Client
Food Waste Digester Facility
Year

2020

Recovered 87% of the digestate as UF permeate
Recovered about 90% of the UF permeate as clean water
  • SWECO
  • Ultrafiltration (UF)
  • Two-Stage Reverse Osmosis™ (TSRO)

Case Study: Ultrafiltration, Food Waste Digester

A 100,000 GPD capacity Food Waste Digester facility form Michigan approached us to create clean water from their digester run-off. Digestate were first screened to remove large abrasive solids and fibers using a low-energy vibratory screen. Screened digested then filtered through our unique UF, designed to treat wastewater without the addition of polymers or processing aids, significantly reducing the operation cost.The UF permeate was of sufficient quality for sewer discharged.

Company Issue / Challenge

Manage Digester run-off, compliance with regulatory permit.

The cost for land application is high and runoff has few nutrients, so paying to truck this material to farm fields is not efficient.

Managing the storage and hauling of leachate is a constant challenge and requires coordination of various trucks throughout the year.

Concentrating the nutrients in the leachate for storage and later land application with manure would be most efficient.

What We Delivered

1

Site Assessment

We processed the raw digestate through an 18” diameter vibratory screen using a Market Grade 35 screen (447 microns with 37.9% open area). The screened digested then filtered through our unique UF. Our proprietary UF system uses stainless-steel modules containing multiple porous tubular UF membranes. For this project, we used a tubular membrane with an average pore size of 0.02 μm. We recovered about 87% of the digestate as UF permeate at a high average flux rate of ~40-10 GFD. The approach produced better quality water, while reducing the OPEX cost for the client.

Impact & Benefits

Our leachate filtration system is designed to recover more than 90% of the liquid as clean water for direct discharge.

1

Ultrafiltration

Recovered 87% of the digestate as UF permeate
2

Water Reclamation

Recovered about 90% of the UF permeate as clean water

Analysis of Ultrafiltration Process Streams

PARAMETERUnitUF FeedUF PermeateUF ConcentratePercent Removed by UF
Total Solidsmg/L 15,900 5,700 52,60464%
Biochemical oxygen demand (BOD)mg/L 673<149.2 NA>78%
Chemical oxygen demand (COD)mg/L 16,460 800 41,90095%
Ammoniacal Nitrogenmg/L 1,020 971 1,2105%
Organic Nitrogenmg/L 650 39 3,43994%
Total Kjeldahl nitrogen (TKN)mg/L 1,670 1,010 4,66140%
Phosphorusmg/L 28112.2 1,50096%
Potassiummg/L 1,010953 1,3006%
Sulfurmg/L 8425.2 40770%
Calciummg/L 441141 1,82168%
Magnesiummg/L 7552.6 20330%
Sodiummg/L 1,1301,120 1,3181%
Ironmg/L33.20.2319699%
Manganesemg/L0.7930.071491%
Zincmg/L1.66n.d.9100%
Coppermg/L0.42n.d.2100%
Conductivityms/cm14.113.9NAn/a
pHS.U.7.878.048n/a

n/a: not applicable; n.d.: not detected , NA: not analyzed

As expected, the UF removed the vast majority of the total solids, organic nitrogen, and phosphorus from the digested food waste sample, producing a transparent permeate. The COD reduction was 95% and the BOD reduction was greater than 78%.

Analysis of Two-Step Reverse Osmosis Process Streams

PARAMETERUnitTSRO FeedTSRO PermeateTSRO ConcentratePercent Removed by TSRO
Total Solidsmg/L 5,700200 28,10096%
Chemical oxygen demand (COD)mg/L 80022 5,40097%
Ammoniacal Nitrogenmg/L 97110.5 1,17099%
Organic Nitrogenmg/L 390.2 6099%
Total Kjeldahl nitrogen (TKN)mg/L 1,01010.7 1,23099%
Phosphorusmg/L12.2n.d.9.69100%
Potassiummg/L9532.7 1,650100%
Sulfurmg/L25.2n.d.74.4100%
Calciummg/L141n.d.113100%
Magnesiummg/L52.6n.d.164100%
Sodiummg/L1,120114 8,28090%
Ironmg/L0.23n.d.0.38100%
Manganesemg/L0.071n.d.0.157100%
Zincmg/Ln.d.n.d.0.05100%
Coppermg/Ln.d.n.d.0.1100%
Conductivityms/cm13.90.7139.3n/a
pHS.U.8.045.718.27n/a

n/a: not applicable; n.d.: not detected , NA: not analyzed

These data indicate that the TSRO produced very clean water with very low levels of N, P, and K. Only 10.1 mg/L of ammonia and 17.2 mg/L of total nitrogen was detected in the RO permeate. The high levels of sodium in the concentrate are an artifact of batch concentration on our pilot unit and is not expected commercially.

Liquid Pictures

Scroll the gallery to see pictures of the materials from our filtration equipment.

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