Goal: By integrating vacuum degassing before mechanical dewatering, struvite can be specifically precipitated to reduce GHG emissions and improve the dewatering result.

The objectives of P-recycling from the sludgeliquor of sewage sludge and the operation of sludge dewatering leads to a conflict of interests. The main target of sludge dewatering is to reach optimal dewatering results due to high disposal costs. High concentrations of dissolved phosphate have a negative effect on the dewaterability of sewage sludge, but are necessary for phosphorus recycling. Also struvite precipitates in the centrate water pipes with a high phosphate level in the sewage sludge. The high pressure inside modern dewatering decanters dissolves more CO₂ into the sludge and pH value of the sludge inside the bowl decreases. Laboratory tests showed that the Mg²⁺ concentration in the sludge liquor increases as pH decreases. Upon relaxation to ambient pressure after centrifugation, CO₂ is stripped out, causing the pH to rise and leading to struvite precipitation.

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Through targeted crystallization tests, KBKopp can determine the optimal operating point based on temperature and magnesium and calcium concentrations, enabling trouble-free dewatering.
Incorporating vacuum degassing allows for the targeted precipitation of SP before mechanical dewatering. Thisprocess reduces GHG emissions and improves dewatering efficiency.

Source: KB Kopp

KBKopp can conduct preliminary tests and providesupport for large-scale trials.