Disinfection of Pipelines - Disinfection of Pipelines and Storage Facilities Field Guide - page 54

Table 3-12 Total chlorination time needed based on slug size

Slug Size 10% 15% 20% 25% 30% 35% 40% 45% 50%

Chlorination
time, hr

30 22.5 15 12.5 10 8.75 7.5 6.75 6

❑ This method uses a slug of 100 mg/L chlorinated water as a
slug that moves along the length of the pipeline. The slug
is a percentage of the total length of the pipeline. The slug
volume is calculated from Table 3-6 and calculator c3-6.
❑ The amount of chlorine chemical needed for the job is
calculated using c3-8, 9, or 10, depending on the length and
size of pipe and the chemical used. In the situation where
the slug is produced by continuously feeding the chlorina-
tion chemical, the withdrawal rate is calculated from c3-7
to achieve a 3-hr contact time at every point along the pipe-
line. Tables 3-10 and 3-11 show the feed rate needed to
match with the fill rate (withdrawal rate) of the pipeline.
Study the examples below to gain a more complete under-
standing of how to make this calculation.

Volume of slug calculator. Choose the size of the slug
(percent of total volume) based on the time to complete the job
(Table 3-12). For example, if only 10 hr are available to complete
the chlorination, a 30 percent slug would be the minimum size
necessary.
For the slug method, calculate the withdrawal rate using the
following calculator to ensure 3-hr contact time at all points
along the pipeline. Choose the matching chlorination chemical
solution feed rate from Table 3-10 or 3-11.
Table 3-12 shows the total time needed to complete the disin-
fection for various sizes of slugs. If the slug is 30% of the length of
the pipeline to be disinfected, the procedure will take 10 hours
(including creating the slug and then moving the slug so that
there is a 3-hr contact time). This table is helpful to select the
size of the slug based on the time needed to complete the job.