Improving stability of anaerobic biological reactors using composite ion exchangers

Abstract

Instability in anaerobic biological processes is caused primarily by the inhibition of methanogens due to (i) the buildup of volatile acids and a consequent reduction in pH under BOD overloading and (ii) heavy metal contamination of the feed. A three-year long study confirmed that the process stability can be greatly improved by retaining composite ion exchangers (CIX) within the anaerobic reactors. CIX is a polymeric ion exchanger with imino-diacetate functional group and thus can buffer the pH and arrest cationic heavy metals. Because of its cloth-like texture and thin-sheet morphology, CIX is compatible in a biological medium with a high solids content. After three years of operation, CIX did not foul and retained its original exchange capacity. Use of CIX in anaerobic bioreactors is particularly attractive for high-strength biological wastewater where unforeseen fluctuations in feed compositions are rather common.