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This article states that for plate settlers, "an effective spacing is about 0.3 m, but no optimization studies are known to have been published." It also claims that plate settlers make no difference, or disrupt the system, which is contrary to what we have seen in the lab.
4. Sarkar, Sudipto, Dibyendu Kamilya, and B.C. Mal. "Effect of geometric and process variables on the." Water Research 41 (2007): 993-1000.
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5. "Tube Settler Systems for Clarification." Welcome to Brentwood Industries. 15 Apr. 2009 <http://www.brentwood-ind.com/water/tubesystems_main.html>
Brentwood Industries explains why the effluent quality is greatly improved out of sedimentation tanks when tube settlers are present.