Wastewater Treatment Operator Certification Practice Test

If the sludge in an aeration tank is dark and has low dissolved oxygen (DO), what type of sludge is it likely to be?

1. Heavy Sludge

2. Chlorinated Sludge

3. Septic Sludge

4. Healthy Sludge

The correct answer is: Septic Sludge

The presence of dark sludge with low dissolved oxygen (DO) levels in an aeration tank is indicative of septic sludge. Septic sludge typically forms under anaerobic conditions, where the decomposition is predominantly carried out by anaerobic bacteria that thrive in low oxygen environments. This sludge often has a darker color due to the accumulation of organic matter and the breakdown products from these bacterial processes. The low DO level is a hallmark of these anaerobic conditions, suggesting that the microbial activity is not effectively utilizing oxygen, which is essential in more aerobic processes. In contrast, healthy sludge, which is usually lighter and has a flocculent texture, thrives in aerobic conditions where oxygen is readily available, promoting the growth of aerobic bacteria. Heavy sludge may indicate high levels of solids but does not inherently signify low DO or dark coloration. Chlorinated sludge, on the other hand, would typically show signs of chemical treatment and may not exhibit the same characteristics as septic sludge. The conditions described in the question strongly correlate with septic sludge, making it the appropriate identification in this scenario.