PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
CONTENT
III.3.2 PREFEASIBILITY FOR THE USE OF WETLANDS
EJECUTIVE SUMMARY
3.2.1 PHYSICAL ASPECTS ......................................................................................... 1
A) PRESENT POPULATION AND ITS PROJECTION ......................................................................... 1
B) ECONOMICAL ACTIVITIES .............................................................................................................. 2
C) INDUSTRIES AND MAIN POLLUTANTS ......................................................................................... 3
D) DRAINAGE AND POTABLE WATER SUBSTRUCTURE DIAGNOSIS ........................................... 3
E) VOLUMENES OF GENERATED WASTEWATER ............................................................................ 5
3.2.3 FLOW MEASURE AND CHARACTERIZATION OF WASTEWATER. ............... 7
A) MEASURE ......................................................................................................................................... 7
B) SAMPLING AND FIELD ANALYSIS.................................................................................................. 7
C) LABORATORY ANALYSIS ............................................................................................................... 8
3.2.4 PRIMAY REQUIREMENTS OF WATER QUALITY FOR AGRICULTURAL
REUSE. ........................................................................................................................ 8
3.2.5. TREATMENT ALTERNATIVES ......................................................................... 8
A) PRE-SELECTION CRITERIA ............................................................................................................ 8
B) NATURAL PROCEDURES FOR DISCHARGES TREATMENT WASTEWATER FOR THE
MEXICALI VALLEY POPULATIONS ..................................................................................................... 9
C) ARTIFICIAL WETLANDS. ............................................................................................................... 10
D) ALTERNATIVES PROPOUSED ..................................................................................................... 11
3.2.6. ANALYSIS AND EVALUATION OF ALTERNATIVES. .................................. 11
A) VICENTE GUERRERO, VENUSTIANO CARRANZA AND GUADALUPE VICTORIA
POPULATION ...................................................................................................................................... 12
B) REHABILITATION AND IMPROVEMENT OF CD. MORELOS WASTEWATER TREATMENT
SYSTEM. .............................................................................................................................................. 13
3.2.7. PRELIMINARY COSTS ESTIMATING ............................................................. 13
3.2.8. CONCLUSIONS ............................................................................................... 15
III-0
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
III.3.2 PREFEASIBILITY FOR THE USE OF WETLANDS
3.2.1 PHYSICAL ASPECTS
The villages considered in the present study, represent the most populous in the Valle
de Mexicali, in which, their sewer systems allow the planning of systems for treatment
and reuse of their effluents. These villages are:




Guadalupe Victoria
Vicente Guerrero (Los Algodones)
Venustiano Carranza (Estacion Coahuila, Km. 57)
Ciudad Morelos (Cuervos)
A) PRESENT POPULATION AND ITS PROJECTION
The Mexicali District has about a third of the total population in the state. Considering
the growth rate for 1995 (2.6%), the growth in the 4 villages under study have been
estimated in order to provide the systems with a flexibility range as to their
dimensioning, which is in direct function of the number of inhabitants. The resulting
values are shown in the following table:
ESTIMATE GROWTH OF POPULATION IN 4 CITIES OF MEXICALI
VALLEY
VILLAGES
Guadalupe Victoria
VenustianoCarranza
Vicente Guerrero
Ciudad Morelos
P(1995)
13,252
5,655
3,982
7,205
P(2000)
15,067
6,429
4,527
8,192
P(2010)
19,476
8,311
5,852
10,589
P(2020)
25,175
10,743
7,565
13,687
It’s advisable to point out that the figures in the table above imply the global population
growth, but not the one of the population served with drainage net, which consequently
could become contributors to the treatment system.
III-1
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
The following chart shows the obtained results:
FIG. 3.2.2
POPULATION'S PROJECTION
25000
22143
20000
INHABITANTS
17130
15067
15000
13252
12039
10000
9449
9313
8192
7205
5000
5655
3982
7310
6653
6429
5147
4527
0
1995
2020
2010
2000
YEAR
Guadalupe Victoria
Venustiano Carranza
Vicente Guerrero
Ciudad Morelos
B) ECONOMICAL ACTIVITIES
For the four villages under study, it can be established that the main economical activity
is agriculture and, in a less degree, cattle breeding, commerce and services, as shown
in the following land distribution percentages:
AGRICULTURE
CATTLE BREEDING
HARVEST
OTHERS
86.1%
3.8%
2.8%
12.3%
This is due, among other factors, to the fact that the Mexicali District has an important
substructure to allow all of its cultivating area to be an irrigation one (87% of the total
available in the state), giving in higher productivity.
In the villages under study, established commerce and services are practically not
significant in relation to economical resources production, since they rather small
commercial establishments intended to satisfy local demand. Industrial activity is
practically nonexistent.
III-2
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PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
C) INDUSTRIES AND MAIN POLLUTANTS
No industrial and/or commercial pollutant activity is detected in the four villages under
study. This situation can be corroborated by the results obtained in the characterization
campaign.
In any case, the main source of pollution can be attributed to the agricultural return
waters, wich can carry synthetic organic remnants developed from the use of fertilizers,
herbicides, plaguicides, etc.
D) DRAINAGE AND POTABLE WATER SUBSTRUCTURE DIAGNOSIS
Drinking water
As a source of supply of drinking water, there is a group of deep wells, specifically 2
deep wells in Vicente Guerrero, 3 in Cd. Morelos, 2 in Guadalupe Victoria and one in
Venustiano Carranza with the distribution system:
CONDITION OF SERVICES IN 4 VILLAGES OF MEXICALI VALLEY
POTABLE WATER
Villages
Population
Average
Drinking
Population
1995
endowment
water
Served
l/inhab.d*
Intakes
Guadalupe
13,252
352.63
3700
6,210
Victoria
Venustiano
5,655
346.45
1251
4,767
Carranza
Vicente Guerrero
3,982
346.45
1200
3,223
C.d. Morelos
7,205
346.45
2362
5,782
*source: Ref.2
%
Population
Served
46
84
81
80
As we can see, excluding the case of Guadalupe Victoria, the service coverage by
means of pipe system surpasses 70% and for the Venustiano Carranza population, it
reaches 84%, wich is remarkable, considering they are rural villages. On the other side,
the individual endowment is very high, if we consider that the endowment for cities with
more than 50,000 inhabitants reach 254.6 l/inhabitant. d.
Drainage.
In relation to the drainage and sanitation services, the basic in formation is shown in the
following chart:
III-3
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PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
Villages
Guadalupe
Victoria
Venustiano
Carranza
Vicente
Guerrero
C.d.Morelos
Population
1995
13,252
DRAINAGE SERVICES CONDITION
Discharges
Population
Generated
Benefited
Flow (l/s)
1,957
5744
22
Annual volume
(m3)
693,800
5,655
815
5229
16
504,600
3,982
520
2323
10
315,400
7,205
1,011
3684
23
725,300
As we can see, in spite of the fact that drainage coverage is important, it is still
insufficient, except for Vicente Guerrero. Individual discharges not shed into the
drainage net, are conducted to septic or absorption tanks or in some cases, disposed of
in the open air.
Organic matter inflow, expressed as the concentration of Biochemical Oxygen Demand,
is shown in the following chart, in which a comparison is made between consulted
references and results obtained from the characterization campaign accomplished for
this studio.
ORGANIC MATTER INFLOW IN THE WASTEWATERS OF 4 MEXICALI VALLEY VILLAGES
Villages
Organic
Annual total
Average
Reported
matter inflow
inflow1
concentration
concentration
(Kg./inhab.d) (tonBOD5/year)
calculated
mg/l2(BOD5total
mg/l(BOD5total)
Guadalupe Victoria
0.054
261
376
123
Venustiano Carranza
0.054
111
220
98
Vicente Guerrero
0.054
78
249
254
C.d Morelos
0.054
142
196
322
Sources: 1.-ref.2
2.-SYCMA characterization program 1998
It can be deduced from this, that real concentrations, measured from compound
samples collected from each of the main discharges in the 4 villages, under study, are
different from the expected ones when adopting the 54g/inhab.d of BOD 5 criteria. For
design purposes, it is recommended to are considered to be representative of the
present conditions of each one of the discharge.
Existing treatment systems.
The only village having a treatment system is Ciudad Morelos, a sampling was carried
out on it to complement its functioning diagnosis. The evaluation was accomplished from
the measurements of the total COD and the concentration of total suspended solids.
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PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
Removal percentage was determined to these values and the results are shown in the
following chart:
Parameters/
date
CD MORELOS POND SYSTEM EFFICIENCY
November 27th
Units
Influent
Effluent
Total COD
Total suspended solids
mg/l
mg/l
495
100
Total COD
Total suspended solids
mg/l
mg/l
495
52
Total COD
Total suspended solids
mg/l
mg/l
208
9
November 28th
237
27
November 29th
597
138
72
14
% Removal
efficiency
58.00%
91.00%
52.00%
48.00%
76.78%
80.56%
According to these data, the system efficiency is rather low, since the facultative ponds
are designed regularly, according to Gloyna, for organic matter removal efficiencies
between 80 and 90%, either in terms of the BOD5, or the COD, parameter used in this
case.
In addition, the suspended solid values in the effluent are low, which suggests that
ponds are functioning rather as sediment reservoirs.
E) VOLUMENES OF GENERATED WASTEWATER
Measurement of wastewater discharge volumes, for the villages under study, constitute
a fundamental stage in the planning of systems for treatment and final disposal of
residual liquids.
It has been estimated, for this studio purposes, that in the future and thanks to the
actions flatted to the predicted improvement for the villages mentioned, it can be
established as an approximation, that 75% of water supplied to the village is poured into
the drainage and a maximum caption of 75% of sewage generated in each one of the
villages.
Like, the following calculation can be made for the flows provided for the treatment.
III-5
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
PREDICTED EVOLUTION FOR THE WASTEWATER DISCHARGES IN 4 VILLAGES AT
MEXICALI VALLEY
Villages
Population Endowment Demand m3/d Wastewater
Wastewater
2000
l/inhabitant.
flow m3/d
Flow l/s
Guadalupe Victoria
15,067
250
3,766.75
211808
24.52
Venustiano Carranza
6,429
250
1,607.25
904.07
10.46
Vicente Guerrero
4,527
250
1,131.75
636.60
7.36
C.d. Morelos
8,192
250
2,048.00
1152.00
13.33
Total
34,215
250
8,553.75
4,811.49
55.67
Villages
Population Endowment Demand m3/d Wastewater
Wastewater
2010
l/inhabit
flow m3/d
flow l/s
Guadalupe Victoria
19,476
250
4,869.00
2,738.81
31.7
Venustiano Carranza
8,311,
250
2,077.75
1,168.73
13.53
Vicente Guerrero
5,852
250
1,463.00
822.94
9.52
C.d. Morelos
10,589
250
2,647.25
1,489.08
17.23
Total
44,228
250
11,057.00
6,219.56
71.99
Villages
Population Endowment Demand m3/d Wastewater
Wastewater
2000
l/inhabi.d
flow m3/d
Flow l/s
Guadalupe Victoria
25,175
250
6,293.75
3,640.23
40.97
Venustiano Carranza
10,743
250
2,685.75
1,510.73
17.49
Vicente Guerrero
7,585
250
1,891.25
1,063.83
12.31
Cd. Morelos
13,687
250
3,421.75
1,924.73
22.28
Total
57,170
250
14,292.50
8,039.53
93.05
According to this calculation, the construction of wastewater treatment systems can
follow a modular growth in terms of the increase of both the population and the drainage
substructure, attaining this way a better programming of the required investments. Like
this, it is possible to propose a preliminary construction program, based on the flows and
independently from the treatment processes proposed.
In terms of operation flexibility and response opportunity in respect to the increase of the
contribution flow, the modular capacities wich better adapt to each necessity, are the
ones that correspond to 10 l/s and 15 l/s. This way the suggested growth program is the
following:
Guadalupe Victoria. Construction of 2 initial modules of 15 l/s in 1999-2000 and one
more of 15 l/s for the period 2010 -2020.
Venustiano Carranza. Construction of 2 modules of 10 l/s during 1999-2000 to cover
the necessities until year 2020.
Vicente Guerrero. Construction of one module of 15 l/s during 1999-2000 wich will
cover the requirements in the considered period.
III-6
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
Ciudad Morelos. Construction of the tertiary complement module of 15 l/s in 1999-2000
and another of 10 l/s before year 2010.
Because it is predictable that total coverage of villages will not be reached concerning
drainage service, it is possible to suggest an impulse to the construction of uni or
multifamily treatment systems.
3.2.3 FLOW MEASURE AND CHARACTERIZATION OF WASTEWATER.
In order to determine the main characteristics of wastewater generated in the 4 villages
under study, a measuring and characterization campaign was carried out at their main
discharges between November and December 1998.
A) MEASURE
At each monitoring station, flows measure were carried out every 2 hours, during 24
hours, for 3 alternate days. There are considerable differences between the measured
values and the one reported earlier for year 2000, and they are shown in the following
chart:
Villages
Guadalupe Victoria
Venustiano Carranza
Vicente Guerrero
Cd. Morelos
Total
Q l/s
(measured)
(1998)
(average)
11.92
13.91
4.44
8.66
38.93
Q l/s
(calculated)
(2000)
% Difference
24.52
10.46
7.36
13.30
55.64
48.61
133.4
60.32
65.11
69.96
Such differences are basically because they are both estimations for the future, and the
established percentage as a criteria in the before mentioned chart.
In any case, it is recommended for the final design of the systems to consider a longer
flow campaign to establish more precisely the amounts of wastewater enter to drainage
systems.
B) SAMPLING AND FIELD ANALYSIS
Simultaneously to the flow at selected monitoring stations, six individual samples were
collected each day, at each one of them, at intervals of 4 hours. Part of the collected
III-7
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
sample was used for the field analysis, determining parameters such as: ambient
temperature and sewage temperature, pH value, electrical conductivity, dissolved
oxygen, and additionally, observations related to aesthetic aspects such as color and
odor were made.
C) LABORATORY ANALYSIS
With the remaining volume of the individual samples collected, previously preserved, a
compound sample was integrated in relation to the expense of 24 hours for each station.
The preservation a storing of samples, were carried out through ice preservation, in
order to maintain a temperature close to 40 C.
Results from characterization of sewage, as well as their analysis is shown in a detailed
way in the final report of this study.
3.2.4 PRIMAY REQUIREMENTS OF WATER QUALITY FOR AGRICULTURAL
REUSE.
In the case of the 4 villages under study, it is evident that the nature of their economical
activities must lead to application of the effluent of treated wastewater in the agricultural
irrigation, specifically of crops not intended for the direct consumption to the population
and there fore with less quality requirements.
In this sense, selection of the most appropriate processes must be established in terms
of such requirements. Considering the minimum quality characteristics required by the
crops, the absence of toxic elements must be established both for plants and for
animals, in any concentration, as well as the excessive concentration of salts that affect
soils.
Sodium content is regularly high in treated wastewater, in such a way that it is required
to state the soil use techniques to mitigate the possible problems caused by a high value
of the sodium absorption relation (SAR).
3.2.5. TREATMENT ALTERNATIVES
A).- PRE-SELECTION CRITERIA
The criteria when selecting the operation sequence and the single procedure to make up
the right treatment are based on the comparison of the requirements in space, operation
maintenance and control of the starting inversions, the operating and maintenance
III-8
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PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
investments and the quality. The following chart shows some examples of advantages
and disadvantages of these procedures, relating them to those being studied.
PROCEDURE
TREATMENT PROCEDURE COMPARISONS
ADVANTAGES
DISADVANTAGES
Imhoff tank
Stabilitzation ponds
Wetlands (Vegetable filters,
marjal filters, wetlands)
Trickling filters
Good efficiency in suspended
solids removal.
Low Cost.
The operating and maintenance
requirements are few.
No reagent required
Once in a while maintenance
required
(Sludge and skims)
Low space required
Not generated aesthetic
problems.
Low Cost.
Moderated operating and
maintenance requirements.
High flexibility with organic
loading.
High efficiency to removal
pathogen and helminthes
Effluent reaches quality for
reuse.
Good removal organic material
efficiency.
Accept high organic loading.
Moderated maintenance and
operations requirements.
Good efficiency removal of
nutrients and organics material.
Effluent with possibility to reuse.
Access to procedure control
simplified operating system.
Minimum consumption energy
Initial moderate inversion
The process is adaptable to
available space.
Medium efficacy organic
material removal (40%)
Low flexibility front high load.
It is not possible control
procedure
Effluent can not get, by himself,
the quality reuse
High space requirements
Anaerobial ponds can generate
nasty odors, presence of rats,
flies and mosquitoes.
Susceptible at extreme
weather, it involves mayor
volume of treatment
assignation.
High space requirements
Requirements of sludge
disposal.
High amount of subproducts
The efficiency is lower than
activated sludge.
Generate some aesthetic
inconvenient.
Generally require posttreatment filtration and
pretreatment sedimentation.
B) NATURAL PROCEDURES FOR DISCHARGES TREATMENT WASTEWATER
FOR THE MEXICALI VALLEY POPULATIONS
The CESPM has presented to the COCEF a project related to sanitation systems for
several communities at Mexicali Valley. In this request it is stated: “this project consists
III-9
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
in several ways to improve the waster treatment in Cd. Morelos and other inhabited of
Mexicali Valley.... It will also consider the utilization of vegetation produce in wetlands
like a protein vegetable base. The usage of alternate technology for other countries will
be considered in the setting of the project”.
On the other hand, the observations gotten in those communities make us suppose that
artificial wetlands can produce a feasible alternative. The presence of tule tree and
some other kinds of scrub, in the channels which receive the wastewater in Cd. Morelos,
getting in this way “spontaneous wetlands”. This permits to state that it will be
convenient to set these procedures,
To evaluate if artificial wetlands has an effect on the quality of the wastewater, some
sampling were made, in those two channels were there was scrub. The results show a
positive effect, talking about Venustiano Carranza allows to guaranteethat the efficiency
in removing organic material was of 42% an removing suspended solids was of 71.43
%.
In Vicente Guerrero the removing of organic material reach 45% with a maximum of
68.71 %. On the other hand removing suspended solids goes up to 91.12 % and 83.2%,
which indicates the high possibilities of the system treatment
All this may indicate good results out we can’t establish any statement yet, the results
are significant. The only problem is the extreme weather during winter, to consider for
design.
C) ARTIFICIAL WETLANDS.
The wetland is a system formed by a saturated substratum (sand or grave) vegetation,
water and animal life (micro and macroscopic), which may simulate a natural swamp
and is designed for treatment wastewater. There are 2 kinds:

 FREE SURFACE WETLANDS. These systems typically consist of basin or channels, with
some sort of subsurface barrier to prevent seepage, soil or another suitable medium support
the emergent vegetation, and water at a relatively shallow depth flowing through the unit.
The area is approximately to 50 to 75% higher than submerged wetlands, the water surface
they are also susceptible to weather changes.

 SUBMERGED-BED WETLANDS. It is a constructed wetland with subsurface water flow
typically consists of trench or bed underlain by impermeable material to prevent seepage
and containing a medium that supports the growth of emergent vegetation. The media used
have included rock or crushed stone, gravel and different soils, either alone or in various
combinations.
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PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
The wetland characteristics let them get several geometrical shapes that are adaptable
at any space. The selecting of vegetation is mainly important.
As a secondary treatment, the quality produce for wetlands, let it be able to be used in
any crop, when it is used as tertiary treatment the quality reach permit the use in a
widely kind of crops.
D) PROPOSED ALTERNATIVES
Taking into consideration the population studied, we way conclude that the basic
treatment of wastewater includes natural wetland and stabilization ponds.
There are 5 proposals on criteria, they all are being evaluated taking into consideration
their benefits and the expenses. It is important establish, that Cuidad Morelos has a
rehabilitate treatment system, and the village doesn’t count with disposable land, only
the alternatives evaluated will be the existent treatment system.
The next chart indicates all the proposals.
ALTERNATIVES
Locality
Guadalupe Victoria
Venustiano Carranza
Vicente Guerrero
Ciudad Morelos
I
II
III
IV
V
Imhoff tank and
submerged
wetland
Imhoff tank and
free watersurface wetlands
Pond and free
water-surface
wetlands
Pond and
submerged
wetland
Primary pond and
stabilization pond
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
3.2.6. ANALYSIS AND EVALUATION OF ALTERNATIVES.
For the treatment system selection in order to each locality, were taken into
consideration the goals and the characteristics of the wastewater, the disposable area,
the geographical–physical characteristics of the selected or proposed place, the human
resources, the materials and the investment needed.
The criteria employed was:
 REACH THE SUITABLE EFFLUENT QUALITY TO REUSE IN IRRIGATION.
 THE SELECTED PROCEDURES AND THE EQUIPMENT MUST BE FLEXIBLE AND EASY TO
OPERATE AND MAINTAIN.
 THE PROCEDURE MUST TAKE INTO CONSIDERATION THE WEATHER CODITIONS OF THE
AREA.
 THE ACTIVITY OF THE OPERATOR MUST BE THE LEAST, BECAUSE ALMOST THERE ISN’T
ENOUGH HUMAN RESOURCE.
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PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
 THE MACHINERY MUST HAVE ENOUGH FLEXIBILITY RESPECT MAXIMUM LOADING.
 IT MUST REQUIRE THE LEAST COST POSIBLE.
 THE SPACE MUST BE THE LEAST POSIBLE.
 THE PROLIFERATE NOXIOUS VECTORS MUST BE AVOID.
A) VICENTE GUERRERO, VENUSTIANO CARRANZA AND GUADALUPE VICTORIA
POPULATION
The chart 3.2.6.show the evaluations of different criteria to evaluation of 5 propose
alternatives. The scale is from 1 to 5 and the concepts are the following:
a) Removal of polluting agent (BOD5, TSS, Nitrogen and pathogens).
b) Area required.
c) Operation and maintenance requirements.
d) Control requirements.
e) The environmental conditions susceptibility.
f) Vector presence.
g) Costs.
The chart presents the results contrasting the alternatives, the adding must show the
most convenient one.
CHART 3.2.6 ALTERNATIVE EVALUATIONS
ALTERNATIVES
CONCEPT
Removal BOD5
Removal TSS
Removal Nitrogen
Removal
pathogen
bacteria
Area required
Operating required
Control required
Maintenance required
Physical
conditions
susceptibility
Presence of vectors
Expenses
Totals
I
IMHOFF AND
SUBMERGED
WETLAND
II
III
IMHOFF AND
POND AND
FREE SUFACE FREE SURFACE
WETLAND
WETLAND
IV
POND AND
SUBMERGED
WETLAND
5
5
5
5
5
4
3
2
4
3
2
5
V
PRIMARY POND
AND
STABILIZATON
POND
3
2
4
5
5
5
5
4
5
4
5
4
4
4
5
4
3
2
3
3
3
3
3
4
1
2
3
2
5
4
3
3
2
5
4
52
3
5
48
2
3
33
3
2
36
1
1
26
We can observe the best alternative is Imhoff tank and submerged wetlands, this
alternative presents with the best benefits.
III-12
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
At the same time, the proposed alternatives are evaluated under economical
requirements the best is Imhoff tank and submerged wetlands.
Even the costs of the wetlands submerged are cheaper than the free surface wetlands,
the less susceptibility for the proliferation of noxious vectors make the first one better.
B) REHABILITATION AND IMPROVEMENT OF CD. MORELOS WASTEWATER
TREATMENT SYSTEM.
For Cd. Morelos it is required, for the rehabilitation and improvement of actual treatment
system:
1.-Cleaning the distributing influent channel.
2.-Covering and proofing distributing channel.
3.-Rehabilitation influent Parshall check out, throat and hydraulic jump
4.-Cleaning and deposition in sewer line of the 4 pond and the throwing away of the
waste.
5.-Cleaning and checking of the edges ponds in the 4 systems.
6.-Hydraulic restructure the input and output of 4 basins ponds.(it’s recommendable use
the scheme of rehabilitation Mexicali I pond, as it were say, influent better distribution
and effluent harnessing
7.-Cleaning of the input channel.
EQUIPMENT NEEDED
1. Building up a screaming and grit removal channel parallel to actual distribution
channel.
2. Artificial wetland construction. The principal vegetation will be tule. It must be include
a fast filtering bed to hold algae, and other kind of particle.
3. Parshall installment and the machinery with weirs to measure pond’s flow, at
intermediary points
4. Building and equipment effluent pumping well.
3.2.7. PRELIMINARY COSTS ESTIMATING
This study considers the land cost average $0.78/m 2, due the lands are near habitations
zones, agreement with the No. 41 decree published by the H. XVI Legislature from Baja
California State.
In the next graphics present the behavior of construction cost in the modules 10 l/s and
15 l/s against the volume of wastewater treated. The representing process in this
graphics are submerged wetlands, free surface wetlands and facultative ponds.
III-13
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
TREATMENT SYSTEMS BUILDING COST BEHAVIOUR.
FACULTATIVE POND COST BEHAIVOUR.
ESTIMATED COST
1400000
1200000
1000000
800000
600000
400000
200000
0
86
173
346
518
691
864
1037
1210
1296
1339
3
FLOW m /d
BEHAVIOUR OF BUILDING COST TO FREE SURFACE
WETLANDS IN MEXICALI CITY.
PESOS COST
600000
500000
400000
300000
200000
100000
0
86
173
346
518
691
864
1037
1210
1296
1339
3
FLOW m /d
BEHAVIOUR OF WETLANDS SUBMERGED COSTS.
2000000
1800000
PESOS COST
1600000
1400000
1200000
1000000
800000
600000
400000
200000
0
86.40
172.80 345.60
518.40 691.20 864.00 1036.80 1209.60 1296.00 1338.75
FLOW m3/d
III-14
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.
PURSUIT ACTIONS FOR THE INTEGRAL PROJECT OF SANITATION OF MEXICALI, B.C.
STUDY FOR THE REUSE OF TREATED WASTEWATER OF MEXICALI I AND II
PREFEASIBILITY FOR THE USE OF WETLANDS AT THE MEXICALI VALLEY.
EJECUTIVE SUMMARY
3.2.8. CONCLUSIONS
 Wastewater treatment in Mexicali Valley, can be made under biological and natural
systems, specifically artificial wetlands.
 The results of the alternatives show the order for the recommendable sequences:
1.- Imhoff tank + submerged wetland
2.- Imhoff tank + free surface wetland
3.- Primary pond + submerged wetland.
4.- Primary pond + free surface wetland.
5.- Primary pond + stabilization pond.
 For the primary treatment, the Imhoff tanks are the best option. Because they
present advantages, in construction, operation, control and costs, with respect
primary facultative ponds.
 The best option is for the submerged wetlands, even it is more expensive than the
free surface wetland, factor like less land requirement, less susceptibility of weather
changes, do not favor grow of noxious vectors.
 Since the grades are the best for alternatives I and II, the option is free surface
wetland, it has to take into consideration the inconvenient before mentioned.
 Stabilization ponds are not recommendable, because the wetlands ponds options is
more attractive in terms of effluent quality, operation easiness.
 For Ciudad Morelos an actual pond rehabilitation is needed, as well as a
pretreatment construction and artificial wetland with 15 modules lesser than the other
3 villages.
 Respect construction, all material and human resources are disposable in the
villages.
 The uni or multi familiar modules can be suggested, for communities that present
difficulties in the integration to the drainage systems
III-15
SERVICIOS Y CONSULTORIA PARA EL MEDIO AMBIENTE S.A DE C.V.