There is a considerable diversity of district heating (DH) technologies, components and interaction in EU countries. The trends and developments of DH are investigated in this paper. Research of four areas related to DH systems and their interaction with: fossil fuels, renewable energy (RE) sources, energy efficiency of the systems and the impact on the environment and the human health are described in the following content. The key conclusion obtained from this review is that the DH development requires more flexible energy systems with building automations, more significant contribution of RE sources, more dynamic prosumers' participation, and integration with mix fuel energy systems, as part of smart energy sustainable systems in smart cities. These are the main issues that Europe has to address in order to establish sustainable DH systems across its countries.

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Microbial contamination and biodiversity were determined for the drinking water samples collected from selected points of the water supply system in Wrocław, Poland. All tested samples met the requirements of Polish law, i.e., the Regulation of the Minister of Health. However, the antibiotic resistant bacteria were found. The correlation between the distance of sampling points from water treatment plants and their microbial contamination was not established. Nevertheless, the Na Grobli treatment plant seemed to produce water of higher microbial quality than the Mokry Dwór treatment plant at the moment of sampling. The identification of representative isolates was performed with 16S rRNA gene sequencing and MALDI-TOF mass spectrometry and the results of these two methods were compared, indicating some discrepancies. Nevertheless, bacteria dwelling in drinking water in Wrocław belonged to the phyla Actinobacteria, Proteobacteria (α-, β-, γ-Proteobacteria) and Firmicutes. The determination of antibiotic resistance profiles showed that 12 from 17 tested isolates revealed resistance to at least one antibiotic and two strains were multi-drug-resistant.

Although antibiotic-resistant bacteria (ARB) have been isolated from tap water worldwide, the knowledge of their resistance patterns is still scarce. Both horizontal and vertical gene transfer has been suggested to contribute to the resistance spread among tap water bacteria. In this study, ARB were isolated from finished water collected at two independent water treatment plants (WTPs) and tap water collected at several point-of-use taps during summer and winter sampling campaigns. A total of 24 strains were identified to genus or species level and subjected to antibiotic and disinfectant susceptibility testing. The investigated tap water ARB belonged to phyla Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes. The majority of the isolates proved multidrug resistant and resistant to chemical disinfectant. Neither seasonal nor WTP-dependent variabilities in antibiotic or disinfectant resistance were found. Antibiotics most effective against the investigated isolates included imipenem, tetracyclines, erythromycin, and least effective – aztreonam, cefotaxime, amoxicillin, and ceftazidime. The most resistant strains originate from Afipia sp. and Methylobacterium sp. Comparing resistance patterns of isolated tap water ARB with literature reports concerning the same genera or species confirms intra-genus or even intra-specific variabilities of environmental bacteria. Neither species-specific nor acquired resistance can be excluded.

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