Many operators of industrial processes use the sewerage system as an effective and relatively environmentally-friendly route for the treatment and disposal of water-based process waste.
However, discharging waste water to the sewers must be done via a consent issued by the sewerage undertaker which operates the sewerage system in that area, usually the water companies. The relationship between process operators and the sewerage undertaker is governed by the Water Industry Act 1991 (see Water Industry Act 1991 on page 20 of EEF Register of Environmental Legislation).
Discharge to sewer – consents
The process operator is restricted by consent conditions regarding the following characteristics of the effluent:
- volume of effluent and rate of discharge;
- key parameters that should not be exceeded:
- BOD & COD (Biological Oxygen Demand & Chemical Oxygen Demand);
- TSS (Total Suspended Solids);
- temperature;
- pH (alkalinity - acidity); and
- concentrations of specific substances.
- prohibited substances that should not be discharged, for example:
- free oil;
- flammable or explosive substances (for health and safety as well as environmental reasons); and
- chlorinated degreasing solvents.
The conditions can also include discharge times and frequency.
The sewerage undertaker makes a charge for the water it treats. The various regional sewerage undertakers (e.g. Thames, Severn Trent, Dwr Cymeru, etc.) use variations on a charging scheme called the ‘Mogden formula’ which includes the following elements:
Charge = R +[(V + Bv) or M] + B(Ot/Os) + S(St/Ss)
Where:
|
R |
Cost of reception and conveying waste to sewage works (unit cost/m3). |
|
V |
Average cost of primary treatment at sewage works (unit cost/m3). |
|
Ot |
Chemical oxygen demand (COD) of trade effluent after one hour settlement at ph 7 (mg/l). |
|
Os |
COD of crude sewage after one hour settlement (mg/l). |
|
St |
Total Suspended Solids of trade effluent (mg/l). |
|
Ss |
Total Suspended Solids of effluents received at the treatment works (mg/l). |
|
Bv |
Additional volume charge if there is biological treatment (unit cost/m3). |
|
B |
Biological oxidation treatment of settled sewage. |
|
S |
Cost of treatment and disposal of primary sludge. |
|
M |
Treatment and disposal where effluent goes to a sea outfall (M for marine). |
1. Ot and St are determined from analysis of trade effluent samples, averaged over a charging period. The other figures are set by each water company to reflect their operating costs for the average strengths of crude sewage arriving at their sewage treatment works.
2. Important elements in the formula are:
* discharge volume; and
* discharge quality (in terms of TSS and COD).
The formula compares the quality of a particular trade effluent discharge with that of the quality of sewage received by the sewerage undertaker at its sewage treatment works.
The structure of the formula is such that, depending on specific circumstances, operators introducing effluent management techniques, including effluent treatment, can reduce volume and improve quality of effluent, thus incurring lower (perhaps significantly lower) charges for discharging.
It is the sewerage undertaker’s responsibility to ensure that the producer of the effluent stays within the conditions of the consent. They can be expected to take samples at regular intervals to confirm compliance. Failure to comply can result in the producer being prosecuted by the sewerage undertaker.
As well as process water, any workplace will also be the source of wastewater from toilets, hand washing facilities, kitchens, catering facilities, etc.. Small scale discharges from sinks in laboratory areas and waste water from activities such as the mopping of floors will also be expected.
This kind of output is usually assessed by the sewerage undertaker on a per capita basis. The site operator will normally be required to make a declaration to the sewerage undertaker stating the average occupancy of their premises. A fee for the ‘domestic’ water usage of the site is then calculated, based on occupancy rates.
Linking sewer discharges to controlled water
The water that gets discharged to the sewerage system is returned to the natural environment after treatment in a sewage treatment works. Like any other company which discharges to controlled waters, a sewerage undertaker can also be prosecuted by the Environment Agency.
Sewerage undertakers are careful to control their customers’ emissions, especially those which could impair the operation of the sewage treatment works. (For example, biocides which could kill the micro organisms which are used to digest organic wastes.)
If a discharge by a process operator results in a sewage treatment plant breakdown and a subsequent pollution incident, the culprit may be prosecuted both by the sewerage undertaker and by the Environment Agency.
Safe storage and spill prevention
There are regulatory requirements regarding the safe storage of materials on commercial sites. Waste materials of all sorts must be stored securely (see SI1991/2839 as amended on page 25 of EEF Register of Environmental Legislation). This includes, for example, containers such as skips where waste materials such as paper or plastic sheeting can blow away and block watercourses, and liquid wastes stored in drums must be in bunds if stored out of doors.
Other oils are covered by separate regulations (see SI 2001/2954 on page 20 of EEF Register of Environmental Legislation) which require bunding and other measures.
The Environment Agency’s inspectors have legal rights of entry to inspect sites which might pose a risk to controlled waters (see Env Act 1995 Sch 22 on page 21 of EEF Register of Environmental Legislation). They can also serve notices which force site operators to improve precautionary measures such as bunds (see SI 1999/1006 on page 19 of EEF Register of Environmental Legislation).
Saving water and protecting water supplies
The pipework and water fittings in premises must be to a certain standard to prevent problems such as back syphonage of contaminated water into the drinking water supply system. Fittings should be designed with the conservation of water in mind. (see SI 1999/1148 on page 21 of EEF Register of Environmental Legislation).
The relevant regulations are enforced by the sewerage undertaker and local authority building inspectors.
Abstraction
Many companies take water directly from controlled waters either to use in their processes or to ‘impound’ as part of their fire-fighting systems.
Abstraction from controlled waters is regulated by the Environment Agency. Any abstraction from surface or groundwater will require a licence from the Environment Agency.
Before the agency will allow abstraction to take place, the competing requirements of other potential users of the water resource will be taken into account (e.g. in drought conditions, if too much water has been removed from a catchment area, the low water levels downstream may impair the exploitation of the river for fishing).
Similarly excessive abstraction of groundwater in coastal areas can cause infiltration of salt water into the aquifer.