Bio-Dredging: Cost-Saving Sludge Digestion For Lagoons

By Chip Bettle, Co‐Inventor & Executive Vice President of Engineering, Absolute Aeration, LLC

The City of Royston is a town located in Northeast Georgia operating a wastewater treatment plant that is comprised of a two‐pond (lagoon) system.

James “Butch” Watson, the city’s water/wastewater superintendent, was challenged to drive down the costs of future dredge events and prevent additional damage that may occur to their liner during a dredge.

In 2011 Absolute Aeration LLC, creators of the Blue Frog patented technology, approached the City of Royston’s leadership team to be the first municipal application in Georgia to install revolutionary technology that utilizes natural processes that enhances in situ sludge digestion (bio-dredging).

Absolute Aeration LLC is an environmental technology firm that utilizes proven natural processes to treat wastewater. Documented results support enhancing natural biological processes as a realistic opportunity to increase the effective treatment capacity of an existing lagoon system and meet effluent discharge criteria while driving down the costs of sludge management. Our design strategy provides cost-­effective solutions for lagoon owners to meet discharge standards at a significantly lower investment cost.

Wastewater treatment lagoons are the oldest and most commonly used methods for treating wastewater. Traditional methods to remove biosolids (sludge) from lagoons is typically accomplished by adding chemicals or by mechanical dredging, a disruptive and costly process that can cause damage to infrastructure such as liners, and to the environment. Disposal methods such as application onto farmland or landfilling are running into increased regulatory restrictions and public concerns about what’s contained in the biosolids (sludge). Excessive build‐up of sludge can potentially intensify odors and increase effluent concentrations of BOD, TSS, nutrients like ammonia, and pathogens.

The City of Royston, Georgia Background
The first pond in the Royston treatment system was a well‐mixed aerated system; the second pond has three cells; the first cell was a sludge accumulation cell, the second cell was utilized for stabilization, followed by chlorination and discharge (third cell). All permit requirements were routinely met. Sludge was dredged from the second pond cell once every 3 to 5 years at a cost of $150,000.00 per event. A previous dredging event damaged the liner, costing $125,000.00 to repair (cost is for the repair‐damaged area only).

The Science behind Blue Frog Technology to Bio-dredge In Situ
Absolute Aeration has discovered methods to apply established biochemical science that translates into reliable operating processes for wastewater treatment – moving beyond pilot studies to extensive field testing, and scaling up to practical systems.

The Blue Frog System (BFS) mimics natural bodies of water, keeping the water in three distinct layers employing a three‐step process:

Step One:
Select for Indigenous sludge digesting bacteria.

• Shear helps Nature form a dense, spherical biofilm ("biogranule") that turns solids into gas at the base of the water column.

Step Two:
The surface is aerated to convert soluble BOD into insoluble BOD.

• Fresh biosolids sink to the bottom‐dwelling biogranules for conversion to gas.

Step Three:
Clean, thin surface water is redirected to the bottom of the water column to reject floating solids like blue green algae.

• Sinking solids are digested in situ at the bottom of the clarifier process.
• Clarified water is aerated, chlorinated, and discharged.

Documented Results in Royston:

The City of Royston’s 6-­month average results ending in June 2014:

Pollutant	Results (mg/l)	Monthly Permit Requirements (mg/l)
BOD	20	30
TSS	20	90
Ammonia	8.3	17.4
Residual Sludge	1.5’(4” of dense biogranules + 14” of low density fluff)

 

Google earth picture prior 2011	Google earth picture after 2012

There were five significant issues uncovered and resolved during the project implementation:

1. Sludge digestion (bio-dredging) is at a controlled rate, slow and steady, not fast.

• Sludge digestion is a multi-­step, choreographed natural process with a stinky intermediate step (volatile fatty acids (VFA)).
• The waste from one step is the food for the next step. When one step is faster than the next, the system is no longer in equilibrium. A corollary to this rule is: " If the system stinks, the odor goes directly to the mayor's office".

The issue was resolved by changing the rotation of the Cell 1 circulators to slow the process down.

2. Sludge reduction was normal in Pond 2 Cell 1, but not in Cell 2.

• When the liner was damaged, a dam was built around the Pond 2 Cell 1 inlet and the pond was lowered to make the repair. The temporary dam was not removed.
• The bacterial selector in Pond 2 Cell 1 was unknowingly placed directly over the temporary dam. Selected bacteria could not escape and colonize Cell2.
• The issue was resolved by installing a 20ft pipe to transfer Cell 1 water outside the dam area and then relocate the bacterial selector to the new transfer point.

3. An industrial client discharged potent antibacterial cleaning compounds all at once. Pond 1 turned black and died.

• The issue was resolved by pumping water from Pond 2 Cell 1 to Pond 1 for 12 hours to re‐inoculate

4. As ancient sludge is turned to gas, previously entombed trash is released.

• Downstream pump strainers require periodic cleaning to eliminate fouling.
• The issue is resolved by periodically cleaning the screen until the trash inventory passed through the system.
• The pump/screen was rebuilt to pivot around the center of gravity to make the cleaning process effortless.

5. Oxygen addition improved when rising bubbles are released into horizontally radial‐outflowing water.

• The issue was resolved by relocating aeration hose outside the circulator. Bubbles rise into horizontal, diverging flow lines, turning each bubble 90° and separating one bubble from the next to minimize coalescence.

A joint development for wastewater technology requires three key commitments:

1. A city’s water/wastewater superintendent and a city’s leadership team that is committed to promoting sustainability that results in reducing over-­all costs.

2. Two‐way communication and data sharing to understand and be proactive to resolving the issue before a crisis occurs.

3. A continued partnership that results in minimizing ongoing costs long-‐term to achieve project objectives.

About the author: Chip Bettle is Co‐Inventor & Executive Vice President of Engineering for Absolute Aeration, LLC, Greeley, CO, USA. Chip is a chemical engineer who utilizes his unique perspective, straddling both science and engineering, to lead Absolute Aeration in process development. Chip designs complex, low cost solutions to meet regulated discharge requirements. As an inventor he has over 35 approved U.S. patents.

For further information, contact Brandi Waters, Absolute Aeration Customer Service Manager at (386) 233.5074 or email: brandi@bluefrogsystem.net.