Division 1.7.2.2 Waste water treatment
United Kingdom
| Technique | Description |
|---|---|
| Primary treatment | Physico-chemical treatment, such as equalisation, neutralisation or sedimentation. Equalisation (e.g. in equalising basins) is used to prevent large variations in flow rate, temperature and contaminant concentrations and thus to avoid overloading the waste water treatment system |
| Secondary (biological) treatment | For the treatment of waste water by means of microorganisms, the available processes are aerobic and anaerobic treatment. In a secondary clarification step, solids and biomass are separated from effluents by sedimentation, sometimes combined with flocculation |
| a) Aerobic treatment | In aerobic biological waste water treatment, biodegradable dissolved and colloidal material in the water is transformed in the presence of air by microorganisms partly into a solid cell substance (biomass) and partly into carbon dioxide and water. Processes used are:
The generated biomass (excess sludge) is separated from the effluent before the water is discharged |
| b) Combined anaerobic/aerobic treatment | Anaerobic waste water treatment converts the organic content of waste water by means of microorganisms in the absence of air, into methane, carbon dioxide, sulphide, etc. The process is carried out in an airtight tank reactor. The microorganisms are retained in the tank as biomass (sludge). The biogas formed by this biological process consists of methane, carbon dioxide and other gases such as hydrogen and hydrogen sulphide and is suitable for energy generation. Anaerobic treatment is to be seen as pretreatment before aerobic treatment, due to the remaining COD loads. Anaerobic pretreatment reduces the amount of sludge generated from biological treatment |
| Tertiary treatment | Advanced treatment comprises techniques, such as filtration for further solids removal, nitrification and denitrification for nitrogen removal or flocculation/precipitation followed by filtration for phosphorus removal. Tertiary treatment is normally used in cases where primary and biological treatment are not sufficient to achieve low levels of TSS, nitrogen or phosphorus, which may be required e.g. due to local conditions |
| Properly designed and operated biological treatment plant | A properly designed and operated biological treatment plant includes the appropriate design and dimensioning of treatment tanks/basins (e.g. sedimentation tanks) according to hydraulic and contaminant loads. Low TSS emissions are achieved by ensuring the good settling of the active biomass. Periodical revisions of the design, dimensioning and operation of the waste water treatment plant facilitate achieving these objectives |