Organic vs. Hydraulic LoadingsOn-site Treatment Systems

J. R. (Jack) Harman, P.E.North Carolina Annual OnSite Wastewater

ConferenceOctober 18, 2010

Paradigm Shift

• World English Dictionary (n.) A radical change in an underlying belief or theory.

• There is a Paradigm Shift when there exists an acceptance by a majority of a changed belief, attitude, or way of perceiving things.

Perception

• WE NEED TO CHANGE OUR PERCEPTION OF HOW WE LOOK AT SIZING OF PRETREATMENT DEVICES

• USING ORGANIC LOADING SPECIFIC TO THE INTENDED WASTEWATER GENERATORS

• NOT RELYING ON HISTORICAL HYDRAULIC LOADING RATES COMMONLY REFERENCED TO DOMESTIC WASTEWATER CHARACTERISTICS

Typical Raw Domestic Wastewater

Typical Septic Effluent Quality

Comparison of Domestic Wastewater-Influent & Septic Tank Effluent

Suggested Media Filter Loading Rates

Example of Organic ExaminationUsing the IWWS-97-1-Pressure Dosed Sand Filter NC Approval As An Example: BOD <300 mg/l; TSS < 200 mg/l…….TS-2 Effluent Quality For BOD Effluent < 10 mg/l

Design Hydraulic Loading Rate: 2.5 to 5.0 gpd/s.f.Doses per Day: 24 to 48Recirc. Ratio: 2:1 to 5:1; (Note: A 3:1 Recirc Ratio Returns 3 Parts (3/4) of the Sand Filter Effluent

Back To The Recirc Tank While Discharging 1 Part (1/4) To The Drainfield. Therefore, A 3:1 Ratio Doses 4 Times The ADF To The Filter Per Day To Achieve A Discharge Of 1 ADF.

EXAMPLE: A 480 gpd Facility Has BOD=300 mg/l Influent Treated By A Septic Tank & Pressure Dosed Recirc Sand Filter.

RSF Size: 480 gpd / 5.0 gpd/s.f. = 96 sq.ft.# BOD/Day: 0.00048 mgd * 300 mg/l * 8.34 #/gal = 1.2 # BOD/DayFrom Previous EPA Table, BOD Reduction by Septic Tank: 120 mg/l / 250 mg/l = 48%Therefore, # BOD to RSF: 48% x 1.2 #/Day = 0.58 #/Day to RSFOrganic Loading Rate To RSF: 0.58 #/Day / 96 s.f. = 0.006 #/Day/ s.f. (< 0.0083; :. O.K.)

Example #2-Shopping Center

Example #2-Shopping Center Organic Loading Calculation

Example #2-Calculating Organic Load

• Estimated Total Organic Loading to RGF: Filter Size: 50’ x 50’ = 2500 Sq. Ft. Organic Load: 20.2 #/Day / 2500 Sq. Ft. = 0.0081 #/Day/Sq.Ft. At Upper Range of Suggested Loading, O.K.

HOWEVER, NO ALLOWANCE WAS MADE FOR ASTARBUCKS COFFEE SHOP MOVING IN.

Starbucks: 10/07 to 10/08

• Effluent Data From Gravel Media Filter Indicated a Change in Values Around August to October, 2007 when Starbucks First Opened.

• Effluent Strength From Septic Tank Downstream From Starbucks had BOD value ranges of 1,900 mg/l to 2,100 mg/l.

• Effluent From Septic Tank was a “Latte” Color.• Estimated Quantity of Milk/Cream Dumped to

Drain Each Day = > 8 Gallons / Day.

RGF=FUBAR

RGF-POST MORTEM EXAM

A “Lactose” Intolerant Gravel Filter

Conclusions• Characterize the Strength of the Organic

Wasteload to be Treated by the Biological Filter.• Properly Size It with Due Consideration For

Including Perhaps a Factor of Safety.• Do Not Reduce the Size of the Pretreatment

Devices Relying Upon a Reduction in the Water Usage from the Facility.

• If You Cant Estimate The Organic Load (#/Day) Seek Out Reliable Reference Databases for Proper Determinations.