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I see in a previous posting by Darragh he queried when WWTU are tested in the various European test centres there must have come a point at which the BOD/SS/NH4N exceeded the IRL required parameters.
Q) What happened in this instance?
Q) Were the systems desludged during the test?
Q) If a manufacturer sent a small unit to be tested surely it was desludged more often?
I was recently talking to a process engineer for one of Irelands lagest wastewater manufacturers and I asked him how ofter do I need to clean out my seconday wastewater treatment unit.
This was his response to the various questions:
The test requirements in some countries only allow for 4 results above the target standard, and as you say when the plant becomes full of sludge it needs to be de-sludged. Problem for manufacturers is the sewage strength coming in is a bit variable, so if the test requires BOD of say, 400mg/l then the test house draws the feed with higher sludge content and the plant fills up quickly. The first the manufacturer knows is when the solids in the effluent go up, and by the time he has a result he may well have two over the limit before it can be de-sludged. De-sludgeing during the test isn’t a problem as long as it is put in the report.
The German requirements specify specific volumes in each compartment.
Most 6 PE plants will run for 12 months on normal loadings, single house roughly 3-4 PE, so if loaded at 6 PE they may well need to be de-sludged after 8 months.
Bottom line is, when the unit is full of sludge it will need to be de-sludged.
I'm assuming that the whole issue of desludging and maintaing systems is going to be a costly exercise given the new Water Services Ammendment.
Perhaps before homeowners purcahse wastewater systems they should check off the manufacturer how often the system they are selling needs to be desludged! |
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