Comparison of Primary and Secondary Treated Wastewater in Drip Dispersal

Transcription

1 Comparison of Primary and Secondary Treated Wastewater in Drip Dispersal John R. Buchanan, Ph. D., P. E. Assistant Professor Biosystems Engineering & Soil Science Institute of Agriculture The University of Tennessee

2 Comparison of Primary and Secondary Treated Wastewater in Drip Dispersal Question When using drip dispersal, should the quality of the effluent be a design parameter? Will primary-quality effluent cause significant differences in the design and operation of drip systems as compared to secondary-quality effluent? Slide 2

3 Comparison of Primary and Secondary Treated Wastewater in Concerns Drip Dispersal Will higher strength wastewater form a clogging layer that could change the hydraulic characteristics of the soil? Is the distribution of the effluent into the soil sufficiently dispersed such to maintain aerobic conditions even with higher BOD loading? Slide 3

4 Slide 4 Comparison of Primary and Secondary Treated Wastewater in Argument Drip Dispersal Drip can maximize soil-water-oxygen contact Aerobic conditions can be maintained Dosing and resting cycles Thus Biomat formation will be minimal even with higher strength effluent With forward-flushing of drip laterals and back flushing of filters, the drip system will work well with high-strength effluent

5 Hypothesis Slide 5 No significant difference. In biomat formation In emitter clogging Recognizing that the flushing schedule will be modified for the primary-quality water Both laterals and filters In the quality of the soil-water beneath the application of effluent Organic carbon Total nitrogen Soil micro-organisms

6 Difficulties of Field Research Have to minimize variables Need consistent and dependable source of wastewater Need to install two identical drip fields Same soil type One field receives septic tank effluent The other field receives secondary-quality effluent Wastewater needs to be from the same source Slide 6

7 Partial Solution Subdivision with STEP system Approximately 100 homes Recirculating sand filter Drip dispersal with 90,000 feet of drip tubing Slide 7

8 Measured Parameters Soil Solution Slide 8 Suction cup lysimeters Randomly selected locations within drip field Each field has 12 lysimeters Three at 12 Three at 24 Three at 36 Three at 48 (or to bedrock)

9 Installation of Sensors in Very Heavy Soil Hand augers are good work-out devices portable hydraulicallydriven soil probes are easier on the back Slide 9

10 Creating Two Drip Fields 1000 feet of tubing in each field Laterals on two-foot spacing Emitters on two-foot spacing 0.62 gallon per hour emission, pressure compensated Vibratory plow Four zones each field Slide 10

11 Layout One Field 100' of tubing 200' of tubing 300' of tubing Layout of Four Zone Drip Dispersal System 400' of tubing Supply Side Manifold Flush Return Manifold Slide 11

12 Layout Big Picture From STEP System Septic Effluent Dose Tank Recirculating Sand Filter Septic Effluent Field Secondary Effluent Field Secondary Effluent Dose Tank Slide 12 To Step System Drip Field

13 Before RSF Septic tank effluent Tapped into pressurized sewer line that feeds into the recirculating sand filter Butterfly valve directs effluent to dose tank Slide 13

14 After RSF Secondary quality effluent Dose pump placed in same tank used to pressurize the drip lines Slide 14

15 Soil Loading Load at full design rate Slide 15 Soil rated at 0.1 gpd/ft 2 Each field is 2000 ft gallons per day per field Receive this water everyday grows great grass

16 Collect soil-solution samples pull a vacuum, typically on a Friday pull samples on Monday During summer often not enough soilwater available for sampler Sample Collection Slide 16

17 Nothing Conclusive, Yet Approximately nine months of operation samples from drawn from STE and RSF lysimeters are not statistically different total nitrogen total phosphate total carbon chemical oxygen demand current samples are not different from background three sets of samples taken before initiation of land application Slide 17

18 Total Nitrogen Composite of 12, 24, 36, & 48 Suction Cup Lysimeters TN (mg/l) Feb-05 May-05 Jul-05 Oct-05 Jan-06 Mar-06 Sampling Dates Slide 18 RSF STE

19 Chemical Oxygen Demand Composite of & 48 Suction Cup Lysimeters COD (mg/l) Feb-05 May-05 Jul-05 Oct-05 Jan-06 Mar-06 Sampling Dates Slide 19 RSF STE

20 Slide 20 Visual Differences?

21 At this time, The soil is renovating the higher strength wastewater The water is going somewhere 12 samples are rare - evapotranspiration 48 samples were frequent but soil was not saturated High strength side is slowly losing pressure due to emitter and filter clogging however, lines and filters have not been flushed yet Slide 21

22 Acknowledgements Project Funding Tennessee Valley Authority Jennifer Brogdon, Project Leader Tennessee Department of Agriculture Nonpoint Source Program in contract with U. S. EPA TDEC Ground Water Protection Tennessee Onsite Wastewater Association (TOWA) THANKS! Slide 22

23 Questions Institute of Agriculture The University of Tennessee Slide 23