1. A fluid processing apparatus, comprising:a fluid inlet tube, N column bed units in parallel connection, and a fluid outlet tube;
each column bed unit containing a crystallization promoting medium (CPM) as a fluid processing medium for processing the fluid flowing therein;
said N column bed units are all in fluid communication with the fluid inlet tube;
wherein N is an integer greater than 1, and except a first one of the column bed units, each column bed unit is provided with one check valve upstream thereof in an inflow direction, each check valve being designed to open and close under a specific fluid pressure;
wherein when a total number of the check valves is two or more, at least two check valves have different opening pressure thresholds and different closing pressure thresholds from each other;
wherein the CPM is a medium having nucleation sites of an atomic size on its surface which promote formation of crystals of a substance, when the substance dissolved in a fluid flows through the CPM, the substance is to form a crystal and grow at the nucleation sites, when the crystal grows to a certain size, the crystal is flushed off by the fluid to release reusable nucleation sites.