The present study considered the use of a by-product from winemaking for the treatment of wastewater from hemp retting process. To evaluate if different obtained extracts of grape marc (BRE-extract of refrigerated grape marc, BUE-extract of dried grape marc, BLE-extracted of lyophilised grape marc, BLM-ultrasound soaked lyophilised grape marc, BLM fUS-soaked lyophilised grape marc, no ultrasound treatment) are feasible to be used for the wastewater treatment. The chosen parameters (pH, turbidity, dissolved oxygen and conductivity) were monitored over 14 days and it was observed that starting with day 8 the measured values for all parameters remained constant.