Specifications
7.4 Maintenance and Cleaning
7.4.1 Maintenance
The membranes should be checked during their operation continuously by the operator, particularly
if sustained use results in an increase of pressure drop or a change to a coarse bubble pattern. The
latter leads to a distinct reduction of the oxygen transfer rate, because only a slight part of the perfo-
rated membrane excessively blows. Diffusers should be cleaned from deposits (carbonates, iron and
aluminium salts, biological slimes, …) in regular based periods, described by operating instructions.
The build-up of such deposits depends on waste and the special operating conditions of the waste
water treatment plant.
After the switching off and draining the aeration basin or the pulling up of the retractable aerator
grid consider that sludge deposits on the membranes do not dry and cure. Dried deposits impair the
function of the diffuser in further operation.
7.4.2 Mechanical Cleaning
The recommended cleaning procedure of biological deposits is to physically dislodge the growth
either through gently brushing the substance off or using a high pressure water jet cleaner
1)
. A dis-
tance of about 50 cm should be kept between membrane and nozzle in order to avoid damage to
the membrane through a too sharp jet of water.
During phosphorus precipitation pure Al-sulphate and Fe-sulphate do not attack the membrane mate-
rial chemically. However isolated strong-sticking deposits can occur, which can be removed in the
initial stage with a high pressure water jet cleaner.
7.4.3 Chemical Cleaning / OSHA Regulation MSDS
2)
The common method for chemical cleaning of carbonate scaling is the metering of formic acid to the
air stream. This process can be carried out without basin draining.
Depending on the degree of soiling concentrated formic acid (85 vol. %) should be added twice a
year with a commercial grade metering pump into the air stream. Adjust maximum air flow rate per
diffuser and add within one hour about 100 cm
3
/ 3.4 fl. oz. formic acid per diffuser. To remove the
formic acid subsequently from the system, flush at least 2 hours at unchanged air flow rate.
The exact amount and proportion depend on the degree of soiling, composition of the waste water
as well as the operating conditions and can only be determined by means of appropriate tests.
Pipings, valves and connectors must be acid-resistant.
The use of chemical cleaning agents and additives is not allowed and results in the loss of guaran-
tee.
1)
Follow safety guidelines of manufacturer of pressure-washer.
2)
Formic acid is dangerous and can cause severe injuries and death. Professional equipment and specially trained
personel required. Follow all safety instructions with the use of formic acid.
