A modular plasma treatment system has interchangeable and easily accessible inner and outer electrodes that concentrically nest within an outer housing of one or more plasma reformers. The inner and outer electrodes have self-centering features that allow for blind-fitting of the interchangeable inner and outer electrodes during electrode replacement and maintenance. A plurality of reformers that generate different types of plasmas are preferably arranged serially to allow for a mixture of separate plasmas within the same reaction area and to increase utilization of short-lived radicals.