In-Situ Biosolids Reduction and Lagoon Capacity Recovery Using PrO₂ Oxygen Technology
Case Study Overview
1. Facility Background
The City of Hart BioPure Treatment Facility is located approximately one mile east of Hart, Michigan. The facility treats slightly over one million gallons per day (MGD) of wastewater. Approximately 98% of influent flow originates from two local vegetable processing facilities, resulting in seasonally elevated volatile suspended solids (VSS) loading.
Treatment is lagoon-based, with aeration provided by fine bubble diffusers. The North Aeration Basin has a nominal capacity of nine million gallons with a planned retention time of nine days. Waste activated sludge is directed to one of two sludge holding basins, each with an approximate capacity of four million gallons. Historically, accumulated biosolids have been hauled off-site and land applied.
2. Regulatory and Asset Context
The City has expressed concern regarding long-term reliance on land application of biosolids. In Michigan, transport and land application of biosolids is restricted during the first quarter of the year. Similar regulatory trends are emerging internationally.
The BioPure facility underwent significant capital upgrades during 2024–2025, including planning for an additional South Aeration Basin. In parallel, the City sought operational strategies to reduce accumulated biosolids and preserve existing lagoon assets.
3. PrO₂ Technology Overview
The Eden Lakes PrO₂ system is a leased, fully maintained oxygen delivery system. The system generates nearly pure oxygen and dissolves it under pressure into the water. Using this patented technology, the oxygen remains suspended, providing high oxygen transfer efficiency.
At Hart, a 5 GPM PrO₂ unit was deployed. The system required only an electrical connection (maximum draw approximately 57 amps) and a clean-water feed.
4. South Aeration Basin — Initial Deployment (April–May 2025)
The PrO₂ system was first deployed on April 29, 2025, in the South Aeration Basin. The basin has a nominal capacity of four million gallons. At the time of deployment, sludge depth was measured by facility staff to average approximately four feet, with the upper two feet consisting of loose sludge that thickened with depth. The basin had been filled in February and remained undisturbed prior to treatment.
Ongoing analysis of sludge characteristics was conducted during May.
After approximately one month of PrO₂ operation:
- Microscopic examination indicated minimal remaining biological activity
- Volatile Suspended Solids (VSS) measured approximately 7%
- Biochemical Oxygen Demand (BOD) levels were low
- Dissolved Oxygen (DO) increased from approximately 3 mg/L to 7 mg/L
5. North Aeration Basin — Energy and Solids Evaluation (May–July 2025)
Following completion of work in the South Aeration Basin, Eden Lakes proposed relocating the PrO₂ system to the North Aeration Basin, which receives incoming wastewater.
The objective of this deployment was to evaluate whether the PrO₂ system could reduce biomass and energy consumption under active aeration conditions. Applicators were installed on May 28, 2025.
During the evaluation period, the facility collected data on flow, Total Suspended Solids (TSS), VSS, and electricity consumption. Average electricity use increased by approximately 36% following PrO₂ deployment. Over the same period, influent TSS increased by approximately 87%, while flow remained relatively constant.
Despite increased loading and no sludge wasting during the period, basin biomass declined by approximately 2%. When normalized to energy use per pound of solids treated, the results indicate an estimated 27% reduction in energy consumption per unit of solids.
Due to construction activities, the PrO₂ system was shut down on July 1, 2025.
6. East Sludge Holding Basin (August–September 2025)
On August 15, 2025, treatment began in the East Sludge Holding Basin. At the start of treatment, TSS was estimated at approximately 9,000 mg/L, with a volatile fraction of approximately 70%. Due to limited biological activity, additional microbiology was introduced.
Treatment continued until September 2, 2025. The final recorded TSS was approximately 195 mg/L. No biosolids were hauled off-site during this period. Following treatment, the decision was made to relocate the PrO₂ system to the West Sludge Holding Basin.
7. West Sludge Holding Basin (September–November 2025)
On September 2, Eden Lakes deployed the PrO₂ system in the West Lagoon.
At the time of installation, the lagoon surface was fully covered by a thick sludge layer.
September 2, 2025 — Initial Conditions
- Dissolved oxygen (DO): 0.19 mg/L
- Odor and physical sludge characteristics consistent with septic conditions
- Manual movement through sludge was difficult due to density
- Initial laboratory testing measured Volatile Suspended Solids (VSS) at 23,500 mg/L
- 2.35% VSS in the lagoon
Due to the extremely high solids loading and low dissolved oxygen at startup, Eden Lakes introduced additional microbiology one week after deployment to support biological activity.
Following startup, odor conditions improved rapidly, with odors dissipating within approximately one week. Over the course of the treatment period, basin conditions continued improvement in surface water quality.
After 35 days, staff were able to decant 1 MG million gallons of water from the lagoon.
October 7, 2025 — Ongoing Treatment
Treatment in the West Lagoon continued through November 19, representing a total treatment window of 78 days.
An additional 1 MG were decanted.
Final VSS testing measured 6,350 mg/L, reflecting a net reduction of 17,150 mg/L across the basin.
Using the West Lagoon volume of 4,000,000 gallons (15,141,643 liters) and the observed change in VSS concentration, the mass of biosolids destroyed during this period was calculated to be approximately 571,500 lbs (259,179 kg) of organic biosolids (as VSS).
This represents an average biosolids destruction rate of approximately 7,330 lbs/day (3,323 kg/day) over the 78-day treatment window.
During this treatment period, no biosolids were hauled off-site, and the lagoon condition improved substantially based on direct operator observation.
“In practical terms, the West Lagoon transitioned from septic, sludge-blanketed conditions to a significantly improved operating condition while destroying an estimated 571,500 lbs (259,179 kg) of biosolids (as VSS) with no hauling required.”
8. North Aeration Basin — Winter Redeployment (December 2025)
On December 12, 2025, the PrO₂ system was redeployed in the North Aeration Basin. During this period, industrial flows decrease and municipal flows comprise a larger proportion of influent. At the time of redeployment, approximately half of the fine bubble diffusers were turned off.
The objective of this phase is to evaluate the ability of the PrO₂ system to digest solids while the basin remains in active operation under winter conditions.
9. Cost and Asset Implications
Across sludge holding basin deployments, the total cost to recover approximately two million gallons of lagoon capacity was approximately $50,000, equating to an effective cost of approximately $0.025 per gallon.
Historical liquid biosolids hauling costs were approximately $0.07 per gallon, excluding permitting and mobilization.
Given the high initial volatile solids content, organic biosolids mass reduction is believed to exceed volumetric reduction, with inorganic residuals remaining in the basins.
10. Conclusions
The staged deployment of the PrO₂ system across multiple basins at the City of Hart BioPure Treatment Facility demonstrates how targeted oxygen nanobubble delivery can be used as an operational tool to manage biosolids, recover lagoon capacity, and defer capital expansion.
All operational decisions remained under the authority of City staff, and outcomes reflect site-specific conditions and collaborative evaluation.
Confirmation of West Lagoon Findings (January 7, 2026)
To confirm the findings from the lab test, Paul and one of the operators sludge judged the West Lagoon by drilling through the ice in 45 locations and confirmed that the amount of sludge left in the lagoon was 0.65%, down from 2.35% on September 2.
Waiting for the ice to be thick enough to work on, the PrO₂ had been out of the West Lagoon for a month at the time the readings were taken. The lagoon had been isolated from the start of September and through the entire process.
Schedule an Evaluation
- Location: City of Hart BioPure Wastewater Treatment Facility (Michigan, USA)
- Prepared by: Mark Weise