Treatment Plants for Phosphorus Removal from Wastewater
We see that if the adsorption of phosphorus was the only possibility, the plant would
only be able to function for about a year. Due to precipitation the time of operation is
normally much longer.
10.5. Operation of plants for phosphorus
removal
In this section only operational problems in connection with chemical precipitation
will be discussed as our operational experience is mainly obtained from such plants.
Operational problems will be discussed under the following headings:
a.
Safety problems.
b.
Mechanical and measuring problems.
c.
Process problems.
a. Safety problems
The precipitants are either moderately strong acids, such as Fe+++, Fe++ and AI+++ or,
in respect of Ca(OH}z/CaO, relatively strong bases. Therefore the chemicals should
be handled with caution in due respect of the danger of eyes and skin effects. For
hydrated lime, Ca(OH)z, and unhydrated lime, CaO, it further applies that the
powdered substances may give severe dust problems. To safeguard against dust
problems, closed dosing systems should be used.
b. Mechanical and measuring problems
Corrosion may be a problem when using iron and aluminium salts. Plastics are
suitable materials for pipes and containers. Furthermore, clogging problems should
be observed. Precipitants are technical grade products with a certain content of
insoluble material. These materials tend to clog pipe bends, valves etc. Besides, the
insoluble material may cause damaging wear in pumps. Aluminium sulphate, for
example, contains aluminium oxides which are excellent grinding agents.
In chemical precipitation systems, the measuring of pH is essential for the process
monitoring and/ or control. Here it should be observed that the coating of the pH
electrode may lead to erroneous measurements and hence erroneous closings.
Coating problems are also found when for example measuring conductivity, turbidity, oxygen, etc.
c. Process problems
Process problems are here understood as problems in complying with the effluent
requirements for phosphorus. In this respect it is important to distinguish between
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We see that if the adsorption of phosphorus was the only possibility, the plant would
only be able to function for about a year. Due to precipitation the time of operation is
normally much longer.
10.5. Operation of plants for phosphorus
removal
In this section only operational problems in connection with chemical precipitation
will be discussed as our operational experience is mainly obtained from such plants.
Operational problems will be discussed under the following headings:
a.
Safety problems.
b.
Mechanical and measuring problems.
c.
Process problems.
a. Safety problems
The precipitants are either moderately strong acids, such as Fe+++, Fe++ and AI+++ or,
in respect of Ca(OH}z/CaO, relatively strong bases. Therefore the chemicals should
be handled with caution in due respect of the danger of eyes and skin effects. For
hydrated lime, Ca(OH)z, and unhydrated lime, CaO, it further applies that the
powdered substances may give severe dust problems. To safeguard against dust
problems, closed dosing systems should be used.
b. Mechanical and measuring problems
Corrosion may be a problem when using iron and aluminium salts. Plastics are
suitable materials for pipes and containers. Furthermore, clogging problems should
be observed. Precipitants are technical grade products with a certain content of
insoluble material. These materials tend to clog pipe bends, valves etc. Besides, the
insoluble material may cause damaging wear in pumps. Aluminium sulphate, for
example, contains aluminium oxides which are excellent grinding agents.
In chemical precipitation systems, the measuring of pH is essential for the process
monitoring and/ or control. Here it should be observed that the coating of the pH
electrode may lead to erroneous measurements and hence erroneous closings.
Coating problems are also found when for example measuring conductivity, turbidity, oxygen, etc.
c. Process problems
Process problems are here understood as problems in complying with the effluent
requirements for phosphorus. In this respect it is important to distinguish between
346