Wastewater Reuse and Risk

Presented at the International Conference on Integrated Concepts on Water Recycling, Wollongong, NSW, Australia,1417 February 2005.

Desalination 187 (2006) 2940

Wastewater reuse and risk: definition of key objectives

M. Salgota*, E. Huertasa, S. Weberb, W. Dottb, J. HollenderbaLaboratori dEdafologia, Facultat de Farmcia, Universitat de Barcelona, Avda. Joan XXIII,

s/n. 08028, Barcelona, SpainTel. +34 (93) 402-4494; Fax +34 (93) 402-4495; email: [email protected]

bInstitute of Hygiene and Environmental Medicine, RWTH Aachen, Pauwelsstrae 30, D-52076 Aachen, Germany

Received 23 November 2004; accepted 29 April 2005

Abstract

Wastewater reclamation holds promise as an important water resource as the desire to develop arid regionscontinues to place increasing demands on finite water resources. The debate surrounding the consumption of reclaimedwastewater finds risk managers pondering the question of what types of water quality standards might be set in orderto provide the proper level of safety associated with the use of reclaimed wastewater. We propose quality categoriesfor different reuses such as irrigation or indirect aquifer recharge with different requirements towards microbial andchemical parameters. Based on recent existing guidelines and risk estimations, microbial and chemical limits for eachcategory were compiled. Since economic calculations are very important, analytical costs are included and measure-ments frequency is proposed. Biological parameters have to indicate all potential pathogenic organisms includingviruses, bacteria and parasites from different origins. The selected biological indicator parameters most used in rulesand regulations are coliforms and E. coli, indicating the occurrence of a former faecal contamination and the possiblepresence of all pathogens occurring in faeces of warm-blooded animals. In the case of wastewater reuse, biologicalparameters have to indicate all potential pathogens causing infection diseases and/or intoxication in all living beingsincluding plants and animals. The large number of possible chemical parameters in relation with wastewaterreclamation and reuse has to be adapted and minimized with respect to the origin of the sewage, the extent of thetreatment process and the intended use. These parameters must cover a broad spectrum of toxicological and ecologicalrisks as well as possible technical disorders. Risk assessment and risk management are also necessary.

Keywords: Risk assessment; Wastewater reuse; Microbiological and chemical parameters

*Corresponding author.

doi:10.1016/j.desal.2005.04.0650011-9164/06/$ See front matter 2006 Elsevier B.V. All rights reserved.

M. Salgot et al. / Desalination 187 (2006) 294030

1. Introduction

Wastewater reclamation and reuse have beenthe subject of a number of studies dealing withwater quality for some time, especially in relationto microbiological criteria. During the lastdecade, chemicals have also been incorporatedinto the oberservation panel, thus enlarging thenumber of parameters to be determined for safereuse of wastewater.

Reclamation and reuse hazards are usuallydefined according to standards issued or recom-mended by local authorities or internationalagencies. When trying to study the rationale ofsuch an approach, there are several inconsis-tencies, namely the adequacy of control para-meters, a certain lack of definition of theappropriate sampling points, the number ofsamples and analysis necessary, and the cost ofthe analytical work.

In any case, if standards are to be met, itappears that planning steps, economic calcula-tions, and social tasks are to be performed forsuccessful reclamation and reuse practices. Then,it seems obvious that scenarios must be built forthe correct comparison of the different possiblealternatives, including all the data needed to reacha correct decision.

From the zero scenario (no reuse) to thetheoretically more expensive one (reclamation orseawater desalination using reverse osmosis),adequate tools are to be used in order to helpstakeholders to decide the best option for theincrease of available water resources. Among thetools, decision support systems are the mostuseful for gaining good information, but otherstudies must also be undertaken to determine thenecessary technologies and schemes. As healthhazards are one of the main constraints for reuse,it appears that risk assessment, based on hazardcalculations, is basic for several definitions inreclamation and reuse projects.

A discussion came up on the adequacy of themain parameters used (coliform-derived stan-

dards, nematode eggs), the suggested ones, thenumber of samples compulsory for the legalsafe reuse, and on the price of the analytical worknecessary to fulfil legal requirements. Ifpreventive risk management concepts (mainlyHACCP) are used, the number and periodicity ofanalysis are reduced to the established criticalcontrol points, which will decrease costs. Stan-dards, HACCP systems, and good reuse practicesmust be considered in an integrated way in forefficient management of the reclamation prac-tices. A final question is issued: can classicalreclamation be competitive with other watersources if all the compulsory actions areperformed?

2. Microbiological and chemical parametersconcerning reclaimed wastewater reuse

The risks concerning reclaimed wastewaterreuse can be classified into biological and chemi-cal risks. The biological and chemical parametersof interest are described in more detail below.

2.1. Microbiological parameters

The increase of health hazards and concerns inrelation to wastewater, the growing number ofwastewater treatment facilities, and the need forobtaining additional water resources throughwastewater reuse have forced the necessity ofusing more precise and sophisticated biologicalcontrol tools for wastewater recycling. Due to thecosts and complexity of analyzing actual patho-gens, it should be considered [1] that wastewaterprofessionals and regulators have relied fordecades on traditional faecal indicators (Table 1)to predict potentially high pathogen levels beingsufficient to guarantee high-quality standards.

The scientific community was always awarethat detection and quantification of E. coli are notenough to define the quality of a certain waste-water treated, reclaimed, or discharged into the

M. Salgot et al. / Desalination 187 (2006) 2940 31

Table 1Types of waterborne pathogens and used indicators [2]

Waterborne pathogens Indicators Observations

Bacteria E. coli, Faecal coliforms, Total coliforms,Enterococcus fecalis,Staphylococcus aureus, Salmonella spec.,Clostridium perfringens, Pseudomonasaeruginosa, Legionella pneumophila

Faecal coliform (FC) determination ismore usual; E. coli determination isslowly substituting FC. Other bacteria areused for bathing waters, groundwater, etc.

Viruses Enterovirus, Hepatitis A virusBacteriophages

An accepted indicator still does not exist.Bacteriophage is being studied in thissense.

HelminthNematode Nematode eggs (Ascaris, Trichuris,Ancylostoma as indicated by the WHO)

Discouraging: many negative results inmany countries. Egg viability is notrequired.

Other helminths(i.e., Taenia)

Unknown In some cases important for risk related toanimal health

Protozoa (includes Giardia,Cryptosporidium, Amoeba,Balantidium, etc.)

UnknownThe presence of one of them could indicatethe presence of the other

Analytical tools not well developed untilnow

Fungi, algal toxins Unknown Few cases detected

environment. Some pathogens are more resistantto conventional wastewater treatment (includingchlorination) and its sources are not warm-blooded animal faeces. Therefore, E. coli is aninsufficient tool to reflect the quality changes dueto wastewater treatment processes, conventionalor advanced, extensive or intensive. In addition,it does not permit the control of wastewaterdisinfection.

Otherwise, the long period of time needed toproduce results is a negative feature in the ana-lytical work, but not only related to E. coli deter-mination. However, new molecular biologicalmethods are under development that enable afaster determination of specific microorganisms[3]. It is necessary to define more suitable indi-cators in order to establish the biological qualityof different types of wastewater (Table 1). Forexample Enterococcus faecalis and even sporesof Clostridium perfringens are known to be moreresistant against disinfection than E. coli andtherefore may be used for its control. Otherwise,

the current analysis using bacterial indicatorsdetects only the quality of a wastewater singlesample and not the constant quality during agiven time.

Campos also reported on the difficulty ofdefining microbiological quality of the media thatreceive reclaimed wastewater, particularly theagricultural systems where reclaimed water isused for irrigation [4]. Plants, soil, groundwater,run-off and the atmosphere can and must be con-trolled separately from the reclaimed wastewater.Campos also indicated the need to establish andrealize joint studies of all media implied in waste-water reuse systems. An additional difficulty isthe lack of reference figures for the content ofpathogen organism in media other than water.

As indicated previously, several groups oforganisms are determined by using indicators(i.e., pathogen bacteria by E. coli), althoughothers (i.e., Giardia lamblia) do not have usefulindicators and must be determined directly(Table 2).


Table 2Organisms usually determined in wastewater treatment, and reuse [2]

Type/organism Usually/theoreticallyemployed as

On research Observations

Total coliforms Bacterial indicator Not widely usedFaecal coliforms/E. coli

Faecal indicator Faster methods Most used method, despite theproblems and discussions

Bacteriophage Faecal indicator Most suitable one Somatic, F-specific andBacteroides fragilis HSP40 andRYC2056 phages

Bacterial count Indicator for aerobic,heterotrophic bacteria

Amount of DNA/RNA Recovery of not more than 10%

Nematode eggs Nematode and helminthindicator

Better concentrationmethods. Viability

Recovery of not more than 70%

Giardia lamblia Direct detection ofcysts

Better concentration anddetection methods. Viability

In wastewater, false positives canbe found in high numbers

Cryptosporidiumparvum

Direct detection ofoocysts

Better concentration anddetection methods. Viability

In wastewater, false positives canbe found in high numbers

Until now, indicator-based standards havebeen used to define a suitable reclaimed waterquality. Nevertheless, it must be stated that thehealth risk related to reuse is defined by severalaspects: the microbial agent, the human host, andthe environment in which the infection process ismediated [5]. As it is the interaction of thesecomponents which produces human disease, riskis dependent on defining the exposed population,the microbial characteristics, and the environ-mental setting in which the exposure occurs. Thehuman health risks associated with the ingestionof waterborne pathogens could be theoreticallyand numerically defined by using statisticalmodels that calculate the probability of individualinfection or disease as a result of a single expo-sure event. These types of calculations [6] couldbe a good tool when fully developed in the future.

It has been suggested in a WHO report [7] thatthe epidemiological method must be employedfor determining health risks associated with reusepractices. Nevertheless, it seems not to be a goodtool, as stated by Cooper and Olivieri [8]. It

appears that traditional epidemiological methodsare not sensitive enough to tease out cases thatmight be associated with recycled water from thebackground incidence of these ailments in thecommunity.

2.2. Chemical parameters

Internationally, there is an increasing require-ment for the inclusion of chemical parameters inguidelines or regulations concerning reuse ofreclaimed wastewater. The main reason is thatchemicals in low concentrations may show nodirect toxic effects but do show long-term chroniceffects or bioaccumulation. Environmental con-cerns are a further important factor because seve-ral organisms show high sensitivity to somechemicals. Several national irrigation regulationscontain physicochemical or chemical parameters,but there is considerable variation among theseguidelines, particularly regarding identifiablevalues and the limited parameters. Recent guide-lines concerning wastewater reuse and irrigation


Table 3Overview of the compiled chemical limits for reclaimed wastewater reuse from existing guidelines and proposed chemicallimits depending on the specific use

Parameter/chemical category Unit 1 2 3 4

Private, urbanand irrigation

Environmentaland aquaculture

Indirectaquiferrecharge

Industrialcooling

pH 6.09.5 6.09.5 79 7.08.5BOD mg /L 1020 1020COD (or TOC) mg /L 100 70100 (1) 70100 70 (1)Dissolved oxygen mg/L >0.5 >3 >8 >3AOX g/L 25UV 254 absorbance cm!1103 3070 3070 10Electrical conductivity S/cm 3000 3000 1400TSS mg/L 10 10 10Active chlorine (only ifchlorination)

mg/L 0.21.0 0.05 0.05

Total Kjeldahl N mg/L 1520 1020 10Ammonium-N mg/L 220 1.5 0.2 1.5

Parameters of medium analytical frequency (monthly, once per year)

Sodium absorption ratio (SAR) mmol/L0.5 5 5Na mg/L 150 150200 200As mg/L 0.10.02 0.10.02 0.005B (total) mg/L 0.41.0 0.41.0 0.2Cd mg/L 0.005 0.005 0.003Cr (total) mg/L 0.10.01 0.10.01 0.025Cr III mg/L 0.1 0.1Cr VI mg/L 0.005 0.005Hg mg/L 0.0010.002 0.0010.002 0.0005Pb mg/L 0.1 0.1 0.005Nitrate mg/L 25F (total) mg/L 1.52.0 1.52.0Chloride mg/L 250 250400 100 400Sulphate mg/L 500 500 100Total P mg/L 25 0.2 0.2Surfactant (total) mg/L 0.5 0.5Mineral oil mg/L 0.05 0.05

Parameters of low analytical frequency (once per yearonce per 5 years)

Al mg/L 15 15Ba mg/L 10 10Be mg/L 0.1 0.1Co mg/L 0.05 0.05Cu mg/L 0.21.0 0.21.0Fe mg/L 2 2Li mg/L 2.5 2.5Mn mg/L 0.2 0.2


Table 3, continued

Parameter/chemical category Unit 1 2 3 4

Private, urbanand irrigation

Environmentaland aquaculture

Indirectaquiferrecharge

Industrialcooling

Mo mg/L 0.01 0.01Ni mg/L 0.2 0.2 0.01Se mg/L 0.010.02 0.010.02Sn mg/L 3 3Th mg/L 0.001 0.001V mg/L 0.1 0.1Zn mg/L 0.52.0 0.52.0CN (total) mg/L 0.10.05 0.10.05Pesticides (total) mg/L 0.05 0.05Pesticides and their metabolites,per subst. (country specific)

mg/L 0.0001

Pentachlorophenol mg/L 0.003 0.003Synthetic complex-forming subst.,per subst. (e.g., EDTA)

mg/L 0.0001 0.0001 0.0001

Chloride solvent (total, if AOX > limits)

mg/L 0.04 0.04

Tetrachloroethylene, trichloro-ethylene

mg/L 0.01 0.01

Disinfection (by)products (only if chlorination)NDMA mg/L 0.0001a 0.0001aTrihalomethane mg/L 0.03 0.03Aldehyde (total) mg/L 0.5 0.5Aromatic organic solvent (total) mg/L 0.01 0.01Benzene mg/L 0.001 0.001PAH (total) mg/LBenzene(a)pyrene mg/L 0.00001 0.00001Phenol (total) mg/L 0.1 0.1Endocrine active substances (E-Screen)

mg/L 0.0001a 0.0001a 0.0001a

Pharmaceuticals (per subst., e.g.,carbamazepine, X-ray contrast)

mg/L 0.0001a 0.0001a 0.0001a

aProposed value.

have been developed in Italy and Israel [911].These are more specific concerning chemicalparameters than former existing regulations inother parts of the world.

There are many physical and chemical para-meters that can be determined in relation towastewater reclamation and reuse: from the

simplest ones (pH, EC) to the most complicatedand expensive (endocrine disruptors) ones asshown in Table 3. Simple parameters such assalinity, E. coli, turbidity, TSS, organic matter,DOC and others, N- and P-related can give usefulinformation depending on the final use of re-claimed water. They can give information about


Table 4Cost calculation and proposed measuring frequency of physicochemical and chemical quality parameters

Parameter Example/indicators Measuringfrequency

Costs Importance forchemical cat.(Table 5)

Physico-chemical

pH, EC, turbidity, TSS, colour Sodium absorption ratio (SAR), UV 254

+++++

Very low 1414

Organic sumparameters

COD (TOC, DOC), BOD, DO, AOX +++++

Lowmedium

1414

Nutrients,minerals

Total-N, NH4+-N, Total-P, NO3!SO42!, CN!, F!, Cl!

+++++

Low Low

1414

Residualchlorine

Cl2 (if chlorination) Disinfection products/by-products (e.g., NDMA)

++++

Low Very high

1, 2, 41, 3

(Heavy)metals

As, Cd, Cr(III,VI), Hg, Pb, B, Al, Ba, Be, Co, Cu,Fe, Li, Mn, Mo, Ni, Se, Sn, Th, V, Zn

+++

Medium Medium

1, 2, 31, 2

Organic micro-pollutants

Surfactants Mineral oilPesticides (e.g., Diuron; 2,4-D) Complex-forming substances (e.g., EDTA) Chloride solvents (if AOX > limit, e.g., TCE)AldehydeAromatic organic solvents (e.g., benzene)PAHs (e.g., benzo(a)pyrene)PhenolsPharmaceuticals (e.g., carbamazepine, x-ray contrast media, sulfamethoxazole), endocrine disruptors (E-Screen)

++++++++++++

MediumMediumHigh HighHighMediumHighHighMediumVery high

1, 21, 213131, 21, 21, 21, 21, 213

Frequency: +++, permanentlyweekly; ++, monthly once per year; +, once per 15 years.Costs per analysis: very high, >200; high, 60200; medium, 2060; low, 620; very low,


Table 5Microbial and chemical water quality categories for different final uses of reclaimed wastewater (adapted from CEDEX,[21])

Microbialcategory

Chemicalcategory [12]

Specific final use

I 1 Residential uses: private garden irrigation, toilet flushing, home air conditioningsystems, car washing.

No categorya Aquifer recharge by direct injection. II 1 Bathing water.III 1 C Urban uses and facilities: irrigation of open access landscape areas (parks, golf

courses, sport fields, etc.). Street-cleaning, fire-fighting, ornamental impoundmentsand decorative fountains.

C Irrigation of greenhouse crops.C Irrigation of raw consumed food crops. Fruit trees sprinkler irrigated.C Unrestricted irrigation.

IV 1 C Irrigation of pasture for milking or meat animals.C Irrigation of industrial crops for canning industry and crops not raw-consumed.C Irrigation of fruit trees except by sprinkling.C Irrigation of industrial crops, nurseries, fodder, cereals and oleaginous seeds.

2 Impoundments, water bodies and streams for recreational use in which the publicscontact with the water is permitted (except bathing).

V 1 Irrigation of forested areas, landscape areas and restricted access areas. Forestry.2 Aquaculture (plant or animal biomass).3 Aquifer recharge by localized percolation through the soil.

VI 2 Surface water quality, impoundments, water bodies and streams for recreational use inwhich the publics contact with the water is not permitted.

VII 4 Industrial cooling, except for the food industry.

aDirect aquifer recharge should be drinking-water quality; potable water should not be produced from reclaimed wastewaterwithout advanced tertiary treatment such as reverse osmosis or percolation through the soil (i.e., indirect aquifer recharge).For microbial categories, see Table 6.

wastewater after conventional treatment pro-cesses [13,14]. Some of these chemicals areknown or suspected of deleterious implications tothe environment, but only part of them is knownto be related with toxicity to humans. There isevidence that endocrine-disrupting chemicalssuch as the synthetic estrogen 17--ethinyl-estradiol, are discharged via treated sewageeffluents and occur in the environment in con-centrations that may detrimentally affect aquaticorganisms [15,16]. In addition, it is known thatseveral persistent organic pollutants includingsome pesticides or polar pharmaceutics may also

enter groundwater by infiltration through the soilpassage, during processes such as bank filtration[17] or even permeate through reverse osmosistreatment.

Until now, only in some cases, organic micro-pollutants are included in the recommendationssuch as total and mineral oils, persistent sub-stances, and pesticides. Especially for recharge ofgroundwater for drinking water purposes and foragricultural use, it is important to take thesepollutants into account. On the other hand, theirdetermination is very expensive and it is difficultto find an indicator for such a huge number of


Table 6Cost calculation of microbiological analysis

Parameter Cost Important for microbial category (Table 5)

Legionella High I, IIIVE. coli and similar Very low IVIIEnterococci (Salmonella) Low IVIINematode eggsTaenia

MediumMedium

IVII V

Giardia and Cryptosporidium High IIII, VIBacteriophage Low IIII, VIEnterovirus High IIII, VIVII

Costs per analysis: Very high, > 200; high, 60200; medium, 2060; low, 620 ; very low,


Table 7Overview of the compiled and estimated microbiological limits for reclaimed wastewater reuse I (bacteria)

Use Total bacteria(cfu/mL)

Faecal coliformsa(cfu/100 mL)

Clostridium perfringens (cfu/mL)

Legionella(cfu/100 mL)

Enterococci(cfu/100 mL)

Salmonella(cfu/mL)

I


reclaimed wastewater reuse were set (Table 3).Important values not mentioned in the guidelineswere estimated, including ecological effect con-centrations described in the literature.

3. Risk assessmentThe main objective of risk assessment is to

identify the risks and to evaluate scientific infor-mation that is available to decide whether ahazard exists and what the magnitude of thathazard may be [23]. The estimates calculated bythe risk assessment method are used as a basis fordeciding on actions to eliminate, reduce or other-wise manage the risk under consideration. In thefuture, health risk management and assessmenttools have to be established for reclaimed waterquality standards. A full version of existing rulesand data on epidemics and microbiologicalquality, and also toxicity registers, needs to beperformed in the near future, based on theevidence obtained in this way. At the same time,health risk data will be useful for reducing thecosts for reclamation and reuse, not using expen-sive treatments where they are not needed andusing them where the risk is higher. There is thena positive impact due to a reduction in sanitarycare derived from a reduced possibility of infec-tions, work-time losses due to illnesses, and animproved quality of life.

Risk assessment can provide a statement ofrisk, but the risk manager still needs to decidewhat constitutes an adequate level of protection.Aside from quantifying the uncertainty impact indetermining the level of protection provided inthe final policy document, another way to use arisk value in setting public policy is to balancecosts of additional regulation (treatment andmonitoring) with the risk of infecting or affectingthe human population, i.e., in a cost-benefitanalysis.

Rather than relying simply on the benefits ofaverting a theoretical illness, a cost-benefitanalysis views societal costs of illness and lost

productivity as providing an economic gain.Meeting the objective of minimizing exposure tothe risk of infection or toxicity may require adelicate balancing act in which microbial riskassessment (or the corresponding for toxicity) isused to weigh the benefits of changing waste-water reclamation policies. It is important torecognize that risk assessment is just one tool thataids the risk manager in establishing realisticwater quality objectives [24].

Regulators are attempting to regulate to lowerrisk levels that are commensurate with lowerpathogen or chemical pollutant concentrations.As one tries to increase removal or inactivation inorder to obtain lower pathogen concentrations orfewer pollutant concentrations, the cost of treat-ment increases exponentially. Ideally, the riskmanager must weigh social costs and benefitsagainst the cost of increased regulation [24].

4. Conclusions

Reclaimed wastewater can be reused for dif-ferent applications. Use-depending water qualitycategories were specified. For each category spe-cific microbial and chemical limits are proposedand the analytical costs are assessed. To reducethe analytical effort, the parameters are gradu-ated, the most important parameters being ana-lyzed more frequently than less importantparameters.

For setting guideline limits for reclaimedwastewater reuse, more microbial and chemicalrisk assessment is required. The microbiologicalparameters usually determined are insufficient orimproper to perform a complete risk analysis.More data are needed for parasitic parameters andviruses. The list of chemical parameters in exist-ing guidelines is either incomplete or excessive;therefore, it is necessary to find adequate indi-cators. This can be performed by quantitativechemical as well as quantitative microbial riskassessment.


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Wastewater Reuse and Risk