title: Activated sludge flocculation: direct determination of the effect of calcium ions.
abstract: The effect of calcium on activated sludge flocculation dynamics is investigated using a unique experimental technique. The technique allows on-line analysis of the size of activated sludge flocs during flocculation and provides valuable insight into the mechanisms of flocculation. Activated sludge samples were firstly sonicated for 3 minutes at 50 W and then stirred at 100 rpm. The floc size was subsequently measured on-line using a Malvern Mastersizer/E. For concentrations of calcium less than 4 meq/L no significant increase in final floc size was observed even though an increase in the initial rate of change of floc size could be seen. Addition of calcium greater than 4 meq/L resulted in a dramatic increase in floc size. Results from this investigation support the theory that cations are involved in flocculation through cationic bridging, and will be used in ongoing investigations to model the flocculation process.
authors.affiliation: Advanced Wastewater Management Centre, University of Queensland, St Lucia, OLD 4072 Australia.
authors.forename: C A
authors.initials: CA
authors.lastname: Biggs
authors.forename: A M
authors.initials: AM
authors.lastname: Ford
authors.forename: P A
authors.initials: PA
authors.lastname: Lant
mesh_terms: D002122:Calcium Chloride / Q000008:administration & dosage / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D005427:Flocculation; D007474:Ion Exchange; D010316:Particle Size; D012722:Sewage / Q000032:analysis / Q000737:chemistry* / Q000382:microbiology; D014873:Water Pollutants / Q000032:analysis; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
chemical_list: D002412:Cations; D012722:Sewage; D014873:Water Pollutants; D002122:Calcium Chloride