When chemical phosphorus removal, how to add the right agent?
The most commonly used agents for chemical phosphorus removal are iron and aluminum salts, and iron and aluminum ions can react with phosphate to produce precipitates.
Pharmaceuticals
Aluminum salts will generally use aluminum sulfate or polymeric aluminum chloride, iron salts generally use polymeric ferric sulfate
Polymeric aluminum chloride, polymeric ferric sulfate, aluminum sulfate, medicine are good
Where to use the drug
The drug can be added to the primary sedimentation tank, before the wastewater into the biological section to deal with the phosphorus, this dosing method is called pre-dosing, the tank needs to install the agitator in order to let the drug and wastewater fully mixed.
Pre-dosing can reduce the total phosphorus content in the biological section, and the phosphorus removal agent is also basically a flocculant, so the pre-sedimentation can help reduce the biological section treatment load, but the agent itself will have a lot of impact on the biological section, it will affect the pH, and iron salts will also make the filler in the biofilter produce yellow rust.
The agent can also be added to the aeration tank effluent or secondary sedimentation tank inlet water, directly acting on the biological section, this dosing method is called synchronous dosing.
Synchronous dosing has less impact on the sludge and can help the mud-water separation in the secondary sedimentation tank, which is currently used in most wastewater plants.
It is also possible to make a separate tank for dosing after the secondary sedimentation tank and separate it from the biological section, this way is called post-dosing. The post-dosing area is generally called the depth treatment unit, where other operations can be performed in addition to adding phosphorus removal chemicals, which is more costly, but has no effect on the biological section.
How much medicine to use
As you can already see in the chemical formula written at the beginning, the treatment of
1 mol of phosphorus requires 1 mol of iron or aluminum salt.
But there is a gap between theory and practice, iron and aluminum salts are usually used as flocculants, because iron and aluminum ions will react with the OH in the sewage to form a flocculent precipitation.
Phosphorus and OH to grab metal ions, the addition of drugs may not add more, usually calculated by 1 mol phosphorus injection 1.5 mol aluminum salt or iron salt.
Then convert the moles into mass units to get that 2.7g of iron ions or 1.3g of aluminum ions are needed to treat 1g of phosphorus, and then calculate the mass of the required agent by the chemical formula of the agent composition.
The most critical thing to calculate the amount of drug used is to know how much phosphorus to be removed, there are two formulas to help calculate, because the amount of water in each wastewater plant is different, the phosphorus in the formula is calculated according to the concentration, otherwise the right number.
Phosphorus that needs to be removed with about agent
PPrec=PEST-PER
The above formula applies to the completed sewage plant, but also need to add phosphorus removal drug must be because the biological section can not get, the amount of drug used depends on the gap of the excess, how much excess with how much.
PPrec =PIAT- PER-PBM- PBioP
This formula is applicable to wastewater plants in the design stage, the actual fighting power of the sludge in the biological section is not known, and both PBM and PBioP need to be estimated based on the influent BOD5 concentration.