Activated Sludge Process - Wastewater Operators - page 334

Solution:

Total Suspended Solids In = 2445 mg/L × 2.6 MGD × 8.34 = 53,017 lb/day

Total Suspended Solids Out = 17 mg/L × 2.6 MGD × 8.34 = 369 lb/day

Sludge Solids Out = 8470 mg/L × 0.5 MGD × 8.34 = 35,320 l b/day

⎡ ⎣ 53,017 lb/day - (369 lb/da y + 35,320 lb/day) ⎤ ⎦ × 100

Mass Balance = = % 32.7

53,017 lb/day

The value indicates that the sampling point, collection procedure, or
laboratory procedure is producing inaccurate data upon which to make
process control decisions. Or, more solids are entering the settling tank
each day than are being removed. This should result in either (1) a solids
buildup in the settling tank, or (2) a loss of solids over the effluent weir.
Investigate further to determine the specific cause of the imbalance.

8.14.7.3 Mass Balance Biological Process

Solids are produced when biological processes are used to remove
organic matter from wastewater. The mass balance for an aerobic bio-
logical process must take into account both the solids removed by physi-
cal settling processes and the solids produced by biological conversion
of soluble organic matter to insoluble suspended matter or organisms.
Research has shown that the amount of solids produced per pound of
BOD 5 removed can be predicted based on the type of process being used.
Although the exact amount of solids produced can vary from plant to plant,
a series of k factors has been developed that can be used to estimate the
solids production for plants using a particular treatment process. These
average factors provide a simple method to evaluate the effectiveness of
a facility's process control program. The mass balance also provides an
excellent mechanism to evaluate the validity of process control and efflu-
ent monitoring data generated. Table 8.3 lists average k factors in pounds
of solids produced per pound of BOD removed for selected processes.

8.14.7.4 Conversion Factors

Conversion factors depend on the activated sludge modification
involved. Factors generally range from 0.5 to 1.0 lb of solids per pound of
BOD removed (see Table 8.3).

8.14.7.5 Mass Balance Calculation

BOD 5 In (lb) = BOD (mg/L) × Flow (MGD) × 8.34

BOD 5 Out (lb) = BOD (mg/L) × Flow (MGD) × 8.34

Solids Produced (lb/day) = [BOD in (lb) - BOD out (lb)] × k

TSS out (lb/day) = TSS out (mg/L) × Flow (MGD) × 8.34