01 November 2015
Posted in Center Information
Principal Investigator: Dr. Debra Reinhart, P.E., BCEE, UCF
Leachate management is an expensive and challenging task for landfill operators. Wastewater treatment plants 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 and at what volumetric ratios under various wastewater treatment processes, and to understand 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 their behavior at WWTPs. For field studies, two different scenarios were evaluated: in Scenario 1, WWTPs do not accept leachate (control) and in Scenario 2, WWTPs accept leachate. By analyzing and comparing samples with and without leachate, the persistence in the treatment process and effects of leachate addition on effluent quality can be assessed. Raw leachate was collected at the landfills just prior to the point of discharge into the municipal sewer system. Wastewater was sampled at the WWTP influent and after clarification and disinfection every 4 hours over a 24-hour period. Data collected in this study were analyzed to understand the fate of DON and dissolved organic carbon (DOC) during various WWTP unit processes.
Leachate detection limits in wastewater were determined by 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 the minimum 65% requirement for disinfection when using membrane filtration prior to disinfection (NWRI, 2003). This behavior was also observed in the field as the UV transmittance of wastewater effluent was 55% at a leachate volumetric ratio of 0.1%.
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. UV and fluorescence were both useful in fingerprinting the leachate. 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. More data will be collected during Year 2 of the study to validate these observations as they were based on a limited number of observations.