Belgian Experiences in the Ozonization of Water

After reviewing the uses of ozone in the preparation of drinking water, high purity water for Pharmaceuticals industries, and swimming pools throughout Belgium, a discussion of technological developments made at the Tailfer plant (serving Brussels) concerning the uses of ozone is presented. These subjects include analytical and monitoring techniques developed for ozone, procedures for ozone contacting employed at this plant, treatment of ozone contactor off–gases, and the use of oxygen–enriched process gas to produce supplemental amounts of ozone required periodically. Capital and operating cost data are presented.     

Guideline for Measurement of Ozone Concentration in the Process Gas From an Ozone Generator

A joint meeting of members of the Quality Assurance Committees of the International Ozone Association Pan American Group (PAG), European-African Group (EAG), and Nippon Islands Group (NIG) was held in Oxford, Ohio on November 8 and 9, 1995. The purpose of the meeting was to establish a single, shared guideline for ozone concentration measurement in the gas phase and, in particular, from commercial ozone generators.     

Experimental Evidence of Gas-Liquid Boundary Controlled Reactions in UV-Ozone Systems

Oxalic acid is chosen as a model compound to study the UV + O₃ reactions in an heterogeneous continuous gas sparging reactor. Oxalic acid has the advantage of not reacting significantly with ozone alone, and when oxidized with O₃ + UV radiation, the reaction is of the single-step type : HOOC-COOH + O₃ (UV) = 2 CO₂ + H₂O + O₂. The reactions are of zero order as long as no additional alkalinity is introduced into the system. Evidence is that the photolysis of ozone is produced in the gas phase and that the reaction occurs in the gas-liquid boundary layer.     

Influence of Temperature on Bacterial Development in Waters

Microbiological stability in water mains has become an increasing problem for waterworks where more and more surface water is used for distribution requirements. Even when surface water is treated, appropriately, it usually contains a higher amount of organic compounds than does groundwater, and during certain periods, can attain temperatures between 20 and 25°C. Furthermore, ozonization applied during treatment modifies structures of the dissolved organic materials.

Twenty bacterial strains capable of aftergrowth were isolated starting from ozonized surface water, from water of subterranean origin, and from a mixture of these two types of water. Six typical strains were used to determine the importance of the temperature factor on aftergrowth in five types of waters of different characteristics.

Three criteria for the evaluation of aftergrowth are: the growth rate factor (r₂), the growth yield (maximum number of germs/mL when growth stops), and the latency time (in hours). The results, in triplicate, obtained from growth curves then were submitted to an analysis of variance by two cross classifications.

It was established that aftergrowth is related to the classical Pseudomonas and Azobacter families, but also to the species of Bacillus, Corynebacter, Micrococcus, Vibrionaceae, and even Enterobacter. Furthermore, it has been proven that the temperature factor is most important in all aspects, as an increase in water temperature enhances all growth characteristics: shortening of the lag-phase; increase in growth-rate factor; and yield.

Under practical conditions, the significant growth delay is very important. With Pseudomonas putida, the lag-phase is on the order of three days at +7.5°C and 10 hours at +17°C.     

The feasibility of coagulant recycling by alkaline reaction of aluminium hydroxide sludges

Coagulant recycling appears to be economically attractive as much by the reduction of fresh chemical dosing as by the simplification of the sludge disposal. The present paper has studied the feasibility of aluminium coagulant recovery by an alkaline treatment of sludge. The study was carried out on sludge obtained from the drinking-water treatment plant of the Brussels' Intercommunal Waterboard located at Tailfer on the river Meuse. The general conditions are summarized as follows and given as guidelines:

• to limit the starting sludge concentration to a threshold below 20 g l⁻¹ dry wt concentration;

• to optimize the alkalisation process which means a pH between 11.4–11.8 for NaOH and 11.2–11.6 for Ca(OH)₂;

• to choose between NaOH and Ca(OH)₂ is optional but heavy metals contained in the sludge are reduced by a factor of 10–15 by using lime instead of NaOH;

• to use a settling process to recover the supernant before recycling and therefore best limit the recovery to 25–30% of the coagulant even though when using sodium hydroxide, an 80% recovery is possible.

When restricting the recycling to less than 50% of the coagulant (for instance 25–30%) no detrimental effect on the treatment performance was detected in conditions of this laboratory investigation.     

HORACE BROWN MEMORIAL LECTURE A REALISTIC VIEW ON THE ROLE OF RESEARCH IN THE BREWING INDUSTRY TODAY

Present-day economic pressures stimulate technological innovations toward more rapid processing and to minimise both capital and production costs. Fermentation and maturation practices in most production plants are essentially unchanged from the low productivity batch processes. In terms of process economics two alternatives exist—moving to greater volume accelerated-batch processing and applying fully continuous high rate fermentation systems. Central to these issues are the growth controlling aspects of yeast performance in brewery fermentations. The importance of dissolved oxygen on lipid metabolism, yeast growth and beer flavour, the precise role of storage carbohydrates and the critical nature of the glycolytic/gluconeogenic junction in controlling fermentation performance are reviewed. The objectives of process optimisation are to build up sufficient yeast concentrations to gain optimal rate and extent of attenuation and desired flavour development whilst balancing but not over-expending wort nutrients for growth and maintenance. In this regard great promise may lie with new technologies including yeast oxygenation and immobilised cell systems. Particular emphasis is placed upon the ways in which this may be technically achieved and attention is drawn to the complexity of innovation management. Practical implications of factors benefiting and adversely affecting fermentation efficiency and beer flavour in both traditional and continuous immobilised cell systems are discussed.     

Crystal Structure and High-Temperature Thermoelectric Properties of the Mo<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Ru<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Sb<Subscript>7</Subscript> Compounds

Zintl phases are currently receiving great attention for their thermoelectric potential typified by the discovery of a high ZT value in Yb₁₄MnSb₁₁-based compounds. Herein, we report on the crystallographic characterization via neutron and x-ray diffraction experiments, and on the thermoelectric properties measured in the 300 K to 1000 K temperature range, of Mo₃Sb₇ and its isostructural compounds Mo_3−x Ru _x Sb₇. Even though Mo₃Sb₇ displays rather high ZT values given its metallic character, the partial substitution of Mo by Ru substantially improves its thermoelectric properties, resulting in a ZT value of ∼0.45 at 1000 K for x = 0.8.     

Influence of ZnO Inclusions on the Low-Temperature Thermoelectric Properties of CoSb3

CoSb₃ composites with different amounts of ZnO nanoparticles (2?wt.% to 12?wt.%) were prepared from nanosized ZnO (commercial) and micron-sized CoSb₃ (obtained via solid-state reaction) particles mixed in solution and freeze dried. The resulting powders were densified by spark plasma sintering. The samples were characterized by x-ray diffraction and scanning electron microscopy. It was found that ZnO forms micron-sized clusters at the grain boundaries of the matrix material. The thermoelectric properties (electrical resistivity, thermopower, and thermal conductivity) were measured in the 2?K to 300?K temperature range. Both the electrical and thermal conductivities were observed to decrease with increasing ZnO content. The dimensionless figure of merit ZT was improved by up to 30% at 300?K for the sample containing 2?wt.% ZnO.     

Determination of Residual Ozone or Chlorine Dioxide in Water with ACVK – an Updated Version

The determination of residual ozone or residual chlorine dioxide can be carried out with Acid Chrome Violet K (C.I. code no. 61710, formerly 6170), now available as dye for analytical use under the name of Alizarin Violet 3R (Aldrich 22, 783-8; MW 622.25). The discoloration of the dye in an NH₃-NH₄CI buffered solution of pH 8.1 to 8.5 is specific both for ozone and for chlorine dioxide without interference of chlorine, chloramines, chlorite or chlorate ions in concentrations possibly encountered in treated drinking water.

Detection limit : 0.02 mg L^?l: standard deviation : 0.01 mg L^?l are obtained both for ozone and chlorine dioxide.