14
ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN MEXICO: STATE OF THE TECHNOLOGY OSCAR MONROY*, GRACIELA FAMA ´ , MO ´ NICA MERAZ, LETICIA MONTOYA and HERVE ´ 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) Abstract—Due to the nascent wastewater treatment practice in Mexico there is great opportunity to introduce anaerobic digestion as the core of the wastewater treatment processes. Nevertheless, this requires an understanding of all the technical, economical and financial aspects that limit its development. According to the National Water Commission, in 1995 municipal and industrial wastewater were produced at rates of 232 and 168 m 3 s 1 respectively, but only 20 and 12% of these volumes were treated, often with very low eciencies. In order to increase the treatment capacity of the country, approximately US$ 4515 million managed by the banks for development are supposed to be available to invest in environmental projects. Other financing mechanisms exist through treasury incentives and penalties. Within this situation, anaerobic digestion has grown although not at the required rate and bigger investments are being made on conventional aerobic and physicochemical technologies. Presently there are in the country 85 anaerobic wastewater treatment plants treating 216,295 m 3 d 1 with an installed volume of 228,551 m 3 . UASB reactors account for 74% of the installed volume and national companies have supplied 76% to the anaerobic market. Proper integration of the anaerobic digestion processes for water recycling and energy recovery has not been achieved and there is a big need to demonstrate economic and ecological sustainability. # 2000 Elsevier Science Ltd. All rights reserved Key words—anaerobic 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 to this 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 102 plants or 4.8 m 3 s 1 per year (Table 2). Despite this relative high growth rate (compared to the econ- omic growth), the gap between the treated 47 m 3 s 1 and the produced 232 m 3 s 1 of sewage is still very large (Table 1), giving place for advanced and inexpensive 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 filters, 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 eciencies higher than 75 and 26% (199 plants) have an eciency lower than 50%. This is because the treatment systems are of dierent types as shown in Fig. 1. Average capacity of these plants is 42 L s 1 ranging from 5000 to 1 L s 1 . 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 Britain 0043-1354/00/$ - 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 le Developpement (IRD), France.

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Page 1: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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.

Page 2: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

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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

Page 4: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

Page 5: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

Page 6: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

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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

Page 8: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

Page 9: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

Page 10: ANAEROBIC DIGESTION FOR WASTEWATER TREATMENT IN … · Key words—anaerobic digestion, wastewater, Mexico, technology, industrial, domestic, municipal, bio-gas use, treated water

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

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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

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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

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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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