A shock load is defined as what?

• A. A large quick increase of organic loading on the system
• B. A sudden drop in flow
• C. A steady, mild increase in BOD
• D. A minor sedimentation event

Answer: (A)

A rapid, large surge in organic loading entering the treatment system. This means a sudden spike in the amount of biodegradable material (often measured as BOD) that the plant must treat in a short period. When this happens, the microorganisms in the treatment process have to metabolize a lot more organics quickly, which can quickly consume dissolved oxygen in aerated basins and disrupt settles or nitrification, leading to poorer effluent quality or process upset. Such spikes can come from a sudden industrial discharge or a dump of high-strength wastewater. A sudden drop in flow changes the hydraulic load rather than the organic load, so it isn’t a shock load. A steady, mild increase in BOD develops gradually and doesn’t produce the immediate disruption characteristic of a shock. A minor sedimentation event involves solids handling, not the rapid organic load increase.