Wastewater Treatment - Harstad

Harstad Sør RA is a new wastewater treatment plant (WWTP) located close to the city center in Harstad. The WWTP receives relatively diluted domestic wastewater from 8200 inhabitants from several pumping stations. In addition, it also receives septic and external sludge. The treatment requirement is primary treatment (>50 % suspended solids reduction and >20 % BOD5 reduction).

The process solution consists of an inlet pump station followed by a pre-treatment stage with mechanical step screens. Screenings are washed, compacted and transported to a container through a screw press followed by a shredder. The primary treatment technology applied at this WWTP is based on coagulation and flocculation using a cationic polymer followed by separation on rotating belt filters from Salsnes filter. The sludge is removed from the from the filtermesh by a scraper and high-pressure washing is used for automatic cleaning of the filtermesh. This compact technology only uses 1/10th of the land required for conventional sedimentation technologies. This makes rotating belt filters a very attractive solution in urban areas. Furthermore, this filtration technology is well proven and also very energy efficient.

The treatment efficiency at the WWTP is high and in average > 60 suspended solids and > 50 % BOD5 is removed. The sludge treatment consists of a sludge pumping systems, sludge storage tanks, polymer dosing, dewatering though a screw press and closed ventilated containers for dewatered sludge. The state-of-the-art screw press that dewaters the sludge to > 30% dry matter without addition of polymer, when polymer is added the dry matter concentration reach approximately 40 %.

The external sludge and septic reception system consists of a receiving trough for emptying a septic truck, a wash drum for removing coarse materials, a sludge pumping station, sand separator/washer and sludge storage tank. From the sludge storage tank external sludge is pumped to the primary treatment stage for further treatment. Primary treatment plant with belt filters and septic tank reception, total supplier process and electrical / automation: design, execution and process responsibility.