N

A

C L E A R I N G H O

SMALL FLOW

S

A collection of

professional papers on

the study of onsite and

small community

wastewater issues

Volume 3, Issue 1, Winter 1997

Journal

N

ATIONAL SMALL FLOW

S

C L E A R I N G H O U S E

The

Flows

Smallll
The Small Flows Journal Volume 3, Issue 1, Winter 1997

Contents

Printed on Recycled Paper

NATIONAL SMALL FLOWS

CLEARINGHOUSE

1

Contents

From The Editor ........................................................................... 2

by Cathleen Falvey

RESEARCH

A Decentralized Wastewater System

for a Small Residential Development in California ...................................................3

by Ron Crites, P.E.,

 Craig Lekven, P.E.,

 Steve Wert, C.P.S.S., W.W.S., and

 George Tchobanoglous, Ph.D., P.E.

Shallow Intermittent Sand Filtration:

Microorganism Removal ..................................................................................... 12

by Robert W. Emerick,

 Rebecca M. Test,

 George Tchobanoglous, Ph.D., P.E., and

 Jeanne Darby, Ph.D., P.E.

NSFC News/Resources ............................................................... 23

Manuscript Guidelines.................................................................25

The Small Flows Journal

Sponsored by:

U.S. Environmental Protection Agency

Steve Hogye, Project Officer

Municipal Support Division

Office of Wastewater Management

Washington, D.C.

National Small Flows Clearinghouse

West Virginia University

John L. Mori, Ph.D., Manager,

Environmental Services and

Training Division

 Peter Casey, P. Eng.,

Program Coordinator

Jill A. Ross, Publications Supervisor

Cathleen Falvey, Editor

Daniel Gloyd, Graphic Designer

Technical Advisor

Patricia Miller, Ph.D.,

Virginia Department of Health

International Standard Serial Number

1079-1531

The Small Flows Journal

National Small Flows Clearinghouse

West Virginia University

P.O. Box 6064

Morgantown, WV 26506-6064

(800) 624-8301/(304) 293-4191

http://www.nsfc.wvu.edu

Reprints

For permission to reprint information

appearing in The Small Flows Journal,

please send a letter of request to

the editor.

The Small Flows Journal is funded by

the U.S. Environmental Protection

Agency (EPA). The contents of this

journal do not necessarily reflect the

views and policies of the EPA, nor does

mention of trade names or commercial

products constitute endorsement or

recommendation for use.

NAT

C L E A R I N G H O

SMALL FLOW

S

A collection of

professional papers on

the study of onsite and

small community

wastewater issues

Volume 3, Issue 1, Winter 1997

Journal NATIONAL SMALL FLOWS

C L E A R I N G H O U S E

The

Flows

Smallll
The Small Flows Journal Volume 3, Issue 1, Winter 1997

T

he technical papers in this third issue of The Small Flows

 Journal examine innovative wastewater technologies that

can provide solutions for small communities (i.e., communities with populations less than 10,000 or that handle less

than one million gallons of wastewater flows per day). The

information will be of interest to many local officials and small

community leaders, as well as to public health officials, wastewater engineers, consultants, and other wastewater professionals.

The first paper, A Decentralized Wastewater System for a Small

Residential Development in California, presents a case study of an

innovative wastewater system designed for a very small community. The system uses a combination of alternative technologies to

provide for wastewater collection, treatment, disinfection, and

reuse. The disinfected wastewater is then used to irrigate a small

landscaped area nearby. Readers interested in wastewater reuse or

the alternative technologies described will find the paper informative, as will small communities considering similar solutions.

Shallow Intermittent Sand Filtration: Microorganism Removal,

the second technical paper in this issue, is a follow-up to a study

published in our previous issue. The new research examines the

effect of specific hydraulic loading rates, dosing frequencies, and

media on the filters’ ability to remove microorganisms from the

wastewater. The results of this study are important to wastewater

professionals and communities who use this technology.

In addition, beginning on page 23, this issue includes news and

information from our publisher, the National Small Flows

Clearinghouse (NSFC). The NSFC also publishes the newsletters

Small Flows and Pipeline and offers a variety of information,

resources, technical assistance, and other services to small

communities concerning wastewater issues. Readers who would

like more information about the NSFC’s products and services

should call (800) 824-8301 or (304) 293-4191.

We hope that you find this issue of the journal to be as interesting

and informative as past issues. If you are not yet on our mailing

list and would like to receive a subscription, please fill out and

return one of the subscription information cards on page 25.

.

Sincerely,

Cathleen Falvey

Editor

The Small Flows Journal

From the Editor

2

From the Editor NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

Terry Bounds, P.E.

Roseberg, OR

Craig Cogger, Ph.D.

Washington State University, Puyallup,

Research and Extension Center

James Converse, Ph.D.

Biological Systems Engineering Dept., University of Wisconsin

Brian Cooper, C.E.T.

Simcoe Engineering Group, Ltd., Pickering, Ontario

Donald Gray, Ph.D.

Professor of Civil Engineering, West Virginia University

Michael Hines, M.S., P.E.

Quantum Engineering Corporation, Knoxville, TN

Anish Jantrania, Ph.D., P.E.

Technical Services Engineer, Virginia Department of Health

Craig Jowett, Ph.D., P. Eng.

Research Associate Professor

Waterloo Centre for Groundwater Research, University of Waterloo

Jim Kreissl

Environmental Engineer, Center for Environmental Research

U.S. Environmental Protection Agency

George Loomis

Research Soil Scientist

Natural Resources Science Dept., University of Rhode Island

Roger E. Machmeier, Ph.D., P.E.

Professor Emeritus, University of Minnesota

Karen Mancl, Ph.D.

Associate Professor of Agricultural Engineering

The Ohio State University

Richard J. Otis, P.E.

Vice President, Ayres and Associates, Madison, WI

Michael H. Ogden, P.E.

Southwest Wetlands Group, Santa Fe, NM

Sherwood Reed, P.E.

Consultant and Principal

Environmental Engineering Consultants, Norwich, VT

A.R. Rubin, Ph.D.

Extension Specialist and Associate Professor

North Carolina State University

Jerry Stonebridge

President, Stonebridge Construction, Inc., Langley, WA

George Tchobanoglous, Ph.D., P.E.

Professor of Civil Engineering, University of California, Davis

Jerry Tyler, Ph.D.

Associate Professor, University of Wisconsin

A.T. Wallace, Ph.D., P.E.

Professor, Department of Civil Engineering, University of Idaho

Ted Walker, R.E.H.S.

Sonoma County Health Department, Sonoma, CA

Editorial Review Board

From the Editor
The Small Flows Journal Volume 3, Issue 1, Winter 1997

A Decentralized Wastewater System

for a Small Residential Development

in California

3

I

n rural areas without wastewater

collection systems, developers

traditionally have had one method of

wastewater treatment available to

them—individual septic tanks with soil

absorption fields. While these systems

may be appropriate and adequate for many

developments, there are site conditions

that can restrict their use, including

inappropriate or limited soils, high

TECHNICAL

by Ron Crites, P.E.,

Craig Lekven, P.E.,

Steve Wert, C.P.S.S., W.W.S., and

George Tchobanoglous, Ph.D., P.E.

ABSTRACT: An innovative system was designed to provide for wastewater collection,

treatment, disinfection, and reuse for a small residential development in California. The

system combines the use of septic tanks, screened effluent filter vaults, high-head effluent

pumps, small-diameter variable grade sewers, pressure sewers, a recirculating granular

medium filter, an ultraviolet light disinfection unit, a subsurface drip irrigation system for

wastewater reuse, and a community soil absorption field for winter-time disposal. The

system has performed beyond required standards for wastewater reuse.

A Decentralized Wastewater System

for a Small Residential Development

in California

groundwater, and elevated nitrate concentrations in groundwater, among other

factors. In some cases, developers may not

want to use septic systems because of the

homeowners’ required involvement in

keeping the systems operating properly.

Where traditional septic systems are not

appropriate or desired, small, decentralized

community wastewater systems can be

designed to collect, treat, and dispose of

the wastewater generated from developments. The system considered in this paper

is an example of a small community

design that also provides for wastewater

disinfection and reuse.

Stonehurst is a 47-lot subdivision located

near the city of Martinez in Contra Costa

County, California, approximately 25

miles east of San Francisco. The subdivision is located in a hilly, rural area that did

not have a wastewater collection system.

An overall view of the rolling terrain is

shown in photo 1. The use of conventional

 Stonehurst Development

PHOTO 1

view of the rolling terrain at

Stonehurst development,

Contra Costa County, California
The Small Flows Journal Volume 3, Issue 1, Winter 1997

septic tank/soil absorption systems was

originally approved for the subdivision.

However, the developer, Security Owners

Corporation of Martinez, wanted to

implement a community wastewater

collection, treatment, and disposal system

that would also provide for wastewater

disinfection and reuse. The rationale for

this approach was to free homeowners

from concerns about possible absorption

field failures and to protect the environment while providing for the subsurface

irrigation of a small community park for

the residents. As of January 1997, 15 of

the 47 lots have been developed and are

contributing wastewater to the system.

The wastewater system that was designed

and constructed for the Stonehurst

development incorporates a number of

innovative technologies. The system uses

1,500-gallon (5,680-liter), two-compartment water-tight septic tanks with

screened effluent filter vaults at each

connection. The system also employs

high-head effluent pumps, small-diameter

variable grade sewers, two pressure

sewers, a recirculating granular medium

filter, an ultraviolet (UV) light disinfection unit, a subsurface drip irrigation

system for wastewater reuse, and a

community soil absorption field for

winter-time disposal, when needed.

The system is designed to meet California

standards for wastewater reuse, which

require disinfected wastewater to have a

30-day average biochemical oxygen

demand (BOD5) and total suspended

solids (TSS) of 15 mg/L, a settleable

solids of 0.1mL/L, and a total coliform

concentration equal to or less than 23

most probable number (MPN) per 100

mL. The system began operation in

August 1993 with approximately six

homes connected to the system.

4

PHOTO 2

A view of typical homes in the

Stonehurst development. Homes

located below the roadway are

provided with STEP systems.

R. Crites, P.E., C. Lekven, P.E., S. Wert, C.P.S.S., W.W.S, and G. Tchobanoglous, Ph.D., P.E.

The Wastewater System

FIGURE 1

flow diagram for wastewater

treatment facilities at the

Stonehurst development
The Small Flows Journal Volume 3, Issue 1, Winter 1997

5

TABLE 1

Stonehurst subdivision wastewater system design criteria

Wastewater Collection

Stonehurst’s wastewater collection system

is composed of three segments: a smalldiameter variable-grade gravity sewer, a

pressure sewer, and a pressure sewer force

main. The system is designed so that at

full build-out, septic tank effluent from 32

of the lots discharges to a 2-inch (50.8-

mm) variable-grade gravity sewer located

in the roadway of the development. The

collection sewer drains into a wet-pit

pump station.

The remaining 15 of the lots are located at

elevations below the roadway (see photo

2) and cannot be served by a gravity

system. Septic tank effluent pumps

(STEP) are used to pump septic tank

effluent from the low-lying lots into the

pressure sewer. The pressure sewer used to

connect the 15 low-lying lots also discharges to the wet-pit pump station. The

combined flow is pumped through a force

main from the wet-pit pump station to the

treatment plant.

The centralized pump station was designed to reduce the operation and

maintenance requirements for the collection system by reducing the total number

of individual pumps requiring service.

Wastewater Treatment

The principal elements of the wastewater

treatment system include: a recirculating

granular medium filter for treatment and a

UV system for disinfection. A schematic

flow diagram of the treatment system is

shown in figure 1. Design criteria for the

treatment plant and disposal/reuse

facilities are summarized in table 1.

Recirculating Granular Medium Filter.

Treatment of the septic tank effluent is

accomplished with a recirculating granular

medium filter that is divided into two

sections (see photo 3). Each filter section

includes a recirculation tank, recirculation

pumps, and a recirculating gravel medium

filter. Each half of the filter consists of 24

A Decentralized Wastewater System for a Small Residential Development in California

PHOTO 3

A view of half of the recirculating gravel

medium filter is in the foreground. The

building in the background is used to house

the UV disinfection unit.

Description Value

number of lots available 47

number of homes contributing wastewater 15

design flow per lot 300 gal/d (1,140 L/d)

total flow at build-out 14,100 gal/d (53,374 )L/d

recirculation tank volume 14,100 gal

granular medium filter

 surface area 4,700 ft2 (437m2)

 hydraulic loading rate 3 gal/ft2•d (120 mm/d)

 minimum recirculation ratio a 5:1

 filter medium characteristics

 effective size, d10 3 mm

 uniformity coefficient <2

 depth of filter medium 2 ft (0.6 m)

ultraviolet disinfection

 type open channel package unit

 number of UV modules 3

 lamps per UV module 2

 minimum UV dose 95 mW•s/cm2

community drainfield

 trench dimensions 24 in wide x 36 in deep

 (610 mm x 915 mm deep)

 total trench length 5,000 linear ft (1,524 m)

 total drainfield area 2.5 acres (10,117 m2)

 design loading rate 2.8 gal/lineal ft•d

 (0.0348 m3/m•d)

drip irrigation system

 emitter type non-clog, buried (6–12 in)

 reuse area 1 acre park (4,047 m2)

 reuse crops landscape, trees, and shrubs

a based on wastewater flow to treatment plant

description value
The Small Flows Journal Volume 3, Issue 1, Winter 1997

Expericmental Design and Data

area has shallow, silty clay loam soils

underlain by very soft, fractured sandstone. Soil depth in the absorption field

varies from 20 to 30 inches (508 to 762

mm). Soil was tested using a shallow well

pump-in test from which saturated

hydraulic conductivity was determined.

The hydraulic conductivity was used to

design the soil absorption field to accept

the daily wastewater flow plus additional

flows during peak rainfall periods.

The soil absorption field is currently being

used for disposal year round until more

homes are built and the amount of

wastewater flow increases. A number of

monitoring wells, located downhill from

the absorption field, are checked on a

quarterly basis and have been dry.

The dosing tank also serves as a water

storage reservoir for a subsurface drip

irrigation system located at a small

community park area near the subdivision

entrance. The dosing tank is designed to

provide adequate storage volume underneath the absorption field dosing siphons

for the operation of the subsurface drip

irrigation system.

Non-clog drip emitters are buried in short

lengths of gravel-filled PVC pipe. The

park is landscaped with drought-tolerant

6

R. Crites, P.E., C. Lekven, P.E., S. Wert, C.P.S.S., W.W.S., and G. Tchobanoglous, Ph.D., P.E.

PHOTO 4

A view of the UV disinfection unit

located in a building next to the

gravel medium filter—the UV

system consists of three modules,

each of which has two lamps.

inches (0.6 m) of 3-mm gravel sandwiched between layers of drain rock,

which is coarse, washed gravel, approximately 1 to 2.5 inches (25 to 63 mm) in

diameter. The 3-mm gravel is washed and

rounded (not crushed) and contains less

than two percent material finer than a

number 10 sieve (2 mm).

Wastewater treatment is achieved through

biological, chemical, and physical action

within the filter. Treated effluent from the

bottom of the filter is conveyed back to

the recirculation tank. Wastewater is

pumped from the recirculation tank to the

filters at regular (adjustable) time intervals, usually set for five minutes every

half hour. Wastewater is circulated

through the filter approximately five times

before being diverted by a float valve

system to the UV supply sump. At the

time of publication, only one half of the

recirculating granular medium filter is

being used.

Wastewater Disinfection. Disinfection

of the treated wastewater is achieved

using UV light (see photo 4). Treated

wastewater flows through an open channel

containing six low-pressure mercury

vapor lamps, which emit UV light at a

wavelength of 254 nm (see table 1) that

inactivates most bacteria and pathogens.

Two small pumps are used to transport the

treated wastewater to the UV system.

Wastewater Reuse/Disposal

The treatment plant effluent is pumped to

a 3,000-gallon (11,356-liter) dosing tank

at the top of a nearby hill. Two dosing

siphons in the tank alternately feed the

two halves of a pressure-dosed, 2.5-acre

(10,117 m2) community soil absorption

field. A series of hydrosplitters ensures

that the absorption field trenches are all

dosed evenly.

The soil absorption field was located on a

hilltop because the soils in most other

areas within the development were

extremely high in clay and had seasonal

high groundwater. The absorption field
The Small Flows Journal Volume 3, Issue 1, Winter 1997

will be disconnected from the potable

water piping and connected to the

reclaimed water piping.

Operation and Maintenance

To ensure proper operation and maintenance of wastewater systems, the regional

water quality control board that includes

Stonehurst in its jurisdiction only recognizes responsible agencies or districts (not

individuals) for system operation and

maintenance. To comply, a county

sanitation district was formed to serve as

owner of the Stonehurst community

wastewater system. The wastewater

system operation and maintenance is

funded through annual property assessments. The special district is administered

by the Contra Costa County Department

of Public Works. Contra Costa County has

contracted for the daily operation and

maintenance with ES2, a national firm

that specializes in the operation of

wastewater treatment plants.

As noted previously, the wastewater

system at Stonehurst began operation in

August 1993. By September 1996, the

flow to the treatment system was approximately 20 percent of the design flow at

2,800 gal/d (10,600 L/d). During the

period from June 1994 through September

1996, the monthly flow has varied from

about 5 to 25 percent of the design flow

anticipated at full build-out. Based on

daily meter readings from the first 15

homes that have come on line, the flow

per home, which is about 180 gal/d (680

L/d), is less than the expected 300 gal/d

(1,140 L/d).

At the present time, the hydraulic loading

on the granular medium filter is about 1.2

gal/ft2 • d (48 mm/d) using half

of the filter. The characteristics of the

septic tank effluent applied to the recirculating gravel filter are reported in table 2,

along with typical septic tank effluent

data as reported in the literature. As

7

trees and shrubs. Three drip emitters are

provided for each tree and one for each

shrub. Application rates for the drip

system were determined based on the

needs of the vegetation and the rate of

evapotranspiration anticipated. At full

build-out, reclaimed water will provide

100 percent of the landscaped water

demands at the one acre park. In the wet

season, reclaimed water not needed for

irrigation purposes will be disposed of

automatically in the pressure-dosed

community soil absorption system.

Routine maintenance of the drip irrigation

system will include periodically dosing the

lines with chlorine to prevent clogging.

Well water is currently being used for

irrigation of the park until reclaimed water

volumes are adequate to maintain the

landscaping. In time, the irrigation system

TABLE 2

quality of septic tank effluent

applied to recirculating gravel filter

at Stonehurst, along with

comparative data on septic tank

effluent characteristics

A Decentralized Wastewater System for a Small Residential Development in California

Performance Data

BOD5 mg/L 100 - 130 80 - 300

COD mg/L 430 - 600 300 - 500

TSS mg/L 65 - 92 30 - 90

settleable solids mL/L < 0.1 < 0.1 - 0.4

turbidity NTU 15 - 40

pH unitless 7.0 - 7.5 6.5 - 8.5

NH4-N mg/L-N 60 - 65 20 - 60

NO2 + NO3 mg/L-N 0.0 - 1.0

organic N mg/L-N 10 - 40

TKN mg/L-N 30 - 100

total N mg/L-N 30 - 100

total P mg/L-P 6 - 12

oil and grease mg/L 20 - 40

MBAS mg/L 5 - 20

total coliform MPN/100/mL 106

 - 107

fecal coliform MPN/100/mL 105 - 106

fecal streptococcus MPN/100/mL 104 - 105

indigenous phage PFU/mL 500 - 5,000

a BOD5 = 5-day 20 C biochemical oxygen demand, COD = chemical oxygen demand

 TSS = total suspended solids, pH = hydrogen ion concentration

 NH4= ionic form of ammonia nitrogen, NO2 = nitrite nitrogen

 NO3 = nitrate nitrogen, TKN = total kjeldahl nitrogen (organic N + NH4)

 P = phosphorus, MBAS = methylene blue active substances

b only the indicated constituents are monitored

c from Crites and Tchobanoglous (in press)

constituent a unit Stonehurst b typical range
The Small Flows Journal Volume 3, Issue 1, Winter 1997

8

shown in table 2, the reported constituent

concentrations at Stonehurst are typical of

septic tank effluent.

Constituent Removal Data

Summary of performance data for the 28-

month period from June 1994 through

September 1996 are presented in table 3.

Both monthly and quarterly values are

reported. The reported monthly values for

five-day biochemical oxygen demand

(BOD5) are based on an average of at

least two samples per month. Monthly

values reported for TSS, chemical oxygen

demand (COD), pH, and total coliform are

based on an average of at least four

samples per month. The reported quarterly

values are based on grab samples.

The measured data for the individual

constituents are reported in terms of the

range of values observed, the arithmetic or

geometric mean, and the median. Either

the arithmetic or geometric mean are

reported depending on the nature of the

statistical distribution of the monthly or

R. Crites, P.E., C. Lekven, P.E., S. Wert, C.P.S.S., W.W.S., and G. Tchobanoglous, Ph.D., P.E.

TABLE 4

statistical parameters for the average

monthly values of TSS and COD

TABLE 3

performance data for

Stonehurst wastewater

treatment system

constituent a unit period b to date range mean mean median

reporting samples arithmetic geometric

observed values c

Statistic a TSS COD

 minimum value 2.0 mg/L 1.0 mg/L

 maximum value 15.0 mg/L 18.0 mg/L

 sum 156.5 mg/L 163.8 mg/L

 number of data points 28 28

 arithmetic mean 5.6 mg/L 5.9 mg/L

 median 4.9 mg/L 5.0 mg/L

 RMS 6.3 7.1

 standard deviation 2.9 4.1

 variance 8.6 16.6

 standard error 0.6 0.8

 coefficient of skewness 1.2 1.2

 coefficient of kurtosis 1.7 1.1

a The values of the coefficient of skewness and kurtosis for a

 normal distribution are equal to zero, as computed.

statistic a TSS COD

sample total

Performance dated for Stonehurst wastewater treatment system for the 28-month

period from June 1994 through September 1996. Effluent samples taken following

recirculating gravel filter and UV disinfection as shown in figure 1.

BOD5 mg/L monthly 56 0 - <5 <5 <5

COD mg/L monthly 120 1.0 - 18.0 4.7 5.0

TSS mg/L monthly 118 2.0 - 15.0 5.0 4.9

pH unitless monthly 120 6.96 - 8.65 d d 7.61

total coliform MPN/100mL monthly 118 <2 - 12.5 d d <2

NH 4 mg/L quarterly 9 0 - 15 e e 0.0

NO3 mg/L quarterly 9 3.55 - 37.0 12.5 12.2

TKN mg/L quarterly 9 0 - 3 e e 0.4

oil and grease mg/L quarterly 9 0 - 12 e e 0.0

TDS mg/L quarterly 9 340 - 770 630 656

EC μmhos/cm quarterly 9 433 - 1,200 894 1,000

a TDS = total dissolved solids, EC = electrical conductivity

b Monthly values for BOD5 are based on an average of two samples per month. Monthly values for

 TSS, COD, pH, and total coliform are based on an average of at least four samples per month.

c Arithmetic or geometric means are reported depending on the distribution of the monthly values

 (see table 4).

d Mean values cannot be reported for pH, which is a logarithmic function, and for total coliform,

 which is based on a Poisson distribution.

e Unable to define nature of distribution because of the number of zero values reported.
The Small Flows Journal Volume 3, Issue 1, Winter 1997

9

Statistical Analysis of Data

To determine whether the arithmetic mean

can be used to describe the observed

monthly values, a statistical analysis was

performed. The results of the statistical

analysis for the TSS and COD data are

reported in table 4. Statistical parameters

are given for both TSS and COD, assuming that the distribution of average

monthly or the log of the monthly values

is normally distributed.

As reported in table 4, both the TSS and

COD data are skewed, as the coefficient

of skewness for a normal distribution

should be zero. Given that the value of the

coefficient of kurtosis for a normal

distribution should also be zero, it is clear

that both distributions are relatively

peaked. As reported below, both distributions were found to be logarithmically

distributed.

A plot of the TSS and COD data on

logarithmic probability paper is shown in

figure 2. The finding that the distributions

of the effluent concentration values for

TSS and COD are log-normal is consistent with the findings of Niku et al.

(1979). Based on an analysis of the data

from a number of treatment plants, Niku

et al. concluded that the log-normal

distribution for effluent BOD and TSS

may be used to predict the effluent quality

performance and the reliability of wastewater treatment plants. The fact that the

TDS and conductivity data are normally

distributed is also consistent, given that

the principal constituents that contribute

to these values are related more closely to

the water supply and that these constituents are not normally removed during

conventional biological treatment.

Assessment of Performance Data

Based on the data reported in table 3, the

treated effluent more than meets the

applicable effluent discharge criteria

standards. The monthly BOD values are

consistent with the results that have been

reported by others as summarized in table

5. In general, the effluent monthly BOD,

A Decentralized Wastewater System for a Small Residential Development in California

FIGURE 2

log-probability plot

of average monthly

TSS and COD data

TABLE 5

comparison of performance of

recirculating gravel filters

quarterly data. As shown, all of the values

reported for BOD were either reported as

zero or less than five. As a result, both the

mean (assumed to be normally distributed)

and the median values are reported as less

than five.

The reported monthly values for TSS and

COD were found to be log-normally

distributed (i.e., skewed), as discussed

below. Because of the number of zero

values reported, it was not possible to

define the nature of distribution for the

total kjeldahl nitrogen (TKN), ammonium

ion (NH4), and oil and grease values. The

total dissolved solids (TDS) and conductivity values were found to be normally

distributed.

Comparison of performance of recirculating gravel filters

 Medium Loading rate, Effluent

Location size, mm gal/d•ft 2 BOD 5

, mg/L

 Stonehurst, CA 3.0 1.2 a <5

 Oregon b 1.2 1.45 2.7

 Paradise, CA c 3.0 2.5 8

 Paradise, CA c 3.0 2.5 12

a Design value at full build-out = 3.0 gal/d•ft 2; currently half of the filter is used.

b Ronayne et al., 1984

c Nolte and Associates, Inc., 1992

 medium loading rate, effluent

location size, mm gal/d • ft 2 BOD5, mg/L
The Small Flows Journal Volume 3, Issue 1, Winter 1997

10

R. Crites, P.E., C. Lekven, P.E., S. Wert, C.P.S.S., W.W.S., and G. Tchobanoglous, Ph.D., P.E.

TSS, and COD values are considerably

better than those achieved in conventional

centralized wastewater treatment systems,

especially with respect to COD

(Tchobanoglous and Burton, 1991).

Another unusual feature of the treatment

process is its robustness.

The robustness of a treatment process can

be assessed by considering the ratio of the

P90 to P50 or P50 to P10 values on the

logarithmic-probability curve. In a

perfectly stable system, all effluent values

will be constant, resulting in a plot of zero

slope and a ratio of one. A system with

significant variability will typically result

in a plot with a steep or discontinuous

slope beyond a cumulative probablility

value of 80 percent.

From figure 2, the ratio of the P90 to P50

values for TSS and COD are 2.0 and 2.6,

respectively. Typical corresponding values

for the activated sludge process are about

2.5 and 3.4 (WEF, 1991). The markedly

steeper slopes observed with very small

activated sludge systems are indicative of

less stable systems.

The opportunity to reclaim wastewater

from individual residences in small rural

developments in a decentralized facility is

an effective means of saving water,

providing reliable wastewater services,

and meeting regulatory requirements. The

use of new equipment and technologies,

such as screened effluent pump vaults,

low-flow high-head pumps, smalldiameter variable slope sewers, recirculating granular medium filters, three-way

diversion valves, UV disinfection, and a

combination of community absorption

field and subsurface drip irrigation has

made the implementation of small

treatment systems a far more reliable

undertaking. To date, the Stonehurst

decentralized wastewater system

has exceeded all expectations by performing beyond required standards for

wastewater reuse.

 Conclusion

System implementation and construction

was accomplished by the owners Scott

and Jim Busby of Security Owners

Corporation. The project was planned and

the soil acceptance rates were determined

by Steve Wert. Operating data were

provided by Bill Perley of ES2, the

operating company.

wonkcdel

Crites, R. and G. Tchobanoglous. In press.

Decentralized wastewater management systems. New York: McGrawHill, Inc.

Niku, S., E. D. Schroeder, and F.J.

Samaniego. 1979. Performance of

activated sludge processes and

reliability-based design: JWPCF 51,

no. 12: p 2841.

Nolte and Associates, Inc. 1992. Literature review of recirculating and

intermittent sand filtration operation

and performance, prepared for the

Town of Paradise and the Central

Valley Regional Water Quality Control

Board, Sacramento, Calif.

Ronayne, M. A., R. C. Paeth, and S. A.

Wilson. 1984. Oregon Onsite Experimental Systems Program, Oregon

DEQ, U.S. Environmental Protection

Agency Office of Research and

Development, EPA/600/2-84-157,

Washington, D.C.

Tchobanoglous, G., and F. L. Burton. 1991.

Wastewater engineering: treatment,

disposal, and reuse. 3d ed. New York:

McGraw Hill, Inc.

Water Environment Federation (WEF).

1991. Design of municipal wastewater

treatment plants. WEF manual of

practice, no. 8. ASCE manual and

report on engineering practice, no. 76.

Alexandria, Va: WEF.

Acknowledgments

References
The Small Flows Journal Volume 3, Issue 1, Winter 1997

LOWS

EARINGHOUSE

SMALL FLOWS

INGHOUSE

NAL SMALL FLOWS

NATIONAL SMA

CLEARINGH

NATIONAL SM

CLEARING

11

A Decentralized Wastewater System for a Small Residential Development in California

 Ron Crites, P.E.

Ron Crites is Director of Water

Resources with Nolte and

Associates, Inc., Sacramento,

California, and was project

manager for the Stonehurst

project.

If you would like more information about this project, write to Ron Crites, P.E., Nolte and

Associates, Inc., 1750 Creekside Oaks Drive, Suite 200, Sacramento, CA 95833.

Craig Lekven, P.E.

Craig Lekven was the design

engineer for Nolte and Associates, Inc., Sacramento, California, and is currently biosolids

program manager with the

Sacramento Regional County

Sanitation District.

Steve Wert, C.P.S.S.,

 W.W.S.

Steve Wert is a consulting soil

scientist and wastewater sanitarian from Roseburg, Oregon.

 George Tchobanoglous,

 Ph.D., P.E.

George Tchobanoglous has

recently retired as a professor

emeritus in the Department of

Civil and Environmental Engineering at the University of

California, Davis.
The Small Flows Journal Volume 3, Issue 1, Winter 1997

Shallow Intermittent Sand Filtration:

Microorganism Removal

Shallow Intermittent Sand Filtration:

Microorganism Removal

12

by Robert W. Emerick,

Rebecca M. Test,

George Tchobanoglous, Ph.D., P.E., and

Jeannie Darby, Ph.D., P.E.

ABSTRACT: Twelve shallow circular sand filters (0.38 m deep, nominal diameter of

1.2 m) were loaded intermittently with primary effluent to evaluate the effects of hydraulic

loading rate (HLR)—coupled with a high dosing frequency (DF)—and filter medium

characteristics on the removal of indigenous coliphages, total coliforms, turbidity,

chemical oxygen demand (COD), and total suspended solids (TSS). HLRs between 0.041

and 0.162 m/d were applied during an 84-day period at a DF of 24 doses/d. Two types of

filter media were investigated: medium-size and coarse sand and crushed glass. Effective

sizes ranged from 0.44 to 3.3 mm, and uniformity coefficients ranged from 1.3 to 5.0.

Average removal rates greater than 94, 96, and 92 percent occurred for turbidity, TSS,

and COD, respectively, regardless of medium characteristics. Removal of microorganisms

was found to be affected by the combination of HLR and DF, with an increase in HLR at a

constant DF resulting in a decrease in the log removal of both total coliforms and

indigenous coliphages. Indigenous coliphages appeared to be more sensitive to changes

in HLR than seeded polioviruses.

.

TECHNICAL

frequently reported cause of groundwater

contamination associated with disease in

the U.S. (Powelson and Gerba, 1994).

Intermittent sand filters (ISFs), because of

their relatively low construction cost and

their minimal maintenance and energy

requirements, have been used as supplemental pretreatment for the soil absorption

system at individual residences, small

clusters of homes, business establishments, and rural communities to provide

consistent, high quality effluent (Ball,

1991). Modern ISFs are typically 0.5 to

1 m deep and are operated at hydraulic

loading rates (HLR) varying from 0.016 to

0.070 m/d (Ball, 1991) [1]. Typical dosing

frequencies (DF) are 3 to 6 doses/d

(Tchobanoglous and Burton, 1991). The

vast majority of research related to ISFs

I

n the U.S., approximately 60 million

people use onsite systems for wastewater treatment and disposal. Onsite

systems typically consist of a septic

tank for primary treatment and a soil

absorption system for secondary treatment

and disposal. However, unsuitable soil and

site conditions can preclude the use of

such systems due to concerns of contamination of the groundwater by nutrients,

bacteria, and viruses.

One of the greatest concerns over groundwater contamination is the occurrence

and movement of viruses, which have

been found to survive septic tanks and

move with the percolating wastewater

through the disposal field and the soil to

reach groundwater (Hain and O’Brien,

1979). Septic tank systems are the most
The Small Flows Journal Volume 3, Issue 1, Winter 1997

has been directed toward optimizing the

removal of organic material and nutrients

(Grantham et al., 1949; Furman et al.,

1955; Schwartz and Bendixen, 1970;

Marshall and Middlebrooks, 1974; U.S.

EPA, 1980; Siegrist and Boyle, 1981;

Anderson et al., 1985; Andreadakis, 1987;

Pell and Nyberg, 1989a,b,c; Pell et al.,

1990; Peeples et al., 1991; Darby et al.,

1996). The removal of bacteria (principally coliform bacteria) by ISFs is also

well documented (Salvato, 1955; Allen,

1971; Marshall and Middlebrooks, 1974;

U.S. EPA, 1977; Dymond, 1981; Ronayne

et al., 1982; Anderson et al., 1985).

However, of the studies that have investigated the removal of viruses by ISFs from

wastewater (Green and Cliver, 1974; U.S.

EPA, 1978; Wang et al., 1981; Gross and

Mitchell, 1990), none have focused

specifically on operation of modern fieldscale shallow ISFs for optimal indigenous

virus removal.

Darby et al. (1996) demonstrated that

0.38-m deep ISFs were capable of

producing average removal rates of

between 90 and 99 percent for biological

oxygen demand (BOD), total suspended

solids (TSS), organic and ammonia

nitrogen, and turbidity and at least 81

percent for chemical oxygen demand

(COD), regardless of medium characteristics, when dosed with primary effluent at

an HLR of 0.163 m/d or less and a DF of

12 to 24 times/d. The study presented

herein is an extension of the work

reported by Darby et al. with the purpose

of evaluating microorganism (principally

indigenous coliphage) removal from fieldscale shallow ISFs.

The experimental facilities were the same

as those used in Darby et al. (1996).

Twelve shallow sand filters were loaded

intermittently with effluent from the

primary settling tank of the University of

California, Davis wastewater treatment

plant. The experimental filters are shown

in photo 1. A complete description of the

filters’ construction, except for media

type, has been reported previously (Darby

et al., 1996). A description of the filter

media, filter design and operating parameters, sampling, and laboratory analyses

are provided below.

Filtering Media

The depth of the medium in each filter

was 0.38 m. Two filter media were used:

(1) washed and kiln-dried medium-size

and coarse sand with effective sizes (ES)

and uniformity coefficients (UC) of 0.65

mm and 3.8, and 3.3 mm and 1.3, respectively, and (2) crushed glass from a

recycling center that was washed on a

number 100 mesh screen with an ES and

UC of 0.44 mm and 5.0, respectively. The

particle size distributions of the filter

media are shown in figure 1 on page 14.

The medium-size sand was chosen for

study because it has characteristics typical

of those used in conventional ISFs

(Tchobanoglous and Burton, 1991). The

coarse sand was chosen for study because

it is less likely to clog over an extended

operating period, due to the large pores

present. It should be noted that the

effective size of the coarse sand is almost

an order of magnitude larger than is

typical for use with ISFs.

13

PHOTO 1

view of experimental filters with

covers removed

Shallow Intermittent Sand Filtration: Microorganism Removal

Experimental Methods
The Small Flows Journal Volume 3, Issue 1, Winter 1997

14

Crushed glass was chosen as a filter

medium for study because it has chemical

characteristics that are similar to sand

and, therefore, would be expected to

remove contaminants in a similar manner.

Crushed glass currently has a cost of

$19.60/m and is readily available. The use

of crushed glass is particularly advantageous in communities where adequate

filter sand is not available locally,

resulting in sand costs up to $26/m. Glass

can be supplied by local glass recycling

efforts, eliminating the need to import

filter media from distant locations, and

can be crushed either on site using a

portable crusher or at a local gravel

processing plant. As the use of crushed

glass in ISFs becomes more common, the

price may decrease accordingly.

Filter Design and Operating

Parameters

The design and operating parameters of

the filters are summarized in table 1.

Three filter medium sizes, three HLRs,

and a single DF were investigated

resulting in five different treatment

configurations. Redundancy was incorporated into the experimental design to

ensure completeness in data collection in

case of unforeseen problems with one or

more filters and to provide process

replication to ensure that reported

observations were typical (e.g., filters 2,

3, and 4 were identical; filters 5, 6, and 7

were identical; and filters 8, 9, and 10

were identical). The DF utilized, 24

doses/d, was the optimal DF for wastewater contaminant removal reported by

Darby et al. (1996). The HLR and filter

medium were varied such that the effect

of each parameter could be investigated

systematically and independently.

Sampling

Grab samples were collected from the

sampling ports connected to the effluent

outlet pipe. The sampling port was

R. W. Emerick, R. M. Test, G. Tchobanoglous, Ph.D., P.E., and J. Darby, Ph.D., P.E.

FIGURE 1

filter medium particle size

distribution

TABLE 1

filter medium

characteristics and

applied loading

Hydraulic Hydraulic

Effective Uniformity loading application

Filter Filter size, coefficient, rate, rate,

number material mm UC m/d mm/dose

1 crushed glass 0.44 5.0 0.040 1.7

2 medium sand 0.65 3.8 0.040 1.7

3 medium sand 0.65 3.8 0.040 1.7

4 medium sand 0.65 3.8 0.040 1.7

5 medium sand 0.65 3.8 0.081 3.4

6 medium sand 0.65 3.8 0.081 3.4

7 medium sand 0.65 3.8 0.081 3.4

8 medium sand 0.65 3.8 0.163 6.8

9 medium sand 0.65 3.8 0.163 6.8

10 medium sand 0.65 3.8 0.163 6.8

11 coarse sand 3.3 1.3 0.163 6.8

12 coarse sand 3.3 1.3 0.163 6.8

Note: All filters were dosed at a dosing frequency of 24 times/day.

 hydraulic hydraulic

 effective uniformity loading application

 filter filter size, coefficient, rate, rate,

 number material mm UC m/d mm/dose
The Small Flows Journal Volume 3, Issue 1, Winter 1997

opened and allowed to flow for

approximately five minutes before

sampling. Samples were collected over an

84-day period during the summer. An

influent sample was collected each time

effluent sampling occurred. Air temperatures were obtained from a climatological

data collection facility 2 km from the filter

site. The actual temperature of the media

and the wastewater were not measured

during the study.

Laboratory Analysis

Samples were immediately cooled and

analyzed within three hours for naturally

occurring coliphages, total coliforms, TSS,

turbidity, and COD. All laboratory analyses

were in accordance with Standard Methods,

17th edition, except as noted below.

Indigenous coliphages are bacterial

viruses and were selected as the viral

indicator because, like human enteric

viruses, they occur naturally in wastewater

and are associated with wastewater solids

(Lehrer and Cabelli, 1993). The removal

of indigenous coliphages, therefore, may

indicate the likely removal of human

viruses. The coliphage detection procedure

used was a modified version of Coliphage

Detection (Proposed) (method 9211D)

outlined in Standard Methods, 19th

15

edition—the difference being that E. coli,

American Type Culture Collection

(ATCC) 15597, was used as the host

bacterium. Three replicate plates were

made of each dilution with the median

value of the replicates used for data

presentation.

Total coliform bacteria were selected as

the bacterial indicator because of their

frequent use in permit discharge

requirements. The multiple tube

fermentation technique was used to

determine the most probable number

(MPN) of total coliform bacteria per 100

mL (method 9221 B). TSS was measured

according to method 2540D. Turbidity

was measured with a HACH Model

2100A turbidimeter. COD was determined

colorimetrically following digestion.

Characteristics of the wastewater applied

to the filters during the study period were

similar to that described in Darby et al.

(1996) and are presented in table 2. The

values of BOD and TSS were in the lower

one-third of the range that is typical for

septic tank effluent. The air temperature

during the study period had an average

high of 27oC with a coefficient of variation of 26 percent and an average low of

9oC with a coefficient of variation of 42

percent.

Overall Performance

Effluent quality from all of the filters was

excellent. Although TSS, COD, and

turbidity removal was not the focus of this

investigation, spot checks were conducted

on the filters to assess their overall

performance. Because no problems were

ever encountered with the filters, and the

performance of all the redundant filters

were never statistically different, the data

for all of the redundant filters were

Shallow Intermittent Sand Filtration: Microorganism Removal

Results and Discussion

TABLE 2

quality of wastewater

applied to filters a

quality of wastewater applied to filters a

Parameter Unit Range

turbidity NTU 18 - 38

COD mg/L 98 - 226

BOD5 mg/L 38 - 105

TSS mg/L 20 - 38

NH3-N mg/L-N 6.1 - 23.6

nitrate + nitrite mg/L-N 0.0 - 1.1

organic N mg/L-N 3.3 - 6.2

indigenous phage b PFU/mL 640 - 2520

total coliform b MPN/100/mL 4.9 x106 - 1.1x107

a adapted from Darby et al. (1996) except where noted

b measured during the course of this study

parameter unit range
The Small Flows Journal Volume 3, Issue 1, Winter 1997

doses/d. Removal of coliform bacteria and

coliphages did not significantly change

over the study period. The data points in

figure 2 for total coliform and coliphage

removal at each HLR are the average of at

least 14 and 6 measurements, respectively,

taken over the course of 84 days.

Bacterial indicator. As shown in figure 2,

an increase in the HLR resulted in a

decrease in the log removal of total

coliforms. This result is not unexpected

and is consistent with results reported in

16

TABLE 3

summary of treatment achieved

with intermittent sand filters (dosing

frequency = 24 times/day)

R. W. Emerick, R. M. Test, G. Tchobanoglous, Ph.D., P.E., and J. Darby, Ph.D., P.E.

grouped together for data analysis and

presentation. A summary of the performance is provided in table 3.

All of the filters, regardless of medium

type or HLR, were able to remove

turbidity to less than 2 nephelometric

turbidity units (NTU), reduce TSS to less

than 2 mg/L, and remove COD to less

than 20 mg/L. There were no statistically

significant differences in the performance

of any of the filters in removing TSS,

COD, and turbidity. The results from this

study are the same as those

reported by Darby et al.

(1996). The ability to remove

contaminants to such low

levels in the filters utilizing

the coarse sand (ES = 3.3

mm) is significant because the

indication is made that largesize sand, when coupled with

a high DF, is capable of

producing a high quality

effluent. The benefit of using

coarse sand as the filter

medium is that the chance of

clogging over extended time

periods is minimized, even

when using a relatively high

HLR. As reported in table 3,

crushed glass performed

essentially the same as the

medium-size sand at a loading

rate of 0.04 m/d. Additional

research needs to be conducted on the long-term

stability of each filter medium

in resisting clogging.

Effect of HLR and DF on

Microorganism Removal

The effect of HLR, coupled

with a DF of 24 doses/d, on

total coliform and coliphage

removal is illustrated in figure

2. Both total coliform and

coliphage removal performance were evaluated for

medium-size sand (d10 = 0.65,

UC = 3.8) at a DF of 24

 percent removal effluent concentration a

 mg/L except NTU for turbidity

parameter Average Minimum Maximum Average Minimum Maximum

crushed glass

HLR = 0.040 m/d

turbidity 98.1 97.7 98.5 0.40 0.31 0.50

TSS >99 >99 >99 ND ND ND

COD 95.2 93.4 97.1 8 5 11

medium sand

HLR = 0.040 m/d

turbidity 98.3 97.6 99.0 0.36 0.22 0.47

TSS >99 >99 >99 ND ND ND

COD 95.8 93.5 99.4 7.2 1.0 11.0

medium sand

HLR = 0.081 m/d

turbidity 98.1 95.3 98.8 0.40 0.26 0.90

TSS >99 >99 >99 ND ND ND

COD 95.2 93.5 96.5 8.2 6 11

medium sand

HLR = 0.163 m/d

turbidity 96.4 88.4 98.7 0.75 0.27 2.2

TSS >99 >99 >99 ND ND ND

COD 95.2 94.1 97.1 8.2 5 10

coarse sand

HLR = 0.163 m/d

turbidity 94.0 86.8 97.3 1.3 0.60 2.5

TSS 96.2 93.4 98.7 1.4 0.78 2.0

COD 92.2 88.7 94.7 13.3 9 19

concrete and

filter sandb

turbidity 97 91 99 0.7 0.3 1.7

TSS 98 94 >99 0.4 ND 1.8

COD 94 81 >99 8.8 1.0 42.0

a ND = nondetectable amounts in 2 liters of sample

b data taken from Darby et al. (1996) for the purpose of comparison

mg/L except NTU for turbidity

b

 percent removal effluent concentration a

parameter average minimum maximum average minimum maximum
The Small Flows Journal Volume 3, Issue 1, Winter 1997

17

the literature (U.S. EPA, 1978;

Dymond, 1981). A removal of 2 to 4

logs is reported as being typical

(Anderson et al., 1985; Ronayne,

1982; Salvato, 1955).

Viral indicator. An increase in the

HLR also resulted in a decrease in the

log removal of indigenous coliphages

(see figure 2). There was not a

statistically significant difference

between the removal of total coliform

bacteria and the removal of indigenous

coliphages. In considering the reduction of indigenous coliphages in this

study, it is useful to define a new term,

the hydraulic application rate (HAR).

The HAR is defined as:

HAR (m/dose) =

The importance of the HAR is illustrated in table 4.

 At an HLR of 0.040 m/d and a DF of

24 doses/d, the resulting HAR is

0.00167 m/dose, which corresponds to

about 9 percent of the field capacity of

the filter. With such a light HLR at

each dose, the applied water is retained

in the upper layer of the filter and does

not immediately penetrate to the lower

layers. Only with subsequent applications (doses) is the water displaced

into the lower layers of the filter in a

more-or-less plug flow regime (Boller

et al., 1993).

When the HLR is increased to 0.163

m/d, the value of the HAR is 0.00679

m/dose, which corresponds to 36

percent of the field capacity. As the

HAR increases, saturated conditions

are more likely to occur along with

deeper penetration into the filter of the

applied dose and the potential for some

direct wash-through due to more

significant deviations from plug flow

conditions (Boller et al., 1993).

Viruses pass more easily in saturated

flow because under saturated flow

conditions, viruses can be carried

Shallow Intermittent Sand Filtration: Microorganism Removal

FIGURE 2

microorganism log

survival plot

TABLE 4

analysis of volume

per dose for various

hydraulic loading

rates and dosing

frequencies

DF (dose/d)

HLR (m/d)

HLR, Dosing Hydraulic Field

m/d frequency, application ratea, capacity filledb

,

 doses/d m/dose percent

0.040 1 0.040 210

2 0.020 105

4 0.010 53

8 0.005 26

12 0.00333 18

24 0.00167 9

0.081 1 0.081 426

2 0.040 210

4 0.020 105

8 0.010 53

12 0.00675 36

24 0.00338 18

0.163 1 0.163 858

2 0.082 432

4 0.041 216

8 0.020 105

12 0.014 74

24 0.00679 36

a HAR calculated with equation 1.

b Field capacity filled= HAR

field capacity of filter

 surface area of filter

where field capacity is defined as (5%) x (total volume of filter) as

per Bouwer, 1978, and total volume, surface area, and depth of

each filter is 0.431 m3, 1.13 m2, and 0.38 m, respectively.

HLR, dosing hydraulic field

m/d frequency, application rate a, capacity filled b,

 doses/d m/dose percent

(1)
The Small Flows Journal Volume 3, Issue 1, Winter 1997

due to the coat protein structure and

therefore are more sensitive to an increase

in shear forces that result with an increase

in the HAR. This hypothesis would imply

that indigenous coliphages are more

sensitive indicators for filter virus passthrough testing than are polioviruses.

Effect of Medium Type on

Microorganism Removal

Medium type was studied for its influence

on microorganism removal at both a high

and low HLR. In testing a low HLR of

0.04 m/d, medium-size sand and crushed

glass were compared. In testing a high

HLR of 0.163 m/d, medium- and coarsesize sand were compared. A summary of

the results of these comparisons is

provided in table 5. As reported in table 5,

medium type was not a significant factor

in either total coliform or coliphage

removal. The sand and glass filters were

similar in ES (0.44 and 0.65, respectively), but differed in their UCs (5.0 and

3.8, respectively). When loaded at an

HLR of 0.04 m/d, the coliform and

coliphage log removals for the glassmedium filter and the medium-size-sand

filter were not significantly different

statistically at the 95 percent confidence

level; the filters performed similarly.

Performance comparison between the

medium-size sand (ES = 0.65 mm and UC

= 3.8) and coarse sand (ES = 3.3 mm and

UC = 1.3) when loaded at an HLR of

0.163 m/d also did not result in statistically significant differences at the 95

percent confidence level.

The results of this study are not consistent

with previous studies in which it was

reported that removal of bacteria was

found to decrease with an increasing ES

(Marshall and Middlebrooks, 1974; Allen,

1971; Dymond, 1981). Although media

size differences in this study were even

greater than that reported in other studies

and would lead to the expectation that

effects would be observed in microorganism removal, the effects were likely

overshadowed by the high overall removal

18

along with the percolating water and can

break through even the most tortuous path

(Sproul, 1975; U.S. EPA, 1977; Powelson

and Gerba, 1994). In unsaturated flow (as

is expected in this study), the liquid flows

at a slower rate and in a film over the

surface rather than filling the pore spaces,

and, as a consequence, there is greater

opportunity for the viruses to contact the

absorbing surface (U.S. EPA, 1977).

Additionally, unsaturated conditions allow

deeper oxygen penetration in the pore

spaces, providing for greater biological

activity, which is positively correlated

with virus removal (Sproul, 1975).

An important difference is noted between

the sensitivity of indigenous coliphages to

changes in HLR and the sensitivity of

viral indicators that have been reported in

the literature. In a seeded virus study, the

U.S. EPA (1978) reported that a one or

more log difference in effluent poliovirus

concentration resulted when the HLR was

increased from 0.05 to 0.50 m/d, an order

of magnitude increase. In this study it was

found that a one or more log difference in

effluent indigenous coliphage concentration results from a simple doubling of the

HLR, from 0.04 to 0.08 m/d. The relevant

difference in experimental design between

this study and U.S. EPA (1978) is that

the U.S. EPA study utilized a one dose/d

DF, whereas a 24 doses/d DF was utilized

in this study. The difference in DF has

been discussed above and would lead to

the expectation that the opposite results

should have occurred: a greater sensitivity

to HLR should have been observed in the

U.S. EPA study compared to this study.

The finding of greater sensitivity in the

current study to an increase in HLR is

hypothesized to be the result of the type of

virus used as the viral indicator. Because

virus removal is principally an adsorption

phenomena, the virus coat protein likely

plays an instrumental role in removal.

Adsorption has been found to be affected

by virus charge (Burge and Enkiri, 1978)

and hydrophobic effects (Farrah et al.,

1981; Farrah, 1982). Thus, indigenous

coliphages may be less easily adsorbed

R. W. Emerick, R. M. Test, G. Tchobanoglous, Ph.D., P.E., and J. Darby, Ph.D., P.E.
The Small Flows Journal Volume 3, Issue 1, Winter 1997

19

rates associated with the high DF (and

corresponding low HAR) used in this

research. DF has been found to affect the

removal of bacteria, with higher DF

leading to greater bacterial removal

(Ronayne, 1982).

For the conditions studied in this research,

the following conclusions can be drawn:

ISFs with a relatively shallow bed

depth (0.38 m) are capable of removing

both bacteria and viruses from wastewater. Both total coliform and coliphage removal are dependent on HLR in

the range of 0.040 to 0.163 m/d when

coupled with a DF of 24 doses/d. A

decrease in the HLR results in an increase in the log removal of both total

coliforms and indigenous coliphages.

Indigenous coliphages may be more

suitable indicators for testing filters for

virus removal than polioviruses

because they are more sensitive to

increases in HLR than are polioviruses.

Additional research is required to

ascertain the type of coliphages most

commonly found in wastewater and

their specific mechanism for removal.

The influence of medium type on

microorganism removal can be

minimized by utilizing a high DF. It is

hypothesized that the resulting low

HAR maximizes plug flow conditions

leading to greater microbial contaminant removal.

Crushed glass is effective as a filter

medium for the removal of TSS, COD,

turbidity, total coliforms, and indigenous coliphages. Performance and

cost of crushed glass medium is

similar to that for sand.

 The donation of pumps and dosing

system controls by Orenco Systems, Inc.

(Roseburg, Oregon) is gratefully acknowledged. Recycled glass was provided by

the Washington State Community Trade

and Economic Development Department

and the Stuth Company, Inc. (Maple

Valley, Washington).

wo

1. 1 m/d is equivalent to 24.54 gal/ft2 • d

Allen, T. M. 1971. Effective grain size and

uniformity coefficients role in performance of intermittent sand filters.

Technical Paper No. 9. Environmental

Quality Research and Development

Unit. New York State Department of

Environmental Conservation.

American Public Health Association.

1989. Standard methods for the

examination of water and wastewater.

17th ed., Washington, D.C.

Anderson, D. L., R. L. Siegrist, and R. J.

Otis. 1985. Technology assessment of

intermittent sand filters. Municipal

Shallow Intermittent Sand Filtration: Microorganism Removal

Conclusions

Acknowledgments

Notes

TABLE 5

effect of HLR on

microorganism log

reduction as a function

of medium size

References

————————————————————————————————————————

HLR = 0.04 m/d HLR = 0.163 m/d

——————————————— ———————————————

crushed medium-size medium-size coarse

glass sand sand sand

d10 = 0.44 mm d10 = 0.65 mm d10 = 0.65 mm d10 = 3.3 mm

Parameter UC = 5.0 UC = 3.8 UC = 3.8 UC = 1.3

————————————————————————————————————————

Coliphage 3.1a 2.9a 0.9a 0.8a

Total coliform 3.4a 3.0a 1.6c 1.8c

————————————————————————————————————————

Note: Numbers with the same superscripts are statistically the same at the

95 percent confidence level. Numbers with different superscripts are

statistically different from each other at the 95 percent confidence level.

HLR = 0.04 m/d HLR = 0.163 m/d
The Small Flows Journal Volume 3, Issue 1, Winter 1997

20

R. W. Emerick, R. M. Test, G. Tchobanoglous, Ph.D., P.E., and J. Darby, Ph.D., P.E.

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Andreadakis, A. D. 1987. Organic matter

and nitrogen removal by an onsite

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Water Research 21, no. 5: 559–565.

Ball, H. B. 1991. Sand filters: state of the

art and beyond. On-site WWT 6: 105–

113.

Boller, M., A. Schwager, J. Eugster, and V.

Mottier. 1994. Dynamic behavior of

intermittent sand filters. Water Science

and Technology 28, no. 10: 99–107.

Bouwer, H. 1978. Groundwater hydrology. New York: McGraw-Hill, Inc.

Burge, W. D., and N. K. Enkiri. 1978.

Virus adsorption by five soils. Journal

of Environmental Quality 7, no. 1: 73–

76.

Darby, J. L., G. Tchobanoglous, M. A.

Nor, and D. Maciolek. 1996. Shallow

intermittent sand filtration: performance evaluation. The Small Flows

Journal 2, no. 1: 3–15.

Dymond, R. L. 1981. Design considerations for the use of on-site sand filters

for wastewater treatment. Master’s

thesis. Department of Civil and

Environmental Engineering. Pennsylvania State University.

Farrah, S. R., D. O. Shah, and L. O.

Ingram. 1981. Effects of chaotropic

and antichaotropic agents on elution of

poliovirus adsorbed on membrane

filters. Proceedings of the National

Academy of Science U.S.A. 78, no. 2:

1229–1232.

Farrah, S. R. 1982. Chemical factors

influencing adsorption of bacteriophage MS2 to membrane filters. Applied

and Environmental Microbiology 43,

no. 3: 659–663.

Furman, T. D., W. T. Calaway, and G. R.

Grantham. 1955. Intermittent sand

filters—multiple loadings. Sewage and

Industrial Wastes (march): 260–276.

Grantham, G. R., D. L. Emerson, and A.

K. Henry. 1949. Intermittent sand filter

studies. Sewage Works Journal 21, no.

6:1002–1015.

Green, K. M. and D. O. Cliver. 1974.

Removal of viruses from septic tank

effluent by sand columns. Proceedings

of the National Home Sewage Disposal

Symposium. ASAE, 137–143.

Gross, M. A., and D. Mitchell. 1990. Virus

removal by sand filtration of septic

tank effluent. ASCE Journal of

Environmental Engineering 116, no. 4:

711–720.

Hain, K. E., and R. T. O’Brien. 1979.

Survival of enteric viruses in septic

tanks and septic drain fields. New

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N.M.

Lehrer, A. J., and V. J. Cabelli. 1993.

Comparison of ultraviolet and chlorine

inactivation of f male-specific bacteriophage and fecal indicator bacteria in

sewage effluents. WEF Specialty

Conference Series: Planning, Design,

and Operations of Effluent Disinfection Systems. May 23–25. Whippany,

N.J., 37–48.

Marshall, G. R., and E. J. Middlebrooks.

1974. Intermittent sand filtration to

upgrade existing wastewater treatment

facilities. Utah Water Research

Laboratory, College of Engineering,

Utah State University at Logan.

Peeples, J. A., K. M. Mancl, and D. L.

Widrig. 1991. An examination of the

role of sand depth on the treatment

efficiency of pilot scale intermittent

sand filters. Proceedings of the 6th

National Symposium on Individual and

Small Community Sewage Systems

(Chicago, December 16–17). ASAE

publication n10-911. St. Joseph, Mich.:

ASAE.

Pell, M., and F. Nyberg. 1989a. Infiltration of wastewater in a newly started

pilot sand-filter system: Part I.

Reduction of organic matter and

phosphorus. Journal of Environmental

Quality 18: 451–457.

_____. 1989b. Infiltration of wastewater

in a newly started pilot sand filter

system: Part II. Development and

distribution of the bacteria population.

Journal of Environmental Quality 18:

457–462.
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_____. 1989c. Infiltration of wastewater

in a newly started pilot sand filter

system: Part III. Transformation of

nitrogen. Journal of Environmental

Quality 18: 463–467.

Pell, M., F. Nyberg, and H. Ljungren.

1990. Microbial numbers and activity

during infiltration of septic tank

effluent in a sub-surface sand filter.

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1354.

Powelson, D. K., and C. P. Gerba. 1994.

Virus removal from sewage effluents

during saturated and unsaturated flow

through soil columns. Water Research

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Ronayne, M. P., R. C. Paeth, and T. J.

Osborne. 1982. Intermittent sand filter

design and performance—an update.

Proceedings of the 47th Northwest OnSite Wastewater Disposal Short

Course. 12242.

Salvato, J. A. Jr. 1955. Experience with

subsurface sand filters. Sewage and

Industrial Wastes 27, no. 8: 909–916.

Schwartz, W. A., T. W. Bendixen, and R.

E. Thomas. 1967. Project report of

pilot studies on the use of soils as

waste treatment media. In-house report

prepared for the Federal Waste

Pollution Agency. Cincinnati, Ohio.

Siegrist, R. L., and W. C. Boyle. 1981.

Onsite reclamation of residential

greywaater. Proceedings of the Third

National Symposium on Individual and

Small Community Sewage Treatment.

ASAE:176–186.

Sproul, O. J. 1975. Virus movement in

groundwater from septic tank systems,

in: W. J. Jewell and R. Swan (eds)

Water Pollution Control in Low

Density Areas: Proceedings of the

Rural Environmental Engineering

Conference. University Press of New

England. 135–144.

Tchobanoglous, G., and F. L. Burton.

1991. Wastewater engineering:

treatment, disposal, and reuse. 3d ed.

New York: McGraw Hill, Inc.

U.S. Environmental Protection Agency

(EPA). 1977. Alternatives for small

wastewater treatment systems: On-site

disposal/septage treatment and

Shallow Intermittent Sand Filtration: Microorganism Removal

disposal. Municipal Environmental

Research Laboratory. Cincinnati,

Ohio. EPA 625/4-77-011(vol. 1).

_____. 1978. Management of small

waste flows. Municipal Environmental Research Laboratory. Cincinnati,

Ohio. EPA 600/2-78/173.

_____. 1980. Design manual. Onsite

wastewater treatment and disposal

system. Municipal Environmental

Research Laboratory. Cincinnati,

Ohio. EPA 625/1-80-012.

Wang, D., C. P. Gerba, and J. C. Lance.

1981. Effect of soil permeability on

virus removal through soil columns.

Applied and Environmental Microbiology 42, no. 1: 83–88.

 Robert W. Emerick

Robert Emerick is a doctoral student in

the Department of Civil and Environmental Engineering at the University

of California, Davis.

Rebecca M. Test

Rebecca Test currently works with

Concern/America in Santa Ana,

California. At the time of this research,

she was a graduate student in the

Department of Civil and Environmental

Engineering at the University of

California, Davis.

continued on page 22
The Small Flows Journal Volume 3, Issue 1, Winter 1997

NAT

CLEARIN

AL SMALL F

EARINGHOU

ATIONAL SMA

Jeannie Darby,

Ph.D., P.E.

Jeannie Darby is an associate

professor in the Department of Civil

and Environmental Engineering at

the University of California, Davis.

George Tchobanoglous,

Ph.D., P.E.

George Tchobanoglous has recently

retired as a professor emeritus in the

Department of Civil and Environmental Engineering at the University of

California, Davis.

.

If you would like more information about

this article, write to Jeannie Darby, Ph.D.,

P.E., Department of Civil and Environmental

Engineering, University of California,

Davis, 116 Everson Hall, Davis CA 95616.

22

Papers are now being accepted for

upcoming issues of The Small Flows

Journal, the only juried technical journal

devoted specifically to small community

wastewater issues. Its mission is to

provide a forum for the presentation and

exchange of new ideas and methodologies

for solving wastewater issues for small

communities (i.e., communities with

populations under 10,000 or communities

handling less than one million gallons of

wastewater flows per day).

For additional information about the

journal, manuscript submission guidelines,

and publication deadlines, contact

Cathleen Falvey, editor, at 1-800-624-

8301, ext. 5526, or mail to Editor, The

Small Flows Journal, National Small

Flows Clearinghouse, West Virginia

University, P.O. Box 6064, Morgantown,

WV 26506-6064.

CALL FOR PAPERS

The Small Flows Journal

CALL F O

R

P

A P E R S
The Small Flows Journal Volume 3, Issue 1, Winter 1997

NSFC News / Resources NSFC News / Resources

23

NSFC To Release Unique

Onsite Report

A unique report about onsite wastewater

systems across the U.S. is being finalized

and will be available soon from the National

Small Flows Clearinghouse (NSFC).

Titled National Onsite Wastewater

Treatment: A National Small Flows

Clearinghouse Summary of Onsite Systems

in the United States, 1993, the report provides

a comprehensive examination of onsite

system information collected from 1,567

local health agencies across the country.

“The NSFC has never attempted a study of

this scope before,” said NSFC Technical

Assistance Specialist Tricia Angoli, who

coordinated the project. “We learned a lot

from the experience, and we have a

considerable amount of information to

pass on to the public.”

The Small Flows Journal

Online—NSFC Develops

World Wide Web Site

The National Small Flows Clearinghouse

(NSFC) went online last fall with its

World Wide Web site.

Accessible via the address http://

www.nsfc.wvu.edu, the site is updated

regularly and now includes the latest

issues of the NSFC’s publications: Small

Flows, Pipeline, and The Small Flows

Journal.

The NSFC’s Guide to Products and

Services, which includes descriptions of

more than 300 free or low-cost items, is

also online, along with a listing of new

products. An e-mail link allows for quick

and easy ordering. Helping America’s small communities meet their wastewater needs

http://www.nsfc.wvu.edu

(800) 624-8301 • (304) 293-4191

Part of that information includes onsite

system permit and installation costs,

reasons for onsite system failures, the

number of homes using onsite systems,

and information about who inspects them.

The study uncovered both similarities and

differences across states in the ways that

systems are managed. This knowledge

reinforces the fact that no one situation is

unique, Angoli said.

The information represents the 1993 data

of health departments who responded to

an NSFC questionnaire. Data are presented individually by state, as well as

summarized nationally.

The complete report will be available

soon by calling (800) 624-8301 or (304)

293-4191 and ordering Item #WWBKGN89.

Once available, it also may be ordered via

the NSFC’s Web site (see the article

above). As of press time, the cost of the

report had not yet been determined.

In addition, the NSFC’s Web site provides

a link to the NSFC’s Wastewater Treatment Information Exchange Bulletin

Board System, discusses new or enhanced

program activities and services, offers

public education information under the

section “Wastewater Trivia”, and includes

more than a dozen links to other wastewater-related sites.

The NSFC invites you to visit us online

and to leave messages or suggestions to

the Web master under the “Contact Us”

section.
The Small Flows Journal Volume 3, Issue 1, Winter 1997

24

ETI Project To Disseminate

Innovative Technology

Information

Fact sheets that detail innovative wastewater technologies will be available soon

through the National Small Flows Clearinghouse (NSFC) as part of the U.S.

Environmental Protection Agency’s (EPA)

Environmental Technology Initiative

(ETI).

The NSFC has been collecting information since October 1995 on approximately

600 innovative wastewater technology

projects that were funded through the now

defunct EPA Construction Grants Program. Under this program, about $1.1

billion was allocated for innovative

technologies.

“The benefits gained from the Construction Grant-funded Innovative and Alternative (I/A) projects have been extremely

valuable,” said Clement Solomon, NSFC

senior technical assistance specialist.

“This project represents the next logical

step in assessing the lessons learned from

these I/A projects, and in making sure that

information reaches those in the wastewater profession.”

The information collected about these I/A

projects will be used to develop 10 to 15

fact sheets this fiscal year. In addition,

information about all I/A Construction

Grants facilities will be housed in the

NSFC’s Facilities Database.

This newly redesigned database will

serve as a networking tool by providing

facility operator and manager contact

information, so others can reach them to

discuss specifics about their particular

treatment and disposal technologies. The

database also houses information about

other innovative, alternative, and conventional systems around the country that

serve a population of 10,000 or fewer or

have flows of less than one million

gallons per day.

The database complements the information detailed in the technology fact sheets.

The fact sheets include specifics about

design/system specifications, performance

reliability and residuals, system limitations, operation and maintenance, and cost.

According to Solomon, fact sheets on

ultraviolet light, chlorine, and ozone

disinfection technologies and on fine pore

aeration will be available soon. Other fact

sheets are planned to address the following technology categories:

• clarifiers,

• digestion,

• energy conservation and recovery,

• filtration,

• fixed film biological reactors,

• land treatment, and

• nutrient removal.

Completed technology fact sheets will be

promoted in future issues of Small Flows

and Pipeline and also will be available via

the NSFC’s Web site (see article on page

23). The NSFC welcomes information

about specific wastewater facilities for

inclusion in its database. Information may

be submitted by calling the NSFC at (304)

293-4191 or (800) 624-8301 and requesting a Facilities Database Collection Form

or by accessing the form via the Web.

ETI

Environmental Technology Initiative
The Small Flows Journal Volume 3, Issue 1, Winter 1997

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Authors warrant that the manuscript is

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Submit all manuscripts to:

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Contact the National Small Flows Clearinghouse to obtain a copy.

Manuscripts that are prepared on a personal

computer or Macintosh should be submitted in

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