Is it possible to increase treatment capacity by 30% without expanding the plant?
In the textile industry, increased production results in higher wastewater flow rates and greater organic loads. When available space is limited, upgrading a conventional biological treatment plant may require new tanks, complex civil works, significant investment, and changes to the existing layout.
MBBR technology – Moving Bed Biofilm Reactor – offers an alternative approach: increasing the system’s biological treatment capacity within a compact footprint and, whenever possible, integrating the technology into existing structures.
MBBR in textile wastewater treatment
MBBR stands for Moving Bed Biofilm Reactor, a biological treatment process based on biofilm growing on moving carrier media.
Plastic elements known as carriers are placed inside the reactor. These carriers move continuously through the water and provide a large, protected surface area on which the microorganisms responsible for the biological degradation of pollutants can grow.
In conventional activated sludge plants, the biomass is mainly suspended in the water in the form of biological flocs. In the MBBR process, by contrast, a significant proportion of the bacteria grows as a biofilm attached to the carriers.
This configuration makes it possible to retain a larger amount of active biomass within the reactor without proportionally increasing the tank volume or the concentration of suspended solids.
How the process works
Before reaching the MBBR reactor, the industrial wastewater must be properly pretreated. Preliminary treatment stages may include screening, equalization, pH adjustment, removal of oils, fats, fibres and heavy solids, and cooling where necessary.
Equalization is particularly important in the textile industry, where flow rate, COD, temperature, colour, salinity and pH can vary significantly depending on the production cycles.
In aerobic tanks, the air supplied through diffusers performs two functions: it provides the oxygen required by the microorganisms and keeps the carriers in continuous motion.
In anoxic reactors designed for denitrification, the carriers are instead kept in motion by mechanical mixers, without introducing oxygen.
Special retention screens keep the carriers inside the tank while allowing the treated water and detached biomass to pass on to the subsequent treatment stages.
Biofilm formation
Microorganisms colonise the internal and external surfaces of the carriers and use the organic substances present in the wastewater as a source of carbon and energy.
Biodegradable pollutants are mainly converted into carbon dioxide, water, new biomass and simpler compounds.
Depending on the system configuration, the MBBR process can be used to remove:
- biodegradable COD and BOD;
- ammonia nitrogen through nitrification;
- nitrates through denitrification;
- a portion of biodegradable industrial organic compounds.
The biofilm is partly self-regulating. When it becomes excessively thick, the movement and collisions between the carriers promote the detachment of older biomass.
For this reason, a downstream solids-separation stage is required after the reactor. This may involve sedimentation, lamella clarification, dissolved air flotation (DAF), filtration, ultrafiltration or MBR membranes.
Why MBBR is well suited to plant upgrades
MBBR technology is particularly attractive when the capacity of an existing treatment plant needs to be increased without radically modifying the available infrastructure.
In conventional activated sludge systems, biological treatment capacity depends on the concentration of suspended biomass, sludge age, oxygen availability and the capacity of the final clarifier.
An excessive increase in MLSS may result in higher oxygen demand, settling problems and overloading of the clarification stage.
With MBBR, an additional population of microorganisms attached to the carriers is introduced. Biological treatment capacity can therefore be increased without a proportional rise in suspended biomass.
The technology can be used as a biological pretreatment, a pre-oxidation stage, the main treatment process, a nitrification stage, or as preparation for MBR, ultrafiltration and reverse osmosis processes.
When carriers are added directly to an activated sludge tank, the configuration is generally referred to as IFAS – Integrated Fixed-Film Activated Sludge. In this system, suspended biomass and biofilm operate simultaneously.
MBBR and the upgrading of existing treatment plants
MBBR technology is particularly attractive when the capacity of a biological treatment plant needs to be increased without radically modifying the existing infrastructure.
In conventional activated sludge systems, biological treatment capacity depends on several parameters, including:
- suspended biomass concentration;
- sludge age;
- the ratio between organic load and microorganisms;
- oxygen availability;
- sludge settling characteristics;
- final clarifier capacity.
An excessive increase in suspended solids concentration may raise oxygen demand, worsen sludge settleability and overload the final solids-separation stage.
With the introduction of carriers, the system gains an additional population of attached microorganisms. It therefore becomes possible to increase biological treatment capacity without increasing suspended biomass to the same extent.
Advantages and limitations
MBBR technology makes it possible to increase the amount of active biomass available without proportionally increasing tank volume. This makes the process particularly suitable for upgrading existing treatment plants, especially where space is limited. The biofilm attached to the carriers also promotes the retention of slow-growing microorganisms, improves biological stability and provides greater resistance to moderate variations in flow rate and organic load.
However, system performance depends on the correct design of the aeration system, uniform carrier movement, the carrier filling ratio, and the availability of oxygen and nutrients. Efficient downstream solids separation is also required, as part of the biofilm naturally detaches from the carriers.
MBBR primarily acts on the biodegradable fraction of COD. It does not directly remove, TDS, silica, metals, refractory colour or persistent organic compounds. When it is required to comply with very restrictive normative at discharge, then the process must be integrated with systems like: Chemical Advanced Oxidation (CAO), multimedia-filtration or membrane processes.
Pretreatment also plays a critical role: fibres, fats and solids may hinder carrier movement, clog the retention screens and reduce process efficiency. MBBR should therefore not be regarded as a universal solution, but as a biological technology to be incorporated into a treatment line designed according to the actual characteristics of the wastewater and the required final water quality.
Conclusions
MBBR technology is a compact and flexible solution for upgrading industrial biological treatment plants where available space is limited.
The use of moving carriers makes it possible to retain a high concentration of active biomass within the reactor, improving the degradation capacity for biodegradable pollutants without proportionally increasing tank volume.
When pretreatment, equalization, aeration, carriers, biomass and solids separation are designed as parts of a single integrated process, MBBR can help make a treatment plant more stable, compact and easier to upgrade.
Final performance nevertheless depends on accurate wastewater characterization, proper system sizing and integration with any additional treatments required to meet discharge, reuse or water-recovery targets.
