Lagoons are a popular method of wastewater treatment for smaller municipalities—they are energy-efficient, easy to operate, and low maintenance. However, when a lagoon system reaches capacity or underperforms, sometimes the immediate reaction is to replace it with a mechanical plant, with its high capital and construction costs, operational complexity, and more demanding maintenance.
It’s not necessary to undertake the hassle and expense of building a mechanical plant when an existing lagoon system is not providing sufficient treatment or requires expansion. Triplepoint’s innovative LRAS advanced lagoon treatment process can provide more treatment in the same footprint—more than quadrupling capacity in terms of both flow and influent loadings—while preserving the low cost and operational simplicity of an existing serviceable lagoon system.
The LRAS Solution
Triplepoint’s LRAS process is an innovative activated sludge/lagoon hybrid that facilitates the growth of a highly concentrated biological floc that consumes organic content at a faster rate. It was developed with the engineers and operators of Coopersville, MI, in response to their need to supercharge treatment in their existing lagoon system when a new dairy facility moved to town.
Case Study: Coopersville, MI
Coopersville is a small community in western Michigan that is home to approximately 5,000 residents. A rural town, it has for 25 years relied on its lagoon-based wastewater treatment system, chosen because of its low overhead requirements, ease of maintenance, and relatively simple and flexible operation. In 2011, a new dairy facility made plans to enter the Coopersville community.
This meant that in addition to increased hydraulic loadings, Coopersville’s lagoon operators could expect spikes in BOD from the typical residential levels of 250mg/L to anywhere from 600–2,000mg/L, with occasional, unpredictable “slugs” of up to 4,000mg/L. While the dairy would positively impact the Coopersville economy, they were facing a mandatory upgrade and expansion of their wastewater system. How could Coopersville leverage their effective lagoon system, yet accept the dairy processor’s wastewater without massive disruption and capital expense?
The engineers and operators knew that they needed a few things for certain in this municipal and dairy wastewater lagoon:
- Proper Mixing—The new dairy facility was going to be discharging massive amounts of BOD into Coopersville’s lagoons. Much of this would be in the form of solids; in order to avoid huge sludge buildup, there would have to be a complete-mix environment in the wastewater lagoon.
- Efficient Aeration—With huge, unpredictable swings in BOD a certainty, consistently high DO (dissolved oxygen) would be necessary. The aerators would need to run efficiently on typical days, yet be equipped to handle days when BOD levels reached 5x the usual amount.
- Rapid Digestion—To increase capacity while ensuring proper treatment, bacterial content in the lagoons would have to be high to consume organic content at a rapid rate.
- Retrievability—With such massive influent BOD levels, this system could not afford to be down for any amount of time. As a result, maintenance would need to be quick and occur without taking the whole system offline (i.e. draining).
- Cost Control—Estimates for replacing the existing lagoon system with a mechanical plant reached $15–18 million, accounting for the construction of aeration tanks that could handle BOD up to 4,000mg/L, and increased operations and maintenance expense.
LRAS advanced lagoon treatment
Triplepoint’s LRAS process built around MARS aeration meets all the criteria:
- Proper Mixing—Each MARS unit’s coarse bubble static tube creates a turbulent churning action that moves up to 7,000 gallons per minute.
- Efficient Aeration—MARS’ fine bubble diffusers surround the static tube, maximizing oxygen transfer efficiency (OTE) while minimizing energy consumption.
- Maximized Biological Floc—LRAS creates a potent mixed liquor that recirculates into the lagoon, increasing treatment levels.
- Retrievability—The MARS Aerator is self-weighted, portable, and equipped with a stainless steel tether and locator float. Individual units can easily be pulled to the surface when necessary for cleaning or maintenance without taking the lagoon offline.
- Cost-Effective—LRAS leverages an existing lagoon system, minimizing capital costs and mechanical equipment. And, due to MARS’ high airflow per unit and mixing capability, fewer diffusers are needed, reducing energy costs.
Moreover, the individual MARS units are connected to a single, centralized, on-shore blower, with no moving parts in the water—critical for cold Michigan winters, when submerged and surface aeration can freeze up and malfunction, halting treatment and creating a maintenance headache.
Coopersville reconfigured their lagoon system to incorporate the LRAS process, dividing one quiescent cell into two MARS aerated cells, each providing the complete-mix water column necessary to handle all the high incoming loads and RAS (Return Activated Sludge).
After aeration, a circular clarifier or dissolved air flotation system is used to separate the water from the solids. This both removes BOD and suspended solids in preparation for discharge, but also super-concentrates the organic waste with the bacteria, creating a mixed liquor which is then reintroduced into the aeration cell for treatment. The rate at which the solids accumulate depends on the amount of polymer used, allowing the operator to control the bacterial concentration.
Due to the volume of the lagoon and long sludge age, the LRAS system can easily handle slugs in loading and peak flow events. As a result, it’s not necessary to have a large crew of operators or to be on call 24/7—the LRAS is able to absorb the shock and continue to meet discharge requirements.
“We started up taking raw dairy waste since day one, and the system handled every bit without a violation. That’s phenomenal for a new activated sludge plant, and we still have not had a violation since startup,” boasts Coopersville’s chief operator, Steve Luke. “It eats up everything it takes in. It handles the unpredictable ‘slugs’ great,” he continues, “even with only one [of two] cell[s] in operation.”
Because the MARS aerators are portable, Coopersville never has to take the system offline for maintenance. “In an activated sludge plant, you have to drain the aeration cells for aerator maintenance…With the MARS, we just use a boat to clean the membranes or change them out when necessary; we never have to take the cell offline.”
“This plant runs on a staff of only three,” Steve explains. “If you’ve got a good treatment plant that runs excellently, that sure gives you a lot of extra time to do other jobs. People need to know that. This system isn’t a time stealer.”
Coopersville’s upgrade to LRAS Advanced Lagoon Treatment leveraged their existing lagoon system, allowing them to accept high BOD wastewater from a new dairy processing plant while minimizing capital and operational costs.