Application of Moving Bed Biofilm Reactor (MBBR)

Application of Moving Bed Biofilm Reactor (MBBR)

Application of Moving Bed Biofilm Reactor (MBBR)

    This review paper present the MBBR and IFAS technology for urban river water purification including both conventional methods and new emerging technologies. The aim of this paper is to present the MBBR and IFAS technology as an alternative and successful method for treating different kinds of effluents under different condition. There are still current treatment technologies being researched and the outcomes maybe available in a while. The review also includes many relevant researches carried out at the laboratory and pilot scales. This review covers the important processes on MBBR and IFAS basic treatment process, affecting of carrier type and influent types. However, the research concluded so far are compiled herein and reported for the first time to acquire a better perspective and insight on the subject with a view of meeting the news approach. The research concluded so far are compiled herein and reported for the first time to acquire a better perspective and insight on the subject with a view of meeting the news approach. To this end, the most feasible technology could be the combination of advanced biological process (bioreactor systems) including MBBR and IFAS system.

    The BioCellTM media are suitable for a moving bed biofilm reactor (MBBR) system to provide a self-shedding, self-regulating growth biofilm treatment process. The media can be used for MBBR treatment alone or as an integrated fixed membrane activated sludge (IFAS) process to enhance the effective capacity of existing activated sludge systems.

    The BioCellTM medium used in MBBR media or IFAs is a continuous motion caused by air injection and agitator. Specific density of the media can be adjusted between 0.95-1.05 g/cm3 according to customer requirements. However, it should be considered that with the formation of biofilm on the surface of the medium, the actual density of the carrying media will increase.

    The main characteristic of Moving Bed Biological Reactor (MBBR) configurations is that there is no sludge recycle from a secondary clarifier. MBBR is essentially a simple, once-through process, where all of the biological activity takes place on the biomass carriers. MBBR is usually followed by a solids separation system such as a secondary clarifier or DAF, in order to separate bio-solids produced in the process from the final effluent. The main advantage of MBBR is robust and simple reduction of soluble pollutants (soluble BOD or COD, NH4 +, etc.), with minimal process complexity, utilizing a significantly smaller footprint when compared to conventional aerobic treatment methods. MBBR is typically used for either high load industrial applications or for robust simple-to-operate municipal facilities.

    The Integrated Fixed-film Activated Sludge (IFAS) process combines the advantages of conventional activated sludge with those of biofilm systems by combining the two technologies in a single reactor. Typically, an IFAS configuration will be similar to an activated sludge plant (utilizing all of the different process configurations such as MLE, UCT, Bardenpho, etc.), with biomass carriers introduced into carefully selected zones within the activated sludge process. This allows two distinct biological populations to  act  synergistically, with the MLSS degrading most of the organic load (BOD), and the biofilm creating a strongly nitrifying population for oxidation of the nitrogenous load (NH4+). IFAS is typically used to upgrade existing plants in order to enable extensive Nitrogen removal, or in designing new plants with significantly smaller footprints for extensive BOD and Nitrogen removal.

     The diffuser is the special design for MBBR bio carrier media aeration system. The coarse-bubble design is employed to mix the suspended media evenly throughout the reactor  while  providing  the  mixing energy required to slough old biofilm from the internal surface area of the media and maintain the dissolved oxygen required  to  support the biological treatment process.

    Coarse bubble diffuser is made of stainless steel (SUS304 or SUS316L is optional).The  coarse bubble diffuser provides maximum aeration and mixing efficiency.The standard length of diffuser is 600 mm. A 600mm long diffuser can achieve a 1250mm air release circumference.It has a service life of over 15 years. 

    The dissolved air flotation(DAF) system is designed to remove suspended solids(TSS), biochemical oxygen demand (BOD5), and oils and greases (O&G) from wastewater. Contaminants are removed by using a dissolved aqueous solution of water produced by injecting air into the recirculating stream of clear DAF effluent under pressure. The recycle stream is then mixed with the upcoming wasterwater in the internal contact chamber. Air bubbles and contaminants rise to the surface and form a floating bed material that is removed by a surface skimmer into the internal hopper for further processing.

    The initial section of dewatering drum is the Thickening Zone, where the solid-liquid separating process takes place and where the filtrate will also be discharged. The pitch of the screw and the gaps between the rings decrease at the end of dewatering drum, hence increasing its internal pressure. At the end, the End Plate further increases the pressure, so as to discharge dry sludge cake.

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    In traditional activated sludge plants, biomass form flocks are kept suspended in wastewater and then separated from treated water in a settler; most biomass is re-circulated to the biological tanks, the excess is extracted and sent to sludge treatment.

    Luigi Falletti, University of Padova

    This technique is the most widespread and well known in the world to treat biodegradable municipal and industrial wastewater (including paper mill wastewater); but it has also disadvantages: it requires large tanks, and pollutant removal efficiency is strongly affected by sludge settleability.

    In moving bed biofilm reactors (MBBR) biomass grows as biofilm on plastic carriers that move freely into wastewater; tanks are similar to activated sludge reactors, and they have screens or sieves to avoid carriers’ loss; aerated reactors are mixed by aeration itself, while anoxic and anaerobic reactors are mixed mechanically. MBBR can be classified into two categories:
     
            pure biofilm reactors: biomass grows only on carriers without suspended sludge and without sludge recirculation;
   
            hybrid reactors: in the same tank biomass grows both as biofilm on carriers and as suspended sludge; part of sludge is re-circulated.
       
    MBBR have several advantages if compared to traditional activated sludge tanks and to fixed biofilm reactors (trickling filters, submerged biofilters):

    -biofilm has high specific activity, therefore high pollutant removal efficiencies can be achieved with smaller tanks than the ones required by activated sludge;

    -in plants with a series of MBBR a specialized biomass grows in each tank;

    –risk of clogging with MBBR is much lower than with fixed biofilm reactors, no backwashing is required since biofilm in excess is detached from carriers by reactor turbulence itself, and can be separated from treated water by settling or flotation;

    -this technology is very flexible in plant conduction: in pure biofilm reactors, the filling degree can be varied according to process requirements, in hybrid reactors also sludge recirculation rate can be varied.

    Several kinds of carriers are used in MBBR: they can be classified according to material, shape, porosity, dimensions, specific surface. Among these characteristics, specific surface is particularly important: it represents the surface which is available for biofilm growth pr. cubic meter carriers. For each kind of carrier, part of specific surface is protected and the remaining part is external; biofilm grows almost only on protected surface, because external surface is exposed to collisions among carriers and against reactor walls; so the effective specific surface is only a protected one. First biofilm growth on carriers requires some weeks; bacteria produce surfactant substances, so some scum can be observed during the first days in plant starting [1, 2, 3, 4].

    Carriers can be introduced in MBBR in variable amounts: filling degree is the ratio between the carriers’ apparent volume and the tank volume, and it can vary from zero to a maximum value that depends on the carriers’ characteristics. With higher filling degree, total biofilm surface and pollutant removal efficiency increase, but higher mixing energy is required. The most widespread carriers are made of polyethylene or polypropylene, their density is about 0.95, and usual filling degrees’ range is 30–60%; the characteristics of some kinds of carriers produced by AnoxKaldnesTM Company are listed in table 1.

    Possible configurations

    Mbbr sewage treatment can be applied for wastewater treatment in several plant configurations:

    1. pure MBBR biofilm before an activated sludge plant: this solution is common for concentrated wastewater treatment;

    2.upgrading of overloaded activated sludge plants by conversion into hybrid MBBR;

    3.tertiary biological treatment by pure biofilm MBBR after an activated sludge plant;

    4.complete biological treatment by series of MBBR: pre-denitrification, oxidation, nitrification, post-denitrification.

    MBBR have been and are applied to treat municipal wastewater [5, 6, 7, 8, 9] and industrial wastewater including paper mills [10, 11, 12], winery [13] and dairy [14]. This paper deals with the results of some European full-scale plants with MBBR for paper mill wastewater treatment.

    Industry nr. 1&nbsp;produces about 18.000 m3d-1&nbsp;wastewater with 2.500–3.500 mg/L COD. The wastewater treatment plant (picture 1) is made of a coarse screen, a primary settler, a fine screen, a cooling system, dosage of nutrients (nitrogen and phosphorus salts), a biological section and a final clarifloculation. The biological section has a first aerated pure biofilm MBBR filter media with 2.500 m3&nbsp;volume filled with 40% NatrixTM&nbsp;– O carriers, an activated sludge oxidation tank with 7.500 m3&nbsp;volume and sludge concentration 4-6 kgSSTm-3, and a secondary settler. The plant must remove at least 90% of COD, 99% of BOD5; maximum pollutant concentrations in final effluent are: TSS < 50 mg/L, tot-N < 4.7 mg/L, P < 0.3 mg/L.

    On average basis, the plant has treated an effective organic load of 59.000 kgCODd-1, the first MBBR has removed 51% of COD and the following activated sludge oxidation tank has removed 75% of remaining COD; the whole plant has removed 90% COD and has always respected emission limits.

    Industry nr. 2&nbsp;produces about 18.000 m3d-1&nbsp;wastewater with 2.000-2.500 mg/L COD. The wastewater treatment plant (picture 2) is made of a cooling system, dosage of nutrients (nitrogen and phosphorus salts), pH correction and a biological section. The biological section is made of two serial aerated pure biofilm MBBR with 1.900 m3&nbsp;volume each filled with 20% NatrixTM&nbsp;– O carriers, an activated sludge oxidation tank with 10.000 m3&nbsp;volume and sludge concentration 2-5 kgSSTm-3, and a final settler. The plant must remove at least 70% COD, 50% total nitrogen and 50% total phosphorus; moreover, maximum TSS concentration in final effluent is 30 mg/L.

    On average basis, the plant has treated an effective organic load of 38.000 kgCODd-1, the two MBBR have removed 35% COD, the whole plant has removed 70% COD and has always respected emission limits.

    Industry nr. 3&nbsp;produces 2.800 m3d-1&nbsp;wastewater 800-1.300 mg/L COD. The wastewater treatment plant (picture 3) is made of an equalization tank with 600 m3&nbsp;volume, a primary settler (with fiber recovery), dosage of nutrients (nitrogen and phosphorus salts) and a biological section. The biological section is made of a pure biofilm aerated MBBR with 500 m3&nbsp;volume filled with 68% AnoxKaldnesTM&nbsp;– K1 carriers, and a secondary settler with polyelectrolyte dosage. Maximum pollutant concentrations in final effluent are: TSS < 35 mg/L, COD < 160 mg/L, BOD5< 40 mg/L.

    On average basis, the biological section has treated an effective organic load of 2.660 kgCODd-1, and has removed 90% COD; the final effluent has always respected emission limits.