Suspended growth wastewater treatment may be the most common form of biological wastewater treatment in use today, but it’s far from the most efficient. Here are some common side effects that you ought to be aware of when you’re considering investing in suspended growth wastewater treatment, and how attached growth systems (AGS) compare:
Large volume of sludge production
A shocking amount of sludge is produced using suspended growth wastewater treatment: On average, it generates 0.75 lbs. of solids per 1 lb. of BOD removed. That means a 1 MGD plant with 250 mg/L of BOD influent produces about 1,564 lbs. of sludge per day – or over a half million lbs. of sludge per year!
From waste-activated sludge pumping, digestion, thickening and storage to hauling, disposal and filing regulatory paperwork, sludge management is costly. According to the EPA, it represents 40 to 60 percent of the total budget for a wastewater treatment facility.
In order to maintain a large mass of microorganisms in the system, suspended growth plants need to return activated sludge that settles in the secondary clarifiers back to the aeration tank. This requires pumping and operational control which, in turn, requires energy, pump maintenance and close process monitoring.
How AGS compares: Why tolerate such high operational costs? Attached growth biofilm systems like the Nebula® MultiStage Biofilm System from Aquarius Technologies, can be designed to reduce sludge by up to 80%. Also, because microorganisms remain attached to the surface of the fixed media, no sludge return pumping is required, and microorganisms tend to slough off of the media in well-formed flocs and settle rapidly in the settling basin.
Frequent oversight required to adjust process parameters
With suspended growth systems, the operator must constantly be aware of conditions that could lead to poorly settling sludge or inadequate removal efficiencies. This requires constant monitoring of a number of parameters:
- The wastewater quality,
- The type and quantity of microorganisms in the aeration basin,
- The amount of dissolved oxygen in the aeration basin,
- The rate at which the biological solids settle and how well they compact, and
- Many other conditions.
To address system changes, the operator must adjust the amount of biological solids in the system, the amount of oxygen provided, the rate of return of biological solids from the clarifier to the aeration basin, and may have to make other process adjustments. All of these require operator attention and time.
In addition, activated sludge plants sometimes experience periods of poor performance due to poorly settling solids. During these times, the operator must take steps to respond that often involve even more intensely monitoring plant conditions.
In general, this type of biological wastewater treatment system requires additional energy, operational oversight and maintenance to produce the desired effluent quality. That adds up to higher operating costs
How AGS compares: Attached growth systems operate with little operator intervention and monitoring and generally use simple, low maintenance equipment. As a result, their operating costs are significantly lower than suspended growth treatment systems.
Inability to handle large increases in influent flow
Suspended growth systems are susceptible to performance deterioration due to hydraulic and organic load variations. Rapid flow increases may wash microorganisms out of the aeration tank at precisely the time that a high concentration of them is needed. Consequentially microorganisms being washed out of the system with the clarifier effluent, result in significantly reduced performance.
How AGS compares: Because the microorganisms are attached to the media in an attached growth biofilm system, they are not susceptible to wash out with increased flows. Also, attached growth biofilm systems typically have a greater mass of microorganisms, making them better able to handle organic load increases.
It’s time to stop wasting money
Attached growth biofilm systems offer numerous advantages that can help you reduce the operational costs and increase the efficiency of your wastewater treatment plants. Get answers to your questions: email us or call us at 262-268-1500.
