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ANAEROBIC DIGESTION FOR WASTEWATER
TREATMENT IN MEXICO: STATE OF THE TECHNOLOGY
OSCAR MONROY*, GRACIELA FAMAÂ , MOÂ NICA MERAZ,
LETICIA MONTOYA and HERVEÂ MACARIE{M
Department of Biotechnology, Universidad Auto noma Metropolitana-Iztapalapa, Apdo. Postal 55-535,Me xico, D.F. 09340 Mexico
(First received 1 July 1998; accepted in revised form 1 July 1999)
AbstractÐDue to the nascent wastewater treatment practice in Mexico there is great opportunity tointroduce anaerobic digestion as the core of the wastewater treatment processes. Nevertheless, thisrequires an understanding of all the technical, economical and ®nancial aspects that limit itsdevelopment. According to the National Water Commission, in 1995 municipal and industrialwastewater were produced at rates of 232 and 168 m3 sÿ1 respectively, but only 20 and 12% of thesevolumes were treated, often with very low e�ciencies. In order to increase the treatment capacity of thecountry, approximately US$ 4515 million managed by the banks for development are supposed to beavailable to invest in environmental projects. Other ®nancing mechanisms exist through treasuryincentives and penalties. Within this situation, anaerobic digestion has grown although not at therequired rate and bigger investments are being made on conventional aerobic and physicochemicaltechnologies. Presently there are in the country 85 anaerobic wastewater treatment plants treating216,295 m3 dÿ1 with an installed volume of 228,551 m3. UASB reactors account for 74% of theinstalled volume and national companies have supplied 76% to the anaerobic market. Properintegration of the anaerobic digestion processes for water recycling and energy recovery has not beenachieved and there is a big need to demonstrate economic and ecological sustainability. # 2000Elsevier Science Ltd. All rights reserved
Key wordsÐanaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-
gas use, treated water reuse
INTRODUCTION
There is a great public concern in Mexico for the
origin and fate of water and wastewater. Due tothis concern and to the recent environmental laws,there has been a great investment in municipal
water supply and wastewater collection and treat-ment (see Table 1).
Municipal wastewater
Since 1988 the growth rate of municipal waste-water treatment plants (WWTP) has been of 102plants or 4.8 m3 sÿ1 per year (Table 2). Despite this
relative high growth rate (compared to the econ-omic growth), the gap between the treated 47 m3
sÿ1 and the produced 232 m3 sÿ1 of sewage is still
very large (Table 1), giving place for advanced andinexpensive technologies.A closer analysis of the small fraction of treated
wastewater will show that out of the 946 municipal
treatment plants, approximately 40% are stabiliz-
ation ponds. The second largest number corre-
sponds to activated sludge plants which together
with oxidation ditches, aerated ponds and trickling
®lters, make up another 40% of the treatment sys-
tems. From these plants, only 755 (79%) are in op-
eration, 41% (312 plants) have BOD removal
e�ciencies higher than 75 and 26% (199 plants)
have an e�ciency lower than 50%. This is because
the treatment systems are of di�erent types as
shown in Fig. 1. Average capacity of these plants is
42 L sÿ1 ranging from 5000 to 1 L sÿ1. The front
columns in Fig. 1 show the distribution of the
plants which are not in operation. It can be seen
that, probably due to overloading conditions, most
of them are stabilization ponds (9% of total) and
primary treatment systems (3% of total). Aerobic
processes account for 30% of the nonoperating fa-
cilities due to lack of aerator's maintenance.
Moreover, very few of them have sludge treatment
facilities, which added to the high operating and
investment costs, make them a nonviable option in
the long term.
Wat. Res. Vol. 34, No. 6, pp. 1803±1816, 2000# 2000 Elsevier Science Ltd. All rights reserved
Printed in Great Britain0043-1354/00/$ - see front matter
1803
www.elsevier.com/locate/watres
PII: S0043-1354(99)00301-2
*Author to whom all correspondence should be addressed;e-mail: [email protected]
{Invited researcher from Institut de Recherche pour leDeveloppement (IRD), France.
Industrial wastewater
According to the National Commission for
Water (CNA), by 1994, industrial wastewater wasproduced at a rate of 168 m3 sÿ1, 12% being treatedin 282 treatment plants, 61% released untreated to
the environment and 27% discharged to sewers.The sugar cane industry generated 39% of thisvolume, 21% the chemical industry, 22% the paper,petrochemical and oil industries and 18% was pro-
duced by other industries.
LEGAL, ECONOMIC AND FINANCIAL ASPECTS
In 1988 the Mexican government issued the
General Law for the Ecological Equilibrium and
Environmental Protection which triggered an
intense activity to match the Mexican industry dis-
charge standards to those of their partners in the
NAFTA (North America Free Trade Agreement).
This activity is characterized by: (a) the continuous
inspection of industrial discharges with consequent
partial or total closures, (b) penalization for the
amount of wastes discharged (CNA, 1993), (c) an
advertised fund availability for any kind of pol-
lution control facilities, (d) hundred of studies for
the preparation of Ecological Guidelines (INE,
1993±1994) and programs for human resources
training (Jime nez, 1995).
Table 1. Drinking water and sewage nets, coverage and growth rate in 1995. MWW=municipal wastewatera
Flow rate (m3 sÿ1) Population covered % Growth rate (% per year)
Drinking water net 272 86.2 4.34 (population based)Total MWW produced 232 ± ±MWW in sewers 120 69 8.47 (population based)MWW treatment 47.6 14.5 14 (plants based)
aSource: CNA (1995±1996).
Table 2. Growth pattern of municipal wastewater treatment plants. n.d.: non determineda
Year No. of plants Treated ¯ow rate (m3 sÿ1) Expected removal (103 kg BOD5 dÿ1)
1988 233 14.0 3021989 256 15.2 3431990 310 19.3 4181991 361 25.1 5411992 577 29.1 6271993 650 34.8 7501994 825 38.4 8301995 946 47.6 n.d.
aExtracted from Sancho (1992) and CNA (1995±1996).
Fig. 1. Operating and nonoperating municipal wastewater treatment plant distribution per type.SP=stabilization ponds, AS=activated sludge, PT=primary treatment, BF=trickling ®lters,AP=aerated ponds, OD=oxidation ditches, IT=Inmho� tank, ZZ=others (biological disks, counter-
¯ow aeration, lemna pond), from CNA (1995±1996); MejõÂ a (1993).
Oscar Monroy et al.1804
The Environmental Budget grew from US$ 6.6
million in 1989 to US$ 78 million in 1992 (Cero n,
1993). Currently, according to the Secretariat of
Ecology (Semarnap), from 1995 to 2000, there will
be an investment in the environmental market of
US$ 4515 million (La Jornada, 1996). These funds
will come from banks for development and from
national and foreign private investments. To our
knowledge these banks do not provide readily avail-
able fresh funds for most of the middle and large
sized industries. For this reason, industries tend to
invest on their own pro®t expense rather than bor-
rowing from banks. Their sel�nancing has been
propelled by charges on COD, SS and wastewater
volume discharged as well as the cost on tap water.
Discharge limits should be gradually reduced all
over the country during the next twelve years to
reach a 20:20 (BOD5:SS) quality for water reuse, as
stated by the guideline NOM-003-ECOL-1997,
recently edicted. NOM-001-ECOL-1996 establishes
30:40 as the maximum permissible limits for pollu-
tants in wastes discharged into super®cial waters.
The guideline NOM-002-ECOL-1996, does not
establish limits for BOD5:SS in e�uents discharged
into urban or municipal sewage systems. These
guidelines take into account the producer's socioe-
conomic level, infrastructure and population size.
E�uents should adequate to particular discharge
limits depending on the discharge site's dilution ca-
pacity and use of water. Treatment processes to
meet the discharge consents are left to the user's
choice.
Cities with larger treatment facilities, turn out to
contract the services from foreign or national pri-vate companies which invest under service contractsto build and operate new or existing facilities under
a BOT (build, operate and transfer) scheme, whilethe government faces the responsibility with thepublic. Contracts can include a total privatization
of the facilities or its recovery by the municipalityupon an agreed number of years. This system pro-vides the cities with wastewater treatment plants at
no initial cost, nevertheless these kind of contractshave been, thus far, di�cult to negotiate due to therisks involved with the long term operation ofplants.
DEVELOPMENT OF ANAEROBIC DIGESTION IN MEXICO
The use of anaerobic digestion (AD) for waste-water treatment started late in Mexico compared tothe European countries or even to North America.The ®rst digester was constructed by 1987 (see Fig.
2). Further development was rather slow since until1991 the rate of digester's construction remainedaround one to four reactors per year. It is only in
1992, with 16 reactors built that a signi®cantgrowth of 400% was achieved. During the two sub-sequent years, the rate of reactor's construction
remained higher than 10 per year, reaching a maxi-mum of 19 in 1993. However, decreased abruptly in1995 due to the economic crisis after a 100% deva-
luation of the peso in December 1994.Since 1996, a recovery has been noticed despite
the reduction of public and private funds availableto solve environmental problems. Presently, 85 full-
Fig. 2. Anaerobic WWTP constructed per type of wastewater (domestic and industrial) and origin oftechnology (national or foreign), by April 1998.
Anaerobic digestion in Mexico 1805
scale reactors are in operation in Mexico. Theirtotal installed volume is 228,551 m3 and they aretreating 216,295 m3 dÿ1 (2.5 m3 sÿ1) wastewater and
590 tons COD per day, which is equivalent to apopulation of 12.3 million, considering 160 L con-sumed per inhabitant per day and 300 mg
COD Lÿ1. These represent 0.62% of the total gen-erated wastewater volume and 3.69% of the treatedwastewater (5.5% of industrial and 2.93% of mu-
nicipal).
Type of wastewater treated
As shown in Fig. 2, the ®rst reactors were built
in Mexico to treat industrial wastewater. Two
years later (1989) however, the ®rst UASB reactor
treating sewage was built as a 50 m3 demon-
stration unit at the campus of the Universidad
Auto noma Metropolitana±Iztapalapa (UAM-I), fol-
lowed shortly in 1990 by two big units of 2200 m3
each, constructed by the government (Table 5, reac-
tors 2 and 3).
It should be noted that contrary to Europe and
North America but similarly to Brazil, China,
Colombia and India, anaerobic treatment has been
applied in Mexico not only to industrial wastewater
but also to sewage, due to the warm weather and
Fig. 3. Distribution of digesters by April 1998 per number and volume, per type of wastewater and ori-gin of technology.
Fig. 4. Distribution of anaerobic digesters in Mexican industry, by April 1998.
Oscar Monroy et al.1806
limited economical resources. Indeed, 40% of allreactors (almost 40% in volume) are treating dom-estic wastewater (Fig. 3). These reactors include the
biggest UASB built in the world (83,700 m3, 36%of the total reactor's volume) which treat bothindustrial and municipal e�uents and should be
extended to 133,920 m3 in the future (Table 5, reac-tor 7). Most of the reactors treating domestic e�u-ents however are very small, since 32% of them (11
plants) have volumes less than 50 m3, 29% (10plants) have volumes between 50 and 100 m3 andonly 9% (3 plants) have a volume greater than
350 m3.Most of the industrial e�uents treated by AD in
Mexico are typical to this technology over theworld (malt, brewery, dairy and cheese, soft drinks,
yeast, paper, food, potato and fruit processingindustries and pig farms) predominating the brew-ery sector which includes 25.4% of the industrial
reactors (Fig. 4). Nevertheless, some e�uentscharacteristic of local activities like wet co�ee pro-cessing which is seldom treated in the world by AD
are being treated in Mexico (Table 4, reactors 2, 7,35, 37, 38, 42, 51).It is important to notice the absence of anaerobic
reactors in the sugar cane industry despite the dis-
charged volume and their incipient presence in thechemical industry, through two plants treatingwastewater containing dimethyltherephthalate and
therephthalic acid. Research has been done withthis two types of e�uents to improve e�ciencies bysupplementing nutrients and reducing inhibition
(Dura n et al., 1991; Espinosa et al., 1995; Fajardoet al., 1997). Nevertheless, the economic di�cultiesand the lack of development programs faced by the
sugar cane industry will not allow further develop-ment into this ®eld in the near future. The situationcould be di�erent in the case of the chemical indus-try.
Source of the technology
Both national and foreign technologies have been
applied in Mexico. Nevertheless, until 1991, onlyreactors based on local technologies were built (Fig.2). The application of the technology and construc-tion of these units, opened the doors to the inter-
national anaerobic market traders. Leader
companies like the Dutch Biothane and Paques, the
Canadian ADI and the Cuban CENIC, built 20
plants within the 1992±1993 period. These plants
represent 41.5% of the total installed volume
(95,000 m3) and 23.5% of all the plants and are
treating 46% of the COD removed by AD (Tables
4 and 5 and Fig. 3).
Their contribution has declined considerably due
to the previously mentioned economic constraint, as
can be seen in Fig. 2. It is possible to see for
instance that after selling seven plants in two years,
Paques has only built a new plant and increased the
capacity of another one (Table 4, reactors 13 and
34) in the subsequent ®ve years. In the same way,
ADI has only expanded the plant built in 1992
(Table 4, reactor 17). Biothane, with ®ve reactors
sold since 1994 seems to have faced the economical
restraint in a better way, however, four reactors
belong to the same client, the Modelo brewery
(Table 4, reactors 46, 47, 48, 49), which had already
contracted Biothane services before (Table 4, reac-
tors 22, 23 and 24). This foreign introduction was
limited to the treatment of a narrow range of indus-
trial e�uents mostly those from breweries, paper
and yeast factories, whose wastewater are well
known and do not require complex and costly treat-
ment feasibility studies (Fig. 4).
From all the local technologies applied, the one
developed by the UAM-UNAM research groups,
commercialized by Imasa, EnergõÂ a y EcologõÂ a,
Forza, DescontaminAccio n, Tacsa, GTSA, Proesa
and IBTech, has received the best acceptation with
39 UASB reactors built (totaling 40,982 m3). For
some projects, IMASA, EnergõÂ a y EcologõÂ a and
IBTech have even competed successfully with
foreign companies (Noyola and Monroy, 1994).
Also emerging are similar technologies developed
by researchers of the Universidad de Yucata n, that
make up 7 reactors treating industrial wastewater
and totaling 2,592 m3 (MaganÄ a and MaganÄ a, 1996),
commercialized in this case by PYSA. Those devel-
oped by Semarnap, that account for 6 reactors
treating domestic wastewater totaling 88,261 m3
(RodrõÂ guez and Altamirano, 1995) and by AITA,
S.C., for the co�ee processing industries with 4
Table 3. Type of reactors constructed in Mexico related to the type of wastewater treated and the origin of technology
Type of reactor Up¯ow ®lter Hybrid Low ratea Modi®ed Chinese EGSB UASB
Reactors (in number) (%) 4.76 16.5 2.35 1.18 2.35 71.8Reactors (in volume) (%) 0.34 1.75 23 0.01 1.06 73.8Reactors built by national companies (%) 75 100 50 100 100 70.5
% of reactors treatingIndustrial waste waters 50 93 100 100 100 49Municipal waste waters 50 7.14 0 0 0 51
aIncludes ADI-BVF and lagoons.
Anaerobic digestion in Mexico 1807
Table
4.Anaerobic
digesters
treatingindustrialwastew
aterin
Mexico
Reactor
number
Yearof
construction/
actualstate
Location
Designer/
constructora
Reactor
typeb/
volume
(m3)
Typeof
wastew
ater
Treated
¯ow
rate
(m3dÿ1)
COD
(mgLÿ1)
Pretreatm
ent
Operating
temperature
(8C)
Bvb
(kgCOD
m3dÿ1)
HRTb
(days)
COD
removal
(%)
Posttreatm
ent
Treated
wateruse/
discharge
Biogas
production
(m3dÿ1)/use
Sludge
treatm
ent
Sludge
use/disposal
11987in
operation
Celaya,
Guanajuato
IPN
108
Lubricants
(mechanical)
432
700
None
20
2.8
0.25
99.9
Aerobic
reactors
Recycled
toprocess
Vented
None
±
21988,in
operation
Bola
deOro
Coatepec,Ver.
Inireb
AF/250
Wet
co�ee
processing
22.5
5000
Heatingtank
35
0.45
11
97
(BOD)
Settler,sand
®lter
Toriver
basin
Vented
Sundrying
Fertilizer
31991,in
operation
Protapsa,
Guanajuato
IPN
UASB/4.5
Food
18
1000
None
38
40.25
80
Land
in®ltration
Wellinjection
Vented
None
±
41991,in
operation
Moulinex,
Guanajuato
IPN
UASB/4.5
Industrial
domestic
goods
18
700
Grease
interceptor
tank
38
2.8
0.25
97
Aerobic
bio®lter
Watering
Vented
None
±
51991,in
operation
CentraldeMalta
S.A.deC.V.,
Puebla
Imasa
UASB/2400
Malting
3800
1700
Screening,grit
chamber,
homogenization
30
2.69
0.63
77
Activated
sludge,
chlorination
Toriver
basin
Flaredup
None
Toland
61992,in
operation
CuauÂhtemoc
Moctezuma,S.A
.deC.V.Toluca,
Edo.deMe xico
Imasa
UASB/480
Brewery
9072
4056
Screening,
primary
settler,
homogenization
tank
25±30
7.66
0.53
80
Activated
sludge,
chlorination
Toriver
basin
6480¯aredup
Thickening,
anaerobic
digestion,®lter
press
Fertilizer
71992,in
operation
Tlapexcatl,
Veracruz
Cirad
(National)
Hybrid/10
Wet
co�ee
Processing
3±4
3000±6000
Primary
settler,
¯otation
18±20
32.5±3.3
70
Aeration,sand
®lter
Toriver
basin
7.7/C
ooking
facilities
Sundrying
Fertilizer
81992,in
operation
CORP.BIM
BO,
Planta
Barcel,
Edo.deMex.
EnergõÂ a
yEcologõÂ a
UASB/300
Bakeryand
snacks
605
2119
DAF,grit
chamber
26
4.27
0.5
85
Aerobic
biodisc,
chlorination
Watering
Vented
None
±
91992,
inoperation
CuauÂhtemoc
Moctezuma,S.A
.deC.V.Tecate,
B.C.
Paques
UASB/
2�
700
Brewery
3100
5100
Screening,
primary
settler
acidi®cationtank
30±32
11.3
0.45
85
Activated
sludge,
chlorination
Toriver
basin
3000¯aredup
Anaerobic
digestion,band
®lter
Sold
as
inoculum
10
1992,in
operation
CuauÂhtemoc
Moctezuma,S.A
.deC.V.
Guadalajara,Jal.
Paques
UASB/
2�
925
Brewery
5600
4200
Screening,
primary
settler,
acidi®cationtank
30±32
12.71
0.33
85
Activated
sludge,
chlorination
Tosewer
5900¯aredup
Anaerobic
digestion,band
®lter
Sold
as
inoculum
11
1992,in
operation
Jugosdel
Valle,
MexicoCity
Paques
UASB/380
Fruitpacking
1140
3700
Screening,
acidi®cationtank
30
11.21
0.33
80
Aerobic
biodisc,
secondary
settler,
chlorination
Tosewer
1800¯aredup
None
Sold
as
inoculum
12
1992,in
operation
Kim
berly
Clark
Orizaba,Veracruz
Paques
UASB/1320
Paper
factory
2200
9160
DAF,
Acidi®cationtank
30±40
15.26
0.6
85
None
Tosewer
8500
boiler
None
Sold
as
inoculum
13
1992,in
operation
Unipak,Morelos
Paques
UASB/190
Paper
factory
650
4000±6000
DAF,
acidi®cationtank
35
13±20
0.29
60
H2Soxidation
tank
Tosewer
1000¯aredup
None
Land®ll
extention
1998,in
operation
UASB/100
250
10±15
0.4
14
1992,in
operation
Embotelladora
de
Campeche,
Camp.PYSA
/user
Hybrid/250
Softdrinks
350
4574
Screening,
neutralization,
homogenization
26
6.4
0.72
85
Activated
sludge,
chlorination
Wellinjection
Iron®ltration
andvented
Drying
Fertilizer
15
1992,in
operation
Embotelladora
del
Caribe,
CancuÂn,
Q.R
.
PYSA
/user
Hybrid/320
Softdrinks
475
3864
Screening,
neutralization,
homogenization
30
5.73
0.7
85
Activated
sludge,
chlorination
Wellinjection
Iron®ltration
andvented
Drying
Fertilizer
16
1992,in
operation
Embotelladora
de
Chetumal,Q.
Roo.
PYSA
/user
Hybrid/160
Softdrinks
155
3500
Screening,
neutralization,
homogenization
28
3.4
185
Activated
sludge,
chlorination
Wellinjection
Iron®ltration
andvented
Drying
Fertilizer
17
1992,in
operation
Toluca,Estadode
Me xico
ADI
ADI-BVF/
2�
14250
Yeast
3400
23000
Homogenization
tank,heating
35
1.6
14
62
(COD)
Aerobic
SBR
Tosewer
30000
None
None
Oscar Monroy et al.1808
Table
4(continued
)
Reactor
number
Yearof
construction/
actualstate
Location
Designer/
constructora
Reactor
typeb/
volume
(m3)
Typeof
wastew
ater
Treated
¯ow
rate
(m3dÿ1)
COD
(mgLÿ1)
Pretreatm
ent
Operating
temperature
(8C)
Bvb
(kgCOD
m3dÿ1)
HRTb
(days)
COD
removal
(%)
Posttreatm
ent
Treated
wateruse/
discharge
Biogas
production
(m3dÿ1)/use
Sludge
treatm
ent
Sludge
use/disposal
17
extention
1996,
inoperation
Toluca,Estadode
Me xico
ADI
ADI-BVF
20000
35
1.6
14
89(BOD)
Boiler
18
1992,in
operation
ElSauzCortazar,
Guanajuato
UAM-Ic/U
serLagoonfed
asUASB/
4000
Cheese
500
4430
Grease
interceptor
tank
26
0.55
885
Aerobic
and
waterhyacinth
lagoons
Irrigation
Vented
Noneed
Noneed
19
1993,in
operation
LaCaperucita
Quere taro
UAM-Ic/U
ser
UASB/
2�
88.4
Cheese
88
1874
Grease
andsolid
tramps,
homogenization
tank,DAF
29
0.94
275
Sand®lter,
chlorination
Irrigation
Vented
None
None
20
1993,in
operation
LIC
ONSA
San
Antonio
dela
Isla,Edo.de
Me xico
Tacsa
Hybrid/172
Milkrehydration
345
2132
Homogenization,
grease
interceptor,
neutralization
tank
18
4.26
0.5
75d
Activated
sludge
Tosewer
222Vented
None
Toland®ll
21
1993shut-
down
Liconsa
San
Isidro,Morelos
Forza
UASB/85
Milkrehydration
260
2032
Neutralization,
gritchamber
24
6.21
0.33
75
Activated
sludge
Watering
138.6
vented
None
Toland®ll
22
1993,in
operation
CervecerõÂ a
ModeloCiudad
ObregoÂn,Sonora.
Biothane
UASB/1700
Brewery
1800
7000
Screening,
homogenization
tank
32.4
7.45
0.94
85
Extended
aeration,
activatedsludge
Tosewer
Boiler
Storagetank
Sold
as
inoculum
23
1993,in
operation
CervecerõÂ a
del
Tro pico,
Tuxtepec,Oax.
Biothane
UASB/3000
Brewery
3816
7000
Screening,
homogenization
tank
35
8.9
0.78
85
Activated
sludge
Tosewer
Boiler
Storagetank
Sold
as
inoculum
24
1993,in
operation
CervecerõÂ a
Zacatecas,Zac.
Biothane
UASB/5000
Brewery
5016
6849
Screening,
homogenization
tank
30
6.87
0.99
85
Extended
aeration,
activatedsludge
Tosewer
Boiler
Storagetank
Sold
as
inoculum
25
1993,in
operation
Imexa,Puebla
Biothane
UASB/500
Yeast
221
17000
Homogenization
tank
32
7.52
2.26
75
None
Toriver
basin
Flaredup
Storagetank
Sold
as
inoculum
26
1993,in
operation
PetrocelTampico,
Tamaulipas
Biothane
UASB/
2�
2400
Petrochem
ical
(dim
ethyl-
terephthalate)
2028
18500
Screening,
homogenization
tank
30.4
7.5
2.37
95
Extended
aeration,
activatedsludge
Tosea
Flaredup
Storagetank
Sold
as
inoculum
27
1993,in
operation
CuauÂhtemoc
MoctezumaS.A
.deC.V.Navojoa,
Sonora
Imasa
UASB/1816
Brewery
5356
2690
Screening,
primary
settler,
homogenization
tank
25±35
7.93
0.34
80
Activated
sludge,
chlorination
±Flaredup
Thickening,
aerobic
digestion,
®lter
press
±
28
1993,in
operation
CuauÂhtemoc
MoctezumaS.A
.deC.V.
Monterrey,Nvo.
Leo n
Paques
UASB/2850
Brewery
13825
3000
Screening,
primary
settler,
homogenization,
acidi®cation
38
14.55
0.21
75
Activated
sludge,
chlorination
Tosewer
10600¯aredup
Thickening,
aerobic
digestion,
band®lter
Sold
as
inoculum
29
1993,in
operation
Empaques
Modernos,
Guadalajara,Jal.
Paques
UASB/715
Paper
factory
2200
4500
DAF,
acidi®cationtank
30±40
13.84
0.32
70
Activated
sludge
Reusedand
discharged
tosewer
3000¯aredup
±Sold
as
inoculum
30
1994,in
operation
Rancho``San
Francisco''TeraÂn,
NuevoLeo n
EnergõÂ a
yEcologõÂ a
UASB/191
Pig
farm
140
5828
Screening,grit
chamber,settler,
homogenization
20
4.28
1.36
70
±±
±±
±
31
1994,in
operation
Embotelladora
``LaBufa'',
Zacatecas
PYSA
/user
Hybrid/332
Softdrinks
259
9700
Screening,
neutralization,
homogenization
30
7.56
1.3
80
Activated
sludge,
chlorination
Wellinjection
Flaredup
Press
®lter
Fertilizer
32
1994,in
operation
Embotelladora
del
Suerste,
Me rida,
Yuc.
PYSA
/user
Hybrid/760
Softdrinks
691
4250
Screening,
neutralization,
homogenization
28
3.86
1.1
90
Activated
sludge,
chlorination
Wellinjection
Iron®ltered
andvented
Drying
Fertilizer
33
1994,in
operation
Liconsa
Tla huac,
MexicoCity
Tacsa
UASB/945
Milkrehydration
1210
3000
Grease
interceptor
tank,
neutralization
20
3.85
0.78
70
Activated
sludge,
disinfection
Watering
889vented
None
±
(continued
onnextpage)
Anaerobic digestion in Mexico 1809
Table
4(continued
)
Reactor
number
Yearof
construction/
actualstate
Location
Designer/
constructora
Reactor
typeb/
volume
(m3)
Typeof
wastew
ater
Treated
¯ow
rate
(m3dÿ1)
COD
(mgLÿ1)
Pretreatm
ent
Operating
temperature
(8C)
Bvb
(kgCOD
m3dÿ1)
HRTb
(days)
COD
removal
(%)
Posttreatm
ent
Treated
wateruse/
discharge
Biogas
production
(m3dÿ1)/use
Sludge
treatm
ent
Sludge
use/disposal
34
1996,in
operation
Jumex/La
CostenÄa
Tulpetlac,
Edo.de
Me xico
Paques
UASB/1450
Fruitandchilli
processing
4320
5500
Screening,
homogenization,
DAFacidi®cation
tank
30
13
0.33
90
Activated
sludge,
chlorination
inverse
osm
osis
Recycled
toprocess
10000boiler
None
Sold
as
inoculum
35
1995,in
operation
``Solidaridad
Cafetera
Saban Äa'',
Huatusco,Ver.
AIT
A,S.C.
Hybrid/
2�
40
Wet
co�ee
processing
60
3000±6000
Primary
settler
¯otation
18±20
31.5
75
Lagoon,sand
®lter
Toriver
basin
96¯aredup
Noneed
±
36
1995,in
operation
Granja
porcina
``ElOlvido''
Atzala n,Veracruz
AIT
A,S.C.
Modi®ed
Chinese/30
Pig
farm
36000±8000
None
22
0.6±0.8
10
85
Lagoon
Toriver
basin
20cooking
facilities
None
Fertilizer
37
1996,in
operation
Bene®cio``Prof.
Manuel
Sedas'',
Huatusco,Ver.
AIT
A,S.C.
Hybrid/
2�
225
Wet
co�ee
processing
375
2250
Primary
settler
17±19
1.875
1.2
73
Lagoon,sand
®lter
Toriver
basin
204¯aredup
Noneed
±
38
1996,in
operation
Bene®cio``Vicente
Guerrero'',
Misantla,Ver.
AIT
A,S.C
Hybrid/
2�
50
Wet
co�ee
Processing
50
1500±2500
Primary
settler
18±20
1.83
260
Lagoon,sand
®lter
Toriver
basin
47¯aredup
Noneed
±
39
1996,in
operation
ElYucateco
Me rida,Yucata n
PYSA
/user
Hybrid/10
Condim
ents
processing
4.55
1574
Screen
28
0.71
2.2
96
Chlorination
Wellinjection
Vented
Anaerobic
digestion
Toland®ll
40
1996,in
operation
CPC
AranciaSan
Juandel
RõÂ o,
Qro.
Biothane
UASB/1100
Corn
starch
2700
5060
Watercooling
40
12.4
0.4
88
None
Tosewer
Flaredup
None
None
41
1996in
start-
up
RIC
OLIN
OSan
LuisPotosõÂ ,SLP
IBTech
Hybrid/
2�
200
Candyfactory
173
23,360
Screen,
homogenization
37
10
2.3
85d
Activated
sludge,
®ltration,
chlorination
Toriver
basin
1700¯aredup
Press
®lter
Toland®ll
42
1997start-upBene®cio``Roma''
EmilianoZapata,
Ver.
Biotec
AF/400
Wet
co�ee
processing
57
4000±7000
(BOD)
Heatingtank
20
1.5±2
7±10
>90d
Filtration
Tosewer
Vented
None
None
43
1997,in
construction
ACATEX
Texmelucan,
Puebla
II-U
NAM/
user
EGSB/2332
Textile
industry
1500
2000
Screening,
sedim
entation,
homogeneization
20
1.33
1.5
80d
Anaerobic
lagoon,aerobic
reactor,
sedim
entation
lagoon
Toriver
basin
Vented
Drying
Toland®ll
44
1997start-upAtlaÂntidadel
Sur
Me rida,Yucata n
II-U
NAM/
user
EGSB/80
Sea
foodfactory
60
2000
Screening,grit
chamber
27
1.5
1.3
80d
Aerobic
reactor,
sedim
entation,
chlorination
Wellinjection
Vented
Drying
Fertilizer
45
1997in
construction
Industria
Refresquera
Me rida,Yucata n
PYSA
/user
Hybrid/760
Softdrinks
691
4250
Screen,
neutralization,
homogenization
28
3.86
1.1
90
Activated
sludge,
chlorination
Wellinjection
Iron®ltered
andvented
Drying
Fertilizer
46
1998in
construction
CervecerõÂ a
ModeloMexico
City
Biothane
UASB/
3�
3000
Brewery
5143
6500
Screening
40
3.7
1.75
90d
Activated
sludge
Tosewer
Boiler
None
None
47
1998in
construction
CervecerõÂ a
ModeloTorreo n,
Coah.
Biothane
UASB/
2�
1700
Brewery
1944
6500
Screening
40
3.71
1.75
90d
Activated
sludge
Tosewer
Boiler
None
None
48
1998,in
construction
CervecerõÂ a
Modelo
Guadalajara,Jal.
Biothane
UASB/
2�
2500
Brewery
2856
6500
Screening
40
3.71
1.75
90d
Activated
sludge
Tosewer
Boiler
None
None
49
1998,in
construction
CervecerõÂ a
Modelo
MazatlaÂn,Sin.
Biothane
UASB/
2�
1300
Brewery
1512
6500
Screening
40
3.78
1.72
90d
Activated
sludge
Tosewer
Boiler
None
None
Oscar Monroy et al.1810
reactors totaling 740 m3 (Castillo et al., 1993).Contrary to what happened in Colombia and
Brazil (Borzacconi et al., 1995), some Mexicancompanies have demonstrated the capacity to con-struct large reactors and apply the technology to
the cheese and co�ee industries wastewater, whichhave not been treated before by foreign companies(Fig. 4).
The main di�erences between the national andforeign technologies are the gravity feeding systemand the local construction materials, pipes and
mechanical equipment, used con®dently by local®rms, opposed to the pumping feeding system andthe imported items used by the foreign companies.These di�erences have been re¯ected in the cost for
a particular solution.
Type of reactors applied
Six types of reactors have been applied in thecountry: up¯ow anaerobic ®lters, low rate reactors,modi®ed Chinese, up¯ow anaerobic sludge bed
(UASB), hybrid (UASB reactor with inert supportat the top) and expanded granular sludge bed(EGSB) reactors (see Table 3). However the domi-
nating technology is the UASB con®guration, con-sidering both number and volume, independentlyof the origin of the technology. This is probably a
consequence of the construction simplicity and thelow cost associated to the absence of packing ma-terial.Except in one case (Table 5, plant No. 17), all
anaerobic ®lters and hybrid reactors have beenbuilt by national companies to treat industrial aswell as domestic e�uents. Contrary to what could
be expected, only one Chinese reactor and two lowrate reactors have been constructed. More surpris-ingly, 92% of the volume of this last type of diges-
ter corresponds to one sole plant built by ADI(Table 4, plant No. 17). This single plant represents21% of the total digester's volume installed in
Mexico. In fact, this plant plus the RõÂ o Blanco one(Table 5, plant No. 7) make up almost 58% of thetotal reactor's volume of the country.Finally, the recent introduction of the EGSB
reactors must be emphasized since these reactorsare one of the latest developments in AD. The de-sign applied in Mexico, is a local technology devel-
oped in order to solve some problems observedwith the conventional UASB reactors, during thetreatment of waste waters rich in toxic compounds
such as azo dyes or ammonia (Table 4, plants 43and 44, respectively).
Operation temperature
Most of the plants built in Mexico operate at en-vironmental temperature, which correspond to the
lower level of the mesophilic range (18±308C).Wastewater heating or cooling to reach the opti-mum temperature (35±408C) is only applied in afew plants (Table 4, reactors 2, 17, 40, 42, 50).
Table
4(continued
)
Reactor
number
Yearof
construction/
actualstate
Location
Designer/
constructora
Reactor
typeb/
volume
(m3)
Typeof
wastew
ater
Treated
¯ow
rate
(m3dÿ1)
COD
(mgLÿ1)
Pretreatm
ent
Operating
temperature
(8C)
Bvb
(kgCOD
m3dÿ1)
HRTb
(days)
COD
removal
(%)
Posttreatm
ent
Treated
wateruse/
discharge
Biogas
production
(m3dÿ1)/use
Sludge
treatm
ent
Sludge
use/disposal
50
1998in
construction
Tem
exCosoleacaque,
Veracruz
IBTechc/userUASB/20808
Chem
ical
(Terephthalic
acid)
5000±
6000
10000±15000
Solidstramp,
homogenization,
watercooling
35±40
2±3
3±4
60d
minim
um
Activated
sludge
Toriver
basin
20000±25000
Boiler
None
Toland®ll
51
1998,in
construction
Bene®ciodecafeÂ
``Cerro
de
Cintepec''
Catemaco,
Veracruz
AIT
A,S.C.
UASB/110
Wet
co�ee
processing
29±43
8000±120,000
Primarysettler
20
42.5±3.8
83d
Aspertionand
lagoon
Toriver
basin
120co�ee
dryers
Noneed
Noneed
aBiothaneisrepresentedin
MexicobyTecnologõÂ a
Intercontinental,Paques
byAtlatec,
thecompaniesIm
asa,EnergõÂ a
yEcologõ a,Tacsa,Forza,GTSA,DescontaminaAccio n,ProesaandIB
tech
commercialize
thetech-
nologydeveloped
byUAM-U
NAM.
bAF:anaerobic
®lter;UASB:up¯ow
anaerobic
sludgeblanket
reactor;EGSB:expanded
granularsludgebed
reactor;ADI-BVF:low-rate
up¯ow
sludgeblanket
process;Bv:organic
loadingrate;HRT:hydraulicreten-
tiontime;
DAF:dissolved
air¯otation.
c Redesigned
from
existingfacilities.
dDesigndata.
Anaerobic digestion in Mexico 1811
Table
5.Anaerobic
digesters
treatingmunicipalwastew
aterin
Mexico
Reactor
number
Yearof
construction/
actualstate
Location
Designer/
constructora
Reactor
typeb/
volume
(m3)
Treated
volume
(m3dÿ1)
COD
(mgLÿ1)
Pretreatm
ent
Operating
temperature
(8C)
Bv
(kgCOD
m3dÿ1)
HRT
(h)
COD
removal
(%)
Posttreatm
ent
Treated
wateruse/
discharge
Biogas
production
(m3dÿ1)/
use
Sludge
treatm
ent
Sludgeuse/
disposal
11989,in
operation
UAM-I,Mexico
City
Descontamin±Accio n
UASB/50
56
365
Screenig,gritchamber
32
0.4
21.5
70
None
Tosewer
Vented
None
None
21990,in
operation
Tepeyanco-
Atlamaxac,
Tlaxcala
Sedue
(National)
UASB/2200
2592
600
Screenig,gritchamber
20
0.7
20.3
75±80
(BOD)
Aerobic
andhyacinth
lagoons
±Vented
Drying
±
31990
Quiroga,
Michoaca n
Sedue
(National)
UASB/2200
2592
600
Screening,grit
chamber
20
0.7
20.3
75±80
(BOD)
±±
±Drying
±
41991,in
operation
Ingenio
Puga
Nayarit
National
UASB/75
86
800
Screening,grit
chamber
23
0.9
20.8
80±85
(BOD)
±±
±Drying
±
51992,shutdown
Vitocrista
CubiertosEstado
deMe xico
Forza
UASB/4.25
17
458
Screeninggritchamber
20
1.83
670
UV
disinfection,
anoxic
reactor
Reusedin
toilet
1.4
vented
None
Land®ll
61992,in
operation
CentroCampestre
Ecolo gico
``Asturiano'',
Morelos
EnergõÂ a
yEcologõÂ a
UASB/21.6
87
500
Homogenizationtank
20
26
75
Slow
®ltration
Watering
Vented
±±
71992±1994,start-
up
FideicomisoAlto
RõÂ o
Blanco
Ixtaczoquitla n,
Ver.
Sedue/
Gutie rrezdeVelasco
(National)
UASB/5�
16740
108,000
2400b
Screening,grit
chamber
22.5
318.6
80c
None
Toriver
basin
54000
¯aredup
Incineration
project
Sold
as
inoculum
81993,in
operation
Acatipla,Morelos
Forza
UASB/130
519
550
Screening,grit
chamber
21
2.2
675
Filtrationand
disinfection
Irrigation
38.5
vented
None
Land®ll
91993,in
operation
GrupoBeta
CentroComercial
Forza
UASB/14
47
500
None
28
1.7
775
Filtrationand
disinfection
Tosewer
3±17
vented
None
Land®ll
10
1993,in
operation
Tlalpuente,Edo.
deMe xico
Forza
UASB/2,17
9500
None
20
26
70
Disinfection
Fishculture
Vented
None
None
11
1993,in
operation
Cooporativo
TelevisaSanta
Fe ,
MexicoCity
EnergõÂ a
yEcologõÂ a
UASB/48.4
174
500
Gritchamber,
homogenizationtank
20
1.8
6.6
95
Anoxic
andaerobic
submerged
®lters,fast
®ltration,chlorination
Irrigation
andcleaning
Vented
Sludgetank
±
12
1993,in
operation
Huatecalco
TlaltizapaÂn,
Morelos
EnergõÂ a
yEcologõÂ a
UASB/105
420
500
Screening,grit
chamber
20
26
75
Slow
®ltration,
chlorination
±Vented
±±
13
1993,in
operation
Hotel``Las
Quintas''Morelos
EnergõÂ a
yEcologõÂ a
UASB/25
86
590
Grease
interceptor
tank,screen,
homogenization,
trituration
20
2.04
790
Aerobic
submerged
®lter,sedim
entation,
chlorination
Irrigation
Vented
Sludgetank
±
14
1993,in
operation
``LaParota''
Tem
ixco,Morelos
EnergõÂ a
yEcologõÂ a
UASB/87
346
500
Screen,gritchamber,
homogenizationtank
20
26
75
Slow
®ltration,
chlorination
Irrigation
Vented
Sludgetank
±
15
1993,in
operation
TicumaÂn,Morelos
EnergõÂ a
yEcologõÂ a
UASB(m
odi®ed
Imho�tank)/339
272
533
Screen,gritchamber,
homogenizationtank
20
0.43
30
70
Secondary
settler,
chlorination
±Vented
±±
16
1994,in
operation
Sedena,Nayarit
National
AF/95
112
550
±25
0.65
20.3
50
±±
±±
±17
1994,in
operation
ClubdeTenis
Tepepan,Mexico
City
Cenic
(Cuba)
AF/24
27
±±
20
±21
±Activatedcarbonand
sand®ltration,
chlorination
±±
±±
18
1994,in
operation
Conjunto
habitacionalSan
JoseÂIturbide,
Gto.
GTSA/Sabbia,S.A
.de
C.V.
UASB/100
200
500
Screening
20±25
112
70±80
Aerobic
submerged
®lter,secondary
settler,chlorination
Watering
23.25
vented
None
To
cultivation
land
19
1994,in
operation
``Frac.
Villasde
Vista
Hermosa''
Toluca,Edo.de
Me xico
GTSA
UASB
50
375
Screening
10±20
0.75
12
80±85
Secondary
settler,
chlorination
Watering
13vented
None
Togardens
20
1994,in
operation
NEPSA,Mexico
City
GTSA
UASB/50
100
375
Screening
20±25
0.75
12
80
Rapid
sand®lter
Watering
23vented
±Land®ll
Oscar Monroy et al.1812
Table
5(continued
)
Reactor
number
Yearof
construction/
actualstate
Location
Designer/
constructora
Reactor
typeb/
volume
(m3)
Treated
volume
(m3dÿ1)
COD
(mgLÿ1)
Pretreatm
ent
Operating
temperature
(8C)
Bv
(kgCOD
m3dÿ1)
HRT
(h)
COD
removal
(%)
Posttreatm
ent
Treated
wateruse/
discharge
Biogas
production
(m3dÿ1)/
use
Sludge
treatm
ent
Sludgeuse/
disposal
21
1994,in
operation
Unidad
habitacional
militardePuerto
JuaÂrez,
CancuÂn,
Q.R
.
(National)
UASB/43.2
86
200
(BOD)
Screen,pumpstation,
homogenizationtank
20
0.4
12
80±85
(BOD)
Rapid
sand®lter,
chlorination
Watering
±Drying
±
22
1994,in
operation
Unidad
habitacional
militarde
Champoto n,
Campeche
(National)
UASB/43.2
86
±Screen,pumpstation,
homogenizationtank
20
0.4
12
±Rapid
sand®lter,
chlorination
Watering
±Drying
±
23
1995,in
operation
Ixtepec,Oaxaca
EnergõÂ a
yEcologõÂ a
UASB/75
225
280
Screen,gritchamber,
grease
interceptor
tank,homogenization
20
0.8
870
Secondary
settler,
chlorination
Watering
2.8
vented
±Soil
fertilizer
24
1995start-up
ElSabino,
Chiapas
EnergõÂ a
yEcologõÂ a
UASB/89.6
276
280
Screen,gritchamber,
grease
interceptor
tank,homogenization
20
0.8
870
Secondary
settler,
chlorination,trickling
®lter
Watering
3.4
vented
±Soil
fertilizer
25
1995,in
operation
Esperanza,
Sonora
EnergõÂ a
yEcologõÂ a
UASB/135.36
406
300
Screen,gritchamber,
grease
interceptor
tank,homogenization
20
0.8
870
Secondary
settler,
chlorination
Watering
5vented
±Soil
fertilizer
26
1996,in
operation
Santa
Gertrudis,
Chihuahua
EnergõÂ a
yEcologõÂ a
UASB/21.32
49
300
Screen,gritchamber,
grease
interceptor
tank,homogenization
16
0.7
10
70
Secondary
settler,
chlorination
Watering
0.6
vented
±Soil
fertilizer
27
1996,in
operation
SanLuisRõÂ o
Colorado,Sonora
EnergõÂ a
yEcologõÂ a
UASB/97
290
300
Screen,gritchamber,
grease
interceptor
tank,homogenization
15
0.9
870
Secondary
settler,
chlorination
Watering
2.66vented
±Soil
fertilizer
28
1996,in
operation
ClubPumas,
UNAM
Me xico
City
EnergõÂ a
yEcologõÂ a
UASB/20
80
300
Screen,gritchamber,
grease
interceptor
tank,homogenization
20
1.2
670
Secondary
settler,
chlorination
Watering
Vented
±Soil
fertilizer
29
1996,in
operation
CuautitlaÂn,
CiudadJuaÂrez,
Chih.
TecnoadecuacioÂn
Hybrid/194.4
259
213
Screen,gritchamber
grease
interceptortank
19
0.28
18
87.65
±Land
in®ltration
Vented
Digestion
Tosoil
30
1996,in
operation
Conj.urbano
``Haciendadel
Pedregal'',
AtizapaÂnde
Zaragoza,Edo.de
Me xico
Proesa
UASB/200
572
540
Screening,grit
chamber
22
1.54
8.4
70
Chlorination
Watering
93vented
None
Land®ll
31
1997,in
operation
Chicoase n,
Chiapas
EnergõÂ a
yEcologõÂ a
UASB/68
204
250
Screen,gritchamber,
grease
interceptor
tank,homogenization
20
0.75
870
Secondary
settler,
chlorination
Watering
Vented
±Soil
fertilizer
32
1997,in
construction
Quechultenango,
Guerrero
Ibtech
UASB/350
1200
500
Screening,grit
chamber
21
1.71
755c
Aerobic
lagoon
Toriver
basin
98vented
None
Land®ll
33
1997,in
construction
Colotlipa,
Guerrero
Ibtech
UASB/117
400
500
Screening,grit
chamber
±1.71
755c
Chlorination
Toriver
basin
41vented
None
Land®ll
34
1998in
construction
Ecatepec,Estado
deMe xico
Proesa
UASB/101
397
600
Screening,grit
chamber
20
2.36
650c
Chlorination
Wellinjection
Vented
None
None
aBiothaneis
representedin
MexicobyTecnologõÂ a
Intercontinental,Paques
byAtlatec,
thecompaniesIm
asa,EnergõÂ a
yEcologõ a,Tacsa,Forza,GTSA,DescontaminaAccio n,PROESA
andIB
tech
commercialize
the
technologydeveloped
byUAM-U
NAM.
bAF:anaerobic
®lter;UASB:up¯ow
anaerobic
sludgeblanket
reactor;EGSB:expanded
granularsludgebed
reactor;ADI-BVF:low-rate
up¯ow
sludgeblanket
process;Bv:organic
loadingrate;HRT:hydraulicreten-
tiontime;
DAF:dissolved
air¯otation.
c Designdata.in
op.=
inoperation;in
const.=
inconstruction.
Anaerobic digestion in Mexico 1813
Most of the anaerobic reactors in the world are
also operated under mesophilic conditions since thisallows a greater stability compared to the thermo-philic ones.
Biogas use
Despite that one important factor for the selec-tion of anaerobic treatment is the possibility ofenergy recovery through biogas combustion, this isdone only in 13 plants (Fig. 5). Eleven use it in boi-
lers, one in dryers and two for cooking facilities.This is a worldwide tendency due to the extrainvestment required to achieve such recovery or, as
in the case of domestic wastewater because of thelow biogas production. More worrying is the factthat at least 54% of the plants installed in Mexico
do not even ¯are up the biogas produced and rathervent it directly to the atmosphere, contributing tothe greenhouse e�ect. Some of them however, per-form at least iron ®ltration to remove hydrogen sul-
®de. It should be noticed that in all the plantscommissioned by foreign companies, the biogas isrecovered or ¯ared up and the problem of venting
is con®ned exclusively to locally designed reactorsindependently of the type of wastewater.
Treated water use
The limited water availability in the country hasprovided an incentive to recycle it. As a conse-
quence, in 25 plants (38% national plants), the trea-
ted water is used for irrigation and one of them for®sh culture (Fig. 6). Other uses involve the recyclefor cleaning operations (Table 5, plants 5 and 11)
as well as production processes (Table 4, plant 1).Contrary to the local companies, no reuse has beenprojected for the treated water from 95% of the
digesters built by foreign companies which directlydischarge to the environment or to sewers. Onetreatment plant (Table 4, reactor 34) recentlyacquired an inverse osmosis unit to polish the water
and recycle it to the process. AD e�uents need aposttreatment to be reused and companies applythem as required.
Sludge use
Four companies occasionally sell their sludges as
inoculum for anaerobic reactors at about US$ 60per m3 (Table 4, reactor 9, 10, 11, 12, 22, 23, 24,25, 26 and 34), thus reducing the imported sludge
price ®ve times. Some others, like the cheese indus-try have handed the sludge over at no cost, as partof their commercial agreements.
CONCLUSIONS
Anaerobic digestion can be considered nowadaysas a mature technology in Mexico. Despite its econ-omical advantages it remains as a minor technology
Fig. 5. Biogas uses per wastewater type (industrial or domestic) and technology origin (national orforeign) by April 1998. Notice that F=®ltered and V=vented.
Oscar Monroy et al.1814
compared to other technologies. Some local compa-
nies have shown the capacity to compete success-fully with foreign companies. An e�ort should bemade to promote anaerobic digestion as the core of
a sustainable technology for wastewater treatment.As a ®rst step, biogas utilization and water recy-cling has to be considered. One interesting point is
that, compared to its North American neighbors,Mexico has shown a better acceptation for anaero-bic digestion. Indeed, in 11 years Mexico hasinstalled more than 3 times the number of digesters
built in Canada (26 reactors, the ®rst one in 1982)and more than 90% of the digesters operating inthe United States (89 reactors, the ®rst in 1977,
Hulsho�-Pol, personal communication).
AcknowledgementsÐThanks are given to the companiescited in Table 4 as well as to the CNA and SEMARNAPsta�, whose interest in the subject made this compilationpossible. We also thank Carmen Fajardo for data logging,Adalberto Noyola, Alex Eitner and Look Hulsho� Pol fortheir kind advises, TBW-Frankfurt for providing the fundsand Dick Speece for his kind revision of the manuscript.
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Anaerobic digestion in Mexico 1815
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