How To Improve Biogas Generation In The Food And Beverage Industry

How To Improve Biogas Generation In The Food And Beverage Industry

Anaerobic wastewater treatment processes have been increasing in popularity across the food and beverage industry.

Potato Processing Plant - Anaerobic Digester Jet Mixer

Anaerobic processes effectively treat both the normal industrial wastes (higher concentration than municipal wastes) and the very high-strength/low-volume wastes generated by the industry. A welcome side benefit is the generation of biogas for energy production. A food and beverage company can save money, improve sustainability, and lower its carbon footprint. Other drivers include potential legislation in some states to reduce organic waste in landfills and the significant reduction in land application process viability.

Optimizing biogas generation from the anaerobic reactor is critical to maximizing energy production. This energy can be used in a variety of ways, including back in the production facility. It can also offset energy used in the further aerobic polishing of the wastewater after the anaerobic step. In the food and beverage industry, the anaerobic reactor often receives high-strength wastewater along with waste solids from the aerobic polishing step. Chemical oxygen demand (COD) values are often 2,500 mg/L or more. Any process always works better when well mixed — avoiding hot spots and fostering consistent and sustained biological reactions. Ensuring proper contact between the waste and the microorganisms leads to higher biogas production.

Jet Mixers For Improved Biogas Production

Efficiencies

Jet mixing systems that utilize many nozzles distributed across the bottom of the reactor provide superior distribution of mixing energy. This leads to improved mixing compared to systems with fewer point sources of mixing energy input. The high-velocity jet nozzles efficiently induce secondary flow, supplementing the direct recirculation. This influences reactor contents along the path of each jet nozzle’s plume. The jet plume velocity can be adjustable using a variable frequency drive (VFD) on the pump. But throughout the full range, it is balanced to a safe shear for the floc in the reactor. The directional nature of the jet nozzles also creates a bulk fluid velocity to match the layout to the anaerobic reactor’s geometry. The result is significantly improved overall mixing and biological contact than systems using a few big blades or a large downdraft pumping design.

Food and beverage plants typically contain organic solids in the influent to the anaerobic process that must be broken down. Jets mix from the bottom of the tank, enhancing suspension of solids and ensuring they don’t collect there. Maintaining off-bottom solids suspension is critical to the rate of anaerobic biological degradation of the incoming solids. Even distribution of mixing ensures the entire reactor contents are available for treatment. This optimizes the footprint needed for wastewater treatment leaving valuable land available for production expansion instead. Completely mixed reactor systems can be loaded at higher rates than other anaerobic processes providing they are properly mixed, thus minimizing tank volume. Jet mixers are extremely well suited for these high-rate contact reactors. Jet mixers will also avoid the periodic need to clean out reactors that are poorly mixed due to solids buildup.

As biogas is generated, some mixing will naturally occur due to the rise of the biogas within the mixed liquor. Jet mixers are extremely amenable to working in a gasified environment, working synergistically with the rising biogas.

Flexibility

Jet mixers are very suitable for a variety of geometries. For example, they can be engineered to fit in square or circular tanks, earthen basins, or virtually any type of reactor size or shape. In addition, jet mixing systems are especially good for retrofit projects.

From a mechanical standpoint, the simplicity of jet mixers works well with anaerobic processes. Other mixers may require an interface with the digester cover, but jet mixers have no such challenge. With the trend moving from steel to membrane covers, a mechanical turbine or linear motion mixer with a gearbox in the middle of the tank requires a custom donut-shaped cover and some creative access. The recirculation pumps are the only moving parts of a jet mixing system, and they can be located conveniently for easy maintenance access.

Another advantage is the ability to construct the jet nozzles and/or piping out of a variety of materials. Fiberglass reinforced plastic (FRP) with Kynar® inner nozzles are standard, but some food and beverage customers prefer stainless steel. Materials of construction used normally can handle harsh environments and certainly anything a food and beverage industry might send to the WWTP. However, they can be customized for any specific application.

Reducing Downtime

When using biogas to produce electricity, optimizing run time of the generator or boiler is the primary goal. The simplicity, ruggedness, and dependability of jet mixers ensure that the gas generation should remain consistent. The designer is less concerned with mixing problems affecting the biogas storage volume required to accommodate for downtime. By keeping solids in suspension, tank cleaning requirements are reduced. The flexibility of jet mixers increases the ability to retrofit existing tankage, leading to greater biogas production.

Adding Process Chemicals

Recirculation of the reactor contents through the jet mixing system makes it convenient to add chemicals or micronutrients for enhanced biogas generation. Jet mixers provide very efficient chemical distribution with a rapid basin turnover.

Low Maintenance Costs

Mechanically, jet mixers can boast ease of maintenance, ruggedness, and long service life. They use a simple centrifugal pump with dynamic seals. These pumps are designed to run continuously, with no seal replacement needed. Other than changing oil in the bearing housing, there is minimal maintenance. Many of these pumps have been running for 24 hours per day for 25 years.

 

A Brief Case Study

Here is an example of how jet mixers can boost biogas generation efficiency and optimize existing reactor volume. A food and beverage company installed a jet mixer system in its 1.5-million-gallon earthen basin in 1991. The system performed well; however, the mozzarella cheese producer needed to increase the loading to the WWTP due to production increases. The 18-year-old mixing system was retrofitted with a slightly larger jet mixer with much better energy distribution across the surface area of the basin, with more nozzles and recirculation flow. The facility was ultimately able to treat twice the original organic load in the same anaerobic reactor volume using only 50 percent more energy than the original design. By increasing the mixing only, the organic removal rate increased and biogas generation increased proportionally.

The Value Of A Trusted Technical Partner

When designing a new or retrofitted jet mixing system, it’s important to work with experienced professionals in the industry. To optimize biogas generation, proper recirculation pump size and system configuration (number of nozzles and layout) must be determined. A trusted technical partner can help determine the proper balance between capital costs and overall system efficiency for any given treatment objective. Each anaerobic treatment system is unique. With the proper assistance, food and beverage companies can use anaerobic treatment processes properly fitted with jet mixers to optimize biogas generation. Ultimately, the biogas can be converted to usable energy, a side benefit to responsibly maintaining environmental stewardship through meeting wastewater permits and regulations.

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