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The article discusses a study that developed a novel and effective approach for enzyme immobilization based on entrapment into the walls of poly(N-isopropylacrylamide) (PNIPAAm) cryogels. It details the use of ultraviolet (UV) irradiation technique and hydrogen peroxide as an initiator to prepare the supermacroporous PNIPAAm cryogels containing urease. It is suggested that the PNIPAAm cyrogels could be used as a permeable membrane for direct removal of traces of urea from continuously flowing feed solutions.

The main transformation processes effected by the natural microbial consortium of upper Iskar River with predominant participation of sediment biofilm were simulated in the laboratory by the use of portable devices (chambers). The dynamics of real heterotrophic respiration, organic matter oxidation, denitrification and ammonification were analysed by oxygen depletion, reduction of chemical oxygen demand, nitrate uptake and ammonium accumulation, under the conditions prevailing during high and low flow periods. The experimental results showed fast oxygen consumption and high process rates - indicators for intensive respiration by a heterotrophic microbial consortium and good functioning of the ecosystem component studied. The nitrogen transformations occurred at slower rates but in mutual dynamic balance and their simultaneous realisation was due to precise, adaptive division in time and space. [ABSTRACT FROM AUTHOR]

The aim of this study was to elucidate the role, the space distribution and the relationships of the bacteria from the genus Pseudomonas in a biofilm community during semi-continuous Amaranth decolourization process in model sand biofilters. The examined parameters of the process were as follows: technological parameters; key enzyme activities (azoreductase, succinate dehydrogenase, catechol-1,2-dioxygenase, catechol-2,3-dioxygenase); the number of azo-degrading bacteria and the bacteria from genus Pseudomonas (plate count technique); the amount and the location of Pseudomonas sp. using fluorescent in situ hybridization (FISH). The results showed that the increase of the Amaranth removal rate with 120% was accompanied with increase of the enzyme activities of the biofilm (azoreductase activity - with 25.90% and succinate dehydrogenase - with 10.61%). The enzyme assays showed absence of activity for сatechol-1,2-dioxygenase and catechol-2,3-dioxygenase at the early phase and high activities of the same oxygenases at the late phase (2.76 and 1.74 μmol/min mg protein, respectively). In the beginning of the process (0-191 h), the number of the culturable microorganisms from genus Pseudomonas was increased with 48.76% but at the late phase (191-455 h) they were decreased with 15.25% while the quantity of the non-culturable bacteria from this genus with synergetic relationships was increased with 23.26%. The dominant microbial factors were identified in the structure of the biofilm during the azo-degradation process by using FISH analysis. Furthermore, the inner mechanisms for increase of the rate and the range of the detoxification were revealed during the complex wastewater treatment processes.

The influence of mercury on the transformation processes in the waters and the sediments in the reservoir of a small hydroelectric power plant (SHPP) Lakatnik was simulated in laboratory conditions. SHPP Lakatnik is the first (of nine similar) SHPPs put into exploitation in the middle part of the Iskar River (Bulgaria). In previous studies of the sediments in the reservoir of SHPP Lakatnik, our team found high concentrations of mercury, sometimes exceeding maximum concentration limit (MCL). In model bioreactors we studied the effect of mercury on the dynamics of the following hydrochemical and microbiological indicators: NH 4 + , NO 3 - , NO 2 - , PO 4 3- , chemical oxygen demand (COD), total organic carbon (TOC); aerobic and anaerobic heterotrophs (AH and AnH), Pseudomonas spp. (Ps.), Acinetobacter spp. (Ac.), sulphate-reducing bacteria (SR), denitrifying microorganisms (Dn). We looked for linear correlations among the studied indicators in order to find quick, mutual replaceability among them. The extent to which mercury affects the amount of key microbial groups and the rate of transformation of biogenic elements was calculated in percentages. The microorganism dynamics showed that AH, AnH and Ps. adapt more quickly and their number increased more in the presence of mercury, whereas SR, Dn and Ac. were inhibited to a greater extent by the presence of mercury. Mercury had a marked stimulating effect on Ps., which showed a 312% increase in number at the 192nd hour. The obtained results can be used when decisions have to be taken in risky situations related to increased concentrations of mercury in the sediments.

The Middle Iskar cascade is situated along the middle course of the Iskar River (Bulgaria) after the capital city Sofia and has three small hydroelectric power plants that were put into operation by the end of 2012. The aim of this study was to evaluate the self-purification potential of water in the reservoirs of these plants as an important and necessary condition for their ecological functioning. The assessment was made by hydrochemical parameters (dissolved suspended solids, insoluble suspended solids, total suspended solids, nitrites, nitrates, ammonium, phosphates, chemical oxygen demand, dissolved oxygen) and microbiological parameters (aerobic heterotrophic bacteria and bacteria growing in an Endo medium) and covered a period of three years (2010, 2011 and 2012). Standard methods were applied, mainly colorimetric and microbiological cultivation methods. The obtained results showed high levels of some of the tested indicators during 2012. In the section of the Middle Iskar cascade a high self-purification potential was observed in the reservoirs which maintain good water quality.