Alternative Wastewater Treatment Design for

Alternative
Wastewater Treatment Design for
Panajachel, Guatemala
Sustainable Engineering and
Environmental Health for Development (SEEHD)
Student Group
Department of Civil Engineering
California State University, Chico
November 2010
1
Lead Author:
Alyssa Stutz
Collaborating Authors:
(in Alphabetacle Order)
Paul Anderson
Tim Arnold
Francis Booth
Brendan Finn
Kystle Galindo
Lisa Hall
Nicholas Mcgann
Frank O´Connell
Shane Salvador
Editors:
(in Alphabetacle Order)
Tim Arnold
Stewart Oakley
ALL RIGHTS RESERVED. Copyright © 2010 SEEHD
Table of Contents
Executive Summary .........................................................................................................................1 Figure 1: Proposed Anaerobic 2-Pond System with Facultative Pond ................................... 2 Figure 2: Three WSTR Batch Sequential System................................................................... 3 Table 1: Summary of Findings ............................................................................................... 4 Population Estimates........................................................................................................................5 Figure 3: Population Estimates Plotted on a Yearly Basis. .................................................... 5 Average Daily Flow Estimates ........................................................................................................5 Table 2: Flow Estimates.......................................................................................................... 6 Loading Estimates............................................................................................................................6 Preliminary Treatment .....................................................................................................................6 Bar Rack Design ..........................................................................................................................6 Table 3: Bar Rack Dimensions ............................................................................................... 6 Grit Chamber ...............................................................................................................................7 Table 4: Grit Chamber Dimensions ........................................................................................ 7 Figure 4: Parshall Flume Detail .............................................................................................. 7 Figure 5: Detail of Bar Rack................................................................................................... 8 Figure 6: 3-D and Scale Models of Grit Chamber and Parshall Flume .................................. 8 Available Land Area ........................................................................................................................9 Figure 7: Topographic Map of Basin Outlet........................................................................... 9 Table 5: Pump Efficiencies and Monthly Cost ....................................................................... 9 Wastewater Stabilization Ponds.....................................................................................................10 Feasibility of Facultative Pond ..................................................................................................10 Figure 8: Solar Insulation for Panajachel (data taken from CropWat and NASA) .............. 10 Table 6: Facultative Ponds in Parallel Summary.................................................................. 10 Feasibility of Anaerobic Pond ...................................................................................................10 Table 7: Anaerobic Pond Calculation Summary .................................................................. 11 Table 8: Methane Production................................................................................................ 12 Wastewater Storage and Treatment Reservoir (WSTR) for Type I Irrigation...............................12 Table 9: Fill-Rest-Use Example Cycle ................................................................................. 13 Figure 9: Sequential Batch-Fed System................................................................................ 13 Sequential Batch-Fed System Effluent Quality .........................................................................13 System Configuration ....................................................................................................................14 Figure 10: Route of Pressure Trunk Line ............................................................................. 14 Figure 11: Plan View of Anaerobic Pond System ................................................................ 14 Comparative Life Cycle Assessment of Operation for the Two Alternatives ...............................15 Activated Sludge System ...........................................................................................................15 Anaerobic/facultative or no-pond system ..................................................................................15 References......................................................................................................................................16 Appendix A: Population and Loading Rates .................................................................................17 Appendix B: Activated Sludge Calculations .................................................................................18 Appendix C: N and P Values, Methane, and Facultative and Anaerobic Pond Calculations.......19 Appendix D: Log Removal Calculations.......................................................................................20 Appendix E: WSTR Calculations ..................................................................................................21 Executive Summary
Introduction / Objectives
The object of this project is to design the process for a natural wastewater treatment/reuse system
for the city of Panajachel, Guatemala in order to protect the water quality of Lake Atitlan. This
natural system will serve as a model for other cities within the lake’s drainage basin, and will use
pumping for land disposal/irrigation in lieu of direct discharge into the lake. The final design
will be compared to the currently proposed activated sludge/chemical precipitation system by
using life cycle assessment.
Population Estimates
The population estimates for the years 2011 and 2021 are 14,263 and 17,536, respectively.
Average Daily Flowrate
The average daily flowrate used throughout the calculations of this project is 2,100 cubic meters
per day.
Loading Rates
The Total Suspended Solids (TSS) and the Biochemical Oxygen Demand (BOD5) loading rates
each equate to 526 kilograms per day.
Available Land Area and Pumping Head
The amount of pipe it would take to pump wastewater effluent from Panajachel to the basin
outlet near Papaturro is approximately 18,875 meters and a static pump head (elevation
difference) of approximately 30 meters. The pumping costs rely heavily on the efficiency of the
pump. For a high pump efficiency (basically pumping pure water) the energy requirement would
be near 80,000 kilowatt hours per year or around $17,800 dollars per year. If raw effluent is
pumped, the efficiency of the pump decreases and the cost to pump goes up to roughly $39,890
dollars per year.
Wastewater Stabilization Ponds
The total area required for a facultative pond serving the population of Panajachel is about
17,490 square meters – space that is not available in Panajachel. The total area required for an
anaerobic pond is 438 square meters – space that is available in Panajachel. Ideally, two
anaerobic ponds in parallel should be constructed so that while one pond is being desludged, the
other can be in operation. The ponds would have to be desludged about every 2.8 years. For two
ponds in parallel, and a length to width ratio of 2/1, the length and width for each pond are 21
meters and 10 meters, respectively. The hydraulic retention time is roughly 0.8 days (19.2
hours) which gives an E. Coli Log10 removal of about 0.5. The amount of methane these ponds
would produce is about 67,200 cubic meters per year which equates to 668,232 kilowatt hours of
usable energy per year.
Once the wastewater passes through the anaerobic ponds, approximately 70 percent of the BOD
will be removed. This means that a facultative pond following two anaerobic ponds in parallel
would create a very efficient system. Constructing a facultative pond to follow the two
anaerobic ponds would only require an additional 5,250 square meters which is available.
1
Figure 1: Proposed Anaerobic 2-Pond System with Facultative Pond
2 Anaerobic Ponds
each with
Length = 21 m and
Width = 10 m
Facultative Pond
with
Length = 125 m
And Width = 42 m
Wastewater Storage and Treatment Reservoir (WSTR) for Type I Irrigation
The volume needed for the construction of one WSTR is 340,550 cubic meters, or in terms of
area, 3.4 hectares at a depth of 10 meters. For a three WSTR sequential batch-fed system, a
volume of 252,000 cubic meters or an area of 2.5 hectares (with a depth of 10 meters) is needed
for each pond. A three WSTR sequential batch-fed system will produce a much higher quality
effluent, yet will require three times the amount of surface area (2.5 ha x 3 ponds = 7.5 ha). The
area is available though so a batch sequential system should be constructed.
2
Figure 2: Three WSTR Batch Sequential System
Three WSTRs
each with
Diameter = 179 m
Activated Sludge System
The energy required for aeration and mixing per year is 319,150 kilowatt hours. The annual cost
to operate the plant for electricity alone is $72,396 per year. Ferric chloride will be required to
operate the plant as well – a quantity of 82,070 kilograms per year. The carbon footprint of the
plant based on the electricity consumption is 255,316,580 grams of CO2 equivalent per year. The
chance of the activated sludge system succeeding is small.
Anaerobic Pond System or No pond system (near Panajachel)
The energy required for pumping horizontally 18,875 meters and vertically 30 meters depends
greatly on the pump efficiency. The efficiency of a pump pumping effluent from an anaerobic /
facultative pond system will be greater than the efficiency of a pump pumping raw effluent.
Also, the methane produced from the anaerobic ponds produces more energy than what is
required to pump the effluent to the WSTRs. In either case (pond system or no pond system), the
annual cost is still much less than the activated sludge system. The annual cost to operate the
pumps with high and low efficiencies is $17,690 and $39,890, respectively.
Values for nitrogen and phosphorus produced by the effluent equate to $38,400 per year and
$225,970 per year, respectively.
The likelihood of either alternative to succeed is much greater than that of installing an activated
sludge plant.
3
Table 1: Summary of Findings
2021 Population:
BOD5 Loading [kg/day]:
17,536
526
FACULTATIVE PONDS ONLY
Total Area Req. for Facultative pond [m2]:
Hydraulic Retention Time [days]:
Frequency for Desludging [yrs]:
Area of each pond in parallel [m2]:
Length per pond [m]:
162
Space for Facultative Ponds:
Daily flowrate [m3/day]:
TSS Loading [kg/day]:
17,490
13.6
8.7
8,745
Width per pond [m]:
54
No
PROPOSED ANAEROBIC SYSTEM W/ FACULTATIVE POND
Effluent Pipe Length [m]:
15,100
Pumping Head Required [m];
30
Pumping Energy Requirements [kW-hr/yr]:
77,990 to 175,826
Pumping Cost [USD/yr]:
$17,790 to $39,890
Total Area Req. for Anaerobic pond [m2]:
438
Hydraulic Retention Time [days]:
0.8
Frequency for Desludging [yrs]:
2.8
Area of each pond in parallel [m2]:
219
Length per pond [m]:
21
Width per pond [m]:
10
Space for Anaerobic Ponds:
Yes
Methane Production [m3/yr]:
67,200
Methane Production [kWh/yr]:
668,232
Area of Facultative Pond [m2]:
5,250
Length of pond [m]:
125
Width of pond [m]:
E. Coli Log10 Removal:
1.2
Value of Nitrogen @ $0.40/100g [USD/yr]:
$38,400
Value of Phosphorus @ $58.84/500g [USD/yr]:
$225,970
Likelihood of Success:
Good
WSTR
Area of 1 WSTR [ha] @ depth = 10 m:
Volume of 1 WSTR [m3]:
3.4
340,550
3 WSTR SEQUENTIAL BATCH SYSTEM
Area of 1 WSTR [ha] @ depth = 10 m:
Volume of 1 WSTR [m3]:
2.5
252,000
ACTIVATED SLUDGE SYSTEM
Energy Req. for Aeration and Mixing [kWh/yr]:
Quantity of FeCl3 Required [kg/yr]:
Annual Cost to Operate Plant; electricity
[USD/yr]:
Carbon Footprint [g CO2 equiv/yr]:
Liklihood of Success:
2,100
526
42
319,150
82,070
$72,396
255,320,000
Minimal
4
Population Estimates
The design period for the project is from year 2011 to 2021. The initial estimate of the
population in Panajachel, Guatemala is roughly 12,863 for the year 2006 (Mongabay, 2009).
According to the Central Intelligence Agency World Factbook, the population growth rate in
Guatemala is 2.066%.
Using the following population growth equation:
Where,
N0 = Starting Population
N = Resulting Population
t = Time Elapsed (years)
r = Growth Rate
The population estimates for the years 2011 and 2021 are approximately 14,263 and 17,536,
relatively.
Figure 3: Population Estimates Plotted on a Yearly Basis.
Average Daily Flow Estimates
Assuming the worst case scenario, the daily flow estimates are derived from 100% of the
estimated population of Villanueva for the year 2021. The water usage range used for the design
is 0.08 – 0.12 m3/person-day (Oakley 2005). It is also assumed that there is a range from 70% to
100% of the total water usage that actually goes to wastewater, but for worst case scenario
purposes, 100% will be assumed. To incorporate a safety factor, the remainder of the
calculations will be based off of a flowrate of approximately 2,100 m3 per person per day (see
Table 2).
5
Table 2: Flow Estimates
% Connected to Sewer
2021 Pop.
100%
17,536
Water Usage [m3/person-day]
0.08
0.10
0.12
100% of Water Used goes to Wastewater
90% of Water Used goes to Wastewater
80% of Water Used goes to Wastewater
1,403
1,263
1,122
1,754
1,578
1,403
2,104
1,894
1,683
70% of Water Used goes to Wastewater
982
1,228
1,473
Loading Estimates
The total BOD5 and Total Suspended Solids loadings were calculated using an influent loading
rate of 250 milligrams per liter. To calculate the BOD5 and TSS loadings, averages were taken
from the “Wastewater Problems at Lago Atitlan” powerpoint (Salguero, Oakley and Henry,
2010). Both the BOD5 and TSS loadings were calculated to be 526 kilograms per day. Using a
system with either two facultative or two anaerobic ponds gives BOD5 and TSS loading rates of
263 kilograms per day per pond.
Preliminary Treatment
Bar Rack Design
The design for the Bar Rack was taken from Section 3 of the “Lagunas de estabilizacion en
Honduras” manual (Oakley, 2005). The bar width, depth, spacing, and angle from horizontal
were assumed values from Table 3-1 of the manual. Aluminum was chosen for the bar material
over galvanized steel because it is less expensive and lighter. As long as the bar rack is
maintained, aluminum will work just as well as steel. A length of 1.5 meters for the approach
channel was chosen because it needed to be more than 1.35 meters in length. The depth of the
approach channel is equivalent to the depth of the grit chamber (from Table 4).
Table 3: Bar Rack Dimensions
Bar Width [mm]:
Bar Depth [mm]:
Space between Bars [mm]:
Bar Material:
Angle from Horiz. [deg]:
Length Appr. Chanl [m]:
Depth Appr. Chanl [m]:
Width of Approach Channel [m]:
Approach Velocity [m/s]:
Velocity through Bars:
Head loss through Bars:
Frequency of Cleaning:
Screenings disposal method:
10
30
50
Aluminum
45
1.5
0.136
0.358
0.45
0.5
0.008
Daily
Bury
6
Grit Chamber
The design for the Grit Chamber was taken from Section 3 of the “Lagunas de estabilizacion en
Honduras” manual (Oakley, 2005). The throat size was taken from Table 3-3 of the manual.
Equations used for these calculations are as follows:
Table 4: Grit Chamber Dimensions
Max Flowrate, Qmax [m3/d]:
Max Flowrate, Qmax [m3/s]:
Throat Size, W [m]:
Max Height, Hmax [m]:
R:
Cr:
Z [m]:
Pmax [m]:
Width of Grit Chamber [m]:
Cv:
Length of Channel [m]:
Total Rectangular Area [m2]:
2,100
0.024
0.152
0.182
2.14
0.25
0.046
0.136
0.597
0.98
15
42
Figure 4: Parshall Flume Detail
7
Figure 5: Detail of Bar Rack
Figure 6: 3-D and Scale Models of Grit Chamber and Parshall Flume
8
Available Land Area
Using the topographic map from Google Maps and the satellite image from Google Earth, it was
found that there is practically no land area available for a facultative pond in the proximity of
Panajachel. There were a few locations an anaerobic pond could be constructed, but most, if not
all, of the locations are very close to people’s homes.
The placement of the wastewater storage and treatment reservoir (WSTR) would best be located
outside of the southern basin of Lake Atitlan. The number of WSTRs will be discussed in more
detail later in the report.
Figure 7: Topographic Map of Basin Outlet
The pumping energy requirements and
annual cost of pumping at $0.23/kW-hr
depended mostly on how high in elevation
the wastewater was to be pumped and also
on the pump efficiency. Other factors that
affected price were differing pipe
diameters and C-values for the HazenWilliams equation:
ℎ =6.81⋅ 1.85 1.167
Where V= Fluid Velocity
C= Coefficient of Roughness
L= Pipe Length
D= Pipe Diameter
The friction losses, ℎ , due to the pipe
diameter did not change the monthly amount significantly (i.e. the 18 inch pipe cost roughly $40
more per month than the 36 inch pipe). Similarly, the C-values did not affect the monthly
amount significantly either (i.e. the difference between a C-value of 150 to 100 was about $40
per month more) (Qasim, 2000). Looking closely at the topographic map in Google maps and
using a Lake elevation of 1,560 meters (Lake Atitlan, 2010) it was assumed that the elevation of
Panajachel was about 1,580 meters and that the lowest point to pump the water out of the basin
was about 1,610 meters. This means that the wastewater needs to be pumped a total difference
in elevation of 30 meters and a horizontal distance of approximately 18,875 meters. Table 5
shows the effect of different pumping efficiencies regarding cost per month for electricity.
Table 5: Pump Efficiencies and Monthly Cost
D
in
24
24
24
24
24
24
C
125
125
125
125
125
125
L
m
18,875
18,875
18,875
18,875
18,875
18,875
hfriction
m
0.304
0.304
0.304
0.304
0.304
0.304
Hstatic
m
30
30
30
30
30
30
TDH
m
30.30
30.30
30.30
30.30
30.30
30.30
Epump
Emotor
0.9
0.8
0.7
0.6
0.5
0.4
0.9
0.9
0.9
0.9
0.9
0.9
P
kW
8.92
10.04
11.47
13.38
16.06
20.07
P
kWhr/yr
78,145
87,913
100,472
117,217
140,661
175,826
Cost
USD/yr.
17,727
19,943
22,792
26,591
31,909
39,886
9
Wastewater Stabilization Ponds
Feasibility of Facultative Pond
A facultative pond in Panajachel would require an area of 17,500 square meters or 1.75 ha.
Finding this amount of space would be very difficult to accomplish in Panajachel. If 1.75 ha
were available for the installation of a facultative pond system then it is suggested that two
facultative ponds be constructed in parallel so that while one is being desludged, the other can
remain in operation.
The pond area equations used to calculate the required area were taken from Section 5 of the
“Lagunas de estabilizacion en Honduras” manual (Oakley, 2005). The CSm value was calculated
using the lowest energy value from the CropWat / NASA data.
Figure 8: Solar Insulation for Panajachel (data taken from CropWat and NASA)
Table 6: Facultative Ponds in Parallel Summary
AF per pond [m2]:
Width per pond [m]:
Length per pond [m]:
HRT [days]:
Sludge accumulation rate
[m3/yr]:
Frequency of Desludging [yrs]:
8,743
54
162
~14
820
8.7
Feasibility of Anaerobic Pond
An anaerobic pond in Panajachel would require an area of 440 square meters or 0.04 hectares
(1/40 of the area required for the facultative pond). It is suggested that two anaerobic ponds be
constructed in parallel so that while one is being desludged, the other can remain in operation.
10
The ponds would have to be desludged about every 2.8 years. For two ponds in parallel, and a
length to width ratio of 2/1, the length and width for each pond are 21 meters and 10 meters,
respectively. The hydraulic retention time is roughly 0.8 days (19.2 hours) which gives an E.
Coli Log10 removal of about 0.5. The amount of methane these ponds would produce is
approximately 67,200 cubic meters per year which equates to 668,232 kilowatt hours. The rate
for sludge accumulation in anaerobic ponds in warm climates is 0.04 cubic meters per person per
day (Mara 2003). It is said that rates could be as low as 0.01 but the high value is used in this
case as a factor of safety.
Once the effluent goes through the anaerobic ponds, approximately 70 percent of the BOD will
be removed. This means that a facultative pond following two anaerobic ponds in parallel would
create a very efficient system. If a facultative pond followed the two anaerobic ponds, the
facultative pond would only require 5,250 square meters more of space (which is available).
Table 7 is a summary of the dimensions and volumes needed for an anaerobic system. The pond
area equations used to calculate the required areas and volumes were taken from Section 5 of the
“Lagunas de estabilizacion en Honduras” manual (Oakley, 2005).
Table 7: Anaerobic Pond Calculation Summary
Qmax [m3/day]:
BOD5 [mg/l]:
Volume [m3]:
Depth [m]:
Area required for Single Anaerobic Pond [m2]:
Area required for Single Anaerobic Pond [m2]:
Length [m]:
Width [m]:
Annual Accumulation Volume [m3/yr]:
1/3 Tdesludge [yrs]:
2/3 Tdesludge [yrs]:
Dimensions for 2 ponds in parallel:
Area per pond [m2]:
Width [m]:
Length [m]:
2,100
250
1,750
4
438
0.044
36
12
819
1.4
2.8
219
10
21
Methane Production
Methane is a very important subject when it comes to anaerobic ponds. The amount of methane
produced by the ponds in question could supply roughly four times the amount of energy it takes
to pump the effluent to the wastewater storage and treatment reservoirs. The amount of methane
produced per hour equates to 7.7 cubic meters. This means that the amount of methane produced
per day could supply energy to 800 2-inch burners for an hour (one 2-inch burner requires 0.23
cubic meters of methane per hour).
11
Table 8: Methane Production
BOD5 [kg/day]:
Methane volume [m3/day]:
Methane volume [m3/hr]:
Methane volume [m3/yr]:
Energy [MJ/yr]:
Energy [kWh/yr]:
526 184 7.7 67,197 2,405,635 668,232 Wastewater Storage and Treatment Reservoir (WSTR) for Type I
Irrigation
The CropWat program was used to tabulate the monthly precipitation and reference evapotranspiration at Panajachel to construct the WSTR for Type I irrigation. The vegetative cover
selected was sugarcane which has a high KC value of 1.25. The design percolation rate from the
soil data in the Lake Atitlan basin was assumed to be 180 millimeters per month. A water
balance for a Type I reuse system was calculated and tabulated using the evapotranspiration
values for each month, the monthly values of the hydraulic loading rate based on soil
permeability, the annual volume of wastewater flow, the area requirements for irrigation, the
monthly volumetric loading rates, and the monthly available wastewater volumes.
The volume of a single WSTR is required to be 340,550 cubic meters (this is the estimated
maximum amount of storage required at any given time – see Appendix E). The area required
for a volume this size is approximately 3.4 hectares for a depth of 10 meters or 6.8 hectares for a
depth of 5 meters. According to Duncan Mara in his book Domestic Wastewater Treatment he
states that “During the irrigation season, the WSTR contents are pumped out to the fields to be irrigated, while at the same time there is still a continuous inflow of anaerobic pond effluent. As the irrigation season progresses, there is a progressive deterioration in the quality of the WSTR contents as the retention time in the reservoir of the anaerobic pond effluent becomes correspondingly shorter… For unrestricted irrigation it would be a serious problem.” In essence the hydraulic retention time decreases causing the effluent to fall short of World Health Organization guidelines. Therefore, an alternative to constructing one huge WSTR is to construct a sequential batch-fed
system. Using Mara’s guidance, three sequential batch-fed WSTRs can be used to store and treat
the anaerobic pond effluent. As shown if Figure 9, the WSTR are in parallel and each is
“operated on a cycle of ‘fill–rest–use’. As soon as the contents of one reservoir are used, another
is brought into irrigation service and the one just emptied is refilled in readiness for the next
irrigation season” (Mara, 2003).
12
Table 9: Fill-Rest-Use Example Cycle
Month
January
February
March
April
May
June
July
August
Sepember
October
November
Dececember
WSTR 1
Rest
Rest
Rest
Rest
Use
Use
Fill (1)
Fill (1)
Fill (1/2)
Fill (1/2)
Fill (1/3)
Fill (1/3)
WSTR 2
Fill (1/2)
Fill (1/2)
Rest
Rest
Rest
Rest
Use
Use
Fill (1/2)
Fill (1/2)
Fill (1/3)
Fill (1/3)
WSTR 3
Fill (1/2)
Fill (1/2)
Fill (1)
Fill (1)
Fill (1)
Fill (1)
Rest
Rest
Use
Use
Fill (1/3)
Fill (1/3)
Figure 9: Sequential Batch-Fed System
Sequential Batch-Fed System Effluent Quality
The effluent from a sequential batch-fed system has very good quality due to long hydraulic
retention times. According to Mara “E. Coli numbers decline rapidly during the rest phase: in
studies in northeast Brazil …[it was] found that in WSTR which received organic loadings of
126–162 kg BOD/ha day during the fill phase, E. Coli numbers dropped from 106–107/100 ml of
anaerobic pond effluent to <1000/100 ml during the first 14 days of the rest phase at 25°C.”
(Mara, 2003) 13
System Configuration
Figure 10: Route of Pressure Trunk Line
Elev. of pipe at
Panajachel
1,580 m
Elev. of pipe at
basin low point
1,610 m
Figure 11: Plan View of Anaerobic Pond System
14
Comparative Life Cycle Assessment of Operation for the Two
Alternatives
Activated Sludge System
The energy requirement for aeration and mixing in kilowatt hours per year is about 319,150.
This equates to a total cost (for electricity alone) of $72,400 to operate the plant on a yearly
basis. The carbon footprint of the plant based on electricity consumption is 255,316,580 grams
of CO2 equivalent per year. The quantity of ferric chloride required is 82,070 kilograms per
year. The amount of sludge produced per year is 15,178 cubic meters – which will contain
hazardous chemicals from the ferric chloride and will need to be buried. The likelihood of this
activated sludge system succeeding is very low. The system will very costly to maintain and will
introduce harmful chemicals to an already strained environment.
Anaerobic/facultative or no-pond system
The energy required for pumping horizontally 18,875 meters and vertically 30 meters depends
greatly on the pump efficiency. The efficiency of a pump pumping effluent from an anaerobic /
facultative pond system will be greater than the efficiency of a pump pumping raw effluent.
Also, the methane produced from the anaerobic ponds produces more energy than what is
required to pump the effluent to the WSTRs. In either case (pond system or no pond system),
the annual cost is still much less than the activated sludge system. The annual costs to
operate the pumps with high and low efficiencies are $17,690 and $39,890, respectively.
The amount of methane produced by the ponds supplies roughly four times the energy it takes to
pump the effluent to the wastewater storage and treatment reservoirs. The amount of methane
produced per hour equates to 7.7 cubic meters. This means that the amount of methane produced
per day could supply energy to 800 2-inch burners for an hour (one 2-inch burner requires 0.23
cubic meters of methane per hour).
The amount of sludge that accumulates in the anaerobic ponds is about 820 cubic meters per year
which means the ponds need to be desludged once every 2.8 years (when they are 2/3 full).
Using a BOD/Nitrogen/Phosphorus ratio of 100/5/1, the amount of nitrogen and phosphorus
accumulated in one day is 26 and 5 kilograms, respectively (Viessman, 2009). This means that
the amount of nitrogen and phosphorus accumulated in one year equates to 9,600 and 1,920
kilograms, respectively, which leads to a value for nitrogen of $38,400 per year (at $0.40/100 g)
and a value for phosphorus of $225,970 per year (at $58.84/500 g) (Nitrogen, 2010; Eni
Generalic, 2003).
The likelihood of the anaerobic/facultative pond system succeeding is much higher than the
likelihood for an activated sludge plant succeeding for several reasons. First of all, the monthly
operational cost is much less; in fact, energy is actually produced from the pond system (via
methane) as opposed to being consumed. The amount of energy needed per year to pump to the
WSTR’s is roughly 90,000 kilowatt hours while the amount of energy produced from the
methane is roughly 668,000 kilowatt hours per year. Also, the sludge from the anaerobic ponds
can be dried and used as fertilizer while the sludge from the activated sludge plant will contain
hazardous material from the ferric chloride and will need to be buried. Additionally, in the event
of a natural disaster, the ponds will not be destroyed. An activated sludge plant may be
completely lost and need to be rebuilt.
15
References
CROPWAT 8.0 and CLIMWAT 2.0 for CROPWAT computer programs.
Guidelines for the Safe Use of Wastewater, Excreta and Greywater. Volume 2. Geneva,
Switzerland. World Health Organization, 2006. Print. pp. xvii.
Hearne, Robert. An Analysis of the Feasibility of Irrigation District Transfer in Honduras. North
Dakota State University. Aug 2004. pp 5 < http://ageconsearch
umn.edu/bitstream/20078/1/sp04he04.pdf>
Mara, Duncan. Domestic Treatment in Developing Countries. Sterling, VA: Earthscan. 2003.
Print. pp. 105-112; 145-147.
NASA. Surface Meteorology and Solar Energy. <http://eosweb.larc.nasa.gov/sse/>.
Nitrogen. Chemicool Periodic Table. 9/15/2010 <http://www.chemicool.com
/elements/nitrogen.html>.
Oakley, Stewart M. “LAGUNAS DE ESTABILIZACIÓN EN HONDURAS: Manual de Diseño,
Construcción, Operación y Mantenimiento, Monitoreo y Sostenibilidad.”
Universidad Estatal de California. Junio 2005. Pp. 23, 28, 32, 189.
Salguero, L., Oakley, S., Henry, B., “Wastewater Problems at Lago Atitlan: And Suggested
Remedial Approach.” Powerpoint.
Viessman, Warren, Mark Hammer, Elizabeth Perez, and Paul Chadik. Water Supply and
Pollution Control. 8th ed. Upper Saddle River, NJ: Pearson Education, Inc., 2009. Print. pp. 521522.
World Factbook, The. “Central Intelligence Agency.” 2010. Web. 9 Sep 2010.<https:
//www.cia.gov/library/publications/the-world-factbook/geos/ho.html>.
Qasim, S.R., Motley, E. M., Zhu, G., 2000. Water Works Engineering. Prentice Hall, Upper
Saddle River, New Jersey.
Riddle, J. About Panajachel, Guatemala, Lake Atitlan. 2009. <http://www.panajachel.com/>
.
16
Appendix A: Population and Loading Rates
POPULATION
Rate, r:
0.02066
Year Time, t Population
2006
0
12,863
2007
1
13,132
2008
2
13,406
2009
3
13,685
2010
4
13,971
2011
5
14,263
2012
6
14,561
2013
7
14,864
2014
8
15,175
2015
9
15,492
2016
10
15,815
2017
11
16,145
2018
12
16,482
2019
13
16,826
2020
14
17,177
2021
15
17,536
Flow [m3/day]
% Connected to Sewer
2021 Pop.
100%
17,536
Water Usage [m3/person-day]
0.08
0.10
0.12
100% of Water Used goes to Wastewater
1,403
1,754
2,104
90% of Water Used goes to Wastewater
1,263
1,578
1,894
80% of Water Used goes to Wastewater
1,122
1,403
1,683
70% of Water Used goes to Wastewater
982
1,228
1,473
BOD5 Loadings [kg/day]
351
438
526
TSS Loadings [kg/day]
351
438
526
17
Appendix B: Activated Sludge Calculations
Q [m3/d]:
T [°C]:
BOD Influent [mg/l]:
BOD Effluent [mg/l]:
2,100
25
250
20
?
BODL = 1.6BOD5
Assume β:
Assume α:
Depth of aeration tank diffusors [m]:
Blower efficiency, e:
Transfer efficiency, SOTE:
Mean Cell Residence Time, Θc
[days]:
HRT [hrs]:
Volitile Solids [mg/l]:
Total Suspended Solids [mg/l]:
20
24
2800
4000
?
?
?
Assumed
VRA [m3]:
F / M:
2,100
0.08
Assume HRT is 24 hrs
0.8
0.5
5
0.7
0.28
PX,SSV [kg/d]:
PX,SST [kg/d]:
294
420
VL [m3]:
41.6
ST = 1.0% or 10,000 mg/L
15,178
355
1,105
Required Oxygen
Oxygen Transfer Equation
3
VL [m /yr]:
AOTR, Ro [kg/d]:
SOTR [kg/d]:
Qair,BOD [m3/min]:
9.86 Air Flowrate
4.70 Flow of air for volume of reactor
Need a minimum of 15 m3/1000m3/min for complete mix
Qair,MIX [m3/min]:
Loss in pipe diffuser [atm]:
p1 [atm]:
p2 [atm]:
31.5
0.15
1
1.64
Pw [kW]:
Pw [hp]:
36.4
48.9
Pw [kW-hr/yr]:
Amount of electricity [USD/mo]:
Phosphorus [kg/yr]:
Ferric Chloride Req. [kg/yr]:
319,146
$6,033
255,316,577
72,398
15,782
82,070
18
Appendix C: N and P Values, Methane, and Facultative and
Anaerobic Pond Calculations
Nitrogen [kg/day]
Phosphorus [kg/day]
Nitrogen [kg/year]
Phosphorus [kg/year]
N Value [$/yr]
P Value [$/yr]
26
5
9,601
1,920
38,404
225,968
Faculative Pond Volume Calculation
Qmax [m3/day]:
2,100
BOD5 [mg/l]:
250
CSM [kg BOD/ha-day]:
300
2
AF [m ]:
17,486
2
AF [ha ]:
1.75
Length [m]:
229
Width [m]:
76
Depth [m]:
1.8
3
Volume [m ]:
28,577
TSS [mg/l]:
250
3
Vannual [m /yr]:
819
BOD5 [kg/day]:
526 Methane volume [m3/day]:
184 Methane volume [m3/hr]:
7.7 3
67,197 Methane volume [m /yr]:
2,405,635 Energy [MJ/yr]:
668,232 Energy [kWh/yr]:
Tdesludge [yrs]:
(HRT=7 days)Vmatur. [m3]:
Amatur. [m2]:
Length [m]:
Width [m]:
Depthmatur. [m]:
Total Area [ha2]:
Dimensions for 2 ponds in parallel:
AF [m2]:
Width [m]:
Length [m]:
Anaerobic Pond Volume Calculation
Qmax [m3/day]:
2,100
BOD5 [mg/l]:
250
3
{300 g/m3-d) Volume [m ]:
1,750
Depth [m]:
4
2
AA [m ]:
438
2
AA [ha ]:
0.044
Length [m]:
36
Width [m]:
12
(70% Rem) BODeff [mg/l]:
75
2
AF [m ]:
5,246
2
AF [ha ]:
0.525
2
Total Area [ha ]:
0.6
3
Vannual [m /yr]:
819
8.72
14,700
8167
157
52
1.8
2.6
8,743
54
162
Dimensions for 2 ponds in parallel:
AF [m2]:
219
Width [m]:
10
Length [m]:
21
Faculative Pond Volume Calculation
Qmax [m3/day]:
2,100
BOD5 [mg/l]:
75
CSM [kg BOD/ha-day]:
300
2
AF [m ]:
5,246
2
AF [ha ]:
0.52
Length [m]:
125
Width [m]:
42
Depth [m]:
1.8
3
Volume [m ]:
7,887
19
Appendix D: Log Removal Calculations
Von Sperling’s method was used to calculate the log removal (Mara 2003). The following
equations were used:
Faculative Pond Log Removal Calc
Primary
HRT sm
13.61
KB(20)
KB(T)
δ = (L/B)
0.232
0.325
0.333
-1
a
Ni
Ne
E
Log Rem.
2.626
5.64E+07
3.93E+06
9.30E-01
1.157
Anaerobic Pond Calculation Equations used:
Anaerobic Pond Log Removal Calc
Primary
δ = (L/B)HRT sm
0.83
KB(T)
1
a
Ni
Ne
2.805
0.333
2.029
5.64E+07
1.69E+07
E
7.00E01
Log
Rem.
0.523
Facultative Pond Following Anaerobic Pond Log Removal Calc
Facultative
KB(20)
KB(T)
δ = (L/B)
0.334
0.468
0.333
-1
a
Ni
Ne
E
Log Rem.
Total Log Rem.
1.951
5.64E+07
1.21E+07
7.85E-01
0.667
1.191
20
Appendix E: WSTR Calculations
Month
January
February
March
April
May
June
July
August
September
October
November
December
Total:
Rad
MJ/m²day
17
19
22
22
22
21
21
21
19
18
16
16
Rad
ETo
ETo
Rain
Etc
ETc-P
Pw
Lw
V
Q
ΔS
∑ΔS
kJ/ha-day
172,000,000
188,000,000
215,000,000
222,000,000
215,000,000
213,000,000
210,000,000
206,000,000
194,000,000
182,000,000
159,000,000
155,000,000
mm/day
4
5
5
5
4
4
4
4
4
3
3
3
mm
mm
mm
mm
mm
m3
m3
m3
-110,884
-110,360
-105,116
-73,184
52,147
63,000
41,601
61,614
63,000
59,187
-68,010
-80,466
m3
192,074
81,190
-29,170
-134,286
0
52,147
115,147
156,749
218,363
281,363
340,549
272,539
137
133
164
145
133
124
127
126
114
108
99
105
11
7
56
95
325
449
297
335
614
307
47
31
171
166
205
182
166
155
159
158
142
134
123
132
mm
160
159
149
87
-159
-294
-138
-177
-472
-173
76
101
1,514.74
2,574.00
1,893.43
680.58
180
180
180
180
180
180
180
180
180
180
180
180
340
339
329
267
21
-114
42
3
-292
7
256
281
173,884
173,360
168,116
136,184
10,853
0
21,399
1,386
0
3,813
131,010
143,466
63,000
63,000
63,000
63,000
63,000
63,000
63,000
63,000
63,000
63,000
63,000
63,000
2,160.00
1,479.43
963,469.79
756,000.00
Annual Wastewater Volume, Qa = (2,100 m3/d)*(30 d/mo)*(12
mo/yr) =
756,000 m3\yr
AI = (756,000 m3/yr) / (2.319425 m) =
511,009.34 m2 =
51.1 ha
Vw(p) = (LW(p)/1,000)*AI
Max Storage = 340,550 m3; AWSTR = 3.4 ha at 10 m depth; 6.8 ha at 5 m depth
21