Septic Tank Study - NEHA CERT · OWS1103 Septic Tank Study - Undesser Study Design ... M/D ratio on...

1

2011 NEHA AECOWS1103 Septic Tank Study - Undesser

Water Quality Association

Septic Tank StudyEffect of Cations on Settling and Filter Performance

Pauli Undesser

WQA Director of Regulatory and Technical Affairs

Overview

• Background information

• Introduction to study

• Relevance to regulators

2


Background Information

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

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

2.5

2.0

1.5

1.0

0.5

0

20 gal + 7.5 gal + 7.5 gal + 15 gal = 50 gal

0 10 20 30 40 50 60 70Time (minutes)

Back wash Fast Rinse

Brine DrawSlow Rinse

8

Salt Usage Per Year

9

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

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

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

17

*participants – WQA, CIDWT, NOWRA

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

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

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

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

23

Illustration from www.genie.com

Study Design

• Literature review of current research

• Develop column test setups to simulate tanks

• Evaluate stratification in columns

24

9


Column Set up

25

Septic

Tank

Solids

Overlying

Water

Overlying

Grease

Layer

Input

of water

with

different

cation content

Water Discharge

(below grease layer)

Study Design

• Field testing of redirection of discharge

– The Aquasource Group Inc.

26

Study Design

• All water is softened, discharge to ST1 only

27

Apt Group 1(softened, no regen to ST)

Apt Group 2(softened, regen to ST)

Comm

CenterST3

ST2 ST1

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

11



Relevance to Regulators

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

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


Thank you!

Questions or Feedback

13


Creekwood Chloride Concentrations

Site

Chlorides in the Discharge (mg/L)

Composite Maximum Minimum

Chlorides in the Septic Tank (mg/L)

Average Maximum Minimum

101 55 60.9 50.19

102 15779 1265 2062 439

103 14548 49300 11 431 781 118

104 6577 30000 29.8 566 718 295

105 12304 46400 10.9 1761 2215 802

106 7850 57200 61.3 3557 4812 643

DIR

Average

10563 39650 20.4 499 750 207

Time Clock

Average

11978 53250 36 2194 3030 628

Date post:	07-Sep-2018
Category:	Documents
Upload:	lephuc
View:	215 times
Download:	0 times

Septic Tank Study - NEHA CERT · OWS1103 Septic Tank Study - Undesser Study Design ... M/D ratio on...

Documents