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Greywater Reuse System
Design
Bryce, Manchester
By
Edward Shakes Jnr, PE
November 13, 2019
Contents
Background ............................................................................................................................................. 1
Introduction and Purpose ........................................................................................................................ 1
Proposed System Location ....................................................................................................................... 1
Grey Water Properties and Flow Requirement ........................................................................................ 2
System Design ......................................................................................................................................... 4
Overall System..................................................................................................................................... 4
Barrel Septic Tank System .................................................................................................................... 6
Sand Filter ........................................................................................................................................... 7
Treated Grey Water Storage Tank ........................................................................................................ 9
Irrigation system and requirements ..................................................................................................... 9
Project Resources and Cost ..................................................................................................................... 9
Project Feasibility .................................................................................................................................. 10
Conclusion ............................................................................................................................................. 11
Sources ................................................................................................................................................. 12
1
Background
Water is the most important commodity in the world. It has been the sustenance of life for all biological
beings on the earth. Given the fluctuations in climate change and decreasing water worldwide fresh
water resources, an urgent need is emphasized for proper water management and conservation. The
recycling of greywater is an excellent conservation method that applied to reduce potable water
consumption. Greywater is the wastewater that results from all potable water activities except toilet
use. Properly treated greywater is mainly applied for irrigation purposes and to some extent as potable
water for cleaning and toilet flushing. Effective greywater recycling systems (GWRS) would improve
Jamaica’s climate adaptation efforts by reducing the water supply consumption by the NWC potable grid
network, reducing the abstraction of water from vulnerable surface sources and aquifers, improve water
storage during drought periods, increase utility cost savings of utility supplied water and increase
harvested rainwater storage.
Introduction and Purpose
A GWRS is being designed for the Jamaica National’s (JN) Financing Water Adaptation in Jamaica’s New
Urban Housing Sector project training course for engineers and professionals. An effective system design
would no doubt be set standards and be adopted throughout the island as an effective potable water
supply system for domestic, institutional and commercial use. The development of the proposed GWRS
would integrate best practices for material selection, construction, water treatment and water
conveyance to produce a concept that is sustainable, safe, flexible, economical and reliable.
Proposed System Location
The project area will be at the residence of Mr Edward Shakes Snr and Mrs Elaine Shakes in Bryce,
Manchester. Bryce is located in northern Manchester close to Christiana- the parishes’ second largest
town. The area of the property is approximately 1 acre and includes a garden with ornamental flowers
and plants, and a small farm with vegatables and fruit trees. Most of the residents in the Bryce
community receive potable water via the NWC water supply network grid. However the supply is
unreliable due to aged pipeline infrastructure, system lock offs during high turbidity from the source and
water supply regulations during drought conditions.
In order to improve the conservation of the volume of potable water received from the NWC network a
GWRS will be developed for the Shakes’ residence. Greywater would be received from the kitchen sink,
face basins and bath tubs. The following components of the GWRS would form part of the design:
An piping system to channel greywater to the treatment system
2
A Septic Tank System
A Sand filter
Treated greywater discharge piping to channel water to plants for irrigation.
The location map of the proposed system is shown in figure 1.
Figure 1-Map of project location
Grey Water Properties and Flow Requirement
Grey water from the Bryce Shakes’ residence is discharged from the following fixtures and piping:
bath tub, shower and face basins from three bathrooms
sinks from indoor and outdoor kitchens
outlet piping of the washing machine in laundry room
washing tub from laundry room
The greywater from these fixtures is conveyed by gravity via 37.5mm (1.5”) nominal diameter (DN) PVC
piping to a soakaway pit. The maximum expected greywater flow is determined as shown in table 1
3
below where the it is assumed that 95% of the potable water supply is converted into wastewater that
includes greywater and black water from flushing. Greywater is assumed to be 60% of the total
wastewater. An infiltration of 10% is assumed to account for possible leakage of potable water that may
enter the greywater conveyance pipes.
The chemical constituent concentrations of the greywater influent is shown table 2. These are based on
average values from previous studies that were conducted on the treatment and reuse of greywater.
The required National Environment and Planning Agency (NEPA) and National Irrigation Commission
(NIC) effluent standards for treatment are also shown.
For the proposed treatment system the reduction of BOD, TSS and COD would be focused on for the
irrigation of papaya, guava and bananas trees. These fruit trees should tolerate treated greywater
without disinfection. Reduction of phosphate and nitrogen concentrations for the proposed system
would be minimal for the treatment system and the remaining concentrations are expected to serve as
nutrients for plant growth. However the amount of phosphates would be controlled by limiting the use
of phosphate based detergents and soaps.
Table 1- Average expected greywater flows for the Shakes’ Bryce residence
PARAMETER FLOWRATE
Average daily demand of per person
(cubic metres /day)
0.23
Average number of persons per household 4
Maximum Demand for Household ( cubic
metres /day)= average demand per person x
number of persons per household
0.91
Total Wastewater cubic metres /day) = 95% of
Total Demand
0.82
Greywater flow ( cubic meters/day) = 60% of
Total Wastewater
0.53
Infiltration (cubic meters/day) = 10% of Total
Greywater flow
0.05
Total Influent Greywater (cubic meters/day) =
Greywater flow +infiltration
0.59
4
Constituent
Influent
Required Effluent
for Irrigation
Biochemical Oxygen
Demand, BOD, mg/L
150
15
Chemical Oxygen Demand
,COD, mg/L
200
90
Suspended Solids, SS , mg/L
100
15
Total Nitrogen TN , mg/L
10
N/A
Ammonium Nitrogen, NH3-
N,mg/L
10
N/A
Total Phosphates TP , mg/L
5
N/A
Table 2- Greywater influent and effluent constituent concentration
System Design
Overall System
The proposed greywater treatment system of the Shakes’ residence is comprised of suitable collection
and process equipment that is expected to treat greywater for irrigation. Greywater will be collected
from the bathtubs, showers and face basins from three bathrooms; the washing machine and wash tub
from the laundry room; and sinks from the indoor and outdoor kitchens. Conveyance of the raw
grewater will be carried out through existing and proposed 37.5 mm (1.5”) PVC piping to the septic
tanks. The Septic Tank will allow for removal of scum, settling of solids and biological treatment of the
influent to reduce mainly BOD, TSS, and COD to significant concentrations. Further treatment will then
be carried out by a Sand Filter to facilitate further BOD, TSS, COD, TN, TP and Faecal Coliform. The
effluent from the sand filter would then be passed to a storage vessel. Treated greywater will then be
conveyed through 18 mm diameter PVC via gravity to banana, papaya and guava fruit trees.
A by-pass with a valve would be made to the existing soakaway pit for diverting excess raw grey water
and to facilitate maintenance to the treatment system. A schematic of the proposed layout of the
treatment systems is shown in figure 2 below with all the system components equipment and piping.
5
Figure 2-Proposed Greywater Treatment and Recycle System
6
Barrel Septic Tank System
Grey water from the house would enter then tanks from the 37.5mm PVC piping. As grey water passes
through each tank, scum is accumulated at the surface and solids settle at the bottom. Treated water is
conveyed through the outlet pipes that are located below the scum films (figure 3). As the grey water
passes through each tank the amount scum and solids are progressively reduced. Treated grey water
from the outlet is then conveyed to sand filter. It is expected that significant suspended solids and
biochemical oxygen demand (BOD) concentrations be reduced at the final outlet of the septic tanks.
A retention time of 1 day would be applied for the septic tank system.
The volume of the system should be, V = 0.59 m3/d x1
= 0.59 m3 or 156 US gallon
Commercially available plastic drums or barrels would be used for the tanks. Since one (1) plastic barrel
has a volume 55 gallons, the amount of plastic barrels required are:
156 US gal/55 = 2.8 or 3 barrels
The expected effluent concentrations of BOD, COD and TSS using average removal rates of 40%, 40%
and 50% respectively are:
BOD leaving the Septic Tank = (1-0.40) x 100 = 60 mg/L
COD leaving Septic Tank = (1-0.40) x 200 = 120 mg/L
TSS leaving Septic Tank = (1- 0.5) x 120 = 60 mg/L
Figure 3- Barrel Septic Tank System
7
The septic tank system will be constructed using tree (3) plastic barrels in series along with 37.5mm
diameter PVC pipe connections. All necessary materials for the tank would be acquired and stored
appropriately. A trench would then be excavated at an area a litter larger than the tanks. The tanks
would then be placed in the trench at a depth of ¾ of the height the each tank. Holes in the tanks would
then be bored/and or drilled to assemble the inlet and outlet pipes. After the tank is fully assembled,
gravel would then be placed along the sides and corners of the trench to support the septic tanks. A
typical construction is shown in figure 4.
Figure 4- Barrel Septic Tank System in Construction
Sand Filter
A sand filter will be applied after the septic tanks for further reduction in mainly BOD, COD, TSS and
faecal coliform. A 55 US gallon plastic drum would be used with sand filer media supported by gravel.
The surface area required for the filters will be designed based on the average greywater flowrate of
0.59 m3/ day and a filtration rate of 2.4 m3/day/m2 of the sand media.
The surface area = the flow rate of the greywater x filtration rate
Surface area = 0.59/ 2.4 = 0.25 m2
8
Since the plastic drum has a diameter of 22.5 inches or 0.57 m, the cross-sectional area
= 0. 572 x 3.281/ 4 = 0.27 m2
Since this barrel area is larger than the required filtration area it should be sufficient for use.
Like the septic tank system the sand filer would be placed in a trench with backfilled gravel at a depth of
¾ of the barrel height.
A diagram of the sand filter is shown in figure 5.
Figure 5- Sand Filter
The expected effluent concentrations of BOD, COD and TSS using removal rates of 90% for all
constituents are:
BOD leaving ABR = (1-0.90) x 60 = 6 mg/L
COD leaving ABR = (1-0.90) x 120 = 12 mg/L
TSS leaving ABR = (1- 0.90) x 60 = 6 mg/L
These concentrations are acceptable for irrigating the proposed fruit trees.
9
Treated Grey Water Storage Tank
A plastic storage tank will be applied to store treated greywater from the sand filters. The capacity i s
determined as follows below:
Since the treated greywater should be stored for no more than one (1) day. The volume is equal to the
greywater flow rate x storage time
= 0.59 m3/d x 1 d = 0.59 m3
In US gallons the volume is equal to 0.59/0.00378 = 156 US gallons
A 200 US gallon plastic tank would be used since this capacity is the nearest size that is available locally.
Irrigation system and requirements
The required irrigation area for the Shakes’ residence proposed greywater recycle system would be
calculated based on the average greywater flow rate. Assuming that the banana, guava and papaya
trees would require around 2 inches or 0.051m of water per week the area for irrigation is determined
as follows:
Area = flow rate / mm of water x 7 days
= 0.59/0.051 x 7 day
= 81 m2
A drip type irrigation system would be established using 19mm ( ¾ inch) diameter pvc pipes.
This system is expected the increase the yield of banana, guava and papaya that which are affected by
seasonal drought periods.
Project Resources and Cost
The proposed greywater treatment and recycle system can be executed with unskilled and semi-skilled
human resources. In this case the project would be mostly executed by Mr. Edward Shakes Jnr and two
(2) labourers that include the caretaker for the property and a local labourer or farmer. The project is
expected to be completed in one (1) week that accounts for material acquisition, installation and
10
construction. A preliminary cost of $ 126,500 JMD is estimated and is broken down in table 3 as follows:
Description
Cost /JMD
55 US gallon Plastic Barrels
20,000.00
200 US gallon tank
12,000.00
1.5" and 0.75" PVC Pipes and fittings
30,000.00
1 yard gravel
4,000.00
1 yard sand
4,000.00
Material transportation
20,000.00
Labour
25,000.00
Subtotal
115,000.00
Contingency (10% of subtotal )
11,500.00
Grand Total
126,500.00
Figure 6-Expected Cost for the Shakes' Bryce Residence Greywater Recycling System
Project Feasibility
The feasibility of the project is assessed based on cost savings for irrigating the proposed fruit trees
without the use of the NWC supply grid and cost savings generated by growing the fruits rather than
purchasing them from the supermarket.
Cost savings per year without using NWC supplied water for the irrigation area
= cost per liter of potable water from NWC x volume used per year
= $ 0.133 / L x 0.59 cubic meters per day x 1000 L x 365 days
= $ 28,641.55
Cost savings from growing the fruits rather than purchasing them is equal to the estimated yield value
for one year. According to property owner Mr. Edward Shakes Snr , this is estimated to be $45,000
yearly.
11
The total cost savings = 28,641.55 + 45,000 = $73,641 per year
The payback period = Project Cost/ Total yearly savings
= 126,500/73,641 = 1.71 years or 1 year and nine months.
Since there is virtually no operational and maintenance costs associated with the greywater treatment
and recycling system the project is economically viable. The system equipment is also durable and is
able to exceed a life time of over five (5) years.
Conclusion
A greywater treatment and recycling system is proposed for the residence of Mr. Edward Shakes Snr and
Elaine Shakes. This system consists of septic tanks, a sand filter, and a storage tank with relevant piping
and will be applied to treat raw greywater to a quality that is capable of irrigating banana, papaya and
guava trees. The entire system is estimated to cost some $126,500 and is economically feasible with a
payback period of less than two (2) years.
12
Sources
Stauffer and Spuhler . Sustainable Sanitation and Water Management (SSWM). Septic Tank. Retrieved
on November 13, 2019 from < https://sswm.info/factsheet/septic-tank>
Stauffer and Spuhler. Sustainable Sanitation and Water Management (SSWM). Non-planted Filters.
Retrieved on November 13, 2019 from <https://sswm.info/sswm-university-course/module-6-disaster-
situations-planning-and-preparedness/further-resources/non-planted-filters>
Morel, Antoine. Greywater Treatment on a Household Level in Developing Countries. Retrieved on
November 4, 2019 from<
https://www.uvm.edu/~ewb/Documents/Grey%20Water%20in%20Developing%20Countries.pdf>
Septic Tank <https://discussions.texasbowhunter.com/forums/showthread.php?t=123727
National Environment and Planning Agency .Minimum Requirements for Wastewater and Excreta
Management in Jamaica. pp 21. Retrieved on November 4, 2019 from <
https://www.nepa.gov.jm/Development-Invest-Man/Volume%203%20-
%20Infrastructure,%20Utilities%20and%20Communication/Section%204%20-
%20Waste%20Water%20Treatment%20System.pdf>