Collection tank that allows solids to settle and be decomposed by anaerobic bacteria.
Treatment Level: Primary
Relative Cost: medium
Amount of Maintenance Interaction: low
Beneficial Byproduct: little (compostable sludge)
Advantages
- Long accepted practice with many on-line O&M resources.
- Very efficient at retaining solids, oils & greases.
Disadvantages
- Must be careful not to flush products that are harmful to the tank bacteria.
- Unpleasant to clean if no pumping service is available.
- Secondary treatment and sludge disposal options needed.
Operation & Maintenance
- Inspect every 3 – 5 years to check for level of solids, odors or insects in vicinity of tank, and pump function
- Remove accumulated solids when tank is 1/2 to 2/3 full, or nearing outlet pipes
- Only add microbes to improve waste digestion if no on-site secondary treatment is provided.
Blackwater vs Graywater?
- Can treat both in combination, but diverting the graywater will help make the tank & secondary treatment measure smaller
Secondary Treatment Options
- Liquid (effluent): Drain fields(typical), soak pits, peat filters, treatment wetlands, aquaculture
- Solids (sludge): Drying bed, windrow, off-site disposal
Additional Notes:
- Need to locate in an area with easy access for inspection & maintenance
- Holding tank is typically concrete, fiberglass, or plastic & is water tight
- Best to have multiple chambers for cleaner effluent
- Typically pump to secondary practice
- Watch what you flush! Minimize bleaches & chlorine, don’t use caustic products or drain cleaners as these things can kill the beneficial bacteria in the tank
