Increased carboxylate production in high-rate activated A-sludge by forward osmosis thickening

Cristina Cagnetta, Arnout D'Haese, Marta Coma, Ruben Props, Benjamin Buysschaert, Arne Verliefde, Korneel Rabaey

Research output: Contribution to journalArticlepeer-review

24 Citations (SciVal)
258 Downloads (Pure)


Domestic wastewater represents a considerable feedstock for organics but the high dilution makes their recovery typically unsuccessful. Here we investigated three routes to 10-fold concentrate the organics using Forward Osmosis (FO) (Draw solution (DS) 2.2 M MgCl2): directly on domestic wastewater, A-sludge, or secondary sludge, with the end goal of increasing volatile fatty acid (VFA) yield from subsequent 9-day fermentation tests. Forward osmosis concentrated the total COD by a factor of 8.2 ± 1.2, 10.1 ± 2.4 and 4.8 ± 0.2 with respect to the raw streams of wastewater, secondary sludge and A-sludge. The soluble fraction of the COD was concentrated up to 3.5 times in the A-sludge and 2.1 times in the secondary sludge; the result of a combined effect of the chemical action of Mg2+ (diffused from the DS) on sludge disaggregation and cell lysis, and the physical action of recirculation and air-scouring of the A-sludge in the FO-unit.
The FO-concentrated A-sludge produced 445 ± 22 mg COD-VFA g-1 CODfed, which was 4.4 times higher than for the untreated A-sludge. No VFA were produced from untreated secondary sludge, but after FO-concentration 71 ± 5 mg COD-VFA g-1 CODfed could be reached. Due to the low organics in wastewater even after FO-concentration (1.08 ± 0.08 g COD L-1), no notable VFA production occurred. The combination of A-stage technology and membrane technology for dewatering and COD concentration could be a key advancement to increase VFA production from domestic wastewater, whereby at least 45% of the COD can be recovered as valuable VFA.
Original languageEnglish
Pages (from-to)68-78
JournalChemical Engineering Journal
Early online date19 Nov 2016
Publication statusPublished - 15 Mar 2017


  • Carboxylate fermentation
  • Forward osmosis (FO)
  • AB system
  • Volatile fatty acids (VFA)
  • Waste activated sludge (WAS)


Dive into the research topics of 'Increased carboxylate production in high-rate activated A-sludge by forward osmosis thickening'. Together they form a unique fingerprint.

Cite this