assessment of biomethanation potential of selected industrial organic effluents in india

Resources, Conservation and Recycling

35 (2002) 147–161

Assessment of biomethanation potential ofselected industrial organic effluents in India

Kusum Lata *, Arun Kansal, Malini Balakrishnan,K.V. Rajeshwari, V.V.N. Kishore

Tata Energy Research Institute, Darbari Seth Block, Habitat Place, Lodhi Road,New Delhi 110 003, India

Received 19 March 2001; accepted 21 September 2001

Abstract

Anaerobic digestion is gaining wider acceptance in the present scenario over aerobictreatment due to production of biogas, which can be further used for meeting a part ofenergy demand. On the basis of primary and secondary data, the energy potential by theanaerobic digestion of the effluent from some of the polluting industries has been estimatedin this paper. The pulp and paper industry has been found to have the maximum potentialamong others of the order of 1131 GWhe/a followed by distillery with a contribution of 830GWhe/a to a total potential of 2963 GWhe/a equivalent electric energy. A total potential of565 MW plant installation with anaerobic digestion technology has been estimated. Thepaper also describes the nature of wastewater generated by each sector, status of technologiesfor that sector in India and policy measures, which should be adopted for their large-scaleadoption. © 2002 Published by Elsevier Science B.V.

Keywords: Biomethanation; Bioenergy potential; Industrial wastewater; Anaerobic digestion; Effluenttreatment; Dairy effluent; Distillery effluent; Pulp and paper effluent; Sugar effluent

www.elsevier.com/locate/resconrec

Abbre�iations: COD, chemical oxygen demand; CSTR, continuous stirred tank reactor; BOD,biochemical oxygen demand; HRT, hydraulic retention time; KVIC, khadi and village industrialcommission; LPG, liquefied petroleum gas; SRT, solid retention time; STP, standard temperaturepressure; UAFP, upflow anaerobic filter process; UASB, upflow anaerobic sludge blanket; VSS, volatilesuspended solids.

* Corresponding author. Tel.: +91-11-4682100/4682111; fax: +91-11-4682144/4682145.E-mail address: [email protected] (K. Lata).

0921-3449/02/$ - see front matter © 2002 Published by Elsevier Science B.V.

PII: S0921 -3449 (01 )00112 -4

K. Lata et al. / Resources, Conser�ation and Recycling 35 (2002) 147–161148

1. Introduction

Industrialization can be considered a desirable option owing to its contribution tothe national economic growth. However, it exerts considerable pressure upon thenatural resources, along with an increased demand for energy. In addition, the wastegenerated by the industries is a major environmental concern and the disposal ofeffluents without appropriate treatment could have long term adverse effects,especially upon the local vegetation and aquatic life. Thus, it is imperative for highlypolluting industries to adopt a suitable waste treatment process for the clean disposalof high-strength wastewater. Anaerobic digestion is one such technology, which isgaining wider acceptance in the present scenario over aerobic treatment. This is dueto benefits such as lower energy requirements, high degree of waste stabilization, highorganic loading rates, lower production of excess sludge, easier preservation of welladapted sludge which can be kept unfed for a period of more than a year withoutany deterioration, and the production of biogas which can be further used for meetingpart of the energy demand.

This paper presents the findings of a survey conducted to estimate the total energygeneration potential from the anaerobic digestion of industrial wastewater in India.The data is primarily based on research publications and questionnaires sent tovarious industries as well as on information obtained through personal communica-tion. The emphasis is essentially on sectors, which generate either large volumes orhigh strength or a combination of large volume and high strength wastewater. Thusdistillery, sugar, dairy and pulp and paper industries are covered. In addition, thestatus of commercial installations as well as specific requirements and constraints tobiomethanation in each of these sectors is also discussed.

2. Methodology

Primary data was collected by sending approximately 300 questionnaires, whichcomprised of description of the manufacturing process, raw material used, wastegeneration rate per unit of production, sources of wastewater generation, wastewatercharacteristics, details of treatment plant, plant performance etc. The questionnaireswere also sent to a number of Indian consulting firms involved in turnkey executionof the anaerobic technologies in Indian industry. In addition, visits were made to afew installations. The responses of the questionnaire survey received are summarizedin Table 1.

Since the number of responses was less of the order of 10% of total questionnairesent, information was also gathered from the published research papers anddocuments to fill in the information gaps.

3. Distillery

India has about over 200 large and medium scale distilleries of which half are yetto attain satisfactory performance levels with regard to installation and operation

K. Lata et al. / Resources, Conser�ation and Recycling 35 (2002) 147–161 149

of effluent treatment plants (CPCB, 1997a). The alcohol manufacture is basedeither on molasses or malt-barley as the raw material and the final product rangeincludes industrial alcohol, rectified spirit, pure alcohol and beverage alcohol.The manufacturing process involves dilution of molasses with water followed byfermentation with cultured and developed yeast. The fermented solution (wash)contains 6–8% alcohol and is distilled with low-pressure steam to obtain rectifiedspirit or neutral alcohol as the final product. The residue of the distillationprocess is the spent wash, which is a strong organic effluent. The other wastesfrom the process include yeast sludge (which is usually mixed with spent wash),floor washes, waste cooling water and waste from the operations of yeast recov-ery or by-products recovery processes. Based on the responses of our question-naire survey, the typical wastewater characteristics from a composite distillery arepresented in Table 2.

Anaerobic treatment of distillery wastewater is an accepted practice and vari-ous high rate anaerobic reactor designs have been tried at pilot and full-scaleoperation. Some of these are hybrid reactor (Bardiya et al., 1995), fixed film(Manihar, 1995), and continuous stirred reactor (questionnaire survey). Perfor-mance of the few reactors and their scale is summarized in Table 3. Ramendraand Awasthi (1992) have reported that a combination of anaerobic and aerobicfermentation is a proven technology for distillery effluent treatment. However, tomake the anaerobic process viable, the effluent needs pretreatment for pH andtemperature adjustment. Also lime scrubbing of biogas is needed for H2S re-moval if the biogas is to be used for power generation.

Manihar (1995) conducted pilot studies on a 100 l fixed film reactor with varyingchemical oxygen demand (COD) loading in order to optimize the treatmentefficiency and methane production. The unit consisted of separate reactors foracidification followed by biomethanation. The 20 l acidification reactor was con-stantly agitated and operated at a hydraulic retention time (HRT) of 2.5 d to obtaina COD reduction of 10–15%. The fixed film methane reactor consisted of a 100 l

Table 1Response received to the questionnaire survey

Type of industry Response received

Distillery 3Sugar 4Pulp and paper industries 7Starch 1Textile 7

3Edible oilConsultants 2Total 27


Tab

le2

Cha

ract

eris

tics

ofef

fluen

ts

CO

D(g

/l)

BO

D(g

/l)

Tot

also

lids

(g/l

)Su

spen

ded

Typ

eof

indu

stry

Oil

and

grea

seV

olat

ileso

lids

Was

tew

ater

pHso

lids

(g/l

)ge

nera

tion

(g/l

)(g

/l)

80–1

20N

AN

AN

A90

–110

35–5

04.

0–5.

5D

isti

llery

efflu

ent

12-1

6(l/l

ofal

coho

l)3.

5Su

gar

indu

stry

NA

0.2-

1.8

(m3/t

onof

NA

NA

4–7

1.8–

3.2

720–

1.5

suga

r)N

A0.

03–1

.9N

A0.

07–0

.24

1.12

–3.3

65.

6–8

0.32

–1.7

5D

airy

efflu

ent

2l/

l(C

hilli

ngpl

ant)

4.5

l/l

(Int

egra

ted

plan

t)0.

310.

082

NA

1.51

NA

NA

Cof

fee

pulp

ing

2.80

5–5.

5


Table 3Performance of the reactors operating for distillery waste

COD loadingReactor type Volume Methane yieldScale COD reductionrate (%)

25 kg/m3 d 0.4 m3/kg CODFixed filmPilot 100 l 60–70reduced

NA 0.4–0.45 m3/kg CODPilot 100 m3/d 65–70Fixed filmreduced

48–50 kg/m3 d 3.10 m3/(m3 d)Pilot 70Hybrid 1.5–1.6 mldNA 13,100 m3/(m3 d)3.75 mld 65–70Full UASB

UASB 7 mld NA 24,000 m3/(m3 d) 90–92FullNA 0.5 m3/kg CODFull 9.5 mld 70CSTR

reduced

fixed bed filled with random polyvinyl carbonate rings having a void volume of 97%and surface area of 320 m2/m3. The reactor was operated in the upflow mode witha varying recirculation rate of 15–25 times the inlet effluent rate. The maximumCOD loading rate achieved was 25 kg/(m3 d) with an overall COD reduction of60–70%. The methane yield was 0.4 m3/kg COD reduced with methane content of60–70%. Work has also been done by Vaidyanathan et al. (1996) to design a twostage anaerobic digester for treatment of distillery waste. Biokinetic coefficients ateach stage as estimated from their experiments were: sludge production constant(Y) 0.065 and 0.203, decay constant (kd) 0.0014 and 0.0014, half rate substrateconcentration (ks) 5.396 and 3.998 mg/l, biochemical oxygen demand (BOD)removal rate constant (kb) as 0.11 and 0.08 per day, respectively.

An anaerobic diphasic fixed film reactor for biomethanation of distillery spent-wash has been investigated by NEERI (National Environment Engineering Insti-tute), Nagpur. A pilot plant of 10 m3/d capacity has been set up at WesternMaharashtra Development Corporation Distillery, Chitali, District Ahmednagar,Maharashtra. COD reduction of 65–70% and biogas yield of 0.4–0.45 m3/kg CODreduced have been achieved. The biogas contains 65–70% methane. A 1.5–1.6 mlddiphasic anaerobic plant based on hybrid reactor i.e. upflow anaerobic filter systemhas also been installed at Daurala Sugar Works, Daurala (UP, India) (Bardiya etal., 1995). The acid phase digester was designed for 34–36 h HRT with CODloading rate of 48–50 kg/(m3 d), while the methane phase reactor has a HRT of9–10 d with a COD loading rate of 9–11 kg/(m3 d). A COD reduction of about70%, with a biogas production rate of 33–35 m3/m3 of effluent or 3.10 m3/(m3 d)with a methane content of 63–65% has been reported.

Jalgaonkar (1995) has reported two successful installations of Upflow AnaerobicSludge Blanket (UASB) reactor for distillery effluent at Haryana DistilleriesLimited, Yamunagar and Sanjivani Sahakari Sakhar Karkhana, Kopargaon, Ma-harahtra. These plants treat 375 and 700 m3/d of effluent, respectively. COD andBOD reduction of 65–70% and 90–92% has been achieved with a final concentra-tion of 100 and 50 g/l, respectively. The corresponding gas production


was 13 100 and 24 000 m3/d, respectively. In yet another installation (questionnairesurvey) a 950 m3/d continuous stirred tank reactor (CSTR) at a distillery in districtKolhapur, Maharashtra, has a designed HRT of 15–18 d which could bring about70% reduction in COD with a gas yield of 0.5 m3/kg COD reduced.

The total production of alcohol during the year 1994–1995 was 1165×106 l(Cooperative Sugar, 1998). Based on the performance of these plants, it is estimatedthat distilleries have the potential to generate a total of 560×106 m3/a of biogas ifall distilleries opt for anaerobic digestion. Assuming the calorific value of biogas as5300 kcal/m3, this amounts to 830 GWhe/a and translates to 158 MW of powerplant. A biogas based power plant of 1 MW capacity has been installed andcommissioned during the year 1997–1998 (Chauhan, 1998) at K. M. Sugar MillsLimited (distillery unit), Faizabad, UP. The plant generates 0.4 MWh of electricityper month using 12 000 m3/d of biogas at a production cost of Rs 2 per k Wh.

Being a high strength effluent producer, severe pollution control regulations haveto be met by the distillery sector. This forces the sector to adopt effluent treatmentmethods for meeting discharge standard prior to disposal. In such a scenario,distilleries are one of the most suitable areas for energy generation throughbiomethanation. However, still there is need for a post treatment process afteranaerobic digestion in order to conform to the norms set by central pollutioncontrol board (CPCB). Even though 145 out of 254 distilleries in the country haveadopted anaerobic digestion for wastewater treatment (Chauhan, 1998), it is yet tobe implemented in the remaining units. The latter are hesitant partly due to the lackof information on successful installations based on anaerobic digestion. For in-stance, Western Paques India Limited reports that 50% of its UASB installations inIndia are for distillery wastewater (personal communication). Still it is difficult toobtain the reliable plant scale data of these installations because distilleries areunwilling to divulge the digester performance due to fear of reprisals from thepollution control authorities.

4. Sugar

There are about 393 large and medium scale sugar mills in India with aproduction figure of about 20×106 ton of plantation white sugar in the 1995–1996season. Of these units, about 26% are yet to attain satisfactory performance levelwith regard to installation and operation of effluent treatment plants (CPCB,1997a). The sugar manufacturing process broadly involves the following steps: (a)extraction of sugarcane juice, (b) clarification of the juice by the addition of limeand sulphur dioxide to heated juice at 70 °C, (c) concentration of the clear juiceafter clarification to 60% solids, (d) syrup sulphitation and crystallization, and (e)centrifugation, drying and bagging the sugar crystals. The manufacturing processprimarily produces bagasse and press mud as waste. The former is normally used asfuel in boilers while the latter is employed either for soil enrichment or forbiomethanation. In addition, the process generates wastewater, with the typicalcharacteristics (questionnaire survey) as summarized in Table 2.


Sugar mill wastewater is acidic in nature and thus requires pH correction prior toanaerobic treatment. Since sugar manufacturing is a seasonal activity, the processneeds to be restarted at the beginning of each season. Most industries, which weresurveyed, had installed a two-stage process (anaerobic followed by aerobic) forwastewater treatment with a reported COD reduction of 70–75% in the anaerobicprocess. Table 4 summarizes the capacities and performance of the reactors forsugar effluent. Radwan and Ramanujam (1995) have attempted the use of rotatingbiological contactor (RBC) for the treatment of synthetic sugar effluent. CODreduction was reported in the range of 90–97%. A pilot scale study on a 2.83 m3

capacity UASB reactor at a sugar mill at Satha, Aligarh in northern India(Khusheed et al., 1997) demonstrated a COD reduction of up to 80%. The unit wasoperated at 34 °C with a HRT of 5.5 h and an average COD loading rate of 13kg/(m3 d). The average methane gas recovery was 0.22 m3/kg COD removed. Themethanogenic activity of the sludge, sludge yield coefficient and the solid retentiontime (SRT) were 0.56 (kg COD CH4)/(kg VSS d), 0.34 kg VSS/kg COD and 34 d,respectively.

Pathe et al. (1995) have investigated the UASB reactor for the treatment of sugareffluents. Bench scale performance studies indicated that the reactor has consider-able potential to treat sugar mill effluents effectively. More than 90% COD removalwas observed at a low loading of up to 13 kg/(m3 d) which reduced to about 80%COD removal for 25 kg/(m3 d) at HRT ranging from (4–24) h. The methane yieldwas observed to be in the range of (0.34–0.28) m3/kg COD removed. Reddy andShivalingaiah (1997) also studied UASB reactor coupled with extended aerationunit for the treatability of sugar wastewater. The study on 1.5 l UASB and 2.9 lextended aeration unit reported biogas production of 0.225 m3/kg of COD de-stroyed with overall COD efficiency of 95%. Treatment of sugar mill wastewaterusing anaerobic filter was studied by Sastry et al. (1990). Their study revealed that

Table 4Installation performance in sugar industry

Loading rateType of reactor COD reductionVolumeScale Methane yield(%)

Waste water802.83 m3Pilot 0.22 m3/kg13 kg/m3 dUASB

COD reducedUASB 13 kg/m3 d 0.34–0.28NALab 90

m3/kg CODreduced

95UASB1.5 l 0.23 m3/kgLab 1.8–7.2 kg/m3 dCOD reduced

Press mudKVIC85 m3Pilot 75100 m3/tonNA

Lab 0.25 m3/kgNANA1 lCOD reduced


the wastewater of cane sugar mills is amenable for treatment in upflow anaerobicfilters. They used granite bed of 135 cm with a liquid column height of 30 cm. Intheir experiments, the specific biogas yield varied from (0.073–0.519) m3/kg CODadded with methane contents ranging from 61.8 to 74% at COD loading rates of(1.8–7.2) kg/(m3 d). This experimental data established the yield coefficient (Y) as0.10 per (mg VSS mg BOD), decay coefficient (Kd) as 0.06 per d, maximum specificgrowth rate (Umax) as 1.01 per d and the first order rate constant as 1.2 per h. Thecoefficient, rate of substrate utilization (k) was 10 per d and half velocity coefficient(ks) was 1.201 g/l.

Apart from the effluent, the sugar cane press mud can also be treated byanaerobic digestion. Sudhir (1996) reported that the organic content of this wastewas 110 g/l of COD and 80 g/l of BOD. Press mud produced is about 40 kg/ton ofsugar cane crushed. At the Ugar Sugar Works Ltd. in Karnataka, four Khadi andVillage Industries Commission (KVIC) floating type biogas plants, each having acapacity of 85 m3, have been installed for the treatment of pressmud. The influentslurry has a total solids content of 5% and the HRT is 18 d. The plant is able toproduce biogas of about 100 m3/ton of press mud with a methane content of 55%.The COD removal efficiency works out to be 75%. A similar study by Sanchez etal. (1996) reported a methane yield value of 0.25 m3/kg COD removed in 1 lreactor.

Based on data collected, it is estimated that a tonne of sugar can generate energyequivalent to 2 GWhe/a from 1.35×106 m3 of biogas. Thus, a plant of 0.4 MW canbe installed from the waste obtained from sugar industries. However, as most of thestreams are recycled, wastewater generation is limited in this sector. In fact, goodhousekeeping practices can significantly reduce the quantity of effluent. Also, sincepress mud is conventionally applied on land as manure, it is essential to know theexact quantity, which can be diverted for anaerobic digestion. The latter wouldutilize it more effectively. Besides, the press mud after anaerobic digestion will haveless smell as compared to raw mud, with minimal deterioration in nutritional value.

5. Dairy

There has been a remarkable growth in milk production and milk processingcentres (dairies) in India during the past decades. The dairies collect milk from theproducers and then either bottle it for marketing or produce various processedfoods. At present, there are 127 large and medium scale integrated dairy plants inthe country. Of these, about 50% of the units are yet to attain satisfactoryperformance level with regard to installation and operation of effluent treatmentplants (CPCB, 1993). The liquid waste from a dairy originates from several sourcessuch as the receiving station, bottling plant, cheese plant, butter plant, condensedmilk plant, dried milk plant and ice-cream plant. The characteristics of thecomposite wastewater of an integrated dairy (CPCB, 1993) are summarized inTable 2.


Roy and Chaudhuri (1996) conducted pilot scale experiments on a 20 m3/d fixedfilm reactor for biomethanation of dairy wastewater. The reactor was packed withplastic media up to a height of 2.23 m leaving a gap of 0.4 m at the bottom. CODfeeding into the digester was 40 kg/d at a flow loading of 20 m3/d and the designedmean cell residence time was 25 d. About 77% COD reduction was achieved andthe methane gas production at standard temperature and pressure (STP) was 0.33m3/m3 of wastewater. In another laboratory scale experiment (Sammaiah et al.,1991) an upflow anaerobic filter process was investigated with granite stone of 51%bed porosity as immobilizing media. Steady state efficiency of COD removal in therange of 62.8–91.3% with the specific methane yield varying between (0.078–0.4)m3/kg COD added was obtained.

Laboratory experiments have also established the feasibility of UASB process forthe treatment of dairy wastewater. Mehrotra and Jain (1997) studied the perfor-mance of a 2.8 l capacity UASB reactor using simulated dairy wastewater. Thereactor was found to remove COD by 90% at a COD loading rate of 8 kg/(m3 d)and optimum HRT of (8–10) h. Specific methane yield was observed to be 0.41m3/kg COD with a sludge loading rate of 0.6 g COD/(g VSS d). Bench scale studiesundertaken by Shastry and Kaul (1996) on a UASB reactor revealed optimumCOD loading conditions to be 3.6 kg/(m3 d) with a retention period of 1 d at aninfluent concentration of 3.6 g/l. The COD removal efficiency obtained was 80%with a specific methane yield of 0.3 m3/(m3 d). Maximum substrate removal rate forCOD concentration of 3.6 g/l was 5.88 kg/(m3 d). The methane content wasobserved to be 71%. The performance of the reactors is summarized in Table 5.

The potential of energy generation from dairy industry effluent (assuming 3 l/l ofmilk processed) works out to be 8.4 kWhe/ton of milk processed. The effluent needssimple post-treatment such as water pond to meet the discharge standards. Thetotal milk processed in India during 1994–1995 was about 64.1×106 ton (CIER’S,1998). Therefore, it is possible to generate 365×106 m3 of biogas equivalent to 540GWhe/a energy on a countrywide basis through the anaerobic digestion of dairyindustry wastewater. This works out to a power plant of 103 MW capacity.However, most of the dairy industries employ aerobic plants for the effluenttreatment and thus installing an anaerobic plant after demolishing the existingaerobic unit is not an acceptable option. Moreover, being in the small-scale sectormost of them do not find it economically feasible to install a treatment plant eventhough the high strength effluent does not meet the pollution limits.

6. Pulp and paper

Indian paper mills can be broadly classified into large mills (with a productioncapacity of more than 10 000 ton/a), small mills (producing less than 10 000 ton/a)and small waste paper based mills. The pulp used by the mills is produced utilizingdifferent cellulosic materials such as bamboo, bagasse, rice or wheat straw andwaste paper. Most of the large paper mills in India are integrated pulp and papermills, while a few produce pulp only and some purchase pulp to produce paper


Tab

le5

Inst

alla

tion

perf

orm

ance

inda

iry

and

pulp

and

pape

rin

dust

ry

Met

hane

yiel

dC

OD

redu

ctio

n(%

)T

ype

ofre

acto

rSc

ale

Vol

ume

CO

Dlo

adin

gra

te

Dai

ryef

fluen

t0.

33m

3/m

377

40kg

/(m

3d)

Pilo

t20

m3/d

Fix

edfil

mU

AF

P62

.8-9

1.3

NA

NA

Lab

0.07

8–0.

4m

3/k

gC

OD

adde

d0.

41m

3/k

gC

OD

redu

ced

908

kg/(

m3

d)2.

8l

Lab

UA

SB80

UA

SBN

A3.

6kg

/(m

3d)

0.3

m3/(

m3

d)L

ab

Pul

pan

dpa

per

efflu

ent

0.45

–0.5

0m

3/k

gC

OD

redu

ced

65-7

05

kg/(

m3

d)F

ull

13,0

00m

3C

STR

0.4

m3/k

gC

OD

redu

ced

41P

ilot

UA

SB3.

81m

310

kg/(

m3

d)

Tab

le6

Cha

ract

eris

tics

ofpu

lpan

dpa

per

mill

efflu

ent

Sour

ceW

aste

wat

erge

nera

tion

(m3/t

onof

pape

rm

anuf

actu

re)

PH

CO

D(g

/l)

BO

D(g

/l)

Tot

also

lids

(g/l

)

14.6

3N

A8–

109.

8N

AP

ouch

erw

ashe

rN

A9.

255.

25St

raw

beat

er7–

8N

AH

essi

anbe

ater

sN

A7–

82.

1N

A3.

885.

918.

81P

ulp

mill

(bla

ckliq

uor)

1.8

NA

7–9

1.35

NA

6–7

0.35

0.14

Pap

erm

achi

ne0.

975.

08C

ombi

ned

efflu

ent

7–9

230

2.98


only. Reports indicate that of the 279 large pulp and paper mills, two-third do nothave adequate wastewater treatment facilities (CPCB, 1997b).

Pulp is conventionally manufactured either by the Kraft process, sulphite processor by mechanical pulping. Majorities of the Indian mills use the Kraft process,which involves digestion of chipped cellulosic raw material with chemicals likesodium sulphate, sodium hydroxide and sodium sulphide at high temperature andpressure. After digestion, the pulp is washed, bleached and sent to the paper mill.Washing of pulp produces black liquor, which contain 98% of digested chemicalsused for the digestion. The recovery and reuse of chemicals is essential both toimprove the economics of paper manufacture and also to avoid pollution relatedproblems. The volume and characteristics of the wastewater generated in the sectorvaries widely and depends upon the size of operation, manufacturing process, rawmaterial used and conservation measures adopted. The typical wastewater charac-teristics from pulp and paper mills (Goyal, 1997) is given in Table 6.

In addition, pulp and paper mill effluents contain variable amounts of materialssuch as lignin, sulphate, and chlorides that are non-biodegradable, toxic or in-hibitory to the biological process. The effects of these can be partially mitigated byequalization of the wastewater, pH correction, nutrient addition and by incorpora-tion of recycle and bypass facilities. Sharma and Bandyopadhyay (1991) studied thefeasibility of anaerobic filters for the treatment of pulp and paper mill waste. Theyused burnt earthenware rings of pottery clay as filter media. Wastewater was fed atCOD concentrations up to 6 g/l. Maximum COD removal of 84.4% was achievedfor an influent COD concentration of 4.183 g/l, operated at hydraulic loading of129.92 l/(d m3). The organic loading was 0.43 kg/(m3 d) and the maximum gas yieldcoefficient of methane was 0.425 l/(g d) of COD destroyed.

Two large-scale plants in India for anaerobic treatment of pulp and paper millwastewater are installed at Pudumjee Pulp and Paper Mills, Pune and Satia PaperMills, Punjab. Pudumjee Pulp and Paper Mills operates a CSTR type anaerobictreatment plant with a total capacity of 13 000 m3. The designed HRT is 50 h withloading rate of 5 kg/(m3 d). BOD and COD removal efficiency is reported to be inthe 85–90% and 65–70% range, respectively. Gas yield is between 0.45 and 0.50m3/kg COD with a methane content of 75%.

Naithani and Mathur (1997) have reported a UASB based pilot plant commis-sioned at Satia Paper Mills with a capacity of 3.81 m3. The plant was designed tooperate at a COD loading rate of 10 kg/(m3 d) with a BOD reduction of 80% anda biogas yield of 0.4 m3/kg of COD removed. The methane content was 72% andthe plant performed for 60% of the designed capacity. The COD reduction was 41%and the biogas production rate was 0.45 m3/kg COD removed. Performance of thereactors for pulp and paper effluent is summarized in Table 5. Based on thisexperience, it is estimated that paper mills in India can generate about 287kWhe/ton of paper production. During the year 1996–1997, the total production ofpaper was 3.94×106 ton (CIER’S, 1998) which implies that 1131 GWhe/a of energycan be generated. This works out to a 215 MW capacity power plant installationfrom pulp and paper wastewater if the anaerobic process treated all the effluent.


Table 7Characteristics of edible oil extraction and refining process effluent

COD (g/l) Oil and greaseProtein (g/l)PHProcess Total dissolved solids(g/l) (g/l)

7.5–8.0 0.10Solvent 1.00 NA NAextractionplant

12.00 0.40NA NA3.0–4.0Refinery plantNA12.0 NA NA 3.00Boiler house

5.0–10 NA 3.20–6.00 0.40 NAComposite

Even though pulp and paper mill effluent is a prime candidate for anaerobictreatment, instances of its use are limited. One reason is the presence of toxiccomponents in the effluent, which results in non-adaptation of the microorganisms.Apart from identifying cultures, which can adapt to toxic compounds in theeffluent, another solution would be to segregate the waste streams such that thestreams containing large concentration of chemicals are diverted away from theanaerobic digestion process. This could aid considerably in the effective implemen-tation of anaerobic digestion technology in the pulp and paper sector.

7. Other industries

Other processes such as the manufacture of edible oils and coffee pulpingproduces effluents, which can be considered for anaerobic digestion. The recoveryof oil from oil seeds is typically carried out by solvent extraction, which involvesseed preparation, extraction with food grade hexane and refining. Seed preparationis done by cooking with steam followed by crushing into flakes. Refining involvesdegumming, neutralization, bleaching and odor removal, after which the oil isfiltered before packing.

The entire extraction and refining process generates 57 m3/ton effluent of refinedoil (questionnaire survey) with the typical characteristics given in Table 7.

Information regarding the feasibility of anaerobic process for treatment of edibleoil industry wastewater is very scanty. However, the effluent characteristics indicatethat anaerobic treatment would be possible and therefore, it needs to be investi-gated further. Assuming that a suitable reactor could be developed for 70%reduction in COD with a methane yield of 0.2 m3/kg of COD destroyed, the energygeneration potential from wastewater of an edible oil manufacturing plant would beabout 70.8 kWhe/ton of oil produced. Production of edible oil during the year1994–1995 touched 7×106 ton (CIER’S, 1998). On this basis, power plant installa-tion capacity would be 87 MW from 310×106 m3 of biogas equivalent to 458.62GWhe energy.

Coffee processing is another industry that generates large volumes of effluents.This is a seasonal industry that normally operates from November to February.


The process which includes pulping of fruit to remove outer skin and mucilage andcleaning of seeds, is quite water intensive and generates wastewater of about 5m3/ton of fresh coffee fruit processed. Typical pulping wastewater characteristics(Sampath, 1997) are shown in Table 7.

The effluent composition indicates that it has a good potential for biomethana-tion. However, no practical case study is available in India. Fernandez and Chacin(1997) studied the treatment of simulated wastewater from coffee under ther-mophilic and mesophilic conditions and concluded that mesophilic anaerobicdigestion can be used successfully to treat synthetic, ground coffee waste and thata better performance could be achieved by avoiding the potassium inhibitory effectby the use of calcium in the reactor feed. However, no data on the gas yield wasreported. Assuming a 70% COD reduction by anaerobic digestion along with amethane yield of 0.2 m3/kg COD removed, coffee effluent has the potential togenerate LPG of about 1.45 kg/ton of coffee produced. In the year 1994–1995,India produced about 43×103 ton of coffee (CIER’S, 1998) which translates to1.35×106 m3 of biogas or 2.0 GWhe/a and 0.4 MW of power plant installation.

8. Conclusions

This work presents the findings of a survey on the bioenergy generation potentialfrom the anaerobic digestion of selected organic wastewater. The emphasis is onlarge volume, high strength wastewater and covers distillery, sugar, dairy and pulpand paper industries. The main points, which emerge from this study are listedbelow:

(1) The total energy generation potential from the anaerobic digestion ofindustrial wastewater is estimated to be 2963 GWhe/a equivalent electric energy.This is equivalent to a 565 MW power plant installation. However, most of thework done in India is still at laboratory or pilot scale indicating a wide gap betweenR&D efforts and full-scale technology implementation. Therefore, these estimatesprovide only a preliminary indication of the biogas generation potential fromvarious effluents.

(2) The maximum bioenergy generation potential exists in pulp and paperindustry assuming that black liquor is treated. This sector can generate electricenergy of 1131 GWhe/a. Distilleries and sugar is another potential area with acombined capacity of 832 GWhe/a equivalent electric energy per annum. Inaddition, some power can be generated by anaerobic digestion of press mud too.However, the technology for using press mud for biomethanation in the sugarindustry requires further development.

(3) Effluents from edible oil manufacture and coffee pulping units can be treatedanaerobically. However, little work has been done in this area and therefore, pilotscale testing is required.

High rate anaerobic digestion technologies were established in India during early1990s. Most of the plants installed prior to this period were based mainly on theconventional aerobic process. Therefore, policy measures like subsidies and fiscal


incentives are required to encourage industries to convert their existing aerobicplants to anaerobic units if the full potential is to be realized. Also, even todaymany consultants typically recommend aerobic process as it can reliably achievedischarge standards. This tendency needs to be curtailed.

Even though anaerobic process has significant economic advantage over theaerobic process, it is necessary to understand that anaerobic digestion is anend-of-pipe treatment technology only and is not a profit making venture. There-fore, instead of emphasizing the payback period, industries should invest more forthe process automation and control in order to have reliable and consistentperformance of the process. In addition, enforcement agencies can also recommendthe adaptation of high rate anaerobic digestion technologies. It may also be usefulto divert the existing government subsidies given for installation of new anaerobicdigestion plants to push the industries for the conversion of their existing aerobicplants to anaerobic process.

In general, there are many more of the success stories known for aerobicinstallations in comparison to anaerobic ones. Thus, there is a need to promote,popularize and develop confidence in anaerobic digestion technology by promotingR&D and awareness and highlighting the advantages associated with the process.This would help in achieving the maximum potential of energy generation fromindustrial effluents.

Acknowledgements

The research team is indebted to Dr R.K. Pachauri, Director General, TataEnergy Research Institute for his encouragement. The authors are also grateful toall the industries those who responded to the questionnaire and provided informa-tion for this study.

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assessment of biomethanation potential of selected industrial organic effluents in india

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