Get Full Government Meeting Transcripts, Videos, & Alerts Forever!
Get email alerts on the Wastewater Plant Operations topic
No spam. Unsubscribe anytime.
Spring Hill staff outline corrective plan for wastewater plant nitrogen and digester issues; technical fixes likely to be expensive
Summary
Staff reported improved nitrogen readings and recommended next steps after TN‑POP technical assistance, but said the converted digester is likely the bottleneck that will require design and capital work.
City staff told the Board of Mayor and Aldermen on Aug. 18 that operational changes and a state‑run optimization program (TN‑POP) have driven down nitrogen levels at the Spring Hill Water Reclamation Plant, but that solids handling and a converted digester will likely require major capital fixes.
Staff recapped a multi‑year sequence of problems and repairs: in 2023 new oxidation ditches were brought online and later required liners and other fixes; digester pumps failed in late 2023 and required extended repairs; the city later rented a belt press to remove excess sludge and has continued operational work. Jessica (wastewater staff) said the plant has seen a marked improvement in weekly nitrogen measurements: the last 12 weekly samples reported in the meeting were below the 4 mg/L target, and a recent influent/effluent comparison showed a drop from an influent number near 60 mg/L to an effluent near 0.879 mg/L in a sampling period—the staff described that as a meaningful operational improvement.
Staff explained, however, that the structure currently used as a digester was originally built as an oxidation ditch and was repurposed to save capital costs in an earlier expansion. The facility now holds a higher water column than a purpose‑built digester, which complicates solids decanting and consistent solids processing. That inconsistency affects centrifuge and dewatering equipment performance and increases the risk of bypasses.
Engineering staff presented two main paths for corrective work: (1) modify the existing structure to function as a plug‑flow activated sludge unit or add baffles and mixing upgrades as a lower‑cost retrofit, or (2) design and build a new purpose‑built anaerobic/aerobic digester and repurpose the existing structure back to its original oxidation role. The latter option would be more expensive but would give increased operational reliability and might allow staff to pursue a plant rerating that increases permitted capacity (discussed as up to a potential 7.5 MGD rating in planning documents), subject to detailed engineering and Tennessee Department of Environment and Conservation (TDEC) review.
Staff reported they have engaged TN‑POP (Tennessee Plant Optimization Program). TN‑POP teams performed a plant visit and provided operational recommendations; staff said those operational changes are a primary reason nitrogen results have improved. The next steps discussed with the board were: draft an updated technical memorandum describing digester options, send it to TDEC/TN‑POP for feedback, and issue an RFQ to assemble consultant capacity to design and implement the preferred option. Staff warned that major digester or structural work would be a multi‑million‑dollar project likely requiring capital budgeting and staged engineering.
Board members praised staff for operational progress while asking for additional detail on costs and sequencing. Staff said they will prepare the technical memo, pursue consultant contracts under a forthcoming RFQ program and return with options and cost estimates for the corrective action plan.
