The resulting blend can yield a blend in all proportion from 1/99 PBI/PEKK to 99/1 PBI/PEKK.

Should reactors be of complete mix type they are required to have at least two differentiated aerobic zones and two differentiated anoxic zones.

Method using an apparatus for wastewater treatment are disclosed.

This system produces the necessary turbulence to ensure that the contents of the pot are completely mixed, as well as providing concentrations of dissolved oxygen greater than 2 mg/l.

The light emitter (15) can be formed as an integral mixture of light-emitting materials and insulating materials or as separate layers of light-emitting and insulating materials.

In the composition, the carbon black serving as a conductivity imparter has been surface-treated with the ingredients (E) and (F) by the integral blending method.

The header pipe (34) may connect with a plurality of a floating air supply laterals (36) which float on the surface of the wastewater contained in a complex mix zone (28).

The gap region is made narrow to prevent the formation of vortices that tend to entrain input materials in isolated regions and thus prevent their thorough mixing with each other.

The copolymer can be polymerized continuously by using a polymerization apparatus comprising a completely-mixing reactor and a piston-flow-type reactor connected in series, and then granulated.