Onsite Wastewater Treatment Systems

Overview

George Loomis and David KalenNew England Onsite Wastewater Training Program

CELS NRS Cooperative ExtensionCELS - NRS Cooperative Extension University of Rhode Island

Presentation outlinePresentation outline

• Review of conventional septic system• Overview of I&A technologiesg• Applications – where and how can

they be usedthey be used

Onsite wastewater system facts:• 25% US population use these systems% p p y• Number same for past 35 years• About 30% of CT residents rely on them• Nitrogen, phosphorus & pathogens are

common contaminants

Why remove N, P and pathogens?Why remove N, P and pathogens?

• Nitrogen can pollute drinking water, promotes algae blooms in salt water

• Phosphorus promotes algae bloomsin freshwaterin freshwater

• Pathogens can find their way into drinking water wells / reservoirsdrinking water wells / reservoirs, swimming areas, shellfish

Conventional Septic System

Water table

Septic tank = solids settling and digesting areaDrainfield = treatment zone for N,P, and pathogensDrainfield treatment zone for N,P, and pathogens

• P and pathogen removal is soil and site specificN l d t• N removal does not occur

Conventional septic system i icharacteristics

• Gravity displacement of wastewater• Gravity displacement of wastewater • Plug flow movement through system • Flow based upon social clock (socially

dosed)dosed)• Drainfield sized to handle peak flow

• No active feedback to system maintenanceoperatoroperator

Conventional septic systemy

designflow = peak

w

flow

flow

time8:00 am 8:00 pm

Septic tank Risers to surfaceSeptic tank

Sanitary PVC tee Effl t

Risers to surface

Sanitary PVC tee Effluent screen

2 compartment

• Solids separator and storage• Anaerobic digester

P id h d li t ti ti (t h l ttl lid )• Provide hydraulic retention time (to help settle solids)• Does not ‘store’ surge of wastewater

Distribution box to drainfield

D-box

l t llaterals

Goal – help provide even distribution to each lateral

Trench with a fully-developed biomat

Even distributionof wastewater hasoccurred due to biomat acting as a membrane-typea membrane typefilter.

Other conventional drainfield types

Galley Drainfield

Native BackfillAccess Port

6’-10’ Perforated Concrete Chamber

C h d StCrushed Stone

1.5 - 4’ air filled soil to water table

Other conventional drainfield types

Flow diffuser drainfield

Native Backfill

Access Port

3.5’-5.5’

Crushed Stone Perforated Concrete Chamber

1.5 - 4’ air filled soil to water table

When organic inputs exceed removals by beneficial b t i d il l d bbacteria, and soil pore spaces are clogged by organic material, then hydraulic failure occurs.

Classic failure defined :• Wastewater on ground surface

F il• Failure to treat wastewater

Cesspool

• Substandard and antiquated system q y• Often in contact with seasonal high water table• Poor treatment and dispersal of wastewater

Any questions on y qconventional septic

systems?systems?

• Storage capacity in septic tankI t di t t t t t• Intermediate treatment steps

• Designed to remove specific contaminants • Control wastewater flow through system g y• Maximize N, P, and pathogen removal

Innovative and alternative treatment systems

Advances in I&A technology

Treatment train design that compliments ne t

Focus :• Treatment train design that compliments next

treatment step

• Enhancing primary treatment

• Promoting better wastewater distribution - time• Promoting better wastewater distribution - time dosing

• Improving efficiency of advanced treatment step(s)• Improving efficiency of advanced treatment step(s)

• Enhancing treatment in drainfields

• O&M and management

Time dosing systemsg yw

designflow =

flow flow

average flow

time8:00 am 8:00 am

Areal fill systems used to meet verticalseparation and fill perimeter requirementsseparation and fill perimeter requirements

• Reinforced need for large lotsReinforced need for large lots and/or retaining walls

• Altered stormwater flow

• Changed character of neighborhood

Typical applications for I&A technology

Critical resource areas -

TN Treatment Standard• < 19 mg/L concentration, and

• > 50 % TN reduction

Pathogen Guidelineg

• < 1,000 fecal coliform counts per 100 ml

Applications for I&A technology

• Totally unsewered watersheds• 30 - 70 % of systems are cesspools30 70 % of systems are cesspools • Very permeable unconfined aquifers • Groundwater contamination risk• 8 houses / acre on shallow wells• Surface water eutrophication risk• Shellfish closures

W t lit t d d f t l d tWater quality standards for coastal pond systems• 0.3 - 0.5 mg/l TN and 14 counts / 100 ml F. coliform

Site Example

• 25 - 50 ft. well setbacks• Shallow water tables

Wet soils• Wet soils• Limited buffers and

access / spacep

Site Example

• 2,500 ft2 lot• Critical resource area• Cesspool in groundwater• Tidal flushing twice daily• No natural soil• No natural soil• Completely impervious

surface

Rhode Island Aqua Fund Onsite Demo Project

Types of IA systems installed1984

ca.1996

• RUCK• ATUs• Single pass sand filters

ca.1984

ca.1996 S g e pass sa d te s• Recirc. sand filters• Early textile filters• Foam biofilters• Foam biofilters• Shallow narrow pres. drainfields• Bottomless sand filters - early • Modular peat filters• Textile filters • Fixed activated sludge systems g y• Bottomless sand filters – current• Denite upflow filters• Trickling filters• Trickling filters• UV disinfection• Soil treatment area renovation technologies

ca.2008

1) Si l d

Advanced intermediate technologies

1) Single pass sand filters

- Good pathogen and organic reductionPoor N removal- Poor N removal

- For freshwater bodies, welled areas, drinking water reservoirs, shellfish areas (w/ no eutrophication threat)

2) Modular peat filters

• Modular units Ab b t t• Absorbent peat

• Pathogen reduction technologytechnology

• Organic reduction

3) Recirculating sand filterstargeting Nitrogen removaltargeting Nitrogen removal

Meets most state treatment standards:treatment standards:

> 50 % TN removal

< 19 mg / l TN concentration

4) Textile filters• Modular 4 X 8’ footprint• Absorbent felt-like media

A d N d ti• Approved N reduction system in several states

5) Fixed activated sludge system

Bl t t• Blower motor aerates• Electrical energy needsare higher for this system

• Approved nitrogen removalpp gsystem

M d l it• Modular units• Absorbent open cell foam• Small footprint

6) Foam biofilters • Some states approve for N reduction

7) Ultraviolet light di i f ti itdisinfection units

• Pathogen reduction stepM t f ll d d• Must follow advanced treatment process

Drainfield options used with advanced treatment technologies .g

Shallow narrow drainfields

B tt l d filt

Shallow narrow drainfields

Bottomless sand filter(similar to SPSF but not covered with soil)

Bottomless sand filters as Drainfield option

• Limited site disturbance; small footprintLimited site disturbance; small footprint• Must follow advanced treatment system• Installed at grade or above grade (W.T. dependent)

SN drainfield components

• Cover (shield) with inspection ports

• End port for clean out d di l h dand distal head

• End feed manifold• Backfilled with native

soil1 ”• Lateral supported by 14”

long, notched 1” PVC pipepipe

2) Pressurized shallow narrow drainfield2) Pressurized shallow narrow drainfield (cross section)

Pressurized shallow narrow drainfield

Treatment performance

T i l I&A t h lTypical I&A technology effluent characteristics:

Has low to no odor

Is slightly cloudy or as g y yclear as tap water

How the technologies are being usedHow the technologies are being used

Maintaining Village character – Wickford, RI

Advanced treatment unit in basement of above historical building serves serves retail at street level and multi-family above, and eliminates direct discharge to coastal waters.

Bottomless sand filter provides at-grade drainfield in alley between buildings. Lot line

Alternative t fsystems for

very tight spaces

• Modular system • Poured in place tank

C fil• Compact filter• All in basement• 900 gpd systemgp y

Applications for failed systems upgrade

Failed cesspool

Conventional system approach

PL

4 feet above grade!

Selected approach

PL

media filter bottomless sand filter

System footprint

This is the entire il bl fspace available for

system components, machines staging soilmachines, staging, soil stockpile, access, and workers.

Light weight and modular components h l k t iblhelps make a system possible

Plan View

BSF w/ Category 1 System

7 X 48 foot Raised Bottomless Sand Filter following two textile filters (Design HLR = 1,200 gpd

actual HLR = 640 gpd)).

O ti d M i tOperation and Maintenance

• Is not difficult• Is not difficult• Is not expensiveIs not expensive

• But, IS ESSENTIALBut, IS ESSENTIAL

Thanks for your kind attention !

www. uri. edu / ce / wq / owtc