Chemical and Bacterial Quality of Aeration-TypeWaste Water Treatment System Discharge

by Samuel V. Panno, W.R. Kelly, K.C. Hackley, and C.P. Weibel

AbstractOn-site waste water treatment systems are a potential source of chemical and bacterial contamination to ground water in

areas with highly susceptible aquifers such as the sinkhole plain of southwestern Illinois. Ground water from wells, cavestreams, and water that discharges from the numerous springs in this area is typically contaminated with nitrate and entericbacteria and thus may pose a health hazard to those who come into contact with it. In order to determine if the most populartype of on-site waste water treatment systems in the study area was a potential source, samples of effluents discharged at theland surface from 23 domestic aeration-type on-site waste water treatment systems were collected to characterize their waterquality and bacterial contents. Most of the effluents contained relatively large concentrations of sodium (Na1), chloride(Cl�), nutrients (nitrogen [N], phosphate [PO4

3�], and potassium [K1]), and enteric bacteria. Ion concentration ranges (inmg/L) were Na1 (46 to 416), Cl� (21 to 618), N (4.7 to 67), PO4-P (1.4 to 48), and K1 (6.0 to 257). The sources of elevatedNa1 and Cl� were human waste and NaCl used in the water softening systems of the houses. Ammonium was usually thedominant inorganic N species, indicating incomplete oxidation of the waste water. Discharge of Na1, Cl�, and nutrientscould also have negative impacts on ground water and surface water quality, subsurface and surface aquatic ecosystems, andvegetation. Our characterization of effluent from these waste water treatment systems revealed their generally poor qualityand the likelihood that they can contaminate ground water in areas with highly vulnerable aquifers.

IntroductionApproximately one-third of all houses in the United

States use on-site waste water treatment systems (AmericanGround Water Trust 2005). The three most popular types ofon-site waste water treatment systems are as follows: septictanks feeding a leach field, sand filters, and aeration systems(Figure 1). The vast majority of on-site waste water treat-ment systems are leach field–type septic tank systems, andprevious surveys in the midwestern United States suggestedthat between 50% and 70% of these systems discharge wastewater that is responsible for ground water and surface watercontamination (Aley and Thomson 1984; Bigari 1994).Leach field–type waste water treatment systems are passiveand rely on natural processes. They consist of a settling tankwhere scum (e.g., grease) and sludge are separated fromwaste water, and anaerobic bacteria are allowed to breakdown solid waste. Waste water is directed to a distributionsystem where organic waste can be further digested byanaerobic bacteria. This occurs as the water is gravity fil-tered through an absorption field of narrow gravel beds andunderlying natural soil (Figure 1). The final stage relies on

aerobic bacteria in the soil zone to further ‘‘cleanse’’ theeffluent of pathogens. If properly maintained and witha thick enough soil zone, these systems can operate as de-signed; however, regular maintenance of these systems isoften neglected (Michaud 2005). Consequently, this type ofsystem is known to contaminate ground water and surfacewater, primarily with fecal bacteria. In addition, by-productssuch as nutrients (including ammonium [NH4

1], nitrate[NO3

�], organic N, phosphate [PO43�], potassium [K1]),

organic carbon, as well as sodium (Na1) and chloride (Cl�)can create ground water and surface water contaminationproblems (LeBlanc 1985; Mandel and Haith 1992; Postmaet al. 1992; Harman et al. 1996; Panno et al. 2002, 2006).Such systems have been implicated in the spreading of dis-eases from both pathogenic viruses and bacteria via groundwater and surface water (Scandura and Sobsey 1997; Borch-ardt et al. 2003a, 2003b).

Sand filters or mounds are similar to leach field–typesystems in that they have a settling tank and rely on anaer-obic bacteria to digest organic material. However, insteadof gravity flow to an absorption field, the waste water ispumped to the absorption field near the top of a constructedsand mound (Figure 1). The sand beneath the absorptionfield acts as a soil for filtering solids and where aerobicbacteria provide a final stage for biodegradation of organic

No claim to original US government works.Journal compilationª 2007National GroundWater Association.

Ground Water Monitoring & Remediation 27, no. 2/ Spring 2007/pages 71–76 71

materials. These systems are used in areas where soils arenot amenable to leach field–type systems (e.g., soil depth istoo shallow or soil is not permeable enough) (U.S. EPA1997; American Ground Water Trust 2005).

Aeration systems are miniature water treatment facili-ties and are becoming more popular in the United States.Again, the system begins with a settling tank, and wastewater flows into a mixing chamber where an aerator swirlsair through the waste water. The air and nutrients stimulategrowth of aerobic bacteria that decompose the organic mat-ter. Following aeration, the water flows to a clarification cham-ber where it can be chlorinated and filtered (Figure 1).Because aerobic systems use a higher rate process, theireffluent quality is reportedly superior to septic systems andthe treated water is allowed to discharge directly to the sur-face (U.S. EPA 2000). In order to be discharged at the sur-face, the effluent must comply with U.S. EPA secondarytreatment guidelines, primarily biological oxygen demand(BOD) and suspended solids levels less than 45 mg/L, andfecal coliform (FC) concentrations less than 400 colony

forming units (cfu)/mL (Illinois Department of PublicHealth [IDPH] 2005). Because leach field– and sand filter–type systems discharge to the soils and aquifer, and proba-bly because of sampling difficulties, the quality of theireffluent has no guidelines.

Because of the popularity and abundance of aeration-type waste water treatment systems in rural areas of south-western Illinois’ sinkhole plain (Figure 2), they constitutea potential source of contamination to ground water fromwells, cave streams, and springs in the karst aquifer (Pannoet al. 1996, 1997, 2005). The purpose of this investigationwas to characterize the chemical composition and bacterialcontent of effluent being discharged to the environment bydomestic aeration-type waste water treatment systems inorder to determine their potential as a source of groundwater contamination in an area with a highly susceptibleaquifer. While a number of researchers have examined thechemical and biological character of leach field–type efflu-ents, we are unaware of any studies examining effluentfrom aeration-type, on-site, waste water treatment systems.

Figure 1. Simplified diagrams of the three most popular types of domestic waste water treatment systems in the United States.Modified from American Ground Water Trust (2005).

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MethodsEffluent samples were collected from the surficial dis-

charge pipes of 23 domestic, professionally maintained, on-site aeration systems in Monroe County, Illinois (an areawith extensive karst features), during the summers of 1996through 2000. The systems have been operating between2 and 11 years at the time of sampling. Effluent sampleswere analyzed in the field for temperature, pH, Eh, andspecific conductance (SpC), using meters that allow tem-perature compensation in accordance with standard fieldtechniques (Wood 1981). Effluent was pumped through0.45 lm filters to collect samples for cation and anionanalysis; however, samples designated for NH4

1 were notfiltered. Unfiltered water samples collected from 20 of theaeration systems were tested for bacterial indicators(total aerobic [TA], total coliform [TC], FC, and fecalenterococcus [FE]), and for bacterial genera and speciesidentification. All samples were transported to the labora-tory in ice-filled coolers and kept refrigerated at approxi-mately 4�C until analyzed.

Concentrations of cations in water samples were deter-mined with a Thermo-Jarrell Ash Model ICAP 61e Induc-tively Coupled Argon Plasma Spectrometer. Solutionconcentrations of anions (including NO3) were determinedusing a Dionex 211i ion chromatograph with Ionpac AG14Guard Column, Ionpac AS14 Analytical Column, and AnionSelf-regenerating Suppresor-11 (4 mm). Ammonium wasdetermined using the Berthelot Reaction and a Bran andLuebbe TRAACS 2000 colorimeter. Details for these analyt-ical methods and complete chemical data for the septic sys-tem samples may be found in Panno et al. (2005). Mostcation and anion analyses were conducted at the IllinoisState Geological Survey (ISGS), Champaign, Illinois; NH4

1

analyses were conducted at the Illinois State Natural HistorySurvey, Champaign, Illinois. Bacterial analyses were con-ducted within 24 h of sample collection at the Department ofAgriculture’s Animal Disease Laboratory in Centralia, Illi-nois. TA, TC, FC, and FE were determined using standardmethod filtration techniques using Endo broth, FC agar, andKF enterococcus agar (American Public Health Association1989; Cason et al. 1991). Bacterial species and genera weredetermined using Millipore HAWG filters (45 lm pore size)and the filter membranes placed on a tryptose blood agarplate and incubated at 37oC for 48 h. Isolated colonies wereselected for Gram staining and microscopic identification(Clesceri et al. 1991; Cason et al. 1991).

Results and Discussion

Effluent Water QualityThe inorganic chemical composition of effluents from

the sampled aeration systems reflected the composition oftheir city source water and the treatment of and waste addedto the water at each house. The municipal water (treated Mis-sissippi River water from Alton, Illinois) is a Ca-HCO3 typewith relatively low concentrations of nutrients (Table 1).Effluent from the aeration systems reflects the addition ofnutrients and the effects of water softeners and ranged froma Ca or mixed cation-HCO3 type water to a Na-Cl typewater. The pH of the effluent was typically lower than that ofthe source water because of the effects of oxidation of NH4

1

(Wilhelm et al. 1994). The effluent contained a relativelylarge range of concentrations of salts, nutrients, and boron(B): Na1 (46 to 416 mg/L), Cl� (21 to 618 mg/L), K1 (6.0to 257), NO3

� (<0.02 to 26 mg/L), NH4-N (0.09 to 67),PO4-P (1.38 to 48), and B (0.05 to 1.73) (Table 1).

Water Softener SaltThose effluent samples that fell into the range of Na-Cl

type water were from households that used water softeners.Effluent from these households can contain Na1 and Cl�

at concentrations in the thousands of milligrams per literdue to the large amount of brine solution used for backflushing ion exchange resins. If NaCl is added to watersoftening systems at rates in accordance with manu-facturers’ recommendations for moderately hard water withserving a family of four (~1.8 to 2.7 kg/d), a single watersoftening system may discharge close to 1000 kg/year ofdissolved NaCl to nearby surface water and ground water.

The Na1 and Cl� concentrations of septic effluentdepend greatly on when samples are collected; if samplesare collected during or immediately following rechargingof the water softener ion exchange column, Na1 and Cl�

concentrations can be up to 100 times greater than duringnormal operation. This occurred just prior to our collectionof an effluent sample from the septic tank of a leach field–type waste water treatment system where Na1 and Cl�

concentrations in the effluent were 2740 and 5620 mg/L,respectively (data in Panno et al. 2005). Elevated con-centrations of Cl� have been found in ground waterdowngradient from on-site septic systems (e.g., Harmanet al. 1996). Public buildings with their own waste water

Figure 2. Location of the study area in southwestern Illinois’sinkhole plain.

S.V. Panno et al./ Ground Water Monitoring & Remediation 27, no. 2: 71–76 73

treatment facilities can be even worse. An extreme exam-ple is a large teaching/day care facility in Verona, NewYork, where 270 kg of water softener salt were consumedat the facility per month or 3240 kg per year (Ash 1993).Chloride concentrations in a monitoring well adjacent tothe facilities’ leach field were as much as 16,400 mg/L(Panno et al. 2006).

NutrientsNutrients present within effluent samples included

N (median 23 mg/L), PO4-P (median 5.9 mg/L), andK1 (median 17 mg/L). The median NO3-N concentrationwas 1.25 mg/L, although four samples had NO3-N con-centrations greater than 10 mg/L. Ammonium-N (median16.9 mg/L) was the dominant inorganic N species in abouttwo-thirds of the aeration system (NH4

1 adds to the BODin waste water). This suggests that these systems are notcompletely oxidizing the waste water, otherwise NO3

� wouldbe the dominant N species. Boron is used as a whiteningagent in laundry detergents and is commonly elevated inseptic effluent (Smith 2002); the median B concentration ofour effluent samples (0.47 mg/L) was over an order ofmagnitude greater than that of the source water (Table 1).Relative to the low concentrations of these constituents inthe source water, we assumed that these constituents werederived from household sources that included humanwaste, water softener backwash, and laundry detergents.

Bacterial CompositionConcentrations of the bacterial indicators were elevated

in almost all of the aeration system samples. TA bacteria

were greater than the upper detection limit (30,000 cfu/100 mL) in 76% of the samples, and TC were greater thanthe upper detection limit (4000 cfu/100 mL) in 70% of thesamples. FC and/or FE were detected in 18 of the 20 sam-ples, and concentrations greater than 400 cfu/100 mL werefound in 59% of the samples. In Illinois, the state and localregulatory limit for FC in discharge from such systemsis 400 cfu/100 mL (IDPH 2005; Monroe-RandolphBi-County Health Department 1994). The presence of rela-tively large concentrations of fecal bacteria show that theeffluent is a potential source for ground water contamina-tion. The bacterial content was in excess of regulatorylimits for all the systems that were not operating aerobi-cally (as indicated by the predominance of NH4-N overNO3-N). Even for systems that were operating aerobically,as indicated by the predominance of NO3-N, about 40%had noncompliant levels of FC bacteria.

Eighteen genera and species of bacteria were identi-fied in the aeration system effluent samples. The domi-nant bacteria were Pseudomonas and enteric bacteriasuch as Escherichia coli, Streptococcus faecium, andS. faecalis (Table 2). The presence of enteric bacteriasuggests that human viruses may also be present in theeffluent (Geldreich 1996) and ground water (Chapelle1993). Because many of the on-site waste water treatmentsystems in this area discharge directly or indirectly intosinkholes, these systems may provide a constant sourceof enteric bacteria and possibly viruses to the shallowkarst aquifers in the area. Enteric bacteria are commonlyfound in private wells, cave streams, and most springsin the area (Panno et al. 1996, 1997, 2002; Taylor et al.2000).

Table 1Descriptive Statistics of Selected Ions for Samples of Effluent from 23 Private Aeration Systems and Municipal

Water Used by Most of the Homeowners

Parameter Range Median Mean SD Source Water1

pH (pH units) 5.8–7.5 7.1 7.0 0.4 7.2–7.7Eh (mV) �31–614 333 291 195 NDSpC (lS/cm) 805–2894 1125 1247 504 NDAlkalinity (CaCO3) 117–608 264 280 172 104–198Na 45.5–416 87.9 130 104 20–25K 6.0–257 17.0 27.4 49.4 <5.0Ca 33.0–142 68.1 72.8 27.3 45–60Mg 2.27–40.6 24.3 24.1 7.37 20–25Sr 0.07–0.66 0.26 0.26 0.13 0.06–0.16B 0.05–1.73 0.47 0.55 0.44 <0.05SiO2 6.66–31.0 14.1 15.8 6.54 10–15SO4 8.45–130 91.6 75.2 35.3 40–60Cl 20.8–618 86.7 137 148 30–40Br <0.05–0.36 0.09 0.10 0.09 0.02–0.05NO3-N <0.02–25.9 1.25 4.85 7.53 3.0–4.0NH4-N 0.09–66.5 16.9 19.3 19.6 0.5–1.0(NO3 1 NH4)-N 4.67–66.9 23.3 24.1 16.5 3.5–5.0PO4-P 1.38–48.0 5.89 9.31 10.1 0.9–1.0

Notes: Concentrations in mg/L unless stated otherwise. Chemical data for effluent samples may be found in Panno et al. (2005). ND ¼ no data.1Range of municipal source water from Waterloo, Illinois (S. Boyd, Illinois American Water Company, unpublished data).

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ConclusionsGround water from wells, within caves, and discharging

from numerous springs in the study area is typically con-taminated with enteric bacteria and thus poses a health haz-ard to those who come into contact with it. Characterizationof the chemical and bacterial composition of effluent fromaeration-type on-site waste water treatment systems was con-ducted to determine if they could be a potential contaminantsource. Aeration-type on-site waste water treatment systemsare designed to produce effluent of higher quality than tra-ditional leach field–type systems and consequently aretypically allowed to discharge at the land surface; all ofthe systems sampled in this study discharged at the surfacesomewhere within or in close proximity to a sinkhole. How-ever, our results indicate that the effluent quality was poorand potentially could contaminate both ground water andsurface water. Very large concentrations of Na1, Cl�, nutri-ents (N, P, and K1), and enteric bacteria were found in mostof the effluent samples. The fact that NH4

1 was the dominantinorganic N species in most of the samples (the dominantion should have been NO3

�) indicates that there wasincomplete oxidation of the waste water.

The results of our investigation clearly indicate thataeration-type on-site waste water treatment systems can bea significant source of Na1, Cl�, nutrients, and bacterialcontamination to ground water in areas with highly vulner-able aquifers. The Na1, Cl�, and nutrients in the effluentfrom any type of on-site waste water treatment systems,particularly from houses with water softeners, could havenegative impacts on surface and subsurface aquatic ecosys-tems, and surface vegetation along streams.

AcknowledgmentsThe authors thank Don Keefer, Jon Goodwin (ISGS),

Randy Locke (Illinois State Water Survey [ISWS]), andtwo anonymous reviewers for their valuable comments.This research was supported with funds from the IllinoisDepartment of Natural Resources, ISGS and ISWS divi-sions. Publication of this article has been authorized by thechiefs of the ISGS and ISWS.

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Table 2Bacterial Species Isolated from Samples of Aeration System Effluent and

Percent of Samples with Each Species (n ¼ 20)

Bacterial Species Percent Present Source

Pseudomonas spp. 100 Common in soil, uses cellulose as substrateEnterococcus faecium 86 Fecal matter from warm-blooded organismsEscherichia coli 86 Fecal matter from warm-blooded organismsKlebsiella pneumoniae 82 Common in soil and animalsE. aureus 59 Fecal matter from warm-blooded organismsE. faecalis 55 Fecal matter from warm-blooded organismsBacillus spp. 41 Common in warm, moist soilSerratia spp. 41 Common in soil and live on decaying matterEnterobacter aerogenes 14 Coliform common in public water suppliesEnt. aggolomerans 14 Coliform common in public water suppliesEnt. cloacae 14 Coliform common in public water suppliesProteus mirabilis 14 Fecal matter from warm-blooded organismsAeromonas hydrophila 9.1 Cold-blooded vertebrates (e.g., frogs)Citrobacter spp. 9.1 Coliform common in public water suppliesEnterobacter spp. 9.1 Coliform common in public water suppliesBacillus cereus 4.5 Common in warm, moist soilCitrobacter freundii 4.5 Coliform common in public water suppliesE. sciuri 4.5 Coliform common in public water suppliesE. xylosis 4.5 Inhabitant of human skinK. oxytoca 4.5 Coliform common in public water suppliesProteus spp. 4.5 Fecal matter from warm-blooded organisms

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Biographical SketchesSamuel V. Panno, corresponding author, is a senior geochemist

at the Illinois State Geological Survey in the Isotope Geo-chemistry Section. He received his MS from Southern Illinois Uni-versity at Carbondale and his BS from Oregon State University atCorvallis. Illinois State Geological Survey, 615 E. Peabody Drive,Champaign, IL 61820-6964; (217) 244-2456; fax (217) 244-2785;panno@usgs.uiuc.edu.Walton R. Kelly is a groundwater geochemist in the Center for

Groundwater Science at the Illinois State Water Survey. He re-ceived his Ph.D. from the University of Virginia, his MS from CaseWestern Reserve University, and BS from Duke University. IllinoisState Water Survey, 2204 Griffith Drive, Champaign, IL 61820-7120; (217) 333-3729; fax (217) 244-0777; kelly@sws.uiuc.edu.Keith C. Hackley is a senior geochemist at the Illinois State

Geological Survey in the Isotope Geochemistry Section. He re-ceived his Ph.D. and MS from the University of Illinois atChampaign-Urbana, and his BS from Pennsylvania State Univer-sity, University Park. Illinois State Geological Survey, 615 E.Peabody Drive, Champaign, IL 61820-6964; (217) 244-2396; fax:(217) 244-2785; hackley@isgs.uiuc.edu.C. Pius Weibel is a geologist at the Illinois State Geological

Survey in the Quaternary Geology Section. He received his Ph.D.and MS from the University of Illinois at Champaign-Urbana,and his BS from the University of Wisconsin-Platteville. IllinoisState Geological Survey, 615 E. Peabody Drive, Champaign, IL61820-6964; (217) 333-5180; fax (217) 244-2785; weibel@isgs.uiuc.edu.

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