Effect of limited aeration on the thermophilic anaerobic treatment of high-sulfate refractory wastewater

A thermophilic up-flow anaerobic sludge blanket (UASB) reactor was used to treat high-sulfate refractory wastewater from a sulfite pulp mill. The microorganisms were inhibited significantly as the result of sulfate reduction. Based on the consideration that the limited aeration may strip hydrogen sulfide out and oxidize part of the sulfide into nontoxic elemental sulfur, limited aeration was introduced into the reactor later to reduce the inhibition. The reactor showed much better running stability and higher treatment capacity thereafter. COD removal increased from 40%~50% to 60%~70% when the organic loading rate (OLR) was doubled. This study verified that some methanogens could be aerotolerant while some of the fermentation bacteria might be sensitive to the incomplete anaerobic surroundings.