The effect of hydrolysate and eluate recirculation on the solubilization and recovery of carbon and nutrients from waste activated sludge during microwave-alkali treatment was systematically investigated. The results showed that the recirculation strategy significantly enhanced the accumulation of sCOD, PO43--P, and TAN in both hydrolysate and eluate, with concentrations increasing by up to 4–9 times depending on recirculation conditions. Despite the enhanced accumulation, the dissolution efficiencies of sCOD, TP, and TN remained stable or even decreased with increasing recirculation cycles, indicating that component accumulation does not necessarily translate into improved recovery. This discrepancy was attributed to the re-association of soluble components with hydrolyzed sludge residues at elevated concentrations, which could be effectively mitigated by elutriation. Furthermore, the recirculation strategy significantly reduced the generation of hydrolysate and eluate as well as water consumption by approximately 75%, demonstrating its potential for process intensification and cost reduction. Overall, this study reveals that recirculation enhances mass transfer and component accumulation, while the overall recovery performance is fundamentally constrained by sludge disintegration and phase redistribution mechanisms.
This study presents the first United States evaluation of a rapid endotoxin-based method for near-real-time microbial monitoring of recreational waters. Conventional culture-based fecal indicator bacteria (FIB) methods require 18–48 h for reporting, limiting timely public health responses to contamination events. To address this limitation, a rapid field-deployable method capable of detecting endotoxin risk in <15 min was evaluated against standard microbial water quality methods across nine freshwater sites in coastal Georgia, USA.The rapid method demonstrated promising diagnostic performance relative to standard methods, particularly with Colilert-18®, achieving a sensitivity of 87.0%, a positive predictive value of 88.9%, and an area under the receiver operating characteristic curve (AUC) of 0.764 (95% CI: 0.589–0.912; p < 0.0066). Similar performance was observed relative to Enterolert® (sensitivity = 88.6%; AUC = 0.745; p = 0.0065). In contrast, associations with plate-based methods were weaker and not statistically significant. The assay also demonstrated relatively low replicate variability (mean CV = 18.1%), comparable to Colilert-18® (22.7%; p = 0.081) and significantly lower than the plate-based methods evaluated (ColiBlue-24®: 43.4% of sets exceeding CV 30%, p = 0.019; Petrifilm®: 64.5%; p ≤ 0.0002), indicating good analytical reproducibility. Correlations between continuous endotoxin response values and culture-based microbial concentrations were generally weak, likely reflecting the broader detection of endotoxins from multiple Gram-negative bacteria rather than specifically targeting FIB. Overall, these findings suggest this rapid approach may serve as a practical screening tool when used alongside confirmatory laboratory-based methods for recreational water quality assessment, emergency response during spills, and resource prioritization.
In a high-resolution investigation of a karst spring impacted by wastewater contamination, we measured electrical conductivity, turbidity, flow cytometric cell counts, organic micropollutants, fecal indicator bacteria, viruses, and antibiotic resistance genes. This multi-indicator approach captured similarities and contrasts of contamination dynamics and resolved wastewater impact more robustly than any parameter alone. Shifts in easy-to-measure parameters (electrical conductivity, turbidity, flow cytometry) occurred concurrently with microbiological and chemical contamination indicators identifying these parameters as promising early-warning proxies. The increase of organic micropollutants like acesulfame (maximum ∼40 ng/L), fecal and viral markers (e.g., coliforms and crAssphage, maximum ∼89 MPN/mL and ∼555 gene copies/mL), and antibiotic resistance genes like sul1 (maximum ∼900 gene copies/mL) confirmed wastewater as origin of contamination. 35 h after the wastewater pulse, a second peak of turbidity and antibiotic resistance genes occurred without the presence of bacterial and viral or chemical indicators. The versatility of flow cytometry allowed a differentiation between different turbidity origins while being available in near-real-time. While the wastewater peak was associated with an ∼8% increase in the proportion of cells with high nucleic acids, the second peak without bacterial contaminants showed solely an increase in dead cells. In general, rather than seeking one universal indicator, effective real-time monitoring in karst groundwater requires integrated, high-resolution, multi-parameter observation. These findings provide evidence for additional tools to identify wastewater pulses not only in karst aquifers, but also in other highly dynamic aquifer systems and streams, thereby improving vulnerability assessment and risk management of water resources.
Wetlands are frequently described as the "Earth's kidneys" because they are among the most complex, productive, and valuable ecosystems globally. However, rapid urbanization has caused widespread wetland degradation and loss, leading to the depletion of ecosystem services and the emergence of serious environmental problems. A comprehensive understanding of how urbanization reshapes wetland landscape patterns, water quality, and biodiversity remains insufficient. Based on 1637 records retrieved from the Web of Science Core Collection, this review combines bibliometric analysis with a qualitative synthesis of 726 studies that met the predefined eligibility criteria to examine urbanization-driven wetland changes from both stress-response and management-response perspectives. The results show that urbanization degrades wetland ecosystems primarily through three interconnected pathways: fragmentation and loss of wetland landscapes, deterioration of water quality due to runoff and pollutant inputs, and biodiversity decline driven by habitat loss and ecological imbalance. At the same time, management responses accompanying urban development, including policy innovation, technological monitoring, restoration investment, and ecological planning, can create opportunities for integrated wetland conservation and urban development. Future urban planning should place greater emphasis on sustainable wetland management and promote the coordinated integration of wetland conservation, restoration, and urban growth.
