Phosphate dynamics in an urban sewer: a case study of Nancy, France

Microbial source tracking to elucidate the impact of land-use and physiochemical water quality on fecal contamination in a mixed land-use watershed

Escherichia coli has been widely used as a fecal indicator bacterium (FIB) for monitoring water quality in drinking water sources and recreational water. However, fecal contamination sources remain difficult to identify and mitigate, as millions of cases of infectious diseases are reported yearly due to swimming and bathing in recreational water. The objective of this study was to apply molecular techniques for microbial source tracking (MST) to identify sources of fecal contamination in a representative mixed land-use watershed located in the Appalachian Mountains of the United States of America (USA). Monthly samples were collected over one year at 11 sites, including the confluence of key first-order streams in the study watershed representing distinct land-use types and anticipated fecal sources. Results indicated that coupled monitoring of host-specific MST markers with the FIB E. coli effectively identified sources and quantified fecal contamination in the study watershed. Human-associated MST markers were abundant primarily at developed sites, suggesting septic or sewer failure is a key source of fecal input to the watershed. Across the dataset, samples positive for E. coli and human MST markers were associated with a higher pH than those samples from which each target was not detected, thereby suggesting that acid mine drainage in the watershed likely contributed to inactivation or loss of culturability in E. coli. In addition, this research provides the first evidence that the BacCan-UCD marker is present in fox feces and can influence MST results in areas where substantial wildlife activity is present. Identifying the sources of fecal contamination and better understanding the impact of in-stream physiochemistry throughout this study will help to develop sustainable and effective watershed management plans to control fecal contamination to protect drinking water sources and recreational water.

A critical review of wastewater quality variation and in-sewer processes during conveyance in sewer systems

In-sewer physio-biochemical processes cause significant variations of wastewater quality during conveyance, which affects the influent to a wastewater treatment plant (WWTP) and arguably the microbial community of biological treatment units in a WWTP. In wet weather, contaminants stored in sewer deposits can be resuspended and migrate downstream or be released during combined sewer overflows to the urban water bodies, posing challenges to the treatment facilities or endangering urban water quality. Therefore, in-sewer transformation and migration of contaminants have been extensively studied. The compiled results from representative research in the past few decades showed that biochemical reactions are both cross-sectionally and longitudinally organized in the deposits and the sewage, following the redox potential as well as the sequence of macromolecule/contaminant degradation. The sewage organic contents and sewer biofilm microorganisms were found to covary but more systematic studies are required to examine the temporal stability of the feature. Besides, unique communities can be developed in the sewage phase. The enrichment of the major sewage-associated microorganisms can be explained by the availability of biodegradable organic contents in sewers. The sewer deposits, including biofilms, harbor both microorganisms and contaminants and usually can provide longer residence time for in-sewer transformation than wastewater. However, the interrelationships among contaminant transformation, microorganisms in the deposits/biofilms, and those in the sewage are largely unclear. Specifically, the formation and migration of FOG (fat, oil, and grease) deposits, generation and transport of contaminants in the sewer atmosphere (e.g., H₂S, CH₄, volatile organic compounds, bioaerosols), transport and transformation of nonconventional contaminants, such as pharmaceuticals and personal care products, and wastewater quality variation during the biofilm rehabilitation period after damages caused by rains/storms are some topics for future research. Moreover, systematic and standardized field analysis of real sewers under dynamic wastewater discharge conditions is necessary. We believe that an improved understanding of these processes would assist in sewer management and better prepare us for the challenges brought about by climate change and water shortage.

Use of fermentation processes for improving the dissolution of phosphorus and its recovery from waste activated sludge

Recycling phosphorus from waste activated sludge has attracted a lot of interest to tackle the problem of phosphorus stocks depletion and the increase in food demand. In this study, the use of fermentation processes was investigated to enhance phosphorus dissolution from waste activated sludge to improve its recycling. Two fermentation processes, bioacidification and dark fermentation, were used on two different sludges fermented with wheat starch syrup in continuous operating conditions. Hydrogen yield from the co-substrate fermentation with waste activated sludge reached 3.9 mmolH₂.gCOD_cosubstrate^-1 yield during dark fermentation process and was negligible during bioacidification. Dissolved phosphorus in the waste activated sludge increased by 68% during bioacidification and by 43% during dark fermentation. In both processes, phosphorus dissolution was accompanied by iron, calcium and magnesium dissolution. Results show that fermentation enhances phosphorus dissolution in waste activated sludge to improve its recovery along with hydrogen and organic acids.

Aggregating ability of ferric chloride in the presence of phosphate ligand

Complexing anions such as phosphate or silicate play an ambivalent role in the performance of hydrolyzing metal coagulants: On one hand, they significantly interfere with the hydrolytic pathway of conventional iron or aluminum coagulants, the associated destabilization mechanism remaining rather elusive; on the other hand, they have been shown to be key ingredients in the formulation of innovative coagulant solutions exhibiting improved removal efficiency, their action mechanism at the molecular scale being presently poorly understood. In this paper, we explore the effect of small additions of phosphate ligand on the chemical coagulation of silica nanoparticles with ferric chloride. Transmission Electron Microscopy-Energy Dispersed X-ray Spectroscopy (TEM-EDXS) combined with Extended X-ray absorption Fine Structure Spectroscopy (EXAFS) at the Fe K-edge are used to provide an insight into the nature of coagulant species, whereas jar-tests, laser diffraction, Small Angle X-ray Scattering (SAXS), and electrophoretic mobility, are used to investigate the aggregation dynamics of silica particles in the presence of phosphate ligand. We show that, in spite of a slight increase in the consumption of iron coagulant, the addition of phosphate significantly improves the formation of silica aggregates provided that the elemental Fe/P ratio remains above 7. Such effects originate from both a large increase in the overall number of coagulant species, the binding of a phosphate ligand terminating the growth of polymeric chains of edge-sharing Fe octahedra, and a change in the nature of the coagulant species that evolves with the Fe/P ratio, small polycations built-up from Fe-oligomers linked by phosphate tetrahedra being eventually formed. Those non-equilibrium nanosize Fe-P coagulant species assemble the silica nanoparticles to form hetero-aggregates whose structure is consistent with a Diffusion-Limited Cluster Aggregation mechanism.

Improved sulfide mitigation in sewers through on-line control of ferrous salt dosing

Water utilities worldwide spend annually billions of dollars to control sulfide-induced corrosion in sewers. Iron salts chemically oxidize and/or precipitate dissolved sulfide in sewage and are especially used in medium- and large-size sewers. Iron salt dosing rates are defined ad hoc, ignoring variation in sewage flows and sulfide levels. This often results in iron overdosing or poor sulfide control. Online dosing control can adjust the chemical dosing rates to current (and future) state of the sewer system, allowing high-precision, stable and cost-effective sulfide control. In this paper, we report a novel and robust online control strategy for the dosing of ferrous salt in sewers. The control considers the fluctuation of sewage flow, pH, sulfide levels and also the perturbation from rainfall. Sulfide production in the pipe is predicted using auto-regressive models (AR) based on current flow measurements, which in turn can be used to determine the dose of ferrous salt required for cost-effective sulfide control. Following comprehensive model-based assesment, the control was successfully validated and its effectiveness demonstrated in a 3-week field trial. The online control algorithm controlled sulfide below the target level (0.5 mg S/L) while reducing chemical dosing up to 30%.

Population mobility and urban wastewater dynamics

Dynamic influent models, which have been proposed to test control strategies using virtual wastewater treatment plants, should be as realistic as possible. The number of inhabitants in the catchment at any given time and their ways of life are among the parameters affecting the quality of these models. Census data related to work and school commutes were used to evaluate the number of people present in a given urban area. Based on the example of a large urban catchment (Grand Nancy, France), the results show that a population increase of 30% could occur during working hours resulting from the imbalance between workers leaving and coming into the catchment. Combined with information related to the local way of life, variation in the population helps to explain changes in wastewater flow rate and pollution (carbon, nitrogen, phosphorus and heavy metals), which present several maxima reflecting daily activities, such as bladder voiding, meals, the use of washrooms, etc. However, no well-defined variation patterns for pH and conductivity, which are linked to the concentrations of anions and cations in the wastewater, were observed. Slight reductions (up to 10% on Sundays) in the flow and pollution load were observed on weekends as the commuter flow decreased. Census data proved to be efficient in helping to understand the daily pattern of urban wastewater characteristics.

Iron mineralogy as a fingerprint of former steelmaking activities in river sediments

Submerged sediment cores were collected upstream of a dam in the Orne River, northeastern France. This dam was built in the context of steelmaking to constitute a water reservoir for blast furnace cooling and wet cleaning of furnace smokes. The dam also enhanced sediment deposition in the upstream zone. This study was performed to unravel the contamination status of sediments and to evidence possible contribution sources. The sediment layers were analyzed for water content, grain size, chemical composition, crystalline phases at a bulk scale and poorly crystalline and amorphous phases at a sub-micrometer scale. Visual aspect, texture, color, and chemical and mineralogical analyses showed that the settled sediments were mainly composed of fine black matter, certainly comprising steelmaking by-products. Those materials were highly enriched with Fe, Zn, Pb and other trace metals, except for a relatively thin layer of surficial sediments that had settled more recently. Bulk mineralogy revealed crystalline iron minerals, such as magnetite, goethite, wuestite and pyrite, in the deep layers of the sediment cores. Furthermore, microscopic investigations evidenced the presence of ferrospheres, goethite nanoparticles and newly formed Fe-aluminosilicates; all originating from the former steelmaking facilities. The variation of iron mineralogy, combined with specific chemical profiles and other sediment features, demonstrate the different contributions that constitute the sediment deposit. Furthermore, chemical and mineralogical features of goethite and Fe-aluminosilicates could be used as a fingerprint for such contaminated sediments.

Abnormal pH elevation in the Chaobai River, a reclaimed water intake area

The pH is a primary index reflecting water quality in rivers. The Jian River and Chaobai River are two reclaimed water intake areas which have elevated pH. This elevated pH has a marked effect on both the phytoplankton, species in water and vegetation on the shore. Understanding the main reasons causing pH elevation in river water has important implications for river ecosystem management and the improvement of water quality and can provide a theoretical basis for the direction of water quality improvement. For this reason, each biogeochemical and physical process influencing pH changes in water was quantified along the flow direction in the Wenyu to Chaobai reclaimed water diversion project, in which proton consumption and production by such processes were monitored and calculated at five monitoring sections. The calculations indicated that photosynthesis and denitrification were the primary reasons for the increase of pH in the Jian River and Chaobai River. Oppositely, carbonate precipitation and sediment decomposition restricted the increase of pH in both rivers. In addition, CO₂ emission to the air also promoted a increase of pH in the Jian River, while CO₂ absorption from the air restricted the increase of pH in the Chaobai River. NO₃^- nitrogen in reclaimed water was not efficiently removed and the reclaimed water flow condition in the intake area created favorable conditions for photosynthesis of algae breeding and denitrification by microorganisms. Therefore, biogeochemical and physical processes that promoted the increase of pH were greater than inhibiting processes and the pH gradually increased along the flow direction. The contribution rates of photosynthesis and denitrification for the increase of pH were 55.48 and 27.09%, respectively, in the Jian River and 78.08 and 21.92%, respectively, in the Chaobai River. In addition, CO₂ emission contributed 17.43% of the increase in pH in the Jian River.

Speciation of phosphorus in Lake Dang of Ngaoundere-Cameroon

In this study, we investigated the nature of phosphate phase present in sediment of Lake Dang. The phosphate speciation was determined by sequential extraction method. The concentration of phosphate in solution was measured by the ammonium molybdate method with ascorbic acid as the reducing agent. Water and sediment (surface and bottom) were sampled at eight points around the lake by taking into account activities around the lake during dry and rainy seasons. The results showed five forms of phosphorus presents in the sediments. The rank order obtained was Res-P < P-L < P-OM < P-Ca < P-Fe with the prevalence of inorganic phosphorus (P-L + P-Ca + P-Fe) than organic phase. The average phosphorus (P) content was 133, 86, and 52 μg g(-1) for the surface layer (A, 0-5 cm), medium layer (B, 5-10 cm), and bottom layer (C, 10-15 cm), respectively. This P-content depletion with depth can be explained mainly by oxygen depletion with depth which enhance P desorption. Except P-L form, the P contents were higher in rainy season compared to the dry season. The results of principal component analysis indicate that inorganic phosphorus (P-L + P-Ca + P-Fe) were linked and were provided mainly by car-washing. It appears clearly that phosphorus content vary significantly during the seasons. These results showed also that the amount of (P-Fe) is higher than the others whatever the season. This P form is easily labile and bioavailable which suggest that it can unfortunately enhance greatly the eutrophication of Lake Dang.

Microscale investigations of the fate of heavy metals associated to iron-bearing particles in a highly polluted stream

As it flows through a dense steelmaking area, the Fensch River does transport iron-rich particles and colloids, displaying high contents in metallic contaminants (Zn, Cr, Pb, Cu, Ni, and As). Chemical analysis using inductively coupled plasma mass spectrometry (ICP-MS) was carried out on three compartments-waters, suspended materials, and sediments-along the river linear. The variations of metallic trace element concentrations along the river were shown to be partially related to external inputs (industrial and domestic wastewaters and urban surfaces leaching). However, some discrepancies of element partitioning were evidenced. Pb, Cu, and Mn tend to concentrate in suspended particulate and in dissolved fraction, while Cr and As follow the trend of Fe and concentrate within sediments of the most downstream station, just before the junction with Moselle waters. Zn appears strongly associated to iron-rich particles, resulting in a decrease of its concentration in waters for the last station. Along the Fensch linear, the variation of metal partitioning between water and particulate phases is accompanied with strong modifications of the nature and mineralogy of iron-rich particles, as evidenced by microanalyses using electron and X-ray beams. The combination of bulk analyses using ICP-MS and microanalyses applied to the three compartments allowed us to propose a three-step process "settling-weathering-resuspension" to explain Zn partitioning.

Effects of pH, Temperature, Dissolved Oxygen, and Flow Rate on Phosphorus Release Processes at the Sediment and Water Interface in Storm Sewer

The effects of pH, temperature, dissolved oxygen (DO), and flow rate on the phosphorus (P) release processes at the sediment and water interface in rainwater pipes were investigated. The sampling was conducted in a residential storm sewer of North Li Shi Road in Xi Cheng District of Beijing on August 3, 2011. The release rate of P increased with the increase of pH from 8 to 10. High temperature is favorable for the release of P. The concentration of total phosphorus (TP) in the overlying water increased as the concentration of DO decreased. With the increase of flow rate from 0.7 m s(-1) to 1.1 m s(-1), the concentration of TP in the overlying water increased and then tends to be stable. Among all the factors examined in the present study, the flow rate is the primary influence factor on P release. The cumulative amount of P release increased with the process of pipeline runoff in the rainfall events with high intensities and shorter durations. Feasible measures such as best management practices and low-impact development can be conducted to control the P release on urban sediments by slowing down the flow rate.

pH dynamics in sewers and its modeling

pH variation in sewers has a significant effect on hydrogen sulfide production and emissions, and hence its accurate prediction is critical for the optimization of mitigation strategies. In this study, the nature and dynamics of pH variation in a sewer system is examined. Three sewer systems collecting domestic wastewater were monitored, with pH in all cases showing large diurnal variations. pH in fresh sewage in all three cases had a very similar trend with maximum pH in the range of 8.5-8.7. pH variation in fresh sewage followed the same pattern as the sewage flow rate, suggesting that sewage pH is influenced by household water use. Nitrogen content of the wastewater was found to be the most influential factor causing pH variation in fresh sewage, with the total ammonium concentration variation well correlated with the pH variation. A methodology for predicting pH variation in sewers is developed and calibration protocols proposed. The methodology, which is based on the concept of charge balance, was validated using titration curves and field pH data. Measurement of the total ammonium concentration in fresh sewage was found necessary and adequate for the calibration of the charge balance-based pH model.

Phosphate recovery using hybrid anion exchange: applications to source-separated urine and combined wastewater streams

There is increasing interest in recovering phosphorus (P) from various wastewater streams for beneficial use as fertilizer and to minimize environmental impacts of excess P on receiving waters. One such example is P recovery from human urine, which has a high concentration of phosphate (200-800 mg P/L) and accounts for a small volume (≈ 1%) of total wastewater flow. Accordingly, the goal of this study was to evaluate the potential to recover P from source-separated and combined wastewater streams that included undiluted human urine, urine diluted with tap water, greywater, mixture of urine and greywater, anaerobic digester supernatant, and secondary wastewater effluent. A hybrid anion exchange (HAIX) resin containing hydrous ferric oxide was used to recover P because of its selectivity for phosphate and the option to precipitate P minerals in the waste regeneration solution. The P recovery potential was fresh urine > hydrolyzed urine > greywater > biological wastewater effluent > anaerobic digester supernatant. The maximum loading of P on HAIX resin was fresh urine > hydrolyzed urine > anaerobic digester supernatant ≈ greywater > biological wastewater effluent. Results indicated that the sorption capacity of HAIX resin for phosphate and the total P recovery potential were greater for source-separated urine than the combined wastewater streams of secondary wastewater effluent and anaerobic digester supernatant. Dilution of urine with tap water decreased the phosphate loading on HAIX resin. The results of this work advance the current understanding of nutrient recovery from complex wastewater streams by sorption processes.

Isotopic tracing of clear water sources in an urban sewer: A combined water and dissolved sulfate stable isotope approach

This paper investigates the potential of stable isotopes of both water (deltaD and deltaOH(2)O18) and dissolved sulfate (delta(34)S and deltaOSO(4)18) for determining the origin and the amount of clear waters entering an urban sewer. The dynamics of various hydrological processes that commonly occur within the sewer system such as groundwater infiltration, rainwater percolation, or stormwater release from retention basins, can be readily described using water isotope ratios. In particular, stable water isotopes indicate that the relative volumes of infiltrated groundwater and sewage remain approximately constant and independent of wastewater flow rate during the day, thus demonstrating that the usual quantification of parasitic discharge from minimal nocturnal flow measurements can lead to completely erroneous results. The isotopic signature of dissolved sulfate can also provide valuable information about the nature of water inputs to the sewage flow, but could not be used in our case to quantify the infiltrating water. Indeed, even though the microbial activity had a limited effect on the isotopic composition of dissolved sulfate at the sampling sites investigated, the dissolved sulfate concentration in sewage was regulated by the formation of barite and calcium-phosphate mineral species. Sulfate originating from urine was also detected as a source using the oxygen isotopic composition of sulfate, which suggests that deltaOSO(4)18 might find use as a urine tracer.

Sources, nature, and fate of heavy metal-bearing particles in the sewer system

A preliminary insight into metal cycling within the urban sewer was obtained by determining both the heavy metal concentrations (Cu, Zn, Pb, Cd, Ni, Cr) in sewage and sediments, and the nature of metal-bearing particles using TEM-EDX, SEM-EDX and XRD. Particles collected from tap water, sump-pit deposits, and washbasin siphons, were also examined to trace back the origin of some mineral species. The results show that the total levels in Cu, Pb, Zn, Ni, and Cr in sewage are similar to that reported in the literature, thus suggesting that a time-averaged heavy metal fingerprint of domestic sewage can be defined for most developed cities at the urban catchment scale. Household activities represent the main source of Zn and Pb, the water supply system is a significant source of Cu, and in our case, groundwater infiltration in the sewer system provides a supplementary source of Ni and Cd. Concentrations in heavy metals were much higher in sewer sediments than in sewage suspended solids, the enrichment being due to the preferential settling of metal-bearing particles of high density and/or the precipitation of neoformed mineral phases. TEM and SEM-EDX analyses indicated that suspended solids, biofilms, and sewer sediments contained similar heavy metal-bearing particles including alloys and metal fragments, oxidized metals and sulfides. Copper fragments, metal carbonates (Cu, Zn, Pb), and oxidized soldering materials are released from the erosion of domestic plumbing, whereas the precipitation of sulfides and the sulfurization of metal phases occur primarily within the household connections to the sewer trunk. Close examination of sulfide phases also revealed in most cases a complex growth history recorded in the texture of particles, which likely reflects changes in physicochemical conditions associated with successive resuspension and settling of particles within the sewer system.