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Trade Effluent Discharges

Licence Parameters and Limits
Water Pollution Discharge Licences are issued under Section 4 and Section 16 of the Local Government Water Pollution Act 1977 and 1990, in order to allow companies and other bodies to discharge a controlled amount of trade effluent to a public sewer, surface waters or ground waters.

Chemical parameters relating to the content of the trade effluent, are set out in a licence following a laboratory analysis of the effluent to be discharged. Limits are assigned to each parameter included on the licence. Any discharge containing concentrations of a substance greater than the limit stated on the licence is considered an exceedance. Some parameters are included on Discharge Licences as standard e.g. pH and temperature. These have standard limit values of 6-10 and 420 ºC respectively, 250 ºC for discharges to waters.

Other core parameters include soluble organics such as Biochemical Oxygen Demand (B.O.D),Chemical Oxygen Demand (C.O.D) and suspended solids. For industries discharging to waters, limits for these parameters are based on Royal Commission Standards subject to the availablity of a ten-fold dilution. The main aim is to minimise these discharges. In large industries were 0n-site treatment facilities are available, concentrations of B.O.D and C.O.D equivalent to domestic sewage strength are standard for trade effluent discharges to the foul sewer.

In general trade effluent should not be stronger than domestic sewage. For those effluents over and above domestic sewage strength limits of approximately, 327mg/l B.O.D, 688mg/l C.O.D and 334mg/l SS are expected. Limits set on licences approximating these figures are considered reasonably acceptable. However the limits are based on the content of the trade effluent and these general rules are used only as a guideline.

Parameters such as OFG, Detergents, Sulphates and Heavy Metals are included on licences where applicable. Again general standard concentrations of OFG 100mg/l, Detergents 100mg/l and Sulphates 400-500mg/l are used. Sulphates are a particular problem in high concentrations in public foul sewers as they can lead to corrosion of the concrete pipes. A concentration of 1000mg/l is considered acceptable for concrete sewers.

Heavy Metal limits are based on the dilution available in the sewer system. Generally metals such as Zinc, Copper and Nickel are accepted at concentrations of 1 ppm individually. Total heavy metal concentrations should not exceed 5ppm. Other more toxic metals e.g. Cadmium are accepted under the Cadmium Regulations S.I. No 294/ 1985 (Local Government Water Pollution Act 1977). These Regulations would apply to electroplating industries and they are included in IPC licences issued by the E.P.A .

General conditions for petroleum and solvents are included on licences were applicable. Generally the effluent discharge shall not contain petroleum hydrocarbons, organic solvents or other volatile organics (including dissolved methane gas and chlorinated organic solvents) which would give rise to flammable or explosive vapours in the sewer.

Exceeding Licence Limits
To date no official ranges have been established to divide exceedances into minor or major categories.

In general any exceedane of a licence limit is recorded and the company warned of the event. The company is warned of each occurance, action is advised and if it is not taken prosecution may ensue.

However in all cases of an exceedance the parameter involved is taken into account. For example an exceedance in pH of an effluent could be considered serious the first time it occurs. In surface waters a decrease in pH can be detrimental to fish life and in a public sewer alterations can affect the efficiency of the treatment process. An exceedance in B.O.D were there is a sewer overflow would have a direct affect in surface waters and groundwater flowing to rivers, lakes or streams. Solvents in high concentrations can create hazardous conditions in sewers particularly for personnel working there, OFG’s create long term problems in Treatment Works and Sulphates cause corrosion to pipeline.

All trade effluents should be monitored with a frequency based on the strength of the effluent. This may occur on a daily, weekly monthly, quarterly or yearly basis as necessary. The frequency of sampling is set down in the licence. All cases of an exceedance are individually assessed and action taken based on the above points.

A register of all Trade Effluent Discharge Licences to Waters and to Sewers is held in the Water Services Section.