Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1993-11-15
1996-01-02
Hruskoci, Peter A.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210738, 210801, 210804, 210199, 210205, C02F 156
Patent
active
054805597
DESCRIPTION:
BRIEF SUMMARY
LIQUID TREATMENT
This invention relates to a method of treating a liquid containing suspended matter, for example sewage, and to equipment for use in the treatment of such liquid. More particularly, but not exclusively, the present invention relates to a simple, relatively cheap alternative to the currently available sewage treatment techniques.
Sewage is the general term used to describe domestic and industrial wastewater. Such wastewater generally contains particulate organic and inorganic matter (i.e. suspended solids) and often has a high microbial content. In addition, other components such as phosphates, nitrates as well as various impurities from industrial processes and domestic sources may be present in solution or as colloids (very small unsettleable particles).
The purpose of sewage treatment is to clean wastewater in order to remove undesirable components therefrom such that the resultant effluent may be safely disposed of, for instance to the sea or to a river. In particular, it is important that degradable organic matter in the sewage is removed since such organic matter, if left to decompose aerobically, will drastically reduce the oxygen available to support life in the body of water into which it is discharged. For obvious environmental reasons, the removal of pathogenic microorganisms from the sewage is also highly desirable.
As a result of this concern for the environment, the purity standards required by the relevant authorities for the final effluent resulting from a sewage treatment plant are becoming increasingly stringent. Thus, in Europe, the European Commission has set, or intends to set, high standards for the levels of suspended solids and bacterial (and, in some cases, viral) content in final effluent from sewage treatment works, as well as for the biochemical oxygen demand (BOD) of the resultant effluent. The National Rivers Authority (NRA) in the UK is also setting stringent targets; failure to comply with standards may result in legal action with heavy fines. In the United States, the standards are equally stringent.
In conventional sewage treatment, the incoming sewage is subjected to initial screening and grit separation and is then subjected to a series of stages which result in the cleaned effluent: typically, the stages are as follows:
Typically, primary settlement will remove all gross and a proportion of the fine solids from the sewage, but will not normally reduce the microbial, colloidal or dissolved constituents of the ongoing material. This material is therefore subjected to biological treatments and subsequent secondary settlement steps to remove further settleable solids and oxidisable organic material from the effluent. At this stage, it is common for the effluent to be disposed of and, typically, sewage works effluents have more than 10.sup.6 coliform organisms/100 ml; however, some existing official requirements necessitate still further tertiary treatment for removal of additional contaminants in the wastewater, such as any ammonia or other forms of nitrogen and phosphates. In order to reduce bacterial content, it is usual to employ disinfectants, such as chlorine, but these have a secondary deleterious effect on the receiving water.
Another disadvantage of current settlement techniques (apart from their inability to reduce substantially the levels of bacteria) is that they are very slow and, as a result, extremely large basins are required in order to handle even modest flows.
Chemical treatment of sewage is well known. In particular, lime is known as a coagulant in sewage stabilisation and in sludge conditioning prior to filtration. The lime may be used with separate addition of other flocculants/coagulants. In addition, metal coagulants, for instance, aluminium and ferric compounds, are widely used in wastewater treatment. In addition, polyelectrolytes (cationic, anionic or nonionic) are often used for improving the quality of finished water for drinking and domestic purposes.
Separators known as "Hydro-Dynamic" separators are low energy devices which op
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Hruskoci Peter A.
Hydro International plc
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