EFFECT OF AEROBIC DIGESTION, ANAEROBIC DIGESTION, AND AMMONIA ON THE VIABILITY OF OOCYSTS OF CRYPTOSPORIDIUM PARVUM AND THE EGGS OF ASCARIS SUUM IN SEWAGE SLUDGES
Abstract:In this work, ASCARIS SUUM eggs and CRYPTOSPORIDIUM PARVUM oocysts inoculated into biosolids in chambers were compared to eggs and oocysts added directly as spikes to single-stage, 1-liter, anaerobic and aerobic biosolids. The digesters were maintained at 37°C, 47°C, and 55°C, had 10-day detention times, and were fed thickened primary sludge containing 4% solids. The A. suum eggs and C. parvum oocysts were added to the digesters at the concentrations of 1,000 and 50,000 per ml of biosolids in a single spike. 10,000 of the eggs and 2 × 106 oocysts were also added to the biosolids within each of the small chambers, and the chambers were placed in the biosolids at the same exposure times as in the spiked samples. Samples were collected for viability determinations at each sampling time, and the percentage of viable parasites was determined by culture under aerobic conditions at room temperature for eggs or by a dyepermeability assay for oocysts. An additional study using ammonia examined the ability of eggs to survive at pH 13 in biosolids to which was added 0, 1, and 10% (w/v) ammonium sulfate. The results showed that there were no statistical differences observed in the viability of C. parvum oocysts extracted from the chambers and the digested biosolids. There was a statistical difference observed between the sampling procedures (spiked sample or chamber sample) of the A. suum eggs exposed to aerobic digestion at 47°C with the eggs dying much more rapidly in the chambers than they did within the spiked biosolids. At 37°C in aerobically digested sludge, the eggs in the chambers maintained a slightly higher viability (about 10%) than was observed with the eggs added directly to the digester. The results indicated that the chambers could be used in most situations to determine the viability of oocysts and eggs conveniently without using large quantities of these parasites to conduct experiments and without worrying about producing large quantities of contaminated sludges that would require proper disposal. The work also showed that the oocysts of CRYPTOSPORIDIUM PARVUM are much more sensitive to sludge treatment processes than are the eggs of ASCARIS SUUM with almost all oocysts being destroyed by only 4 days of anaerobic digestion at 37°C.
Document Type: Research Article
Publication date: 2001-01-01
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