Performance of a continuous stirred tank reactor with immobilized denitrifiers and methanogens

Abstract

Water denitrification by a coimmobilized mixed culture of denitrifiers and methanogens to simultaneously remove nitrate and excessive carbon source, methanol, in a continuous stirred tank reactor was investigated. Complete denitrification occurred at a methanol to nitrate nitrogen (M:N) ratio of ≥2.62. Ratios beyond 2.62 methane formation took place resulting in the depletion of excess methanol. The quality of the effluent solution was found to be markedly dependent on nitrate loading. At a constant M:N ratio ∼3.2, a complete nitrate and methanol removal could be attained when the influent nitrate concentration was <385 mg N/L; otherwise, the hydraulic retention time (HRT) was operated >2 hr (at a constant influent nitrate around 100 mg N/L). The surplus methanol was verified to be converted directly into methane when complete denitrification was achieved. Moreover, a sufficient correlation was found between the biological activity and the redox potential.