Production of carboxylates from high rate activated sludge through fermentation

Abstract

The aim of this work was to study the key parameters affecting fermentation of high rate activated A-sludge to carboxylates, including pH, temperature, inoculum, sludge composition and iron content. The maximum volatile fatty acids production was 141mgCg(-1) VSSfed, at pH 7. Subsequently the potential for carboxylate and methane production for A-sludge from four different plants at pH 7 and 35°C were compared. Initial BOD of the sludge appeared to be key determining carboxylate yield from A-sludge. Whereas methanogenesis could be correlated linearly to the quantity of ferric used for coagulation, fermentation did not show a dependency on iron presence. This difference may enable a strategy whereby A-stage sludge is separated to achieve fermentation, and iron dosing for phosphate removal is only implemented at the B-stage.

Sidestream RAS Fermentation for Stable Bio-P Combined with Short Cut Nitrogen Removal in an A/B Process

“…The study showed that the initial BOD of the sludge appeared to be the key in determining the yield produced from A-stage sludge. The maximum VFA production found from fermenting A-stage sludge was 141mg C g -1 VSSfed at a pH of 7 (Cagnetta et al, 2016). This is similar to VFA yield found from fermenting primary sludge which expects to produce a VFA yield of 0.15 kg VFA measured as COD per kg of TSS (Oldham and Abraham, 1994).…”

“…This form of fermentation has not been studied in depth with only one other A-stage fermentation study performed so far. The study performed by (Cagnetta et al, 2016) evaluated key parameters that affect the fermentation of HRAS. The study showed that the initial BOD of the sludge appeared to be the key in determining the yield produced from A-stage sludge.…”

“…This additional nutrient load to the mainstream system also must be treated and can be seen in Figure 4.13. The average VFA yield is lower than VFA yields that could be produced by a primary sludge fermenter because of the longer retention time needed to perform cell lysis before sludge hydrolysis and fermentation can occur fully (Cagnetta et al, 2016). Fractionation of the A-stage WAS fermenter VFA was examined and is shown in Figure 4.15.…”

Taking the technical microbiome into the next decade

“…The application of the A-stage in the full-scale municipal wastewater treatment plant of Nieuwveer, Breda, the Netherlands (Meerburg et al, 2016), and Strass, Austria (Wett et al, 2007), enables up to 30-50% energy savings. Recently, the production of carboxylates through fermentation Asludge was investigated to obtain higher-value products, yet, COD conversion efficiencies remained below 30% (Cagnetta et al, 2016). An alternative approach resides in the production of polyhydroxyalkanoates (PHA), using mixed cultures, directly from wastewater in the activated sludge (Salehizadeh and Van Loosdrecht, 2004) or from the fermentation broth (Kleerebezem et al, 2015).…”

Microbial technology with major potentials for the urgent environmental needs of the next decades

“…It appears that for the future wastewater treatment, the production of biogas should no longer be directed to energy recovery, rather biogas and the nutrients present in wastewater must be tuned for reuse by upgrading them into valuable molecules (Cagnetta et al, 2016). The recent advances in single cell protein production, which is the production of protein-rich feed and food, using recovered nutrients and organics, open possibilities for new microbial technological applications to short-circuit nutrient and energy cycles into more efficient processes (Matassa et al, 2015).…”