Difference in sporogenous bacterial populations in thermophilic (55 degrees C) and mesophilic (35 degrees C) anaerobic sewage digestion

Abstract

Spores, sporeforming vegetative cells, and asporogenous populations were enumerated in two semicontinuous anaerobic fermentors digesting municipal primary sludge at 35 and 55 degrees C for more than 87 days. In the 35 degrees C fermentor, the anaerobic total population was 312.5 X 10(6)/ml, with 25.0 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 23.1 X 10(6), 59.2 X 10(6), 26.2 X 10(6), and 7.3 X 10(6)/ml, respectively, with 2.8 X 10(6), 6.7 X 10(6), 3.4 X 10(6), and 1.5 X 10(6)/ml being sporogenous, respectively. The sporeformers accounted for 8.0 to 20.0% of each of the respective populations. In the 55 degrees C fermentor, the anaerobic total population was 512.5 X 10(6)/ml, with 336.6 X 10(6)/ml being sporogenous. The populations that digest casein, starch, pectin, and cellulose were 97.7 X 10(6), 190.7 X 10(6), 75.8 X 10(6), and 11.2 X 10(6)/ml, respectively, with 47.8 X 10(6), 110.6 X 10(6), 43.3 X 10(6), and 5.1 X 10(6)/ml, respectively, being sporogenous. The sporeformers represented 45.5 to 65.7% of each of the respective populations. The numbers of thermophilic sporeforming vegetative cells in the 55 degrees C fermentor were 9.0 to 19.8 times higher than their counterparts in the 35 degrees C fermentor. Most sporeformers were in the vegetative state in the 35 and 55 degrees C fermentors. After 18 days of fermentation at 55 degrees C, sporeformers carried out most of the digestion; however, the digestion was shared by both sporeformers and asporogenous bacteria after 87 days of fermentation. In the 35 degrees C fermentor, asporogenous bacteria digested most of the sludge. During the 18- and 87-day experimental periods, sporeformers were never predominant.