What requirement must plants with a capacity greater than 30 million gallons per day meet regarding flocculation equipment?

Plants with a capacity greater than 30 million gallons per day must provide at least two sets of flocculation equipment in parallel to ensure redundancy and operational reliability. This requirement is set in recognition of the importance of flocculation in the treatment process, which is crucial for effective coagulation and sedimentation. By having two sets of equipment running in parallel, plants can maintain flocculation processes even if one set requires maintenance or experiences a malfunction. This redundancy is vital for meeting regulatory standards and minimizing the risk of compromised water quality due to equipment failure.

Other choices do not address the need for redundancy or operational assurance when dealing with such high capacities. Single equipment setups could lead to significant treatment disruptions, making parallel systems preferable for large-scale operations. Using only paddle flocculators or relying on sequential operation also restricts flexibility and responsiveness in process management.