By Joo Nian Ng

The Background
Being a profound biological wastewater treatment solution provider with more than 20 years of experience in MBBR technology, it is sometimes necessary for us to explain thoroughly to our clients what MBBR is and how an MBBR process looks like. Questions that arise quite frequently from our clients would be: “How to calculate the required amount of the carrier media?” and “How do you quote your carrier media?” As we dug deeper into these questions, we learnt about different ways of calculating the amounts of carrier media required by our clients, such as calculations that are based on the tank volume, water volume, etc.

[STOP! This is ridiculous!]

General Rule for Calculation
The basic and correct way to determine the required amount of MBBR carrier media in a wastewater treatment application depends on the organic load that needs to be removed, which is directly influenced by the flow rate, influent and effluent concentrations.

Organic Load = Flow Rate x (Influent Concentration – Effluent Concentration)

Once the organic load to be removed is known, the required carrier media quantity can be calculated. Different types of carrier media have their own different removal rate or efficiency. Yet, this removal efficiency is strongly depending on the application and water temperature.

For a serious calculation, these factors must be put into consideration first before deciding on the removal efficiency of a carrier media. After all, the one that actually treats the wastewater is the bacteria that grows on the carrier media and not the carrier media itself. As a living organism, the activeness of the bacteria is influenced by the surrounding conditions and the substances to be degraded by the bacteria. To draw an example: Who would prefer to eat ice cream during cold weather?

Once the removal efficiency is determined, we can calculate the carrier media requirement for a certain wastewater application:

Carrier Amount =          Organic Load
                                         Removal Efficiency

Story: Tom and His Eleven Trained Workers
Tom owns a production factory. Every day, the factory produces 10 kg of a certain product. Based on his experience, Tom knows that on average, one trained worker with correct tools could manage to pack and ship out 1 kg of the product daily. Being a predictive man, Tom considers the probability that one worker might get sick. To be on the safe side, he has eleven trained workers instead of ten. This helps him to prevent the warehouse from an overcapacity, in case that one of them is sick or the factory has to increase its production capacity. With his eleven trained workers and correct tools, Tom’s factory operates smoothly every day without trouble.

Now, let us look at the biological wastewater treatment process. As compared with Tom’s factory, the “product” is equivalent to the organic load to be removed by means of wastewater treatment, whereas the trained workers and tools are equivalent to the carrier media and biomass in the wastewater treatment process, respectively. Similar to the workers who cannot pack and ship out the products without tools, the carrier media without biomass cannot remove the organic load from the wastewater.

If one day, Tom’s factory starts producing another type of product that requires a different packing method, what Tom needs to do is to wait for his workers to get familiar with their new working tools instead of dismissing his eleven workers and hiring a new group, respectively. The same applies to biological wastewater treatment, too: The biomass that grows on the carrier media will gradually adapt itself for being able to remove a different type of organic load or load’s concentration, respectively.

Characteristic of a Good MBBR Carrier Media
For Tom to make sure that his factory can run smoothly, he needs both, skilled workers and a good set of tools for his workers, respectively. The lack of one of the two will slow down the packing speed. For biological wastewater treatment with the MBBR process, besides of the biomass, the carrier media that acts as the housing for the bacteria is also very important.

A good MBBR carrier media provides more than just a protected habitat for the bacteria to grow but also ensures that all bacteria that grow on it are sufficiently supplied with nutrients for their metabolism. During the metabolism process, the bacteria consume dissolved organic substances. In other words, the wastewater is biologically treated. Without sufficient nutrients, the growth of the bacteria is hindered or, still worse, the bacteria die off. These phenomena will reduce removal efficiency and lead to unqualified wastewater discharge. Hence, a proper selection of the carrier media is essential. This decision will affect both, the organic removal performance and the cost required to run the plant.

A good MBBR carrier has the following characteristics:

• A large protected surface area to maximize the amount of biomass,
• A porous surface to strengthen the biomass’s adhesion,
• An optimal substrate diffusion depth to ensure the metabolism,
• Wear-resistance for durability.

In terms of the treatment, a good MBBR carrier media makes sure that all biomass is active to remove the organic substances from the water. From the user´s point of view, a good MBBR carrier media eases the operation and provides all forms of savings, such as in construction and operation.

Summary
Although an MBBR carrier media might just be a plastic piece (or of other materials), its role in wastewater treatment is vital to keep the biomass active in order to deliver the highest organic removal performance.

In a wastewater treatment application, the required amount of MBBR carrier media depends on the organic load that needs to be removed by means of the bacteria’s metabolism. The water temperature and the type of substrate influence this metabolism rate.

Finally, it might be elaborate to provide your solution supplier with all the necessary information or even annoying to answer all their wastewater-related questions that seem never-ending. In the long term, it is for your own good. It is rather more worrying if your supplier asks nothing about your wastewater.

About the Author
Joo Nian Ng works at Multi Umwelttechnologie AG.

Note:

• Product = Organic Load
• Worker = Carrier
• Tools = Biomass
• 11th Worker = Safety Factor

Mutag BioChip Checklist

• Surface Area: 5,500 m2/m3
• Surface: Porous and rough
• Diffusion Depth: Optimal via 1.1 mm thickness and self-cleaning effect
• Durability: Protection ring + lightweight

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