Extraction of extracellular polymers from activated sludge using a cation exchange resin

The extraction of water soluble extracellular polymeric substances (EPS) from activated sludge was investigated. The extraction procedure was based upon cation exchange using a cation exchange resin (CER). Activated sludge from two different types of treatment plants responded very similarly to the extraction procedure. The EPS yield was enhanced by increasing the stirring intensity, the amounts of CER added and by increasing the extraction time. For the chosen extraction procedure the yield was twice as high as other commonly used procedures. The extract 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 depended on how the extraction was performed. The ratio between protein and carbohydrate was found in the range 3.9–5.1 depending on the extraction time. Humic compounds and DNA were the compounds most easily extracted. HPSEC investigation of the extract revealed that the extraction did not significantly degrade the EPS. Some cell lysis was identified during the extraction for extraction times greater than 1–2 h by observing a decrease in cell number (stained by DAPI, CTC and acridine orange). The lysis was not considered a significant problem for contaminating the EPS. Measurements of the cell number and cell size distribution in the sludge suggested that the cell mass did not account for more than approximately 10–15% of the total organic fraction of the investigated sludge. Two extraction strategies were formulated. One for a very gentle and one for a very effective method. Analytical methods for analysis of sludge and EPS extracts were compared and discussed. A corrected Lowry method for analyzing protein as well as humic compounds was implemented and found suitable.