Pretreatment Krofta DAFs in the dairy industry
DAFs have played an important function as a pretreatment step (clarification) as before discharge to a POTW by substantially reducing fats,oils and grease (FOG), total suspected solids (TSS), insoluble BOD and COD. This would be for milk processes plants, butter plants, ice cream plants and dairy plants that have added new products such as ice cream mixes, flavored creamers and some cultured products.
Pretreatment to reduce FOGs, TSS or BOD/COD
Pretreatment Krofta DAFs can also be used as a pretreatment step ahead of Krofta aerobic or anaerobic treatment processes to reduce FOG’s, TSS or BOD/COD to reduce the size of the aerobic/anaerobic systems. Many high rate aerobic and anaerobic systems benefit substantially if much of FOG’s, TSS and BOD is reduced before treatment. Certain high rate aerobic systems may experience difficulties in start-up or operation with higher levels of fats, oils and grease. The MBBR media can become coated complicating the start-up/lengthening the start-up time. FOG’s can also change the density of the bio-mass media increasing maintenance on the system with such items as more frequent cleaning of sensors, probes, etc.
Pretreatment for high rate aerobic systems
For high rate aerobic systems, it not uncommon to see a Krofta DAF used as a pretreatment step before the biological reactor(s) as well as after the biological step to remove any bio-solids coming off the process. Krofta DAFs have demonstrated superior performance against traditional gravity clarification before and after a biological reactor. DAFs can be both a very good clarifier as well as an equally impressive thickener of bio-solids after. DAF can typically achieve twice the solids concentration of a gravity clarifier after aerobic biological treatment. DAFs also do not suffer loss of performance during start-up and if there is a plant upset when filaments develop in the bio-mass when specific changes occur in the process.
Pretreatment for high rate anaerobic processes
DAFs manufactured by Krofta have been used very successfully as pretreatment for high rate anaerobic processes such as UASB and UAC reactor designs. Specifically in operations where there can be reasonable amounts of oils and solids, Krofta DAFs can effectively reduce the condition where oils in the anaerobic feed can coat and change the overall density of the anaerobic granules. This condition can cause the bio-mass to float to the top of the reactor. Under specific conditions, these granules can be lost to the effluent, possibly requiring the reactor to need replenishment of granules from another reactor or by purchasing granules.
Small decrease in RAS temperature
For low rate anaerobic reactors such as CSTR’s, Krofta DAFs have shown to be very effective in reducing operating costs over traditional separators as well as external gravity separators. Krofta DAFs can achieve separation of solids from both the RAS/WAS streams in 3 to 5 minutes. This results in a DAF design that is both very small in footprint as well as in northern climates there would be only a very small decrease in RAS temperature. In several documented cases, the Krofta DAF lost less than 1 deg. F as opposed to the gravity separator where the overall temperature loss was 12 to 15 deg. F. What that means to the process is that with lower heating needs, more bio-gas from the process can be directed to higher value uses such as electrical power generation of more important plant uses.
Reduce of Phosphor
Krofta DAFs can also be added to reduce increasingly important nutrients such as P. A DAF manufactured by Krofta has demonstrated the ability to reduce total P using a selected metal salt and a flocculent. The choice of metal salts and a flocculent will be best determined from jar testing since the dairy stream will differ plant to plant.