Moving from conventional to THP digestion has achieved yields of 2.3-MW of green electricity and 85% energy independence

THP at Seafield Wastewater Treatment Works

When Scottish Water’s existing thermal dryers for biosolids treatment at the Seafield Wastewater Treatment Works (WwTW) were no longer the best economic, or environmental answer, our team was there to help.

Our team collaborated with Veolia on a solution to install a two-train system using the Cambi™ modular thermal hydrolysis process (THP) B6 process, two steam boilers, and associated equipment—designed for 100 tons dry solids of sludge a day. This process pasteurizes the leftover solids from wastewater treatment, including diverting the indigenous sludge to the new pre-thickener centrifuges. From there, the thickened sludge is transferred to a buffer silo. Once complete, energy recovery is amplified, and the 99.99% pathogen kill enables the diversion of the sludge from landfill and instead be used in agriculture.

Strict time limits for when each of the six digesters could be offline drove our team’s strategy of combining an aggressive ramp-up rate and conversion from conventional to THP. The digestion process was replicated and hydrolyzed in lab tests using sludge from Seafield to optimize the digester commissioning phase. The promising results from the testing allowed for an accelerated progression to full scale and confidence in the system to meet the performance guarantees.