Sludge Watch ==> Tackling Emerging Contaminants at POTWs

[Maureen Reilly]

www.pollutioneng.com/CDA/Articles/Cover_Story/ca2b1784466be010VgnVCM100000f932a8c0

Tackling Emerging Contaminants at POTWs

by Stephen Harper, Ph.D., P.E. and Parikhit Sinha, Ph.D.
Posted: November 5, 2006




Mostly unrealized until a decade ago, a group of chemical contaminants 
collectively known as endocrine disruptors (EDs) or emerging contaminants 
(ECs) have been slipping through sewage treatment plants and depositing into 
streams, lakes and groundwaters worldwide. These contaminants have been 
implicated in widespread reproductive and immunological damages among many 
wildlife species[1] (Figure 1).

Effects ascribed to these chemicals are largely irreversible and heritable 
(via postulated epigenetic expressions). Effects on humans are not as clear 
but disturbing evidence is emerging for certain chemicals. Modeling suggests 
that most pharmaceutical compounds that escape treatment are safe but this 
is not universally true. Meanwhile, irrespective of potential development 
issues, ECs are being used as biomarkers to indicate the presence of sewage 
in unintended receptors.




Figure 1: Testicular dysgenesis and related conditions observed in 
comparative vertebrate groups.

Faced with concerns regarding chemicals in foods that might cause such 
effects, Congress passed the Food Quality Production Act in 1996. Since 
then, the EPA, the E.U. and Asia have deployed hundreds of scientists to 
examine better methods of detection for ECs, risk assessments, and controls. 
Wastewater treatment plants, particularly publicly owned treatment works 
(POTWs) will play a central role.

Whereas conventional discharges from POTWs are currently limited to a few 
ppm, and some toxic organics have been controlled to a few ppb, these 
newfound contaminants will likely be regulated at ppt levels. They have been 
demonstrated to cause harmful effects in wildlife – and possibly humans – at 
levels as low as 0.01 percent of dosages previously deemed toxic. 
Dose-response toxicity curves that include prenatal and early childhood 
vulnerabilities no longer follow a linear form and are now classified as 
non-monotonic


Outside of the pollution control arena, governments will work to re-regulate 
several hundred chemicals. Many will be regulated in recognition of 
potential additive effects. For example, the EPA is currently regulating 
certain pesticide groups as what it calls “combinations” of chemicals, on 
the basis of endocrine disruption effects. Like dioxin isomers and 
metabolites handled with toxicity equivalence factors, the agency has 
examined and ruled on combinations of pesticides (e.g., organophosphates, 
triazines) with countermeasures formulated for the group rather than its 
individual components.

Numerous toxicologists have shown additive effects of ED compounds in vitro 
and in vivo, however, results of mechanistic studies with different ED 
compounds and groups of compounds have been too variable to allow group 
classification. Even among pesticides, for example, the EPA elected not to 
group chemicals as structurally similar such as thiocarbamates to 
dithiocarbamates, finding no common mechanism of toxicity.

A likely outcome is that EC regulation will address individual compounds as 
well as small groups of chemicals that share a common mechanism of action, 
such as:
Estrogenic receptor agonists and receptor antagonists (These might be 
separated into natural and synthetic)
Androgenic receptor agonists or antagonists (mechanistic classifica-tions)
Classes of pharmaceuticals (based on structure or functionality)
Fragrances
Fire retardants
Plasticizers
The latter three also may fall into a larger mechanistic grouping.


The future of wastewater treatment

POTWs are the last stop for most consumer chemicals prior to re-entering the 
environment. Nearly 80 percent of U.S. citizens are on public sewers, and 
U.S. households spend 1.5 percent of their income on water and 
wastewater.[2] POTWs provide the largest opportunity for addressing the 
EC/ED issue as quickly as possible. Recognizing that POTW controls may not 
address non-point sources, the EC/ED issue is/will also affect the 
development of new non-point discharge regulations.

Despite an explosion of published studies on occurrence, fate and effects, 
EC discharges to surface waters continue largely unabated in most of the 
U.S. and Europe today. There are exceptions where water is scarce and reuse 
of wastewater is high, such as Tuscon, Ariz., and Las Vegas. There, 
treatment of ECs has occupied sufficient attention with the monitoring of 
large effluent polishing ponds and constructed wetlands. In Europe and parts 
of the U.S., bank-filtration of river waters or groundwater recharge has 
been used to mitigate ECs, but this is considered more of a water treatment 
process than an improvement to wastewater treatment.

It is important to distinguish where wastewater treatment ends and water 
treatment begins. Anything less than 100-percent effluent reuse represents a 
discharge to the environment, and the operational goal becomes protection of 
wildlife in the environment. Otherwise, the goal is protection of humans 
(and their pets). The former concerns POTWs and is the focus here.


New burdens and diagnostic tools

As regulations emerge and take hold, municipalities may expect to be 
burdened and assisted by new analytical methods for routine detection 
[3,4,5] and control. These new measurements might encompass any or all of 
the following:
1. An additional 50 to 200 compounds (out of thousands) added to the toxic 
organics list that dischargers monitor and report as toxic releases 
annually. Some compounds will require detection levels as low as 1 ppt.

2. A new version of the whole effluent toxicity test (water fleas and 
minnows as presently used have not been detecting endocrinicity). The EPA 
and others are studying some species as endpoints.

3. Standardization of surrogate tests to provide rapid screening-level 
results (plus or minus 40-percent accuracy) on reproductive impacts in hours 
rather than weeks. The EPA and others have developed and are using a wide 
variety of immunoassays and receptor gene tests. These will be important for 
the new round of nano-toxicity reduction evaluations, and nano-toxicity 
identification evaluations, which will inevitably be required. These tests 
have met with mixed results insofar as quantitative reproducibility and 
linear transferability.

4. New tests that indicate antibiotic resistance in effluents – these are 
less developed than reproductive tests and have been under-evaluated 
compared with EDs.




Figure 2.

ECs in sewage effluents

In sewage, ECs derive from chemicals carried by feces and urine 
(pharmaceuticals and natural hormones) plus a variety of personal care 
products (e.g. detergents, sanitizers, low-level disinfectants in hand 
soaps, mouthwashes, toothpastes). Stormwater runoff carrying agricultural, 
industrial or transportation-derived contaminants may enter POTWs, as well 
as byproducts from agricultural activities (biocides and veterinary 
pharmaceuticals including hormones).

Most chemicals entering POTWs are completely removed. However, a number pass 
through, either in the effluent water or in the byproduct sludge. This may 
be disposed of on land, allowing leaching of chemicals back into the 
environment.

The concentration ranges of the most widely observed hormones, pesticides, 
pharmaceuticals, alkylphenolic detergents and metabolites, plasticizers, 
fragrances, and fire retardants escaping POTWs are represented in Figure 2. 
These data were taken from several studies and surveys in the U.S., Europe 
and Asia. Most of the studies to date were cast with a wide net, with the 
objective of identifying effluent compounds and occurrence concentrations. 
Only a few have focused on why compounds are not removed, or how to 
influence removal rates via POTW designs and operations. Even fewer have 
examined degradation kinetics of EC compounds and mixtures in a POTW matrix.

A number of studies have examined add-on processes such as carbon adsorption 
and various advanced oxidation schemes. There is no single, comprehensive 
treatment approach that will fit all situations cost-effectively. Among the 
classical on-the-shelf treatment technologies, advanced oxidation appears 
the most comprehensive. Fire retardants, for example, may require oxidation 
and carbon adsorption.


Future regulatory levels

Risk assessments that can withstand scientific criticism and legal scrutiny 
are still far from complete for many ECs. It is premature to assume future 
targets but available information allows for speculation. For example, 
studies with different animals suggest the no-observed-effect-concentration, 
or NOEC, for ethinyl estradiol (EE2), the most potent sex-changer, is less 
than 10-12 moles (less than1 ng/L). This is equivalent to 5 to 25 ng/L of 
the less potent E2, and 10 to 50 ng/L E1.

EE2 itself should not be hard to remove to these levels in POTWs. In many 
studies it has been removed to non-detect levels (usually less than 0.1 
ng/L). Increasing sludge retention time, or SRT, and hydraulic retention 
time, or HRT, increases EE2 degradation, as does the use of membrane 
biological reactors (MBRs). Natural and synthetic hormones are also very 
susceptible to photo-oxidation.

The harder task will be the removal of other compounds that act like 
hormones (or anti-hormones) such as fire retardants, alkyl phenols, BPA and 
phthalates, fragrances, and certain pharmaceuticals. Based on their chemical 
structure, it is harder for these chemicals to align with the hormone 
receptors in tissues, and estrogenicity occurs at higher concentrations than 
for strict estrogens. Hence, these compounds are called “weak estrogens.”

Their strength (relative to EE2 or E2) has been measured using a variety of 
in-vitro immunoassays referenced against a variety of in vivo tests. 
Immunoassays and receptor gene methods have produced a slightly fuzzy 
picture of individual compound strengths, but steroids have been confirmed 
to be 100 to 1,000 times more powerful than non-steroid mimics or antigens. 
These specialized assays also have been instrumental in characterizing 
additive effects, which appear to be relatively linear as a function of 
relative strength.

Factoring in these considerations, POTW effluents may expect to be regulated 
as follows:
A total-mixture (sum of) limit on strict steroids (estrogens or androgens) 
somewhere between 1 to 5 ng/L,
Individual limits for selected pharmaceuticals and consumer chemicals in the 
1 to 50 ng/L range, with a cumulative total between 50 and 100 ng/L. The 
cumulative total may also be expressed as a sum limit of steroid mimics 
and/or steroid blockers (antiestrogens and antiandrogens).
Limits for many individual pesticides around 1 ng/L (or less) and a total 
biocide limit of 50 to 100 ng/L.
Limits for total plasticizer compounds such as BPA and phthlates, in the 
range of 100 to 1,000 ng/L
Limits for individual fragrance compounds in the 10 to 50 ppt range (100 to 
1,000 total)
New limits for most metals but particularly for arsenic, mercury and lead. 
Present limits may be expected to decrease by one to three orders of 
magnitude from today’s limits. Some will land in the 1 to 50 ng/L range.
To meet these projected limits, improvements at POTWs will be required. 
These might consist of existing process modifications, pretreatment steps or 
polishing steps. Examination of the chemicals that escape treatment reveals 
that almost all contain one or more of the following recalcitrant features:
Aromatic rings, often containing a nitrogen bond in the ring
Hydroxy groups on the aromatic ring
Chlorine elements on the ring or on linear branches


In-plant modifications

Several researchers have indicated that longer SRTs or HRTs can offer higher 
treatment levels on some of the persistent compounds. Others have presented 
data that are inconclusive on this matter. Generally, it can be assumed that 
extended SRT or HRT will help, but these have not been confirmed as 
sufficient stand-alone improvements. Other modifications for improving 
aromatic ring cleavage, dehalogenation or hydrolysis within the existing 
configuration of POTWs have received virtually no attention.


Pretreatment options

If the halogens can be removed from – or the aromatic rings opened before 
contacting – the activated sludge microbes, the degree of EC treatment 
within the aeration basin or sludge digesters may be dramatically improved. 
However, commercially viable processes for selective dechlorination or 
oxidation of particular compounds do not exist. Any redox agents used to 
chemically dechlorinate or simplify aromatic rings would be competed by all 
other organics in the incoming water.


Polishing options

Processes used to polish the effluent from the activated sludge step are 
easier to locate and apply than pretreatment options. A number of classical 
treatment processes have been tested on effluents and drinking water 
intakes. Most react to a fair degree with some compounds but none of the 
available processes completely remove all of the persistent compounds 
identified in Figure 2. Advanced oxidation processes with ozone and 
ultraviolet light or peroxide and ultraviolet light offer the most promise.

The good news is that there remains ample opportunities for innovation. For 
example, the author’s company, O’Brien and Gere, is testing treatment 
processes to remove active pharmaceutical ingredients from clients’ 
manufacturing effluents. The company has already identified situations where 
MBRs can be used to a distinct advantage. Despite fairly unanimous findings 
that ozone is effective on many organic compounds, scientists also have 
encountered several situations where the gas was ineffective for various 
reasons.

Just like with ED, selecting or applying effective treatments will require 
understanding combinations. Sometimes the targeted active pharmaceutical 
ingredients or EC may be easily treated in a pure solution, but poorly 
treated in a wastewater mixture. Matrix effects and competitions will impact 
results and, at times, obscure or deter progress. Cross-media contaminants 
transfer will occupy significant attention and ECs may affect sludge 
disposal rules. Thus the industry finds itself consistently re-learning old 
lessons and revisiting familiar issues, only at much lower concentrations.


References

1 Edwards T.M., Moore B.C., Guillette LJ. 2006. Reproductive Dysgenesis in 
Wildflife: A Comparative View. Intl. Journ. of Andrology. 29: 109-121

2 USEPA Clean Watersheds Needs Survey 2000 Report to Congress - 
www.epa.gov/owm/mtb/cwns/2000rtc/toc.htm

3 Lange F., Lorenz W. Combination of Multi-component methods for ultra-trace 
determination of neutral and acidic pharmaceutical residues and endocrine 
disrupting compounds in water, In Proc. 4th International Conference on 
Pharmaceuticals and Endocrine Disrupting Chemicals in Water, Minneapolis, 
MN, 2004

4 Richardson S.D., Ternes T.A. 2005. Water Analysis: Emerging Contaminants 
and Current Issues, Anal. Chem. 77: 3807-3838

5 Hanselman, T.A., Graetz, D.A., Wilkie, A.c., Szabo, N.J., Diaz, C.J. 
Determination of Steroidal Estrogens in Flushed Dairy Manure Wastewater by 
GC-MS. J. Environ. Qual., 35,695, 2006



Additional references for this article are available on request.


Stephen Harper, Ph.D., P.E. and Parikhit Sinha, Ph.D.

Dr. Stephen Harper is senior technical associate at O’Brien & Gere. He can 
be reached at (404) 219-1526 or e-mail at harpersr at obg.com.

Dr. Parikhit “Ricky” Sinha is a senior scientist in O’Brien & Gere’s 
Eco-Sciences practice. He can be reached at (215) 628-9100 or by e-mail at 
sinhap at obg.com.