Effects of variations of extracellular polymeric substances and soluble microbial products on activated sludge properties during anaerobic storage.

Anaerobic storage always takes place in wastewater treatment plants or sludge handling processes. Although extracellular polymeric substances (EPS) and soluble microbial products (SMP) are well known to be the two important chemical parameters to influence sludge properties, few studies have demonstrated the coexisting effects of the two biopolymers on sludge characteristics during anaerobic storage of activated sludge. The experiments, conducted with acetate as the substrate at 35 degrees C and 25 degrees C and with glucose at 35 degrees C, indicated that EPS content decreased significantly in the first two or three days and later slightly increased in all runs, while SMP concentration varied gradually from 66-105mg l(-1) to 330-420mg 1(-1), increasing almost linearly with anaerobic storage time. All the components in EPS decreased after anaerobic storage, especially protein, which was the dominant organic compound in both EPS and SMP with more than 60% of the total amounts of the two biopolymers. Protein and DNA in SMP increased to a large extent and mainly contributed to the three-to five- fold increase in the total amount of SMP, while carbohydrates in SMP remained at a relatively low level. From statistical analysis, some major correlations could be obtained: a weak correlation existed between SMP and EPS; SMP were much more significantly correlated than EPS with sludge properties (biomass, specific resistance to filtration, sludge volume index and relative hydrophobicity of sludge surface). The results indicated that SMP, not EPS, significantly influence the sludge dewatering and settling properties, being deteriorated by more SMP production from cell lysis during anaerobic storage.