Water Treatment Contractors – AVLON INC & MBBR Technology
Water treatment contractors mostly uses Moving Bed Biofilm Reactor (MBBR) processes to improve reliability, simplify of STP operation. This technology requires less space than traditional wastewater treatment systems. The MBBR process is an attached growth biological wastewater treatment process. That is, the microorganisms that carry out the treatment are attached to a solid medium, as in trickling filter or RBC systems. By contrast, in a suspended growth biological wastewater treatment process, like the activated sludge process, the microorganisms that carry out the treatment are kept suspended in the mixed liquor in the aeration tank.
In the conventional attached growth biological treatment processes, like trickling filter or RBC systems, the microorganisms are attached to a medium that is fixed in place and the wastewater being treated flows past the surfaces of the medium with their attached biological growth. In contrast, an MBBR process utilizes small plastic carrier media upon which the microorganisms are attached. The MBBR treatment processes typically take place in a tank similar to an activated sludge aeration tank. The carrier media are kept suspended by a diffused air aeration system for an aerobic process or by a mechanical mixing system for an anoxic or anaerobic process, A sieve is typically used at the MBBR tank exit to keep the carrier media in the tank.
Primary clarification is typically used ahead of the MBBR tank. Secondary clarification is also typically used, but there is no recycle activated sludge sent back into the process, because an adequate microorganism population is maintained attached to the media.
Water treatment contractors and use of MBBR Media Support Carrier System.
Water treatment contractors in MBBR processes use plastic media support carriers similar to those shown in the figure below. As shown in that figure, the carrier is typically designed to have a high surface area per unit volume, so that there is a lot of surface area on which the microorganisms attach and grow. Media support carriers like those shown in the figure are available from numerous vendors. Two properties of the carrier are needed for the process design calculations to be described and discussed in this course. Those properties are the specific surface area in m2/m3 and the void ratio. The specific surface area of MBBR carriers is typically in the range from 350 to 1200 m2/m3 and the void ratio typically ranges from 60% to 90%. Design values for these carrier properties should be obtained from the carrier manufacturer or vendor.
Single Stage BOD Removal MBBR Process Design Calculations
An MBBR single stage BOD removal process may be used as a free-standing secondary treatment process or as a roughing treatment prior to another secondary treatment process, in some cases to relieve overloading of an existing secondary treatment process. In either case the key design parameter for sizing the MBBR tank is the surface area loading rate (SALR), typically with units of g/m2/day, that is g/day of BOD coming into the MBBR tank per m2 of carrier surface area. Using water treatment contractors design values for wastewater flow rate and BOD concentration entering the MBBR tank, the loading rate in g BOD/day can be calculated. Then dividing BOD loading rate in g/day by the SALR in g/m2/day gives the required carrier surface area in m2. The carrier fill %, carrier specific surface area, and carrier % void space can then be used to calculate the required carrier volume, tank volume and the volume of liquid in the reactor.
Two-Stage BOD Removal MBBR Process Design Calculations.
A two stage MBBR BOD removal process may be used instead of a single stage process. In this case, a high SALR “roughing” treatment will typically be used for the first stage and a lower SALR will typically be used for the second stage. This water treatment contractors will result in less total tank volume needed for a two-stage process than for a single stage process. Also, a two-stage MBBR process can typically achieve a lower effluent BOD concentration than a single stage MBBR process.
Single Stage Nitrification MBBR Process Design Calculations.
An MBBR single stage nitrification process would typically be used as a tertiary treatment process following some type of secondary treatment that reduced the BOD to a suitable level. A typical flow diagram for a single stage MBBR process for nitrification is shown in the figure below. As shown on the diagram, the BOD level should be low enough so that the BOD load to the nitrification process is less than 0.5 g/m2/day. Note that alkalinity is used in the nitrification process and thus alkalinity addition is typically required.
Two-Stage BOD Removal and Nitrification MBBR Process Design Calculations
A two stage MBBR process may also be used to achieve both BOD removal and nitrification. Nitrification with an MBBR process requires a rather low BOD concentration in order to favor the nitrifying bacteria in the biomass attached to the carrier. Thus, the first stage for this process is used for BOD removal and the second stage is used for nitrification. A typical flow diagram for a two stage MBBR process for BOD removal and nitrification is shown in the figure below. As in the single stage nitrification process alkalinity is used for nitrification, so alkalinity addition is typically required.
Denitrification Background Information
In order to carry out denitrification of a wastewater flow (removal of the nitrogen from the wastewater), it is necessary to first nitrify the wastewater, that is, convert the ammonia nitrogen typically present in the influent wastewater to nitrate. Nitrification will only take place at a reasonable rate in an MBBR reactor if the BOD level is quite low. Thus, water treatment contractors an MBBR denitrification process will need a reactor for BOD removal, one for nitrification, and one for denitrification. The nitrification reactor will always follow the BOD removal reactor, because of the need for a low BOD level in the nitrification reactor. The denitrification reactor may be either before the BOD removal reactor (called pre-anoxic denitrification) or after the nitrification reactor (called post-anoxic denitrification).
Post-Anoxic Denitrification Process Design Calculations
Process design of a post-anoxic denitrification MBBR system, requires sizing an MBBR tank for BOD removal, one for nitrification and one for denitrification. For all three of these reactors the key design parameter for sizing the MBBR tank is the surface area loading rate (SALR), typically with units of g/m2/day, that is g/day (of the parameter being removed in that reactor) coming into the MBBR tank per m2 of carrier surface area in the reactor.
Using design values for wastewater flow rate and concentration of the removed parameter entering the MBBR tank, the loading rate in g/day can be calculated. Then water treatment contractors dividing the loading rate in g/day by the SALR in g/m2/day gives the required carrier surface area in m2. The carrier fill %, carrier specific surface area, and carrier % void space can then be used to calculate the required carrier volume, tank volume and the volume of liquid in the reactor.
