Methods and systems for treating an aqueous effluent from a metathesis reactor, such as a metathesis-based biorefinery, are generally disclosed. In some embodiments, the aqueous effluent is generated from washing the metathesized product with an aqueous medium. In some embodiments, such wash streams are chemically treated to reduce their toxicity and to facilitate disposal. In some embodiments, such wash streams are treated to recover at least a portion of the catalyst residue, so as to facilitate catalyst recovery.