Water/Wastewater Laboratory Calculations - Basic Mathematics for Water and Wastewater Operators - page 231

16 Water/ Wastewater

Laboratory Calculations

Waterworks and wastewater treatment plants are sized to meet current needs, as well
as those of the future. No matter the size of the treatment plant, some space or area
within the plant is designated as the lab area, which can range from being the size of
a closet to being fully equipped and staffed environmental laboratories. Water and
wastewater laboratories usually perform a number of different tests. Lab test results
provide the operator with the information necessary to operate the treatment facility
at optimal levels. Laboratory testing usually includes determining service line flush-
ing time, solution concentration, pH, chemical oxygen demand (COD), total phos-
phorus, fecal coliform count, chlorine residual, and biochemical oxygen demand
(BOD), to name a few. The standard reference for performing wastewater testing is
contained in Standard Methods for the Examination of Water & Wastewater.
In this chapter, the focus is on standard water/wastewater lab tests that involve
various calculations. Specifically, the focus is on calculations used to determine the
proportioning factor for composite sampling, an estimation of flow from a faucet,
service line flushing time, solution concentration, BOD, molarity and moles, normal-
it y, settleability, settleable solids, total solids, fixed and volatile solids, suspended
solids, volatile suspended solids, biosolids volume index, and biosolids density index.

FAUCET FLOW ESTIMATION
On occasion, the waterworks sampler must take water samples from a customer's
residence. In small water systems, the sample is usually taken from the customer's
front yard faucet. A convenient flow rate for taking water samples is about 0.5 gal-
lons per minute (gpm). To estimate the flow from a faucet, use a 1-gallon container
and record the time it takes to fill the container. To calculate the flow in gallons per
minute, insert the recorded information into Equation 16.1:

Flow (gpm) = Volume (gal) ÷ Time (min) (16.1)

■ Example 16.1
Problem: The flow from a faucet filled up the gallon container in 48 sec. What was
the flow rate from the faucet in gallons per minute? Because the flow rate is desired
in minutes the time should also be expressed as minutes:

48 sec ÷ 60 sec/min = 0.80 min

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