The high performance of non-free Fe in the electro-Fenton system has been rarely reported. Herein, such performance was observed using rod-shaped erdite for PMS activation in an electric field. Erdite was synthesised at 90 °C with the direct recycling of waste waterwork sludge. It had one-dimensional structure of the (FeS2)nn– group and was spontaneously hydrolysed in neutral water to release Fe/S-bearing colloid, but it contributed to the removal of 1.5 % p-nitrophenol only. The erdite hydrolysis was inhibited in the electric field but continued by adding PMS. Free radicals of •OH and SO4•− were generated. The removal efficiency of p-nitrophenol increased to 44.6 % by adding erdite/PMS and to 98.7 % in the presence of erdite/PMS in the electric filed, which was more than two times of the electro-Fenton reaction with ferrous halite or pyrite. Less than 25 mg/L free Fe was released into water by adding erdite, but 180 mg/L of that was released by adding ferrous halite. Thus, non-free Fe played a key role to activate PMS in three steps: (1) the involvement of structural Fe to ferric Fe by PMS activation; (2) the enhanced attachment of ferric Fe as non-free Fe on colloid/erdite in the electric field; (3) the reduction of ferric Fe into ferrous Fe by adjacent S in colloid/erdite. The Tafel and open-circuit voltage tests showed that the electric field stabilised the (FeS2)nn– group to terminate the hydrolysis of Fe-S bond and accelerated the attachment and the reduction of ferric Fe as the erdite hydrolysis continued by PMS. In summary, electric field and structural S of Fe/S-bearing colloid had synergistic effect on the cycling of non-free Fe2+/Fe3+ for enhancing PMS activation.