Addressing conventional and emerging contamination in resource-limited rural water supplies: a full-scale before-after evaluation of a process upgrade and exploratory surrogate analysis of PFAS and antibiotic removal

Existing research on emerging-contaminant removal has focused on urban water treatment plants or single contaminant classes under laboratory conditions. However, resource-limited mountainous rural water supplies, where conventional pollutants and trace emerging contaminants—per- and polyfluoroalkyl substances (PFAS) and antibiotics—co-occur as a composite pollution burden, cannot be adequately managed by the existing infrastructure. This study adopts a rural-systems perspective, evaluating a full-scale before-after upgrade at a small mountainous rural plant in northeastern Chongqing to determine whether cost-appropriate process intensification can simultaneously resolve conventional noncompliance and reduce emerging-contaminant loads. We quantified the simultaneous removal of five PFAS and nine antibiotics and examined potential surrogate relationships between emerging contaminants and routine organic indicators. The upgraded process achieved effluent turbidity (0.22 ± 0.03 NTU) and reduced total PFAS from 10.8-11.3 to 3.06 ± 0.60 ng/L (72.9%), compared with 10.7% removal by the conventional process. Long-chain PFAS removal exceeded 83%, whereas short-chain compounds reached 53%–60%. Total antibiotic removal improved from 23.4% to 82.6%. After the upgrade, the total concentrations of PFAS and antibiotics showed positive correlations with UV absorbance at 254 nm, dissolved organic carbon, and permanganate index along the treatment train. These findings provide preliminary, site-specific evidence and a reference for similar rural water supply scenarios, although broader validation across multiple sites and seasons is warranted.