How to manage pH levels in trade waste
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Trade waste is released into our sewerage network. To make sure it’s safe for release, the pH levels must be balanced.
What is pH?
A pH level shows how acidic or alkaline a solution is. If a solution’s pH level is too high or too low it might be considered dangerous, and cannot be released into our sewerage network.
A pH of seven is neutral.
An acidic solution has a pH value below seven.
An alkaline solution has a pH level above seven.
We accept trade waste that has a pH value between six and ten.
You can find more information about our trade waste requirements in our Trade Waste Acceptance Criteria.
Why is pH important?
Trade waste with a pH level below six or above ten may present a risk to our sewerage network and the people who help to keep it running.
Risks to health and safety
If trade waste is too alkaline it may generate ammonia gas. Ammonia gas is poisonous if it is inhaled.
If trade waste is too acidic it releases hydrogen sulphide, which has a strong odour and is highly toxic.
We can’t accept trade waste with high levels of ammonia or sulphide, even if the trade waste’s pH levels are between six and ten. If this occurs, we will vary the Trade Waste Acceptance Criteria.
Risks to our sewer pipes
Acidic trade waste damages our sewer pipes. We regularly monitor our sewers to check for damage. We’ve seen through these checks that acidic trade waste causes corrosion to our pipes.
How do you correct the pH levels in your trade waste?
If the pH levels in your trade waste are too high or too low you will need to correct them. Trade waste pH levels must meet the acceptance criteria specified in your trade waste agreement.
Low flow trade waste
If you have a low trade waste flow there are two options available.
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Standard neutralisation tanks work for some smaller trade waste sites, like school laboratories. You’ll need to get in touch with us to see if this option is suitable for your trade waste.
You can use a batch tank to store trade waste and manually adjust its pH levels, before releasing it into a sewer. Batch tanks work for trade waste generated from activities that use strong acids or alkaline ingredients, like metal etching or radiator repairs.
Figure 1 shows a single probe set up, where the valve is closed until the tank’s pH level is correct. Each batch of trade waste is handled separately. You may need multiple batch tanks if there is waste constantly flowing into the batch tank. This means one batch of influent can be stored, while another batch is corrected.
High flow trade waste
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If your site has high volumes of trade waste you need to be able to continuously release it into the sewer network. A pH neutralisation system allows for continuous trade waste release and is the best option for most high volume trade waste sites.
A pH neutralisation system may include the following:
- A mixing tank, like an equalisation tank, with at least a 20-minute retention time.
- A way to ensure the contents of the mixing tank are well mixed and uniform. This can be done using. mechanical agitation, pump recirculation or air sparging.
- An instrument to measure the pH levels, like a pH probe.
- Acid and/or alkaline material, to neutralise the effluent.
- Chemical dosing pumps.
- A feedback controller (for automatic pH adjustment).
- A visible and audible alarm that notifies you when the pH levels are too high or too low.
- A separate pH probe to validate and record the pH levels prior to sewer discharge.
- A shut-off valve and a contingency plan for flow diversion.
- An online logging system that measures pH, flow and temperature data five minute intervals.
There are different types of trade waste sites that might need a pH neutralisation system, each with different requirements.
Contact a qualified technical specialist to help with the design and installation of your pH neutralisation system. You can find a list on our Industrial trade waste service providers page.
To ensure adequate mixing and pH correction is occurring in the mixed tank the effluent is tested in the test sump prior to being discharged to sewer. When pH is out of specification and effluent cannot be discharged to sewer the flow is diverted, either to another tank or back to the pH correction system’s influent, for additional neutralisation.
Figure 2: a standard pH neutralisation setup (for continuous flow)
Place pH probes in the well-mixed effluent. The effluent they are measuring should be the effluent that is going to be released into the sewer. There should always be a probe measuring the pH level of the effluent downstream of the pH neutralisation system.
Engage a qualified technical specialist to help you determine what the best set points are for your pH neutralisation system. As a guide, don’t program the set-points at exactly six or ten (the discharge limits) but rather with a safety margin. This will minimise the chance of effluent with non-compliant pH levels being released.
The correct safety margin depends on:
- the pH variability of the waste stream
- how effective the dosing chemicals are
- flow rates
- The agitation within the mixing tank.
An automatic diversion valve makes sure that non-compliant effluent isn’t accidentally released into the sewer. We may ask for this as part of your trade waste agreement.
It is recommended that the measured final pH values of the effluent be recorded on a regular basis, whether manually per batch or via an electronic data-logger at 5 minute intervals.
This will help:
- troubleshoot process problems
- identify opportunities for reducing the amount of pH adjustment chemicals you need
- identify where set-points should be.
Sometimes we ask you to log your data with us. This is specified in trade waste agreements.
There are many different types of industrial effluents. We recommend consulting a technical specialist for advice on what is best for your circumstances. Store all chemicals safely, according to their specific requirements.
