Jan Dick

Bio-deposition of a calcium carbonate layer on degraded limestone by Bacillus species

To obtain a restoring and protective calcite layer on degraded limestone, five different strains of the Bacillus sphaericus group and one strain of Bacillus lentus were tested for their ureolytic driven calcium carbonate precipitation. Although all the Bacillus strains were capable of depositing calcium carbonate, differences occurred in the amount of precipitated calcium carbonate on agar plate colonies. Seven parameters involved in the process were examined: calcite deposition on limestone cubes, pH increase, urea degrading capacity, extracellular polymeric substances (EPS)-production, biofilm formation, ζ-potential and deposition of dense crystal layers. The strain selection for optimal deposition of a dense CaCO3 layer on limestone, was based on decrease in water absorption rate by treated limestone. Not all of the bacterial strains were effective in the restoration of deteriorated Euville limestone. The best calcite precipitating strains were characterised by high ureolytic efficiency, homogeneous calcite deposition on limestone cubes and a very negative ζ-potential.

Cleaning of concrete fouled by lichens with the aid of Thiobacilli

Concrete specimens weathered for over a decade in the moderate Belgian climate, showing a black organic outer layer that mainly consisted of lichens, were cleaned with a new biological technique. A mixture of sulphur oxidising bacteria of the genusThiobacillus supplemented with an appropriate nutrient was applied to a fouled concrete surface, either by sprinkling or by submersion. The aim was to remove the fouled layer in such a way that the surface is uniformly cleaned. The general effect of the technique was evaluated by colorimetry and microscopy. Two sets of weathered concrete specimens, containing blast furnace slag cement or ordinary portland cement, were investigated. The effectiveness of the technique depended on the cement type of the concrete specimens. The effect on the ordinary portland cement concrete specimens was in some cases up to a factor 2 stronger than the result on the blast furnace slag cement specimens. The sprinkling treatment was about 50% as effective as the submersion treatment but was very promising in the case of in situ acidification. A side effect was the formation of a gypsum layer on some of the specimens, resulting in a whiter colour.

Involvement of NO in gastric emptying of semi‐solid meal in conscious pigs

Abstract  The influence of non‐selective nitric oxide synthase (NOS) inhibition on gastric emptying of a semi‐solid meal was studied in conscious pigs. Antro‐duodenal motility and fundic compliance were also assessed to evaluate the mechanisms at the origin of potential alteration in gastric emptying pattern. NG‐nitro‐l‐arginine methyl ester (l‐NAME; 20 mg kg−1 i.v.) delayed gastric emptying (half‐emptying time of 128.98 ± 16.86 min vs 73.74 ± 7.73 min after saline, P < 0.05, n = 6) as a result of decreased proximal gastric emptying. No changes were observed for distal gastric emptying as a result of unchanged antral motility. Similarly, no changes were noted on duodenal motor patterns either in the fasted or in the fed state. l‐NAME decreased fundic compliance in fasted state (49 ± 11 mL mmHg−1vs 118 ± 15 mL mmHg−1 after saline, P < 0.05, n = 6). As this phenomenon is expected to increase emptying rate, the gastroparesis induced by NOS inhibition is thus likely to originate from distal resistive forces. It is concluded that NO positively modulates gastric emptying.

Antisense knockdown of inducible nitric oxide synthase inhibits the relaxant effect of VIP in isolated smooth muscle cells of the mouse gastric fundus.

Our previous results showed that the non‐selective nitric oxide synthase (NOS) inhibitor L‐NG‐nitroarginine (L‐NOARG) and the selective inducible NOS (iNOS) inhibitor N‐(3‐(acetaminomethyl)‐benzyl)acetamidine (1400W) inhibited the relaxant effect of vasoactive intestinal polypeptide (VIP) in isolated smooth muscle cells of the mouse gastric fundus, suggesting the involvement of iNOS. The identity of the NOS isoform involved in the VIP‐induced relaxation in isolated smooth muscle cells of the mouse gastric fundus was now further investigated by use of antisense oligodeoxynucleotides (aODNs) to iNOS. Incubation of isolated smooth muscle cells with fluorescein isothiocyanate (FITC)‐labelled aODNs showed that nuclear accumulation occurs quickly and reaches saturation after 60 min. The in vivo intravenous administration of aODNs to iNOS, 24 and 12 h before murine tumour necrosis factor alpha (mTNFα) challenge, significantly reduced the nitrite levels induced by the mTNFα challenge. Intravenous administration of aODNs to iNOS in mice, 24 and 12 h before isolation of the gastric smooth muscle cells, decreased the inhibitory effect of the NOS inhibitors L‐NOARG and 1400W on the relaxant effect of VIP, whereas neither saline nor sODNs had any influence. Preincubation of the isolated smooth muscle cells with aODNs almost abolished the inhibitory effect of L‐NOARG and 1400W on the VIP‐induced relaxation, whereas sODNs failed. These results illustrate that the inhibitory effect of NOS inhibitors in isolated smooth muscle cells of the mouse gastric fundus is due to inactivation of iNOS. iNOS, probably induced by the isolation procedure of the smooth muscle cells, seems involved in the relaxant effect of VIP in isolated gastric smooth muscle cells.

Ureolytic phosphate precipitation from anaerobic effluents.

In this work, the elimination of phosphate from industrial anaerobic effluents was evaluated at lab-scale. For that purpose, the ureolytic method previously developed for the precipitation of Ca(2 + ) from wastewater as calcite was adapted for the precipitation of phosphate as struvite. In the first part of the study, computer simulations using MAPLE and PHREEQC were performed to model phosphate precipitation from wastewater as struvite. The results obtained showed that relative high concentrations of ammonium and magnesium are needed to precipitate phosphate as struvite. The total molar concentrations ratio of Mg(2 + ):PO(4) (3-)-P:NH(4) (+) required to decrease PO(4) (3-)-P concentrations from 20 to 6 mg PO(4) (3-)-P/l at pH 8.4-8.5 was estimated on 4.6:1:8. In the second part of the study, lab-scale experiments with either synthetic wastewater or the anaerobic effluent from a vegetable processing industry were carried out in batch and continuous mode. Overall, the continuous operation at a hydraulic retention time (HRT) of 2.4 h and an added molar concentration [Mg(2 + )]:[PO(4) (3-)-P]:[NH(4) (+)] ratio of 1.6:1:2.3 resulted in a constant pH value in the reactor (around 8.5) and an efficient phosphate removal (>90%) to residual levels of 1-2 mg PO(4) (3-)-P/l. Different operational conditions, such as the initial phosphate concentration, HRT and the use of CaCl(2) or MgO instead of MgCl(2), were analysed and the performance of the reactor was satisfactory under a broad range of them. Yet, overall, optimal results (higher phosphate removal) were obtained with MgCl(2).