Leachate management is an expensive and challenging task for landfill operators. Wastewater treatment plant operators are more frequently refusing to accept leachate due to operational challenges even though the specific impacts on effluent quality are not well understood. The goal of this research was to study the nature and fate of recalcitrant, UV-absorbing, and nitrogen-containing organic compounds in leachate that is co-treated with domestic wastewater. This study aimed to quantify leachate dissolved organic nitrogen (DON), to evaluate the extent to which leachate DON contributes to effluent WWTP total nitrogen (TN) concentration, the volumetric ratios leachate is received and under various wastewater treatment processes, and the potential for leachate organic matter (LOM) to interfere with meeting UV transmittance requirements in WWTP effluents.

Leachate and wastewater combinations were evaluated in the laboratory and in the field using both traditional analysis and advanced spectroscopic tools to explore the structural and biochemical properties of LOM and its behavior at WWTPs. For field studies, two different approaches were evaluated by sampling over 24-hour and 8-hour periods in the presence and absence of leachate in the wastewater influent. By analyzing and comparing samples with and without leachate, the persistence in the treatment process and effects of leachate addition on effluent quality was assessed. Raw leachate samples were collected at the landfills just prior to the point of discharge into the municipal sewer system. In the first approach, wastewater was sampled at the WWTP influent, after clarification and disinfection every 4 hours over a 24-hour period and in the second approach, influent and effluent samples were collected at the WWTP headworks and following disinfection every hour over an 8-hour period. Data collected in this study were analyzed to understand the fate of DON and dissolved organic carbon (DOC) after treatment under various WWTP unit processes.

Leachate detection limits in wastewater were determined by laboratory dilution studies; leachate can be detected and quantified using ultraviolet–visible (UV-Vis) spectroscopy in wastewater down to 0.01% by volume. This dilution study also brought to light that even at a leachate volumetric ratio of 0.01% the UV transmittance was below 65%, which is typically expected for activated sludge effluent (Metcalf and Eddy, 2003). Similar behavior was also observed in the field as the UV transmittance of wastewater effluent was 65% at a leachate volumetric ratio of 0.1%.

Leachate samples collected from 17 landfills showed average concentrations of 16.6 mg/L bDON and 16.2 mg/L rDON. In addition, the rDON fraction showed higher humic acid concentration relative to bDON fraction. It is apparent from this study that leachate can have significant effects on wastewater quality at relatively low volumetric ratios. These effects were detected by a decrease in UV transmittance and color (which can interfere with disinfection), an increase in effluent DOC, which can lead to violations in permits or the production of disinfection byproducts (DBPs), and an increase in influent DON which can exert oxygen demand and potentially persist in the effluent. UV and fluorescence were both useful in fingerprinting the leachate in the influent. These effects, however, can be managed by ensuring that leachate discharge is maintained at acceptable dilution ratios and evenly spread out over the discharge period taking into consideration variability in wastewater flow throughout the day.

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