Nitrogen Removal

Using Saturated Upflow

Woody Fiber Media

2017

Onsite Wastewater Mega Conference

October 24, 2017

Larry Stephens, P.E.

Acknowledgement

Some of this material comes from Stewart Oakley, Department of Civil Engineering

California State University, Chico as part of the University Curriculum Development for

Decentralized Wastewater Management, with content edited for this presentation

Chemistry of Nitrogen

Nitrogen can exist in nine various forms in the environment

due to seven possible oxidation states:

Nitrogen Compound Formula Oxidation State

*Organic nitrogen Organic-N -3

*Ammonia NH3 -3

Ammonium ion NH4+ -3

*Nitrogen gas N2 0

Nitrous oxide N2O +1

Nitric oxide NO +2

Nitrite ion NO2- +3

Nitrogen dioxide NO2 +4

*Nitrate ion NO3- +5

The Nitrogen Cycle in Soil-Groundwater

Systems

Transformation of the principal nitrogen compounds in soil-

groundwater systems (Organic-N, NH3-N, NH4+-N, N2-N, NO2

--N,

and NO3--N) can occur through five key mechanisms in the

environment:

Fixation

Ammonification

Synthesis

Nitrification

Denitrification

Biological Nitrification

Nitrification is the biological oxidation of NH4+ to NO3

- through a

two-step autotrophic process by the bacteria Nitrosomonas

and Nitrobacter:

Nitrosomonas

Step 1: NH4+ + 3/2O2 NO2

-- + 2H+ + H2O

Nitrobacter

Step 2: NO2- + 1/2O2 NO3

-

Environmental Effects of Nitrogen Discharges

Health Effects from Groundwater Contamination with Nitrates

Methemoglobinemia – most often cited concern

Carcinogenesis

Birth Defects

Surface Water Pollution with Nitrogen

Eutrophication

Oxygen Demand through Nitrification

Ammonia Toxicity to Aquatic Organisms

Sources of Nitrogen Discharges to

Groundwater

Agricultural Activities:

Can be a significant source of nitrate in groundwater from . . .

Excessive or inappropriate use of nitrogen-based nutrientsources:

• Commercial fertilizers

• Animal manures

• Types of crops utilized (Fixation in legumes)

Atmospheric Deposition

Onsite Wastewater Systems

Control of Nitrogen Discharges from Onsite

Systems

Public health agencies have tried to minimize the

impact of nitrate from septic systems by:

Limiting the number of onsite systems in a given

area (i.e. control lot sizes)

Promoting alternative onsite treatment

technologies that provide nitrogen removal

Nitrogen Dynamics in Septic

Tank-Soil Absorption Systems

Septic Tanks:

The removal of Total-N within septic tanks is on the

order of 10 to 30%, with the majority being removed

as particulate matter through sedimentation or

flotation processes.

Because of the septic tank's anaerobic (very little

oxygen) environment, nitrogen exists principally as

Organic-N and NH3-N/NH4+-N (TKN).

Nitrogen Dynamics in Septic Tank

and Soil Absorption Systems

Subsurface Absorption Trenches:

Nitrogen can undergo several transformations within

and below subsurface absorption trenches:

Adsorption of NH4+-N in the soil

Volatilization of NH3-N in alkaline soils at a pH above 8.0

Nitrification and subsequent movement of NO3- -N towards

the groundwater

Biological uptake of both NH3-N/NH4

+-N and NO3- -N

Denitrification if the environmental conditions are

appropriate

Water flow through a trench

Infiltrative Surface:

Where water enters the soil

Biologically Active Zone:

Commonly called the “biomat”,

is where the majority of the

treatment occurs

Vadose (unsaturated) Zone:

Zone that provides additional aerobic

treatment, disperses water, adsorbs

pollutants (eg, phosphorus).

(NITRIFICATION HAPPENS HEAR)

R.J. Otis

Figure 7: Nitrate Nitrogen Concentrations in Septic Tank Effluent and

Vadose Zone Receiving Nitrified Effluents

0

10

20

30

40

50

60

70

Jun-96 Jul-96 Aug-96 Sep-96 Oct-96 Nov-96 Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97

Date

Nit

ra

te N

itro

gen

Co

ncen

tra

tio

n, m

g/L

as

N

Vadose Zone Beneath Trench

Septic Tank Effluent

Source: NDWRCDP

How Biological Denitrification

Can Occur in an Onsite System

NO3- can be reduced to N2 gas under ANOXIC (very low oxygen)

conditions, through heterotrophic biological denitrification as

shown in the following unbalanced equation:

Heterotrophic

Bacteria

NO3- + Organic Matter N2 + CO2 + OH- + H2O

Water flow through a trench

Infiltrative Surface:

Where water enters the soil

Biologically Active Zone:

Commonly called the “biomat”,

is where the majority of the

treatment occurs

Vadose (unsaturated) Zone:

Zone that provides additional aerobic

treatment, disperses water, adsorbs

pollutants (eg, phosphorus).

(NITRIFICATION HAPPENS HEAR)

R.J. Otis

Denitrification

A large variety of heterotrophic bacteria can use nitrate in

lieu of oxygen for the degradation of organic matter under

anoxic conditions.

If O2 is present, however, the bacteria will preferentially

select it instead of NO3-. Thus it is very important that anoxic

conditions exist in order that NO3- will be used as the

electron acceptor.

A carbon source (food) is required as the electron donor for

denitrification to occur.

Treatment Processes for

Onsite Nitrogen Removal Systems

Sequential Nitrification/Denitrification Processes:

(Figure 10)

STEP 1 --- Nitrification (aerobic process)

Conversion of Organic N and Ammonia to Nitrite

and then Nitrate

STEP 2 --- Denitrification (anerobic/anoxic process)

Conversion of Nitrate to Nitrogen Gas

Biological Nitrification

pH and Alkalinity Effects:

The optimum pH range for nitrification is 6.5 to 8.0.

Nitrification consumes about 7.1 mg of alkalinity (as CaCO3) for

every mg of NH4+-N oxidized.

In low alkalinity wastewaters there is a risk that nitrification will

lower the pH to inhibitory levels.

Biological Nitrification

Temperature Effects:

Temperature has a significant effect on nitrification that must

be taken into consideration for design.

In general, colder temperatures require longer cell residence

times in suspended-growth systems and lower hydraulic

loading rates in attached-growth systems due to slower growth

rates of nitrifying bacteria.

Summary – Nitrogen Removal

Nitrogen removal first requires oxidation to nitrate – “nitrification”

Aerobic process

Slow growing bacteria – requires long cell residence time

Uses up alkalinity

Following oxidation to nitrate – “denitrification” required

Anaerobic process (anoxic conditions - very low DO)

Requires food source – carbon

Produces some alkalinity

Both processes are temperature sensitive

Examples of Onsite Nitrogen Removal

Technologies

Suspended Growth:

Aerobic units w/pulse aeration

Sequencing batch reactor

Attached Growth:

Single Pass Media Filters (SPMF)

Recirculating Media Filters (RMF)

RMF w/Anoxic Filter

RMF or Other Aerobic Treatment Followed by Anoxic Filter

w/external carbon source

RUCK system

Note: This is not intended to be an exhaustive list.

Treatment Processes for

Onsite Nitrogen Removal

Table 1

Examples of Onsite Biological Nitrogen Removal from the Literature

Total-N Removal Effluent Total-N

Technology Examples Efficiency, % mg/L

Suspended Growth:

Aerobic units w/pulse aeration 25-61 37-60

Sequencing batch reactor 60 15.5

Attached Growth:

Single Pass Sand Filters (SPSF) 8-50 30-65

Recirculating Sand/Gravel Filters (RSF) 15-84 10-47

Multi-Pass Textile Filters 14-31 14-17

RSF w/Anoxic Filter 40-90 7-23

RSF w/Anoxic Filter w/External Carbon Source 74-80 10-13

RUCK System 29-54 18-53

Recent Research Using

An Upflow, Saturated, Organic Media

Source water is aerobically well-treated effluent

utilizing geotextile packed-bed filters

Upflow using pump/pressure feed to control contact

time

Saturated media to limit oxygen and create anoxic

conditions

Bio-degradable organic media as a carbon source

(food source for bacteria)

Credits

This research was financially supported by Craig Cihak

of Craig’s Cruisers, a private business owner

planning to build a privately owned, public

wastewater treatment system to serve a resort

community in western Michigan.

The research was conducted at a wastewater treatment

facility owned by Brookfield Township in Eaton

County, MI that serves homes around Narrow Lake

and is operated by SCS Systems, LLC.

Source of aerobically treated

(nitrified) wastewater effluent

from existing treatment works

Supply line to

test

equipment

Test Apparatus

VIEW OF THE TEST APPARATUS

SHOWING THE TEST CONTAINER

AND THE FEED CONTROL VALVES

AND PLUMBING

Turf Reinforcement

Matting Placed Over

Stone in Bottom

Stone Placed in Hopper

Bottom Around Inlet

Shredded Bark Mulch

Media Placed Over

TRM

Test Column Assembly

Test Column Assembly

Another Layer of

TRM Over Media

1” Layer of Stone Over TRM

(Overflow Shown)

Test Container Filled

with Shredded Bark

Mulch Media

Media Size

Wastewater Feed Assembly

Low voltage motorized

valve controlled by

programmable timer

Influent

Sampling Tap

Pressure

Control Valve

Influent Feed Line

with Nitrified Effluent

Transformer

Test Container with

Organic Media

Electrical Feed From

Programmable Timer

Test Column Overflow Assembly

Test Container

with Media

Overflow at Top

Effluent Discharge

Effluent Sampling

Tap

Flow

Media Averages 24” in Diameter and is

Approximately 33” in Depth

Gross Volume is ~ 75 Gallons

Secondary Treatment

Using Media Filters

Nitrification Occurs Here

Anoxic Denitrification

Reactor

To Final Dispersal

Soil Component

Schematic of Treatment System for N Removal

STEP

Tanks Primary

Treatment

Background Information

1. Media – Non-treated shredded bark mulch

2. Reactor commissioned ~ Dec. 1st, 2015

3. Initial setting for empty bed contact time of 2 days

(empty bed = container volume without media)

4. Changed flow settings to increase empty bed

contact time to 3.2 days on July 29, 2016

Results . . .

Warm Weather Results . . .

Other results of interest . . .

Explanation of BOD Change?

Secondary

“Aerobic”

Treatment

Anaerobic

Bark Mulch

Reactor

To Final Dispersal

Soil Component

Septic

Tank

What would this look like for a home system?

Nitrification Denitrification

NO3 N2

Sizing Criteria ---

1. Denit. reactor – upflow

2. Fed by pump, overflow by

gravity to drainfield

3. 3 days EBCT = 500 to 750

gallon container

EXPECTED RESULT . . .

< 10 mg/l Nitrate and T.I.N.

Upsized Denitrification Filter Design

for 100,000 GPD

THIS MAY ROCK YOUR WORLD !!!

Or . . . Consider this?

Let’s think about what happens beneath

those mound systems we have been

installing over the last 30 years!

Stone Bed

Sand Fill

Original grade

and topsoil

Prepared surface

beneath mound, leaving

topsoil in place!

Aerobic

ConditionsNitrification

Saturated anaerobic or

anoxic conditions----------------------------------------------------

Organic topsoil as a

carbon source

Denitrification

Questions?

Larry Stephens, P.E.

Stephens Consulting Services, P.C.

Haslett, MI

scscons@yahoo.com