Cynthia Carliell-Marquet

Determination of changes in wastewater quality through a treatment works using fluorescence spectroscopy.

Fluorescence spectroscopy was used to characterize municipal wastewater at various stages of treatment in order to understand how its fluorescence signature changes with treatment and how the signal relates to biochemical oxygen demand (BOD) and chemical oxygen demand (COD). The impact of size fractionation on the fluorescence signal was also investigated. Fluorescence measurements were taken for unfiltered and filtered (0.45 and 0.20 μm) samples of crude, settled and secondary treated wastewater (activated sludge and trickling filter), and final effluent. Good correlations were observed for unfiltered, diluted wastewater samples between BOD and fluorescence intensity at excitation 280 nm, emission 350 nm (Peak T1) (r=0.92) and between COD and Peak T1 intensity (r=0.85). The majority of the T1 and T2 signal was found to be derived from the<0.20 μm fraction. Initial results indicate that fluorescence spectroscopy, and changes in Peak T1 intensity in particular, could be used for continuous, real-time wastewater quality assessment and process control of wastewater treatment works.

The digestibility of iron-dosed activated sludge.

The impact of chemical phosphorus (P) removal on anaerobic digestion (AD) has long been debated, possibly because there is no general consensus of the definition of impaired AD, but also because of the different assessment methods used. This research surveyed 12 wastewater treatment plants to compare the relative digestibility of iron-dosed with undosed activated sludge during two batch test trials. Results showed that iron-dosed sludge negatively impacted AD by reducing the volume of biogas (12%) and methane (5.5%) produced from the same amount of volatile solids fed. Possible reasons for reduced biogas production include lower levels of bioavailable P and iron in iron-dosed sludge, which may hinder the ability of micro-organisms to metabolise organic substrate.

An examination of the treatment of iron‐dosed waste activated sludge by anaerobic digestion

Abstract Anaerobic digestion is an important sludge treatment process enabling stabilisation of the organic fraction of sewage sludge prior to land application. Any practice which might retard the anaerobic digestion process will jeopardize the stabiKty of the resulting digested sludge. This paper reports on an investigation into the relative digestibility of iron‐dosed waste activated sludge (WAS) from a sewage treatment works (STW) with chemical phosphorus removal (CPR), in comparison to WAS from a works without phosphorus removal. Two laboratory scale anaerobic digesters (51) were fed initially with non iron‐dosed WAS (Works M) at a solids retention time of 19 days. After 2 months the iron‐dosed CPR sludge (Works R) was introduced into the second digester, resulting in a 32 % decrease in biogas production and an increase in the methane content of the biogas from an average of 74 % to 81 %. Pre‐treatment of the CPR sludge with sodium sulphide and shear, both alone and in combination, caused the gas production to deteriorate further. Pre‐acidification and pre‐treatment with EDTA did result in an enhanced gas production but it was still not comparable with that of the digester being fed with non‐iron‐dosed sludge. The daily gas production was found to be linearly related to the amount of bound iron in the sludge.

Methodological approaches for fractionation and speciation to estimate trace element bioavailability in engineered anaerobic digestion ecosystems: An overview

ABSTRACT Optimal supply of trace elements (TE) is a prerequisite for microbial growth and activity in anaerobic digestion (AD) bioprocesses. However, the required concentrations and ratios of essential TE for AD biotechnologies strongly depend on prevailing operating conditions as well as feedstock composition. Furthermore, TE in AD bioreactors undergo complex physicochemical reactions and may be present as free ions, complex bound or as precipitates depending on pH, or on the presence of sulfur compounds or organic macromolecules. To overcome TE deficiency, various commercial mineral products are typically applied to AD processes. The addition of heavy metals poses the risk of overdosing operating systems, which may be toxic to microbial consortia and ultimately the environment. Adequate supplementation, therefore, requires appropriate knowledge not only about the composition, but also on the speciation and bioavailability of TE. However, very little is yet fully understood on this specific issue. Evaluations of TE typically only include the measurement of total TE concentrations but do not consider the chemical forms in which TE exist. Thus detailed information on bioavailability and potential toxicity cannot be provided. This review provides an overview of the state of the art in approaches to determine bioavailable TE in anaerobic bioprocesses, including sequential fractionation and speciation techniques. Critical aspects and considerations, including with respect to sampling and analytical procedures, as well as mathematical modeling, are examined. The approaches discussed in this review are based on our experiences and on previously published studies in the context of the “COST Action 1302: European Network on Ecological Roles of Trace Metals in Anaerobic Biotechnologies.”

Fate of Trace Metals in Anaerobic Digestion

A challenging, and largely uncharted, area of research in the field of anaerobic digestion science and technology is in understanding the roles of trace metals in enabling biogas production. This is a major knowledge gap and a multifaceted problem involving metal chemistry; physical interactions of metal and solids; microbiology; and technology optimization. Moreover, the fate of trace metals, and the chemical speciation and transport of trace metals in environments--often agricultural lands receiving discharge waters from anaerobic digestion processes--simultaneously represents challenges for environmental protection and opportunities to close process loops in anaerobic digestion.

A novel laboratory method to determine the biogas potential of iron-dosed activated sludge

Sludge biogas potential is often reduced by iron-dosing, the extent of the reduction being related to the nature of the sludge and the dosing process. The aim of this research was to develop a rapid laboratory method to measure the impact of iron-dosing on the biogas potential of activated sludge, taking into account the mechanisms that may be decreasing biogas yield. To validate the method, sequential extraction (SE) was used to fractionate iron and phosphorus in the sludge before and after iron-dosing. The laboratory-dosing regime increased total iron and phosphorus in the sludge but decreased their bioavailability, producing sludge with a similar inorganic composition to full-scale chemical P removal (CPR) sludge. Laboratory-dosed sludge produced 12-20% less biogas and 9-21% less methane when anaerobically digested, in comparison to the same undosed sludge. This method should help water companies and academics to more closely simulate iron-dosing in the laboratory.

Significance of Vivianite Precipitation on the Mobility of Iron in Anaerobically Digested Sludge

Anaerobic digestion requires a balanced availability of micro-nutrients with ideal growth conditions to reach optimal organic degradation and biogas production. Iron is the most abundant of the essential metals in an anaerobic digester and its mobility has a strong impact on microorganisms through its own bioavailability, but also through its influence on the bioavailability of other metals. Most previous research on iron mobility in anaerobic digestion has focused on sulfide as the controlling anion because digesters traditionally are sulfide rich and phosphate poor. However, chemical phosphorus removal (CPR) at wastewater treatment works (WWTW) can elevate phosphate concentrations in the digester 10-fold or more. The goal of this research was hence to examine the accepted wisdom of iron-sulfide dominance prevailing in all anaerobic digesters and by evaluating the potential for iron phosphate formation in municipal digesters treating CPR sludge. To fulfil this aim, iron compounds were identified experimentally from full-scale digesters at WWTW with CPR and the most likely iron species identified through modelling according to their thermodynamic probability of formation under the specific environmental conditions experienced in each anaerobic digester. Experimental and modelling data were then combined to identify the main chemical reactions controlling iron mobility in those anaerobic digesters. Results show that speciation of iron in the sampled anaerobic digesters was controlled by the solid phase through a primary reaction (sulfide precipitation to form pyrite and ferrous sulfide) and secondary reaction (phosphate precipitation to form vivianite). However, iron-sulfide precipitates represented only 10-30% of the total iron in the sampled digesters, while iron-phosphate precipitates represented more than 70%. The significance of the high quantity of vivianite in these digesters is that phosphate-rich anaerobic digesters will be more iron-mobile environments than sulfide-rich digesters, with iron being more readily exchanged between the solid and liquid phases during digestion, implying a higher level of bioavailability and the tendency to interact more readily with organic and inorganic counterparts.

Dissipation and Recycling: What Losses, What Dissipation Impacts, and What Recycling Options?

This chapter describes the activities in the Dissipation and Recycling Node of Global TraPs, a multistakeholder project on the sustainable management of the global phosphorus (P) cycle. Along the P supply and demand chain, substantial amounts are lost, notably in mining, processing, agriculture via soil erosion, food waste, manure, and sewage sludge. They are not only critical with respect to wasting an essential resource, but also contribute to severe environmental impacts such as eutrophication of freshwater ecosystems or the development of dead zones in oceans. The Recycling and Dissipation Node covers the phosphorus system from those points where phosphate-containing waste or losses have occurred or been produced by human excreta, livestock, and industries. This chapter describes losses and recycling efforts, identifies knowledge implementation and dissemination gaps as well as critical questions, and outlines potential transdisciplinary case studies. Two pathways toward sustainable P management are in focus: To a major goal of sustainable P management therefore must be to (1) quantify P stocks and flows in order to (2) identify key areas for minimizing losses and realizing recycling opportunities. Several technologies already exist to recycle P from different sources, including manure, food waste, sewage, and steelmaking slag; however, due to various factors such as lacking economic incentives, insufficient regulations, technical obstacles, and missing anticipation of unintended impacts, only a minor part of potential secondary P resources has been utilized. Minimizing losses and increasing recycling rates as well as reducing unintended environmental impacts triggered by P dissipation require a better understanding of the social, technological, and economic rationale as well as the intrinsic interrelations between nutrient cycling and ecosystem stability. A useful approach will be to develop new social business models integrating innovative technologies, corporate strategies, and public policies. That requires intensive collaboration between different scientific disciplines and, most importantly, among a variety of key stakeholders, including industry, farmers, and government agencies.