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A microwave-enhanced acid digestion method that was integrated with inductively coupled plasma-atomic emission spectrometry was developed and validated for determining total, soluble, and precipitated sulfur in wastewater treatment sludges. The coefficient of variation of this method was less than 4.0%. The recovery of dosed sulfur from sludge samples was between 97.1% and 100.5%. The composition of sulfur in primary and waste-activated sludge (WAS) before and after anaerobic digestion at 35 and 55 degrees C was characterized by employing this developed method. There was not an apparent relationship between the precipitated sulfur and nonsoluble iron concentrations in sludges. Raw WAS had a more consistent organic sulfur fractionation because of its relatively homogeneous composition. The organic-sulfur-containing components (proteins) of WAS had reduced degradability as compared with that in primary sludge during anaerobic digestion. Digestion at 55 degrees C increased solubilization but not ultimate conversion of organic sulfur in sludge.

The City of St. Petersburg (Florida) Southwest Water Reclamation Facility achieves significant levels of nitrogen (N) and biological phosphorus (P) removal. N removal is via SND from operating the aerated zones at low DO. Despite the low DO operation, very good biological P removal performance is achieved. P removal is sustained at mixed liquor summer temperatures reaching 30°C. Full-scale performance data and detailed bench-scale testing were conducted to assess the N and P removal at low DO. Full-scale results showed that the plant achieves effluent total inorganic nitrogen (TIN) and total phosphorus (TP) concentrations of approximately 2.0 mgN/L and 0.5 mgP/L, respectively, at an average influent C: N ratio of 7:1. Specific nitrification rate (SNR) and specific denitrification rate (SDR) testing indicated that the population of nitrite oxidizing bacteria (NOB) is repressed significantly due to the low DO operation and that nitrite-shunt occurs at the plant. Phosphorus release and uptake (PRU) tests indicated that the low DO operation did not hinder the uptake of phosphate and biological P removal was achieved at the low DO conditions.

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