Sidestream treatment - WWTP Hengelo

WWTP Hengelo
Hengelo, The Netherlands

NAS-ONE® volume:  3.300 m3


Influent flow: 850 m3/day


Nitrogen load: 1,500 kg N/day


Removal efficiencies: 80% TN, 90% NH4-N

Nitrogen removal

Sludge processing optimisation

The Vechtstromen Water Board has converted the Hengelo WWTP into an energy plant, which produces the energy required by the wastewater treatment plant and powers another 3,500 households on top. To make the treatment plant energy-positive, sludge processing was optimised. Sludge processing consists of thermal hydrolysis (TH) pre-treatment followed by mesophilic sludge digestion.

NAS-ONE® sub-stream treatment

The wastewater (reject water) of the energy plant contains such high levels of nitrogen due to the breakdown of sewage sludge that it cannot be treated according to the regular water treatment process. Colsen installed a NAS-ONE® sub-stream treatment system (UAV-GC) at Hengelo WWTP after it was granted the European tender for “Sub-stream treatment at Hengelo WWTP” in December 2016.

NAS ONE Hengelo

Applied technology

The NAS-ONE® reactor at Hengelo WWTP treats reject water from a TH system, resulting in a greater COD and higher TSS pollutant load. Together, these factors disqualify standard anammox systems,

but thanks to advanced aeration control and extensive sludge selection methods in the NAS-ONE® reactor, this reject water can still be treated efficiently with anammox. NAS-ONE® technology can cut operating costs by 40% compared to conventional nitrogen removal methods, contributing to the overall cost and energy-efficiency of the energy plant.

Would you like to know more?
Ask Robin !

Robin Jordaens , Technologist / Process Engineer