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M. Reimanis, L. Mezule, J. Ozolins, J. Malers and T. Juhna

Nowadays electrochemical disinfection has gained an increasing attention as an alternative to conventional drinking water disinfection, since it is regarded as environmentally friendly, amendable to automation, inexpensive, easily operated and is known to inactivate a wide variety of microorganisms from bacteria to viruses and algae. We found that along with increasing the number of electrodes in our equipment from 2 to 24, the resistance of chlorine-generating electrolytic cell and specific work of electric current decreased. During the electrolysis the amount of generated Cl2 increased along with the increase of chloride ion concentration in the solution and the intensity of electric current. The technological process parameters (flow rate, current intensity) have been established to obtain a predetermined amount of generated chlorine during the electrolysis process. A comparison of flow and circulating (3 times) regimes for electrolysis of tap water with chloride ion concentration below 10 mg/L showed that circulation is necessary to generate active chlorine (above 1 mg/L).

At the same time, when no circulation was performed, even a 0.9 A treatment was not enough to generate detectable levels of free chlorine. Electrochemical disinfection of tap water with non-stoichiometric titanium oxide electrodes was effective enough to inactivate both metabolically active and cultivable bacteria E. coli to undetectable levels within 15 minutes at 0.5 A current intensity.

Open access

A. Vevers, A. Kromanis, E. Gerins and J. Ozolins

Abstract

The casting technology is one of the oldest production technologies in the world but in the recent years metal additive manufacturing also known as metal 3D printing has been evolving with huge steps. Both technologies have capabilities to produce parts with internal holes and at first glance surface roughness is similar for both technologies, which means that for precise dimensions parts have to be machined in places where precise fit is necessary. Benchmark tests have been made to find out if parts which are produced with metal additive manufacturing can be used to replace parts which are produced with casting technology. Most of the comparative tests have been made with GJS-400-15 grade which is one of the most popular cast iron grades. To compare mechanical properties samples have been produced using additive manufacturing and tested for tensile strength, hardness, surface roughness and microstructure and then the results have been compared with the samples produced with casting technology. In addition, both technologies have been compared in terms of the production time and production costs to see if additive manufacturing is competitive with the casting technology. The original paper has been written in the Latvian language as part of the Master Thesis within the framework of the production technology study programme at Riga Technical University.

Open access

V. Lakevičs, J. Brovkina, V. Stepanova, I. Dušenkova, J. Ozoliņš, G. Šuļga and L. Bērziņa-Cimdiņa

Currently there is an increasing interest in application of natural clay minerals in production of various products, including sorbents for waste water treatment. For practical application of clay as a sorbent, it is significant not only to establish its properties, but also to be able to modify them. Only during the last twenty years, an increasing effort has been directed to systematic studies of clay sorption properties. A special attention has been devoted to improvement of clay sorption properties, which could allow to scientifically develop various sorbents for collection of oil products, such as oil spills from water surface, water processing and cleaning of waste waters from heavy metal ions, organic and inorganic admixtures, etc.

In this study, surface properties of Latvian Triassic (Vadakste deposit) smectite-containing clay samples were examined, in order to develop cheap, clay-based sorbents of high quality. Using sedimentation method, the granulometric composition of natural clay samples was determined. Surface morphology of the obtained samples was studied by using scanning electron microscopy. Sorption properties of natural Vadakste deposit clay samples were modified by thermal treatment, as well as by adding a natural modifier based on hemicellulose and lignin (HLS). This type of clay modification has almost never been used in practice. Optimal thermal treatment conditions and HLS modification conditions were determined for the natural clay samples. It was found that water absorption decreased with increasing the thermal treatment temperature from 300 to 500 and 800 °C, however silicone oil and rapeseed oil absorption doubled at the same time. After adding HLS to clays within the range of 0.053% to 0.13%, both water and oil absorption doubled. The ability of natural and modified clay samples to adsorb copper and zinc ions from the corresponding salt solutions was investigated. The obtained results proved that the developed clay-based sorbent granules can be used for removal of copper and zinc ions from waste water, for collection of oil and oily substances; and as a cheap, environmentally safe pet litter.

Open access

G. Bagrade, V. Šnábel, T. Romig, J. Ozoliņš, M. Hüttner, M. Miterpáková, D. Ševcová and P. Dubinský

Abstract

45 red foxes (Vulpes vulpes) from various regions of Latvia were examined by necropsy between 2003 and 2008 for the presence and infection intensity of Echinococcus multilocularis. The overall prevalence was 35.6 %, with the intensity of infection ranging from 1 to 1438. Although a limited number of foxes were examined, the prevalence was high and infected animals were found throughout the country. Considering the increasing number of humans infected with echinococcosis in Latvia since 2002, the situation is highly suggestive of a recent emergence of E. multilocularis. DNA sequences of four fox isolates were examined by multilocus analysis of mitochondrial and nuclear genes (cox1, nad1, rrnS, atp6, actII). All isolates were allocated to the predominant genetic form in Europe, with partial affinity of one isolate to a genotype that had previously been reported from southern Germany.