Organic vs. Hydraulic Loadings On-site Treatment Systems J. R. (Jack) Harman, P.E. North Carolina Annual OnSite Wastewater Conference October 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 Examination Using 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 48 Recirc. 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: mgd * 300 mg/l * 8.34 #/gal = 1.2 # BOD/Day From 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 RSF Organic Loading Rate To RSF: 0.58 #/Day / 96 s.f. = #/Day/ s.f. (< ; :. 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. = #/Day/Sq.Ft. At Upper Range of Suggested Loading, O.K. HOWEVER, NO ALLOWANCE WAS MADE FOR A STARBUCKS 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.