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| Resource Centre : Glossary |
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Suspended solids - the solids which are suspended in sewage or effluent. Escherichia coli (E. coli) - an indicator organism for measuring the quantity of bacteria in the sewage. Disinfection - removal of bacteria in sewage. Nutrient Removal - removal of nutrients (such as nitrogen and phosphorus) in sewage, which can promote the growth of new living organisms. Excessive nutrients lead to over-abundant growth of water plants and organisms, which can deplete oxygen levels and kill fishes. Preliminary Treatment (Screening) - includes screening and removal of grit. Solids larger than 6 mm in diameter as well as grit which consists of sands, bone pieces etc are removed from the sewage. Primary Treatment - involves screening, removal of grit and a primary sedimentation process. Solid waste and suspended solids are removed from the sewage. Primary treatment usually removes between 30% and 40% of BOD, and 55% to 65% of suspended solids. Chemically Enhanced Primary Treatment (CEPT) - chemicals are added during the CEPT process to enhance the removal of suspended solids and pollutants with oxygen demand. The Stonecutters Island sewage treatment works removes 74% of BOD and 83% of suspended solids. Secondary Treatment - the sewage is purified by means of biological treatment processes after the sewage has undergone primary treatment. The organic matter in the settled sewage is decomposed by micro-organisms in the biological treatment process. This process can remove between 80% and 90% of BOD and suspended solids. Tertiary Treatment - sewage is further treated by physical, chemical, biological or a combination of these processes. The usual objective is to reduce nutrients levels in discharged effluent. Biological Aerated Filters (BAF) - an advance treatment process characterized by flexible operations and compact size. Environmental Impact Assessment (EIA) - a statutory process for assessing the impact on the environment of certain projects and proposals.
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