Harstad Wastewater Treatment Plant

In response to the space and efficiency demands of urban wastewater treatment, Inrigo delivered a compact, high-performance solution for Harstad Sør RA—serving approximately 8,200 inhabitants and processing both domestic wastewater and external sludge.

The facility required primary treatment, with a focus on removing suspended solids and reducing BOD₅ (biochemical oxygen demand). Conventional sedimentation would have required substantial land area—a challenge in an urban setting. Inrigo’s answer: a smart, space-saving design using rotating belt filters from Salsnes Filter, reducing the footprint by 90% compared to traditional methods.

Treatment Process Overview

1. Inlet & Pre-treatment
   Wastewater enters the plant through a pump station and is directed through mechanical step screens to remove coarse debris.
2. Coagulation & Flocculation
   A cationic polymer is added to promote flocculation—causing fine particles to aggregate into larger flocs.
3. Filtration
   The pre-treated water is filtered through rotating belt filters, which capture suspended solids while allowing clarified water to pass through.
4. Sludge Handling & Cleaning
   Captured sludge is scraped from the filter mesh, which is automatically cleaned using high-pressure washing—ensuring consistent performance.

Performance Results

• >60% removal of suspended solids
• >50% reduction in BOD₅
• Significantly reduced space requirements (1/10th of conventional systems)

Advanced Sludge Treatment

Inrigo also engineered and delivered a high-efficiency sludge management system:

• Screw Press Dewatering
  Achieves over 30% dry solids without polymer and up to ~40% with polymer, optimizing sludge volume and handling.
• External Sludge Reception Unit
  Dedicated system for receiving and processing septic and external sludge, including screening and preparation for dewatering.