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We study the effect of ultra-high energy particles collisions near the blackhole horizon (BSW effect) for two scenarios: when one of particle either (i)moves on a circular orbit or (ii) plunges from it towards the horizon. It isshown that such circular near-horizon orbits can exist for near-extremal blackholes only. This includes the innermost stable orbit (ISCO), marginally boundorbit (MBO) and photon one (PhO). We consider generic "dirty" rotating blackholes not specifying the metric and show that the energy in the centre of massframe has the universal scaling dependence on the surface gravity $\kappa $.Namely, $E_{c.m.}\sim \kappa ^{-n}$ where for the ISCO $n=1/3$ in case (i) or$n=1/2$ in case (ii). For the MBO and PhCO $n=1/2$ in both scenarios thatagrees with recent calculations of Harada and Kimura for the Kerr metric. Wealso generalize the Grib and Pavlov's observations made for the Kerr metric.The magnitude of the BSW effect on the location of collision has a somewhatparadoxical character: it is decreasing when approaching the horizon.

Circular orbits and acceleration of particles by near-extremal dirty rotating black holes: general approach