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The main objective of this research was to test the hypothesis that bioavailable protein and, more specifically, the sulfur-containing amino acids within the protein, can be degraded by proteolytic enzymes to produce odor-causing compounds--mainly volatile sulfur compounds (VSCs)--during biosolids storage. To achieve these objectives, samples of digester effluent and cake solids were collected at 11 different wastewater treatment plants in North America, and the samples were analyzed for protein and amino acid content and general protein-degrading enzyme activity. At the same time, cake samples were stored using headspace bottles, the concentration of VSCs were measured using gas chromatography, and olfactometry measurements were made by a trained odor panel. The results showed that the bound cake protein content and methionine content was well-correlated with VSC production and the detection threshold measured by the odor panel.

Eleven dewatered sludge cakes collected from anaerobic digesters at different treatment plants were evaluated for the amount, type, and pattern of odorous gas production. All but one of the sludge cakes were from mesophilic anaerobic digesters. One was from a thermophilic digester. The pattern and quantities of sulfur gases were found to be unique for each of the samples with regard to the products produced, magnitude, and subsequent decline. The main odor-causing chemicals were volatile sulfur compounds, which included hydrogen sulfide, methanethiol, and dimethyl sulfide. Volatile sulfur compound production peaked in 3 to 8 days and then declined. The decline was a result of conversion of organic sulfur compounds to sulfide. In one side-by-side test, a high-solids centrifuge cake generated more odorous compounds than the low-solids centrifuge cake. The data show that anaerobic digestion does not eliminate the odor potential of anaerobically digested dewatered cakes.

This study shows for the first time that overlooked mg/L concentrations of industrial dimethyl sulfoxide (DMSO) waste residues in sewage can cause "rotten cabbage" odor problems bydimethyl sulfide (DMS) in conventional municipal wastewater treatment. In laboratory studies, incubation of activated sludge with 1-10 mg/L DMSO in bottles produced dimethyl sulfide (DMS) at concentrations that exceeded the odor threshold by approximately 4 orders of magnitude in the headspace gas. Aeration at a rate of 6 m3 air/m3 sludge resulted in emission of the DMS into the exhaust air in a manner analogous to that of an activated sludge aeration tank. A field study atthe NEWPCP sewage treatment plant in Philadelphia found DMSO levels intermittently peaking as high as 2400 mg/L in sewage near an industrial discharger. After 3 h, the DMSO concentration in the influent to the aeration tank rose from a baseline level of less than 0.01 mg/L to a level of 5.6 mg/L and the DMS concentration in the mixed liquor rose from less than 0.01 to 0.2 mg/L. Finding this link between the intermittent occurrence of DMSO residues in influent of the treatment plant and the odorant DMS in the aeration tank was the keyto understanding and eliminating the intermittent "canned corn" or "rotten cabbage" odor emissions from the aeration tank that had randomly plagued this plant and its city neighborhood for two decades. Sewage authorities should consider having wastewater samples analyzed for DMSO and DMS to check for this possible odor problem and to determine whether DMSO emission thresholds should be established to limit odor generation at sewage treatment plants.

The effect of pH on phosphine formation during anaerobic cultivation of granular sludge was investigated. The sludge was taken from full-scale anaerobic reactors treating brewery wastewater. Acetate and phosphate were used as the carbon source and phosphorus source respectively. After 10 days cultivation in the dark, results showed that acidic conditions were more favorable for free phosphine production. At pH 5, the optimum concentration 86.42 ng PH3 m-3 of free phosphine was obtained. The level at pH 7 was reduced to 18.53 ng PH3 m-3, about 1/5 of the maximum. The maximum concentration of matrix-bound phosphine of 3.30 ng PH3 kg-1 wet sludge was achieved at pH 6. More than 83% of the total phosphine was matrix-bound phosphine, which accounted for 0.003-0.009 per thousand of the phosphate removal, while free phosphine comprised 0.00002-0.001 per thousand of the phosphate removal. Most of the phosphorus removal from solution was turned into chemical precipitation or was adsorbed by sludge. The mechanism of the phosphate reduction-step in the formation of phosphine production is still unknown. The promotion of phosphine formation by low pH is compatible with an acidic bio-corrosion mechanism of metal particles in the sludge or of metal phosphides which form phosphine at low pH.

The feasibility of full-scale anoxic disinfection of dewatered and digested sludge from Winnipeg, Manitoba with low lime doses and lagoon fly ash was investigated to determine if a class A product could be produced. Lime doses of 50 g, 100 g, and 200 g per kg of biosolids (dry) were used along with fly ash doses of 500 g, 1,000 g, and 1,500 g per kg of biosolids (dry). The mixed product was buried in eight-10 cubic metre trenches at the West End Water Pollution Control Center in Winnipeg. The trenches were backfilled with dirt and trapped to simulate anoxic conditions. Sampling cages were packed with the mixed product and pathogens non-indigenous to Winnipeg's biosolids. The cages were buried amongst the mixed biosolids in the trench. The non-indigenous pathogens spiked in the laboratory were the helminth Ascaris suum and the enteric virus reovirus. Samples were removed at days 12, 40, 69, 291, and 356 and were tested for the presence of fecal Coliform, Clostridium perfringens spores, Ascaris suum eggs, and reovirus. The pH, total solids, and free ammonia content of the mixed product were also determined for each sample. Odor was quantified for samples at both 291 and 356 days. Fecal Coliform bacteria and reovirus were completely inactivated for doses as low as 100 g lime per kg biosolids (dry) and 50 g lime + 500 g fly ash per kg biosolids (dry). Spores of the bacteria C. perfringens experienced a 4-log reduction when treated with 100 g lime per kg biosolids and a 5-log reduction when treated with doses as low as 50 g lime + 500 g fly ash per kg biosolids (dry) after 69 days. Ascaris eggs were completely inactivated in 5 gram packets for all treatments involving 100 g lime per kg biosolids (dry) after 69 days. Class A pathogen requirements were met for all treatments involving a lime dose of at least 100 g per kg biosolids. The odor potential from the produced biosolids is also assessed.