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The use of sewage sludge in anaerobic digestion process: formation, properties, and implementation.
The effect of municipal wastewater treatment, in addition to improving its quality, is sludge formation. Disposal of sewage sludge (SS) is a critical environmental problem that requires careful management. Under current legislation, SS represents waste requiring stabilisation to eliminate pathogenic microorganisms and substances potentially harmful to the environment. Anaerobic digestion (AD) is an efficient method of treating SS, and it produces biogas as a renewable energy source (RES). The efficiency of the process can be increased by combining SS with other organic wastes as cosubstrates. Therefore, AD allows for a twofold benefit crucial for sustainable waste and energy management, i.e. sludge stabilisation and biogas production. Another equally important consideration in the construction of biogas plants at wastewater treatment plants is reducing the plant's operating costs by using the electricity and heat generated in the cogeneration units for the plant's needs. This paper discusses the formation technology and properties of sewage sludge, the legal aspects of using and disposing of SS, the conditions for employing their anaerobic biodegradation, and the co-digestion systems used.
Water Softener Regeneration Effects on the Operation of Domestic Wastewater Treatment Plants: A Preliminary Study
There has been a large amount of scientific research carried out to date on the impact of salty backwash brine from domestic water softeners (WS) on domestic wastewater treatment plants (DWTPs). Experts and practitioners agree that the impact is harmful and there is still a need to look for new technologies. The study of the effect of an increased sodium chloride (NaCl) concentration after softener regeneration is important from the point of view of the operation of DWTPs and soil properties. This paper presents the results of a field study of the concentration of NaCl at the septic tank (ST) drainage point, into which the grey water from the regeneration of the water softener flowed. During the six-month measurements (recorded every 1 min), an increase in NaCl concentration was observed in the septic tank outflow, from an average NaCl concentration of 1.5 g·L−1—between regenerations—to an average concentration of 4.5 g·L−1—after water softener regeneration. The increased NaCl concentration decreased significantly up to 2 days after the water softener regeneration. Temperature changes in the treated wastewater were also measured—during the winter period, temperature differences of up to 10 °C per day were recorded. In the second part of the study, conducted on a semi-technical scale, the effect of brine from the regeneration of the water softener on the hydraulic conductivity (Ks) of the soil from the infiltration drain of the DWTPs studied was assessed. The Ks was determined by analysing the time it took the water to soak into the soil, using the Van Hoorn equation. The results and statistical analysis indicate an increased salt content in the soil absorbing the brine, which may have been influenced by the reduced absorption and capacity of the drain due to adverse physico-chemical changes.
The Influence of Temperature on Rheological Parameters and Energy Efficiency of Digestate in a Fermenter of an Agricultural Biogas Plant
This investigation specifically aims to enhance the understanding of digestate flow and mixing behavior across typical temperatures in bioreactors in agricultural biogas plants, facilitating energy-efficient mixing. Experimental tests confirmed that digestate exhibits non-Newtonian characteristics, allowing its flow behavior to be captured by rheological models. This study validated that digestate rheology significantly varies with temperature, which influences flow resistance, mixing efficiency and overall energy requirements. Two rheological models—the Bingham and Ostwald models—were applied to characterize digestate behavior, with the Ostwald model emerging as the most effective for Computational Fluid Dynamic (CFD) simulations, given its balance between predictive accuracy and computational efficiency. Specifically, results suggest that, while three-parameter models, like the Herschel–Bulkley model, offer high precision, their computational intensity is less suitable for large-scale modeling where efficiency is paramount. The small increase in the accuracy of the shearing process description does not compensate for the significant increase in CFD calculation time. Higher temperatures were found to reduce flow resistance, which in turn enables increased flow rates and more extensive mixing zones. This enhanced mass transfer and mixing potential at elevated temperatures are especially pronounced in peripheral areas of the bioreactor, farthest from the agitators. By contributing a model for rheological behavior under realistic bioreactor conditions, this study supports the optimization of energy use in biogas production. These findings emphasize that temperature adjustments within bioreactors could serve as a reliable control strategy to maintain optimal production conditions while minimizing operational costs.
Beaver Dams as a Significant Factor in Shaping the Hydromorphological and Hydrological Conditions of Small Lowland Streams
Beavers play a key role in creating temporary water reservoirs that significantly impact the natural environment and local river hydrology. The primary aim of this study was to assess the potential of increasing the number of beaver dams (Castor spp.), as an alternative method of water retention in the environment. Research conducted on three small lowland streams in central Poland revealed that beaver dams, even in modified riverbeds, enable the formation of shallow floodplains and ponds. Innovative analyses considered the structural materials of the dams and their impact on river hydromorphology and sediment transport. The findings emphasise the importance of beavers in water retention processes, the stabilisation of water levels during low flows and the protection of biodiversity. The study also demonstrated that beaver dams play a critical role in storing surface- and groundwater, mitigating drought impacts, reducing surface runoff, and stabilising river flows. These constructions influence local hydrology by increasing soil moisture, extending water retention times, and creating habitats for numerous species. The collected data highlight the potential of beaver dams as a tool in water resource management in the context of climate change. Further research could provide guidance for the sustainable utilisation of beavers in environmental conservation strategies and landscape planning.
Preparation of Samples for the Study of Rheological Parameters of Digested Pulps in a Bioreactor of an Agricultural Biogas Plant
The studies of the rheology of digested pulp from agricultural biogas plants have often been fragmentary and non-standardised due to their complexity and time-consuming nature. As a result of measurements, it was possible to develop a procedure and range of measurements for the correct determination of the parameters of the carrier substance. The applicability of the coaxial cylinder measurement system was demonstrated for assessing the rheological parameters of digested pulp from a fermenter that utilises agricultural biomass. To determine the characteristics of solid particles, the Zingg diagram was used, inter alia, allowing the comparison of particles from each fraction. The analysis of the shape and size of solid particles may help to describe the onset of motion of this phase, flow type, or sedimentation type. The authors propose a completely new research approach to obtain an appropriate, repeatable test conditions of medium, which is the carrier liquid from the biogas plant reactor. The proposed methodology and the scenario of the entire study make it possible to achieve scalable and comparable test results in any laboratory. The proposed solution eliminates the influence of most external factors on the sample and rheological measurements, and the effectiveness of the presented procedure was confirmed in tests.
Podajnik biokomponentów sypkich, zwłaszcza do brykieciarek ślimakowych oraz peleciarek oraz sposób produkcji brykietu z biokomponentem sypkim
Modified field method for testing activated sludge condition in chambers with variable wastewater levels
Nitrogen compounds in effluents from a septic tank
The paper presents the results of long-term studies on the concentrations of total nitrogen and ammonium nitrogen in a septic tank effluent. A statistical analysis concerning the sampling day and the season was performed. The mean concentration of total nitrogen in the effluent was 47±9 g N/m3 and the mean concentration of ammonium nitrogen was 33±11 g N/m3. Results on the cumulative distributions of total nitrogen and ammonium nitrogen in the outflow from the septic tank have also been presented.