The impact of reduced phosphorus levels on microbial floc properties during biological treatment of pulp and paper wastewaters.
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.
Liu
J R
JR
Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada.
Liss
S N
SN
D001420:Bacteria, Aerobic / Q000502:physiology*; D019149:Bioreactors / Q000382:microbiology; D002627:Chemistry, Physical / Q000379:methods; D005427:Flocculation; D007220:Industrial Waste; D010209:Paper; D010758:Phosphorus / Q000378:metabolism*; D011108:Polymers / Q000737:chemistry; D012722:Sewage / Q000737:chemistry / Q000382:microbiology; D013696:Temperature; D013997:Time Factors; D014865:Waste Disposal, Fluid / Q000379:methods*
D007220:Industrial Waste; D011108:Polymers; D012722:Sewage; D010758:Phosphorus