Key Steps to Calculate MBBR Volume for 3500m³/D Industrial Wastewater

The first great question in the design of an MBBR for a flow rate of 3,500 m3/day is how much volume does the reactor need? It is essential to get it right so that performance does not drop, and one does not have to bear unnecessary construction and operating expenses. This calculation isn't made only based on the flow; it also takes into account the characteristics of wastewater and desired final quality, organic loads, etc., as well as the filling percentage with media. For example, when two factories have the same daily flow, it may be necessary that the reactors do not be the same size if the two factories produce different waste. Knowing the variables and the calculation methodology can help engineers and operators make better decisions and build systems with consistent and lasting performance.

Confirm Water Quality Standards

The first stage in the calculation of the MBBR volumewill be the checking of any wastewater quality standards that the MBBR Biofilm Carriers plant will have to meet. This is a straightforward goal and helps prevent costly mistakes being made during the initial phase of the design.Check any local, regulatory and/or owner specific discharge limits. Assess key performance parameters, BOD, COD, ammonia Nitrogen, TSS and any other specific industry based parameters. The target values of these parameters will determine the size of the reactor and the quantity of MBBR Biochip Media that is required.Let's say that you have a food processing facility with the following wastewater characteristic of 1,200 mg/l BOD. When the discharge limit is 30 mg/l, the system should be able to eliminate over 97% of the organic load. Different treatment will be needed than a plant that is only required to meet a 100 mg/L BOD reduction before discharge to a municipal plant.Also consider seasonal changes and production schedules. Not all industrial facilities produce the same type of wastewater each and every day. Pollutant levels can be greater in a factory when the plant is operating at full capacity, while the plant is being cleaned or during a product changeover. If only average loads are considered, treatment problems will arise when the loads increase.Gather up laboratory reports as recently as possible. The data collected during the several weeks or months will give a more accurate picture than a single sample. Before making detailed calculations, a wastewater characterization study could be required if historical data is not available.Many engineers develop a basic table that has influent levels, effluent limits and percentage effluent removal for each parameter. This will simplify the estimation of biological loading and calculation of the volume of the reactor in a subsequent design phase.After having established the treatment targets, it is possible to determine the actual pollutant load that is entering the MBBR system on a daily basis. That number will serve as the basis for sizing the reactor properly.

Refer to Tank 3D Drawings

Once treatment targets have been confirmed, the next step is to look at tank drawings. A 3D drawing can give a lot of information to help determine if there's enough space for the proposed MBBR volume or if some changes will be required.First of all, examine the length, width and depth of the water in the tank on the drawings. These dimensions are used to determine the Gross Tank Volume. For a tank measuring 20 m long x 10 m wide x 5m depth will have a nominal capacity of 1,000 m3. This is a starting point & may not be available for bio-treatment.Examine closely the internal structures of the model. The effective treatment area can be decreased by baffle walls, inlet chambers, outlet zones, support columns and media retention screens. In other retrofit applications, engineers find that the volume they believe they would need in the tank is actually quite limited due to equipment in the tank.A comprehensive 3D drawing is also used to determine aeration layouts and media movement areas. The MBBR media needs to be freely circulated in the reactor. Media flow can be restricted in dead zones if blocked by a pipe, beam or poor placement of a partition. The areas should be checked before finalising the volume calculations.As an example, a concrete basin for activated sludge treatment may be in place in a manufacturing plant. This tank looks large enough to fit the needs of an MBBR system at first look. The design team will be reviewing the 3D model and may find that there are large areas within the basin that are used for internal channels and equipment which reduces the available biological volume. If it is discovered early, it won't require redesign later.In addition, when possible it is useful to compare the drawing dimensions to actual site dimensions. In some older facilities, there may be changes that have not been recorded in the original plans.Once the dimensions of the tank and the usable volume of the reactor are determined, the organic load for the system needed on a daily basis can be calculated, and compared to the treatment capacity of the selected MBBR media.

Professional MBBR Quantity Calculation

After the wastewater targets and available tank volume are known, the next step is to carry out a professional MBBR quantity calculation. This process is used to find a suitable amount of biofilm carrier media to process the daily pollutant load and to provide a treatment performance.First of all, determine the total organic load that enters the system daily. Typically based on flow and influential BOD or COD. If a plant is treating 3,500 m³/day and the influent BOD is 800 mg/L then the daily BOD load is about 2,800 kg/day. This value forms the basis for the sizing of the media.Then, the design loading rate of the selected MBBR media needs to be calculated. The various types of carriers have varying biological capacities and protected surface areas. The loading rate should be equal to the purpose of treatment and characteristics of the wastewater and operating conditions. It is important that realistic design values are used, as unrealistic assumptions could result in poor treatment outcomes after startup.If the maximum permissible loading rate is established, then divide the daily pollutant load by the media treatment capacity, that is to say the volume of media required to do this. The ratio of the media volume to reactor volume can now be validated. Typical media fill levels for industrial applications will generally range from 40%-70%, dependent on the process and application. If for example the system has adequate capacity in the tanks, but a higher fill level would seem to be necessary to meet challenging discharge criteria. The plant designers might elect to increase reactor size, design an additional stage or use a media with a higher specific surface area to compensate for the extra media fill level. It is also worthwhile considering including a certain margin for safety into the design. The industrial wastewater may be of variable strength year upon year due to factors such as increased production, introduction of new products or seasonality. A certain degree of safety factored into the design should result in a more stable operation under these increased load conditions. The media capacity calculation is far from just a simple matter of adding a filling to a vessel, but is concerned with the factors affecting design, such as organic load, discharge levels, reactor volume and media specification, in the long term performance of the system.