Xenobiotic Organic Compounds in Grey Wastewater

XENOBIOTIC ORGANIC COMPOUNDS IN GREY WASTEWATER:

A MATTER OF CONCERN?

E. Eriksson*, M. Henze and A. Ledin

Environment & Resources DTU, (Formerly Department of Environmental Science and Engineering,) Technical University of Denmark, Bygningstorvet, Building 115, DK-2800 Lyngby, Denmark. E-mail: , ,

*Corresponding author

ABSTRACT

A crucial point with respect to alternative handling of grey wastewater is the risk related to the presence of different types of pollutants including xenobiotic organic compounds (XOC’s). Low and variable efficiency in the treatment could be the result when biological methods are used in the treatment steps before reuse for e.g. toilet flushing. Contamination of soil and receiving waters will be of importance when grey wastewater is either used for irrigation or infiltrated. It is necessary to know which compounds and concentration ranges that are common in order to be able to evaluate the risk related to alternative handling of grey wastewater. In this work, grey wastewater from bathrooms was analysed with respect to XOCs, both qualitatively and quantitatively. The qualitative analyses positively identified 180 different XOC’s where the dominating compounds were long chained fatty acids and esters. The quantitative analyses included 99 different compounds and summary parameters. Among them were e.g. anionic detergents (up to 125 µg/l), cationic detergents (up to 2100 µg/l), di-(ethylhexyl)-phthalate (up 39 µg/l) and 2,4- and 2,5-dichlorphenol (up to 0.13 µg/l). A number of the compounds identified may present a risk to the environment if the wastewater is infiltrated or irrigated without any previous treatment or to the active micro-organism population in a biological filter that usually are used for treatment of grey wastewater before reuse.

KEYWORDS

Grey wastewater; greywater; alternative handling; reuse; xenobiotic organic compounds

INTRODUCTION

There is a growing demand in the society for introducing integrated decentralised sanitary systems providing opportunities to save and reuse wastewater. The awareness that the centralised urban sanitation systems used for treatment of wastewater today may well be very effective, but may also be expensive and resource consuming, is probably the main reason behind this interest. Another reason to look for alternative handling of wastewater is the water shortage, which is a problem in several parts of the world. One way to reduce the need for freshwater is to reuse wastewater, after some decentralised, low or high tech treatment or without any treatment at all depending on the sources and the reuse applications.

There is a focus today on the possibility for reusing the grey wastewater. The term refers to wastewater produced in households, office buildings, hotels, schools as well as some types of industries, where there is no contribution from toilets or heavily polluted process water. This means that grey wastewater corresponds to wastewater produced from bath tubs, showers, hand basins, washing machines, commercial laundries and dish washers, as well as kitchen sinks. This fraction of wastewater has been estimated to account for roughly 75 volume-% of the combined residential sewage (Hansen and Kjellerup, 1994 and references therein).

One possibility for recycling of grey wastewater is to use it for urinal and toilet flushing. It has been estimated that 32 % of the total household water consumption could be saved by reusing grey wastewater for flushing toilets (Karpiscak et al, 1990). Vehicle and window washing, fire protection and concrete production are examples of other suggested usages. Outdoor reuse like infiltration into the ground and thereby making a shortcut in the hydrological cycle is an obvious alternative. The grey wastewater could also be used for garden irrigation and in agriculture, and to develop and preserve wetlands.

The major problem related to all the suggested alternatives for reuse of grey wastewater is the different types of risks related to handling and exposure (humans, animals, crops and ornament plants) to grey wastewater. The risk for spreading of diseases, due to exposure to micro-organisms in the water will be a crucial point for almost all alternatives suggested above and has been given attention in published literature as well as in the regulations from authorities (see e.g. Christova-Boal et al, 1996; Feachem et al, 1983). However, contamination of soil and receiving waters (primary groundwater) as well as growing crops, due to the content of different types of pollutants including XOC’s is another risk, that has not yet been deeply discussed. This could e.g. lead to a deteriorating quality of the groundwater. Reuse of grey wastewater for e.g. toilet flushing will require some treatment. Usually decentralised, low-tech solutions are selected, like biological filters. However, there is an obvious risk for low and variable efficiency of these filters due to the presence of toxic XOCs, that will negatively affect the active micro-organism population in the filters. Other risks not yet discussed are the possible development of resistant bacteria due to the continuous exposure to preservatives that originates from the household chemicals.

In general terms, grey wastewater has lower concentrations of organic matter (measured as the summary parameters BOD and COD), some of the nutrients (N and K) and micro-organisms compared to traditional municipal wastewater (Ledin et al., 2001). The concentration of phosphorus varies in a relatively broad range depending on the contribution from washing detergents, which is the primary source for P in grey wastewater. The variations are a function of the product used as well as the laws and regulations in the country. The concentrations of heavy metals have been reported to be relatively low according to data compiled by Ledin et al. (2001). No information with respect to the quantities of xenobiotic organic compounds (XOC’s) has been found in the literature. However, two studies, reporting on the presence of XOC’s in grey wastewater was found (Ledin et al., 2001). Santala et al. (1998) used a screening method with GC-MS and showed that the major part of the organic compound consisted of detergents and their amount corresponded to 60% of the measured COD. The other study, also describing the results from a GC-MS screening of shower wastewater, revealed that the even-numbered long chain fatty acids of C10 to C18 originating from soap were present (Burrows et al., 1991).

These very limited results concerning the presence of XOC’s in grey wastewater are not representative for the number of XOC’s that could potentially be present. There were 18 million synthetic substances known by science in 1998 (Platt McGinn, 2000) and it has been estimated that some 20 000 substances are circulating in the Swedish technosphere (Kemikalieutredningen, 2000). In municipal wastewater have at least 500 different compounds been identified and quantified (Eriksson et al., 2001) and some these compounds could be expected to be present in grey wastewater as well, since the main sources for the XOC’s are different types of chemical products, such as laundry detergents, soaps, shampoos, toothpaste’s and perfumes. It has been found from the information available in the declaration of contents present on common household products that at least 900 different substances or groups of substances could be present in grey wastewater (Table 1). The major compounds were fragrances and flavours. Other large groups were preservatives, solvents and surfactants used in detergents, dishwashing liquids and products for personal hygiene i.e. non-ionic, anionic and amphoteric surfactants.

Table 1. Groups of compounds found in common household chemicals in Denmark and Sweden (from Eriksson et al., 2001).

211 of these approximately 900 different substances were selected to assess an environmental risk assessment. This selection was based on the information possible to compile with respect to fate (e.g. toxicity, bioaccumulation, biodegradation and mobility) in the environment. Out of these identified to be potentially present in household chemicals. Out of them 66 were categorised as priority pollutants. Among these were different types of surfactants (anionic, nonionic, cationic and amphoteric), preservatives and softeners.

The objective for the present study was to evaluate the risk related to alternative handling of grey wastewater with respect to the presence of XOCs. In order to be able to do that, it is necessary to have a good characterisation of grey wastewater with respect to this very heterogeneous group of compounds and that is why the major focus has been on analyses for XOCs in grey wastewater form bathrooms.

MATERIAL AND METHODS

Sampling

Grey wastewater samples were taken in Bo90, a tenant owner’s society located in the central part of Copenhagen, Denmark. The building has 17 apartments, where 38 inhabitants are living; 22 adults (age 18-74) and 16 children (age 2-15). The grey wastewater produced originates from the showers and hand basins in the building, where the daily production is approximately 750 L. All samples were taken at the inlet to a grey wastewater treatment facility that has been installed in order to treat the wastewater on-site and reuse it for toilet flushing. The samples were taken in glass bottles and transported cold and in the dark to the laboratory, where the analyses started immediately.

Analyses

The grey wastewater was analysed with respect to; i) screening analyses with purpose to identify the XOCs present and ii) quantitative analyses for a selected number of XOCs.

The analyses in the first part included solid phase extraction with four different solid phases. The neutral polar organic compounds were extracted and pre-concentrated on C18 (IST Isolute) and HLB (Waters Oasis) and were sequentially eluted with hexane, hexane:diethyl ether (1:1), diethyl ether, methanol:water (1:1), methanol:water (8:2) and methanol according to the procedure described by Paxéus and Schröder (1996). SCX (IST Isolute) columns were used for extraction and pre-concentration of bases and the compounds were sequentially eluted with acetonitrile and methanolic ammonia. All extracts were reduced to a volume of 200 µL by a stream of pure nitrogen gas or by rotary evaporation. The organic acids were extracted and pre-concentrated on Empore anion exchange discs (Chrompack) and in-vial-derivatised with methyliodide (Eriksson and Ledin, 2001). A Hewlett-Packard 6890 Series chromatograph and a HP 5973 MS detector were used for the GC analysis, while the injections were performed with a Varian 8200 CX Autosampler. Tentative identification of the organic compounds were obtained from searching in the NIST MS-library (Version 1.1a) and the library NBS75K in the Enhanced ChemStation G1701AA. The compounds were considered positively identified if their spectra and retention time correlated with that of an external standard or if the spectra corresponded with the spectra’s from the two libraries.

Quantitative analyses were performed, in the second part of the study, either in our laboratory according to the methods give above, after calibration of the GC-MS signals with known concentrations of standards or by a commercial laboratory according to their standard methods. The analyses included 99 different compounds and summary parameters. Furthermore, semi quantitative results were obtained from the qualitative analyses by comparison between the chromatographic area of the selected compounds and the chromatographic area of the internal standard with a known concentration.

General hydrochemical characterisation (pH, temperature, alkalinity, electrical conductivity, oxygen content, BOD, COD, tot-N, and tot-P) was also included in the sampling protocol.

RESULTS AND DISCUSSION

Qualitative analyses

180 different XOCs were positive identified in the grey wastewater from the qualitative analyses. The dominating compounds were the long chained fatty acids (C10-C24) and their esters e.g. methyl-, butyl-, hexadecyl- and octadecyl-esters. Other important groups of compounds were the fragrances and flavourings e.g. Eucalyptol, Eugenol, Coumarin, Menthol and Hexyl cinnamic aldehyde, where in total more than 40 fragrances and flavours were identified (Table 2). It can also be noted that several miscellaneous compounds, which not directly were deriving from the household chemicals have been identified e.g. medicinal residuals, flame-retardants as well as the drugs nicotine and caffeine. Notably was also the insecticide Malathion, which was found in a number of samples.

The presence of medicine residuals and drugs can be explained by excretion from humans during showering, tooth brushing and washing (present on the skin or in the mouth or urination (during showering)). Flame-retardants could be originating from clothes and therefore also be present on the skin, while Malathion is used as the active ingredient in a louse shampoo and can be purchased at the Danish pharmacies. It was later confirmed that the tenants had used this type of shampoo during the sampling period.

Table 2. Groups of compounds found by screening in grey wastewater from Bo90.

The group “Preservatives” consists of six preservatives and two antioxidants. The antioxidants found were butylated hydroxytoluene (BHT) and Ethyl antioxidant 762. Among the observed preservatives were e.g. citric acid and phenoxy acetic acid as well as Triclosan. The latter is mainly used as antibacterial agent in toothpaste. A semi quantification indicated an average concentration of 0.6 µg triclosan/L. The emulsifiers identified were long chained fatty esters, alcohols and amines e.g. hexa- and octadecanol and N,N-dimethyl-1-dodecaneamine.

The three plasticizers; di-(ethylhexyl) phthalate (DEPH), di-(ethylhexyl) adipate (ester of hexanedioic acid) and di-(ethylhexyl) sebacate (ester of decanedioic acid) were positively identified as well as one UV-filter/sun screen agent, Parasol MOX.

Quantitative analyses

Quantitative analyses for the fatty acids (C8 to C18) showed that the dominating acids were lauric acid (C12), oleic acid (C18:1) and stearic acid (C18:0) (Table 3). It was also shown that some of the chlorophenols, which are preservatives and pesticides were present, as well as four phthalates.

Relatively small amounts of the BTEX’s were measured in the inflow to the treatment plant (Table 3). They are e.g. used as solvents for organic fragrances and dyes in the otherwise water based chemicals.

Table 3. Concentration ranges (µg/L) for some XOC’s quantified in the grey wastewater.

Benzene

Toluene

Nonylphenol

Anionic detergents

N.D. = not detected

sqa. = semi quantitative analyses

The anionic detergent LAS were found in the concentration range from <25 to 125 µg/L in the grey wastewater (Table 3). Corresponding values for the cationic detergents were <100 to 2100 µg/L. In this case will the cationic detergents mainly derive from hair conditioners and not from fabric softeners, since the laundry wastewater were not included. The content of the nonionic detergents included were below the detection limits for the applied methods.

A majority of the compounds found by quantitatively and qualitatively analyses were also found to be on the list of possible present compounds deriving from household chemicals (Eriksson et al., 2001). Among these were the long chained fatty alcohols and acids, as well as the long chained fatty esters. Several fragrances as citronellol, coumarin, eugenol, farnesol, geraniol, isoeugenol and hexyl cinnamic aldehyde and some preservatives e.g. citric acid, salicylic acid and triclosan were identified in the grey wastewater as well as present on the list over potential compounds. Other examples are the phthalates e.g. dibutyl and dimethyl phthalate and methyl phenol.

The major differences were that the grey wastewater also contained a number of chemicals not deriving from household chemicals e.g. medicinal residuals as well as degradation products mainly caused by hydrolyzation of some XOCs.

CONCLUSIONS

Almost two hundred different XOCs were identified in grey wastewater from bathrooms in a building with apartments (i.e. grey wastewater originating from showers and hand basins). A majority of these compounds were among those compounds that earlier had been proposed as potentially present compounds e.g. the long chained fatty alcohols and acids, e.g. hexa- and octadecanol and octadecenoic acid as well as the long chained fatty esters e.g. isopropyl myristate. Several fragrances like citronellol, coumarin, eugenol, farnesol, geraniol, isoeugenol and hexyl cinnamic aldehyde were identified as well as some preservatives e.g. citric acid, salicylic acid and triclosan. Other examples are the phthalates e.g. dibutyl and dimethyl phthalate and methyl phenol. The measurements also showed that unwanted and unexpected compounds like biocides and insecticides could be present as well as chemicals not directly deriving from household chemicals e.g. flame retardants and medicine residuals.

Among the XOCs found in the grey wastewater were several characterised as high priority compounds i.e. with high environmental impact. Among those compounds were e.g. fragrances like hexyl cinnamic aldehyde. This means that the presence of XOCs in grey wastewater may constitute a risk to the environment if the water is infiltrated or irrigated without any previous treatment. However, the information about toxicity, bioaccumulation and biodegradation for these compounds is limited and the number of compounds classified as priority compounds may drastically increase if more information will become available. Furthermore the number of XOCs could also be expected to increase if other analytical methods are applied in the work for characterisation of grey wastewater.

REFERENCES

Burrows, W.D., Schmidt, M.O., Carnevale, R.M., and Schaub, S.A. (1991) Nonpotable reuse: Development of health criteria and technologies for shower water recycle.Wat. Sci. Tech. 24 (9) 81-88.

Christova-Boal, D., Eden, R.E., and McFarlane, S. (1996) An investigation into greywater reuse for urban residential properties. Desalination 106: 391-397.

Eriksson, E. and Ledin, A. (2001) Analyses of organic acids by solid phase extraction in combination with in-vial-derivatisation and elution. (Manuscript in preparation).