Leakage-driven mains renewal
Frank Rogalla of Black & Veatch, Caroline Scruggs and Gary Hunter discuss endochrine-disrupting chemicals, and methods of their removalIn bio-organisms, glands of the endocrine system secrete hormones which act to control body functions, including reproduction, growth, and development. An endocrine disruptor is a substance that changes the function of the endocrine system, affecting the way an organism or its progeny reproduce, grow, or develop. It is generally accepted that the three main classes of endocrine disruption endpoints are
- Estrogenic (natural oestrogen blocked or mimicked)
- Androgenic (natural testosterone blocked or mimicked)
- Thyroidal (thyroid function affected directly or indirectly)
Numerous studies over the past 70 years have demonstrated endocrine disruption in a variety of organisms, including gulls, marine gastropods, frogs, fish, and alligators, as a result of exposure to pesticides, steroids, surfactants, plasticisers, and other synthetic chemicals - there are over 200 species with known or suspected adverse reactions to endocrine disruptors.
Endocrine disrupting chemicals (EDCs) and pharmaceutical and personal care products (PPCPs) are ubiquitous in the environment because of their seemingly endless number of uses and origins in residential, industrial, and agricultural applications. EDCs can be derived from both anthropogenic and natural sources. PPCPs are chemicals that enter the environment through use of human and veterinary pharmaceuticals and myriad other products such as antibiotics, analgesics, fragrances, sunscreen, mouthwash, bug spray, and cosmetics.
Some PPCPs are also EDCs, but the terms are not interchangeable and the associated environmental contamination concerns can be very different. Although the potential hazards associated with some EDCs such as DDT have been known for decades, the environmental and health effects of EDCs and PPCPs in general are only beginning to gain worldwide attention. The list of known and suspected EDCs continues to grow; some of these chemicals, along with their primary sources, are presented in Figure 1.
There are various pathways by which organisms can be exposed to EDCs and PPCPs by contamination of the water cycle. As WwTWs in service today have not been specifically designed to remove them, EDCs and PPCPs enter the water environment largely through treated effluent in various types and amounts. Inputs to water bodies from agricultural or feedlot operations can also be significant in some areas, making controls quite challenging.
Thus, some micropollutants will not be completely degraded or removed in the treatment process, and it is even possible that some EDCs may be generated, either as metabolites or degradation products, or as disinfection byproducts. Aquatic organisms are exposed to these chemicals through direct contact in the water environment, and negative effects of WwTW discharges on the reproductive systems of aquatic organisms living in their vicinity have been reported worldwide.
Regulatory and research efforts
In the US, the Safe Drinking Water Act (SDWA) currently regulates a number of possible EDCs such as atrazine, chlordane, DDT, dioxin, cadmium, lead, and mercury. But the maximum contaminant levels for these chemicals are defined by their long-term cancer-causing effects rather than by endocrine disruption. EDCs have not been mentioned specifically in US legislation until 1995, when amendments to the SDWA and the Food Quality Protection Act mandated screening of all chemicals and formulations for potential endocrine activity prior to their use or manufacture where they could contaminate food or drinking water.
In 1999 and 2000, 139 streams were sampled across 30 states in the US as the first nationwide reconnaissance for PPCPs and EDCs. The survey included sampling for 95 constituents from a wide variety of origins, and found that contamination was generally prevalent and widespread. While concentrations tended to be low and rarely exceeded guidelines for drinking water quality, few guidelines or regulations exist concerning EDC or PPCP contamination of drinking or natural waters, as their toxicological significance still needs to be established.
The USEPA is establishing a reference dose for perchlorate, which may become the first pollutant to be regulated in the US for endocrine-disrupting toxicity.
The agency is also considering regulation of atrazine and other triazines based on endocrine-disruption endpoints, and California is already considering regulations for EDCs and PPCPs in indirect potable reuse applications, prompting to establish monitoring programs now. Several European countries and Japan have begun phasing out or limiting the use of a few specific EDCs. Typical concentrations observed in some wastewaters are listed in Table 1.
Biological treatment on EDCS
Secondary biological treatment is the key process at WwTWs capable of removing most if not all estrogenic activity. Many different studies have been performed to determine and compare the effectiveness of biological processes for EDC removal, and have demonstrated that activated sludge systems have the potential to remove many suspected EDCs to a fairly high degree.
It is likely biological process can be optimised to improve removal further as the effects of SRT, HRT, and other parameters are analysed. The first demonstration projects in the UK for EDC removal from wastewater are under way with Thames Water and Severn Trent Water. As scientists determine ways to optimise the biological process for affordable enhancement of EDC removal, it is also critical to examine disinfection to ensure that improvements in biological treatment efficiency are not negated by the byproducts produced in the downstream disinfection step.
Advanced oxidation processes (AOPs) for EDC removal
Though biological processes are usually the most cost-effective means of removing organics from wastewater, physical and/or chemical treatment methods, such as disinfection and oxidation processes more typically associated with water treatment, may be a better option if these substances are toxic or non-biodegradable. Carbon dioxide and water are the products of complete oxidation of various pollutants. The following subsections review several different AOPs.
Ozone has been commonly used for disinfection in water treatment, and its application for wastewater disinfection and EDC/PPCP removal at WwTWs is a current subject of investigation. Ozone is a powerful but selective oxidant. During ozonation, molecular ozone and hydroxyl radicals, to some extent, may transform EDCs and PPCPs. Though it has a high specific lethality for most types of micro-organisms, its oxidation of many inorganic species and classes of organic compounds may be kinetically hindered. Increasing the ozone dose in an attempt to increase oxidation power also potentially increases DBP formation.
When waters being treated contain bromide, bromate can be formed, and brominated organic compounds are of particular concern. It is also possible that organic DBPs are formed from oxidation of natural organic matter (NOM) present in wastewater effluent. Thus, a beneficial approach may be the use of ozone at a dose as low as possible, in combination with a less selective oxidant to maximise oxidation power without increasing byproduct formation, as discussed in the next subsection.
During ozonation on a BNR effluent to determine whether trace levels of nonylphenol and BPA could be removed, very low effluent pollutant concentrations were measured for ozone doses of 8g, 10g, and 15g O3/m3, with no appreciable increase in removal rate with dose. In a German pilot unit, application of ozone to BNR effluent resulted in some removal of more than 50 trace organic pollutants that are typically found in wastewater effluent, with removal efficiencies frequently higher than 90%. Three important EDCs - E1, E2, and EE2 - were effectively oxidised or degraded by ozone, and they were shown to lose most of their oestrogenic potency in the process.
In addition, antibiotics were no longer detected in the effluent. However, the nature and concentration of ozonation byproducts were not identified.
Peroxone, or O3/H2O2, has been used for a number of years to remove trace pollutants from groundwater, and as part of a multiple-barrier approach in potable water treatment. Because of the hydroxyl radicals formed, peroxone has been found to be very effective for removal of EDCs. As the removal of ozone-resistant micropollutants is strongly dependent on water characteristics addition of H2O2 to accelerate formation of hydroxyl radicals from ozone decomposition is recommended in cases with lower organic matter content and high alkalinity.
The ozone/UV combination is particularly useful where turbidity and colour content are elevated, as in situations with a high proportion of industrial users or poor final clarification. Substances such as AOX, PAK, organotin compounds, pesticides, phenols, chlorinated aromatics, and phthalates are degraded with ozone/UV, and the removal of hardly biodegradable substances is improved.
Pilot trials performed in Germany showed that, in addition to achieving high removal efficiencies of several organic trace pollutants, ozone treatment led to an increase in UV transmittance from 59.2% to 84.1%. This improvement in transmittance resulted in better conditions for UV disinfection. In comparison with peroxone, ozone, and UV, ozone/UV treatment resulted in the highest level of disinfection - a 4.4 log reduction of E.coli. So, in addition to oxidation of persistent substances, ozone/UV treatment disinfects the water to a high degree.
As UV/peroxide forms hydroxyl radicals, it has been shown to remove trace pollutants such as DBPs, toxic organics, NDMA, EDCs, and 1,4-dioxane. For some specific trace pollutants, only UV may be needed, though the UV doses may have to be extremely high to obtain appreciable removal of most EDCs or PPCPs Of the AOP options, UV/peroxide may result in the lowest DBP formation, though pilot testing should be conducted for confirmation.
Costs are site-specific, depending on the flow rate, water matrix, and type of pollutant being removed. Equipment costs for this option are possibly the lowest of the AOPs at about £70/m3, but to put this in perspective, this means that the equipment cost for a 15Ml/d facility may be as high as £1M, which does not even include the cost of the building.
As future regulations may be established for some EDCs in WwTW effluent, various studies have demonstrated that activated sludge systems have the potential to economically remove many suspected EDCs to a high degree. However, if the biological process cannot be optimised to achieve adequate EDC removal, one of several AOPs can be used to try to control EDCs while also providing disinfection, oxidising and removing pollutants without generating a sidestream requiring further treatment.
Properly designed combinations of UV plus hydrogen peroxide, ozone plus hydrogen peroxide, and UV plus ozone can oxidise EDCs and other contaminants, as these combinations are designed specifically to increase the concentration of hydroxyl radicals, which have less selectivity as oxidants and react quickly with many organic and inorganic compounds.
Substances that are difficult to biodegrade and are not removed are oxidised, forming byproducts may be more amenable to biodegradation, so that AOPs can be followed by a biological process for further degradation.
However, the risk of byproduct formation needs to be further addressed. As byproducts formed through treatment with AOPs are suspected of having toxic properties and are generally present in much higher concentrations in WwTW effluent than EDCs, it is important to ensure that efforts to control EDCs by oxidation are not counterproductive to achieving a high-quality effluent.
More information will be presented at the CIWEM Conference on Endocrine Disrupting Chemicals in the Water Environment in Nottingham on March 30. Visit www.aqua-enviro.net/calendar.asp. E-mail email@example.com
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