Onsite Wastewater Treatment Systems Overview

Transcription

1 Onsite Wastewater Treatment Systems Overview George Loomis and David Kalen New England Onsite Wastewater Training Program CELS - NRS Cooperative Extension University of Rhode Island

2 Presentation outline Review of conventional septic system Overview of I&A technologies Applications where and how can they be used

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

4 Why remove N, P and pathogens? Nitrogen can pollute drinking water, promotes algae blooms in salt water Phosphorus promotes algae blooms in freshwater Pathogens can find their way into drinking water wells / reservoirs, swimming areas, shellfish

5 Conventional Septic System Water table Septic tank = solids settling and digesting area Drainfield = treatment zone for N,P, and pathogens P and pathogen removal is soil and site specific N removal does not occur

6 Conventional septic system characteristics Gravity displacement of wastewater Plug flow movement through system Flow based upon social clock (socially dosed) Drainfield sized to handle peak flow No active feedback to system maintenance operator

7 Conventional septic system design flow = peak flow flow 8:00 am 8:00 pm time

8 Septic tank Risers to surface Sanitary PVC tee Effluent screen 2 compartment Solids separator and storage Anaerobic digester Provide hydraulic retention ti time (to help settle solids) Does not store surge of wastewater

9 Distribution box to drainfield D-box laterals l Goal help provide even distribution to each lateral

10 Trench with a fully-developed biomat Even distribution of wastewater has occurred due to biomat acting as a membrane-type filter.

11 Other conventional drainfield types Galley Drainfield Access Port Native Backfill 6-10 Perforated Concrete Chamber Crushed Stone air filled soil to water table

12 Other conventional drainfield types Flow diffuser drainfield Access Port Native Backfill Crushed Stone Perforated Concrete Chamber air filled soil to water table

13 When organic inputs exceed removals by beneficial bacteria, and soil pore spaces are clogged by organic material, then hydraulic failure occurs.

14 Classic failure defined : Wastewater on ground surface Failure to treat wastewater

15 Cesspool Substandard and antiquated system Often in contact with seasonal high water table Poor treatment and dispersal of wastewater

16 Any yquestions on conventional septic systems?

17 Storage capacity in septic tank Intermediate t treatment t t steps Designed to remove specific contaminants Control wastewater flow through system Maximize N, P, and pathogen removal Innovative and alternative treatment systems

18 Advances in I&A technology Focus : Treatment train design that compliments next treatment step Enhancing primary treatment Promoting better wastewater distribution - time dosing Improving efficiency of advanced treatment step(s) Enhancing treatment in drainfields O&M and management

19 Time dosing systems flow design flow = average flow 8:00 am 8:00 am time

20 Areal fill systems used to meet vertical separation and fill perimeter requirements Reinforced need for large lots and/or retaining walls Altered stormwater flow Changed character of neighborhood

21 Typical applications for I&A technology Critical resource areas - TN Treatment Standard <19 mg/l concentration, and >50 % TN reduction Pathogen Guideline < 1,000 fecal coliform counts per 100 ml

22 Applications for I&A technology Totally unsewered watersheds % 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 t Water quality standards for coastal pond systems mg/l TN and 14 counts / 100 ml F. coliform

23 Site Example ft. well setbacks Shallow water tables Wet soils Limited buffers and access / space

24 Site Example 2,500 ft 2 lot Critical resource area Cesspool in groundwater Tidal flushing twice daily No natural soil Completely impervious surface Rhode Island Aqua Fund Onsite Demo Project

25 Types of IA systems installed ca.1984 RUCK ATUs ca.1996 Single pass sand filters Recirc. sand filters Early textile filters Foam biofilters Shallow narrow pres. drainfields Bottomless sand filters - early Modular peat filters Textile filters Fixed activated sludge systems Bottomless sand filters current Denite upflow filters Trickling filters ca.2008 UV disinfection Soil treatment area renovation technologies

26 Advanced intermediate technologies 1) Single pass sand filters - Good pathogen and organic reduction - Poor N removal - For freshwater bodies, welled areas, drinking water reservoirs, shellfish areas (w/ no eutrophication threat)

27 2) Modular peat filters Modular units Absorbent b peat Pathogen reduction technology Organic reduction

28 3) Recirculating sand filters targeting Nitrogen removal Meets most state treatment standards: > 50 % TN removal < 19 mg / l TN concentration

29 4) Textile filters Modular 4 X 8 footprint Absorbent felt-like media Approved N reduction system in several states

30 5) Fixed activated sludge system Blower motor aerates Electrical energy needs are higher for this system Approved nitrogen removal system

31 Modular units Absorbent open cell foam Small footprint 6) Foam biofilters Some states approve for N reduction

32 7) Ultraviolet light disinfection i units Pathogen reduction step Must follow advanced d treatment process

33 Drainfield options used with advanced treatment technologies. Shallow narrow drainfields Bottomless sand filter (similar to SPSF but not covered with soil)

34 Bottomless sand filters as Drainfield option Limited site disturbance; small footprint Limited site disturbance; small footprint Must follow advanced treatment system Installed at grade or above grade (W.T. dependent)

35 SN drainfield components Cover (shield) with inspection ports End port for clean out and ddistal lhead End feed manifold Backfilled with native soil Lateral supported by 14 long, notched 1 PVC pipe

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

37 Pressurized shallow narrow drainfield

38 Treatment performance Typical I&At technology effluent characteristics: Has low to no odor Is slightly cloudy or as g y y clear as tap water

39 How the technologies are being used

40 Maintaining Village character Wickford, RI Advanced treatment unit in basement of above historical building serves serves retail at street level and multifamily above, and eliminates direct discharge to coastal waters. Bottomless sand filter provides atgrade drainfield in alley between buildings. Lot line

41 Alternative systems for very tight spaces Modular system Poured in place tank Compact filter All in basement 900 gpd system

42 Applications for failed systems upgrade Failed cesspool

43 Conventional system approach P L 4 feet above grade!

44 Selected approach P L media filter bottomless sand filter

45 System footprint This is the entire space available for system components, machines, staging, soil stockpile, access, and workers.

46 Light weight and modular components helps make a system possible

47 Plan View

48 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)).

49 Operation and Maintenance Is not difficult Is not expensive But, IS ESSENTIAL

50 Thanks for your kind attention! www. uri. edu / ce / wq / owtc