Yes. A trade effluent discharge can change significantly while its total daily volume stays exactly the same. Different cleaning chemicals, production ingredients, operating temperatures or discharge schedules can alter the characteristics of wastewater entering a public foul sewer.
For an industrial operator, an unchanged daily discharge volume is therefore not enough to establish that the effluent remains within existing trade effluent consent conditions. The nature of the effluent and the way it reaches the sewer matter independently of daily quantity.
Volume is only one discharge characteristic
Consider a food production facility using the same amount of water before and after a recipe change. The wastewater volume may remain stable, but different ingredients could alter organic loading, suspended solids or acidity.
A manufacturing site replacing its washdown chemical might similarly change effluent composition without changing the number of cleaning cycles. Even if the cleaning operation consumes identical quantities of water, the substances entering the drainage system may differ.
Relevant characteristics include:
- Chemical composition: The substances present and their concentrations, including constituents introduced by new materials or cleaning products.
- Acidity or alkalinity: Changes in pH resulting from revised processes or cleaning arrangements.
- Discharge temperature: Warmer or cooler wastewater caused by process heating, cooling or altered production methods.
- Physical characteristics: Changes in solids, oils, fats or other materials carried in the wastewater.
- Flow rate: The quantity entering the sewer over a particular period, rather than the daily total alone.
In England and Wales, section 121 of the Water Industry Act 1991 allows trade effluent consents to contain conditions concerning composition, discharge rate, daily quantity, timing, temperature and acidity or alkalinity.
Consequently, an operator needs to consider the specific conditions attached to its consent, not simply whether total consumption or discharge volume has increased.
Process changes affecting consent conditions
Changes that appear minor within production planning can have a different significance at the final discharge point.
A revised cleaning cycle
Switching to a stronger cleaning formulation may change the concentration or type of chemicals entering the drainage system. Combining cleaning stages could also produce shorter, more concentrated discharges.
A different production recipe
New raw materials may affect the organic or chemical composition of wastewater. The significance depends on which substances enter the drain and how existing treatment or separation arrangements perform.
Changes in discharge temperature
Altered heating or cooling processes may change wastewater temperature. This matters where the consent specifies a temperature condition, even when the quantity released remains unchanged.
A different discharge pattern
Suppose a factory previously discharged wastewater across an eight-hour shift but now releases the same quantity during two shorter periods. Its total daily volume remains constant, while the peak discharge rate may increase considerably.
Consent conditions can address both the maximum rate and permitted periods of discharge, making timing a separate consideration.
When to review discharge conditions
The appropriate point to review consent is when a proposed process change could affect a controlled discharge characteristic, rather than waiting for a higher daily volume to appear.
Begin by comparing the existing consent with the proposed production arrangements. Obtain the relevant information about incoming materials, chemical products, treatment stages, flow timing and expected wastewater characteristics.
Existing effluent sampling results can provide a baseline for comparison, but they may not represent the changed process. Where the expected composition, temperature or discharge pattern is uncertain, review process records and available analytical evidence, then determine whether further sampling or assessment is needed.
The sewerage undertaker responsible for the receiving public sewer determines the relevant consent requirements. Where the proposed discharge would fall outside existing consent conditions, the operator should contact the undertaker and obtain the necessary consent variation or other formal agreement before making that discharge. An unchanged daily volume does not authorise changes to controlled characteristics.
For sites introducing new processes, the Trade Effluent Consent service addresses discharge descriptions, supporting information and relevant consent considerations. Operators managing several changing activities may also need a broader industrial environmental services review.
The useful comparison is between the characteristics authorised by the existing consent and those expected from the revised operation. Equal volume does not necessarily mean an equivalent discharge.
