The light scattering method is a valuable tool for accessing particle size and structure mainly due to fast and the nonintrusive nature of the measurement. The method is based on a scattered intensity pattern and depends on particle volume, particle morphology, the light wavelength and the scattering angle. The light scattering model, for particles characterised by a fractal structure, is enabled with the use of the Rayleigh-Gans-Debye theory under constrained assumptions. The range of validity of the Rayleigh-Gans-Debye is limited when primary particles constituting aggregate have a size close to the wavelength. In this work, a range of particle sizes was characterised in order to achieve a better understanding of the relationship between flocs size and its fractal dimension. Hence, the width of the power law regime is discussed. What is more, a specific fractal dimension value of activated sludge flocs was found for each of the analysed wastewater treatment plant, which suggests that the spatial structure of suspensions constituting the activated sludge is an individual characteristic of each treatment facility. It has been shown that activated sludge consists of microflocs from the range of 1–10 μm, which constitute approximately 90% of all the population.

It is often only at the operation stage of a wastewater treatment plant that there is a need to adjust the treatment process in terms of variable hydraulic capacity, increased pollutant load, high/low concentration of suspended biomass, or the unfavorable phenomenon of reduced sedimentation capacity of the activated sludge. One of the ways to improve the treatment process efficiency is to increase the biologically active surface by using bio-carriers in the form of fibers, materials, or bio-balls. This paper presents the results of a wastewater treatment plant operation during the period of six months after the implementation of the integrated fixed-film activated sludge (IFAS) technology. The research showed that microorganisms developed both in the activated sludge and on the fibers, positively influencing the activated sludge condition. During the start-up of the IFAS process, ciliates predominated over the other species. However, as oxygen content was high (2 mg/dm³ and more) and textile beds were used, the protozoan population developed intensively, and small metazoans became increasingly common. Throughout the research period, nitrifying and phosphorus-accumulating bacteria were observed both in the activated sludge and on the fibers. Between the 59th and 184th day of operation, numerous microorganisms were detected on the fibers and in the activated sludge, testifying to low biological oxygen demand, good aerobic conditions for nitrification, and long sludge age. However, the process seemed to break down after day 72, when the occurrence of metazoan led to reduced sludge production; after day 88, chemical oxygen demand and total suspended solids in the outflow increased, and oligochaetes and rotifers dominated the suspended sludge and fibers. Results also showed that the textile bed and low ammonia concentration became an excellent substrate for the development of Stentor sp. With regard to chemical and biological oxygen demand, total nitrogen- and total phosphorus-effluent concentrations were mostly within the legally permissible limits throughout the 184 days of operation.

With an increasing frequency of extreme weather events wastewater treatment plant operators face a need to increase plant hydraulic capacity while continuing to comply with effluent quality requirements. An economically attractive way to meet this challenge is to significantly improve secondary settling tank performance and therefore assure safe wet weather plant operation. The objective of this study was to evaluate gravimetric selection technology conducted in hydrocyclones as a way for improving activated sludge settling characteristics in continuous flow BNR with a long sludge retention time and assess its ability to form granular sludge. Long term operational data and sludge morphology monitoring data were analysed. A significant drop in sludge volume index (SVI) (to values under 50 ml/g) and increase in return activated sludge solids concentration (to values above 20 g/L) was observed. Hydrocyclone installation consistently, selectively retained denser, larger flocs in the system and after a start-up phase large granules begin to appear. Gravimetric selection did not prevent the seasonal filamentous biomass outgrowth and temperature drop at the beginning of winter resulted in rapid rise of SVI and SST sludge blanket height especially after heavy rain. Technology under study proved to be effective under certain process conditions but it needs further research to consistently maintain low SVI values throughout the whole year.

The study presents the original research results of morphological parameters of activated sludge flocs taken from the Wastewater Treatment Plant located in Brzeg Dolny. It has been shown that activated sludge suspension consisted of small flocs below 10 μm in proportion of fibrous and circular...

As cities expand and human activity increases, peri-urban areas – regions on the outskirts of cities – are developing rapidly. This affects water quality including pollutants and antibiotic resistant bacteria and genes. While urban water systems have been studied extensively, peri-urban water systems are less understood. Researchers tested water and sewage quality at seven locations in a peri-urban area serving over 2,500 people during spring and winter. The research results showed that microplastics were not present in samples of raw or tap water, or in treated sewage. However, microplastics were found in raw sewage, raising environmental and health concerns. Antibiotic resistance genes were present in most samples except for drinking water from the supply network though it still contained some microorganisms. After sewage was discharged into a river antibiotic resistance gene levels increased by about 50%. The most common resistance genes in raw sewage were tetA and blaTEM. Wastewater treatment effectively removed over 90% of integrase genes in both seasons helping to reduce the spread of resistance. These results show the need for more research to understand and address water contamination risks in peri-urban areas.