Inclusion of an anaerobic selector to a plant configuration not only contributes to
biological phosphorus removal, but also forms big and heavy flocs with excellent
settleability (Metcalf & Eddy, 2003). A review paper referring to UCT and Α2Ν
method comparison states that UCT systems reduce excess sludge production,
whereas in warm climates, such as the Greek one, they are more efficient than the
Α2Ν systems (Hao et al., 2001). Furthermore, recent experimental results confirmed
the suggestion that nitrous oxide is produced by PHA-driven denitrification in
activated sludge processes (e.g. A2N) (Meyer et al., 2005). However, a comparative
study of the herein presented system and a two-sludge system could actually give
more efficient information. Therefore, such experiments are conducted currently in
our laboratory