Septic Tank Study Effect of Cations on Settling and Filter Performance

Transcription

1 Septic Tank Study Effect of Cations on Settling and Filter Performance Pauli Undesser WQA Director of Regulatory and Technical Affairs Water Quality Association Overview Background information Introduction to study Relevance to regulators 2 Background Information Water Quality Association 1

2 Softener and Septic Numbers 85% of US water is considered hard US EPA estimates Softener installations at ~10 million Septic systems in 26 million existing homes Septic systems in 40% of new homes 4 What is a water softener? Cation exchange resin Removes hardness ions (Ca ++, Mg ++, etc) Also removes most metallic ions such as Iron, Lead, Barium, Radium, Mercury, etc Whole house installation 5 Softener Performance 6 2

3 Time Clock vs DIR Time Clock regenerates based on time DIR regenerates based on demand Regeneration spans 1-2 hrs Regenerations occurs <1-2 times per week 7 Regeneration Process gal gal gal + 15 gal = 50 gal Back wash Brine Draw Slow Rinse Fast Rinse Time (minutes) 8 Salt Usage Per Year 9 3

4 History Early 70 s unspecified septic failures noted and softeners being blamed Specified failures Poor maintenance Tree root infiltration Unwanted objects in system Hydraulic overloading Driving or parking over system 10 History Mid 70 s county and DE bans began Late 70 s investigations into softener discharge were conducted 11 WQRF Supporting Reports Septic Tank/Water Softener Potential Effects of Water Softener Use on Septic Tanks Soil Absorption On-Site Wastewater Systems University of Wisconsin-Madison The Effect of Home Water Softener Waste Regeneration Brines on Individual Aerobic Wastewater Treatment Plants NSF International 12 4

5 Purpose of Supporting Studies Is softener discharge toxic to bacteria in the system? Do flow rate and volume discharges have an effect on settling and floatation? Do discharges reduce percolation of water due to swelling of soil particles? 13 Results from Supporting Studies Water softener waste stimulate biological action in anaerobic or aerobic systems The volume and flow rate of softener wastes do not cause deleterious problems in anaerobic or aerobic systems. Discharge does not interfere with percolation and might improve soil percolation, in fine textured soils. 14 Why are we here? Contentions still remain that softener discharges cause septic failures Reported issue is lack of defined layers in septic tanks Regulators still question whether restriction of discharges to septic tanks is necessary 15 5

6 History ~2000 state bans in CT, OR, and TX 2003 TX rescinded/revised ban 2009 WERF water softener workshop Now need more research of stratification 16 Recent Studies Creekwood, NC Study* Investigated salt and solids stratification Showed lower salt levels with DIR softeners Systems functioned well regardless of discharge Did not show variations in stratification *participants WQA, CIDWT, NOWRA 17 Recent Studies cont d Novak et. al, VA Tech An imbalance in the monovalent to divalent (M/D) cation ratio can lead to poor settling of solids in aerobic systems Excessive sodium (M) in relation to calcium (D) and magnesium (D) may lead to poor settling, lack of clear zones which could clog outlet filters. 18 6

7 Data Weaknesses The Creekwood study did not address M/D cation ratios Impact of M/D ratio on stratification Impact of M/D ratio on protein and polysaccharides Effluent filter clogging Novak et. al research did not address residential anaerobic applications 19 Introduction to WQRF Septic Study Water Quality Association Study Overview Researcher Dr. Novak Funding WQRF Steering Committee WQA, NOWRA, NSF Question How does softener discharge effect the M/D cation ratio and septic system performance? 21 7

8 Study Goals In a residential anaerobic application, how does the M/D ratio affect: Dissolved and suspended solids? Ability of FOG to stratify? Proteins and polysaccharides? Effluent filter performance? Overall operation of a septic system? 22 Anaerobic Septic Tank Illustration from 23 Study Design Literature review of current research Develop column test setups to simulate tanks Evaluate stratification in columns 24 8

9 Column Set up Overlying Grease Layer Input of water with different cation content Overlying Water Water Discharge (below grease layer) Septic Tank Solids 25 Study Design Field testing of redirection of discharge The Aquasource Group Inc. 26 Study Design All water is softened, discharge to ST1 only ST3 Apt Group 1 (softened, no regen to ST) Comm Center Apt Group 2 (softened, regen to ST) ST2 ST1 27 9

10 Study Design Batch anaerobic digestion studies Sodium impact on degradation rates Determine quality of the overlying water Evaluate chloride impact on nitrification If insufficient information in literature 28 Study Goals Relationship between settling behavior and the M/D ratio Estimate the optimal M/D ratio Effect of cation ratios on separation of FOG Batch toxicity testing to determine cation toxicity If necessary, develop model operational guidelines 29 Testing Timeline May 2011 Study kick off June 2011 Begin testing May 2012 Wrap up testing June 2012 Tentative date for final report 30 10

11 Relevance to Regulators Water Quality Association Relevance to Regulators If no measureable effect Figure out next step Negative impact when softener is inefficient and/or the sodium content is high Work to include installer education or certification in regulations 32 Relevance to Regulators (cont d) Negative impact even when softener is efficient and low sodium content Further investigation Negative impact if discharge is redirected Review current redirection regulations 33 11

12 Summary Septic systems have unspecified failures and softeners are being blamed Earlier studies showed softener discharge does not negatively impact bacteria growth, percolation, nor stratification Stratification studies have weaknesses 34 Summary (cont d) The WQRF study will investigate the effect of M/D ratio on septic tank performance Focus on stratification and effluent filter clogging The outcome may shed light on softener discharge impacts on septic tank performance 35 Water Quality Association Thank you! Questions or Feedback 12

13 Creekwood Chloride Concentrations Site Chlorides in the Discharge (mg/l) Composite Maximum Minimum Chlorides in the Septic Tank (mg/l) Average Maximum Minimum DIR Average Time Clock Average