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Critical Review pubs.acs.org/est
Review of Organic Wastewater Compound Concentrations and Removal in Onsite Wastewater Treatment Systems Laurel A. Schaider,* Kathryn M. Rodgers, and Ruthann A. Rudel Silent Spring Institute, 320 Nevada Street, Suite 302, Newton, Massachusetts 02460 United States S Supporting Information *
ABSTRACT: Onsite wastewater treatment systems, such as septic systems, serve 20% of U.S. households and are common in areas not served by wastewater treatment plants (WWTPs) globally. They can be sources of nutrients and pathogen pollution and have been linked to health effects in communities where they contaminate drinking water. However, few studies have evaluated their ability to remove organic wastewater compounds (OWCs) such as pharmaceuticals, hormones, and detergents. We synthesized results from 20 studies of 45 OWCs in conventional drainfield-based and alternative onsite wastewater treatment systems to characterize concentrations and removal. For comparison, we synthesized 31 studies of these same OWCs in activated sludge WWTPs. OWC concentrations and removal in drainfields varied widely and depended on wastewater sources and compound-specific removal processes, primarily sorption and biotransformation. Compared to drainfields, alternative systems had similar median and higher maximum concentrations, reflecting a wider range of system designs and redox conditions. OWC concentrations and removal in drainfields were generally similar to those in conventional WWTPs. Persistent OWCs in groundwater and surface water can indicate the overall extent of septic system impact, while the presence of well-removed OWCs, such as caffeine and acetaminophen, may indicate discharges of poorly treated wastewater from failing or outdated septic systems.
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INTRODUCTION Wastewater effluent is the primary source of pharmaceuticals, hormones, consumer product chemicals, and other organic wastewater compounds (OWCs) commonly detected in surface water, groundwater, and drinking water.1−5 Since many OWCs interact with biological systems, their ubiquity in aquatic systems raises concerns about ecological health effects and potential human exposures through drinking water. Hormones and other endocrine active compounds in surface waters have been linked to increased proportions of intersex fish, elevated female:male ratios, and physiological alterations in male fish.6,7 Antibiotics in groundwater can alter microbial community structure and microbially mediated nitrogen biotransformation processes.8,9 For the most part, OWCs are not currently regulated in drinking water, and existing toxicity data are inadequate to assess potential risks from chronic low-dose exposures. Nonenforceable health-based guidelines for drinking water have been developed by governmental agencies and researchers for some per- and polyfluoroalkyl substances (PFASs), pharmaceuticals, and organophosphate flame retardants (OPFRs).10−15 Studies in wastewater treatment plants (WWTPs) have shown that OWC removal and transformation depend on treatment type, wastewater composition, and chemical characteristics.16−18 Activated sludge processes remove many OWCs through biological transformation, volatilization, and settling of particlebound compounds. Some OWCs are more persistent, requiring © XXXX American Chemical Society
longer solids retention times or advanced treatment processes such as reverse osmosis.19−21 Other OWCs are highly persistent across many types of treatment, including some OPFRs (e.g., TCEP), fragrance compounds (e.g., galaxolide), pharmaceuticals (e.g., carbamazepine), and PFASs (e.g., PFOS).21−23 In the U.S., onsite wastewater treatment systems serve about 20% of residences, including half of mobile homes,24 and are also prevalent in other developed countries.25−27 They are common in developing countries where centralized systems have not been built.28 Septic systems are among the approaches for improving sanitation infrastructure to meet the U.N. Millenium Development Goals.29 Septic systems discharge into groundwater, often in areas that rely on domestic drinking water wells.30,31 The presence of nearby septic systems has been linked to infection and diarrhea in children32 and chronic exposure to Cryptosporidium33 in areas served by domestic wells. Septic systems can be significant contributors to nutrient pollution into coastal waters34,35 and streams,36,37 although this contribution is often underestimated.38 They also have been recognized as sources of OWCs into coastal waters,39−41 lakes and ponds,42−44 groundwater,45,46 and drinking water.30,47,48 Received: September 21, 2016 Revised: April 28, 2017 Accepted: May 8, 2017
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DOI: 10.1021/acs.est.6b04778 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Critical Review
Environmental Science & Technology
Selection of OWCs. From each study, we compiled data for pharmaceuticals and personal care products (PPCPs), hormones, alkylphenols, OPFRs, plasticizers, artificial sweeteners, and other OWCs. We selected 45 OWCs that were analyzed in at least five septic tanks, detected in at least one septic tank, and analyzed in at least five drainfields or five alternative systems. SI Table S2 lists each compound, primary uses, CAS number, octanol−water partitioning coefficient (log Kow, indicates hydrophobicity), octanol-air partitioning coefficient (log Koa, indicates volatility from organic phases, such as soil organic carbon, into air), and environmental biodegradation time frame (using BIOWIN4).68 Data Compilation. We compiled data for dissolved concentrations in wastewater from tables, text, and graphs. In cases where data were only presented in graphs, concentrations were extrapolated using DataThief.69 We did not use DataThief if there was ambiguity about sample identities or if values could not be reliably discerned from the axes. Many compounds were not detected (ND) above their corresponding RL or DL (referred to as a censoring value). We recorded these data as a range from 0 to the censoring value. If a censoring value was not reported, or when values were reported below the RL, we used the lowest detected value for the corresponding matrix (e.g., STE, drainfield leachate) as the censoring value. Some values were reported as estimated that either fell between the DL and limit of quantification (LOQ) or were above the highest point on the calibration curve. Estimated values were flagged and used as reported. We compiled data from each system in two ways: (1) concentrations for individual samples and (2) median concentrations for each system. Details of how median values were calculated for each septic system are provided in the SI. We calculated median and maximum concentrations across all systems for each chemical and sample type (STE, drainfield leachate, alternative system effluent, WWTP effluent). Maximum concentrations were based on all individual measurements. We used median concentrations for each system when calculating medians for a chemical, in order to weight each system the same regardless of sampling frequency. Details of how median values were calculated across septic systems are provided in the SI. Most studies in our compilation reported recoveries of spiked target analytes or spiked surrogate compounds (either isotope-labeled analogues or chemically similar compounds). Most studies did not report correcting measured concentrations on the basis of spike recoveries, although six studies used isotope dilution methods to correct for losses during extraction and analysis. In the vast majority of samples, reported recoveries ranged from 50 to 150%, although in some instances, recoveries as low as 10% were reported, mostly for STE. Some studies reported recoveries of spikes into each individual sample, while others reported recoveries aggregated across multiple samples. Studies that reported recoveries of spikes into individual samples were more likely to have
