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