Discharging trade effluents

• Consent to discharge
• Why have trade effluent consents?
• How are consents determined?
• Staying within consent
• What are you discharging?
• Employee awareness
• Reduce effluent discharges
• Preliminary treatment
• Trade effluent checklist

Consent to discharge

If your company discharges its effluent to a public sewer then your company must possess a current and valid discharge consent from the sewerage operator. The sewerage operator is often the same water company which supplies water to the site although this is not always the case.

Why have trade effluent consents?

It may seem strange that a consent is required to discharge trade effluents since the common belief is that all effluents can and will go down the sewer. This is simply not the case. Because specific trade effluents may contain toxic substances, be highly acidic or alkaline or have qualities which may make their treatment difficult or even dangerous, their discharge via the sewerage system requires regulating. For example highly acidic solutions can result in damage to the sewerage system leading to corrosion of pipework and fittings. Since sewage treatment plants tend to comprise of a biological stage, any toxic materials which are discharged may have a detrimental effect on the biomass required for biological treatment. Dissolved metals, particularly heavy metals, such as tin, mercury and cadmium are all highly toxic in relatively small concentrations. It is important to remember that preliminary treatment systems require careful management and will produce a more concentrated waste stream which will still require disposal.

How are consents determined?

The consent to discharge the trade effluent will include specific parameters, these parameters are likely to include the volume of the discharge (maximum permitted daily or hourly flow rate), the chemical oxygen demand (COD), the pH, the temperature and the suspended solids concentration. The sewerage operator may also require certain specific contaminants to be identified, particularly if some of the contaminants are toxic or the effluent is classified as a special waste. As long as the consent is adhered to then the sewerage operators are legally bound to accept the effluent.

Staying within consent

The consent must be strictly adhered to with regard to the parameters outlined above. Deviation from the consent can result in prosecution. For this reason should the trade effluent be subject to future change in volume or composition then these changes must be discussed with the sewerage operator. It is not legal to simply discharge greater volumes or concentrations of effluent without receiving consent to do so. Most consent's also have a caveat stating the discharger is not allowed toxic materials unless specifically agreed with the water company.

What are you discharging?

Ask yourself do you know exactly what you are discharging to sewer? If you do not then you could be breaching your consent. Identify which processes on site produce an effluent that is discharged to sewer. Ensure that for each process you know the volume of effluent produced and the contaminants which the effluent will contain. It is important to keep a record of what is actually discharged so that this can be related to the consent. Try and be as specific as possible with regard to the contaminants discharged, it may be necessary to send samples off-site for some analyses. If this is the case then determine how often these analyses are required. For example a table for each process may have the following format:

Table 1. Hypothetical effluent generated from metal finishing bath No. 1. Week Commencing 24/11/03

The weekly totals for the volumes and the contaminant loads for each process can then be placed in a summary table which can be compared with exactly what the consent states may be discharged to sewer. If the data shows that the consent is being breached then the discharge of effluent must be stopped immediately and the sewerage operator contacted. If the consent is being approached with regard to any of the parameters then again the sewerage operator should be contacted and a revised consent discussed. The impact that a reduction in volume or pollutant concentration will have on cost can be checked using the Mogden Formula Tool available on the EOC website.

Employee awareness

It is important to make all employees aware of the necessity to accurately record the effluents being discharged to sewer, particularly those employees concerned with and responsible for emptying and discharging effluents from specific processes. Remember that the addition of new processes will add to the volume and contaminants being discharged so effluent produced by any new processes must be checked to ensure that the consent will cover the additional volume, contaminant concentrations and loads.

Make sure that any visiting contractors to site are aware that they must not discharge any effluents to sewer without first checking with the relevant member of personnel that they may do so. Do not be tempted to discharge any effluent whose composition you are not completely sure of irrespective of its volume. If an effluent has been discharged which you suspect may contain contaminants which are not approved by the consent then contact the sewerage operator immediately. This may allow the operator to take remedial steps, if you do not do this and are identified as the cause of pollution the legal and clean up costs are likely to be much larger.

Ensure that a site plan identifies all access and entry points to the sewerage system. Make those persons responsible for discharging effluents aware of the access and entry points highlighting that these are specifically for trade effluents only. Ensure that any surface water drains on site cannot be mistaken for foul sewer drains. Additionally it is important to take precautions that uncontaminated surface water cannot enter foul sewers since this will add to the volume being discharged and potentially could result in a breach of consent. It is therefore important to be sure that surface water which does not go to a foul sewer is not contaminated by processes or products from onsite.

Reduce effluent discharges

In an effort to reduce the volume of effluent being discharged, consider whether any of the effluents produced by some processes could be re-used or recycled by another process or whether specific tanks need to be emptied so frequently. To gain an in depth understanding of how much water is being used on site a water mass balance needs to be produced. This should identify exactly how much water enters the site, where and how it is used and finally where and how much is discharged. Data is available for estimating how much water an employee will use in a day for handwashing and toilet flushing. To accurately measure where water is being used, some form of flow monitoring or sub-metering may be required. The more accurate the data produced the greater the opportunity to identify where water may be lost and also where water savings can be made which can then lead to financial savings.

Preliminary treatment

Since the cost of discharging to sewer is based on the volume discharged and the concentration of contaminants then it could be beneficial to install some form of preliminary treatment system. For example a simple sedimentation tank could remove a large fraction of the suspended solids in the effluent thus reducing the load and the cost. It is important to remember that treatment systems also need to be managed and require regular maintenance to ensure that they are operating correctly. Remember that in the above example, the sludge treatment and disposal costs will also need to be paid. It is therefore a question of whether the benefits of reducing the contaminant load and cost to discharge outweigh the additional maintenance and operational requirements as well as the initial capital costs of a preliminary treatment system. Package plant systems now include reasonably compact granular media filters or membrane systems which are capable of producing extremely high quality effluents which could be recovered and re-used on site thereby further saving water and discharge costs. Additionally, raw materials may be recoverable from specific systems which again may result in some cost benefit.

Trade effluent checklist

The following list comprises key points which should help manage trade effluent discharges however is not intended to be all encompassing:

• Check your discharge consent, is it current and valid for what you discharge?
• Ensure you have the contact details of the sewerage operator to hand in case of an emergency.
• Make sure you know exactly what is being discharged from each process on site.
• Keep accurate records of what has been discharged (volume and contents).
• Check these records against the discharge consent regularly.
• If any of the discharges breach or it is suspected could breach the consent then cease discharging immediately and contact the sewerage operator.
• Make sure all employees and contractors are aware of the protocol for discharging trade effluents - particularly those employees responsible for discharging tanks.
• Ensure that all designated effluent discharge points are clearly marked.
• Investigate the opportunities for saving water, reducing effluent and therefore costs.
• Never discharge any effluent whose composition you cannot be sure of regardless of the volume.
• Investigate the potential of preliminary treatment – could it save you money?

The Netregs website gives more information on trade effluent discharge consents.