Resource Recovery & Reuse

Biogas is produced when organic materials are decomposed by bacteria without the presence of oxygen - a process known as anaerobic digestion. This natural process has been a longtime popular practice for creating renewable energy simply by burning biomass as an organic heat source.

The leftover digestate consists of high solids and high viscosity streams with very high total nitrogen and phosphorus - valuable natural resources. In the past, a popular use of anaerobic digestate was to spray it on farmland as fertilizer. After years of doing this, however, many U.S. states have banned such practices due to pervasive soil saturation resulting in groundwater contamination from excess nutrients.

Want to increase your digester's profitability? Turn your waste into liquid fertilizer!

A nutrient recovery project is under way to recover and sell valuable nutrients to increase the revenue of the biogas plant. The project goal is to remove 100% of suspended solids prior to downstream Reverse Osmosis (RO) to further concentrate and recover the valuable dissolved nutrients from the digestate.

From Cost Stream to Profit Stream

Anaerobic digestion of manure, food processing byproducts, and other waste streams provides a source of low-cost, renewable energy but also generates a high-strength waste stream that contains high concentrations of nutrients, biomass, and organic matter. Processing this waste stream is so costly that it has prevented wider adoption of anaerobic digestion. However, BKT's solution allows the digestate to become a revenue stream by enabling the recovery of nutrients in the digestate as a marketable organic fertilizer. It also concentrates the solids in the digestate, reducing hauling costs for disposal.

BKT employs its anti-fouling FMX membrane filtration system as the basis of a treatment train for the recovery of nitrogen from anaerobic digester effluent (digestate) as a profitable liquid fertilizer. A sample process train is shown below.

Targeted Issues

• Nitrogen and Phosphorus recovery from digestate & organic fertilizer production
• Digestate volume reduction to reduce hauling costs

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 the 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.

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