The consent will contain a number of conditions including those that control the quality and quantity of the discharge. Most consents will contain numeric limits for one or more of the parameters listed below.
Expressed in cubic meters per 24 hour period, the volume is limited and assessed on an individual basis to prevent overloading of the receiving treatment works.
Expressed in litres per second, the discharge flowrate is limited and assessed on an individual basis to prevent sewer flooding.
The standard range of pH in our region is six to 10. Extremes of pH can create unsafe working environments, affect the biological treatment systems in the receiving treatment works and damage the sewer network.
This is limited to a maximum of 43°C at the point of discharge to sewer in order to protect the staff working in our sewers, minimise odours and reduce the risk of explosives atmospheres.
Ammonia is classified as toxic and dangerous for the environment. It is highly toxic to aquatic animals and can cause unsafe sewer atmospheres.
Ammonia is found in sewage, mostly in human urine and some household cleaning products. Some industrial effluents, especially from mining, crude oil processing, metal finishing, pharmaceutical production or food processing facilities may also contain ammonia. This parameter may also be used for charging purposes.
Chemical oxygen demand (COD)
COD is a measurement of the oxygen required to oxidise soluble and particulate organic matter in water. When effluents with high COD levels are discharged in the environment, there will be a reaction of the dissolved oxygen available, potentially causing losses in the ecosystem. This is limited to prevent overloading of the wastewater treatment processes and ensure there is no detrimental impact on the environment.
Soluble organic compounds, residual food waste, sugar, emulsified oils are common sources of COD. This parameter may also be used for charging purposes.
This is controlled to ensure there are no blockages in the sewer and reduce treatment and transportation costs. This parameter may also be used for charging purposes.
Fat, oil and grease
Also known as FOG, this is controlled to prevent blockages in our sewers. It can also cause operational difficulties at pumping stations and treatment works. Some of the most common sources include restaurants, pubs, food processing facilities, automobile service shops and pharmaceutical manufacturing processes.
Sulphate can cause corrosion of concrete sewers and production of odours.
Sulphate is naturally present in surface water and groundwater as water moves through soil and rock formations that contain sulphate minerals. Many industrial wastewaters, particularly those associated with mining and mineral processing, can contain high concentrations of sulphate.
This includes metals as copper, lead, nickel, zinc, chromium, cadmium, antimony, tin, silver, etc. The presence of metals can inhibit biological treatment processes and may accumulate in the environment. An Environmental Impact Assessment is required.
Most common sources of metals in trade effluent are from metal finishing and electroplating activities, mining activities or textile industries.