Conventional Onsite Wastewater Treatment Systems, Alternative Drainfields,, and Distribution Methods

Conventional Onsite Wastewater Treatment Systems, Alternative Drainfields,, and Distribution Methods

This presentation has been modified from the following Alternative Onsite Wastewater Treatment Technologies developed by the National Decentralized Water Resources Capacity Development Project.

NDWRCDP Disclaimer This work was supported by the National Decentralized Water Resources Capacity Development Project (NDWRCDP) with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (EPA No. CR827881-01 01-0) 0) with Washington University in St. Louis. These materials have not been reviewed by the U.S. Environmental Protection Agency. These materials have been reviewed by representatives of the NDWRCDP. The contents of these materials do not necessarily reflect the views and policies of the NDWRCDP, Washington University, or the U.S. Environmental Protection Agency, nor does the mention of trade names or commercial products constitute their endorsement or recommendation for use.

CIDWT/University Disclaimer These materials are the collective effort of individuals from academic, regulatory, and private sectors of the onsite/decentralized wastewater industry. These materials have been peer-reviewed reviewed and represent the current state of knowledge/science in this field. They were developed through a series of writing and review meetings with the goal of formulating a consensus on the materials presented. These materials do not necessarily reflect the views and policies of North Carolina State University, and/or the Consortium of Institutes for Decentralized Wastewater Treatment (CIDWT). The mention of trade names or commercial products does not constitute an endorsement or recommendation for use from these individuals or entities, nor does it constitute criticism for similar ones not mentioned.

Citation Lenning, D., T. Banathy, D. Gustafson, B.J. Lesikar, S. Wecker, D. Wright. 2005. Technology Overview PowerPoint Presentation. in (D.L. Lindbo and N.E. Deal eds.) Model Decentralized Wastewater Practitioner Curriculum. National Decentralized Water Resources Capacity Development Project. North Carolina State University, Raleigh, NC.

Objectives Learn about the following The conventional onsite wastewater treatment system Septic tank Gravel drainfield How the different components in the conventional system work Alternatives to the gravel drainfield Different methods for distribution of effluent in the drainfield

Treatment Processes Variety of physical, chemical and biological processes including: Filtration Sedimentation Aeration Flotation Inactivation Adsorption Ion-exchange Anaerobic Predation Disinfection

Pretreatment Options Traditionally, have been categorized as: Primary solids removal Secondary organics and BOD removal Tertiary nutrient removal Bacteria classified in one of the following three categories Aerobic Anaerobic Facultative

Pretreatment Options Septic tank Grease Traps and Interceptors Aerobic Treatment Unit (ATU) Media Filters Constructed Wetlands Disinfection Other Lagoons, Anaerobic upflow filters

What is it? Septic Tank

Septic Tank Solids settle to bottom, retained by baffle Fats and grease float to top (scum) Wastewater exits through effluent filter

Septic Tank Design considerations Risers Required for pump tanks Can be required for septic tanks

Septic Tank Effluent screen Functions: Help keep solids in tank

Septic Tank Installation considerations Level Flows from inlet to outlet (2-inch difference) Effluent filter Risers Cast-in in-place boot Watertightness test

Subsurface Disposal

Subsurface Disposal Subsurface disposal Effluent is disposed of beneath the ground surface The soil can provide additional treatment Usually the trench bottom is installed three feet below ground surface Can be shallower or deeper under certain conditions

Subsurface Disposal Options Conventional gravel trench Shallow systems Gravelless trenches Prefabricated permeable block panel system Saprolite systems (which will be discussed at a future time) Low pressure pipe (LPP) Fill systems Drip irrigation

Subsurface Disposal Options Conventional gravel trench and shallow systems The main difference is the depth of installation for the trench bottom, conventional systems have a trench bottom depth at 36 inches while shallow systems can be installed at depths of 24 inches or less

Subsurface Disposal Options Gravelless trenches There are three main types of gravelless trenches used in North Carolina Chamber Large diameter pipe Non-gravel trenches (use a different media in place of gravel)

Subsurface Disposal Options Gravelless trenches Chamber systems are made of plastic, open to the bottom and have louvers or openings in the sides for effluent movement

Subsurface Disposal Options Gravelless trenches Large diameter pipe consists of eight or ten inch corrugated polyethylene tubing encased in a synthetic filter fabric

Subsurface Disposal Options Gravelless trenches Non-gravel media which is used as a substitute for gravel in the trench An example is provided below

Subsurface Disposal Options Prefabricated permeable block panel system 6 42 16 6 12 12 + 6 + 16 + 6 = 42

Subsurface Disposal Options Low pressure pipe systems Shallow dosed soil absorption system Pump forces effluent through the distribution lines under pressure Effluent will be evenly dosed over entire drainfield area

Subsurface Disposal Options Low pressure pipe systems

Subsurface Disposal Options Low pressure pipe systems

Subsurface Disposal Options Fill systems A system in which all or part of the trenches are installed in fill, either new file or existing file. The requirements for fill systems are found in Rule.1957(b).

Subsurface Disposal Options Drip irrigation NSFC

Subsurface Disposal Options Drip irrigation

Subsurface Disposal Methods

Subsurface Disposal Methods Effluent can be disposed of beneath the ground surface by two different methods Gravity distribution - which includes parallel and serial distribution Pressure distribution - which includes pressure manifold, LPP, drip irrigation, and siphons

Gravity Distribution Gravity distribution Effluent flows out of one component into the next downstream component and on to drainfield by gravity Inlet of downstream component must be at a lower elevation than the outlet of the upstream component Flow dependent on when and how much flow occurs at the source Distribution considered to be non-uniform over the drainfield It is the simplest and least expensive means of distribution

Gravity Distribution Parallel Distribution In parallel distribution, effluent is distributed to all trenches in the drainfield at the same time

Gravity Distribution Parallel Distribution A distribution box, tee, wye,, or header can be used to split the flow among the lines

Gravity Distribution Serial Distribution In serial distribution, effluent is discharged to the first trench in the system When that trench is full (reaches saturation) the effluent overflows from the first trench to the second trench

Gravity Distribution Serial Distribution University of Minnesota

Pressure Distribution Pressure Distribution Predetermined volumes of effluent are held in a chamber and dosed to the next component This provides: More uniform loading to next component Resting times between doses Costs more and is more complex than gravity flow On-going monitoring & maintenance are important Alarms are required

Pressure Distribution Two types of pressure distribution Demand dosing Time dosing

Pressure Distribution Demand Dosing Dose occurs when sufficient volume of effluent has been collected. Dosing frequency depends on how much wastewater is being generated. There is no control on how much effluent is being dosed daily.

Pressure Distribution Demand Dosing Pump on and off controlled directly by floats

Time Dosing Pressure Distribution Timer controls number of doses per day and dose volume Will allow only certain amount of effluent to be dosed daily Protects downstream components from overloading Useful for controlling surges or big-flow days

Pressure Distribution Time Dosing A timer controls the dosing device.

Pressure Distribution Pressure Manifold Pressurized manifold results in equal amounts of effluent discharging to each receiving pipe Usually discharges to gravity drainfield, though version of this can go to pressurized drainfield Valves may be placed on each outlet pipe allowing resting or repairing

Pressure Distribution Pressure Manifold

Siphon Pressure Distribution Passive device, part of a demand system Power is not required Proper installation is critical Regular operation and maintenance is needed