Wastewater Calculations - Mathematics and Statistics for the Environment - page 714

24.10.11 a verage u se C alCulations
During a typical shift, operators log in or record several parameter readings. The data collected
are important in monitoring plant operation as they provide information on how to best optimize
plant or unit process operation. One of the important parameters monitored each shift or each day
is actual use of chemicals. From the recorded chemical use data, expected chemical use can be
forecasted. These data are also important for inventory control, because an estimate can be made
of when additional chemical supplies will be required. To determine average chemical use, we first
must determine the average chemical use:

Totalchemical used (l b)

Averageuse (lb/day) = (24.109)

Number of days

or

Totalchemical used (gal)

Averageuse (gpd) = (2 4.110)

Number of days

Then calculate the days supply in inventory:

Totalchemical in inventory(lb)

Averageuse (lb/day)

Days supplyininventory = (2 4.111)

or

Totalchemical in inventory(gal)

Averageuse (gpd)

Days supplyininventory = (2 4.112)

■ EXAMPLE 24.80
Problem: The chemical used for each day during a week is given below. Based on these data, what
was the average lb/day chemical use during the week?

Monday 92 lb/day

Tuesday 94 lb/day

Wednesday 92 lb/day

Thursday 88 lb/day

Friday 96 lb/day

Saturday 92 lb/day

Sunday 88 lb/day

Solution:

Totalchemical used (l b) 642 lb

7days

Averageuse (lb/day) = = = 91.7lb/day

Number of days

■ EXAMPLE 24.81
Problem: The average chemical use at a plant is 83 lb/day. If the chemical inventory in stock is 2600
lb, how many days supply is this?

Solution:

Totalchemical in inventory(lb)

Averageuse (lb/day)

2600 lb

Days supplyininventory = = = 31.3 days

83 lb/day