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Wastewater municipality saves $35 million with one-step nitrification/de-nitrification

The Problem

Trinity River Authority, TX (162MGD) needed an optimal nutrient removal strategy for a planned significant expansion in capacity. Assuming a standard two-step nitrification/de-nitrification process, the budgeted capital cost was $50 million.

The Solution

Under the guidance of Leon Downing, PhD, PE, a Consulting Engineer and Northwestern University, McCormick School of Engineering, a one-step nitrification/de-nitrification process was validated over five years by gradually reducing dissolved oxygen (DO) levels to a super low setpoint. Microbe Detectives next generation DNA analysis and other test methods were used to measure changes in the ecology and validate results.

Hypothesis: As we adopt lower aeration operation, ecology will shift and nutrient removal capacity will not be be decreased.

Action: Gradually progressed from 2.0 mg/l to 0.2 mg/l dissolved oxygen (DO) operating conditions over 5 years in 4 aeration basins.

Result: Commamox (CMX) bacteria was validated to emerge and become the primary “workhorse” delivering an improvement in nutrient removal at a super low DO setpoint with a one-step nitrification/de-nitrification process.


Basin Design Savings: $35 million

Pre-study $50 million estimated
Post-study $15 million actual cost

Operating Savings: $490,000/year

$350,000/year aeration savings
$140,000/year chlorine savings

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