The extent to which denitrification can occur under oxygenated conditions in activated sludge systems remains uncertain, despite multiple researchers having studied the phenomena in pure cultures and enrichtments. This study investigated the denitrification capacity of activated sludges sampled from 7 Dutch wastewater treatment plants (WWTPs) with varying process configurations, with the goal of distinguishing between true aerobic denitrification and denitrification occurring in anoxic micro-environments within sludge flocs. Batch experiments were conducted under controlled dissolved oxygen concentrations to quantify nitrogen transformation rates, while image analysis was used to evaluate sludge structural characteristics of fractal dimensions and solidity.
Results indicate that denitrification under oxygenated conditions is largely negligible for conventional activated sludge systems, with only the Dokhaven A-stage sludge exhibiting substantial nitrate reduction at low dissolved oxygen levels. Despite multiple researchers having achieved aerobic denitrification from activated sludges via anoxic/oxic cycling, this selection seemingly does not take place in the multiple oxygen transitions within WWTPs. This suggests that aerobic denitrification is not selected under solely cycling, but is strongly influenced by process-related selective pressures, such as high organic loading and short sludge age. Furthermore, sludge morphology did not show a clear relationship with denitrification capacity under oxic conditions, implying that the presence of dense, compact aggregates alone does not translate to anoxic niches facilitating denitrification in oxygenated environments. ... Read more

This study applied a Community-Based Participatory Research (CBPR) approach to assess water-related challenges on San Cristóbal Island, Galápagos, Ecuador. Data was collected by means of semi-structured interviews (74 households), stakeholder interviews, expert consultations, and additional 150 questionnaires (150 residents) regarding water vulnerability and flood risk. This research assessed lived experiences alongside governance mechanisms, investment plans, and socio-economic status and highlights the individual responsibility and adaptability requirements by residents of San Cristóbal in regards to water scarcity, quality and floods.

The island’s gravity-led distribution network covers 93.07% of households but operates intermittently (3 hours/day), necessitating storage at the household level and shifting maintenance responsibilities to residents. As a result, vulnerabilities differ across and within neighbourhoods according to storage type, cleaning practices, chlorine use and geographic location, none of which show consistent correlation Spatial mapping of the system revealed pressure-sensitive segments, indicating uneven performance across the system, where pressure fluctuations compromise delivery. Moreover, limited contingency support has made neighbourhoods still awaiting connection to the main supply overly dependent on limited sources, leaving them particularly vulnerable during service interruptions.

Reported system failures are widespread: 89% of interviewed households reported at least one problem, most commonly water shortages, high turbidity, and pipe breakages. Vulnerability varies between households depending on the capacity of water reserves and the potential of (re-)contamination. Even for households that report a rigid cleaning regime, these problems are present. The multiple mentions of pipe leakages and muddy water indicate seepage into the pipeline system, suggesting that water quality is compromised before it reaches the households. However, according to soe residents, contamination stems from the source, citing low efficiency at the drinking water treatment plant. This distrust in water quality translates to a high reliance on bottled water, which is uniform across the island despite its associated costs.

Reports on flood-related incidents are highly dependent on location, concentrated in places where local topography, incomplete drainage, or ravine bottlenecks amplify runoff. Notably, 23% of all questionnaire respondents reported that their homes suffer damage from flooding, highlighting the tangible impact of these events on residents. Despite significant municipal spending on flood relief, the creation of predictive flood models is restricted by limited technical knowledge and know-how, causing the infrastructural interventions to remain largely reactive, with affected areas identified only post-event. Comparing municipal investment plans with a resident weighted satisfaction index reveals that spending does not uniformly translate into higher satisfaction. Residents report greater value to reliability and communication with the community. Spatial analysis of the urban area Puerto Baquerizo Moreno shows that socio-economic vulnerability generally increases from coastal to peripheral neighbourhoods, but incomplete infrastructure, water shortages, and flooding do not always coincide with limited municipal support, meaning that some vulnerable areas still benefit from interventions while others remain underserved.

The results highlight how infrastructure performance and governance practices interact to shape everyday water-related vulnerability for the residents of San Cristóbal. The CBPR framework allows for enhancement of urban planning knowledge, with lived experiences of those most affected by it.
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