Technical description
Recycling of industrial effluent is now being practiced by several industries to reduce the demands on freshwater resources and to reduce pollution of the environment. The recycling of industrial effluent was spearheaded by the bauxite/alumina companies operating in Jamaica, and they are the largest recyclers at the present time. The bauxite/alumina industry produces a waste product known locally as "red mud," which consists of over 70% water, enriched with caustic soda and organics.
The waste is thickened to 28% solids and sprayed on a sloping drying bed in a layer 8 to 10 cm thick. The liquid fraction is collected at the toe of the drying bed and is channeled via pipelines to a sealed holding pond. Pumps move the effluent from the holding pond back to the plant via a pipeline where it is recycled through the process. The system consists of:
· Deep mud thickeners (conical vessels).· High pressure pumps and pipelines to the drying beds.
· Drying beds, sealed to prevent infiltration of the effluent to the groundwater.
· An effluent holding pond, also sealed to prevent infiltration of the effluent to the groundwater.
· Recycling pumps and pipelines to the plant.
This technology is described in Part B, Chapter 3, "Wastewater Treatment Technologies and Reuse."
Extent of Use
This technology is used at four bauxite/alumina plants in Jamaica. Efforts are under way to encourage other industries to follow suit and recycle process and waste waters.
Operation and Maintenance
Problems encountered in the operation and maintenance of the system include mechanical breakdowns of the pumps; ruptures of the pipelines, necessitating a total shutdown of the system; and heavy rains that overload the system, resulting in spillage to the environment. The bauxite/alumina companies, all being multinational corporations, have few problems in replacing parts or equipment, and generally maintain a large equipment inventory. Each bauxite company has a preventive maintenance program, which also reduces downtime.
The skills needed to operate the system are varied. Overall direction is provided by the senior production engineer. However, skill levels range from laborers, who turn valves on and off, to chemical engineers, who manage the system.
Level of Involvement
The private sector and the government are involved in the implementation of this technology and in certain facets of the operation. The bauxite/alumina companies provide the capital and the engineering designs, and construct the systems. The government, through several specialized agencies, reviews the engineering designs and grant the permits for construction to proceed. Part of the permitting process involves the conduct of an environmental impact assessment. After the permit is granted, construction of the systems is monitored by the government to ensure that design specifications are adhered to. The relationship between the public and private sectors is cooperative and complementary.
Costs
Initial capital costs vary and are dependent on the volume of work to be done in preparing the site, resettling persons living on or near the site, and making the necessary changes in the plant infrastructure. The minimum investment to date in any one system has been $50 million. Operation and maintenance costs are not available as this information is confidential and proprietary to the bauxite companies.
Effectiveness of the Technology
The system, as designed and operated, is very effective in reducing contamination of groundwater resources. Because it is completely sealed, it does not allow infiltration of liquid effluents, and recycling this fraction reduces the risk of contamination of groundwater resources from effluent disposal. The use of this system has reduced groundwater contamination in one area by 44% since 1985, as reported by the Water Resources Authority. Despite some disadvantages, due predominantly to the large land areas consumed by the drying beds and holding ponds, the application of this technology, in all cases, has proved to be advantageous.
Suitability
The technology is suitable for application in areas where large tracts of non-agricultural land - i.e., in excess of 200 ha - are available. In addition, the land should not be steeply sloped, and a supply of nondispersive clay should be available in close proximity to provide impermeable material for sealing the bottom and sides of the drying beds and holding ponds. The technology can be, and is being, adapted for other situations.
Advantages
· Use of this technology reduces the rate of freshwater withdrawal from aquifers; savings of 4 to 5 Mm3/year of freshwater have been recorded.· Recycling of process water reduces the volume of caustic soda solution needed, as the caustic soda is recycled with the effluent.
· The use of energy, to pump freshwater from depths greater than 100 m, is reduced, thereby saving on the import bill (foreign exchange) for oil.
· Contamination of groundwater is reduced by removing and recycling the liquid fraction of the waste stream that is a risk to groundwater quality; likewise, the retention of a high percentage of the caustic soda in the thickened mud (solid fraction) and in the recycled process water makes this contaminant less available for migration to the groundwater.
· The bauxite/alumina companies are better able to meet the ISO 9000 and ISO 14000 certifications and thereby gain a competitive advantage in the marketplace.
· The decreased input costs reduce operational costs, resulting in higher profit margins for the companies and more tax revenue for the government, increasing both the level of investment in the country and the GDP.
· Better environmental management by the corporate sector results in fewer governmental regulations; other multinational corporations are likely to see such conditions as favorable and invest in Jamaica.
· The incidence of water pollution is reduced, increasing the availability of freshwater for domestic and irrigation uses and reducing the cost of water to citizens; this increases the standard of living and governmental popularity.
Disadvantages
· There is an increased risk of pollution of surface water resources, due to the large size of the holding ponds and the possibility of spillages.· Technical problems within the plants may be experienced, reducing the level of production and affecting the volume of recycled effluent; hence, storage volumes can increase to the point where overflows occur, affecting the environment.
· The quality of effluent may vary significantly, affecting the degree of treatment provided by this technology and thus, potentially, the level of production at the plants.
· The technology is capital-intensive, not labor-intensive, and provides few spin-offs for nearby communities where unemployment may be high.
· As a result of the land-intensive nature of this technology, its implementation may result in the relocation of residents, disrupting their lives and causing great inconvenience; for farmers and other small businesspeople, a new location may be less suitable and/or create the need to seek other employment.
· Agricultural land may be lost in some cases, decreasing food production.
Further Development of the Technology
This technology can be more effective if overflows and spills from the system are managed better. Design parameters, especially relating to the effects of rainfall/runoff and the rate at which the plants can accept recycled effluent to prevent negative environmental impacts, need to be better refined.
Information Sources
Contacts
Basil P. Fernandez, Hydrogeologist and Managing Director, Water Resources Authority, Hope Gardens, Post Office Box 91, Kingston 7, Jamaica. Tel. (809)927-1878. Fax (809)977-0179.
Bibliography
Fernandez, Basil. 1991. "Caustic Contamination of Karstic Limestone Aquifers in Two Areas of Jamaica." In Proceedings of the Third Conference on Hydrology, Ecology, Monitoring, and Management of Groundwater in Karst Terranes. Dublin, Ohio, U.S.A., National Ground Water Association.
