Abstract. The aim of this paper is to identify the general trend of changes and the basic requirements of the most important lagoon system of the Black Sea, on the basis of critical analysis of existing data. A more coherent set of data sampled after 1988 on the basis of some intensive and extensive study and research programmes, including the main trophic parameters and the most representative structural and functional features of this complex of ecotonal lakes, is comparatively analysed together with more fragmentary data previously existing. The structural and functional changes within this complex of lakes were analysed based on 31 most representative variables belonging to the main abiotic and biological compartments of the two main lakes, Razim and Sinoe: dissolved organic carbon, dissolved oxygen, trophic state index TSI, nutrient content and ratio, salinity, chlorophyll, phytoplankton, zooplankton, submerged macrophytes, zoobenthos, fish and birds. Two stages were distinguished in the main structural changes, including morphometric connections with the Danube River and the Black Sea and hydrochemistry and its effects on communities. These transitions were associated with two main driving forces, water desalinisation and rapid eutrophication, and with other two kinds of man-induced changes, local hydrotechnical buildings and long-distance variables operating over the entire Danube River watershed. The information support system for sustainable management of the Razim-Sinoe Lagoon Complex as a part of the Danube Delta Biosphere Reserve, integrating existing data from research programmes and an integrated monitoring system for new data is a final conclusion on further needs.

The paper deals with some aspects regarding the behavior of modern and efficient solutions - for rehabilitation of reinforced concrete framed structures. The paper is devoted to experimental studies on carbon fiber reinforced polymer (CFRP) systems used as strengthening solution for reinforced concrete (RC) frames assumed as existing structures, which were tested as un-strengthened and as (CFRP) strengthened structures. Single span and single story frames (scale 1:2) were designed and detailed according to the Romanian design codes from 1970s under which seismic design was inadequate. The RC design and the magnitude of applied forces were ensuring the failure mechanism, of non-strengthened RC frames, by plastic hinges at columns ends. Then the columns were strengthened by using CFRP materials. The experimental program emphasized some important aspects regarding the behavior and failure by debonding of CFRP strengthening materials applied to RC frames. The analysis of experimental data and theoretical values showed up an increase of resistance and stiffness achieved by strengthening.

The paper describes some studies on the influence of water flow rates through water-supply networks on drinking water quality. Water residence time in pipelines for more than seven days in buried pipes and two days in above-ground pipes promotes the development of biochemical systems when the flow rates are low and very low having detrimental consequences on drinking water quality. These shortcomings are due to the residual chlorine decrease below the allowed technical limits (0.5 m/s) as a consequence of the fact that in distribution pipes, fittings and drain junctions the water flows at low rates reaching far to stagnate over the admitted residences. The case study was conducted on the water-supply network in the city of Timişoara using the EPANET program. The hydraulic parameters (flow, diameter, flow rate, loss of head) of EPANET are correlated with the water stagnation periods (residents) on pipe sections with residual chlorine allowed at every point of consumption. After analyzing the distribution of water flow rates in the network, it was concluded that in almost all situations these were between 0.3-0.9 m/s. For a safe disinfection, the residual chlorine in drinking water must be at least 0.3 mg/L.

This paper presents the results from a study which simulates wastewater depollution processes using advanced biological methods. The experimental research was performed in a static biological reactor, equipped with an air compressor and an agitator / mixer. Synthetic wastewater, prepared with the addition of glucose, was fed into the reactor. The wastewater was subjected to alternating cycles of aeration and slow mixing, for consecutive 3 h intervals within the reactor to ensure the necessary conditions for the reduction of nitrogen based organic compounds within the wastewater. In the successive aeration processes, aerobic / nitrifying microorganisms which developed within the reactor, facilitated the decomposition of organic substances into nitrites and then into nitrates. By stopping aeration and starting the slow mixing cycle the anaerobic / denitrifying microorganisms growing in the reactor consume the necessary oxygen from nitrates and release free nitrogen into the atmosphere, thus completing the process of advanced depollution. Therefore, the experimental procedure highlights the existence of two distinct phases in the development of the depollution process. In the first phase, the biological process is initiated using glucose in order to promote the growth of the bacterial flora. In the second phase (the regime phase), the reduction of mineral and organic pollutants from the wastewater is ensured. The activity of microorganisms in the biological reactor can be further supported by the recirculation of activated sludge retained in the secondary decanter. The proposed technology offers a fast, safe and relatively inexpensive method for advanced wastewater depollution. Bioreactors of this type are recommended in wastewater treatment schemes in the hearth of rural localities, agro-zootechnical complexes and tourist units with seasonal activities due to their fluctuations in hourly wastewater flow rates. Similar approaches can also be considered for the elimination of ammonium compounds in groundwater polluted with animal manure.

Generally, in Romania, the water treatment aimed at removing the classic compounds of iron, manganese, ammonium, nitrates / nitrites, etc. by the known classical technologies (chemical coagulation, precipitation, decantation, slow / fast filtration with free / under pressure, disinfection). When in the raw water, besides the classical compounds, heavy metals semi-metals are also found, together with the classical treatment technologies, advanced technologies are required combined, known as hybrid processes (Electro-coagulation / EC, oxidation, adsorption / exchange ions, membrane filtration -UF / NF / RO), which can lead to the desired results. Along with iron, manganese, ammonium, nitrites / nitrates, arsenic is a naturally occurring element in the Earth’s crust. Arsenic in drinking water is a global problem affecting the population worldwide because the arsenic and its components have carcinogenic properties. Regarding the elimination of arsenic (As) found in the water especially collected from the underground, the studies and researches applied were much more restricted and the applications completely isolated, at present the subject being more intensely approached. This situation is also caused by the fact that the Water Framework Directive no.98_83_CEE, transposed into national legislation, lowered the Arsenic (As) chemical indicator limit to 10 μg As / L (from 50 μg As / L). An alternative / complementary technology with low maintenance costs for underground treatment is Electro-oxidation/coagulation (EC), which has been of increasing interest in the last decade. The use of pilot stations / equipment for studying potential treatment technologies is essential for optimizing the treatment schemes and in order to avoid the implementation of costly technologies that cannot work for various reasons. In this case study, it was analysed comparatively from the efficiency point of view combining and optimizing oxidation-coagulation-filtration technologies in a pilot station for water treatment with iron, manganese and arsenic content, coming from the medium depth underground source (western Romania). In the initially provided technological flow (oxidation with ozone, multimedia filtration and disinfection with hypochlorite for the remanence), an electro-coagulation / oxidation (EC) cell was introduced upstream of the multimedia filter. This process aimed at eliminating the use of chemicals (ferric chloride) from the coagulation process that would have caused the rapid alteration of the multimedia filter and consequently increased operating costs. The results showed that compared to conventional technologies, the EC advantage includes high disposal efficiency, a compact treatment plant and the possibility of complete automation.