Gravel Bed Hydroponic (GBH) systems had been used successfully to treat domestic sewage both in Egypt and the UK and were the subject of intensive research previously. The final phase of this project commenced in 1991 and set out to isolate and characterise bacteria from industrial waste, to investigate changes in the biofilm communities of GBH systems to treat toxic waste at 10th Ramadan City in Egypt and finally to assess ways of improving the performance of such systems.

The principal objectives were:-

(i) to investigate the kinetics of toxic waste biodegradation in a field-scale GBH system and optimise activity using modified bacterial strains.

(ii) to test the performance of a modified field-scale GBH system and predict the detoxification responses at different loading rates.

(iii) to obtain an accurate data-base of variations in sewage flow and clearwater on which to base an engineering design.

(iv) to formulate a series of engineering design methods sufficient to produce a design for GBH systems treating toxic wastes.

Work was done in Egypt at 10th Ramadan City on field-scale GBH beds and in the UK in greenhouse model GBH beds and gravel microcosms. The research strategy involved Egyptian and UK personnel testing ideas in pilot experiments with the model greenhouse system in the UK and then investigating the field-scale beds in Egypt.

Thus the application of GBH to toxic industrial wastes was undertaken in the following ways:-

(i) Construction and monitoring of a model system built under glass and operated at Budd's Farm Sewage Treatment Works, Havant, UK.

(ii) Isolation and characterisation of bacteria present in wastewater and capable degrading toxic chemicals or resisting heavy metals.

(iii) Surveys to describe the character of wastewater produced by an industrial complex at the Tenth of Ramadan City in Egypt.

(iv) Construction and operation of two GBH systems at the inlet and outlet sites of large pond systems at the Tenth of Ramadan site.

Two sets of GBH beds were built at 10th Ramadan City, Egypt; one at the inlet to a series of oxidation ponds, receiving strong, untreated sewage (the INLET beds); the other at the outlet, receiving settled effluent with a high content of dissolved compounds (the OUTLET beds). In this way the GBH beds were challenged to establish their capacity to treat industrial waste by monitoring performance and investigating the consequences of varying flow rate and recirculation on treatment. It was originally proposed to modify the biological components of the systems by seeding with selected bacteria, to increase the potential to degrade and detoxify chemicals in the effluents but this was curtailed due to security and weather problems.

During the project was undertaken in the following fields:

1. Monitoring of water quality indicators on a 2-weekly basis.
2. Assessment of changes in biofilm bacteria.
3. Detection of changes in levels of pollutants in effluent.
4. Impact of an aromatic pollutant, toluic acid, on GBH bed performance.
5. Impact of copper on GBH bed performance.
6. Assessment of flow rate on the GBH bed performance.
7. Effect of recirculation on GBH bed performance.
8. Effect of extended bed length on performance.
9. Tracking of degrading bacteria in biofilm communities.

1. The inlet GBH beds did not perform well. The high solids of the raw sewage caused considerable clogging and this was exacerbated by variations in the supply of wastewater in the main sewer pipe which often starved the beds of effluent. The point of removal of the wastewater from the main sewer was changed several times to maintain supply.

2. Heavy metal contamination of effluents at 10th Ramadan City were consistently low in the effluent entering the GBH beds. This indicates that the oxidation ponds are extremely effective in removing metals. This suggests that preliminary treatment in a lagoon prior to GBH beds would significantly improve performance.

3. GBH beds fed with industrial waste showed evidence of disruption of reed growth. Plants are smaller, usually have spiked leaves and changes in pigment colour. They do not thrive well when the beds are fed with strong effluent, untreated by passage through an oxidation pond.

4. Most success in reducing organic pollutants was achieved when effluent was treated initially by passage through an oxidation pond. Phthalates were a common pollutant but 100 m long GBH beds did not remove them. Some long chain fatty acids and heterocyclic aromatic compounds were completely removed.

5. The effluent emerging from the oxidation ponds was prone to considerable variation in BOD and COD during the study period. Reductions in COD usually varied between 20 and 60% but occasionally exceeded 80%. Analysis showed that GBH beds could treat 45-49% of the COD.

6. Suspended solids were low throughout the study period.

7. Dissolved oxygen often reached saturation in the effluent emerging from the beds but on many occasions none was found. This pattern was clearly linked to the BOD quality of the effluent.

8. Removal of ammonium-N was more obvious as the beds became more established after 2 years of operation.

9. Total oxidised nitrogen levels were low for much of the study period but did rise after 2 years of performance, indicating that nitrification was occurring. This was much longer that for beds fed with domestic effluents.

10. Performance did not appear to deteriorate at higher flow rates.

11. Faecal coliform reductions were lower than expected from previous studies on domestic waste. This may have been due in part to death of protozoa in the biofilm.

12. When the GBH beds were spiked with 1000 mg/l copper, the metal was adsorbed rapidly at the start of the bed and none emerged in the effluent.

13. Studies on the movement of copper showed that it was immobilised in the roots of the reeds and the sediment of the reed-bed.

14. In the model system, copper inhibited nitrification in the biofilm but the system recovered after 2 weeks.

15. Challenge with toluic acid stimulated activity, rather than growth, of existing bacterial populations in the biofilm.

16. Recirculation in the presence of toluic acid stabilised concentrations but these reduce with time. Successive challenges with the pollutant lead to progressively faster rates of degradation of the pollutant.

17. In continuous flow systems, toluic acid caused a decrease in nitrification activity.

18. In general, there was little difference between the capacity of planted and unplanted beds to treat effluent but the planted beds slowed the movement of a toluic acid pulse.

19. The addition of a known degrader of toluic acid to gravel microcosms did not enhance the rate of toluic acid breakdown and the organism did not establish itself in the biofilm.

1. The establishment time for GBH beds receiving a complex mixture of industrial effluents was much longer than for those receiving domestic effluent.

2. Industrial effluent disrupts plant growth in GBH beds and performance efficiency is much more erratic.

3. GBH beds can reduce the COD of industrial effluents but design and operating procedures should allow longer residence times than for domestic wastewaters.

4. The prospects for successful treatemnt to a consistent standard using GBH will be greater if industrial wastewater is treated at the point of production before it enters the sewerage system.

5. Modular systems incorporating vertical and horizontal flows and lagoons will allow flow management according to the complexity of the industrial wastewater.

(a) General

LOVERIDGE, R.F., BONE, D.A. & BUTLER, J.E. (1986) Sewage effluent, a Resource for Agriculture" Middle East Water, 9, No.6, June 1986, 273-276.

BUTLER, J.E. & LOVERIDGE, R.F. (1991) Sewage treatment using Gravel Bed Hydroponics (GBH) in Egypt and the United Kingdom. Appendix 17, Vol.III House of Commons Environment Committee, Fourth Report, Pollution of Beaches. London, HMSO, August 1990. 413.

BUTLER, J.E. & DEWEDAR, A. (1991) Gravel-Bed Hydroponic Sewage Treatment - Performance, Design and Potential for Crop Production". International Conference on Environmental Pollution. Organised by ECPR, DGQA, UNEP and UNESCO, Lisbon 15-19 April 1991. A29/1-A29/8.

BUTLER, J.E. & LOVERIDGE, R.F. (1991) The Application of Gravel Bed Hydroponic Sewage Treatment in Mediterranean Wetlands. Invited paper IWRB Symposium on Managing Mediterranean Wetlands for the Year 2000 and Beyond. Palazzo Regionale dei Congressi, Grado, Italy. 3-10 February 1991.

MAY, E.; BUTLER, J. E.; FORD, M. G.; ASHWORTH, R. W.; WILLIAMS, J. B.; & BAHGAT, M. M. M. (1990) Chemical and microbiological processes in gravel-bed hydroponic systems for sewage treatment. In 'Constructed Wetlands in Water Pollution Control', 539- 542 (Ed. Cooper P.F. & Findlater D.C.). Pergamon Press.

BUTLER, J.E.; MAY, E. & FORD, M.G. (1991) The treatment of industrial wastes at 10th Ramadan City, Egypt, using Gravel Bed Hydroponics. Proceedings of an International Symposium on Emerging Technologies for Hazardous Waste Management. Organised by the American Chemical Society and Georgia Institute of Technology, Atlanta, Georgia.

BUTLER, J.E.; FORD, M.G.; MAY, E.; ASHWORTH, R. F.; WILLIAMS, J. B.; DEWEDAR, A.; EL-HOUSSEINI, M. & BAHGAT, M. M. M. (1993) Gravel-bed hydroponic sewage treatment: its performance and potential. In 'Constructed Wetlands for Water Quality Improvement', pp. 237-247, Ed. Moshiri G.A. 1993 Lewis Publishers, Boca Raton, Ann Arbor, London, Tokyo.

BUTLER, J.E.; LOVERIDGE, R.F.; WILLIAMS, J.B.; MAY, E. & FORD, M.G. (1993) Gravel-bed hydroponic system treatment - an artificial wetland system for preserving the water environment. In: Mndustrial and agricultural impacts on the hydrologic environment', (Eds. Y. Eckstein and A. Zaporozec), Second USA/CIS Joint Conference on Environmental Hydrology and Hydrogeology.; 1993; Washington, USA. : Water Environment Federation .

WILLIAMS, J.B., BAGHAT, M.M.M., MAY, E., BUTLER, J.E. & FORD, M.G. (1994). The potential of Gravel Bed Hydroponic systems to treat sewage and remove pathogenic organisms. Proc. 1st Western Africa Water and Environment Conference, Accra, Ghana. Water Africa Ltd., Liverpool.

WILLIAMS, J.B.; MAY, E.; FORD, M.G. & BUTLER, J.E. (1994) Nitrogen transformations in gravel-bed hydroponic beds used as a tertiary treatment stage for sewage effluents. Wat. Sci. Tech.: 1994, Vol. 29(4), 29-36.

WILLIAMS, J.B., BAGHAT, M.M.M., MAY, E., FORD, M.G. & BUTLER, J.E. (1994). The removal of pathogenic microorganisms during sewage treatment in Gravel Bed Hydroponic constructed wetlands. Proc. IAWQ 4th Conference on the the Use of Wetland Systems in Water Pollution Control, Guangzhou, China.

WILLIAMS, J.B.; BAHGAT, M. M. M.; MAY, E.; FORD, M.G. & BUTLER, J.E. (1995) The potential of gravel bed hydroponic systems to treat sewage and remove pathogenic organisms. Water Science and Technology: 1995, Vol.32 (3), 49-58.

ADDLETON, A.; BROWN, A.; BAHGAT, M. M. M.; LOVERIDGE, R.L.; MITCHELL, J.I.; MAY, E.; FORD, M.G. & BUTLER, J.E. (1996). Potential of Gravel Bed Hydroponic systems for the treatment of industrial wastewater. Proceedings of the 5th International Conference on Wetlands Systems for Water Pollution Control, Vol. 2. September, Vienna, Austria. IWGA

WILLIAMS, J.B.; STOTT, R.; BAHGAT, M.M.; LOVERIDGE, R.F.; ASHWORTH, R.F.; AWAD, A.; MAY, E.; FORD, M.G.; BUTLER J.E. & DEWEDAR A. (1997). Gravel bed hydroponic systems for sewage treatment and reuse. Water Resources Journal, December issue, 32-38, ISSN 0377-8053.

STOTT, R.; JENKINS, T.J.; SHABANA, M. & MAY, E. (1997). A survey of the microbial quality of wastewaters in Ismailia, Egypt and the implications for wastewater reuse. Water Science and Technology, Vol. 35 (11-12), 211-217.

WILLIAMS, J.B.; MAY, E.; FORD, M.G. & BUTLER, J.E. (1997) Gravel bed hydroponic wetlands for wastewater treatment. In: Water, issue 4 (April), DFID Newsletter, pp. 8-9. Published by ODU, HR Wallingford.

(b) Research Monographs on DfID projects

LOVERIDGE, R.F.; BUTLER, J.E.; DEWEDAR, A & AWAD, A. (1995) The growth and yield of crops grown hydroponically using treated sewage effluents. ODA Research Monographs In Wastewater Treatment and Reuse In Developing Countries. Monograph No. 1 University of Portsmouth. ISBN 1 898108 65 X.

WILLIAMS J.B.; ASHWORTH, R.; FORD, M.G.; MAY, E.; LOVERIDGE, R.F.; BAHGAT, M. & BUTLER, J.E. (1995) Physical and chemical aspects of sewage treatment in Gravel Bed Hydroponic (GBH) systems. ODA Research Monographs In Wastewater Treatment and Reuse In Developing Countries. Monograph No. 2 University of Portsmouth. ISBN 1 898108 66 8.

WILLIAMS, J.B.; BAHGAT, M. M. M.; MAY, E.; FORD, M.G.; LOVERIDGE, R. L. & BUTLER, J.E. (1995). Microbial treatment processes in Gravel Bed Hydroponic constructed wetlands. ODA Research Monographs In Wastewater Treatment and Reuse In Developing Countries. Monograph No. 3 University of Portsmouth. ISBN 1 898108 67 6.

STOTT, R.; JENKINS, T.; WILLIAMS, J.B.; BAHGAT, M. M. M.; MAY, E.; FORD, M.G. & BUTLER, J.E. (1996) Pathogen removal and microbial ecology in Gravel Bed Hydroponic (GBH) systems. ODA Research Monographs In Wastewater Treatment and Reuse In Developing Countries. Monograph No. 4 University of Portsmouth. ISBN 1 86137 034 2.

ADDLETON, A.; MAY, E., MITCHELL, J.I.; BAHGAT, M. M. M.; LOVERIDGE, R.L.; FORD, M.G.; DEWEDAR, A. & BUTLER, J.E. (1996) Microbial degradation of aromatic compounds in Gravel Bed Hydroponic (GBH) systems. ODA Research Monographs In Wastewater Treatment and Reuse In Developing Countries. Monograph No. 5 University of Portsmouth. ISBN 1 86137 035 0.

BROWN, A.C.; MAY, E., MITCHELL, J.I.; EL-HOUSSEINI, M.; BAHGAT, M. M. M. & BUTLER, J.E. (1996) Gravel Bed Hydroponic (GBH) treatment of metal contaminated wastewater. ODA Research Monographs In Wastewater Treatment and Reuse In Developing Countries. Monograph No. 6. University of Portsmouth. ISBN 1 86137 021 0.

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