TALKS WITH TERRY – Restart Water Treatment Plants
Ugh, fine, so what about WTP’s? Are they as hard as an STP? Because that was a lot.
Actually no, WTP’s are way easier to start up than an STP; they’re actually made to be shut down without killing off part of the process since they’re by-and-large chemical and physical processes. (Click here to view the whole document: Restart Sewage Treatment Plants & Water Treatment Plants)
Oh good. So what do I need to look out for here?
So you should only have issues if you’ve had to shut your plant down for a long. If you’re running it making small batches of water once a week like we suggested in our previous advice then it should be fine, just make sure you have enough chemicals to run the plant at the higher rate.
Oh yeah, we had to turn our WTP off and leave it for the last 2 months… are we in trouble?
If you’ve had to shut your WTP down for a long time, it’s a good idea to check all of the Mechanical and Electrical equipment to make sure it’s going to run properly (as per the earlier tips on restarting
an STP from scratch). This includes your pumps, compressors, mixers, and valves (both actuated and manual). It’s never a good experience to start up your WTP just to have your dosing pumps spit acid all over the place.
Also, if you haven’t already, take the chance to do some maintenance. If you have a sand filter, check the sand; at the least, make sure it’s at the right level, if you can, take a core of the filter and make sure the layering is good (or do a bit of a dig down into the media).
Check your pumps and make sure all your pump seals and bearings are good, dismantle your dosing pumps and give them a clean and service.
If you have a clarifier, check its structure for signs of rust, check the gear box and mechanical equipment for the scraper drive if it has one. If you’ve got some time, drain it and check the internals.
Check all of your water quality sensors. Your sensors drive the process, control equipment, provide important information and are usually the first and most important warning when something goes seriously wrong. Many sensors can be prone to calibration drift, some don’t like to be dry. There is also the increased chance of fouling, either biological or chemical (e.g. scaling) for sensors that are normally used to seeing flow. Fouling can be especially bad on the raw water side, due to the dirtier nature of the water.
Amphoteric chlorine sensors can be especially prone to issues if they haven’t been stored properly during shut down, and since Chlorine is typically a Critical Control Point for your water treatment process, making sure your chlorine sensor works should be very high on your list of priorities. Even if it has been stored correctly, cross-check the reading using a sample and a DPD test to ensure it’s reading correctly. If you’re not sure about it, replace the membrane and service the sensor and check again. If even that doesn’t help, just replace the sensor, it’s better to deal with the cost of the sensor than the cost of a process failure.
Also check the sensors monitoring your other critical control points (e.g. filtered water turbidity) and ensure they work.
A sensor failure when you start can be a serious delay, especially if you have to source parts that have a four week lead time.
Basically, the better condition your gear is in when you go to start, the easier it’ll be to get going without random failures. Better to spend time now when you’re not being pressured to make water, than after plant start-up.
Right, so, is there anything else we should be watching out for?
Check your chemical dosing systems thoroughly, we mentioned the pumps, but if you have powered lime feeders, powdered activated carbon dosing systems, polymer make-up systems and ETC, check the feeders, hoppers and mixing tanks. This is especially important with materials that can go hard in storage, like Lime.
Re-check your raw water source. Do some jar testing to check and confirm your chemical dosing rates before you start-up. There’s a good chance your raw water hasn’t changed much since you shut down, but there’s always a risk, and a half-day of jar testing is cheaper than a day of lost production.
Okay, so, water’s tested, everything works, can we start now?
Hold up. If you can, it’s good to do a test run of your plant. Start it up and isolate your clear water storages, and direct the water to whatever water recovery circuit or discharge you use. It’s good to run it for a few hours, do a backwash, and put it through its cycles. Take samples and get them tested, this will give you confidence that you’re going to make good water when you start processing in earnest.
Anything else to do after startup?
Once you get your plant back online and working, you should also ensure that your reservoirs and storage tanks are clean and that your network is in good working order.
If your plant has been offline, clean and scour the reservoirs and flush them until you have an acceptable free-chlorine residual (typically a minimum of 0.5 mg/L, but this can be higher if your network has long branches) before you put them back online.
If you’ve been running at a reduced rate, and you’ve been following our advice, you should be checking and topping up your chlorine regularly, but check the free chlorine and pH in the reservoir again just to be sure. You may want to flush the reservoir anyway to ensure the water provided is fresh.
You should also ensure that any portions of the network that have been stagnant or unused are checked and scoured before they are used. This could be accommodation buildings in an un-used section, or offices and kitchenettes in a remote part of the network. Flush out any stagnant water and keep flushing until you get a free chlorine residual in the water. Aim for at least 0.1 – 0.2 mg/L at the furthest point in the network. Also check any critical use areas (kitchens, medical facilities) as well.
Okay, now you should be ready to start up your plants.
If you do need more help, please feel free to contact Simmonds & Bristow for more specalised advice.
For specific advice on your Sewage Treatment Plants or Water Treatment Plants, please contact us
Call 1800 620 690