Relatively short, non-motile filaments (10-20 µm). Irregularly bent filaments with true branching and cell septa without constrictions. Branched mycelium is often observed on this filament. Cells are irregular (1.0 x 1.0-2.0 µm). Filaments are found within the floc structure causing open, lacy, diffuse floc or free in the bulk solution. The filament staining is strongly Gram positive and Neisser negative with Neisser positive granules observed frequently. Short clear spaces may occur in the filament. Usually easy to identify due to its staining characteristics and branching. Intracellular PHB granules frequently observed. No sulfur granules. No attached growth or sheath present. It is the most common cause of foaming, not bulking. Causes floating sludge.

Microthrix parvicella lacks the branching that Nocardia  ( NALO or GALO) has, although it is similar.

( NALO Nocardia amarae-like organisms or GALO Gordona amarae like organisms)

This filament is usually found in environments where there low F/M (0.08-0.35 lbs BOD) and with a long MCRT (10-40 days). High wastewater grease, oil and fat content may also be a cause. Found more commonly in the warmer temperatures.

Reducing sludge age helps. If possible increase grease and fat control on the influent if applicable. Use of a selector helps control filamentous growth. Antifoams usually are needed to physically control the foam initially or water sprays with chlorine.

Nocordia ranks 1st in number of predominance. Common in over 50% of sludge.

Various types of Nocardia exist with different appearances

Nocardia pinensis appears in clusters with a typical "pine tree-like" branching effect with many open, long, individual branches.

Nocardia amarae appears as short fragments of right angled branches in varying lengths.