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Anaerobic MBR

Anaerobic Membrane Bioreactors

CFR’s Anaerobic Membrane Bioreactor (AnMBR) system combines an anaerobic digester with membrane ultrafiltration separation to treat high strength wastewater that is commonly found in the Food and Beverage Industry. Coupling anaerobic digestion with ultrafiltration results in a highly efficient process that can remove >98% of influent Chemical Oxygen Demand (COD) in a single step. Additionally, anaerobic digestion of food waste generates significant volumes of high-quality biogas that can be used as fuel to create renewable energy.

Anaerobic digestion of food waste has become more common as digester technologies have become more reliable and easier to operate. CFR’s AnMBR Technology is a completely automated process that has been proven to be able to handle the biggest challenges the industry can throw at it.

CFR has optimized this design over many years of helping customers manage difficult to treat wastewater in the food and beverage industry. The Anaerobic Membrane Bioreactor process is generally used in one of two ways:

  1. Pre-treatment step for discharge to a municipal sewer system
    1. The Anaerobic MBR generates high quality effluent that can be discharge to the city that is free of surcharges
  2. Pre-treatment step for further aerobic polishing
    1. When direct discharge to a surface body of water is required, the effluent from the Anaerobic MBR can be polished by a simple aerobic process
    2. The Anaerobic MBR digests the bulk of the COD which greatly reduces the size of the downstream aerobic system

CFR’s AnMBR design is a High-Rate Complete Mix Digester that features an internal mixing system with no moving parts. This mixing system allows for maximum efficiency of biomass contact with the wastewater and eliminates solids settling. This also allows for high levels of COD removal while promoting maximum biogas production. The figures below provide data from one of our installations at a dairy processing facility that produces mainly butter along with other dry and fluid milk products. The influent to the Anaerobic Membrane Bioreactor at this facility has anywhere from 10,000-70,000 mg/L COD while the averaging <300 mg/L COD in the effluent.

Digester Influent COD Loading
Figure 1 – Digester Influent COD Loading (mg/L)

Digester Effluent COD Concentration
Figure 2 – Digester Effluent COD Concentration

The Anaerobic Membrane Bioreactor features external tubular crossflow membranes to separate the treated wastewater from the biomass. The membranes are integrated into a CFR designed membrane skid which features its own set of instrumentation and controls. The wastewater flows through the membranes at high velocity to maintain turbulent flow and to scour the membrane surface. The permeate is forced out through the membrane pores while the biomass is retained in the retentate stream and returned to the anaerobic digester.

The ultrafiltration separation step allows for 100% of the biomass to be retained within the anaerobic digestor which promotes superior effluent quality over other conventional anaerobic digestion technologies such as an upflow anaerobic sludge blanket (UASB). By completely mixing the digester and retaining 100% of the biomass, CFR’s Anaerobic Membrane Bioreactor can produce superior effluent quality while simultaneously generating high quality biogas.

The main byproduct of anaerobic digestion is biogas which is composed mostly of methane (50-65%) and carbon dioxide (30-50%). This biogas is stored in the headspace of the anaerobic digester and can be either sent to a flare to be burned off or it can be further conditioned to generate renewable energy. Due to the high organic loadings that are commonly associated with food production wastewater, large quantities of biogas can be generated. This biogas has a high economic value due to the high methane content.

The biogas can be used to fuel on-site boilers, or it can be sent to a Combined Heat and Power Unit (CHP) to generate renewable electrical and thermal energy. Due to the high concentration of methane in the biogas, a significant amount of electricity can be generated as a result. In fact, at food and beverage production facilities it is common to be able to generate enough electricity to power the entire wastewater treatment facility, resulting in a net energy neutral process.

Benefits of Anaerobic Treatment:

  • Can reliably process very large organic loading variations from day to day
  • Can sit idle, if necessary, for long periods in the event of seasonal variations when influent flow and organic loading is low
  • When properly managed, restarts and responds quickly when necessary
  • The AnMBR technology converts up to 99.5% of the biodegradable organics into biogas over the 75-90% conversion with other anaerobic technologies
  • A specialized jet mixing system has no internal moving parts
  • The feed, microorganisms, and any precipitated inorganics are completely mixed in the reactor without the need to maintain specialized microorganism granules
  • The AnMBR technology can accept large quantities of fats and inorganics, which would cause major upsets in other anaerobic technologies
  • A cyclone is used to remove excess precipitated compounds containing calcium, iron, ammonia and phosphorus, among others
  • Anaerobic digestion of food waste produces high quality biogas that can be sent to a CHP unit to generate significant amounts of renewable thermal and electrical energy

Anaerobic Membrane Bioreactors offer the following benefits over a purely aerobic system:

  • Small footprint compared to aerobic systems
  • Produces methane from the organic material that can be used in a variety of energy recovery systems
  • Significantly lower energy costs compared to an aerobic system where the primary energy cost is blower operation
  • Produces 60-90% lower biomass generation compared to an aerobic process
Process of Using an Anaerobic Membrane Bioreactor for Wastewater Treatment
Figure 3 – Process of Using an Anaerobic Membrane Bioreactor for Wastewater Treatment