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Nutrient Recovery from Digestate

 

BKT's FMX technology is a unique anti-fouling membrane filtration system that separates the most challenging high solid, high density and high viscosity digestate to recover valuable nutrients and transform "waste" into a profitable resource for our clients.

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Key benefits of FMX:

  • Fouling prevention mechanism

  • High nutrient recovery rates

  • Small footprint

Digestate is difficult to treat mainly because it is a high solid effluent stream from anaerobic digestion. Since the carbon sources are already converted into methane gas, it is also difficult to treat biologically because it would require significant external carbon sources.

But digestate contains abundant sources of nitrogen and phosphorus, so a fouling-preventive membrane filtration system like FMX can recover these nutrients effectively and efficiently.


Nitrogen Recovery

Nitrogen in digestate can be converted into liquid fertilizer when properly concentrated. FMX can remove high solids from digestate without fouling, performing a critical pretreatment for RO (Reverse Osmosis) to concentrate nitrogen or ammonia for fertilizer.

FMX’s capability to separate liquids and solids from digestate can then allow RO to work as a final step in nutrient recovery.

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Phosphorus Recovery

Phosphorus is one of the important nutrients for the crop grow, but if it is over the limit, then algal bloom can happen. Digestate or livestock manure is one of the main sources of the phosphorus pollution. Phosphorus, however, exists mostly in particulate form, so it can be removed or recovered as a solid. Problem is again how to recover the particulate phosphorus effectively. FMX has done a test to recover the phosphorus from hog manure, and it turned out to recover almost 100% of particulate phosphorus.

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increased Biogas Production

In addition to nitrogen recovery, we can return the concentrate from FMX to the anaerobic digester to boost the efficiency of the digester.

Hydromantis, along with the collaboration with Tetra Tech, has done a study about this methane gas increase, using one of our reference sites in the Netherlands. The result was an impressive 25% increase in biogas production.

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References

 T’Haantje BGP | Netherland

A 6 megawatt anaerobic digester in the Netherlands installed 3 FMX units for the
treatment of digestate. Prior to FMX, the facility had a tubular membrane system
installed, but due to the difficult characteristics of the digestate, the tubular system was
fouled beyond recovery within 3 months.


The first full scale industrial installation of its kind, the FMX has been proven to
effectively and reliably treat digestate. At this installation the FMX is used as a
pretreatment to remove suspended solids prior to a spiral RO system. The RO can then
be used to provide clean water for reuse onsite, while concentrating the nutrients for
sale as a fertilizer.


Not only does FMX provide a reliable and consistent RO pretreatment, but the
concentrated biomass from the FMX can be returned to the digester. By returning the
FMX concentrate, the biogas facility has reported up to a 20% increase in biogas
production. In addition, the returned biomass helps maintain a more stable digester,
decreasing operational downtime of the whole operation.

 Full Scale Digestate Treatment with Nutrient Recovery

Full Scale Digestate Treatment with Nutrient Recovery


Dairy Farm Digestate (Modesto)

Client: Dairy Facility, U.S.A
Goal: Concentrate humic and fulvic acid
Membrane: NF
Average Flux: 52  liter / (m2 • hr)  [21 GFD]
Note: 300 mesh screen pretreatment

  Digestate: Filtrate (a) and Feed (b)

Digestate: Filtrate (a) and Feed (b)

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Hog Farm Digestate (Ringler Farm)

Client: Biogas Plant, U.S.A.
Goal: Treatment of anaerobic digestate while concentrating valuable by products
          Reduce/eliminate tipping fee for digestate effluent
Membrane: UF
Average Flux: 19.3  liter / (m2 • hr)  [11.4 GFD]
Note: Pretreatment process included a 400 micron vibrating screen followed by 890 micron screw press

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 Anaerobic digestate treatment: Filtrate (left), Feed (center), and concentrate (right)

Anaerobic digestate treatment: Filtrate (left), Feed (center), and concentrate (right)


Algal Bloom solutions

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