Cheese Factory | AnMBR

The core technology of the turnkey wastewater treatment facility delivered by Complete Filtration was the Anaerobic Membrane Bioreactor (AnMBR) process. In the AnMBR, Berghof tubular ultrafiltration (UF) membranes are coupled to a Continuous Stirred Tank Reactor (CSTR) digester, allowing the system to handle high organic loading rates while producing a high quality permeate that has no measurable TSS (Total Suspended Solids). It is noteworthy that since the AnMBR can handle high FOG, there is no need for a DAF (Dissolved Air Flotation) upstream of the AnMBR process. Complete Filtration has optimized their AnMBR process over many years of operation to treat high strength and high FOG waste that is common in milk processing applications.

Berghof membranes ensure the complete retention of the biomass within the anaerobic digester and bring a significant improvement in the digestion process, making it more robust, reducing the footprint, and increasing biogas production. In the dairy industry, AnMBR technology offers major advantages over other anaerobic technologies:

• Better effluent quality: AnMBR can remove up to 99 % of the inlet COD (Chemical Oxygen Demand), being a great option as a sole treatment for discharge to a municipal sewer system.
• Ability to handle high TSS and FOG concentrations, which are known to inhibit the operation of conventional anaerobic systems that rely on settling or granular sludge.
• Eliminating the need for primary FOG separation with a DAF system, which generally consumes large amounts of chemicals and generates a sludge that is costly to dewater. FOG is easily converted into biogas instead of being hauled away as a sludge.

As a major requirement, the system was designed with future expansion in mind, by saving space for installing additional membranes to allow for an increase in hydraulic load. Compared with other technologies, AnMBR offers significant benefits in terms of footprint requirements: high organic loading rates reduce the digester volume and the external UF provides a robust and stable filtration, allowing higher design fluxes and minimizing the membrane surface area required. Additionally, DAF pretreatment is avoided, which results in footprint savings, sludge management costs and maximized conversion of organics into biogas.

Although the BOD loading might be on the low end of anaerobic digester applications, this technology was chosen for a few reasons. First, cheese production wastewater is the perfect substrate for anaerobic digestion as it has easy to degrade organics and high protein content allowing natural buffering without excessive caustic consumption. This process can handle frequent swings in hydraulic and BOD loading of 1.5 x and 2.5 x the design basis, respectively.

This technology allows Ellsworth to comfortably meet the City of Menomonie’s discharge limits in single treatment step. On top of that, it produces significantly less sludge and consumes less electricity than a conventional aerobic system. The AnMBR consistently achieves high effluent quality with an overall BOD removal efficiency of > 99.5 %: with 1,587 kg BOD/day (3,500 lb/day) influent load, the system is discharging less than 3.4 kg BOD/day (7.5 lb/day).