EXTRACTION OF EXTRACELLULAR POLYMERS FROM ACTIVATED-SLUDGE USING A CATION-EXCHANGE RESIN

The extraction of water soluble extracellular polymeric substances (EP S) from activated sludge was investigated. The extraction procedure wa s based upon cation exchange using a cation exchange resin (CER). Acti vated sludge from two different types of treatment plants responded ve ry similarly to the extraction procedure. The EPS yield was enhanced b y increasing the stirring intensity, the amounts of CER added and by i ncreasing the extraction time. For the chosen extraction procedure the yield was twice as high as other commonly used procedures. The extrac t consisted mainly of protein but also humic compounds, carbohydrates, uronic acids and DNA were found in significant amounts. The extracted amounts and relative fraction of the individual compounds strongly de pended on how the extraction was performed. The ratio between protein and carbohydrate was found in the range 3.9-5.1 depending on the extra ction time. Humic compounds and DNA were the compounds most easily ext racted. HPSEC investigation of the extract revealed that the extractio n did not significantly degrade the EPS. Some cell lysis was identifie d during the extraction for extraction times greater than 1-2 h by obs erving a decrease in cell number (stained by DAPI, CTC and acridine or ange). The lysis was not considered a significant problem for contamin ating the EPS. Measurements of the cell number and cell size distribut ion in the sludge suggested that the cell mass did not account for mor e than approximately 10-15% of the total organic fraction of the inves tigated sludge. Two extraction strategies were formulated. One for a v ery gentle and one for a very effective method. Analytical methods for analysis of sludge and EPS extracts were compared and discussed. A co rrected Lowry method for analyzing protein as well as humic compounds was implemented and found suitable. Copyright (C) 1996 Elsevier Scienc e Ltd