Ten top ranked causes of poor plant performance
The 10 major causes of poor plant performance are described as
Operator Application of Concepts and Testing to Process Control
-This factor was ranked as the most severe deficiency and lead-
ing cause of poor performance at 23 facilities and was a high-
ranked factor at a total of 89 out of the 103 plants evaluated.
It occurs when a trained operator in a satisfactorily designed
plant permits less than optimum performance. This factor was
ranked when incorrect control adjustment or incorrect control
test interpretation occurred, or when the use of existing
inadequate design features continued when seemingly obvious
operations alternatives or minor plant modifications could have
been implemented to improve performance. The lack of testing
and control were not necessarily the result of inadequate
of or inability to apply learned techniques.
Process Control Testing Procedures - Inadequate process control
testing involves the absence or wrong type of sampling or test-
ing for process monitoring and operational control.
deficiency leads to making inappropriate decisions.
unit process tests such as mixed liquor suspended solids, mixed
liquor dissolved oxygen, mixed liquor settleable solids, and
return sludge suspended solids for activated sludge processes
were seldom or never conducted.
Also, important operating
parameters such as sludge volume index, F/M ratio and mean cell
retention time in suspended growth systems or recirculation
rates in trickling filter plants were usually not determined.
This factor adversely impacted performance at 67 of the 103
Infiltration/Inflow - The results of this widespread problem
are manifested by severe fluctuations in flow rates, periods of
severe hydraulic overloading, and dilution of the influent
wastewater so that both suspended and fixed biological systems
are loaded to less than optimal values. The extreme result is
the "washout" of suspended growth systems as a result of the
loss of solids from the final clarification stage during high
flow periods. This factor was ranked first at 56 of the 103