This paper reports an exploratory study on the use of a sulfite-rich industrial effluent to enable the integration of a sulfite–sulfide–sulfate cycle to the conventional carbon and nitrogen cycles in wastewater treatment to achieve sludge minimization through the non-sludge-producing Sulfate reduction, Autotrophic denitriﬁcation and Nitriﬁcation Integrated (SANI) process. A laboratory-scale sulfite reduction reactor was set up for treating sulfite-rich synthetic wastewater simulating the wastewater from industrial flue gas desulfurization (FGD) units. The results indicated that the sulfite reduction reactor can be started up within 11 d, which was much faster than that using sulfate. Thiosulfate was found to be the major sulfite reduction intermediate, accounting for about 30% of the total reduced sulfur in the reactor effluent, which may enable additional footprint reduction of the autotrophic denitrification reactor in the SANI process. This study indicated that it was possible to make use of the FGD effluent for applying the FGD–SANI process in treating freshwater-based sewage.