Changes in Sampling Program
Data on system performance can be greatly affected by changes in a sampling program. If improper sampling locations or laboratory procedures are used, lab results could vary considerably. When the lab data varies widely from one day to the next, check sampling location, time, and lab procedures for errors. Remember that when considering a major process change first review the plant data. Make only one major change at a time. If two changes are made concurrently, it is impossible to determine which change was responsible for which outcome. Allow one week for a plant to stabilize after a process change. An experienced operator who knows the plant may be able to determine if the proper changes have been made after several days, but some plants require up to one month to stabilize after a change. A good rule of thumb to follow is not to change any process parameter more than ten percent per week.
Responding to Plant Changes
One of the most useful tools that will help when it is time to respond to changing conditions within the treatment plant is a complete and accurate record of the operating history of the plant. Most plants go through seasonal variations. Once the proper response has been figured out, it can be applied successfully each year.
Usually each plant will have some mixed liquor suspended solids concentration where the plant will function best at particular times of the year. As the plant grows older, the loading typically increases and operators will have to respond to this. As the years go by, most operators learn the likes and dislikes of their plant very well.