The fractional composition and potential mobility of particulate phosphorus was investigated in sediment from a deep wastewater stabilization pond. The predominant phosphorus fractions were Fe- and Al-bound P (NaOH-RP) and Residual-P (consisting mainly of organic P), which amounted to 35 and 34% of total phosphorus, respectively. A laboratory study was conducted to determine the influence of various environmental parameters (pH, redox conditions, biological activity and temperature) on phosphorus release from lagoon sediment. Phosphorus release was observed under both anaerobic and aerobic conditions. Anaerobic release was about 1.4-5 times greater than aerobic release. Phosphorus release was redox-sensitive and favoured by high pH values, up to 17.4% of total phosphorus being liberated anaerobically and at high pH. Biological activity favoured phosphorus release, since the amount released under non-sterile conditions exceeded that observed under sterile conditions.

Sediment phosphorus was fractionated before and after the release experiments. The NaOH-RP fraction was sensitive to pH and redox environmental changes, and was readily released under reduced conditions and at high pH. The mobility of the Residual-P fraction was enhanced in incubations involving biological activity due to the decomposition of the organic matter in the sediments, and NaOH–nRP (organic phosphorus) decreased by up to 45% during the incubation of non-sterile suspensions.

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