Core clogging of BIOFOR and chemical soda wash
asked 4 September 2015 asked by Tonino (2580 points)
Hello, for washing protocol: We put the filter in "manual" mode. We stop the wash pumps; from then on we do a dry weather by-pass. For intermediate lifting, we have to limit the flow. We check that the filter is isolated, i.e., influent valve closed, scour air stopped, and wash water inlet closed. We can then open the manual drain valve located in the inspection window at the level of ‘technical Biofor DN gallery’. Here we have to be careful that the level of the waste water tank is as low as possible. We can then measure the level of Biolite in the filter and record it on the Biofor DN follow-up chart. Then once draining is completed, we close the manual drain valve to prevent the wastewater tank from supplying the biofilter WASHING strainers - Biofor in "manual”. Inject 600 liters of soda into a corner of the biofilter to limit its spread. Injection of sodium hydroxide is done via a previously filled vat mounted high so the product moves gravitationally towards the filter. The injection pipe must be installed and locked on a corner of the filter so as not to move and to ensure the minimum amount of Biolite is washed (to preserve the maximum amount of biofilm). Open the raw water inlet valve and let it reach a height as close as possible to 80 cm (0.08 bar) of water. The water level sensor is located forty centimeters below the floor. When it indicates zero, that means we have forty centimeters of water below the floor. Unscrew the drain on the water level sensor to check the supply of water in the biofilter. When the water level sensor indicates 0.08 bar pressure, we shut off the water supply. We should have about 70 m3 of water. We perform a ten minute backwash to mix the soda and water. The backwash send air below the biofilter in order to decompact the filter layer. In the electrical cabinets “post biology” that house the biofilter PLCs, we change the set point of the booster to 12Hz min and 14Hz max in order to get a flow rate of 1200 m3/h. Once the backwash is completed, we reset the booster to the original values. We check that the other boosters are stopped. The principle of backwash is as follows: when using the booster for decompacting, it is in "manual" mode, degassing valve 1 is closed, and valve 2 is open. We start up the booster to achieve a “scour air” flow of 1200m3/h. We let it sit for a few days (a weekend is about right) We complete two backwashes, ten minutes each, during the day with the settings modified as before. (morning and evening) The changing pH must be monitored. If it approaches neutral, that indicates over-consumption of soda, so we have to add more. Resumption of Biofor DN Open the manual drain valve after checking the height of the wastewater water tank, i.e. wastewater tank empty and pumps stopped. Check the pH, particularly in the wastewater tanks. Fill with water at least twice, each time followed by manual flushing. Recheck the pH; if less than 8.5 turn wastewater pumps back on. Perform a wash sequence; pay attention to foaming during washing. Anticipate a hosing down or a de-foamer. If foaming is too great, discharge the foam into the wastewater tank. Then, a maturation must be performed. It involves passing a flow of effluent through the filter. Once filtered, the effluent is collected in the wastewater tank to then get processed by the wastewater channels. The point of maturation is to galvanize the bacteria, that is to say, to ready it to treat the effluent. Under supervision shift from the "auto" mode to "operating mode". Note the different values found in the BIOFORS follow-up file, that is to say the level of the filter material, changes in the pH during the soda wash, head loss and drainage time when flushing performed before and after washing.