Course 1 Unit 3 Part A B C

Course 1 Unit 3 Part A B C D E F Overview of technologies for ecosan (toilets and treatment) Teacher Mariska Ronteltap 1 m. ronteltap@unesco-ihe. org

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 2

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 3

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 4

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: http: //web. mit. edu/urbanupgrading/waterandsanitation/resources/pdf-files 5

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

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 n Some people say that ecosan toilets are those that have urine diversion n Others say ecosan toilets are those which allow reuse of urine and faeces n The term “ecosan toilet” is short, nice and catchy, and translates well into other languages, too! You have to make up your own mind 7

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 8

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

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

Toilet type (faeces/urine) Water per defecation event Water per urination event Water use (L/cap/d) Dry mixed 0 0 0 Dry F/dry U 0 0 0 Dry F/wet U 0 0. 1 0. 4 Wet mixed (vacuum) 1 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 10 50 Conventional urinal N/A 4 -6 N/A Waterless urinal N/A 0 N/A Increasing water use per day Daily water consumption estimate for toilets and urinals Based on: 1 defecation event per day, 4 urination events per day a b 11 Urine-soiled toilet paper must go to separate bin Urine flush water is collected with faeces (urine collected pure by means of a valve, see later in this presentation)

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 Urine 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 “No. Mix toilet”) 12

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) Urine into this hole Faeces into this hole (move cover with 13 foot)

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 p. H increase, see Course 2 Unit 1 “Treatment aspects for urine, faeces and greywater” With special ash dispenser (see Ecosan. Res Discussion forum on 3 October 2006, Aussie Austin) – ash dispense not reliable and 14 common

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 No. Mix 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 15

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) 16 SCOPE, India CREPA, Burkina Faso

Course 1 Unit 3 Part E: 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 17

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: http: //web. mit. edu/urbanupgrading/waterandsanitation/resources/pdf-files 18

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 19 for anal washwater (discharge into a gravel bed).

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 20

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

Elisabeth demonstrating squatting position on UDD squatting toilet 22

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 p. H increase, see Course 2 Unit 1 “Treatment aspects for urine, faeces and greywater” 23 Vault under squatting pan

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 24

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

Ferro cement as a material for toilets (1/2) “Ferro cement is sand 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, Ecosan. Res Discussion Forum 26

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, Ecosan. Res Discussion Forum) 27

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) 28

“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 29 (see next 3 slides) Cost: ~ € 650

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

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 31 Reading

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

UDD toilet (supplier: Wost-Man, Sweden) in Gebers apartment building in Stockholm (August 2007) – in operation since 6 years. 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. 33

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! 34

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 35

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) 36

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 person per day, see Course 1 Unit 2) 37

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

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 39

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 http: //www. urinal. net/archive/Womens. html But not many are waterless! 40

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? 41

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 – http: //www. drytoilet. org/index. html • 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 42

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. ” Ecosan. Res 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? 43

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) 44

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 45

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 46

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. Water. Aid, 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 (www. ecosanres. org/PM_Report. htm) 47

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

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 49

What are drivers for installing UD waterflush 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 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. 50

Roediger “No. Mix 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 51

Course 1 Unit 3 Design feactures and operational issues for Roediger No. Mix 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 http: //www. novaquatis. eawag. ch/publikationen/final_report_E for more details) 52

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 the toilet seat – Perhaps those people would prefer squatting toilets? § In the Roediger No. Mix 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 53

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: http: //www. gustavsberg. com/28081_28158. asp Cost: ~ € 720 Since there is no valve, the urine is diluted during the flushing (at least twice, perhaps even more) 54

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) 55

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

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 waterscarcity problems or where the capacity to treat the faeceswater 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. 57

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) 58

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

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

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!) 61

Foldable UDD toilet “Rescue 25 Camping” model from Swedish company Separett (http: //www. separett. eu/default. asp? id=2453&ptid= ) 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) 62

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