A convenient parameter for tracing leachate from sanitary landfills

0043-1354 80,0901-1283S02 000

|~ater Research Vol. 14. pp. 1283 to 128"/ © Pergamon Press Ltd 1980. Printed in Great Britain

A C O N V E N I E N T PARAMETER FOR TRACING LEACHATE F R O M SANITARY LANDFILLS J. E L L I S

Department of Chemistry, University of Wollongong. P.O. Box 1144, Wollongong, N.S.W. 2500, Australia (Received December 1979)

Abstract--Municipal wastes typically have a high proportion of material of vegetable origin. The elevated concentration of potassium in the leachate produced by bacterial and chemical breakdown of this material serves as a relatively conservative tracer which can be measured easily and accurately. It is particularly suited to preliminary investigations requiring determination of direction of movement of leaehate and extent of dilution by receiving waters.

INTRODUCTION

The latter may be affected by shock loadings in leachate strength created by rainfall fluctuations or the transient presence of toxic chemicals. Total organic carbon analysis (TOC) and chemical oxygen demand (COD) determinations have been suggested as an alternative, but the extent of correlation with BOD5 must first be established by experimerit (Pilkington & Swinton, 1974) and the necessary instrumentation for TOC may not be available. Determination of Kjeldahl nitrogen is time consuming both in the sample digestion step and the subsequent distillation and titration of evolved ammonia.

Recognition of the highly polluting effect of sanitary landfill leachate on adjacent surface and groundwaters has prompted a number of recent studies of the average composition of domestic wastes (Bell 1963; Van den Brock & Kirov, 1971) and of the constituents of the leachate itself (Burrows & Rowe, 1975; Johansen & Carlson 1976; Chian, 1977; Chian & De Walle, 1977). From a chemical viewpoint, a sanitary landfill is a chemical and biological reactor utilising a heterogeneous feedstock and is partially isolated from the atmosphere and from the soil by diffusion gradients determined by the permeability of the fill material and of the adjoining strata. There is cornmonly a redox gradient from an aerobic upper layer • to anaerobic conditions further within. Similarly we typically see a rise in temperature with depth until the zone of actively decaying wastes grades into underlying, largely decomposed organic wastes. Recognition of this zonation is important in predicting the concerttration profiles of particular chemical constituents in the leachate with ageing of the fill material, While the principal chemical pollutants borne in leachate are soluble organic material and nitrogenous compounds and manifest themselves in terms of a very high biochemical oxygen demand (BODs) (up to 54,600 mg 1-1; Griffen et al., 1976), the use of this parameter to monitor the direction of movement of leachate and the extent of contamination of ground and surface waters leaves much to be desired. The test is cumbersome and time consuming: the samples must be refrigerated and processed as soon as possible after collection and, depending on the selected incubation time, five days or more must elapse before the analytical result is to hand (APHA, 1971). Precision is relatively poor and the actual value obtained is a function not only of the dissolved nutrients available for metabolism but also of the extent to which the bacteria present and the seed bacteria have been acclimated to the compounds present in the leachate,

When making an initial assessment of leachate movement within and away from a landfill site there is a need to process a large number of samples of groundwater and surface water to establish the direction of flow of the leachate and the rate of attenuation and dilution by receiving waters. Subsequently one may still require frequent and numerous samples to test the efficacy of control procedures under different meteorological conditions. There seems to be an obvious need for a simpler, more easily and accurarely measurable parameter which could be used for these purposes provided it bears a reasonably close proportionality to the customary parameters of BODs and/or Kjeldahl nitrogen.

METHODS Water samples were collected at monthly intervals from each of the three sampling sites (Fig. i) using 1 1. polythene bottles with washers and screw caps and were analysed within 2 h. The BODs and Kjeidahl nitrogen determinations were according to standard methods (APHA, 1971). For determination of sodium and potassium, the water samples were filtered through a 0.45/am membrane filter and, after suitable dilution with triple distilled water, were analysed by atomic absorption spectroscopy using a Varian Techtron AA6 instrument. The operating wavelengths used were 589.0 nm and 766.5 nm for sodium and potassium respectively.

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DISCUSSION

Various studies on the composition of domestic refuse have established that wide variations exist in the relative proportions of the major constituents: paper; vegetable material; animal wastes; ferrous and other metals; glass; ashes (Bell, 1963; Van den Brock & Kirov, 1971). These variations arise from seasonal and cultural factors. However, in all cases there is a large input of vegetable material and its processed derivative, paper. Furthermore, a previous study on incinerator gas scrubber effluent has shown that virtually all the inorganic ions pre~nt in the effluent are derived from the combustible fraction of the refuse (Law & Gordon, 1979). Possible cations which could be used as tracers for monitoring purposes are Ca, Mg. Na, K, and the heavy metals. Possible anions are phosphate, nitrate, chloride and sulphate. To be suitable as a tracer, an ion should: (a) Be present in much higher concentration in the leachate than in the receiving waters. (b) Have a concentration proportional to the BODs and Kjeidahl nitrogen content of the effluent, (c) Not be rapidly removed by adsorption or ion exchange, (d) Not tend to be precipitated by changes in pH or by reaction with anions or cations in the groundwater or surface water, (e) Not require special precautions in sample storage. (f) Be easily determinable with simple apparatus and minimum labour, Of the above ions, sodium and potassium appeared most likely to meet criteria (c)--(I). These cations do not readily give insoluble compounds or tend to adsorb on the walls of the sampling container and are very easily analysed by atomic absorption or by flame enamission spectroscopy using a simple flame photometer. Like any simple cation, they can undergo ion

exchange with clay minerals, but a laboratory study (Griffin et al,, 1976) has shown that they are attenuated to a moderate degree and their relative affinities for clays are very similar (Grim, 1968) with potassium being preferentially adsorbed. As a result, the persistence of an identifiable enhanced concentration of potassium in a leachate filtering through clay sedJ. ments would depend on the cation exchange capacity of the clay, the distance the leachate has travelled through it and the background K/Na ratio for the groundwater in the area. With these considerations in mind, a study was made of Na and K concentrations at the Russell Vale Waste Disposal Depot. The dominant clay there is kaolinite, which has a much lower cation exchange capacity (1-10 m-equiv 100 g - i) than illite (10-40 mequiv 100 g- ~) or montmorillonite (80--120m-equiv 100 g- ~) (Grim, 1968). Moreover, the unpolluted groundwater had been shown previously to have a potassium concentration of only 1.5-2.4 nag I i (Ellis & Chowdhury, 1976), with sodium concentrations of 67-212 mg 1 l The Russell Vale Waste Disposal Depot is one of two sanitary landfills serving the City of Wollongong (population c. 200,000) on the coast of New South Wales. The site is characterised by low variations in seasonal composition of refuse and is not subject to below freezing ambient temperatures (average maximum and minimum temperatures for February are 26.9 and 17.6 and for July 16.5 and 8.4°; yearly rainfall is 1200 mm distributed throughout the year). It was formerly a quarry providing clay and shale for brickmaking and the material used to cover the fill consists of carbonaceous shale obtained from an adjoining colliery. The site (Fig. 1) is situated 1.8 km from the sea and 1 km from a watershed formed by a 300 m escarpment to the west. It has an area of 20 ha and on the western side is protected from gross infittration of surface water by a catch drain. The creek is isolated from the fill by a box culvert which traverses the site from west to east. To date, refuse has been emplaced mainly on the southern section and the teachate runs essentially in a northerly direction towards the ouffall of the box culvert. Initially, a number of samples were gathered from surface water and groundwater above, within and downstream of the site to establish the direction of water movement (Ellis & Chowdhury, 1976). Thereafter, monthly samples were taken from three sampling points (Fig. 1): (A) A creek upstream of the site (to provide background variations). (B) Leachate flowing from the boundary of the filled area. (C) The same creek as (A) but at the boundary of the site and just beyond the point of discharge of leachate, Samples were analysed for Na, K. BODs and Kjeldahl nitrogen The data are summarised in Table L

A convenient parameter for tracing leachate

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Site A: Na 103-1090; K 1.0-18.8 Site B: Na 375-735; K 28-159 Site C: Na 265-580; K 28-148 The large range of variation of I N n +] and [K +] at site A arises from the very variable flow of water in this creek (which at times becomes a series of stagnant pools) coupled with variations in salt deposition from wind-borne sea spray• The ratio of mean [ K + ] / m e a n I N n ÷] at this site (1.8 x 10 -3) is lower than the relative abundance of these two ions in seawater (3.6 x 10-3), presumably due to selective uptake of potassium by plants and adsorption on clay minerals. At sites B and C the mean concentrations of both Na ÷ and K + have increased, but by far the largest percentage increase is for [K +] (by a factor of 22 at site B). This is attributed to potassium released by the bacterial and chemical breakdown of paper and other vegetable material within the filled area. The concentrations of inorganic ions in plant tissues vary with plant type and even within individual plants, being differentiated with respect to plant organs, tissue age within a given organ and the degree of development of the plant. The rate of uptake and the final concentration of each is also a function of soil type, ratio of ions and various meteorological factors (Doby, 1965). However, potassium is an essential element for plant growth and is taken up selectively by plants even in the presenceof a large excess of sodium (Sutcliffe & Baker, 1976). In contrast, animal tissues are much less rich in potassium and usually contain more sodium. Plants have a very high capacity to accumulate potassium in fertilised soils. Physiologically, potassium functions in two major ways: (a) It forms loose associations with proteins and is an activator of pyruvate kinase and many other enzymes. (b) It is an osmotic regulator in association with organic acid anions (but is not normally replaceable by sodium). Potassium is preferentially accumulated in the large vacuoles which are a prominent feature of many plant cells and would be released upon rupture of the cell walls by the decay processes occurring with the deposited fill. The relationships between [K+], [Na +] and BODs, Kjeldahl nitrogen in the leachate were explored by linear regression analysis of the pairs [K +], BOD~; [Na+'l, BODs; [K+], Kjeldahl nitrogen; I N n + l , Kjeldahl nitrogen for each of the three sampling sites. The respective correlation coefficients, y intercept and slope are listed in Table 2. In general BODs was poorly correlated with ['Na + ] or [K+]. In part this may reflect the poorer analytical precision for this parameter. The I N n +] correlated fairly well' with Kjeldahl nitrogen at both site A and site B.

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J ELLIS Table 2. Regression analysis of K, Na, BODs, Kjeldahl nitrogen Sampling Site

Site A

Site B

Site C

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0226 0.228 -0.008 0.008

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0.193 0.856 -0.488 0.634

0.044 0.601 -0.056 0.222

17.1 31.5 50.4 12.0

K K Na Na

BOD~ KjN BOD5 KiN

0.614 0.408 0.110 -0.106

0.209 0.206 0.013 -0.019

- 3.0 49.4 13.0 81.5

However, the strongest correlation was between [K ÷] and Kjeldahl nitrogen at site B (r = 0.856). In every case the [K +] and Kjeldahl nitrogen at site B were much greater than the corresponding concentrations at site A whereas the [Na +] at site B was sometimes less than that at site A. CONCLUSIONS At Russell Vale, enhancement of I-K +] is a clear indicator of leachate pollution and, given the high proportion of paper and vegetable material normally present in domestic refuse worldwide, it could serve as a simple parameter for probing the direction of movement of leachate in groundwater and the efficacy of leachate reduction measures. The ratio of I'K +] in receiving waters downstream of a landfill to the [K +] upstream provides a direct estimate of the relative contributions of leachate and unpolluted water to the aggregate flow downstream. In the case of Russell Vale, it is clear that during very dry weather, the stream flow below the landfill site is derived mainly from leachate. Sampling of the creek at 200 m intervals showed noticeable enhanced [K ÷] as far as I km downstream at the confluence of this creek with another creek, An obvious circumstance in which the [K ÷] could not serve an an indicator would be when the receiving waters have a high inherent K - concentration, but this is expected to be a rare case (Livingstone, 1963). Because of the slight preferential absorption of K ÷ by clays compared with Na ÷, gradual attenuation of the I'K ÷] would be expected upon extended passage of the leachate through clay strata. Calcareous and other soil types would be expected to have much less effect. The cover material had been shown previously not to be a source of K + enrichment when rainwater or creek water was passed through it (Holland, 1977). The location of potassium within the plant material suggests that, for a given batch of refuse, the [K +] might tend to reach a maximum corresponding to cell wall rupture and then rapidly decline whereas the soluble organic materials derived from breakdown of the

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cell walls might persist much longer and be liberated even from aged fill. In such a circumstance the correlation of [K ÷] with BODs would be vitiated by the low absolute concentrations of both potassium and sodium in the leachate. However, sanitary landfills are normally receiving a regular daily increment of refuse which would compensate for any ageing effect, although the location of the fresh decomposing material with respect to the sampling grid would vary over time. This difficulty would apply to any chosen parameter. Because the potassium is derived mainly from plant material, the [K +] could not be used as a monitoring probe for landfills receiving mainly industrial wastes. The local hydrological/hydrogeochemical environment must be considered when using K + as a tracer and care should be taken to check for its possible entry by contact with concrete, agricultural fertilisers etc. in addition to its derivation from ieachate. In some cases it may be desirable to use potassium concentrations in conjunction with other easily measurable parameters. REFERENCES American Public Health Association (1971) Standard Methods for the Examination of Water and Wastewater,

13tb Edition. APHA, Wa.~hingmn. Bell J. M. (1963) Development of a method for sampling and analysing refuse. Ph.D. Thesis, Purdue University. BurrowsW. D. & Rowe R. S. (1975) Ether soluble constituents of landfill leachate. J. War. Pollut. Control Fed. 47, 921-923. Chian E. S. K. (1977) Stability of organic matter in landfill leachates.Water Res. 11,225-232. Chian S. K. & De Walle F. B. (1977) Characterisation oi" soluble organic matter in leachate. Envir. Sci. Technol. 11, 158-163. Doby G. (1965) Plant Biochemistry, p. 40. lnterscience. New York. Ellis J. & C'howdhury R. N. (1976) An investigation of leachate formation at the Russell Vale Waste Disposal D e p o t . University of Wollongong Research Bulletin No. 38. Griffin R. A., Shimp N. F., Steele J. D., Ruch R. R., White W. A. & Hughes G. M. (1976) Attenuation of pollutants in municipal landfill leachate by passage through clay Envir. Sci. Technol. 10. 1262-1268.

A convenient parameter for tracing leachate Grim R. E. (1968) Clay Mineralooy, pp. 213-221. McGrawHill, New York. Holland A. M. (1977) Flocculation of argillaceous slurries. Ph.D. Thesis, University of Woliongong. Johansen O. J. & Carlson D. A. (1976) Characterisation of sanitary landfill leachates. Water Res. 10, 1129-1134. Law S. L. & Gordon G. E. (1979) Sources of metals in municipal incinerator emissions. Envir. Sci. Technol. 13, 434-437.

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Livingstone D. A. (19631 Chemical composition of rivers and lakes. U.S. Geol. Survey Paper 440G. Pilkington N. H. & Swinton E. A. (1974) Application of total organic carbon measurements and correlations with oxygen demand, parameters. Water 1, 19-21. Sutcliffe J. F. & Baker D. A. (1976) Plants and Mineral Salts, p. 7. Edward Arnold, London. Van den Broek E. & Kirov. N.Y. (1971) The characterisation of municipal solid wastes. Proc. 1971 Australian Waste Disposal Conf., Sydney, pp. 23-29.