Black & Veatch's Frank Rogalla looks at removing endocrine disruptersEndocrine disrupting compounds (EDCs) and pharmaceutical and personal care products (PPCPs) have been implicated in various cancers, reproductive tract disorders and reduction of reproductive fitness. These compounds may cause environmental damage at extremely low (sub µg/l) concentrations or below-detection-limit values, and their presence in water has raised concerns with the public and regulators.
The types of chemicals classed as EDCs or PPCPs can vary among researchers. In some cases certain priority pollutants such as pesticides, herbicides and chlorinated organic compounds are listed as EDCs. While not a comprehensive list, Table 1 presents examples from the literature of compounds that may be classed as either.
Very little is known regarding the fate of these compounds when subjected to conventional wastewater and reclaimed treatment processes. An important point that needs to be addressed in future research is which EDCs and PPCPs are toxic at what environmentally relevant levels. In the US, the American Water Works Association Research Foundation (AwwaRF) and Water Environment Research Foundation (WERF) have both sponsored projects aimed at the identification and treatment of EDCs. Since most of these projects have recently commenced or are about to begin only limited information is available.
One AwwaRF project guided by Southern Nevada Water Authority (SNWA) is examining the effectiveness of conventional and advanced water treatment processes in removing EDCs. Previous analytical techniques developed by SNWA will be used to identify the removal of estrogenic compounds during treatment. The goal of this project is to establish methods of predicting efficiencies of various water treatment processes. WERF is sponsoring a number of research projects regarding the fate of EDCs in WwTWs. One major project is examining the concentration of EDCs in wastewater biosolids. A project jointly funded by AwwaRF, WERF, and the Water Reuse Foundation examined the sources of EDCs and PPCPs in the water industry and identified potential research needs and priorities. A European Union project, POSEIDON, will examine the discharge of PPCPs into the environment from WTWs and WwTWs. To reduce the risks of unforeseeable long-term side effects of PPCPs, POSEIDON is developing methods to limit uncontrolled releases of PPCPs in WwTW effluent.
A recent study indicates those activated sludge WwTWs which are required to meet strict nitrogen and phosphorus limits would have a high potential for removing some PPCPs. Activated sludge facilities with shorter retention times and trickling filters did not appear to achieve effective removal of PPCPs. The study indicated no PPCPs were detected after reverse osmosis and nanofiltration following the nitrification/denitrification processes.
Literature searches revealed little on the removal of some types of EDCs, such as pesticides and herbicides by biological processes. The United States Environmental Protection Agency (USEPA) developed a database on the removal of many toxic organic compounds by wastewater treatment processes ranging from activated sludge to advanced oxidation. Data on EDCs relating to estrogen and steroids is limited and needs to be expanded before removal rates or efficiencies can be determined. Several methods and means of disinfection are available for the removal of EDCs, among them chlorine gas, hypochlorite (either liquid or on-site generated), chlorine dioxide, peracetic acid, hydrogen peroxide, UV and ozone. As part of the AwwaRF research project, a number of these technologies will be examined either alone or in combination. Literature indicates the control of disinfection by-products may reduce the concentration of EDCs discharged after disinfection.
Chlorine systems use chlorine gas and liquid or on-site generated hypochlorite. Gaseous chlorine is the most common means of disinfecting wastewater in the US. Design parameters and dosing requirements for its use are well established for use on reclaimed water. Sodium hypochlorite is a liquid disinfectant that has proven to be reliable for inactivation of fecal coliforms. In fact, it typically achieves performance levels equal to those of chlorine gas. Its effectiveness may be attributed to the fact that sodium hypochlorite disassociates in solution to form hypochlorous acid, which is the same disinfecting agent that is formed when chlorine gas is introduced into solution.
Although sodium hypochlorite has been generated on-site since the 1930s, it has not traditionally been used for disinfection of wastewater effluents. The process uses a brine solution passed across electrodes powered by a low-voltage current to generate chlorine, producing a dilute hypochlorite solution of 0.8%. On-site hypochlorite generation requires the construction of a brine tank, rectifier, electrolytic cells, a product tank, metering pumps and controls.
Experimental studies indicated with sodium hypochlorite, a 90% removal of PPCPs could be achieved using a 1mg/l chlorine residual with detention times ranging from 8-40min. For unrestricted reuse, the State of California Department of Health requires the disinfection system be designed to provide two hours of contact time with a minimum chlorine residual of 5mg/l for 4-log removal of viruses. According to literature sources, if a reuse plant used this method of disinfection, the PPCPs would be removed. Information in the literature regarding removal of EDCs using chlorine was inconclusive. The downside of this technology is that the chlorine residual and contact time for reuse facilities may result in the formation of by-products. In this case, the by-products of EDCs and PPCPs are not known and may form more potent toxins than the parent compounds.
Chlorine dioxide has been used successfully as a disinfectant in WTWs for a number of years. It minimises the formation of disinfection by-products that are regulated under the Safe Drinking Water Act. Current research is being conducted on the use of chlorine dioxide at WwTWs for minimising the formation of disinfection by-products as well. Recent reports on the use of peracetic acid for disinfection of wastewaters, typically treated by physical/chemical processes, have shown a high degree of success. Literature indicates peracetic acid is most often used for treatment of discharges to marine waters. Peracetic acid offers the advantage that it can achieve disinfection objectives (1,000 fecal coliforms) without forming disinfection by-products or requiring a dechlorination step.
A literature search did not reveal any studies on the removal of EDCs and PPCPs through peracetic acid disinfection. Since peracetic acid does not appear to form disinfection by-products, it might have some advantages in the treatment of EDCs and PPCPs. Additional research will need to be completed on the use of peracetic acid for the removal of EDCs and PPCPs in reclaimed water treatment plants.Peroxide bond
While hydrogen peroxide could be used for disinfection, no full-scale facilities have been built utilising this means of disinfection. Additional research, including conceptual design and an economic evaluation, would need to be conducted to verify the use of hydrogen peroxide for disinfecting wastewater. Typically, when hydrogen peroxide is used, it is combined with another disinfection method such as UV or ozone. Literature indicates that when peroxide is used in conjunction with UV or ozone, the formation of the hydroxyl radical occurs. The hydroxyl radical attacks the chemical bonds, breaking it into its elemental components. Since this is a chemical reaction, additional by-products can be formed if the reaction is not completed.
UV light between the wavelengths of 235-270nm has been found to exhibit biocidal action on bacteria and viruses in water, wastewater and process water. UV radiation is readily absorbed by deoxyribonucleic acid (DNA) in certain pathogens found in municipal wastewater. When this energy is absorbed, the pathogen's molecular structure can be altered, resulting the inability to replicate. While this effect can be reversed (referred to as reactivation) under certain conditions, UV radiation has proven effective for the disinfection of municipal wastewater. Research indicated that at UV doses above 3,000 mJ/cm2, only 50-80% removal of PPCPs was obtained. These low removals were due, in part, to the PPCPs being studied adsorbing UV.
As a result of high operations and maintenance costs, ozone as a wastewater disinfectant is currently not as popular in the US as it once was. A 1982 USEPA survey showed over 40 plants using ozone for wastewater disinfection, this number dropped to below 15. With the new emphasis on disinfection by-products, ozone may again become a viable technology for wastewater disinfection. Recent literature showed, using distilled water, that with a CT of approximately 0.5mg-min/l, approximately 100% of the antibiotics being studied could be removed.
Data on EDC and PPCP removal using disinfection technologies at reclaimed wastewater treatment facilities is limited. Literature indicates chlorine disinfection technologies may achieve removals of some types of EDCs and PPCPs if the reaction is completed. UV and ozone also appear viable for the removal of EDCs and PPCPs. The key to effective removal of EDCs and PPCPs will be the performance of the upstream process. WwTWs with long detention times and nanofiltration/reverse osmosis appear to have more effective disinfection processes.