Due to the key role of the biological decomposition process of organic compounds in wastewater treatment, a very important thing is appropriate aeration of activated sludge, because microorganisms have to be supplied with an appropriate amount of oxygen. Aeration is one of the most energy-consuming processes in the conventional activated sludge systems of wastewater treatment technology (may consume from 50% to 90% of electricity used by a plant), which makes it the most cost-generating process incurred by treatment plants. The paper presents the construction of aeration systems, their classification as well as parameters and factors that significantly affect the aeration process e.g., oxygen transfer efficiency, diffuser fouling, methods of dealing with diffuser fouling, diffuser selection. Additionally, there are briefly presented “smart control” systems in wastewater treatment and effect of application control strategy based on Supervisory Control and Data Acquisition system connected with the decrease in the energy consumption for aeration of bioreactors with activated sludge. It is noted that before the process is optimized, the system should be equipped with suitable metering devices. Only when relevant data is available, the improvements can be carried out. However, it’s important, that the operator should regularly maintain good condition and high efficiency of diffusers.

A study was conducted to characterize the raw wastewater entering a modern cost effective municipal WWTP in Poland using two approaches; 1) a combination of modeling and carbonaceous oxygen demand (COD) fractionation using respirometric test coupled with model estimation (RT-ME) and 2) flocculation/filtration COD fractionation method combined with BOD measurements (FF-BOD). It was observed that the particulate fractions of COD obtained using FF-BOD method was higher than those estimated by RT-ME approach. Contrary to the above, the values of inert soluble fraction evaluated by FF-BOD method was significantly lower than RT-ME approach (2.4% and 3.9% respectively). Furthermore, the values for low colloidal and particulate fractions as well as soluble inert fractions were different than expected from a typical municipal wastewater. These observations suggest that even at low load (10% of the total wastewater treatment inflow), the industrial wastewater composition can significantly affect the characteristics of municipal wastewater which could also affect the performance and accuracy of respirometric tests. Therefore, in such cases, comparison of the respirometric tests with flocculation/filtration COD/BOD measurements are recommended. Oxygen uptake rate profile with settled wastewater and/or after coagulation-flocculation, however, could still be recommended as a “rapid” control method for monitoring/optimising modern cost-effective wastewater treatment plants.

Innovative low-temperature disintegration (process temperature 55 °C and oxygen concentration 0.2 mg/dm³) can be an economically rational technology to intensifying energy production from renewable sources. The proposed process can achieve a degree of disintegration—under optimal conditions—of about 50%, which is excellent when compared with other methods of feed pre-treatment. The low-temperature disintegration of distillation residue and waste-activated sludge before the co-fermentation process increased biogas production by 30% and methane production by 65% (over a 26 d duration). The obtained results confirm that the low-temperature disintegration method can be effectively used to pre-prepare this type of feed. At the same time, it was discovered that the Gompertz model can be used to mathematically describe the biogas accumulation curves in the methane co-fermentation processes of the tested feeds (the correlation coefficients were higher than 0.98).

The global crisis of the Coronavirus disease-2019 (COVID-19) pandemic has caused an enormous burden not only on the health, social, and economic sectors but also on many essential municipal services. Water distribution and wastewater management have faced increasing uncertainty due to the possible transmission of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) via aerosols. Additionally, behavioral and social changes have impacted the water/wastewater services and caused the need for adaptation. In this study, the presence of SARS-CoV-2 in the influent of wastewater treatment plant located in Poland was analyzed November–December 2020, while other parameters important for the water/wastewater sector (e.g.: water usage and wastewater quality) were monitored in long-term period (2015–2020) during the working days, and holidays, including the 2020 lockdowns. In all tested wastewater samples, the genetic material of SARS-CoV-2 was detected, which confirmed the utility of wastewater monitoring to analyse the COVID-19 trends in local communities. Another important issue was the elevated presence of surfactants and the observed change in the organic matter structure in raw wastewater generated during lockdowns. Also the NGS approach and 16S rRNA amplicon sequencing confirmed the changes of functional diversity and heterogeneity in activated sludge bacterial community, especially in terms of nutrients removal and biomass separation. Thus, it is crucial to a baseline understanding of how the water-wastewater sector can serve to control disease transmission among the community and which tools should be adopted as countermeasures not only for new water consumption patterns but also for keeping safe and effective wastewater treatment. Graphical abstract

Recovering nitrogen from wastewater is vital for a circular economy, yet conventional air stripping is limited by aerodynamic backpressure and CO₂-induced pH drops. This study evaluates a novel pilot-scale engineering approach for municipal reject water, integrating chemical phosphorus precipitation with a fundamentally redesigned ammonia stripping column. Upstream calcium hydroxide dosing achieved >99.9% phosphorus recovery and spontaneously alkalized the effluent (pH > 12.1), eliminating supplementary caustic addition. The downstream stripping column utilized negative-pressure (vacuum) operation and high-pressure liquid atomization to maximize mass transfer while preventing flooding and alkalinity neutralization. Comprehensive on-site testing established a clear mathematical relationship between aerodynamics and efficiency. Results demonstrate that high-efficiency recovery requires gas-to-liquid (G/L) ratios exceeding 70:1, a threshold uniquely unlocked by this negative-pressure design. Under optimal conditions, the continuous-flow system achieved 87.6% ammonia removal. A low-resistance acid scrubber captured ~100% of the volatilized ammonia (exhaust 0–1 ppm), producing a concentrated ammonium sulfate bio-fertilizer. This integrated technology provides a scalable, applied engineering blueprint for advancing sustainable Water Resource Recovery Facilities.