Implementation of long solids retention time activated sludge process for rural residential community

Seasonal patterns, fate and ecological risk assessment of pharmaceutical compounds in a wastewater treatment plant with Bacillus bio-reactor treatment

Pharmaceutical compounds (PhCs) pose a growing concern with potential environmental impacts, commonly introduced into the environment via wastewater treatment plants (WWTPs). The occurrence, removal, and season variations of 60 different classes of PhCs were investigated in the baffled bioreactor (BBR) wastewater treatment process during summer and winter. The concentrations of 60 PhCs were 3400 ± 1600 ng/L in the influent, 2700 ± 930 ng/L in the effluent, and 2400 ± 120 ng/g dw in sludge. Valsartan (Val, 1800 ng/L) was the main contaminant found in the influent, declining to 520 ng/L in the effluent. The grit chamber and BBR tank were substantially conducive to the removal of VAL. Nonetheless, the BBR process showcased variable removal efficiencies across different PhC classes. Sulfadimidine had the highest removal efficiency of 87 ± 17% in the final effluent (water plus solid phase). Contrasting seasonal patterns were observed among PhC classes within BBR process units. The concentrations of many PhCs were higher in summer than in winter, while some macrolide antibiotics exhibited opposing seasonal fluctuations. A thorough mass balance analysis revealed quinolone and sulfonamide antibiotics were primarily eliminated through degradation and transformation in the BBR process. Conversely, 40.2 g/d of macrolide antibiotics was released to the natural aquatic environment via effluent discharge. Gastric acid and anticoagulants, as well as cardiovascular PhCs, primarily experienced removal through sludge adsorption. This study provides valuable insights into the intricate dynamics of PhCs in wastewater treatment, emphasizing the need for tailored strategies to effectively mitigate their release and potential environmental risks.

Understanding the role of activated sludge in oxygen transfer: Effects of sludge settleability, solids retention time, and nitrification reaction

The current understanding on the oxygen transfer in activated sludge process is primarily developed based on two-phase systems, focusing only on oxygen transfer from air to water. However, this research demonstrates that activated sludge particles significantly impact oxygen transfer from air all the way to the microorganisms. Three bench-scale complete-mix activated sludge reactors, operated under the same influent loading and dissolved oxygen level but different solids retention times (SRTs), were used to develop oxygen transfer performance data as effects of different sludge property parameters. These reactors were also operated under batch modes to further validate the effect of nitrification reaction on oxygen transfer. Results indicate that high overall oxygen transfer efficiency (OTE) is associated with low mixed liquor viscosity, long SRT, and nitrification reaction. Further analyses suggest that low mixed liquor viscosity, which resulted from high sludge settleability or low settled volume of sludge, reduces the thickness of liquid films at all interfaces and the size of air bubbles. Long SRT results in high active nitrifier population and low specific extracellular polymeric substance (EPS). Nitrification reaction, which serves as the rate-limiting step for oxygen transfer, may increase the oxygen transfer driving force. High active nitrifier population also promotes direct air-sludge contact. All of these factors help facilitate oxygen transfer. This research provides a new approach to improve energy efficiency for wastewater treatment, which is to change the activated sludge property by adjusting treatment plant design and operational parameters. PRACTITIONER POINTS: High sludge settleability reduces viscosity therefore liquid film thickness. Long SRT increases active microorganism population and reduces specific EPS content. Nitrification reaction increases oxygen transfer driving force. Direct air-particle contact adds another pathway for oxygen transfer. Nitrification reaction is the rate-limiting step of the oxygen transfer process.

Techno-Economic Evaluation of Ozone Application to Reduce Sludge Production in Small Urban WWTPs

In Chile, small wastewater treatment plants (WWTPs) (treatment capacity of less than 4,800 m3/d) are normally not designed with consideration for the potential valorization of generated sludge. For this reason, they are generally operated at high solids residence times (SRT) (15 d) to promote the decay of biomass, promoting less sludge production and reducing the costs associated with biomass management. Operation at high SRT implies the need for a larger activated sludge system, increasing capital costs. The implementation of a sludge-disintegration unit by ozonation in future WWTPs could enable operation at an SRT of 3 d, with low sludge generation. In this work, we evaluate how the implementation of a sludge-ozonation system in small WWTPs (200–4000 m3/d) would affect treatment costs. Four scenarios were studied: (1) a current WWTP operated at an SRT of 15 d, without a sludge ozonation system; (2) a WWTP operated at an SRT of 15 d, with a sludge-ozonation system that would achieve zero sludge production; (3) a WWTP operated at an SRT of 3 d, with a sludge-ozonation system that would provide the same sludge production as scenario 1; (4) a WWTP operated at an SRT of 15 d, with a sludge-ozonation system that would achieve zero sludge production. Economic analysis shows that the treatment costs for scenarios 1 and 2 are similar, while a reduction in cost of up to 47% is obtained for scenarios 3 and 4.