Which activated sludge process modification is particularly sensitive to bulking?

The activated sludge process modification that is particularly sensitive to bulking is the conventional modification. This process typically involves a simple aeration tank where raw wastewater is mixed with activated sludge to promote biological treatment of the pollutants.

In a conventional modification, the conditions may not allow sufficient control over the microbial population dynamics, making it more susceptible to bulking issues. Bulking occurs when certain types of bacteria, often filamentous organisms, dominate the population, leading to poor settleability of the sludge. This can result in excessive suspended solids in the treated effluent as the floc formed by the activated sludge fails to settle properly.

In contrast, other modifications such as extended aeration or pure oxygen processes are designed to enhance the settling characteristics and control the growth of filamentous organisms. For example, extended aeration provides a longer retention time and lower loading, which can reduce the likelihood of bulking. Similarly, pure oxygen systems can help control the microbial environment more effectively by providing a more stable oxygen supply, thus minimizing conditions that encourage bulking. Thus, while bulking can occur in any activated sludge process, the conventional modification is particularly vulnerable due to its less controlled conditions.