Note: If you haven’t already, you can read Part I here.
A Dead Sea Valley family home with their typical front ‘lawn’.
Photo © Craig Mackintosh
The title may lead you to think we are talking about people who manage pasture or have access to wide areas of rangeland. In fact, we are talking about people whose parents and grandparents were nomadic pastoralists that ranged flocks of animals across vast areas of land with the changing of the seasons. Rangelands in the Middle East were traditionally managed by tribal councils. This form of community-managed rangeland, called the Hima system (PDF), was one of the longest standing and most successful forms of rangeland management in known history. However with the arrival of nation states, the tribal systems of regulation were subordinated to state governments, run by bureaucrats living in the cities. Borders were drawn on the map, cutting across traditional patterns of land use and seasonal migration. Land was nationalised and tribal structures disempowered. In the case of Palestine it was worse, because much of the population was physically displaced, first in 1948 then again in 1967. Many of the latter wave of refugees who were pushed into Jordan have never gained citizenship. Of course the Palestinians in Jordan are now in quite a good situation compared to the Palestinians left in Palestine, but they still lack control over the land resource and hence have no chance to manage broad-scale rangelands as their forefathers did.
The average family compound may be 400-800m2. The rest of the landscape is government land which is effectively commonage. So in such situations it is the “tragedy of the commons” all over. Most of the high quality land in the Jordan Valley is given to investors for irrigated agriculture. What remains is the rocky west facing slopes. There may be some growth of herbage for a couple of months in late winter/early spring, but it is heavily contested by the local Bedouin tribes, as well as anybody else who has animals in the area. There are no longer any regulatory structures to decide who grazes what — it’s just “grab what you can while you can!” Hence anything without a fence around it has been heavily depleted and denuded. That is why people have to import grain from Ukraine to feed their animals for the rest of the year.
So what we are looking at here is not really a rangeland management system, which would require massive resources, real political influence and extensive community cooperation on a wide scale. What we are really talking about here is designing a small scale intensive system that allows a single family to economise on the costs of feeding their sheep in their cramped little domestic compound. And it really ends up having a lot more to do with sewage than you may have expected from the title!
So the design brief is: design a household-scale domestic waste-water treatment and land-application system which will:
- Treat all the household water from a typical Jordan Valley home to a suitable standard (according to Australian regulations) that is safe for both watering livestock and performing surface irrigation of fodder crops, without posing a health risk to either the system operators or the public in general.
- Will fit into an average back yard in the town of Jawfah, Al-Balqa province, Jordan.
- Will produce enough edible (to small ruminants) biomass to significantly affect the domestic economics of the owners who operate it due to a reduction in the need to purchase commercially grown feed.
- Can be constructed with a realistic budget to be fundable by a small grant from a local organisation or donations from individuals.
- Will require a minimum in technical knowhow and labour for establishment, maintenance and operation.
So, we will go through these objectives one by one.
1. Waste water treatment
The Use of Reclaimed Water Guidelines (PDF) distinguishes between four quality categories of treated waste water, which are of suitable standard for different downstream uses. The criteria for these classes are as follows.
Table 1
The document goes on to state that for livestock husbandry activites, including both animal drinking water and irrigation of pasture, reclaimed water should be of Class B quality.
Table 2 – click for larger view
The Disinfection of Treated Wastewater Guidelines (PDF) specifies the necessary processes for treatment of waste water to Class B standard:
Table 3
Hence our system has to put the domestic waste water through both secondary treatment and disinfection processes before it is safe to use downstream. The “On-Site Sewage and Wastewater Management Strategy” (Lismore City Council, 2013 — PDF) defines secondary treatment as follows:
“Secondary Treatment” aerobic biological processing and settling or filtering of effluent received from a primary treatment unit. Effluent quality following secondary treatment is expected to be equal to or better than 20 mg/L BOD5 and 30mg/L suspended solids.
BOD means “biological oxygen demand”. It refers to the amount of oxygen that would be consumed by micro-organisms in order to break down all of the organic material in a litre of the water in question through aerobic processes. If waste water has a high BOD there will be rapid depletion of the dissolved oxygen in it, as the organic materials are consumed by aerobic micro-organisms. In order for this oxygen to be replaced it must diffuse into the water from the surface. If the water has a small surface area and is not moving this diffusion will usually be slow, hence the water will become anaerobic, meaning it has no oxygen left in it. Anaerobic conditions lead to a different micro-biology proliferating in the water, which tends to produce far more toxic and smelly compounds. Hence a high BOD is bad news.
“Suspended solids” refers to non-dissolved particles floating in the water.
But before going through secondary treatment, waste water has to go through “Primary Treatment” — the separation of suspended material from wastewater by settlement and/or floatation prior to discharge to either a secondary-treatment process, or to a land application system. (Ibid.)
Primary treatment should be done in a septic tank. It is worth noting that most rural homes in Jordan are not connected to any sewerage system. We observed that most houses in Jawfa use a cesspit. A cesspit is basically a big hole in the ground (the ones we have seen in Jawfa are approximately 3 x 3 x 3m), lined on the sides with cement block with gaps left between the blocks, and covered over with a concrete slab. There is an inflow pipe but no outflow. Anaerobic breakdown in the cess-pit will gradually liquefy and dissolve any solid organic materials in the waste water. The water along with these soluble breakdown products will infiltrate into the ground. Anaerobic breakdown does not however reduce the dissolved nutrients and high nitrate levels seeping into the ground-water and can pollute it. In severe cases this can be hazardous to human health. Cesspits are no longer permitted under most developed country health and safety regulations and most have now been replaced by septic tanks, where connection to the sewerage system is not an option.
Septic tanks are sealed tanks (which don’t leak into the groundwater). They are large enough to hold all the waste-water from the household for a period of not less than 24 hours. They have an inflow and an outflow with an internal baffle wall, which has a small opening around 50cm below the surface. The baffle separates the tank into two chambers. After flowing into the tank, the vast majority of solid materials in the waste water will either float (as will oils and greases) on the surface, forming a scum, or sink to form sludge. Either way they are trapped in the first chamber. The high BOD of the liquid means it will quickly become anaerobic. The scum also seals the surface of the water, keeping it so. So septic tanks are anaerobic by definition. The solid materials trapped in the tank will undergo anaerobic breakdown into soluble compounds, which will escape from the tank in the effluent. Some solids that won’t break down any further will stay in the tank as sludge. The sludge needs to be emptied every few years when it builds up, and the tank needs extra capacity to store that sludge and still maintain a 24h retention time.
Figure 1
The “Environment & Health Protection Guidelines: On-site Sewage Management for Single Households” (NSW, 1998 – PDF)
Capacity = (V/P/D x NP) + 1550 L
Where V/P/D is the volume of water used per person per day and NP is the number of users. The 1550 L is for sludge storage, based on the assumption that 1550 L of sludge is the amount that will accumulate in around three years, though this is somewhat variable and needs to be checked. The minimum allowable overall storage capacity is 2300L for a tank receiving all household waste water and 2050L for one receiving black water only.
So, how big a tank will we need in Jawfah? Well, the average Jordanian uses around 80L of water per day. But enquiries indicate that water usage in Jawfah may be somewhat more than that, in fact as high as 170L (an average Australian apparently uses 150L for comparison). It’s always best to look at the worst case scenario when planning, which in this case is the bigger number because more capacity means more materials and more budget! So assuming we have a water use of 170L/person/day and 5 people in the house:
Capacity = (170 x 5) + 1550 = 2400 L
In terms of dimensions, a septic tank should have a minimum depth of 1.5m, with a floor sloping 1:10 towards the inlet end. Longer is also better than wider. Hence if we set the internal width of the tank at 0.5m, and the baffle wall has a thickness of 15cm, in order to get a capacity of 2400L we need an internal length of 3.05m and a depth at the inflow of 1.96m. The baffle wall should be set at 2/3rds of the length of the tank from the inlet, so that the inlet chamber is twice the length of the outlet chamber. Ask me for the calculations if you want to check them!
Figure 2: Septic tank basic dimensions and layout
The effluent coming out from a septic tank is expected to have the following load of BOD, suspended solids, nutrients and pathogens:
Table 4
“Environment & Health Protection Guidelines: On-site Sewage Management for Single Households” (From: NSW, 1998 [PDF]
Effluent from the septic tank will now pass onto a secondary treatment system. We are planning to use a reed bed. Clarence Valley Council (2013 – PDF)
“Technical Support Document for OSMS Number 3 – On Site Waste Water Design Guidelines” (PDF) states that:
Reed-beds are an increasingly popular type of secondary treatment device due to their aesthetic appeal, their reliable treatment performance capacities once the reeds are fully established, and their somewhat lower construction costs and maintenance requirements compared to other options. They are also passive devices not necessarily reliant upon power or pumps, and therefore economical to operate in the long term. Reed beds are usually required to be constructed from solid moulds such as plastic tanks or concrete troughs, concrete is preferred.
There are several different types of reed bed, but the one we are planning to use is a horizontal sub-surface flow constructed wetland. This type is optimal because it needs no pumps or moving parts and keeps the water below the surface of the gravel, reducing scope for mosquitoes or flies breeding in the waste water, or for contamination reaching up above the surface. This type of reed bed comprises a gravel medium through which the waste water flows between inlet and outlet, both of which are fixed below the surface of the gravel. Macrophytes (aquatic rooted plants such as reeds, rushes or sedges) are planted in the gravel and their roots grow down to form a network filling the spaces. The roots perform a physical filtering function. They also oxygenate the water, since macrophytes draw oxygen down into their root systems from the air above. Bacterial film also forms over the surface of the gravel and the roots metabolizing and breaking down organic compounds in the water.
“The Use of Reed Beds for the Treatment of Sewage & Wastewater from Domestic Households” (PDF) (Lismore City Council, 2004) states that:
Based on best scientific knowledge at the time a 7 day residence time was thought to produce a secondary treated wastewater (BOD 20mg/L, TSS 30mg/L) and reduce nitrogen by 50%. However, a recent study (Headley & Davison, 2003) has shown that approximately 5 days is required to reduce nitrogen by 50%. Seven days would still be required to produce a secondary treated effluent unless it is a grey-water reed bed where the residence time may be less than 7 days.
So using the basic “7 day rule of thumb” we can calculate the area of reed bed we need given our estimated water use:
Area = (V / DP)
Where V is the volume of water used in 7 days, D is the depth of the water in the reed bed and P is the porosity of the gravel medium (the proportion of the total volume not taken up by the gravel itself). Our model household in Jawfa with 5 people using 170L each per day uses a full 6000L per week. If we set the reed bed depth at 50cm, using 20mm aggregate gravel which has a porosity of 0.4, we will get the following:
Area = 6 / (0.5 x 0.4) = 30m2
Some more research into reed beds threw up some quite tricky calculations by which we can test the assumption that 7 days will give a low enough BOD and TSS to be secondary water. In both cases, at the ambient temperatures in Jawfa, 30m2 is more than enough to treat 6000L per week and get better then required BOD and TSS, even during the coldest month, January. Again, if you want to see (and check) these calculations they are available on request.
Furthermore, if we refer back to The Use of Reclaimed Water Guidelines (EPA Victoria, 2003) (Table 1), helminth reduction was stated as a necessary criterion for the water to be considered as Grade B reclaimed water, suitable for watering animals and irrigating fodder crops. Helminths are parasitic flatworms. The treatment system needs to be effective at removing their eggs from the waste water so they don’t infect the animals drinking it.
Duncan Mara (2003) “Domestic Wastewater Treatment in Developing Countries” states that: “Helminth egg removal in the gravel bed of horizontal-flow wetlands is very efficient: Stott et al (1999*) found that all eggs were removed in a 100m long reed bed in Egypt, with most being removed in the first 25 m.”
Figure 3
Reed bed design should be such that all of the water is on the move through the medium at any one time. This can be achieved by using splitters on the inlets and outlets. However a better way is to use baffles, which force the water to flow on a longer path through the gravel medium. In-fact if we have a gravel medium of 30m2 surface area, we can force the water to pass along a 100m flow path, using baffles. If the whole bed is 10m x 3m, it can be split slices 30cm wide, ten of which run back and forth along the 10m length of the bed. If the baffles themselves are 10cm thick the total bed area will end up 10m x 4m. This design thus both fulfils the 7 day residence criterion for BOS and TSS as well as the 100m length criterion from removal of helminth eggs.
Figure 4
Effluent from the reed bed must now be disinfected to remove any remaining bacteria (which are not removed by the reed-bed). The most effective technique for this is UV radiation which leaves no chemical residues and only requires a small amount of electric power. UV disinfection kits are available for a few hundred dollars in western countries, so if not available locally, one can be purchased and imported for this project quite easily.
The smallest models are sufficient to handle the flow rate of our system which is only 0.6L/min on average.
Reclaimed water use
With the water now treated and disinfected to a Class B standard it can be used for watering the animals and growing fodder with a surface irrigation system. Water will gravity feed via pipe from the reed bed outflow box via the UV sterilizer to a collecting tank. The water stream will now be split into two parts, one for watering the sheep and one will be used for irrigating a fodder crop.
The sheep watering system is quite simple. It will be given priority over the irrigation in the use distribution. Water will gravity feed from the collecting tank to a trough. The water level in the trough is regulated by a ball valve which is protected under a cover at one end so the sheep can’t damage it. When the trough is full the ball valve shuts off the pipe so no more water flows in from the collection tank. When the collection tank fills a dosing siphon is triggered which diverts the full tank of water into the irrigation system all in one go.
Land application system
In order to keep the budget within reasonable limits and reduce the need for skilled technical maintenance, we want to avoid the use of pumps or moving parts as much as possible. Hence we have selected a low cost, low-tech, low pressure (gravity-fed) drip irrigation system. The KB-Drip System (KB stands for “Krishak Bandhu” which means the “farmer’s friend” in an Indian language, not sure which one) was developed in India by International Development Enterprises (IDE). The EDK kits can be customized to suit the land area coverage required and generally cost around $600/Ha, which comes to a mere $0.06/m2. There is a lot more information on these systems available here: Palada et Al. 2011 (PDF).
To estimate how much area coverage we would need for our system let’s consider how much treated waste water we need to “dispose of” each day. Our assumed weekly water use was 6m3 for a family of 5 in Jawfah. If we estimate 10% loss in evapotranspiration in the reed beds and treatment system generally, we have 5.4m3 left to deal with. Then we expect the sheep to drink 0.63m3 per week. So we have about 4.77m3 per week left, which is 682 litres per day.
The lateral drip lines in this system will be 10m long with drip emitters placed every 30cm. Hence a 10m line has 30 drip points. One drip point emits around 2.5litres/hour with 1m of head pressure. Hence 1 line will emit a total of 75 litres per hour. If we have 4 lines the system will use 300 litres per hour. The lines are spaced at 1m intervals and can irrigate a footprint of 1m width, so the area coverage of this system would be 40m2.
Well, how is this going to work when we only have 682litres per day? That is a good question. We use a dosing tank. The irrigated area has to be a bit downhill from the collection tank. The tank has a dosing siphon in it. This is a very clever device which does not let any water out of the tank until it fills up, but then when it is full it opens the outflow so that all the water can flow out in one “dose”. “Designing and Installing On-Site Wastewater Systems: A Sydney Catchment Authority Current Recommended Practice” (PDF) describes the “Flout®” which I guess is a compound of the words “float” and “out”:
Figure 5: The single Flout®
As effluent from the septic tank fills the dosing chamber, the Flout™ … is empty, buoyant, and floats on the surface. High quality, flexible connectors allow the Flout® to rise. When the effluent reaches the maximum level in the chamber, it spills into the opening in the top of the Flout®. This causes the Flout® to sink (Figure 14.7). The effluent now discharges through the pipe exiting the dosing chamber and doses the land application area. The chamber continues to empty down to the top of the Flout® (Figure 14.8). Then the Flout® empties and resumes floating to repeat another cycle.
Figure 6: More Flout®s
So if we have a dosing tank of say 350L volume fitted with a Flout®, each time the tank fills up the water will run out to the drip system in one dose. It will take 1 hour and a bit for the drip system to empty the tank, by when the head of the Flout® will be empty and it with start to float again not letting any subsequent inflow out of the tank till it fills up again. On this cycle the tank should fill up twice per day.
2. Fitting it all into a back yard in Jawfa
Lacking any real data on this, I will give you a rough estimate that a normal family compound in Jawfa is between 400 and 800m2. If the house, car park, associated buildings and the sheep house/pen take up ¾ of all this then we have 100 – 200m2 to play with. Based on the above we are using approximately the following for our systems:
| Septic tank |
5
|
| Reed bed |
45
|
| UV irradiation and dosing tank |
1
|
| Irrigation area |
50
|
| Total: |
101
|
Note that there also has to be a difference in vertical elevation between the treatment systems and the irrigation area, ideally of at least 1m so that water can gravity feed into the drip system. Also there needs to be sufficient space to accommodate foundations, wall and baffle thicknesses, pathways, pipes etc. and for all structures, so these are upper-estimates of how much space would be required in total.
3. Feeding the Sheep
So, what will we grow using this 40m2 irrigated area? I would say it’s best to go with a heavy feeding perennial clumping grass like Napier/Elephant grass (Pennisetum purpureum) which is one of the most productive fodder crops there is. It can be slashed to harvest and re-grow from the base (without any need to re-seed) on a 90 day cycle. This will keep labor to a minimum. One clump of Napier per 60cm is enough since they get big and will be too crowded otherwise. On the intermediate points in the drip line we can put in perennial legumes like leucaena, sesbania or calliandra, which are great high protein fodders, especially the pods. These can be pollarded once a year to 1.5m high so they don’t shade out the Napier. The best time to pollard them would be in the autumn when it starts getting overcast.
In terms of actual kilos of biomass production, Napier grass has been reported to yield up to 85,000kg/Ha dry mass every 90 days with 2000mm rainfall when fertilized with 897kg/Ha of urea (Orodho 2006). This translates into a rate of nitrogen application of N of 98.7g/m2. We expect high levels of fertility in our treated waste water due to residual nitrogen and phosphorus in the water.
How much residual nitrogen do we expect?
Tabel 4 (taken from NSW, 1998 – PDF) indicates typical primary effluent contains 50 – 60 mg per litre of Nitrogen. If we expect the reed bed treatment to reduce this by 50% (Lismore, 2004) we should still have 20 – 30mg/L nitrogen in the reclaimed water. Recall that we are irrigating our land application with 682L/day of water. Hence in 90 days the total waste water applied will be 682 x 90 = 61,380 litres. At a rate of 20mg/L this water will contain a total of 1.22Kg of nitrogen which is distributed over 40m2. Hence this would translate to a rate of 30.96g/m2. This is about 1/3rd of the rate of fertilizer application used in study cited by Orodho (2006). We also expect to be able to apply composted sheep manure as a supplementary solid fertilizer. Potentially liquid bio-fertilizers could also be prepared and added into the dosing tank. So these will be able to make up the difference.
In terms of water, the study referred by Orodho (2006) used rain-fed production at 2000mm annual rainfall. The total water application over our irrigated area will come to around 1800L/m2/year. Interestingly the actual rainfall is around 200mm per year, meaning our plot should get about the same total amount of water per unit area as in the study.
So we should be able to yield high rates of production from Napier grass in a mixed planting with perennial legumes. If we can manage a yield of equivalent to 85,000kg/Ha in 90 days this would translate to a dry matter production rate of 8.5kg/m2 per 90 days, which would yield a total of 34kg/ kg/m2/year which is 1360kg/yr total from our 40m2 plot.
In terms of fodder substitution this is equivalent to 12.4% of the 10,950kg of grain fodder now fed to a flock of 30 sheep.
Then we also have the biomass yield of the reed bed. Burke (2011) indicates that Typha latifolia (cat tails or reed mace) can produce around 36,000kg/Ha dry matter per year. This is also good quality fodder if harvested continually. This would translate into 3.6kg/m2 dry matter, so 108kg/yr from our 30m2 reed bed. This would substitute another 1% of the fodder ration, giving a total of 13.4% substitution.
Looking back at our previous figures from Part I, this is expected to increase the annual profitability of the flock by 36.2% to a total of 1103 JD/year. This is a total increase of JD351/yr from the current situation, which is equivalent to the value of nearly-two extra sheep per year.
Right, well that gives us something to aim for in terms of output. Next we are going to consider how much it will cost to build all this….
Stay tuned for Part III.
~~~~~
Note: We will implement a system like this during an internship in May 2015. So if you want to be a part of that, click here for details. The internship will be half spent building the waste water system on a local household and half spent on the Greening the Desert “Sequel” site maintaining and expanding the systems in place there. Understandably, the PRI can only front funds for project we do on the site, so we are currently seeking partners to help support the project. Please contact me if you know anybody or any organisation that can help.
I’ll also be running a shorter, more general course on using Permaculture for development projects at the PRI Zaytuna Farm, Australia site, starting January 19, 2015.
