1. Household and small treatment systems
Professor Nick Gray
Centre for the Environment
Trinity College
University of Dublin
© Tigroney Press

2. Small Treatment Systems
Required to be:
Cheap
Robust
Compact
Hygienic at site
Odourless
Require little maintenance
Installed and operated by unskilled labour
Based on full-scale units but modified
Problem with scaling up and scaling down.

3. Small Treatment Systems
Choice depends:
Loading
Treatment objectives
Site conditions and location
Effluent discharge requirement
Plant characteristics – power, maintenance
Cost

4. Small Treatment Systems
Cesspools
Impervious
Can not overflow
Minimum capacity 45 d (18m3)
Must be able to completely empty
Adequately vented
Adequately covered

5. Small Treatment Systems
Septic Tanks

6. Small Treatment Systems
Septic Tanks
Single, double or triple chambered

7. Small Treatment Systems
Must be impervious and watertight
Block built must be rendered to make watertight.
Typical cast concrete two-chambered tank

8. Small Treatment Systems
Minimum size of tanks in Ireland for pe2-5 is 3m3; pe 6-10 is 4m3

9. Small Treatment Systems
Modern GRP onion shaped septic tanks from Klargester

10. Small Treatment Systems
Measuring scum and sludge depths

11. Small Treatment Systems
Soil percolation tests required for septic tanks and small-scale treatment systems
One very deep hole is dug to ascertain position of water table down to a minimum of 2m. Minimum depth of unsaturated zone allowed is 1.2 m

12. Small Treatment Systems
Three trial holes should be dug each 1200 x 1200mm square and 750mm in depth, with a smaller hole 300 x 300mm by 400mm in depth in the centre which is used for the percolation (T) test.
A smaller test hole, 300 x 300mm by 400mm in depth, can also be used to carry out a P-test which measures lateral dispersion rather than vertical dispersion as measured by the T-test.

13. Small Treatment Systems
Suitability for a septic tank percolation area based on T or P test

14. Small Treatment Systems
Percolation trench
Depth 850 mm:300 mm of mm washed gravel; pipe laid at a 1 in 200 slope surrounded by clean washed gravel and with 150 mm of similar gravel
over pipe; geotextile layer followed by 300 mm topsoil to ground surface

15. Small Treatment Systems
Irish prescribed required length of percolation pipe
Number of people
in the house
Minimum length
of trench
(m) 4 72 5 90 6
108 7
126 8
144 9
162 10
180
Trench width is 500 mm and no individual trench length should be more than 18 m.

16. Small Treatment Systems
Minimum distances for treatment systems:
Surface water soakaway 5m
Watercourse/stream 10m
Open drain 10m
Lake or foreshore 50m
Any dwelling house 7m septic tank and10m percolation area
Site boundary 3m
Trees 3m
Road 4m
Slope break/cuts 4m
Wells and Heritage features have minimum distances controlled by other factors/legislation

17. Small Treatment Systems
Typical problems
Drainage into surface water
Flooded percolation area

18. Small Treatment Systems
Septic tanks should be emptied every 12 months

19. Small Treatment Systems

20. Small Treatment Systems
Typical RBC unit for single dwelling

21. Small Treatment Systems
Similar in design to standard RBC with or without septic tank area built in.
Often best to have separate septic tank and permit smaller settlement tank to work as second or third septic chamber.

22. Small Treatment Systems
Biocycle

23. Small Treatment Systems
Typical design of a single housing unit incorporating a trickling filter

24. Small Treatment Systems
SR6 was replaced in by a new treatment manual published by the EPA which was replaced in 2010 by the Code of Practice below. These can be downloaded from

25. Small Treatment Systems
Also EPA manual on slightly larger community systems.

26. UK: British Water Codes of Practice
Small Treatment Systems
UK: British Water Codes of Practice
Guide to the Installation of Small Wastewater Treatment Systems
A Guide for Users of Small Wastewater Treatment Systems 
Maintenance and servicing of Small Wastewater Treatment Systems (Package Plants) up to 50 Population Equivalents (PE) and Larger Systems up to 1000PE
Guide to the Desludging of Small Wastewater Treatment Systems
Flows & Loads 3 - Sizing Criteria, Treatment Capacity for Small Wastewater Treatment Systems

27. Small Treatment Systems
FOG (Fat, Oil Grease)
Released from all food preparation areas and solidifies with the sewer.
Causes reduced capacity and possible blockage leading to flooding
Increasing problem due to more intensive rainfall events
Options:
Manual removal
Chemical degreaser
Biological breakdown
Prevention:
FOG traps
In-sewer treatment using biological breakdown via network feeding stations

28. Small Treatment Systems

29. Small Treatment Systems
FOG Control in Dublin City
Since January 2008 DCC requires 2,000 FSEs in Dublin to be licensed for FOG disposal.
Food Service Establishments (FSE) include, but not limited to, hotels, pubs, restaurants, take-aways, canteens, convenience stores, B&B establishments, etc.
Included in trade effluent discharge licence under Section 16 of the Local Government (Water Pollution) Act 1977.

30. Small Treatment Systems
FOG Control in Dublin City
Details:
Some form of grease trapping or grease retention equipment must be installed in order to reduce the levels of FOG in the final discharge.
One-off application fee of €380.
Annual licence fee payable to DCC based on the Polluter-Pays-Principle.
Inspectors will visit each FSE four times a year, or more frequently if required.
Grease traps must be regularly cleaned and the recovered FOG/water mixture must be collected by a licensed waste contractor and disposed of at a licensed facility.
FOG level must not exceed 100 mg/L

31. Small Treatment Systems
Grease Traps
There are two main types of grease traps available, either
a passive retention type or a grease removal type.
Best Management Practices (BMP)
Work practices implemented in the kitchen to ensure that as little solid or oily waste enters the sewer.
Use of strainers in sinks.
Dry wiping and/or pre-rinsing of dishes and pots before they are washed.
Regular inspection and maintenance of the grease management system.
Disposal of FOG
Collection by licensed permit holders
Waste FOG is almost completely recyclable.
Used cooking oil is already collected from large FSEs and recycled.
Reuse options:
Rendered to create tallow.
Production of bio-fuel.

32. Small Treatment Systems
Grease Traps

33. Small Treatment Systems
Grease traps need regular emptying

34. Small Treatment Systems
Reference:
Look at the new EPA Irish code of practice (on-line) for household treatment systems and other online sources listed in the course text