Fume scrubbers are generally built in one of two arrangements:
Counter flow or vertical like the unit pictured on the left and cross flow or horizontal like the scrubber pictured on the right.
Both are PVC construction although the vertical unit has a polypropylene sump. Materials can be any weldable thermoplastic that is compatible with fumes being scrubbed. Many options are available to help your scrubber perform to its fullest capability including sump level controls, pH controls, automatic blowdown, differential pressure indicators and more.