Most sewage treatment plants have a 'discharge consent' issued
by the environment agency. This is a quality of effluent which the
system must achieve in order to discharge to the environment. The
Environment agency carry out random sampling of sewage treatment
plants to ensure they are producing a quality of effluent within
the consented limit. If a system is shown not to achieve the
required consent the Environment Agency are able to pursue a
criminal action against the systems owner (which in a property
group would go to board level) or issue a fine.
A typical consent would comprise of the following elements:
- BOD - Biochemical oxygen demand or BOD is a chemical procedure for determining the uptake rate of dissolved oxygen by the biological organisms in a body of water. BOD measures the rate of oxygen uptake by micro-organisms in a sample of water at a temperature of 20°C over an elapsed period of five days in the dark.
- SS - Suspended solids, this is the amount of solid particles still present in the effluent. The amount of total suspended solids indicates the insoluble content of the sewage. The average strength of domestic raw sewage in the UK is 300 to 400 mg/l.
- NH4 - The nitrogen in sewage is assessed as ammoniacal nitrogen. This indicates the amount of nitrogenous organic matter which has been converted to ammonia. The average strength of crude domestic sewage will have a combined nitrogen content of 40 mg/l to 60 mg/l. pH VALUES. A typical Consent limit is 20mg/litre. The pH of a liquid is a measurement of its acidity ( low figures of 3 to 5.) or alkalinity (high figures of 9 to 12.) with a neutral of 7.0. The average strength of crude domestic sewage is slightly alkaline at 7.2.
Watling Hope carry out final effluent sampling and analysis as part of a sewage treatment plant maintenance contract OR as a stand alone service. After each analysis we provide a written report which is issued to the client certifying performance.
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