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Effluent Flow Distribution: New Developments.

Any approved waste water percolation area is designed to work well provided that hydraulic distribution of the effluent over the area is uniform.  Part of this would be the assumption that distribution over the percolation pipes via a distribution box is even, as long as the box is 'installed with care to achieve a level position' (2009 EPA Code of Practice: Waste Water Treatment Systems for Single Houses). This would mean that these systems are heavily reliant on accurate installation. Off-level installation and moving soil are known as obvious contributors to a poor performancoany waste watetreatmensystem. 

Another known facithaevedistributioaloflow, whicitypicafor domestisystems, idifficult to achieve.Thiiconfirmed by researccarrieout aTrinitCollege Dubli(Gill2005 anPatel:2008)Typicall70% ofheffluencominfrothseptitanwould enter a distributioboaflolowetha0.litrepeminuteThinfluencothwatersurfactensioicombinatiowititsurfacmovement and otheuncontrollablvariable(e.g.a bur opipe odepositioodirt) wilhavstroninfluencothe routfotheffluent.

New Test Result

An Environmental Sciencstudenfrom ISligo recently dedicated hithesion thimatter. A tesrig, resembling a typicaresidential wastwatetreatmensystem,was built tfacilitate hiresearch. He found, quitremarkablythaslightly higheelevated outletin a standard distributiobo(due to tolerancesmay well receivmoreffluenthathloweelevated outletsSe'Test 1' ifigurbelow.Outlets '1'and'6appeareapprox. 1mm. higher elevated thaoutlets '2'and'4'.



closelooathesfindings showethat alight changof slope of a connected discharge pipe played a rather unexpecterole. On thdistributioboxhtiltethentry opipe 2 slightly downwards (without affecting the elevationand thflow decreased. Outlets 4 and 5 wertilted to a slightlmorhorizontal positioand thflowincreased. Se'Test 2' ifigure below. Thesfindings mighindicate whyover thyears,many peoplhavbeefailing to make a percolatiofield woreffectively.


Available solutions


Thstudenalstested a numbeocommerciallavailablsolutionfrocompanies that obviously acknowledge the problewith a common distributioboxThtesregimthat was useis based upoEN12566, representing a typical dailloaoapproximately 600 litresAccesothtesfacility was considereexcellenantherefornot typicallrepresentintrue practicithfield,whicalloweeversolutiotbfitteanadjusted in a highly accuratmanner.Tests were performed witthsystems tilteundevarious angles to replicatfield situations.



Adjustable Weirs

Adjustable weirs are cheap and easy to fit and their function is based on adjusting the outlet elevation. Despite accurate procedures however, all these solutions performed inconsistently. It was also found in all cases that at a slight 1° tilt of the distribution box, a number of the connected discharge pipes received no flow. It seems that these adjustable weirs may only provide some solution when a distribution box in the field is significantly tilted and that after fitting these weirs, the box should be frequently monitored.


 2 Tipping Bucket Mechanism

An alternative solution that was put to the test was a pre-manufactured sample of a 'Tipping Bucket'. This unit is designed to deal with the sensitivity of distributing low flows. It collects a relatively large amount of effluent (approx. 0.7 l.) from the septic tank in one of the two sections of a tray-like tipping container that is placed on top of a hinge. When a certain point of unbalance is reached, the tray suddenly tips and discharges the full amount from that section into the outlets on one side of the distribution box.  At this point, the other section of the tray starts filling and the process repeats itself, approx. 800 times per day.  During  the  tests  it  was  found  that  despite  the  robust principle, substantial amounts of effluent found its way into non-designated outlets after every discharge, particularly when the unit was tilted under a slight angle. This however was considered to be a matter of optimising the geometry.


 3 EffluenFloSplitter

This solution is based on yet another distribution principle. A prototype was made available to IT Sligo for testing. In this system the effluent is guided towards the centre of a convex shaped surface on which it subsequently spreads and runs into separate chambers.

Most remarkable fact was that even at 3° tilt, the unit distributed extremely uniform and consistent. Its compactness and simplicity seem to make it diverse applicable and it would be easy to retro- fit it into any existing manhole. Maintenance and cleaning seems an easy job.



Alternativsolutions enterinthmarketlike the tipping buckeanflosplitteraran indicatiothaconstructive progresicurrentlbeing made ithe fieloeffluendistribution devices.



Frothreview, icoulbconcludethat distributiobaseoleveelevatiooinvert(i.e. a straighforward distribution box,with or without adjustersis principallflawed,performs poorlaninconsistentlanneeds tbabandoned, especially when better alternatives are available.