Advanced Treatment of Landfill Leachate Induced Dissolved Organic Nitrogen (DON) and Its Influence on the Estuarine Algal Community

Landfill leachate is a major source of refractory dissolved organic nitrogen (rDON), which can exacerbate eutrophication and harmful algal blooms in downstream aquatic ecosystems. This study evaluates the effectiveness of two advanced physicochemical treatments - Fenton oxidation and granular activated carbon (GAC) adsorption - for rDON removal from biologically treated landfill leachate blended with sewage, and their impacts on the estuarine algal (phytoplankton) community with in situ algal bioassays. Fenton oxidation achieved 52%–60% rDON removal by converting rDON into ammonium nitrogen (NH4 +-N), enhancing its biodegradability and suitability for subsequent biological treatments. In contrast, GAC adsorption achieved higher removal efficiencies (86%–92%) by physically adsorbing nitrogenous species, including rDON and NH4 +-N, without altering their chemical structure. We deployed in situ algal bioassays to analyze the impacts of advanced wastewater treatment processes on the algal growth dynamics. Bioassays revealed distinct effects on algal growth: Fenton treatment temporarily increased algal biomass due to elevated NH4 +-N levels, while GAC treatment mitigated nutrient availability, inhibiting algal proliferation. While GAC was more effective overall, its regeneration requirements and associated costs pose applicability challenges. Fenton treatment is best suited as a pretreatment step to enhance rDON biodegradability.