Do You Know Your Co$ts? Tom Stow Operations & Maintenance Division Manager Clean Water Services
Would you like to take the stress out of budget prep?
Have you calculated the annual dose for each chemical used? Why not?
Useful information The monthly Facility flow and loads for BOD & Ammonia Total usage of each chemical on an annual basis, not just the $, also the pounds The unit price for each chemical Power Costs and usage Power usage for blowers Monthly amount of rainfall
Annual Flow Each Facility should already have this information It is required on the DMR Total it for either the fiscal or calendar year We use a 2-year average for the total flow to the facility We also add a small rate of growth
We use a 2-year Average FY 2009 FY 2010 Eff Flow Eff Flow Feb-07 1,031 Feb-08 1,100 Mar-07 1,117 Mar-08 1,025 Apr-07 942 Apr-08 905 May-07 958 May-08 846 Jun-07 867 Jun-08 808 Jul-07 918 Jul-08 756 Aug-07 926 Aug-08 762 Sep-07 835 Sep-08 720 Oct-07 991 Oct-08 749 Nov-07 978 Nov-08 836 Dec-07 1,621 Dec-08 943 Jan-08 1410.6 Jan-09 1,200 Total 12,595 Total 10,649 12,0122-yr avg 11,6222-yr avg 240.22% growth 116.21% growth 12,252.4total 11,738.1total
Chemicals When Management has a budget request that is based on real numbers, most of their questions will disappear Flow, Dose & Price = Budget request Might not have full control of the amount of Q or chemical prices; should have control of the dose
Using the Lbs/day formula Budget Request
Sodium Hypochlorite For example: Annual Flow = 15,500 MG Annual dose of chlorine = 3.0 mg/l 15500 * 8.34 * 3 = 378,810 Lbs of chlorine We purchase hypo by the gallon 378,810 Lbs / 1.25 Lbs per gal = 310,250 gallons 310,250 gallons * $0.80/gal = $248,200
Price Increase How to factor in an expected price increase It is easy to estimate a new budget number by inserting the new price per unit 378,810 Lbs / 1.25 Lbs per gal = 310,250 gallons 310,250 gallons * $0.88/gal = $273,020
Optimization After reviewing each chemical, what goals can be set to optimize the dose? Have your Operations Staff help with the calculations so they have buy-in on goals for the next year
How Much Does It Save? A 0.5 mg/l reduction in dose saves you how much money? 15,500 MG*8.34*0.5mg/L = 64,635 Lbs 64,635 lbs / 1.25 lbs/gal = 51,708 gallons 51,708 gal* $0.80/gal = $ 41,300
Use a calculation for each chemical used
Two of the Utilities lend themselves to calculations: Landfill cost for grit & screenings Electrical power Utilities
Garbage Do you currently track your landfill costs? How about the tonnage to the landfill? Do you squeeze the water from the screenings or drain it from the dumpsters? Calculate the tonnage per Million Gallons from invoices and recalculate each year based on new prices or flow amounts
Power What do you pay per kwh? Divide the total kwh each month into the total dollar amount on the bill. Don t get caught up in transmission costs, etc
Power Do you generate power? Do you expect to produce the same amount each year? Calculate how much power is purchased per MG treated Is the flow expected to increase, decrease or remain the same? Recalculate each year
kwh per MG Total kwh Purchased / Total MG For example, if the kwh / MG = 2,000 15,500 MG X 2,000 kwh/mg = 31,000,000 kwh 31,000,000 kwh X $0.07/kWh = $2,170,000
Nutrient Removal Impacts on Power usage More biomass is needed, increases O 2 demand More oxygen demand to convert the ammonia to nitrate Do you remove Phosphorous too? Chemical or Biological treatment Biological treatment may require additional DO in the basin
Power Usage
Calculate the Loading on the Blowers Various ways to do this We get to a common factor, pounds of oxygen needed to treat BOD and Ammonia BOD needs ~1 lb of oxygen per pound of BOD Ammonia needs ~4.33 lbs of oxygen per pound of ammonia Find the total pounds of oxygen supplied by the blowers
Calculate the Loading on the Blowers (continued) Calculate the oxygen supplied 50,000 lbs day of BOD X 1.0 lbs of Oxygen per lb = 50,000 lbs of O2 required 6,000 lbs day of NH3 X 4.33 lbs of Oxygen per lb = 26,000 lbs of O2 required 50,000 + 26,000 = 76,000 lbs of O2/day How much power is required to provide this amount of Oxygen?
Power Usage by Blowers If you don t have a meter on the blowers Total power usage (kwh) by blowers = kwh used by Blowers, calculated from the amps, tracked by SCADA Formula: kwh = total amps * 480 * 0.9 * 1.73 / 1000 Amps*Volts*Motor Efficiency*3-phase factor For example, if the total kwh for the year = 7,000,000 kwh
Oxygen Supplied 50,000 lbs/day of BOD: 50,000 lbs X 365 = 18,250,000 lbs/year 6,000 lbs/day of NH3: 7/12 months for nitrification 7 mths X 30 days = 210 days per year 6,000 lbs X 210 days = 1,260,000 lbs/year
Relationship of kwh to lbs 18,250,000 + 1,260,000 = 19,510,000 lbs O 2 7,000,000 kwh/19,510,000 lbs O 2 =.36 kwh/lb O 2 Track this ratio over time to optimize the process
Is Optimization Possible? What DO residual is in the aeration basin, can it be optimized? What is the header pressure in the system, can it be optimized? Is the Plant loading going up, down or staying the same from year to year? Recalculate each year for the amount of power that will be required
Summary Calculate the power estimate for oxygen supply if you are required to nitrify ammonia kwh per lbs of O 2 required Add the power estimate for the Q to be treated for the year kwh per MG
Summary (continued) Minus on site generation Equals total kwh to purchase Times the cost per kwh from power company Oh, was there a price increase to include? Do a sensitivity analysis for several scenarios Review past years, how close are your estimates? Equals Power budget
Peaking Factor How to determine the peaking factor: The Base Wastewater Flow = Average of the daily flow from the summer months of July, August and September Compare the Base Wastewater Average to the Maximum Day Wet Weather Flow Was it a 1 in 5 year event? Are the rain event totals similar for comparison
Peaking Factor What is your peaking factor? < 4% - Congratulations! > 10% - Shame on you! Find that I&I Is it improving, or not?
Excess Flow You can calculate the cost to treat the Excess Flow per MG for chemicals and power Apply that to the amount of excess flow each winter This puts a price on I&I so cost/benefit analysis can be preformed for repair-replace-treat options
Inflow vs Infiltration How do you know which is coming into your system? Plot the daily flow against the daily rainfall Can you tell from the following graph when there is I&I and when there is only infiltration?
35 3.50 30 3.00 25 2.50 MGD 20 15 2.00 1.50 Inches 10 1.00 5 0.50 0 0.00 10/1/2007 10/8/2007 10/15/2007 10/22/2007 10/29/2007 11/5/2007 11/12/2007 11/19/2007 11/26/2007 12/3/2007 12/10/2007 12/17/2007 12/24/2007 12/31/2007 1/7/2008 1/14/2008 1/21/2008 1/28/2008 2/4/2008 2/11/2008 2/18/2008 2/25/2008 FG Inf flow MGD Rainfall, inches
Does your annual flow track with the annual rainfall?
Flow & Rainfall Million ns of Gallons per Year 13,000 12,000 11,000 10,000 9,000 8,000 7,000 6,000 5,000 45.00 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 Inch hes of Rain per Year 4,000 FY 2001 FY 2002 FY 2003 FY 2004 FY 2005 FY 2006 FY 2007 FY 2008 FY 2009 FY 2010 0.00 Rock Creek Durham Annual Rainfall
Excess Flow Calculations Example: Excess flow for the winter is 900 Million Gallons Previous example for hypo equals $17.60 per MG 900 MG * $17.60 = $15,800 2,000 kwh * 900 MG = 1,800,000 kwh 1,800,000 kwh * $0.07 = $126,000
Questions? Tom Stow Operations & Maintenance Division Manager Clean Water Services www.cleanwaterservices.org