Moving Bed Biofilm Reactor MBBR
Category / type: suspended biomass, activated sludge, extended aeration, biofilm reactor.
Application: small town, hotels, tourist facilities.
Population Equivalents (PE) served: from 2 up to 50 (Packaged and/or site assembled) and more than 50 tailor-made.
Normative references and guarantees: EN 12566-3, d.o.p. According to Regulation (UE) n.305/2011.
Material: concrete, polyethylene, polypropylene, glass-reinforced plastic (GRP).
Moving Bed Biofilm Reactor (MBBR) uses bacteria that grow as a biofilm on plastic support. Plastic filling material are suspended and mixed in an aerobic reactor. Oxygen supply guarantees the increasing of biomass as a bacterial films on plastic material instead of flocs as other aerobic biological plants. It’s an economic and advantageous solution for wastewater treatment to obtain good efficiency results with low energy consumption. It’s a more robust technology and it can resists greater to load variations than conventional biological treatment processes because plastic filling material protects colonies with their high specific surface; shape and features are currently object of research. Their use within aerated and mixed reactor is called moving bed.
This solution should be used to treat high pollutant load both for civil that for industrial wastewater. The plant requires a smaller space (footprint) than a conventional installation as a result of the increase of specific surface needed for the grown of bacterial biofilm.
Membrane Biofilm Moving Bed technology is efficient, compact and easy to apply, it represents an high efficiency choice of treatment both for new plants solution and for existing plants revamping.
How It Works
The main difference between activated sludge conventional plant is the quality of the effluent: there are no bacteria flocs and no dragging risks, while only detached biofilms for death bacteria are present.
The moving bed is realized by material that has a specific gravity slightly lower than water for floating and moving during operating phase. Large bubble aerator are often use to avoid clogging and to ensure the correct mixing of the elements.
Wire or plastic mesh are needed to hold moving beds. A secondary settlement is necessary not as a biomass recovery but only for effluent clarification from detached biofilms.
Stages of the biological reactor allow to select different types of bacteria to specialize the population for some specific treatments (nitrification, denitrification, oxidation, etc.).
Hybrid solution to combine biofilm and suspended bacteria flocs are possible. It can increase biomass concentration, but it requires a secondary clarification equipped by sludge recirculation (pump, pipe, air-lift, blowers).
As all activated sludge systems, the main design factor is organic load measured in kg BOD5. Both from a technical and from a regulatory standpoint (EN 12566-3) it requires the definition of the nominal daily organic load in terms of BOD 5 and the nominal hydraulic flow (QN) in m3.
The main parameters for civil wastewater plants (or equivalent) project is population equivalent (PE); normally it refers to 60 g BOD5 per day and a flow rate from 150 to 250 litre per day.
Population equivalent (PE or sometimes used p.e.) is a conversion value which aims at evaluating non-domestic pollution in reference to domestic pollution fixed by EEC directive (Council Directive 91/271/EEC concerning Urban Waste Water Treatment) at 60 g/day related to BOD5.
European legislation defines Population total (PT) as a sum of population and population equivalent (PE).
A proper wastewater characterisation is possible for incoming organic loads and nutrients better estimation, considering the possibility of dosing additives for biological reactions.
A tertiary treatment, as disinfection or filtration, can be added downstream to increase effluent quality in order to recycle water.
Sizing should be more accurate than primary treatment; biological process requires more constant water supply (therefore organic loads).
For biological line a small flow variability is possible, but it is better to divide it in several lines, typically for medium and large plants.
Equalization tank is always a good solution to ensure a constant flow.
A pretreatment improve system longevity and efficiency: sand and abrasive materials can occupy volume decreasing useful reactor space.
For small domestic wastewater treatment a grease separator on grey water line (kitchen, shower, washing machines dishwasher) is essential to hold organic grease, oil and scum.
Operation and maintenance
MBBR plants operation and maintenance must be carry out by skilled and trained personnel, able to manage biological hazards.
Excess sludge must be removed and treated by a licensed company.
Inlet water must be checked, both to evaluate the treatment performance and to control abnormal intakes of pollutants, that could stop the biological process or allows the development of a not useful bacterial population (for example, filamentous bacteria).
Moving bed and activated sludge plants maintenance operations are similar, but more expensive in case of extraordinary maintenance. To inspect the tanks, filling material must be removed, through a removal operation that is made difficult by the weight of the bacteria.
Membrane bio reactor can treats discontinuous flow rate, since bacterial films population is very resistant.
However, for medium and large plants, an equalization tank is very helpful for peaks mitigation (volume, organics load and dangerous pollutants).
Excess sludge is mostly composed of films disconnected from plastic supports (dead micro-organisms and bacteria) and so it is more stable than conventional sludge coming from wastewater treatment plants.
Long inactivity periods can lead to the arrest of biological reactions and thus requires a new start up of the system.
Moving Bed Biofilm Reactor is a wastewater treatment plant and so, for small installation up to 50 total population it refers to the EN 12666-3 specifications.
The European standard EN 12566-3 “specifies requirements, test methods, the marking and factory production control for packaged and/or site assembled domestic wastewater treatment plants (including guest houses and businesses) used for populations up to 50 inhabitants…”
The manufacturer shall state the nominal organic daily load, expressed in kg of BOD5 or BOD7 per day and the nominal hydraulic daily flow, expressed in cubic meters per day.
Plant’s Nominal Designation is the proper daily organic load value (QN) (3.7).
The small wastewater treatment plant must demonstrate compliance with the performance of efficiency… and to operational data declared by the manufacturer: the declaration must be expressed in percentage.
It is also to be considered that the structural resistance and the hydraulic efficiency must be tested only on a representative model of the product line. Representative model for structural resistance test must be the bigger, supposedly as the one of series with the worst characteristic, while the one for hydraulic efficiency test must be the smaller, presuming the one with the worst efficiency.
The standard describes statics and hydraulics methods to determinate resistance and hydraulic efficiency.
Informations to be included in the test report and in the CE mark are also detailed in ZA.3 annex.
For small domestic wastewater treatment plants up to 50 PT (therefore for activated sludge plants), a Declaration of Performance (DoP), is required, as provided by the EU Regulation. 305/2011.
Features and benefits
The MBBR technology decrease the size of new plants and increase the capacity and the efficiency of existing wastewater plants. It requires less areas, a better yield with low energy consumption than conventional activated sludge plants.
The MBBR process can be used for a variety of different applications: small medium and large industrial plant or civil settlement and it’s very effective in for existing plants revamping.
- compact solution;
- treatment stability and shock loads resistance;
- low energy consumption;
- minimum load loss;
- secondary sedimentation simplification;
- bacteria specialization;
- operational flexibility;
- existing plants revamping;
- few bulking problem;
- stable excess sludge.
- supports biofilm retention needed;
- skilled and trained personnel;
- moving bed handling in maintenance operation;
- pre-treatment and equalization needed.