Zack is a Vice President and Client Services Leader for CDM Smith, Inc. in their Nashville and Memphis, Tennessee offices managing all projects and operations in middle and western Tennessee, north Alabama and Arkansas. Zack earned his bachelor’s and master’s degrees in Civil Engineering from The University of Memphis and has over 20 years of experience in stormwater, water, wastewater and solid waste projects.

Zack is active in the KY-TN sections of AWWA and CWP having previously served in numerous leadership roles including Section Chair for AWWA in 2013-2014 and as the Section Director on the Association Board of Directors from 2019 - 2022. Zack is also a member of the Alabama-Mississippi Section of AWWA.

In 2018, construction began on an expansion project at Franklin WRF to increase capacity from 12- to 16-mgd and produce Class A Biosolids as part of the City’s sustainable long-term approach to biosolids management. The existing solids treatment and disposal consisted of an aging dissolved air flotation (DAF) thickening and belt filter press (BFP) dewatering process, followed by transport of unclassified solids via truck to a landfill requiring a roundtrip of over 100 miles away multiple times a day.

With the goal of producing Class A biosolids, a Cambi thermal hydrolysis process (THP) was installed as the centerpiece of the biosolids system expansion. Solids processing upgrades at the facility also include sludge screening, pre-dewatering centrifuges, anaerobic digestion, post-dewatering screw presses, biogas treatment, and a biogas-fueled combined heat and power (CHP) system. Provisions for future facilities to receive, store and handle fat, oil, and grease (FOG) from local restaurants are included, as addition of FOG to the anaerobic digesters is expected to enhance biogas production. The facility layout also includes space for the future construction of solar dryers. CDM Smith actively participated in startup and commissioning activities with the City and the Contractor. Startup began in 2022 and proceeded sequentially through the treatment process through the Spring of 2023.

One of the first steps for solids startup was commissioning of the pre-dewatering centrifuges to ensure a consistent solids product can be fed to the THP system. One of the two digesters at Franklin was seeded with Class A biosolids from another THP plant prior to introduction of thermally hydrolyzed solids generated at Franklin. The seed sludge is anticipated to be rehydrated and heated during commissioning of the digester mixing and recirculation systems. Upon completion of digester seeding, pre-dewatered sludge can be fed to the THP system and commissioning of thermal hydrolysis can commence. Once the THP system successfully demonstrates performance, the post-dewatering screw presses are to be commissioned, fed from the digesters.

During commissioning activities, biogas production will increase as thermally hydrolyzed solids are introduced to the digester. Digester kinetics and volatile solids reduction will be monitored during startup. The produced biogas will be used in an on-site 800-kW CHP system for power and heat production. Heat from CHP, in the form of steam, will be continuously used by the THP system while the power produced is expected to be equivalent to the electrical usage of approximately 500 average homes.

This presentation will discuss the overall approach to commissioning and startup of one of the first THP projects in the region, as well as lessons learned to date from the process. Performance data will be presented from commissioning activities for digester loading, THP performance, dewatering solids handling, and biogas production.

THP is a relatively new biosolids management technology, and only a few THP units are under operation across America. Experiences and lessons learned from one of CDM Smith’s comparable size projects in Pontiac, Michigan that has been under operation since 2020 were used to improve the startup experience of the Franklin WRF biosolids handling unit. Some of the highlights, similarities, and differences from these two projects will be presented.