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v. Third-person singular simple present indicative form of unfix.

"However, when discharged phosphorus and nitrogen compounds reach levels in the receiving waters that do cause eutrophication, further treatment, the so-called tertiary treatment, which "unfixes" the bound nitrogen in the waste (at great expense) by transforming it through denitrification to nitrogen gas, becomes necessary."

unfixed    unfixes    unfixing   

unsettle    dissolve    unfasten    loose    detach