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.

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