Problem-solving

Even the best-kept water treatment plant will occasionally develop problems, such as a flocculator breaking down or the finished water quality suddenly dropping.  It is the operator's responsibility to ensure that the water plant continues operating in the face of these problems.  This section will introduce to you to a problem-solving pathway that you can use when problems occur at your treatment plant. 

 

 

Identify That There Is a Problem

This step may seem self-evident, but it can actually be the most difficult step in the entire problem-solving process.  In order to recognize that there is a problem occurring at the treatment plant, the operator must be familiar with how the system operates.  He must know how the chemical, electrical, and mechanical processes work so that he will notice any discrepancy in operation.  He should be familiar with the maximum contaminant levels of all of the parameters imposed by state and federal regulatory agencies as well as with the typical levels of each of these parameters in his plant's finished water. 

The operator of a water treatment plant which treats groundwater notices during his routine water tests that the turbidity in the finished water is rising.  Although the turbidity is still well below the maximum contaminant levels, it is above the typical finished water quality for his plant.  He has successfully completed the first step of the problem-solving pathway by identifying that there is a problem. 

 

Pinpoint the Problem

After determining that there is a problem at the plant, the operator must pinpoint the exact cause of the problem.  The following steps can be used to narrow down the search for the problem's cause.

The same problems typically occur over and over again at water treatment plants.  Problems associated with events such as heavy rainfall, spring and fall turnovers of lakes, sluicing from the dam, and algal blooms happen at many treatment plants as fairly regular, seasonal events.  Daily logs are a good source of information to refer to when attempting to determine the source of such problems.  The logs can also tell the operator what has worked to solve similar problems in the past. 

Personal experience is another excellent resource.  The operator should pay close attention when problems do arise and note how they are solved in order to be more prepared for the next situation.  Before any problems occur, he should build his own knowledge of how the plant works by asking questions of his supervisors, reading the on-site manual, and observing the various components of the plant. 

In the case of our example, the operator knows that the source of his plant's water is a well which has not been under the influence of surface water in the past.  Since the daily log for the last couple of years shows no seasonal turbidity problems, he decides that the problem is most likely to come from within the plant. 

The next step is to check basic elements of plant operation for any problems.  The operator first checks the raw water quality, in case surface water has gotten into the groundwater supply during a recent heavy rainfall.  However, the raw water quality has not changed. 

Next, he checks the chemical feed rates throughout the plant.  If the amount of coagulant or other chemicals being fed has changed, he muses, this could affect the finished water quality.  However, the chemical feed rates are the same. 

Third, the operator checks critical systems throughout the plant.  He visually inspects the pump to see if it is indeed pumping, then makes sure the pump control is set to internal, not external.  He visually inspects to see if the coagulant is reaching the feed point (the in-line static mixer) by unhooking the line momentarily.  He checks the feed line for leaks and makes sure that all ball valves are in the open position (valve handle parallel to the pipe.)  Finally, he checks to ensure that the flash mixer, flocculators, and filters are operating. 

Since none of these factors seem to be contributing to the problem, the operator moves on to the next step.

Since there is no obvious cause of the problem in the basic plant operation, the operator next checks to see whether the high turbidity could be a sampling error.  In his plant, water turbidity is sampled continuously by a surface scatter turbidimeter.  So he calibrates the turbidimeter to make sure that the turbidity readings are accurate.  He inspects the turbidimeter for built-up solids or excessive turbidity in the bottom housing, for condensation on the bulb and lens, and to see if the proper amount of water is circulating through the turbidimeter.  If necessary, he cleans the unit and adjusts the flow of water through the instrument. 

In this case, the operator finds no problem in the turbidimeter.

The operator should now use his knowledge of the plant to narrow the search for the problem's source.  The raw water turbidity is normal, the coagulant is being fed into the water properly, and all pieces of equipment seem to be operating.  So the problem must lie between the flash mixer and the clear well. 

The most likely location of a turbidity problem is in the filters, of which this plant has two.  If the water leaving both filters has high turbidity, the problem is likely to be improper feed, high raw turbidity, high color content (due to algae), or even high metal contaminants such as manganese.  Manganese can pass through the filters undetected and precipitate in the clearwell showing turbidity in the finished water. 

However, in this case, the operator notices that the treated water flowing out of one filter is normal while the turbidity is high coming out of the other filter.  So he suspects that the second filter is in need of backwashing.  Visually inspecting the top of the filter shows him that sludge has built up on the top of the media.  The pressure gauge at the back of the filter is high, indicating that the filter has neared its filtering capacity.  By checking the logbook, he can tell that this filter is nearing the end of its normal filter run between backwashing.

The operator now suspects that the high turbidity in the finished water is due to a filter in need of backwashing. 

To make sure that his analysis of the problem is correct, the operator pulls a water sample from the back of the suspect filter to run in the lab turbidimeter.  Testing shows that the water coming out of the suspect filter has a high turbidity while the water coming out of the other filter does not.  This confirms his suspicion, and the operator concludes that the cause of the problem is a filter in need of backwashing. 


Solve the Problem

After pinpointing the problem, the operator should take action to solve the problem.  Then he should double-check to ensure that his action actually had the desired effect.

In the case of our example, the operator solves the problem by backwashing the filter.  After backwashing, he sees that the finished turbidity has returned to its normal level, so he knows he has solved the problem. 


Chlorine leak


The example we have given dealt with a commonplace occurrence at a water treatment plant which had a very simple solution.  Other common problems, such as power outages and chlorine leaks, may have more complex solutions.  SOP's, or standard operating procedures, are written lists of the steps that should be followed in various circumstances to solve problems in water treatment plants.  SOP's should be up-to-date and easy to understand and should always be readily accessible to the plant operator.

 

 

Know When to Call

Despite the utility of SOP's, there are so many unique problems which can occur in a water treatment plant that it is impossible to have written documentation for all contingencies.  The experienced operator will be able to solve the majority of the problems in his plant, but in some cases he may not be able to pinpoint or solve the problem.  Whatever the situation, he must not allow the problem to continue.  If he is unable to correct the problem after an initial investigation, he should call the manager and follow the manager's instructions. 

When calling for help on a problem, the operator should be as honest and accurate as possible.  Even if he thinks that the problem is caused by his own error, it is better to say so and solve the problem than to hide his culpability and allow the problem to continue. 

When dealing with serious problems, the operator should make an effort to remain calm.  The manager may tell him to turn off the filters before the clearwell is contaminated and then to turn off the high service pump.  The first responsibility of any water treatment plant operator is to deliver safe, potable water to his customers, and he should keep this goal in mind at all times.  By following the simple steps in this lesson, the operator can achieve his goal.