Optimization phosphate removal and sludge dewatering Harnaschpolder wwtp

Wastewater Treatment, Energy Factory, Energy & Nutrient Factory, Innovation / new techniques

At Harnaschpolder wwtp phosphate is predominately biologically removed through luxury uptake by Phosphorus Accumulating Organisms (PAOs). These micro-organisms store phosphate within their cells under aerobic conditions as energy-rich polyphosphate granules, along with magnesium, calcium and potassium cations. Under anaerobic conditions at the sludge digestion, polyphosphate and cations are released again. To optimise sludge dewatering and phosphate removal at Harnaschpolder wwtp, Magnesium Hydroxide is added to the digested sludge buffer. Ammonium and phosphate will react with this Magnesium Hydroxide to struvite (MagnesiumAmmoniumPhosphate). This is a full-scale research: all the digested sludge at Harnaschpolder wwtp is treated. The main positive benefits of dosing Magnesium Hydroxide are a more efficient phosphate removal process and an improved sludge dewaterability.


Through Magnesium Hydroxide dosage and optimized control of the dewatering centrifuges, a significant improvement in dewatering results is achieved in the first year of this full-scale research:
- The dry matter content of the dewatered sludge increased by 2% ds content
- The use of dewatering polymer dosage decreased by 20%
- The Phosphorus load returned to head of works is negligible and this is beneficial for the biological Phosphorus removal process. - The Phosphorus effluent quality remained constant, while 55% less Iron Chloride is added to meet the legal phosphorus effluent quality requirements.
- The environmental impact of the phosphate removal and sludge treatment including digestion, dewatering, transport and incineration is reduced by circa 35%

Start of Research
July 2015

End of Research
December 2017

- Mirabella Mulder
- Paul Weij
- Richard Bonte


- Delfluent Services BV
- Delfland Water Authority
- Mirabella Mulder Waste Water Management


Mirabella Mulder
[email protected]