What Is Tertiary Wastewater Treatment, and How Does It Work?
By: Tom Frankel
Post Date: December 2nd 2020
In secondary wastewater treatment, moving bed biofilm reactor (MBBR) media systems provide high-quality, low-cost, and low-maintenance solutions. With various media types to choose from, though, knowing the right MBBR media specification for a given wastewater treatment tank can be a challenge. The guide below will explain what the MBBR process is, discuss MBBR floating media in detail and elaborate on how to choose between different MBBR media types.
Table Of Contents
- What Is the Purpose of MBBR Media?
- What Are the Types of MBBR Media?
- How to Select the Right MBBR Media
- Competitive Comparison
- MBBR Media Calculation
- SSI Aeration Has the Best MBBR Media in the Industry
What Is the Purpose of MBBR Media?
What is MBBR technology in sewage treatment plants (STPs), and what purpose do MBBR media carriers serve?
A bed of MBBR media generally consists of thousands of tiny pieces that suspend themselves throughout a wastewater treatment tank, typically taking up about 50% to 70% of the available space. Their design makes them optimal for hosting beneficial bacteria and promoting their growth. Many types of MBBR media resemble wheel-shaped pasta, with the spokes of the wheel providing valuable surface area for bacterial growth. Others are thin, coin-shaped discs or squares.
MBBR media carriers are ideal for use in aeration tanks. They disperse throughout the tank, and their bacteria help decompose the solid waste. The media are so effective because their design gives them a tremendous amount of surface area for beneficial microorganisms to settle on, so they help increase the number of bacteria available to digest waste.
How do the MBBR media carriers work? In an aeration tank, the tiny MBBR pieces disperse throughout the wastewater, and their tremendous surface area provides a hospitable environment for microorganism growth. The biofilm that grows on the media then decomposes the waste in the tank.
Diffusers send oxygen into the tank to promote continuous microorganism growth, and a mesh sieve in the tank helps keep the media carriers from flowing away with the wastewater. MBBR media carriers have a density similar to that of water, so they mix well with the wastewater to promote consistent waste digestion.
Using MBBR media is particularly advantageous because the tiny pieces take up minimal space, are easy to maintain and digest waste efficiently. The microorganisms on the media can also automatically adjust to changes in the amount and type of waste in the water. Although MBBR systems require some monitoring, they are largely self-sufficient.
What Are the Types of MBBR Media?
Below are a few of the different MBBR media types:
- Sponge-type carriers: Sponge-type MBBR media carriers have high mechanical strength, a high specific surface area, and a rough surface texture optimal for biofilms to take hold on. Their spongy materials are incredibly flexible, though they tend to wear down more easily than other types.
- Chip-type carriers: Chip-type carriers are thin and have a high concentration of fine pores. They are flexible as well, and they offer robust resistance to wear and tear.
- Coin-shaped carriers: Thin, coin-shaped media carriers provide the advantage that wastewater can filter into them from either side of the media, so they are minimally susceptible to fouling. Some thin chip-type media carriers are coin-shaped.
- Tube-shaped carriers: Long, narrow tube-shaped carriers offer an extended MBBR media surface area for microorganism growth. Their shape also helps them suspend evenly within the water column instead of stacking on top of one another. Because of their hollow forms, though, they can sometimes become susceptible to fouling.
How to Select the Right MBBR Media
To select the correct MBBR media for your wastewater applications, you’ll want to consider a few different factors:
Media Surface Area
Adequate surface area is necessary to facilitate microorganism growth. Media surface area sometimes correlates with biodegradation rates, but other factors can affect biodegradation as well, so the correlation is not a perfect one.
In general, a wastewater treatment plant should maximize media surface area while still making sure the media carriers meet the facility’s needs in their other characteristics. MBBR media carriers in the shape of spoked wheels, for example, offer a tremendous surface area for their size to help a plant meet its waste digestion needs.
Performance and Required Biodegradation Rates
Optimal performance and biodegradation rates are critical for helping a plant move wastewater through secondary treatment quickly and efficiently. Performance and biodegradation rates often rise with increased media surface area. They also depend on factors like influent and effluent characteristics, fluctuations in the wastewater’s pollutant concentrations, the tank’s minimum temperature, and the biological metabolisms of the tank’s microorganisms.
In general, to optimize performance and biodegradation rates, plants should seek out MBBR media carriers of the correct shape and material quality to provide efficient, effective waste digestion.
Design and Shape
As we’ve discussed above, the design and shape of MBBR media carriers help determine waste breakdown efficiency and effectiveness. Media carriers with intricate, cut-out shapes tend to offer more surface area per media weight to enhance bacterial growth and promote biosolid breakdown.
The MBBR media carriers’ design should also give them a density close to the wastewater’s density. The right density promotes even dispersal throughout the tank and ensures thorough waste digestion. Different materials offer different densities — the more economical re-granulates, for instance, may have substantial fluctuations in density between carrier pieces, whereas polyethylene may provide more consistency.
The wear-resistant characteristics of MBBR media carriers determine how they hold up to the demands of wastewater treatment. More resistant media carriers last longer and require fewer changes over time. Some MBBR media carriers, such as sponge-types, have limited resistance to abrasion, so they wear out more easily. Chip-type carriers tend to offer better resistance and a longer life span. Tube-shaped versions may suffer wear because the insides of the tubes tend to accumulate biomatter, which then dies and inhibits active waste digestion.
MBBR media systems require relatively little maintenance. Some materials like polyethylene last longer than others and minimize maintenance needs, so facility managers will want to look into different materials and determine what life span the plant requires for its media.
In an industry filled with different types of MBBR media, SSI’s media carriers stand out. SSI’s MBBR systems offer numerous advantages over competitors’, including custom in-house diffuser and media creation, outstanding media and diffuser interactions, and clean systems that will remain free from flies, slugs and other pests. SSI Aeration’s EEvolved MBBR systems also incorporate a patented technology and innovative biofilm that provide superior effectiveness, efficiency and safety.
MBBR Media Calculation
How is MBBR media volume calculated? To calculate the number of media carriers a facility may need for a wastewater tank, it should first determine the organic load of its wastewater. The organic load will be more or less equal to the product of the flow rate and the difference between the influent and effluent concentration.
- Organic load = flow rate x (influent concentration – effluent concentration)
Once a facility has determined its flow rate, it can then calculate the necessary media supply. Generally, the carrier amount is equal to the wastewater’s organic load divided by the media’s removal efficiency.
- Carrier amount = organic load / removal efficiency
An engineer or facility manager will need to check on the removal efficiencies of the different media under consideration and plug those values into the equation to determine the necessary media carrier volume.
SSI Aeration Has the Best MBBR Media in the Industry
To see the benefits of a quality MBBR system in your wastewater treatment facility, make SSI Aeration your trusted source. SSI systems’ advanced hydrodynamics, aeration, media construction, and biofilm make wastewater processes more efficient, reduce maintenance, and help a facility meet its unique wastewater treatment goals.
Request an MBBR quote today.
Mr. Frankel co-founded SSI in 1995 with experience in design and distribution of engineered systems. He is in charge of sales, marketing and operations in the company. Mr. Frankel holds multiple US patents related to diffusers. He is a graduate of Washington University in St. Louis.