin.

Re-examination of the self-incompatibility genotype of apple cultivars containing putative 'new' S-alleles

Abstract Recently, the self-incompatibility (S-) genotypes of 56 apple cultivars were examined by protein analysis, which led to the identification by Boskovic and Tobutt of 14 putative ’new’ S-alleles, S12 to S25. This paper reports a re-examination of the S-genotypes of some of these cultivars through S-allele ’specific’ PCR and sequence analysis. The results obtained by this analysis indicated that the number of S-alleles that are present in apple is probably smaller than the number proposed by Boskovic and Tobutt. The existence of three ’new’ S-alleles (S20, S22 and S24) was confirmed. The existence of two other putative ’new’ S-alleles (S23 and S25) was, however, contradicted. The coding sequences of the S-alleles that correspond to the S10 and the S25 ribonuclease bands as well as those corresponding to the S22 and the S23 ribonuclease bands were shown to be identical in sequence. Interestingly, the S-allele corresponding to the S22 and the S23 ribonuclease bands shared a high sequence identity (99% identity) with S27, which was previously cloned and sequenced from Baskatong, but which was not included in the analysis conducted by Boskovic and Tobutt. Both S-alleles only differ in point mutations, which are not translated into differences in amino-acid sequence. To our knowledge, this is the first report of two S-alleles that differ at the nucleotide level but still encode for identical S-RNases. The implications of these observations for determining the S-genotypes of plants by PCR analysis or protein analysis are discussed.

Structure of hydroxide flocs

Abstract A survey of the literature on floc structure demonstrates that no good structural model for gelatinous hydroxide flocs exists. In this investigation hydrolysing metal salts were used during the coagulation-flocculation of very dilute kaolinite suspensions. The influence of kinetic process parameters on the floc strength is used to prove the validity of a four level organization of hydroxide floc aggregates. The different levels of organization are: primary particles, flocculi, flocs and floc aggregates. The bonds between the particles of the different levels are elastic.

Backwashing and conditioning of a deep bed filter

Abstract The traditional conceptual model explaining the initial effluent degradation as a result of the backwashing, is proved to be insufficient. Mathematically and experimentally it is demonstrated that the initial effluent degradation is 95% due to an inadequate pore structure of the filter bed. An increased coagulant dose at the start of the filtration or a preconditioning of the filter bed during the last minutes of the backwashing operation, can reduce the initial turbidity peak. Such a treatment has also consequences for the complete filter run.

Flocculation of brackish water from a tidal river

Abstract The control of the flocculation of water from tidal rivers is difficult because the water characteristics oscillate rapidly. Especially ionic strength and suspended solids concentration may have 10-fold changes in less than 6 h. Hence a relationship between an optimal dose of coagulant and raw water characteristics was sought with the aid of jar-tests. A pH of 6 was shown to be an acceptable value for flocculation with iron chloride and alum. The influence of change of ionic strength was found to be negligible. Suspended solids concentration proved to be a decisive control parameter. The von Smoluchowski model is appropriate to describe the kinetics of this sweep coagulation.

Chloride pitting and water chemistry control in cooling or boiler circuits

The effect of different anions (bicarbonate, phosphate, sulphate, hydroxyl) on the pitting corrosion by chloride ions has been investigated for a number of ferritic or austenitic steels and nickel alloys at different temperatures up to 175°C. For most of the alloys the normal order of inhibition is PO43 > SO42- ⩾ HCO3, but some anomalies have been encountered for stainless steels at lower temperatures (<100°C), where the inhibitive action of SO42- maybe more pronounced that the inhibition which can be obtained by adding equal amounts of phosphate. In the absence of strongly passivating alloying elements, such as chromium, high SO42 concentrations may have a deteriorative effect. The same result may also be found under cathodic polarization conditions, where SO42- and HCO3 seem to stimulate reductive dissolution of the protective surface layer and may even cause some kind of pitting-type attack.

Floc Strength Measurements Giving Experimental Support for a Four Level Hydroxyde Floc Structure

Abstract A literature survey about floc structure research is given. In this investigation, hydrolysing metal salts were used during the coagulation-flocculation of very diluted kaolinite suspensions. The different experiments are briefly described and explained. The influence of the kinetic process parameters on the floc strength is used to prove the validity of a four level organisation of hydroxydc floc aggregates. The different levels of organisation are: primary particles, flocculi, flocs and floc aggregates. The bonds between the particles are elastic. The influence of the kinetic process parameters on the floc structure is deduced as well.

Thermodynamics and composition of chlorine hydrate

Abstract The HWG and HIG equilibria for the system chlorine-water-chlorine hydrate have been measured for pressures below 2 atm (Eq. 1 and 2). The chlorine concentration and the density of the aqueous solution, in equilibrium with the hydrate along the HWG line, have also been determined (Eq. 3 and 4). The composition of chlorine hydrate has been calculated in three independent ways: ( a ) from the slopes of the HWG and HIG lines in the lower invariant point, ( b ) using the Miller-Strong method with NaCl in the temperature interval 4 to 9°C, ( c ) by a dilatometric method using the measured density of the hydrate. There is a good concordance among the three sets of results.

THE ROLE OF MOLYBDENUM IN THE INHIBITION OF PASSIVITY BREAKDOWN IN NEUTRAL CHLORIDE SOLUTIONS UP TO 250°C

ABSTRACT Several austenitic stainless steels and nickel alloys have been tested for their resistance against localized corrosion in a 0.1 M NaCl solution up to 250°C. The molybdenum containing alloys proof to have a superior resistance against pitting attack up to 200°C. Above 200°C, for all the alloys tested the pitting attack seems to degenerate into different kinds of localized or general attack at rather high potentials. The beneficial action of Mo against pitting corrosion in a neutral 0.1 M NaCl solution can be attributed to its presence as Mo042− (or HMo04−) in the passive film as indicated by the E-pH diagrams for Mo (ref. 1) and not to an insoluble Mo-oxide. The superior resistance of Mo containing alloys against active corrosion in acid solutions on the other hand can be attributed to the presence of an insoluble Mo-oxide (Mo02) as again is indicated by the E-pH diagrams.