Dissolved organic matter (DOM) profiles and nutrient mineralization rates of anaerobically digested biosolids

Authors: FISCHER, S. - University Of Maryland; McCarty, Gregory; RAMIREZ, M. - District Of Columbia Water & Sewer Authority (DCWASA); TORRENTS, A. - University Of Maryland

Submitted to: International Biodeterioration and Biodegradation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2019
Publication Date: 1/15/2020
Citation: Fischer, S., McCarty, G.W., Ramirez, M., Torrents, A. 2020. Dissolved organic matter (DOM) profiles and nutrient mineralization rates of anaerobically digested biosolids. International Biodeterioration and Biodegradation. https://doi.org/10.1016/j.wasman.2019.12.049.
DOI: https://doi.org/10.1016/j.wasman.2019.12.049

Interpretive Summary: In recent decades, wastewater treatment plants have re-engineering their processes to better serve societies as resource recovery facilities that provide treated water and nutrients-rich biosolids, valued by industries and society. Treated biosolids are valued as soil amendments because they can enhance nutrient availability, soil structure, and bulk density properties of agricultural soils. Recently, the District of Columbia Water and Sewer Authority installed an advanced thermal hydrolysis processing (THP) system prior to anaerobic digestion (AD) for the enhanced stabilization of final wastewater residuals but little information is known about how the resulting stabilized biosolids release mineral nitrogen in agricultural soils. One goal of this study was to determine the percent of mineral N released from THP-AD biosolids in 100-day aerobic soil incubations, and whether this differed significantly from AD biosolids without the pre-treatment. The results showed that with this incubation, the fraction of plant-available nitrogen that developed in THP-AD biosolids was not statistically different than the biosolids with either fermentation or no pretreatment prior to anaerobic digestion. Additionally, the combination of several dissolved organic matter characterization techniques reflected similarity in the AD biosolids with different pretreatments. This study provides information needed for formulating recommendations for land application of AD biosolids in agricultural production systems.

Technical Abstract: Nitrogen mineralization rates were determined for Thermal Hydrolysis Processed anaerobically-digested (THP-AD) biosolids and two additional AD biosolids using a 3-month, aerobic soil incubation experiment. The THP-AD is a promising technology for conditioning wastewater treatment biosolids with heat, pressure, and digestion, but there has been limited agronomic evaluation of the resulting product. Starting quality of dissolved organic matter (DOM) from the three AD biosolids over multiple collection dates was also assessed with size-exclusion chromatography (SEC), Fourier transform infrared (FTIR), and fluorescence spectroscopies for differences in refractory or labile moieties. After the 3-month incubation with soil, the fraction of plant-available nitrogen that developed in THP-AD biosolids (20.8 ± 10.0%) was not statistically different than the biosolids with either fermentation (32.6 ± 18.0%) or no pretreatment (34.2 ± 23.0%) prior to anaerobic digestion. The combination of several DOM characterization techniques reflected similarity in the AD biosolids as well. SEC analyses showed that AD-DOMs contained three distinct molecular-weight classes ranging from 165 to 1192 daltons. FTIR spectra contained methyl, unsaturated carbon, and carbonyl signals in all AD-DOMs in contrast to signals detected in waste-activated sludge as well as plant-derived reference material spectra. Fluorescence spectroscopy of AD biosolids-DOM revealed additional humic and fulvic acid associated structures that may be tied additional stabilization of AD solids. The results of this study provide information on both soil mineralization rates and DOM quality of anaerobically-digested biosolids with different pre-treatments pertinent to biosolids application.