Biosolids leachate variability, stabilization surrogates, and optical metric selection

Abstract

Sludge and biosolids organic matter (OM) are increasingly assessed via optical measurements of associated leachates – especially at pilot and bench scales.

Fluorescence and Absorbance Indices for Dissolved Organic Matter from Wildfire Ash and Burned Watersheds

“…This analysis was computed for actual fluorescence maxima and not pre-set peak regions . Computations on actual fluorescence peak maxima are more accurate in diverse applications because maxima can shift outside classically defined bounds first defined for marine samples. , Based on the slope and response range, Sp A is the best fluorescence peak surrogate for these ash samples and concentrations. However, Sp A typically occurs around ex ≈ 250 nm, which is more susceptible to IFE errors than Sp C at ex ≈ 320–360 nm, an issue further discussed in Section S2 .…”

“…For example, Korak et al demonstrated that optical metrics do not reflect property balance principles when computed on the slope or shoulders of fluorescence maxima, rather than peak values. Misaligned optical quantification on slopes of wildfire fluorescence signals could reduce detection or differentiation capabilities. , …”

“…Misaligned optical quantification on slopes of wildfire fluorescence signals could reduce detection or differentiation capabilities. 18,19 Future probes developed to measure ϕ f350 and Sp A would require post hoc IFE fluorescence corrections, in-line IFE corrections, or tests to determine the degree of impact of reporting uncorrected data since current probes do not automate IFE corrections 27,40 This topic is further discussed in Section S2. Neither FI nor HIX performed well in mixing experiments, environmental leachate comparisons, or surface water sample differentiation (Figures 4, 5, and S3) because they do not accommodate the blue-shifted maxima of wildfirederived DOM.…”

“…In large burns, ashes and soils are subject to a range of forest ages, oxygen availability, and temperatures that create spatial heterogeneity of burn severities and combustion conditions. , Limited work has attempted to systematically propose which optical indices work best for differentiating wildfire DOM from unimpacted DOM. Recent analysis of wastewater blends and biosolid leachates demonstrated that optical spectra of these materials significantly contrast aquatic DOM, and not all optical indices statistically capture these differences. Statistically robust measurement of wildfire-derived DOM may also require specific wavelength regions and metrics.…”

DOM Molecular Weight Fractionation and Fluorescence Quantum Yield Assessment Using a Coupled In-Line SEC Optical Property System

“…The application of fluorescence spectroscopy for the study of DOM has gained significant attention over the past 30 years. − Three-dimensional fluorescence excitation emission matrices (EEMs) are popularly used to distinguish source origin and inform physicochemical properties of DOM. − While fluorescence offers the possibility to collect signals with high sensitivity and relative simplicity, − the specific chemical components responsible for DOM fluorescence have yet to be identified . Understanding the chemical characteristics of the main types of fluorophores within DOM would help to address deficiencies in fluorescence analysis, such as spectral overlap between fluorophores and the impacts of local environments on fluorescence signals (see Section S3 in the Supporting Information for an expanded discussion on expected chemical groups responsible for absorbance and fluorescence of DOM).…”