Rapid Digester Start-up for the Lower Reedy WRF Anaerobic Digesters - Taking a Last-Minute Detour

Renewable Water (ReWa) operates a number of treatment facilities in the upstate region of South Carolina. The Lower Reedy WRF facility consists of primary and secondary treatment and has used anaerobic digestion for residuals stabilization for approximately two decades. The existing anaerobic digestion facility consisted of a single digester tank of approximately 1.5 million gallons volume and did not have any a process redundancy. ReWa recently undertook a capital project to construct a new second anaerobic digester tank at the facility to provide process redundancy and provide additional capacity to handle increased residuals production from the treatment facility. The new anaerobic digestion tankage has an operating volume of approximately 1.5 million gallons volume and consists of a post-tensioned concrete tan with a fixed concrete dome cover and linear motion style mixing. The new digestion complex also includes a new digester control house, hot water boiler and digester heating system, membrane digester gas storage facilities and a new enclosed waste digester gas flare. Future work, Phase II with design currently underway, includes rehabilitation of the existing digester complex to extend operating life and improve digester heating and mixing systems. However, late in the construction phase as start-up and commissioning activities for the new facility were nearing completion the existing digester experienced a process failure and had to be removed from digestion service. This process failure resulted in the inability to seed the new digester from the existing on-site digester using an indigenous sludge seed. As a result, the start-up and commissioning team, consisting of representatives from ReWa, the construction contractor, and the design engineer had to make a 'last-minute detour' from the initial start-up plan and import anaerobically digested seed sludge from another ReWa facility. The team was able to rapidly pivot to an imported seed sludge approach and develop a new start-up plan, including revised process control monitoring and measurement tools, to successfully start the anaerobic digestion facilities and restore on-site stabilization activities. The new digester seeding plan utilized approximately 525,000 gallons of imported seed sludge from the ReWA Mauldin Road WRF and represented a total imported seed mass of approximately 250,000 pounds total solids. Seeding was accomplished over a period twelve (12) days from 04/05/2021 to 04/16/2021. During seeding activities, the digester was also fed some indigenous primary and secondary seed sludge from the Lower Reedy WRF. After sixteen (16) days on 04/20/2021 the digester reached its full operating volume and began to overflow and was able to receive 100% of the indigenous Lower Reedy volume and mass and off-site management of these materials was able to cease. Included as figures are the following: Figure 1 & Digester Total and Volatile Suspended Solids Figure 2 & Digester In-Tank VSS/TSS Fraction Figure 3 & Digester In-Tank pH Figure 4 & Digester In-Tank sVFA/sALK Ratio Figure 5 & Digester Daily Feed Volume