successful owts treatment siting –site evaluation –system location design –system sizing...

Successful OWTS Treatment

• Siting – Site Evaluation– System Location

• Design– System Sizing– System Selection and Design

• Installation• Operation/Maintenance

Failure

• A condition that threatens public health by failure to adequately treat sewage or creating potential for direct contact

• Examples:– Pooling on ground surface

– Back up into structure

– Leaking tanks, pump chamber or collection system

– Impacted water quality (surface or ground)

Factors Affecting OWTS Performance

• Soil system performs multiple tasks in typical OWTS– Treat the water to remove contaminants

– Dispose of treated water

• Factors that affect these tasksSoil Wastewater Characteristics

Loading Rates Users’ Lifestyle

O& M Temperature

Rainfall Surrounding Development

Soil

• Texture

• Structure

• Depth

• Compaction

• Landscape Position

Soil Profiles – Typical Layers

Soil Horizons: Soil Properties According to Depth

• Distinct soil horizons or layers; form from weathering processes • Layers have distinct chemical compositions; determines:

– amounts and state of organic matter– amounts of nutrient elements

• Each layer supports varying amounts and types of microbial communities– Surface layers of soils (O layers) are organic– Dominated by organic matter (e.g. leaves, twigs, etc.) (= O1 layer) – Dominated by unrecognizable organic matter in next lower layer

• some decomposition has occurred (O2 layer)– Sub-surface soil layers (A layers): various combinations of organic and mineral

materials which experience increasing amounts of leaching (= eluvial layers)– Lower layers (B layers): experience leaching and horizontal movement of materials

(= illuvial layers) – Lowest soil layers (C layer) experience least weathering; in contact with bedrock

Loading Rates

• Hydraulic overloading is one of leading causes of OWTS failure

• Design flow typically based on number of people in house (assumption generally 2 per bedroom) – 60 gpd/person (common assumption in design)

• Loading rates determined by type of soil

Loading Rates

• Clogging Mat

• Gravitational potential

• Matric Potential

Users’ Lifestyle

• Low-flow devices (toilet, faucets, shower heads, etc.)

• Rainfall collection

• Use of garbage disposals

• Excessive use of FOG

• Laundry habits

• Time in Residence

Wastewater Characteristics

• BOD5 (above 230mg/L will reduce life of system and level of treatment)

• Biologically active chemicals (bleach, antibiotics, etc.)

• FOG

• Other chemicals (Cleaners, solvents, degreasers, etc.)

Operation and Maintenance (O&M)

• Pump Tanks every 3 to 5 years (plan on every 4)– Actual time period should depend on active monitoring

of system

• Conduct at least biannual monitoring of tank levels, baffles, and drainfield– This is the minimum, more frequent monitoring

recommended (required for advanced systems)– Pump tank when sludge layer thickness exceeds 25% of

working liquid capacity of the tank, or if scum layer is within three inches of bottom of outlet baffle

Septic Tank

Temperature and Rainfall

• Temperature– Affects flow and mixing in septic tank– Soil treatment relies on biological activity – Cold slows down biological processes

• 50% loss in activity for 10ºC drop in temp• Activity effectively stops at 2 ºC

• Rainfall– Additional hydraulic load on soil– Reduction in vertical separation– Benefit-dilute nitrates, however also increase transport

rate

Alternative Waste Treatment

• Stabilization Ponds

• Wetlands

• Composting Toilets

• Separation of Waste Streams

• Greywater Sytstems

• Primitive Systems

Facultative Oxidation (Waste Stabilization) Pond

Stabilization Ponds or Lagoons

• Aerobic and Facultative Ponds: • Biologically Rx by complementary activity of algae and

bacteria.• Used for raw sewage as well as primary‑ or secondary‑Rx’d.

effluent.• Bacteria and other heterotrophs convert organic matter to

carbon dioxide, inorganic nutrients, water and microbial biomass.

• Algae use CO2 and inorganic nutrients, primarily N and P, in photosynthesis to produce oxygen and algal biomass.

Stabilization Ponds or Lagoons

• Many different pond designs have been used to treat sewage:

• facultative ponds: upper, aerobic zone and a lower anaerobic zone.

• Aerobic heterotrophics and algae proliferate in the upper zone.

• Biomass from upper zone settles into the anaerobic, bottom zone.

• Bottom solids digested by anaerobic bacteria.

Constructed Wetlands and Enteric Microbe Reductions

• Surface flow (SF) wetlands reduce enteric microbes by ~90%

• Subsurface flow (SSF) wetlands reduce enteric microbes by ~99%

• Greater reduction in SSF may be due to greater biological activity in wetland bed media (porous gravel) and longer retention times

• Multiple wetlands in series incrementally increase microbial reductions, with 90-99% reduction per wetland cell.

Primitive Systems

• Outhouses• Privy• Throne• Palace• Comfort station• Castle• Post office• Johnny

• Stool• Doolie• White house• Hut• WC• Ajax• Bog House• Defacatorium

Mr. Turdley Says-“Don’t be a fecaphobe”