Design flow for residential domestic sewage is normally considered to be 100 gallons per capita per day containing 0.25 pounds of BOD. Some states require sizing based on number of bedrooms and some based on number of people. Check with local and/or state agencies to find out what the actual requirements are. The following examples are reasonable methods for plant sizing:
Select a treatment plant for a four bedroom house with five persons.
.25 pounds BOD/persons day X five persons = 1.25 pounds BOD/day.
A 500-GPD plant can treat 1.25 pounds BOD/day (see chart).
Therefore use a 500 GPD plant. Example 2
Select a treatment plant for a six bedroom house with four persons. A treatment plant for this house should be designed for expansion of the household to seven persons. Two in one bedroom and one in each of the other five bedrooms.
Seven persons X 100 GPD/person = 700 GPD.
.25 pounds BOD/persons per day X seven persons = 1.75 pounds BOD/day.
A 750 GPD plant can treat 1.88 pounds BOD/day. Therefore use a 750 GPD plant.
Chart 1 ECOPOD-N™ Fixed Film Wastewater Treatment System Treatment Plants – Sizes/Capacities
BOD Treatment Capacity (lbs/day) 1.25 1.5 1.88 2.5 3.75