The efficacy of gravel bed hydroponic system in the removal of DDT residues from sewage effluent

ELSEVIER Resources, Conservation and Recycling 14 (1995) 47-52

resources, conservation and recycUng

The efficacy of gravel bed hydroponic system in the removal of DDT residues from sewage effluent

Ahmed Dewedar a, Mohamed Twafic Ahmed b.,, M.M.M. Bahgat a a Department of Botany, Suez Canal University, Ismailia, Egypt

b Department of Plant Protection, Suez Canal University, lsmailia, Egypt

Received 7 March 1991; revised 22 July 1994; accepted 3 January 1995

Abstract

A high performance liquid chromatography method was employed to monitor DDT and some of its metabolites in sewage effluent which had undergone primary treatment. A gravel bed hydroponic (GBH) system was designed to treat the effluent in order to reuse it in agricultural purposes. The system was made of six channels covered with common reeds (Phragmitis australis). High concentrations of DDT-type residues were detected in the effluent. Results indicated the ability of GBH system to remove more than 80% effluent-borne DDT residues.

Keywords: Gravel bed hydroponic system; Sewage effluent; DDT; Phragmitis australis

1. Introduction

The persistence of chlorinated hydrocarbon pesticides and their impact on the environment has provoked considerable concern.

In Egypt, the use of these compounds in agriculture was discontinued in the early 1970s. However, their residues are still persistent in the environment [ 1-3 ]. Contamination of water bodies is particularly crucial because of the importance of water to all forms of life, and because water bodies are the end point of many of the organo chlorine pollutants [4]. Since water, rather than land, is the main constraint to agricultural development in Egypt [5], reuse of waste water is a sound alternative that aligns well with the concept of sustainable agricultural development currently promoted in Egypt. Nevertheless, the presence of such insidious pollutants would limit the reuse of such enormous volumes of waste water.

* Corresponding author.

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48 A. Dewedar et al. / Resources, Conservation and Recycling 14 (1995) 47-52

Many authors have reported different methods of removing organic pollutants from water. Bishop et al. [6] and Rebeck et al. [7] have reported some methods based on settling and coagulation followed by filtration of water. Other methods were based on the use of ozone/ potassium and ozone/UV to eliminate organo chlorine pesticides [ 8 ]. However, the toxicity of the unknown by products of ozone was always a limiting factor [9].

In the present study, a gravel bed hydroponic (GBH) system was employed to remove organo chlorine residues from sewage effluent. The GBH system is an artificial wet land consisting of gravel filled channels lined with an impermeable membrane, through which sewage effluent flows. Channels are planted with common reeds, Phragmitis australis. Treatment is affected by aerobic micro organisms which colonise the gravel and plant root surfaces, and their activity results in conversion of complex organic substances to inorganic substances with a lower oxygen demand. The reeds assist this process by conducting oxygen to the sites of microbial activity [ 10].

Residues of DDT ( 1,1,1-tdchloro-2,2-bis (p-chlorophenyl) ethane), and its major metabolites, DDD ( 1,1,1-dichloro-2,2 bis (p-chiorophenyl)ethane) and DDE (dichloro diphenyl dichloroethane) were monitored in sewage effluent just before flowing through a GBH unit and again at its end. The efficacy of GBH system in removing DDT-type residues was ascertained.

2. Materials and methods

Sewage collected at Abo Attwa treatment plant, Ismailia, Egypt was subjected to primary treatment. Part of the treated effluent ( 150 m 3) was directed to a concrete tank ( 18 × 3 m) and the outlet was equally distributed into the channels of the GBH system. The system consisted of six channels, the first two were 2.4 m wide, 50 m long and 0.6 m deep, and the other four channels were 2.4 m wide, 100 m long and 0.3 m deep. Channels 1 and 6 were filled with lime stone, while channel 5 was filled with basalt. Channels 2, 3 and 4 were filled with gravel. All channels were planted with common reeds (Phragmitis australis), except channel 4 which was planted with napier grass (Pennisetum purpureums) (Fig. 1).

Full plant coverage was attained in channels 3, 4, 5 and 6, while in channels 1 and 2 plant growth covered only 30% and 75% of each channel area, respectively. The edges of each channel were also lined with an impermeable geomemberane. Water flow rate was 20 1/ min for all channels. Sewage effluent was allowed to flow for 16 h per day.

2.1. Apparatus

Liquid chromatography A Beckman high performance liquid chromatograph (model 432), equipped with two

pumps (model 112), solvent programmer (model 340), injector (model 210) and fixed wave length UV detector (model 160) was used in this study.

Column An Ultrasphere C~s (ODS) analytical column (25 cm×4.6 mm i.d.) preceded by a

stainless steel pre column (4.5 cm × 4.6 mm i.d.) was used for reserved phase chromatography.

A. Dewedar et al. /Resources, Conservation and Recycling 14 (1995) 47-52 49

NOTES ON THE CROP BEDS:- TO W A ~ _ _ ~

(i) Beds 1 ans 2 planted with Napier G r a s s l i

harvested at least six times a year. ]

(ii) Bed 4 t planted. ..... / I,- (iii) Beds 3, 4 and 5 planted with

a pattern of the following crops:

Summer-sorghum sunflower, cotton, maize

Winter-sugar beet, safflower, broadbean, o Z

fodder beet.

(iv) Each bed was 2m wide, bed depth 150mm. ~ r~ "

PAIMARY SEWAGE INTO TEE FLOW DISTRIBUTION CHAMBER Im WIDE, im DEEP.

i

am q-Om

CROP

BEDS

i00 nan GRAVEL REJECTS

GRADIENT DOWN EACH BED

0-3m

50m BED 1:201

[00m BED

(i) Beds I, 2, 3, 5 and 6 are planted with

Phragmites australis at 500mm spacings. (ii) Bed 4 is planted with Napier Grass

3m-- 13m 13m-23m REMAINDER at 500mm s~acing 9

1:40. 1:50 1:50 iiii) Sampling points at 0.5m, 10m, 20m 40m, 80m and 100m down each bed

1:20 1:40 1:60 i:i00 (iv) Each bed was 2m wide.

Fig. 1. Details of the reed and crop beds at Abu Attwa, Ismailia, Egypt.

Thin layer chromatography High performance thin layer chromatography was performed on silica gel 60 f 254 pre

coated aluminum plates (Merck, Darmstadt) as a confirmatory test. Plates were developed in n-hexane + benzene (9:1, v /v) . DDT and its metabolites were detected by viewing under UV light.

2.2. Reagents

The solvents -methyl alcohol and n-hexane-were HPLC grade (Merck). Anhydrous sodium sulfate was of granular-reagent grade. Pesticides reference standard p,p-DDT, o,p- DDT, p,p-DDD and p,p-DDE were kindly supplied from the Central Laboratory of Pesti-


cides, Ministry of Agriculture, Dokki. They were originally provided by the National Food Administration, Food Research Department, Uppsala, Sweden.

2.3. Extraction and sample preparation

Sewage effluent was collected from the main outlet of the concrete tank before being treated through the GBH system and again at the end of each channel. Five samples ( 1 liter) each were collected in pre-washed glass containers with ground-glass stopper and stored at 4°C until analyzed.

Each liter was extracted with two portions ( 150 ml) each of n-hexane in a 2-1 separatory funnel. The mixture was shaken vigorously for 3 min before phases were allowed to separate. Solvent extracts were combined and filtered through a bed of anhydrous sodium sulfate. Samples were evaporated to near dryness at room temperature, and residues were quanti- tatively transferred in methyl alcohol ready for analysis.

2.4. Operation conditions and determination

An isocratic operational conditions were set according to the method reported by Ahmed [2]. p,p-DDT, o,p-DDT, o,p-DDD and p,p-DDE were detected and quantitated by moni- toring the UV absorbance of the column elutes at 254 nm. Peak areas were measured by a Spectra Physics ( SP 4100) computing integrator. Sample injections were interspersed with injections of standard solution.

2.5. Extraction efficiency

Known concentrations of p,p-DDT, o,p-DDD and p,p-DDE dissolved in n-hexane were added to 11 of distilled water previously partitioned with hexane. Extraction was conducted as described earlier and the average recoveries recorded were 92%, 93% 95% and 88% for p,p-DDT, o,p-DDT, p,p-DDD and p,p-DDE, respectively. Results were not corrected according to recovery rates.

3. Result and discussion

Residues of DDT and its major metabolites detected in sewage effluent before the GBH treatment and again at the end of the system are shown in Table 1.

Results indicated high concentration level of DDT and its metabolites in the sewage effluent. Edwards [ 11 ] concluded that sewage effluent would tend to be heavily contami- nated with persistent pesticides probably as a result of the high level of the organic matter in sewage. More over, Saleh et al. [ 12] suggested that because of the low solubility of DDT, its occurrence is associated with particulate and colloidal content of waste water. Hence, high levels of DDT-type residues detected in the sewage effluent is likely to have resulted from high levels of organic material in sewage. It is also likely that such high levels of DDT in sewage effluent has resulted from some bio accumulation processes [ 13 ].

A. Dewedar et al. / Resources, Conservation and Recycling 14 (1995) 47-52

Table 1 Residues of DDT and its metabolites detected in sewage effluent and at the end of each channel and frequency of detection

51

Compound Frequency Main Channel

reservoir

1 2 3 4 5 6

p,p-DDT 32 2.64+1.09 0.57+0.164 0.57+0.248 0.36+0.192 0.29+0~306 0.56+0.213 0.40±0.29

o,p-DDT 30 1.885:0.99 0.44+0.309 0.28+0.272 0.755:0.260 0.62+0.472 0.415:0.33 0.51+0.21

p,p-DDD 21"* 2.98+1.22 0.11±0.310 0.345:0.401 0.174-I-0.19 0.31+0,35 0.1685:0.31 0.1845:0.27

p,pDDE 33 3.98±1.103 3.13±3.24 2.455:3.7 0.63+0.232 0.518±0.20 0.59±0.212 0.608:~0.12

Cuncentration//Lg 1 - 1 + SD.

*" Statistically different at P < 0.5.

Results (Table 1) subjected to one-way analysis of variance (Statgraph, version 5) revealed that all channels have significantly reduced the concentration of DDT and its metabolites, with the exception of channels 1 and 2 where residues of p,p-DDE detected at their end points were not significantly different from concentrations detected in sewage effluent. Such relatively inferior performance of channels 1 and 2 could be explained in view of their shorter length, lack of sufficient reed coverage that provided oxygen needed to activate the degradative role of micro organisms and/or the inherit character of DDE, i.e., its relatively more polar nature [ 14].

Table 1 also shows the frequency of detected residues in the sewage effluent and at the end of each channel. DDE and DDT were the most frequent compounds, while DDD was significantly the least.

The ratio of DDT to DDE is of significant bearing in tracing the source of DDT contamination. Allan [ 15] pointed out that in industrialized countries where DDT application is strictly banned, the major available form of DDT is its degradative product DDE, as it comes mainly through food chain, while in developing countries as DDT is still finding its way, comparable levels of DDT and DDE are present.

In the present study (Table 1 and Table 2) comparable concentrations of DDT were detected throughout, thus suggesting equal exposure to DDT as a presumably recently applied agent and to DDE as an end product. It is probable that the continuous application of DDT in Aswan lake as a mosquito larvicide [ 16] is behind the presence of DDT in sewage effluent. Table 2

Percent efficacy of various GBH channels in removing DDT and its metabolites from sewage effluent

Channel Percent removal capacity Average removal capacity

p,p-DDT o,p-DDT p,p-DDD p,p-DDE

1 78 76 96 21 67

2 78 85 89 38 72

3 86 60 94 84 81

4 89 67 90 86 82 5 79 78 94 85 83 6 84 73 93 84 83


The present study has indicated that GBH system has had a significant contribution in removing a large part of sewage-borne DDT residues. Removal capacity of long channels ( 100 m) is about 82%, while that of short channels (50 m) is about 65%. Other reports have emphasized the ability of the GBH system to reduce suspended solids, biochemical oxygen demand as well as coliform bacteria from sewage effluent [ 10].

Considering such views, we strongly recommend the use of long channel GBH systems for the treatment of sewage effluent prior to its use in agricultural purposes.

References

[ 1 ] E1 Sebaie, A.H., 1989. Fate and undesirable effects of pesticides in Egypt. In: Bourdeau, P., Haines, J.A., Klein, W. and Krishna Murti, C.R. (Eds.), Ecotoxicology and Climate. John Wiley & Sons, New York, pp. 359-371.

[2] Ahmed, M.T., 1991. High performance liquid chromatography determination of DDT residues in some commercial brands of milk in Ismallia, Egypt. Z. Gesamate Hyg., 36: 106-109.

[3] Ahmed, M.T. and Ismail, S., 1991. Residues of organo chlorine pesticides in fish, crab and sediment from el Timsah lake, Egypt, and their effect on mitochondrial ATP -as of New Zealand white rabbit. J. Egypt Public Health Assoc., 5: 557-575.

[4] Kerr, S.R. and Vass, W.P., 1973. Pesticides residues in aquatic invertbrate. In: Edwards, C.A. (Ed.), Environmental Pollution of Pesticides, Plemun Press, New York, pp. 134-180.

[5] Biswas, A.K., 1993. Environmentally sustainability of Egyptian Agriculture problems and perspectives. In: Faris, M.A. and Khan, M.H. (Eds.), Sustainable Agriculture in Egypt. Lynne Rinner, Boulder, pp. 59-70.

[ 6] Bishop, D.E., Marshal, L.S., O'Farrell, T.P. and Dean, R., 1965. Activated carbon for waste water renovation and column treatment. 149th National Meeting of American Chemical Society, Detroit, MI.

[ 7] Rebeck, G.G. Dostal, K.A., Cohen, J.M. and Kreissel, J.F., 1965. Effectiveness of water treatment processes in pesticides removal. J.A.W.W.A., 57: 181-191.

[ 8 ] Eckefelder, W.W., Jr., 1989. Industrial Water Pollution Control. McGraw-Hill, New York. [9] Kuo, P.K., Chain, E.S.K. and Chang, B., 1977. Purification of end products resulting from ozonation and

chlorination of organic compounds commonly found in water. Environl Sci. Technol., 11: 1177-1181. [10] May, E., Butler, J.E., Ford, M.G., Ashworth, R., Williams, J. and Bahgat, M.M.M., 1990. Chemical and

microbiological processes in gravel bed hydroponic (GBH) systems for sewage treatment. In: Cooper, P.F. (Ed.), Constructed Wetlands in Water Pollution Control. Pergamon Press, London, pp. 7-17.

[ 11 ] Edwards, C.A., 1973. Pesticides residues in soil and water. In: Edwards, C.A. (Ed.), Environmental Pollution of Pesticides. Plenum Press, New York, pp. 409-458.

[12] Saleh, F.Y.,Lee, G.F.andWolf, A., 1980. Selected organic pesticides, occurance, transformationandremoval from domestic and waste water. J.W.P.C.F., 22: 19-28.

[ 13] Herman, S.G., Garett, R.L. and Rudd, R.I., 1969. Pesticides and the western grebe. In: Miller, M.W. and Berg, G.G. (Eds.), Chemical Fallout. Charles Thomas, IL, pp. 24-53.

[ 14] O'Brien, R.D., 1967. Insecticides Action and Mtabolism. Academic Press, London. [ 15] Allan, A.J., 1983. Chemical Contaminants in Human Milk. Springer-Verlag, New York, Inc. [ 16] E1 Sebaie, A.H., 1993. The Pesticide Hazard. Compiled by Barbra Dinham. Zed Books, London, pp. 141-

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The efficacy of gravel bed hydroponic system in the removal of DDT residues from sewage effluent

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