1. Overview of technologies for ecosan (toilets and treatment)
Course 1 Unit 3 Part A B C D E F
Overview of technologies for ecosan (toilets and treatment)
Teacher
Mariska Ronteltap

2. Course 1 Unit 3 Overview of technologies for ecosan (toilets and treatment) Content of Part 1 (separate file to keep file size < 10 MB): Part A: General issues: groundwater pollution and urine precipitation Part B: Overview of technologies for ecosan concept Part C: Waterless urinals Content of Part 2 (this file): Part D: Overview of toilet types Part E: UDD toilets Part F: UD water-flush toilets

3. “So – shall we split up ?!” Course 1 Unit 3
Part D: Overview of toilet types
“So – shall we split up ?!”
With or without urine diversion (UD)
UD = keeping urine and faeces separate at point of excretion

4. What is underneath your bum when you use the toilet?
The user interface (what the user sees), e.g.:
Toilet seat / pedestal
Squatting pan, squatting slab
Urinal
The receiving unit (what the user doesn’t see), e.g.:
A pit (= hole in the ground, not water tight)
A vault (= container for storage + treatment/drying, water tight)
Septic tank, cess pit
Pipes to sewer system and treatment plant
 many toilet photos only show the user interface

5. Example: VIP latrine with two pits (used by alternating every 6 months)
User interface
Receiving unit
(in this case underground)
VIP = ventilated improved pit
Urine into the ground
Source:

6. Many different toilet types…
Historical dry toilets
“Modern” water flush toilet (?)
“More modern” UDD toilets (??)

7. Should we be talking about “ecosan toilets”?No
I would strongly advise not to use the term “ecosan toilet”
People usually mean a urine diversion dehydrating (UDD) toilet
Remember ecosan is not limited to a specific technology (or toilet type)
But all sorts of toilet types can play a role in an ecosan concept, even the conventional water-flush toilet (see next slide)
The word “dry toilet” can also be misleading (urine is not dry)  use dehydrating instead
Yes
Some people say that ecosan toilets are those that have urine diversion
Others say ecosan toilets are those which allow reuse of urine and faeces
The term “ecosan toilet” is short, nice and catchy, and translates well into other languages, too!
 You have to make up your own mind

8. But can a non-UD water-flush toilet (“WC”, “normal toilet”) possibly be part of an ecosan approach?
Yes! I will show you an example at a restaurant and farm “Waldmichelbacher Hof” in Germany (in Course 2 Unit 4 “Introduction to anaerobic treatment technologies”):
Toilets + animal manure + organic waste  to anaerobic digester
Digestate is applied to fields as fertiliser, therefore closing the loop
Remember: Ecosan approach = aiming for sustainability and closing the loop (between sanitation and agriculture) with whatever technology

9. Range of available toilet types (they can all be used within an ecosan approach; for photos see next slides)
Course 1 Unit 3
Toilet type (faeces/urine)
UD?
Description
Example
Dry mixed No
Faeces + urine mixed, no flush
Conventional pit latrine; VIP latrine; composting toilet
Dry F/dry U *
Yes
Faeces without, urine without flush
UDD toilet, waterless urinal
Dry F/wet U
Faeces without, urine with flush (mini flush)
Wost-Man, Sweden (UD toilet)
Wet mixed (vacuum)
Faeces + urine mixed, vacuum system (very low flush)
Roediger, Germany, vacuum toilet
~ 1 L/flush
Wet F/wet U
Faeces with, urine with flush
UD water-flush toilet by Dubletten, Roediger, Gustavson. Also called
“NoMix Toilet”
Wet mixed (gravity)
Faeces + urine mixed, big flush
Conventional flush toilet (WC), ~ 10 L /flush
Increasing water use per day
UD = with urine diversion * Often wrongly called “ecosan toilet”
UDD = Urine diversion dehydrating
VIP = Ventilated Improved Pit

10. Pictures of different urine diverting toilets
China
Wost-Man, Sweden
Roediger, Germany
Dubletten, Sweden 
dry F/wet U
faeces without, urine with mini-flush
GTZ, Mali 
wet F/wet U
faeces with, urine with flush 
dry F/dry U
faeces without, urine without flush
Collection vault for faeces (for UDD toilet) and urine tank are commonly in basement or below the toilet

11. Daily water consumption estimate for toilets and urinals
Toilet type (faeces/urine)
Water per defecation event
Water per urination event
Water use (L/cap/d)
Dry mixed
Dry F/dry U
Dry F/wet U
0.1
0.4
Wet mixed (vacuum) 1 5
Wet F/wet U
6.5
0.1 (Dubletten)
2.5 (Roediger)
6.9 (Dubletten)a
16.5 (Roediger)b
Wet mixed (conventional) 10 50
Conventional urinal
N/A
4-6
Waterless urinal
Increasing water use per day
Based on: 1 defecation event per day, 4 urination events per day
a Urine-soiled toilet paper must go to separate bin
b Urine flush water is collected with faeces (urine collected pure by means of a valve, see later in this presentation)

12. Two types of UD toilets Faeces UD waterless toilets
UDD or composting
Not “forgiving” to misuse
Requires shift in thinking for those that are used to waterborne sanitation
Need separate drain hole if anal washing with water is custom
Suitable for slums and areas with unreliable water supply
But not just a technology for the poor
UD water flush toilets
Very similar to conventional water-flush toilets
Very easy to use, “forgiving” to misuse
Urine collected with or without water
Faeces always collected with water
(Eawag researchers call this the “NoMix toilet”)
Urine

13. Examples for UDD toilets (squatting type)
Course 1 Unit 3
Examples for UDD toilets (squatting type)
In rural China in 2005:
Approx. 1 million UDD squatting toilets, or 0.4 % of total improved toilets
55% of households have access to improved toilets
(Source: Ina Jurga, CEEP, China)
Cost estimate: € 100 per toilet (Source: Heinz-Peter Mang, Sept 2006)
Faeces into this hole (move cover with foot)
Urine into this hole

14. UDD squatting toilets in China
One bucket for toilet paper, one for ash, and a watering can
Why add ash after defecation? For better dehydration and pH increase, see Course 2 Unit 1 “Treatment aspects for urine, faeces and greywater”
With special ash dispenser (see EcosanRes Discussion forum on 3 October 2006, Aussie Austin) – ash dispense not reliable and common

15. Frequently asked questions about UDD toilets
Query
Answer/solution
Do men have to sit down when urinating (if using a pedestal toilet)?
No, they just have to aim well, but it is always better to provide waterless urinals as well (exception: Roediger NoMix toilet has a valve on the urine pipe which is only activated by sitting on the seat)
What about menstrual blood?
Volume of blood is small; collected and sanitised together with urine or faeces
Can muslims who use water for anal cleansing use these toilets?
A separate collection system for anal washwater needs to be provided right next to the toilet (see next slide)
Can children use these toilets?
Special toilet seats (for pedestals) are available; small children would need help
Do you always have to add ash after defecation?
Not necessarily, but adding either ash, lime, sand, soil, saw dust has some advantages for the drying process (see Course 2 Unit 1)
How can the toilet be cleaned?
A small amount of water is OK, even for dehydrating toilets

16. Toilet designs for “washers” (“washers” use water for anal cleansing, e.g. most Muslims)
Phillipines
(Non-washers = “wipers”)
Drain or hole for anal washwater
(close to wall so that it is not used for urination)
SCOPE, India
CREPA, Burkina Faso

17. Course 1 Unit 3 Part E: UDD toilets
UDD toilets can be squatting or sitting (pedestal) type
Design drawings and more examples for UDD toilets are provided in Course 1 Unit 4
UDD toilet squatting pan

18. Example: Single vault urine-diversion dehydrating (UDD) toilet
This type of toilet is often wrongly called “composting toilet” or “ecosan toilet”
Note: the entire toilet is typically above ground
Vault for faeces collection and drying (no seepage into ground from faeces vault!)
Removal of dried material
Source:

19. Example of faeces vaults of UDD toilets from the outside
Note jerry can for urine collection
CREPA, Ouagadougou, Burkina Faso (Oct. 2006)
These two vaults of a double-vault UDD toilet are semi-permanently closed. The pipe in the middle is for anal washwater (discharge into a gravel bed).

20. Faeces vaults of UDD toilets, inside view
Zimbabwe (photo: Edward Ghuza)
This vault above at CREPA headquarters in Ougadougou, Burkina Faso, had only been used for about two weeks (Oct. 2006).
Ash is added after defecation in all three cases pictured.
CREPA, ecological demo village, Burkina Faso

21. At CREPA headquarters in Ouagadougou, Burkina Faso (West Africa), the staff can now also use a UDD toilet (Oct. 2006)
Simple hand-washing device, see later in this Part E
UDD toilet
Pit latrine
Shower

22. Elisabeth demonstrating squatting position on UDD squatting toilet

23. Inside view of double vault UDD squatting toilet
for anal washing with water
Bucket with ash stands on top of the closed second vault
Why add ash after defecation? For better dehydration and pH increase, see Course 2 Unit 1 “Treatment aspects for urine, faeces and greywater”
Vault under squatting pan

24. The toilet is made from ferro cement, with painted toilet seat
Course 1 Unit 3
The new outside UDD sitting toilet (single vault) of Linus Dagerskog, staff member of CREPA (junior professional with SIDA)
The toilet is made from ferro cement, with painted toilet seat

25. Hole for vault vent pipe (yet to be installed)
Ferro-cement toilet during construction (vault opening at the front), and Elisabeth contemplating the future of UDD toilets in West Africa…

26. Ferro cement as a material for toilets (1/2)
“Ferro cement is sand and cement with wire to give it strength. A ferro cement pedestal is a lot more sturdy than the plastic version but needs quite a bit of work to get a smooth surface. The advantage is that it can be made locally with a minor capital investment compared to the plastic version which requires a roto moulder.”
Source: Richard Holden, 2 Nov 2006, EcosanRes Discussion Forum

27. Ferro cement as a material for toilets (slide 2 of 2)
“Ferrocement is a great, great thing...something that made working daily with DTs so great. In Mexico, we had a fairly extensive program of dry toilet and tank building. We experimented with different prefab models of toilets and tried different methods of construction for water tanks, and in the end, it was ferrocement that came to the rescue. Ferro-cement simplymeans iron + cement and by layering cement on a wire mesh frame we were able to create customized toilets (i.e. small toilets for children) and play around with the location of the divider, etc. Also, we had some good experiences with building large water cisterns.
The pluses are that the materials are general cheap and easy to come by, it is a very relaxing and theraputic exerise that is quite forgiving (more on this later) to mistakes and can be used quite creatively (we even dabbled in decorative flourishes!
The minuses are that it takes a bit of practice, a bit of patience and a willingness to experient and fail. Because goodness knows we had some failures. The cement mix must be just so, and luckily we had a local expert; after showing us once we were able to replicate it.
The other minus (perhaps) is that the toilet is not entirely durable. It is quite good for some years, when treated with a heavy duty paint that can be wiped down, but with use, like all things, the paint wears and the cement chips. It is wasteful, but a nice toilet only takes a couple of days to produce so it is often more time and cost efficient to make a new one, rather than clean, patch and paint an old one.” (Source: Elizabeth Tilley, 1 Nov 2006, EcosanRes Discussion Forum)

28. UDD toilet in Richard Holden’s house in Johannesburg, South Africa
Richard Holden is an ecosan expert and regular contributor to the Ecosanres Discussion Forum
For a description of his entire system see separate presentation “UDD system at Holden’s house” (Extra Materials)

29. “Upmarket” luxurious UDD toilets from Swedish manufacturers
Course 1 Unit 3
Wost-Man “Throne” model
Note box (vault) underneath for faeces collection compartment
Separett “Villa” UDD toilet (see next 3 slides)
Cost: ~ € 650

30. UDD toilet in UNESCO-IHE building
Middle piece to enlarge urine bowl
Cover flap removed in May 2007 to simplify operation (it sometimes got stuck and dirty).
Middle piece also removed (needed cleaning underneath).
Design detail: As the user sits down, the faeces compartment opens (cover flap fulfills aesthetic purposes)

31. Vent pipe
Faeces stains on this side are unfortunately not uncommon (user should remove with moist brush)
Sometimes users throw toilet paper into urine compartment
This (female) toilet was operational at UNESCO-IHE from May 2006 – Aug 2008 (photos taken August 2007) – for more details see presentation under Assigned Reading

32. Toilet from the inside (faeces bin removed)
Note some urine traces visible (needs cleaning up)
fan
Urine pipe to sewer

33. Straight chute from toilet’s faeces hole to faeces collection bin in cellar (emptied to composting site about once per month by users themselves, see next slide).
There is a ventilation system for the chute and bin.
UDD toilet (supplier: Wost-Man, Sweden) in Gebers apartment building in Stockholm (August 2007) – in operation since 6 years.

34. Top right: The Gebers apartment block during our site visit (August 2007)
Top left: External composting of faeces and toilet paper in garden
Left bottom: the amount of composted faeces of 80 people in 6 years!

35. Simple cheap handwashing devices for outdoor use
Remember: if people don’t wash hands after urination/defecation with soap, your nice new toilet may have little impact regarding health outcomes !
Water reservoir with tap at CREPA, Ouagadougou, Burkina Faso
Photo by Peter Morgan (“ecosan patriarch” in Southern Africa), Zimbabwe

36. Plastic water bottle, small hole with little tube at bottom (the tube is from an empty ball pen). For water to flow, open lid of bottle.
Note soap and gravel soak pit below.
Linus Dagerskog during handwashing
(CREPA, Ouagadougou)

37. Handwashing facility on the left, nicely integrated into this outdoor toilet design.
Note reservoir, soap, tap and gravel soak pit
Urine collection in 20 L jerry can. When it is full it is exchanged for an empty one (circa every 3 days for family of 4)
(Remember ~ 1.5 L urine per person per day, see Course 1 Unit 2)

38. Information for users (important for public or shared toilets)
Course 1 Unit 3

39. Prototype of waterless urinals for females
Questions to the ladies:
Would you use such a urinal?
Do you foresee any problems?
Have you seen other female urinals?
CREPA, Ouagadougou, Burkina Faso, Oct. 2006

40. Urinals for females considered “hip”!
The theatre in Winterthur, Switzerland had female urinals in the ladies’wash room, and for a long time they were the talk of the town!
Here you can see more examples
But not many are waterless!

41. Location of UDD toilet: inside or outside of the house?
Advantages of UDD toilet inside of the house:
Improved security, especially for women and children
Higher level of convenience and privacy especially at night
Why are they still often built outdoors?
People who had pit latrines before are used to having them outdoors
People may not trust you when you say that it won’t smell
May be easier access for removal of faeces and urine
More suitable when toilet is shared by several households
May be easier to retrofit if the house is already there and the toilet is added later
Would you prefer to have a UDD toilet inside or outside of your house?

42. Other types of waterless (or “dry” toilets) or just other names for the same thing
Composting toilets (can be with UD, but are typically without) – see Course 2 Unit 6 (“Introduction to composting”)
Global Dry Toilet Club in Finland organises regular Dry Toilet Conferences
Toilet types with names created by Peter Morgan, tried and tested for rural areas of Zimbabwe, Malawi and Ethiopia (for example)
“Arborloo”: Shallow pit composting, without UD (see success story by SUDEA in Ethiopia of 10,000 Arborloos (2-page document can be found under extra materials))
“Fossa Alterna (FA)”: with UD, double-pit (note: this toilet uses pits not vaults)
“Skyloo”: with UD and two vaults (= UDD toilet)
See next five slides for further explanations

43. Why the names Arborloo, FA and Skyloo?
Peter Morgan: “I am the guilty one introducing all these weird names. One has to add some colour to this otherwise often drab subject.” EcosanRes Discussion Forum on 17 Dec 2006
See the next 4 slides for further explanations of these toilet types given by Peter Morgan
Elisabeth: I agree, it’s a nice idea to “popularise” the subject in this way; it’s just that it confused me for a while, not knowing which toilet is which. And if everone calls it different names, then, from a scientific point of view, it can lead to confusions. But for the local population, it may be nice to have these colourful names.
What are other toilet names that you have come across yourself?

44. Arborloo
“The Arborloo, is the toilet which becomes a tree (hence Arbor… once again from the Latin). This is entirely an indigenous concept, as trees have been planted on filled toilet pits for generations in several countries in Africa and elsewhere. In fact compostable kitchen “wastes” are sometimes thrown into disused toilet pits as the volume contracts. Tomatoes, pumpkins and trees seem to grow naturally out of such pits. Planted banana is very popular. But a wide range of trees will grow well. In the Arborloo, the tree must be planted in soil on top of the composting materials.  It is very clear that the contents of this shallow (1 m deep) organic pit helps plants of many types to grow faster. This is particularly apparent in areas where the natural soil is poor and low in nutrients. In the Arborloo, the composting rate is accelerated by the regular addition of soil and ash etc.  These additions also help to reduce the smell and fly nuisance.
The Arborloo concept may be popular at first, where there is space (rural), because it is simple and cheap and the composted materials are not touched by human hand. Also the merits of using composted human excreta on food production can easily be observed.”
An elevated ring beam and slab are placed on top of the shallow pit (the slab has a hole so that it functions as a squatting toilet)

45. Fossa Alterna
“The word Fossa Alterna comes from Latin for alternating pit or hole, in which the composting process of the excreta (faeces and urine in combination) is accelerated by the regular addition of soil and wood ash to the pit contents. It is a shallow pit toilet. Normally pit contents may take some years to fully compost depending on the condition of the pit. In this case composting is normally completed in a year.  The contents are dug out and used in gardens, being mixed with topsoil. This concept makes it possible to alternate pits on a yearly basis on a single site. In warmer climates, and if plenty of soil/ash are added, the process can be completed in 6 months - as in many areas in Malawi for instance.”
Same type of slab is used as for the Arborloo

46. Skyloo (this term is not commonly used)
“The Skyloo – one steps up into it, above the ground and thus takes the first step towards reaching the sky! It is a UD toilet, the ultimate ecosan. Strictly it was the name given to a single vault UD toilet where the solids (faeces, soil and ash) are caught in a container, like a bucket. These are taken out and composted elsewhere. The urine is normally led into a plastic container through a pipe. I have used one myself for several years. It works like a treat.  In Malawi the name seems to have been used to describe any UD toilet.  Huge numbers of UD toilets are being built in South Africa, as Richard has told us. SA has money!”
Remember: Skyloo = UDD toilet

47. Concluding remarks (last slide from Peter Morgan’s posting of 17 Dec 06)
“All 3 systems have their place. It is possible, for instance to start off with an Arborloo (the simplest and cheapest), and upgrade to either the FA or UD direct, using the same slab. Similar upgrades are possible from Arborloo to VIP etc.
Each system has merits of its own and as with everything, some drawbacks. The flexibility of the recycling process makes it adaptable to a wide range of circumstances.
In low cost ecosan projects supported in Malawi  by CCAP (in the north) and COMWASH (in the south) a total of  6126 Arborloos, 3493 FAs and 92 UDs had been built by mid 2006.
WaterAid, Malawi has also supported the construction of about 3000 units in Salima and elsewhere, mostly FAs. These projects are based mostly in the rural areas.
As the unit costs of the system rises, less people are served with a given amount of aid or external support. The systems are upgradeable.  In the peri-urban areas a different approach using UD can be used as we have heard from Siku. It is the flexibility of the approach which is important.”
See also Peter Morgan’s report “An Ecological Approach to Sanitation in Africa: A Compilation of Experiences”, which gives construction and operation details for these toilets (

48. Part F: UD water-flush toilets
Course 1 Unit 3
Part F: UD water-flush toilets
UD water-flush toilets so far are all of the sitting type because they were invented in Sweden
Gustavsberg UD water-flush toilet

49. What is a UD water-flush toilet?
A toilet with separates urine from faeces
Urine is collected pure (e.g. Roediger toilet) or diluted with some flush water (e.g. Gustavsberg toilet)
Urine is collected in urine storage tanks and treated or reused
Faeces are mixed with flushing water and discharged to the sewer
These toilets are designed to work in conjunction with a sewer system
The toilets are more expensive than conventional water flush toilets

50. What are drivers for installing UD water-flush toilets?
Some water savings are possible
However this is not so significant. E.g. with the Roediger toilets, many users flush twice after urinating because the toilet paper doesn't disappear with just one small flush (of course this could be solved by teaching people to put toilet paper in a separate bin!)
Being able to collect urine separately with the following possible aims:
Store and reuse as fertiliser, e.g. in Sweden
Treat separately for nitrogen removal and then return back to the wastewater treatment plant (e.g. this is the concept in Switzerland and the Netherlands) - purpose is to unload the wastewater treatment plant with respect to nitrogen load.
Discharge urine to the sewer system only at night time, to balance the load to the WWTP better.
Treat urine separately for removal of pharmaceutical residues (likely cheaper than treating the whole wastewater stream) - this is a major reason for the Netherlands, where there is a worry about these pharmaceutical residues appearing in surface and groundwater.

51. Roediger “NoMix toilet”
Photos from
GTZ building in Eschborn, Germany;
56 toilets installed Aug 06 (photos taken Oct 06)
Cost: ~ € 1400 per toilet
2-3 L for urine flush,
6-7 L for faeces flush
Rod which activates valve for urine pipe when user sits

52. Design feactures and operational issues for Roediger NoMix toilets
Course 1 Unit 3
Design feactures and operational issues for Roediger NoMix toilets
Two different compartments for urine and brownwater
Urine is collected undiluted by means of a valve located under the toilet seat, triggered when the user sits down
Operational issues:
Toilet paper can also be flushed, but may not disappear with small urine flush (better to put in separate bin); user can decide not to flush after urination
If faeces end up in urine compartment, they can still be flushed and should not contaminate the urine
If user does not sit down, urine is collected together with brown water (because valve isn’t opened)
Cleaning is more cumbersome than for conventional water flush toilets
This type of toilet does not necessarily save water but allows separate collection of urine (see also for more details)

53. The issue of not wanting to sit down on a public pedestal toilet
Many females (and some males?) prefer not to sit down on public toilets for fear of infections
They rather hover over the toilet seat
Perhaps those people would prefer squatting toilets?
In the Roediger NoMix toilet, the valve to the urine tank is only openend if the user pushes down on the toilet seat
Similarly, the Separett UDD toilet has a flap over the faeces compartment that opens when the user sits down

54. Urine drain hole and pipe to urine storage
Gustavsberg UD water-flush toilet at office building of the Waterboard in Meppel, the Netherlands (July 2007)
For more information see here:
Cost: ~ € 720
Since there is no valve, the urine is diluted during the flushing (at least twice, perhaps even more)

55. Above: Small urine flush, controllable by the user (with a separate flush button)
UD water-flush toilet from Swedish company Dubletten (seen in upmarket house in Kullön close to Stockholm, August 2007)

56. Interesting little design feature:
Closed toilet (note hinge for the child seat opening)
Adult seat
Interesting little design feature:
An in-built child seat to make the open sitting area smaller for children
Child seat activated

57. Assessment of UD water-flush toilets
Quite easily acceptable by those who are used to water-flush toilets
This toilet type has also been installed in the Eawag building in Switzerland (20 toilets in July 06) and several places in The Netherlands, e.g. KIWA Water Research building in Nieuwegein (2 toilets in Sept 06)
Not an appropriate solution for low-income areas with water-scarcity problems or where the capacity to treat the faeces-water mixture is not present
It does raise awareness for the concept of urine diversion, which is good
Some people, who could be called “ecosan purists” would not approve of this type of toilet – they prefer the waterless toilet types! But one shouldn’t think in exclusive terms.

58. Course 1 Unit 3
Vacuum toilets (1/3)
Usually without urine diversion (but can also be with UD)
Very low amount of flush water needed
Typically uses only 1 L per flush (compared to 9 L per flush for conventional toilet)
Results in the production of concentrated “blackwater”
This blackwater is usually treated with anaerobic digestion (ongoing research projects on this topic at Wageningen University, The Netherlands)

59. Vacuum toilets (2/3) Vacuum urinal (Roediger)
KfW building, Frankfurt, Oct. 2006
Vacuum toilet (Roediger)

60. Vacuum toilets (3/3)
Vacuum pump station (Roediger) in basement of KfW building, Frankfurt, Oct. 2006
(with Arno Rosemarin, Swedish ecosan specialist at EocsanRes Programme of Stockholm Environment Institute)

61. Example for vacuum toilet and blackwater treatment
At Sneek (the Netherlands), blackwater from vacuum toilets in 80 houses is treated in anaerobic digesters (see also Course 2 Unit 4 “Introduction to anaerobic digestion technologies”).
Blackwater production: 5.6 L/cap/d (1 L water per toilet flush)
Bruno Meulman
Fresh blackwater (not very black!)

62. Foldable UDD toilet
“Rescue 25 Camping” model from Swedish company Separett (
Price could be as low as € 15 for a basic version, which could be applied for emergency sanitation (need to get aid agencies interested in this option)

63. References
Tchobanoglous, G., Burton, F.L., Stensel, H.D. (2003) Wastewater Engineering, Treatment and Reuse, Metcalf & Eddy, Inc., McGraw-Hill, 4th edition. Good book on conventional wastewater treatment