impact of reduced phosphorus levels on microbial floc properties during biological treatment of pulp and paper wastewaters

• Published in: Water science and technology 2007-01, Vol.55 (6), p.73-79
• Main Authors: Liu, J.R, Liss, S.N
• Format: Article
• Language: English
• Subjects: Activated sludge; Bacteria, Aerobic - physiology; Batch reactors; Biological effects; Biological properties; Biological treatment; Bioreactors - microbiology; Chemistry, Physical - methods; Composition; Containers; Control; Extracellular; Flocculation; Gravitation; Gravity; Hydrophobicity; Industrial Waste; Low temperature; Microorganisms; Phosphorus; Phosphorus - metabolism; Polymers - chemistry; Properties; Pulp; Pulp & paper industry; Reactors; Removal; Sequencing batch reactor; Settling rate; Settling velocity; Sewage - chemistry; Sewage - microbiology; Sludge; Surface charge; Temperature; Time Factors; Waste Disposal, Fluid - methods; Wastewater; Wastewater treatment
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2007.214

The effect of limiting P in activated sludge was investigated in laboratory scale sequencing batch reactors (SBRs) fed effluent from a container board mill. Floc characterization included measurement of hydrophobicity, surface charge, and analysis of extracellular polymeric substances (EPS). Reactor performance was assessed by monitoring COD and inorganic P removal, MLSS, and sludge settleability (SVI and batch settling flux) over a period of eight months. Control reactors (BOD:N:P of 100:5:1) were compared to reactors run under P-limited conditions (100:5:0.3; 100:5:0.1). Reactor performance at lower temperatures (14 degrees C; control = 26 degrees C) was also studied to assess the impact of P-limitation. Changes in floc structure and the composition of EPS occurred within 1 to 3 days following a reduction in P levels. There was an insignificant increase in SVI; however, gravitational settling velocity and batch settling flux values for low P floc were consistently higher than for floc generated under control conditions. Lower temperatures (14 degrees C) resulted in a deterioration in floc settling properties at a BOD:N:P of 100:5:1. This impact on settling was significantly reduced at a BOD:P of 100:0.1. Reducing P concentrations in the wastewater treatment system has the potential to improve sludge settleability and reduce final P discharges.