diff --git a/watertap/unit_models/anaerobic_digester.py b/watertap/unit_models/anaerobic_digester.py
index 9e028d4557..748791478e 100644
--- a/watertap/unit_models/anaerobic_digester.py
+++ b/watertap/unit_models/anaerobic_digester.py
@@ -67,7 +67,7 @@
 from idaes.core.util.constants import Constants
 from idaes.core.util.exceptions import ConfigurationError, InitializationError
 from idaes.core.util.tables import create_stream_table_dataframe
-from idaes.core.scaling import CustomScalerBase, ConstraintScalingScheme
+from idaes.core.scaling import CustomScalerBase
 
 from watertap.costing.unit_models.anaerobic_digester import cost_anaerobic_digester