Protecting Infrastructure and Reuse Reliability: Integrated Adaptive Plan for Odor, Corrosion, and UVT

Presentation Description: The City of Modesto operates a 20 MGD two-plant treatment system, with primary treatment at the Sutter Plant and secondary/tertiary treatment at the Jennings Plant. In recent years, the City has faced escalating odor complaints near Sutter, severe hydrogen sulfide (H₂S)-driven corrosion at Jennings, and seasonal ultraviolet transmittance (UVT) drops that jeopardize recycled water compliance. This study integrated field investigations, bench testing, and technology evaluations to develop an adaptive, tiered plan addressing all three challenges concurrently.
Comprehensive monitoring in four major trunk sewers and both plants quantified sulfide mass loads, confirmed two major trunks as dominant contributors (>80% of load to Sutter), and documented extreme H₂S levels at Jennings—averaging over 100 ppm and peaking above 700 ppm at fine screens. UVT declines were found to coincide with seasonal blending of high-BOD, low-pH cannery wastewater with domestic flows, introducing lignins, tannins, and potentially UV-absorbing artificial sweeteners. LC-MS confirmed the presence of five sweeteners in UV influent, though their individual impacts remain to be quantified.
A broad suite of odor/corrosion control options was screened against technical, operational, cost, and UVT-risk criteria. Chemicals with potential toxic by-products or proven UVT impairment were eliminated. Life-cycle analysis showed pure oxygen injection to be 3–6x less costly than chemical dosing for major trunk applications, with nanobubble oxygenation offering potential dual benefits for odor suppression and UVT improvement.
Bench-scale ECO₂ oxygenation tests validated rapid, complete dissolved sulfide removal within 30 minutes and confirmed low oxygen uptake rates, supporting conservative system sizing. The recommended adaptive plan applies a tiered approach: (1) immediate oxygen injection installation at Woodland and Thousand Oaks lift stations; (2) Sutter biofilter optimization, and nanobubble pilot testing; (3) targeted force main treatment via nanobubbles, oxygen injection, or nitrate dosing; and (4) end-of-line H₂S capture at Jennings via biotrickling filters.
Parallel UVT mitigation tiers included reverse blending to isolate cannery flows, nanobubble piloting, targeted compound source characterization, and long-term industrial source control via pretreatment or sewer-use by-laws. This integrated, data-driven strategy enables Modesto to phase investments, respond adaptively to performance data, and meet both odor/corrosion and recycled water reliability goals within operational and financial constraints.