Hydrotech completes demonstration plant at Bioretur’s Stord smolt wastewater site


Hydrotech - Veolia Water Technologies completes demonstration plant at Bioretur’s Stord smolt wastewater site

In the Spring of 2023, Hydrotech - Veolia Water Technologies completed a demonstration plant of their Nutri-pack™ technology at a Bioretur’s smolt wastewater site in Stord, Norway.  The aim of the project was to validate the use of the new Nutri-pack smart controller for wastewater treatment of salmon smolt. Results showed better than expected reduction of Total Suspended Solids (TSS) and nutrients and validated that the smart controller functions as intended in this environment.

Hydrotech’s Nutri-pack is a product designed to chemically pre-treat water before filtration with a drum filter. Water from the fish farm flows through a two-step process: coagulation followed by polymer flocculation. The water treatment process has been used in wastewater treatment at municipal and industrial sites for about 20 years. The new smart controller uses instruments to minimize chemical dosing. This has two advantages: it lowers the consumption of chemicals and it prevents the filter from clogging due to chemical carry-over.


The test period covered a typical cycle of smolt growth. Feed water quality varied over this cycle with the concentration of TSS increasing from 230 - 2467 mg-TSS/l, phosphorus from 5,3 - 29,4 mg-TP/l and nitrogen from 11,0 - 50,9 mg-TN/l. This is important because it demonstrates the performance of the equipment in different conditions and gives key insight into sizing considerations of the system - specifically how large the filtration system needs to be and how often the system needs to be cleaned. The average reduction performance is described in the table below with an image of the feed, filtrate and sludge. It should be noted that for greater TN reduction, Hydrotech works together with its sister Veolia company - AnoxKaldnes.

Lab tests have shown that the total nitrogen concentration in water from this site can be reduced by > 90%.

  • TSS reduced (avg.) by 98%
  • TP by 97%
  • TN by 56%.

The smart controller demonstrated the robustness of this solution, as shown in the graph below. The three horizontal lines are outlet turbidity setpoints (5, 10 and 20 NTU) and the data “NTU, eff” is the actual outlet turbidity. The precision is impressive due to the high volatility in the feed turbidity “NTU, in”. This performance is important to site operators because it significantly reduces the risk of non-compliance and the need for operator intervention.

Bioretur Graph

With the backdrop of impending changes to the water discharge limits from land-based fish farms, this demonstration project gives insight into the value of state-of-the-art wastewater technology.

Read more about the Hydrotech Nutri-pack solution for Aquaculture here!