Date of Award

Spring 2026

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil & Environmental Engineering

Committee Director

Gary Schafran

Committee Member

Mujde Erten-Unal

Committee Member

Christopher Wilson

Abstract

This study evaluated post-aerobic digestion (PAD) with aeration, mixing, and divalent cation addition to improve phosphorus capture, dewaterability, and odor control in thermal hydrolysis process (THP)–treated anaerobic digestate at the Hampton Roads Sanitation District’s Atlantic Treatment Plant. A three-day PAD process was operated under constant air flow (5 LPM) and dissolved oxygen (DO)-setpoint (0.2 mg/L) aeration conditions with Ca(OH)₂ or Mg(OH)₂ dosing. Aeration and mixing alone increased polymer demand by 14–46 % relative to untreated influent, indicating enhanced extracellular polymeric substance release. Chemical conditioning partially mitigated this increase but did not restore polymer demand to baseline levels. Dewatered cake total solids remained near the influent average (29–30%), with minor improvements of up to 2.7 percentage points observed under certain calcium treatments. Overdosing magnesium beyond a 1:1 Mg:P molar ratio provided no additional benefit. Phosphorus removal was greatest under Mg(OH)₂ dosing under 0.2 mg/L DO-setpoint aeration, which reduced orthophosphate and total phosphorus in the filtrate by up to 88% and 86%, respectively. Ca(OH)₂ performed better under constant air flow compared to the 0.2 mg/L DO setpoint aeration setting, increasing total solids by 2% and retaining up to 92% of total phosphorus in the dewatered cake. Phosphorus capture was maximized near pH 8.5; lower and higher pH values reduced retention. Odor analysis showed that ammonia was the most abundant compound by concentration across all treatments, while methyl mercaptan exhibited the highest odor activity values and was the dominant contributor to overall odor perception. Aeration alone reduced total volatile sulfur compound (TVOSC) emissions, whereas the combination of aeration, mixing, and chemical addition increased them. These findings demonstrate that optimizing nutrient recovery, polymer consumption, and odor control in THP-treated biosolids requires balancing aeration intensity, mixing, and divalent-cation dose.

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DOI

https://doi.org/10.25777/xjdq-am75

ISBN

9798197809209

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