Enviroment

University of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
e-mail: petkov@uctm.edu

Received 20 November 2000; Accepted 30 November 2000

The wide application of mercury and its compounds in technics and technology, in chemical and pharmaceutical industry, in medicine and laboratory practice increases the risk of pollution of the environment at the work place and creates hazards for intoxication of the people involved.

The effect of liquid mercury, as well as its vapors on humans is discussed. The acute and chronic intoxication and the conditions at which they are occurring are discussed. In order to prevent them a certain labor safety and hygiene precautions are suggested. The way of demercurization of the work place and the workers is under consideration.

Keywords: mercury, poisoning in humans, precautions, prevention, demercurization.

University of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
e-mail: petkov@uctm.edu

Received 31 October 2000;
Accepted 20 November 2000

One of the basic tasks of the industry is to utilize wastes coming from technological processes so that they do not pollute the natural environment. An obvious and direct consequence of supplying society with water is the problem with the deposition or utilization of sewage sludge. Its solution depends primarily on the knowledge of sludge composition and properties. Investigations on the sludge from wastewater treatment plant in Sofia were carried out. The main characteristics – water and dry mass content, the main components and amount of inorganic and organic parts, the heat value and heavy metals content were determined. According to the results, the possible ways of sludge utilization are discussed.

University of Chemical Technology and Metallurgy
8 Kl. Ohridski, 1756 Sofia, Bulgaria
e-mail: petkov@uctm.edu

Received 31 October 2000; Accepted 20 November 2000

A literary survey presents the possibilities for utilization of sludge obtained during purification of sewage. Data tables are given as an illustration for sludge composition, depending on their origin and the permitted content of heavy metals for sludge used as manure.

The achievement of European and US companies in sludge utilization are presented. Technologies for manufacturing of briquettes, bricks and other building materials are proposed, as well as a waste - free technology for sludge utilization.

University of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
e-mail: tfp@uctm.edu

Received 20 November 2000 Accepted 30 November 2000

The metallurgy utilizes unrecoverable mineral resources.The Bulgarianferrous metallurgy is being supplied only to some extent with our own national iron-containing raw materials.On the other hand the metallurgical industry occupies a second position with respect to the amount of discharged solid waste materials-3%. This fact determines their transformation into highly effective secondary raw materials.

The method for the utilization of polymetallic ores and waste materials can be classified as physical and chemical ones.The most widely occurring physical methods are based on the magnetic properties of the iron oxides and the magnetic enrichment of the materials depends on many factors - the content of the magnetic component, the temperature,the form and the size of the particles,the viscosity of the medium.

The general factor is the strength of magnetic attraction of the particle, directed towards the surface. The chemical methods as pyrometallurgical, hidrometallurdical and combined of main part towards the extraction of nonferrous metals and their use as scrap materials.

The analysis of the methods,elaborated throughout the world,for the treatment of waste materials shows that none of them is an universal one and that the effectively is determined by the specific properties of the waste materials.

Keywords: waste, utilisation, ferromagnetic properties, pyrometallurgy, hydrometallurgy.

University of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
bogdana@uctm.edu

Received 20 November 2000 Accepted 30 November 2000

This paper presents the results of the preliminary study on the sewage sludge dewatering in Sofia Wastewater Treatment Plant with recently installed filterpresses. Samples of raw sludge coming from a thickener, conditioned sludge after preliminary dewatering in filterpress, filtrate and sludge cake were characterized. The change of moisture and organic matter content during the process was studied. The filtrate was characterized by measuring of suspended solids content, COD and BOD. Cake samples were analysed using IR-spectroscopy, silicate analysis, elementary analysis and AAS as well. The rheological characteristics of the raw and conditioned sludge were determined. Their behaviour is non-Newtonian. It could be described by Ostwald-de-Vaele power law rheological model in the case of raw sludge and by Herschel-Bulkley rheological model in the case of the conditioned sludge. The values of the parameters in both models were determined.

A. Petkov, J. Balgaranova, V. Mincheva, G.Georgieva