Revisiting wastewater pH standards: A policy lever for mitigating coastal acidification and enhancing blue carbon.

Global ocean acidification driven by atmospheric CO2 uptake is well recognized; however, coastal zones are subject to additional, localized acidification pressures. Among these, the chronic discharge of low-pH-treated wastewater (often pH 6.0), permitted under many current regulations, represents a significant but often overlooked stressor. This practice introduces highly acidic loads into sensitive nearshore ecosystems that are chemically incompatible with ambient seawater (pH ∼8.1). This perspective argues for reframing effluent pH not only as a pollutant parameter to be bounded but also as a modifiable policy lever. Revising discharge standards to require a minimum effluent pH > 8.0 for marine outfalls offers a novel pathway to mitigate localized coastal acidification. Furthermore, this approach aligns with emerging ocean alkalinity enhancement strategies, potentially enhancing coastal carbon sequestration and offering cobenefits such as reduced metal toxicity. Such a policy shift necessitates technological adaptation but promises significant benefits for coastal resilience and broader ocean sustainability goals.