A recirculating cooling system includes a coolant sampling line, a deterministic lateral displacement (DLD) microfluidic separation device, a monitoring device, and an alert generation device. The coolant sampling line is in fluid communication with a recirculating coolant line, and the DLD microfluidic separation device receives a coolant sample diverted into the coolant sampling loop from the recirculating coolant line via the coolant sampling line. The DLD microfluidic separation device includes a separation array for separating bacteria into an output channel according to a size threshold. The monitoring device monitors a characteristic property of the coolant sampling loop for comparison to a threshold for bacterial growth in the recirculating cooling system. The alert generation device generates an alert to remediate the bacterial growth in the recirculating cooling system responsive to the characteristic property of the coolant sampling loop satisfying the threshold.