ENZYMATIC TREATMENT OF ACTIVATED SLUDGE FOR VOLATILE FATTY ACIDS (VFA) PRODUCTION
Joanna Wawrzynczyk1*, Liza Kullenberg1, Michael Recktenwald2, Olof Norrlöw2 and Estera Szwajcer Dey1
1Pure and Applied Biochemistry, LTH, Lund University, Box 124, SE-22100 Lund, Sweden 2
Recycling Competence Centre, Kemira Kemi AB, Box 902, SE-25109 Helsingborg, Sweden
(free)
Waste activated sludge originating from a local municipal wastewater treatment plant in Lund,
Sweden, was treated with different biological methods. The effects of hydrolytic enzymes and
sodium citrate on sludge solubilization were studied. The released organic matter was further
used for a biosynthesis of volatile fatty acids (VFA). The release of organic matter measured as
soluble COD, carbohydrates, proteins, humic substances and the production of acetate and
propionate was analyzed.
The most effective enzymatic hydrolysis was achieved in the presence of sodium citrate, protease
and lipase. After 4 hours treatment the measured soluble COD was 2240mg/l and total VFA
390mg/l. In control samples significantly lower values were measured: COD 1260mg/l, total VFA
24mg/l. Further incubation/ fermentation (90 hours) gave total VFA values of about 1830mg/l and
1550mg/l from treated and control samples, respectively. The findings showed a positive
correlation between released organic matter and produced VFA. The higher COD was released,
the more VFA was produced. Parallel to the VFA production, the decrease of dissolved
carbohydrates and proteins was observed. These results indicate that organic matter, released by
enzymes from the used sludge, is readily biodegradable. Based on laboratory scale experiments,
preliminary cost estimation showed economical benefits and practicability of enzymatic treatment
of sludge.
KEY WORDS
Carbohydrates, Cation-binding agent, COD, Enzymes, Proteins, Sodium Citrate, Waste Activated
Sludge, Volatile Fatty Acids
