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U.S. sewage sludges were analyzed for 58 regulated and nonregulated elements by ICP-MS and electron microscopy to explore opportunities for removal and recovery. Sludge/water distribution coefficients (KD, L/kg dry weight) spanned 5 orders of magnitude, indicating significant metal accumulation in biosolids. Rare-earth elements and minor metals (Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) detected in sludges showed enrichment factors (EFs) near unity, suggesting dust or soils as likely dominant sources. In contrast, most platinum group elements (i.e., Ru, Rh, Pd, Pt) showed high EF and KD values, indicating anthropogenic sources. Numerous metallic and metal oxide colloids (<100-500 nm diameter) were detected; the morphology of abundant aggregates of primary particles measuring <100 nm provided clues to their origin. For a community of 1 million people, metals in biosolids were valued at up to US$13 million annually. A model incorporating a parameter (KD × EF × $Value) to capture the relative potential for economic value from biosolids revealed the identity of the 13 most lucrative elements (Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a combined value of US $280/ton of sludge.
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Characterization, Recovery Opportunities, and Valuation of Metals in
Municipal Sludges from U.S. Wastewater Treatment Plants
Paul Westerho,*
Sungyun Lee,
Yu Yang,
Gwyneth W. Gordon,
Kiril Hristovski,
Rolf U. Halden,
and Pierre Herckes
School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, Arizona 85287-3005, United States
School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-1404, United States
The Polytechnic School, Ira A. Fulton Schools of Engineering, Arizona State University, Peralta Hall 330A, 7171 E. Sonoran Arroyo
Mall, Mesa, Arizona 85212-2180, United States
Center for Environmental Security, The Biodesign Institute at Arizona State University, Security and Defense Systems Initiative, 781
E. Terrace Mall, Tempe, Arizona 85287-5904, United States
Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, United States
SSupporting Information
ABSTRACT: U.S. sewage sludges were analyzed for 58 regulated
and nonregulated elements by ICP-MS and electron microscopy
to explore opportunities for removal and recovery. Sludge/water
distribution coecients (KD, L/kg dry weight) spanned 5 orders
of magnitude, indicating signicant metal accumulation in
biosolids. Rare-earth elements and minor metals (Y, La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) detected in sludges
showed enrichment factors (EFs) near unity, suggesting dust or
soils as likely dominant sources. In contrast, most platinum group
elements (i.e., Ru, Rh, Pd, Pt) showed high EF and KDvalues,
indicating anthropogenic sources. Numerous metallic and metal
oxide colloids (<100500 nm diameter) were detected; the morphology of abundant aggregates of primary particles measuring
<100 nm provided clues to their origin. For a community of 1 million people, metals in biosolids were valued at up to US$13
million annually. A model incorporating a parameter (KD×EF ×$Value) to capture the relative potential for economic value from
biosolids revealed the identity of the 13 most lucrative elements (Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a
combined value of US $280/ton of sludge.
Nationally, 16 024 wastewater treatment plants (WWTPs) were
identied in 1996, and these facilities provided service to 190
million people, representing 73% of the total population (258
million); this number was expected to increase to 90% of the
U.S. population by 2016 as communities install sewers and as
population increases in urban areas.
Bacterial-based biological
treatment processes purify the wastewater by producing
biomass and transforming nutrients in wastewater as the
bacteria grow. Biomass produced at WWTPs comprise active
bacteria, inert or residual biomass, extracellular polymeric
substances, protozoa and other higher life forms, mineral
precipitates and inuent refractory solids.
This biomass is
separated, during primary and secondary wastewater treatment,
from puried wastewater. The separated biomass, also referred
to as sewage sludge, can be further treated into Class A or B
biosolids prior to land application.
WWTPs produce more
than 8 million tons of municipal biosolids annually in the
and this amount is also increasing because of the
commissioning of new plants and upgrades to existing
Approximately 60% of the sewage sludge in the
U.S. are land applied (grassland, forests, agricultural crop land),
22% are incinerated and the remainder are landlled.
information also shows the presence of both regulated and
nonregulated organic substances in biosolids and tools
developed to estimate their accumulation.
Heavy metals
(Cu, Cd, Zn, Ag) and some trace organics (pesticides,
herbicides,surfactants,sterols,peruoroalkyl substances,
pharmaceuticals, and personal care products) are well removed
from the liquid-phase during biological wastewater treatment
through association with biomass, which is processed into
while the remaining fraction is present in
Special Issue: Critical Materials Recovery from Solutions and Wastes
Received: October 31, 2014
Revised: January 6, 2015
Accepted: January 12, 2015
Published: January 12, 2015
© 2015 American Chemical Society 9479 DOI: 10.1021/es505329q
Environ. Sci. Technol. 2015, 49, 94799488
WWTP euent discharged to rivers or lakes.
There is
recent evidence that engineered nanomaterials may accumulate
in biosolids and be taken up by plants from soils amended with
Many metals are toxic to aquatic organisms and are regulated
in WWTP discharges and biosolids.
Several monitoring
programs document the levels of regulated, toxic metals (As,
Cd, Cu, Pb, Hg, Mo, Ni, Se, Zn) in biosolids,
but few
comprehensive studies exist on a broader range of unregulated
metals in biosolids or their physical-chemical form (e.g., ionic
versus particulate or colloidal forms). This paper aims to ll
existing knowledge gaps for nonregulated metals in biomass
and biosolids.
There has long been interest in recovering elements from
WWTPs, as both a move toward sustainable use of resources
and to oset the cost of wastewater treatment.
a large benet of land applying biosolids is to add bioavailable
nutrients (nitrogen and phosphorus) and organic matter to
However, long-term application of biosolids containing
metals can aect the productivity of soils.
Most attention
of resource recovery has been on improved phosphorus
removal/extraction, and in particular using struvite-based
precipitation processes during anaerobic treatment of sewage
Other strategies and technologies to recover metals
from biosolids include pyrolysis, electrolysis, biobleaching or
other means of lysing cellular matter to release ionic forms of
metals, which can be separated using chemical precipitation,
membranes, or other means.
Recovery of metals directly
from wastewater, and not only biosolids, has also been
suggested for dual benets of reduced pollutant loading and
creating potential economic value.
Gold recovery from
WWTPs may prove to have economic value, as upward of 360
tons of gold worldwide may be accumulating annually in
Several platinum group elements (Pt, Pd, Rh, Ru,
Ir, Os) were present in biosolids in the United Kingdom,
including over 600 ppb of Pt and Pd, which were suggested to
be from automobile catalysts that drained from roadways into
In order to recognize the economic value of
recovering metals from biosolids, additional information is
needed on their occurrence in biosolids and physical form (e.g.,
ionic versus particulate).
The goals of this paper are to provide quantitative data on
(1) distribution of metals between water and biomass phases
during activated sludge treatment; (2) presence of regulated
and nonregulated metals in previously prepared mega-
composites of wastewater biosolids from across the U.S.; (3)
electron microscopy characterization of colloidal metallic
present in biosolids; and (4) potential economic value of
metals in biosolids. To address these goals, liquid and biomass
samples were collected in 2013 from activated sludge WWTPs
in central Arizona, analyzed for a broad spectrum of elements,
and used to compute distribution coecients for each element
between liquid phase (settled supernatant) and return activated
sludge (RAS) biomass phases. The U.S. EPA performed
national sewage sludge surveys in 1989, 2001 and 2006/7. After
completion of the 2001 survey, unused samples were released
to a nationwide repository of biosolids samples. Mega-
composite samples from this nationwide study were charac-
terized after digestion and analysis by inductively coupled
plasma mass spectrometry (ICP-MS) for a broad range of 58
elements, including 30 that have not been previously measured
on similar composite samples.
To our knowledge this is the
most intensive characterization of the size, morphology, and
inorganic elemental composition of biosolids that were
analyzed by scanning electron microscopy (SEM) with energy
dispersive X-ray spectroscopy (EDX). Based upon the
elemental composition in nished biosolids, an economic
analysis was performed using recent market values of puried
elemental prices to assess the maximum value that could be
recognized from recovering these elements, and the potential
value was compared against the current costs of treating
biosolids to prepare them for ultimate disposal using current
strategies (land application, incineration, landlling).
Sample Description. Biosolids samples were obtained
from the National Biosolids Repository, maintained at Arizona
State University by Haldens research group.
Complete details
on the EPA biosolids composite samples collection methods
and other characterization are provided elsewhere
and in
the Supporting Information (SI). Briey, biosolids samples with
130% solid contents were obtained from 94 wastewater
treatment plants in 32 states and the District of Columbia for
the 2001 National Sewage Sludge Survey (NSSS). Sampling
locations were selected by the U.S. EPA to reect a
representative estimate of theoccurrenceofchemical
contaminants in sewage sludge that are disposed of primarily
by land application.
Additional samples were collected in 2013 from two activated
sludge WWTPs in central Arizona, both of which achieve
partial denitrication. Sample locations included settled primary
supernatant, RAS biomass, and secondary settled supernatant;
for one plant that processes biomass into biosolids on-site,
additional samples across anaerobic digestion and dewatering
processes were also collected (see SI Figure S-4). Total
suspended solids (TSS) was determined following the standard
methods for water and wastewater analysis.
distribution coecients (KD) values (L/kg dry weight), which
could also be considered liquid-to-solid ratios, were calculated
by dividing the element content in the return activated sludge
biomass (μg/kg dry weight) by the element content of the
nonltered secondary euent (μg/L).
Sample Digestion and Element Analysis. Using nitric
acid and hydrogen peroxide, samples were microwave digested
in Teon vials, followed by additional digestion steps until all
solids were clear and free of precipitates. Samples were analyzed
by quadrupole ICP-MS (ThermoFisher Scientic iCAP Q, with
CCT option). The instrument passed the mass calibration,
cross calibration and daily performance reports for sensitivity,
stability, oxide production ratio and doubly charged production
ratio prior to sample measurement. Complete description of
digestion, vial cleaning procedures, ICP analysis and quality
control used are in SI.
Electron Microscopy Analysis. Biosolids were dried and
ground into powder with a mortar and pestle. 0.5 g of each
sample was suspended in 5 mL of DI water and sonicated in a
water bath for 1 h. 0.5 mL of solution were diluted with 25 mL
of methanol (99.8%, ACS grade, VWR International) and then
one or two drops of the resultant suspension were dripped on
carbon tape on an aluminum stub or TEM copper grid (Ted
Pella Inc., California). Samples were air-dried at room
temperature (22 °C) before analysis. Scanning electron
microscopy equipped with an energy dispersive X-ray micro-
analysis system (SEM/EDX) (FEG ESEM Philips XL30 with
EDAX system) was used to locate and characterize metallic
particles in biosolids. High-resolution transmission electron
Environmental Science & Technology Article
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Environ. Sci. Technol. 2015, 49, 94799488
microscopy (HR-TEM) coupled with energy dispersive X-ray
spectroscopy (EDX) (Philips CM200 FEG HR-TEM/STEM)
was used to characterize the colloids visually and determine the
chemical composition of the samples.
Distribution of Metals from Sewage into Activated
Sludge Biomass. Liquid and biomass samples were collected
from multiple locations across two WWTPs (see SI Figure S-4).
Tabular data for concentrations of all elements at multiple
locations with these two facilities are summarized in SI (Table
S-1). RAS solids concentration was 5.43 and 5.04 gTSS/L for
WWTP#1 and WWTP#2, respectively. Figure 1shows that
detectable metal concentrations in RAS ranged over 6 orders of
magnitude from 107μg/kg dry wt. (10 g/kg) for the major
elements (Na, Ca, P, K, Mg, Fe, Al) to 101102μg/kg dry wt.
for others (Dy, Yb, Er, Eu, Ir, Tl, Ho, Re). For additional
reference, phosphorus accounted for 3% of the dry weight of
the biomass, which is consistent with the elemental
composition of cellular material.
Figure 2shows the range of sludge-water distribution
coecients (KD) for metals across the biological treatment
process (activated sludge) in both samples. A few liquid euent
samples had metal concentrations below the detection limit; KD
values were not calculated for these metals. KDvalues span a
range greater than 5 orders of magnitude, with KDvalues above
unity indicating a preference for the biomass phase over the
liquid phase. High KDvalues measured in this study
demonstrate a strong anity for a wide range of metals toward
biomass. Even metals (e.g., V, W) that commonly occur as
anionic oxo-anions accumulate in biosolids. Metals with very
low solubility solids (e.g., Ti, Au, Pd) also exhibit high KD
values. Traditionally, distribution coecient (KD), isotherm
(Freundlich, Langmuir) or multisurface (diuse layer) models
for free and organically complexed metals (Cd, Cu, Zn) have
been used to describe relationships between metal accumu-
lation on wastewater biosolids and in soils amended with
Thus, it is possible that both ionic and colloidal
Figure 1. Elemental concentrations in biomass (return activated sludge) for two Arizona WWTPs. Some elements were below detection limits in
WWTP#1 (no bars shown), and other elements (Se, Rh, Te, Tb, Tm, Lu, Pt) were not detected above detection limits in either biomass samples.
Figure 2. Distribution coecients (Log KD) for elements detected in both biomass and settled supernatants at two Arizona WWTPs.
Environmental Science & Technology Article
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Environ. Sci. Technol. 2015, 49, 94799488
or particulate forms of metals accumulated in the biosolids. To
explore this, we imaged submicron sized metals in biosolids
(presented later).
The calculated KDvalues are only for the activated sludge
unit process. Settled solids are further processed using
dewatering systems (e.g., belt lter presses, centrifuges; see SI
for a typical process ow diagram) and sometimes include
anaerobic digestion where the volume of biosolids is lowered to
reduce the cost of hauling and disposing biosolids o-site (i.e.,
transportation and tipping fees). Liquid waste streams from the
dewatering systems and anaerobic digestors are usually
returned to the front of the WWTP treatment train. To
understand these processes, we examined solids handling at
WWTPs that use anaerobic digestion followed by dewatering.
Across these processes, the total daily mass ux of one element
(Ti) into the biosolids processing facility was 5.6 ×103g Ti/
day. Titanium was selected to monitor because its aqueous
solubility is quite low in natural waters.
A large percentage
(84%) of the titanium entering the solids processing ended up
in nished biosolids, while 4.5%, 4.5%, and 7% of the titanium
was accounted for in gravity thickener liquid, belt lter press
thickener liquid and centrifugation liquid, respectively.
Although titanium likely occurs in mineral forms (anatase,
rutile, brookite, silicates) with low solubility, this analysis
indicates that metals are retained within biomass as they are
further processed into biosolids. For more soluble minerals and
elements, return of liquid ows containing these metals to the
front of the WWTP will again allow distribution onto biomass
during activated sludge treatment.
Elemental Composition of Biosolids from Local
WWTP and EPA Mega-Composite Biosolids Samples.
The concentrations of regulated metals (As, Cd, Cr, Cu, Pb,
Mo, Ni, Zn) in the WWTP#1 biosolids (10, 3.6, 36, 436, 24,
7.8, 28, 620 mg/kg, respectively) are roughly 10-fold below
ceiling concentration limits for biosolids intended for land
application based upon EPA Section 503.13 (75, 85, 3000,
4300, 8400, 75, 420, 7500 mg/kg, respectively); mercury (Hg)
was not analyzed and Se was below our detection limits. The
rank order from higher to lower concentrations (Zn > Cu > Cr
> Ni > Pb > Cd) of these regulated elements is consistent with
trends reported elsewhere for biosolids.
To ll data-gaps
where more information is needed for Ba, Mn and Ag,
concentrations in WWTP#1 biosolids were measured as 275,
1500, and 17 mg/kg, respectively. SI Table S-2 shows that
elemental concentrations in the biosolids from WWTP#1 are
similar to those for the ve EPA mega-composites and the 50th
percentile concentrations for a subset of elements reported
biosolids collected from across the U.S. We observed relative
concentrations of trace elements similar to those recently
reported for sewer sludge ash after incineration.
To improve our understanding of element occurrence in
biosolids, a geochemical analysis strategy was employed that
normalizes observed element content to element content in the
upper continental crust.
Enrichment factors (EFs) are
obtained by comparing the abundance of a given trace element
in the biosolids relative to that same trace element in a
reference material. Specically, the EF of an element (X) is
often calculated relative to the average composition of upper
continental crust (UCC)
using Al or Fe as the reference
element (R) where EF = [X/R]sample/[X/R]UCC. The EFs of
selected elements relative to UCC
using Al as the reference
element are shown in Figure 3, with the x-axis presenting
elements in order of atomic mass (low to high). An enrichment
value of unity suggests the ratio to aluminum of that element is
Figure 3. Enrichment factor of elements in biosolids from EPA biosolids mega-composite groups, two Arizona WWTPs and 50th percentile
occurrence data from a previous study on a subset of samples. EF calculated relative to Al. (error bars for Stevensdata show 10th and 90th
percentile values for a prior study;
other error bars show two standard deviations around a mean from replicate digested and analyzed samples (n=
3 to 5)).
Environmental Science & Technology Article
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Environ. Sci. Technol. 2015, 49, 94799488
the same as in crustal material (e.g., soil, dust). Hence under
the assumption that the main aluminum source in wastewater is
crustal material, this means the element also comes mainly from
crustal sources like soil dust. Elements with EF > 10 suggest
that there are other sources (i.e., anthropogenic sources) for
that element. This approach is commonly used to apportion the
sources of trace metals in atmospheric aerosol studies.
element shows consistently an EF < 1, which tends to support
the premise that the main source of aluminum in WWTP
biosolids is crustal (soil dust). This is further supported by the
rare-earth elements (REE) and several minor metals (Y, La, Ce,
Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu) showing a
ratio close to UCC. While REE and minor metals have
industrial applications, it appears that a substantial part of
crustal soil material is present in WWTPs (likely because of
urban runo/stormwater or other sources) and implies the
industrial sources are small and nearly negligible. A few
exceptions occur, such as gadolinium, which is used as a
contrast agent in medical diagnostics and shows a slight
Phosphorus is highly enriched (EF > 100), suggesting its
noncrustal sources (e.g., anthropogenic sources such as foods,
industrial acids, etc.). Phosphorus has a high KD(Figure 1),
indicating that bacteria accumulate P present in wastewater.
Likewise, biosolids have long been recognized to concentrate
(i.e., higher KDvalues) toxic metals (e.g., Cu, Zn, Cd, Ag, Sn,
Pb), and EFs for these metals exceed unity due to their uses in
industry. Calculated EF values for biosolids collected in 2012 at
the two Arizona WWTPs and the ve mega-composite samples
align well with values calculated using concentrations for a
subset of metals reported in the literature (e.g., ref 35 as labeled
in Figure 3). By expanding the suite of metals analyzed, we are
among the rst to show signicant EFs in biosolids of most
platinum group elements (i.e., Ru, Rh, Pd, Pt), which have
likely sources including catalytic converters in cars that
dominate their sources into the environment.
Some of the
elements for which we could calculate partition coecients
onto biomass have KDvalues >100 (Figure 2). Despite having
EFs near unity, indicating they likely have origins in crustal
materials, several of these REEs and minor metals (Eu, Sm, Sr,
V, W, Cr, Gd, Mo, Mn, Sb, Ir) with detectable liquid phase and
biomass concentrations have KDvalues greater than unity. This
suggests that these elements accumulate in biosolids during
biological wastewater treatment. Some elements (e.g., Mo) may
be critical trace nutrients for bacteria, while other elements may
be present in ionic forms or insoluble particulates that
accumulate on the surface of suspended bacterial biolms.
Electron Microscopy Analysis of Biosolids. To explore
possible sources of these elements into the wastewater system
from sources other than natural dustsor soil (i.e., EFs > 1)
and to consider potential biological, physical or chemical means
to recover the elements from biosolids, we analyzed the
morphology of metallic objects in the biosolids. After
conducting SEM-EDX analysis of dozens of samples, we
identied numerous metallic and metal oxide colloids ranging
in size from <100 to 500 nm (Figure 4;SI Table S-3). Several
objects were composed of aggregates containing primary
particle sizes <100 nm. Some objects appear to be incidental
nanomaterials (NMs). For example, particles containing tin
appear teardrop-shaped in Figure 4and may have been tin-
based solder hydraulically sheared from piping. Some colloids
occurred frequently in the biosolids samples (e.g., TiO2), while
Figure 4. SEM images showing morphology of colloidal and particulate-sized inorganic materials in EPA mega-composite biosolids samples.
Elemental composition was determined by EDX analysis during SEM.
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Environ. Sci. Technol. 2015, 49, 94799488
colloids composed of other elements (e.g., Au) were only
observed in one or two samples. Titanium oxides were found
easily in nearly all samples, with morphologies and sizes ranging
from those similar to food grade TiO2found in toothpaste to
micron-size material found in paints.
Silica oxides were
found in forms representing both clays and zeolite structures,
where the latter is used in some foods and washing
Lead and silver suldes were far less frequently
observed than TiO2. Sulde forms of metals can readily form
within activated sludge systems due to bacterial reduction of
sulfate and low solubility of many metal sulde materi-
Gold- or platinum-series containing particulates
were also observed and could result from discharges into sewers
from mining, electroplating industries, electronic and jewelry
industrial catalysts, or automotive catalysts
present in stormwater that enters sewers.
Tantalates are
also widely used in electronics, in part to form protective oxide
layers on surfaces. Many elements with EF > 10 were visualized
as colloids within biosolids using electron microscopy.
Rather than hunting for individual colloidal-scale objects in
samples prepared on electron microscopy stubs/grids, we
attempted to employ elemental mapping across a grid area.
This works well to locate larger-sized or high-abundance
particulates in fairly clean samples but proved less useful in
locatingnanoscale particles while processing our samples
because the latter contains so little elemental mass for the
existing EDX technology to identify and quantify. Elemental
mapping helped locate nanoscale TiO2(conrmed by atomic
ratios of titanium and oxygen from EDX) in or on what appears
to be clay that contains Si, Fe, Al, and traces of Ce (SI Figure S-
1 and S-2). Elemental scanning for rarer elements like silver
necessitates searching large areas; low signal intensity was
observed, indicating few concentrated regions of Ag, which
signify silver nanoparticles or suggest that Ag is distributed
across the biomass (i.e., ions sorbed to biosolids materials).
Emerging research debates the implications of nanosilver,
titanium dioxide, zinc and gold on plants receiving land applied
biosolids or runofrom such lands; far less data or
identication exists for other nanoscale materials that may be
toxic or exhibit catalytic properties.
Despite decades of research on metals and biosolids, this
electron microscopy work is among the rst, to our knowledge,
to present and discuss the morphology of colloidal-size inert
solids in biosolids. The morphology may be very important in
understanding why some elements accumulate in biosolids (i.e.,
KD> 1). The presence of submicron sized particles composed of
regulated, toxic metals in biosolids is not surprising but may be
important in understanding the mechanisms for removing
metals at WWTPs. The common explanation and models for
removal of toxic metals by biological processes at WWTPs view
metals as being present as mostly ions. Models exist for
speciation of metal ions into various aqueous species, and
surface sorption binding models exist for such species onto
wastewater biomass.
The presence of nonionic forms of
metals may help explain some of the variability in metal
removal at dierent WWTPs.
Thus, it is possible that
previous conceptual approaches for metal sorption to biomass
may have oversimplied distribution of metals with biomass by
only considering ionic species. It is likely that colloidal forms of
metals behave dierently than ions where colloids are taken up
by cells or involved in aggregation with biological colloids and
Integration of ICP-MS Concentration and Electron
Microscopy Characterization of Elements in Biosolids.
Data from ICP-MS and SEM/TEM/EDX were interpreted
together to determine the probability of nding metal-based
nanomaterials in biosolids samples by electron microscopy. The
dry mass data (ppm; mg element/kg biosolids) can be useful in
estimating the probability of nding physical objects. For
example, we nd many iron oxides and calcium phosphates
colloids in biosolids by electron microscopy because their metal
contents are very high in biosolids (e.g., 55 000 ppm Fe, 35 000
ppm of Ca). Titanium (1500 ppm) is readily found with
silicates or as TiO2in biosolids. Colloids containing copper
(400 ppm) and silver (15 ppm) are found less frequently.
While we periodically found colloids containing palladium (0.3
ppm) or gold (0.3 ppm), we rarely found colloids containing
yttrium (2 ppm), neodymium (1.9 ppm) or dysprosium (0.3
ppm), which are commercially available and used as oxide
nanopowders. Based upon mass concentrations it should be
more likely to image titanium- than silver- or gold-bearing
particulates when prospectingin biosolids using electron
microscopy. This premise was analyzed in detail (see SI) and
lead to an important conclusion. The likely occurrence for TiO2
or a metal-bearing particulate to be present in an electron
microscopy stub area of 1 μm2follows the following trend from
higher to lower probability of locating: TiO2>Ca>Fe>Zn>
Al > Ba > Cu > Pb > Ag > Sb > Au. The probability of nding a
silver or gold submicron particle is on the order of 105or 106
times lower than nding a TiO2nanoparticle, respectively. The
fact that we observed any in our SEM work is somewhat
Economic Value of Metals in Biosolids. Approximately
60% of U.S. biosolids are recycled and applied to agricultural or
forest lands that benet from the nitrogen and phosphorus
content, but the rate and long-term application amount to
individual elds can be limited by the presence of metals.
The other 40% of biosolids are disposed in landlls or
incinerated, with the ash deposited to landlls. Recycling
options for N and P from biosolids have been proposed,
where nutrients can be separated from metals and organics in
the biosolids. The question arises: what is the economic value
of these nutrients relative to other metals in wastewater
This question was investigated using the metal concen-
trations for the mega-composite biosolids samples (SI Table S-
2) and the spot market price of puried metals (SI Table S-4).
Prices are intended to be more comparative than absolute.
Annual per capita production of biosolids is on the order of 26
Analysis was performed for a community
with a population of 1 000 000 people (28 600 dry tons of
biosolids per year), and the resulting economic potential is
illustrated in SI (Figure S-3 and Table S-4). For this
community, the estimated value of metals in the biosolids
could approach $13,000,000 per year ($460/ton) with greater
than 20% of the value accounted ($2,600,000 per year) for by
gold and silver. These commodity prices represent high purity
elements, so it would take considerable energy and cost to
purify these biosolids. Gold ore grades range from 0.3 to 80 g
per metric ton (g/t), and the biosolids measured here contain
gold ranging from 0.3 to 0.6 g/t which is in the range of values
reported elsewhere of 0.2 to 7 g/t.
It is noteworthy that
phosphorus, which is the focus of many wastewater recovery
systems, has a relatively low economic value ($57,000/year).
Some of the elements may create misleading total values of
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elements in biosolids. Prime examples are rubidium (Rb) or
lutetium (Lu), which are approximately ve to six times more
expensive than gold and are among the most expensive of the
REEs. Rb and Lu concentrations in biosolids are quite low,
have an EF near unity, and because of the low Lu concentration
in wastewater, their KDcould not be determined; Rb has a log
KDof 3.0. Thus, the potential economic value of such
nonenriching metals may be misleading in that it cannot be
easily extracted in practice (SI Figure S-3).
The most promising elements to recover from biosolids
would have high potential economic value (based upon cost of
element in a puried form ($/kg), high concentration in
biosolids (mg/kg)), high EF values indicating the element is
used in anthropogenic products or processes, and a high KD
value indicating the ability of biological processes in WWTP to
accumulate the element. Thus, for each element we developed a
relative potential for economic value from biosolids
parameter (KD×EF ×$Value). Figure 5shows this parameter
for 30 elements having the highest values. This analysis may
help in prioritizing elements to obtain more information on
their occurrence in biosolids, assess potential chemical
processes to recover the elements, and assess market needs
for their purity. Given the observed presence of many metals in
the form of particles rather than ions in this study, this
speciation may play an important role in resource recovery.
Based on our analysis, the top 13 most attractive elements to
recover from biosolids are Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al,
Cd, Ti, Ga, and Cr. Several of these are part of identied energy-
critical-elements (Ga, Pd, Ag, Ir) or critical elements for food
systems (P).
For a community of 1 000 000 people, the
economic value of recovering these elements could be on the
order of $8,000,000 annually or less, depending on the recovery
yield. As can be seen from Figure 5(gray bars), recovering
elements with a high relative potential for economic value
would also address concerns over the toxicity of these biosolids
constituents. Thus, recovering metals could be an economic
and environmental win-win scenario.
The total cost of biosolids treatment is on the order of $300
per ton, which includes anaerobic treatment and thickening etc.
to reduce the water content to roughly 20% solids, plus
additional disposal costs for land application. The economic
value of biosolids if all the elements were recovered in adequate
purity is estimated to be on the order of $100 per dry ton. Per
capita wastewater production in the U.S. is declining due to
increased water conservation measures, but the per capita
pollutant loading is expected to remain stable, thereby resulting
in higher strength wastewaters. Consequently, the metal
concentrations in biosolids may increase in the future, which
would complicate land application but would work in favor of
resource recovery from biosolids. There may come a tipping
point when the costs to recover or sell biosolids based upon
their resource value will be a more economical and sustainable
avenue than land disposal. While it may appear tempting to
reverse industrial point-source discharges into sewers because
this could increase the value of recoverable metals in biosolids,
the authors believe that separation and recovery closest to the
point of use and discharge probably holds the most
environmental benet and opportunities for reuse. It is possible
that regional dierences may exist in the metal concentrations
that contribute to the relative potential for economic value from
sewage sludge or biosolids, and future research should
understand the existing spatial dierences and consider how
these may change in the future. Added environmental benets
would result as well because biosolids contain a suite of organic
pollutants that threaten the health and safety of soils receiving
land applications of biosolids (i.e., biosolids as soil amend-
SSupporting Information
Details on mega-composite sampling, digestion and analysis is
provided. Additional particle imaging and number analysis is
provided. Economic value estimates are tabularized. This
material is available free of charge via the Internet at http://
Figure 5. Relative potential (y-axis) for economic value from biosolids for the top 30 elements based upon a community of 1 000 000 people
producing 26 kg/person-year of dry biosolids. Gray bars indicate elements considered potentially toxic for land application and have dry weight
concentration limits on their land application regulated by the Part 503 Biosolids Rule.
Environmental Science & Technology Article
DOI: 10.1021/es505329q
Environ. Sci. Technol. 2015, 49, 94799488
Corresponding Author
*Phone: 480-965-2885; fax: 480-965-0557; e-mail: p.
The authors declare no competing nancial interest.
This study was partially funded by the Water Environment
Research Foundation (RD831713), National Science Founda-
tion (CBET 1336542 and BCS-1026865, Central Arizona-
Phoenix Long-Term Ecological Research (CAP LTER)), and
USEPA (RD RD83558001) and by awards R01ES015445 and
1R01ES020889 from the National Institute of Environmental
Health Sciences (NIEHS).
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Environmental Science & Technology Article
DOI: 10.1021/es505329q
Environ. Sci. Technol. 2015, 49, 94799488
... The review from Vyrides et al. (2017) thoroughly investigated metals recovery from sewage sludge but only for five of them (aluminum, copper, nickel, silver and zinc). Westerhoff et al. (2015) also addressed the topic of potential recovery from sewage sludge for fifty-three metals using a financial valuation based on availability and obtained optimistic results for some (Ag, Cu, Au, P, Pd, Zn, Ir, Cd, Ga, Cr). On the contrary, Vriens et al. (2017) dismissed metals recovery from WWTP using an importation analysis and alluded to environnemental interest without assessing it. ...
... The similarities for base metals allow the Swiss data to be used for the liquid-phase concentrations ( Fig. 2a) of the twenty-one metals not measured by the French study (Na, Ca, K, Mg, Si, Sr, Mn, Zr, Bi, Ga, Cs, Nb, W, Ge, Hf, Tl, Ta, Te, Be, Au, In). Similarly, the American (Westerhoff et al., 2015) and English (Jackson et al., 2010) data reinforce the Swiss and French results on the SS matrix (Fig. 2b). The German study (Krüger et al., 2014) was used to classify metals according to their concentration in the ISSA matrix ( Fig. 2b), except for seven metals (Bi, Cs, In, Li, Re, Te, Tl) for which no information was available. ...
... To compare ores created by separate geological formations, the grade is expressed in terms of a normalising element rather than the total mass of material. Aluminum is the most commonly used normalising element and Westerhoff et al. (2015) demonstrate the relevance of its use in the case of activated sludge. ...
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After usage, extracted metals end up back to the environment but dispersed at much lower concentrations. Wastewater treatment plants (WWTP) are one of the last sites where metals go through before discharge into the environment. This article assesses the relevance of recovering up to forty-nine metals from WWTP from a strategic, financial and mining perspectives. The WWTP matrices are also compared with other deposits to put forward their relevance as a future urban mine. Results show a strong recovery potential for magnesium throughout the plant. The most suitable matrix to recover chromium and copper is sewage sludge. Palladium, platinum or tungsten, found mainly in incinerated sewage sludge ash would require further investigation. In treated wastewaters, a dozen metals (including calcium, potassium, sodium, silicon, nickel and zinc) are either strongly critical or interesting for financial potential. There are potent incentives to transform WWTP into urban mines to shift towards circular economy.
... mg·kg −1 ), Cr (296.40 mg·kg −1 ), Pb (56.90 mg·kg −1 ), and Cd (1.69 mg·kg −1 ) were comparable with, or lower in the present study than, studies conducted in 48 other cities in China [26], as shown in Table S3. Meanwhile, the concentrations of the REEs in sludge were in the range of 1.38 mg·kg −1 (Tm) to 237.6 mg·kg −1 (Ce) and were significantly higher (Dunn's test, p < 0.05) than those found in Switzerland (0.07-19.0 mg·kg −1 ) [16] and USA (0.02-7.35 mg·kg −1 ) [27]. The massive storage and extensive use of REEs in China lead to abundant REEs in sludge [28]. ...
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Rapid urbanization has caused an increase in the discharge of inorganic elements into the environment; however, the knowledge about the fate and annual variations of multiple elements in wastewater treatment plants (WWTPs) is limited. To understand the distribution and change of those elements, we collected and analyzed wastewater and sludge samples from seven WWTPs in a southeast city of China. Results revealed the elemental concentration ranging from 0.06 μg·L−1 (Tl) to 221.90 μg·L−1 (Mn) in the influent, below the detection limit (Er), to 206.40 μg·L−1 (Mn) in the effluent, and 0.58 mg·kg−1 (Tl) to 309.30 mg·kg−1 (Zn) in the sludge. The removal analysis revealed that rare earth elements (REEs) were removed well from the wastewater with removal efficiencies ranging from 88.03% (Tm) to 97.37% (Sm), while heavy metals were poor, with removal efficiencies ranging from 10.71% (Mn) to 89.17% (Pb). The elemental flux analysis highlighted that activated sludge served as a major temporary storage site for 23 elements, while excess sludge acted as the major sink for REEs. Significant spatial variations were detected among different WWTPs. On the contrary, the temporal variations were insignificant based on the monitoring data from 2010 to 2020, indicating the satisfactory implementation of current environmental regulations.
... Approximately 75% of the US population is connected to a municipal wastewater treatment facility 47 (Westerhoff et al., 2015), which collects sewage containing a diverse range of commensal and 48 pathogenic organisms. Human vertebrate viruses excreted through feces, urine, skin, saliva, and 49 blood can be detected in wastewater to gather insights into viral diseases circulating within a wastewater monitoring as an integral public health surveillance tool for early detection and 55 mitigation of COVID-19 (Kirby et al., 2021). ...
Viruses of concern for quantitative wastewater monitoring are usually selected as a result of an outbreak and subsequent detection in wastewater. However, targeted metagenomics could proactively identify viruses of concern when used as an initial screening tool. To evaluate the utility of targeted metagenomics for wastewater screening, we used ViroCap, a panel of probes designed to target all known vertebrate viruses. Untreated wastewater was collected from wastewater treatment plants (WWTPs) and building-level manholes associated with vulnerable populations in Houston, TX. We evaluated differences in vertebrate virus detection between WWTP and building-level samples, classified human viruses in wastewater, and performed phylogenetic analysis on astrovirus sequencing reads to evaluate targeted metagenomics for subspecies level classification. Vertebrate viruses varied widely across building-level samples. Rarely detected and abundant viruses were identified in WWTP and building-level samples, including enteric, respiratory, and bloodborne viruses. Furthermore, full length genomes were assembled from astrovirus reads and two human astrovirus serotypes were classified in wastewater samples. This study demonstrates the utility of targeted metagenomics as an initial screening step for public health surveillance.
... Extraordinarily, you may not be aware that significant metal loss can take place through sewer systems in major cities. For example, it has been estimated that a city of roughly one million inhabitants flushes $13 million worth of precious metals down toilets and sewer drains on an annual basis (Westerhoff et al., 2015). Dried sewage sludge typically contains gold, platinum, silver and copper. ...
... Aerobic composting (AC) and anaerobic digestion (AD) are the mainstream bio-stabilization technologies that can effectively control pollutants (e.g., disease-causing microorganisms, and toxic organic compounds) (Černe et al., 2019;Rogers, 1996;Westerhoff et al., 2015), and enhance the production of bioactive organic compounds (BOCs) with biological activity on plant-growth (Li et al., 2016(Li et al., , 2018. In recent years, a few researches have focused on the generation of water-soluble BOCs following bio-stabilization process. ...
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Bioactive organic compounds (BOCs) contained in bio-stabilized products of waste activated sludge (WAS) have attracted considerable attention, as they can enhance the fertilizing effect of WAS in land applications. This study investigated the molecular composition and plant-growth-promoting mechanisms of various BOCs in the iostabilized products of WAS. After stepwise fractionation, aerobic composting sludge (ACS) and anaerobic digestion sludge (ADS) were chemically fractioned into five subcomponents, namely dissolved organic matter (DOM) (C1), weakly interacted organic matter (OM) (C2), metal-bonded OM (C3), NaOH-extracted OM (C4), and strongly interacted OM (C5), in sequence. The results showed that fatty acids and carboxylic acid (CAs) present in ACS C2 promoted plant growth and enhanced the ability of plants against stresses by upregulating pathways related to “carbohydrate metabolism,” “lipid metabolism,” “amino acid metabolism,” and “phenylpropanoid biosynthesis.” However, in ACS C4, plenty of amino acids could promote plant growth via upregulating “carbohydrate metabolism” and “amino acid metabolism” pathways. As an important precursor, aromatic amino acids inside ACS C4 also stimulated the production of indoleacetic acids. In ADS C1, amino sugar and phytohormone were the major BOCs causing the up-regulation of “carbohydrate metabolism” and AAA catabolism in “amino acid metabolism” pathways. CAs enriched in ADS C2 stimulated plant growth through “amino acid metabolism” pathway. In summary, alkali extraction can recycle a large proportion of BOCs with low environmental risk from the biostabilization products of WAS. The results from this study provide scientific guidance for safe and value-added resource utilization of bio-stabilization products of WAS in land applications.
... The concentrations at the anaerobic treatment stage follow the order: Mn (21.31 ± Table 3 Influent and effluent characteristics (mean ± standard deviation) for CBOD in mg/L), TSS (mg/L), NH 3 -N (mg/L), and dissolved oxygen (DO, mg O 2 /L)); n = 28-31 samples were detected in anaerobic and primary treatment stages albeit below detection in the chlorine contact chamber before final effluent and prior to discharge (Fig. 5A). The observed trends are in agreement with results from other wastewater treatment plants in Onchoke et al. (2015) and Westerhoff et al. (2015). Except for the primary aeration stages, concentrations of Ag, As, Cd, Hg, Mo, and Se were determined below detection limits. ...
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The present study quantified element concentrations and evaluated the removal efficiencies of the Lufkin Wastewater Treatment Plant (LWWTP): a public municipal wastewater treatment plant in East Texas. Macroelements (Na, K, Mg, Ca, Al, Fe, Se, Zn, P, and S) and microelements (Ni, Pb, Mn, Cr, Mo, Cu, Co, V, As, B, Ba) were detected using ICP-OES and ICP-MS. In addition, the anion concentrations (Br⁻, NO3⁻, NO2⁻, PO4³⁻, F⁻, Cl⁻, and SO4²⁻) and their percent removal from the LWWTP were assessed by using ion chromatography. Whereas macroelements in the influent were above the maximum ceiling limits, the total metal concentrations in the effluent were found below the USEPA (below μg/L) guidelines. In general, the removal efficiencies for metals in LWWTP were ≥ 94%. The removal efficiencies of the anions were > 100% (Br⁻), 16.42% (Cl⁻), 78.89% (F⁻), 182.59% (NO3⁻), > 100% (NO2⁻), 51.81% (PO4³⁻), and 67.01% (SO4²⁻). In addition, Pierson correlation coefficients between the anions and cations, and implications for usage and suggested improvements of the treatment plants are proposed.
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Recently, increasing attention has been paid to heavy metals in sludge. However, limited literature could be found on the distribution characteristics of heavy metals in sludge and their potential risks. In this study, sludges from wastewater plants in Jiangsu Province (China) were selected for the investigation of heavy metal loadings, showing that typical heavy metal levels were in the order of Zn > Cu > Cr > Ni > Pb > As > Hg > Cd, ranging from 154 to 2970 mg/kg, 28 to 1150 mg/kg, 10 to 136 mg/kg, 9 to 262 mg/kg, 0 to 79 mg/kg, 12.1 to 41.6 mg/kg, 0.67 to 19.50 mg/kg and 0.21 to 2.77 mg/kg, respectively. Analysis of the typical heavy metal distribution in sludge indicated that Hg, Zn and Cu were obviously influenced by the degree of industrial intensity and exploitation of human activities, while Ni, Cd, Pb, As and Cr were more evenly distributed. Effects of sewage sources and wastewater-treatment processes on heavy metal levels implied that different industrial wastewaters resulted in different metal contents, but the distribution of Ni, Cd, Pb, As and Cr in different treatment processes was similar. Furthermore, Hg and Cd had the strongest ecological risk, with their levels reaching severe, suggesting that sludge was not recommended for agricultural reuse in this study.
Platinum-containing molecules such as cisplatin figure among oncology's most widely used antineoplastic agents. Cisplatin excreted in the urine usually ends up in municipal wastewater, with a strong toxicological and carcinogenic impact on the environment. Thus, cisplatin should be inactivated before reaching wastewater to attenuate its environmental impact. However, conventional recommended procedures use large quantities of toxic acids, which are not sustainable processes. In this study, a dielectric barrier discharge (DBD) atmospheric pressure plasma reactor is used to degrade cisplatin in wastewater, allowing platinum's recuperation. The article describes the plasma discharge (power, electron temperature, and density) and confirms the most stable operation parameters under Ar and Ar+H2 discharges. Cisplatin is diluted in water or synthetic urine, and plasma treatment is conducted for 30 minutes. The process degrades cisplatin molecules by conversion into platinum-rich nanoparticles (NPs). These nanoparticles are efficiently recuperated by centrifugation and are characterized by transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The mass-balance assessment confirms that more than 90% of cisplatin is degraded and recuperated as Pt-rich NPs.
The accumulation of electronic waste (e-waste) on the ground leads to environmental pollution with toxic metal ions, which subsequently harms all living organisms. Many countries still use hydrometallurgical or manual methods to extract silver ions from e-waste. These methods are unsustainable and highly toxic; therefore, it becomes necessary to introduce new environmentally compatible methods for separating valuable components from objects of various compositions. This article proposes an environmentally compatible method for the extraction of silver ions from multicomponent systems using poly(N-thiocarbamoyl‑3-aminopropylsilsesquioxane). The sorbent surface was studied by Fourier-transform infrared spectroscopy using an attenuated total internal reflection accessory. The concentration of grafted thiourea groups is 1.39 mmol/g according to elemental analysis. It has been determined that this sorbent is capable of quantitatively extracting silver ions in the pH range from 0 to 6 at a concentration of silver ions in the initial solution of 1·10–4 mol/dm3; the static sorption capacity for silver ions under experimental conditions reaches 1.22 mmol/g. When sorption is carried out in dynamic mode, the value of the dynamic capacity before breakthrough is 0.046 mmol/g, and the value of the total dynamic capacity for silver ions is 0.132 mmol/g. The highest desorption (71–78 %) is achieved using sulfuric acid solutions with a thiourea concentration gradient.
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Biosolids are stabilized solids from municipal wastewater treatment that meet federal standards for land application. Good estimates of biosolids N availability are needed to develop sustainable biosolids management programs. We conducted this study to (i) determine the availability and fate of biosolids N applied to a dryland soft-white winter wheat (triticum aestivum L.)-fallow rotation, (ii) determine if N availability predictions for biosolids are applicable under dryland conditions, and (iii) make practical recommendations for biosolids management. We applied dewatered (21-30% solids) biosolids (4.3-5.5% total N; 257-853 lb N/acre) to on-farm test plots at three locations in the 9-12 in, rainfall zone of eastern Washington. Fertilized (anhydrous or aqua ammonia [AA]) and unfertilized treatments were established at each site for comparison. We measured yield an N uptake of grain and straw at harvest, and determined soil profile nitrate N (plus ammonium N, 0-12 in, depth only) before application, during fallow, and post-harvest. We determined apparent N recovery from the soil at the end fallow (ANR(fallow)). Nitrogen release from biosolids as measured by ANR(fallow) was dependable and consistent over the three sites, despite differences in environment among the sites. ANR(fallow) average 29%, similar to predicted values of 26-31%. The lowest biosolids rates (257-330 lb/acre) supplied more available N than AA. Yield, grain N, and flag leaf N all indicate that N was sufficient at the lowest biosolids rates used, and that higher levels of biosolids did not benefit the crop. Drawbacks to higher rates include risks of reduced crop yield (from moisture stress) and quality (from increased protein), and increased risk of nitrate movement below the root zone. Storage of nitrate in the soil profile does not appear to be a reliable strategy for supplying N for a second crop. Lower biosolids rates seem to reduce economic risks to the farmer and reduce leaching risk. Evaluation of low biosolids rates (100-300 lb total N/acre) and second crop response will be valuable in refining biosolids application recommendations.
EPA's 2006-2007 Targeted National Sewage Sludge Survey (TNSSS) is a valuable step in advancing the understanding of what chemical constituents are present in treated sewage sludge. The information from the survey provides important input for EPA and others to evaluate potential uses and associated risks of biosolids generated by publicly owned treatment works. It also fulfills an important commitment under the agency's four pronged strategy for pharmaceuticals and personal care products by providing the first national estimates of which pharmaceuticals, steroids and hormones may be present in sewage sludge and at what concentrations. This chapter summarizes the technical background, sampling and analysis activities, statistical methods, and resulting estimates of pollutant concentrations in treated sewage sludge ("biosolids") that represent Publicly Owned Treatment Works (POTWs) in the contiguous United States with flow rates of at least 1 million gallons per day (MGD). Estimates were produced using data from a national probability sample of 74 POTWs that statistically represent 3,337 POTWs that met the study criteria. The TNSSS was designed to obtain occurrence information on select analytes of interest. The objective of the survey was to obtain national estimates of the concentrations of these pollutants in sewage sludge for use in assessing if exposures may be occurring and whether those levels may be of concern. Estimates from the survey may provide important input to EPA's efforts to evaluate biosolids generated by the nation's POTWs. EPA conducted analyses of sewage sludge samples for 145 analytes, including four anions (nitrite/nitrate, fluoride, water-extractable phosphorus), 28 metals, four polycyclic aromatic hydrocarbons, two semi-volatiles, 11 flame retardants, 72 pharmaceuticals, and 25 steroids and hormones, and minimum and maximum measurements that were encountered among the samples collected in this survey. For 34 of the analytes measured in this survey, this chapter summarizes an in-depth statistical analysis that yielded nationally-representative estimates. For each of the 34 analytes, nationally-representative estimates of the 50th percentile (i.e., median) of the underlying distribution of measurements across POTWs, as well as the 90th, 95th, 98th, and 99th percentiles are presented, along with the mean, standard deviation, and the minimum and maximum measurements. The survey used both well-established multi-laboratory validated EPA procedures as well as three analytical methods that were developed or updated for the survey. The two new methods are single-lab validated methods for pharmaceuticals (EPA Method 1694, (1)), and steroids and hormones (EPA Method 1698, (2)). The updated multi-lab validated method is for flame retardants (EPA Method 1614, (3)). The percent solids in the various sewage sludge samples range from 0.14 to 94.9. To ensure comparability of results, all sample results are reported on a dry-weight basis. Efforts by the Agency to characterize potential risks associated with TNSSS results are currently ongoing..
The chemical composition of natural water is derived from many different sources of solutes, including gases and aerosols from the atmosphere, weathering and erosion of rocks and soil, solution or precipitation reactions occurring below the land surface, and cultural effects resulting from human activities. Broad interrelationships among these processes and their effects can be discerned by application of principles of chemical thermodynamics. Some of the processes of solution or precipitation of minerals can be closely evaluated by means of principles of chemical equilibirum, including the law of mass action and the Nernst equation. Other processes are irreversible and require consideration of reaction mechanisms and rates. The chemical composition of the crustal rocks of the Earth and the composition of the ocean and the atmosphere are significant in evaluating sources of solutes in natural freshwater. The ways in which solutes are taken up or precipitated and the amounts present in solution are influenced by many environmental factors, especially climate, structure and position of rock strata, and biochemical effects associated with life cycles of plants and animals, both microscopic and macroscopic. -from Author
In the field of detergent ingredients, sodium tripolyphosphate, zeolite A and crystalline layered disilicate SKS-6 are well-established builders. The development of new detergent types is giving vise to new application requirements for detergent builders. This article compares product application profiles, ecological behaviour and market trends for these builders.
This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.
The new USEPA regulations for the use of sewage sludges will permit concentrations of particular toxic metals to increase locally on agricultural land by a factor of a hundred or more above present soil concentrations. Short-term field experiments have shown that the adsorptive properties of sludges themselves often prevent excessive uptake of many of these metals into crops, a protection attributable largely to the added organic matter. This protection cannot be considered to be permanent or effective for all toxic meals, as indicated by data from old sludged sites. Differences in degree of protection are evident for greenhouse and field experiments, largely attributable to different rooting patterns and degree of sludge mixing in these two situations. The USEPA reliance on field data for metal uptake by corn (Zea mays L.) has led to an underestimation of phytoxicity thresholds applicable to a wider range of crops, in part because corn is able to root deeply and is metal-tolerant. Also, the decision to use 50% yield reduction and plant top (rather than root) concentrations of heavy metals as phytotoxicity indicators may have obscured incipient toxicity. Long-term field observations (several decades) often show that sludge-applied metals can remain sufficiently available, even in nonacid soils when total metal concentrations are below the proposed EPA limits, to harm sensitive crops and microbes. It is concluded that the ultimate impact of toxic metals from sewage sludges at levels approaching the proposed USEPA limits on various soil-crop systems is potentially harmful.