Env Isssues - Emission and Safety

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0957–5820/04/$30.00+0.00# 2004 Institution of Chemical Engineers

www.ingentaselect.com=titles=09575820.htm Trans IChemE, Part B, July 2004 Process Safety and Environmental Protection, 82(B4): 291–300

ENVIRONMENTAL ISSUES AND MANAGEMENT

IN PRIMARY COFFEE PROCESSINGH. N. CHANAKYA

1,* and A. A. P. DE ALWIS2

1Centre for the Application of Science and Technology to Rural Areas (ASTRA), Indian Institute of Science, Bangalore, India

2 Department of Chemical and Process Engineering, University of Moratuwa, Moratuwa, Sri Lanka

The paper examines the broader environmental issues and environmental management aspects of primary coffee processing in general and more specifically how it isaddressed in India. Primary processing, the production of green beans from the

coffee fruits, is practised to bring out more flavour. Coffee is an important global commodity,yet seen from a systemic view the producers and consumers of such an important commercialcommodity are far apart. Primary coffee processing, with all its attendant environment impact,takes place at the producer end. The consumers in general are unaware of these impacts. The

various methods of processing, the processing steps and the waste discharge associated withthem are reviewed. A review of pollution and associated management methods is presented. Ananaerobic bioreactor design developed and tested in a few Indian coffee plantations as a simplesolution is also described.

Keywords: wet coffee processing; coffee wastewater; biomass immobilized bed reactor; biogasrecovery.

INTRODUCTION

Coffee is an important global commodity and forms asignificant fraction of the export economy of many coun-tries. It is globally traded and at times has ranked second only to oil among traded commodities. Today it is a US$11 billion industry employing around 25 million people world-wide. The early part of this paper contains some background on global coffee movement in order to contextualizethe discussion on environmental management. Table 1 listsaround 55 countries in the world that are involved in producing coffee as a primary agricultural produce (www.ico.org).

The International Coffee Organization (ICO) covers theglobal trade and movement of coffee. Most countries in Table

1 fall into the low-income category according to the World Bank classification of economies. Table 2 presents a list of coffee-consuming nations. Table 2 indicates the per capitaconsumption, the type of roasting preferred and the maintypes of coffee products preferred (i.e. roast and ground,soluble etc.). At present, global coffee consumption patternsare changing quickly. Tables 1 and 2 show that there aredistinct differences between coffee producing and consum-ing countries. Coffee is today a buyer-driven commodity.

After the collapse of the International Coffee Agreement,coffee has been traded in a free market with significant

competition. Trade between producing and consumingcountries consists mostly of green coffee and, to a small

extent, bulk instant coffee. Imported bulk instant coffee isusually blended and re-packed in consuming countries. Theroasted coffee trade is almost always between consumingcountries. As much of the primary environmental impact isrelated to the production of green beans, it could be stated that the impacts, by and large, are felt by the coffee- producing countries (generally in the developing world).

It is interesting to observe the value addition within thiscommodity chain from the producer to the consumer (Figure 1). The amount being paid to the growers and thevalue addition in producing countries are low, and thissituation is therefore not conducive to endogenous environ-mental consciousness. Yet another characteristic of this mode

of production is the resource consumption intensity— measured either as resource used per unit area of cultivationor per unit weight of produce. High resource use intensitydraws resources from nearby areas and leaves behind a largeenvironmental footprint. It is gradually being realized that resource consumption and environmental impact in these primary producing countries are significant, especially for certain types of processing such as wet processing. Thus the producing countries, in addition to the poor financial returns,have to endure significant resource depletion and attendant environmental impact. Typical resource consumption related to coffee production is presented in Table 3 (adapted fromPonte, 2002; Talbot, 1997).

More recently, coffee marketing has increasingly become

concerned with environmental and social issues (Tallontire,2002; Damodaran, 2002). Roasters are prepared to pay a

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*Correspondence to: Dr H. N. Chanakya, Centre for the Application of Science and Technology to Rural Areas (ASTRA), Indian Institute of Science, Bangalore 560012, India.E-mail: [email protected]


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premium for coffee cultivated in an environmentally friendlymanner. This development encourages environment friendlycoffee production and processing. Brazil, Colombia, India,

Kenya, Papua New Guinea and Indonesia are countries that have sustained research into environmentally friendly coffee production and processing.

Coffee Production and Processing in India

India has a 4.5% share of the global coffee market. Theoverall impact of coffee on the environment takes place instages namely, growing, processing and consumption of coffee (Viani, 1995).

Growing coffeeThere are three common species of coffee: robusta,

arabica and liberica. Only the first two are of commercial

importance. Robusta is a high-yielding plant, resistant to disease, growing at lower elevation, characterized by‘harsh’ flavours, containing about 2% caffeine and yielding

1–1.5 kg green coffee per plant per year. It is used in lower grade coffee, generally not found in specialty shops, and isoften used to make soluble (instant) coffee and popular commercial blends. Arabica grows best at altitudes of 3000– 6500 feet, has a refined flavour, contains about 1% caffeineand yields 0.5–0.8 kg per plant per year. It is a coffee that specialty roasters search for and accounts for about 75% of world production. Arabica is susceptible to disease and poor climatic conditions such as frost and drought. It requirescareful cultivation and larger inputs.

Conversion of forest lands to coffee plantations or aban-donment of existing plantations have definite environmentalimpacts, such as loss of biodiversity, habitat fragmentation, pesticide poisoning and soil degradation and erosion. The

removal of natural shade trees in the conversion of ‘shade’coffee to ‘sun’ coffee, etc. is not an area of major concern inIndia.

Agricultural practices such as the use of organic herbicides,inorganic and synthetic pesticides, efficiency of use of inor-ganic fertilizers, etc., determine the environmental issuesarising from them. For instance, the use of agricultural pesticides significantly changes the toxicity characteristics of

Table 1. List of coffee-producing countries in the world.

AngolaBeninBoliviaBrazilBurundiCameroonCentral African Republic

Cote d’IvoireColombiaCongo, Republic of CongoDemocratic Republic of

Costa RicaCubaDominican RepublicEcuador El Salvador Equatorial Guinea

EthiopiaGabonGhanaGuatemalaGuineaHaitiHonduras

IndiaIndonesiaJamaicaKenyaLiberiaMadagascar MalawiMexico Nicaragua Nigeria

PanamaPapua New GuineaParaguayPeruPhilippinesRwandaSierra Leone

Sri LankaTanzaniaThailand TogoTrinidad and

TobagoUgandaVietnamZambiaZimbabwe

Table 2. List of major coffee consuming countries in the world.

Country

Per capita,

kg year 1 RoastingRoasting and

grindingSoluble=

instant

Finland 12.4 Light Sweden 11.45 Light Denmark 11.03 Medium Norway 9.71 Light Netherlands 7.7 Light Belgium=

Luxembourg7.26 Medium

Germany 6.42 Light Switzerland 5.69 Medium

France 5.67 Dark Austria 5.67 Dark USA 4.8 Light Canada 4.34 Light Italy 3.7 Dark Hungary 3.2 Dark Israel 2.58 Dark Cyprus 2.49 Dark Spain 2.46 Dark Yugoslavia 2.25 Dark Greece 2.23 Dark UK 2.19 Medium Australia 2.06 Medium New Zealand 1.78 Medium Japan 1.48 Light Portugal 1.25 Dark Ireland 1 Medium Hong Kong 0.61 Medium

Figure 1. Distribution of coffee income along the coffee chain (1989–1995).

Table 3. A summary of resource consumption statistics (www.secure.speakeasy.net =kalanicoffee=eco.htm Babbu Reddy et al., 2001).

Coffee is an agricultural crop.s the second largest agricultural crop in the world;s the third most heavily sprayed crop in the world.

A coffee tree produces on average 3000–6000 cherries per year. Normally a cherry has two beans. One pound (0.45 kg) of coffee consistsof 4000 beans. One hundred coffee beans make one cup of coffee. Thisrepresents one coffee tree per one pound of roasted coffee.

A typical best quality ‘arabica’ yield is 0.5–0.8kg of green beans per year.

A typical cup of coffee (125 ml) contains approximately 12.2 g of coffee powder.

For average consumption of two cups per day:s the yield from 18 coffee trees is necessary to supply the annual green

bean requirement;s the growth and the maintenance of these 18 plants require 5kg of

chemical fertilizer and 230 g of pesticides;s in producing the green beans 20 kg of pulp would be stripped away as

waste;s 1200 kg of green bean production would require 1 hectare of land.

Trans IChemE, Part B, Process Safety and Environmental Protection, 2004, 82(B4): 291–300

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the wastewater. There is little control over the use of pesticides,as most primary producers are developing countries. In addi-tion to complex organic products, heavy metals could also find their way into the wastewater. Coffee wastes, for example,contain copper, which comes from the application of copper- based fungicide used in the control of coffee diseases.Cenicafe in Colombia has introduced the use of agricultural

biotechnology practices to coffee processing. It introduced integrated pest management (IPM) practices by releasing tinywasps that eat the Broca (coffee berry borer) instead of usinginsecticides. This reduces crop damage to less than 5%. This,carried out with the International Institute of BiologicalControl, had been a pioneering plant biotechnology project (www.cabi.org). Herbicide and synthetic pesticide use inIndian coffee is minimal.

Processing coffeeThe processing steps in coffee may be grouped into primary,

secondary and tertiary steps. Primary coffee processing refersto the processing of coffee fruit to obtain coffee beans (also

called green beans). The next stage refers to hulling, roastingand grinding. Tertiary processing involves making of instant coffee and =or other value addition operations.

Primary processing Primary coffee processing is carried out within coffee

plantations. Primary processing produces green beans fromthe coffee fruit. The coffee fruit consists of coloured exocarp(skin), fleshy yellowish-white mesocarp (pulp), mucilage layers(covering the two beans joined together along the flat sides and made up mainly of pectin) and two coats (first a thin fibroustextured parchment and second a fine membrane, silver skin).

Primary processing is done in two major ways—the dry

and wet methods. In the ‘dry’ method, the fruits are picked and laid out to dry in the sun for 3–4 weeks. A hullingmachine then strips away the outer skin and pulp. The beansare not always consistent in quality and producing high-quality coffee with the dry method is challenging becausethe beans are exposed to climatic conditions during thedrying process. The product is known as the dry natural‘cherry’. Most robusta and very little arabica is processed inthis way. Value added is usually low. Solid wastes aregenerated and they are used as fuel for thermal applications.The ‘wet’ method or ‘washed’ coffee methods are used inlocations with plentiful supplies of fresh water. It is carried out in two steps, pulping and washing. One can note thefollowing distribution of wet and dry processing in the producing countries, although many countries follow bothmethods and the rest aspire to change to wet processing if possible (www.ico.org).

wet processing —Bolivia, Burundi, Cameroon, Colombia,Costa Rica, Cuba, Dominican Republic, East Timor,Equador, El Salvador, Equatorial Guinea, Ethiopia,Guatemala, Honduras, India, Indonesia, Jamaica, Kenya,Malawi, Mexico, Nicaragua, Papua New Guinea,Rwanda, Tanzania, Uganda, Venezuela, Vietnam,Zambia, Zimbabwe;

dry processing —Angola, Benin, Brazil, Central AfricanRepublic, Congo, Congo Democratic Republic, Cote

d’Ivoire, Gabon, Ghana, Guinea, Haiti, Madagascar, Nigeria, Paraguay, Philippines, Sri Lanka, Thailand, Togo.

Pulping The coffee fruit is squeezed between two serrated metal

plates and the skin and the pulp are detached from the seed.The mucilage-coated seeds and fruit skins (with pulp) areseparated into different streams. The skin and pulp arecarried away in a stream of flowing water. In the receivingtank the skin with the pulp is separated out (solid waste)

from the waste water (pulp water). The pulp water most often joins the wastewater stream. However, wherever thereis an acute shortage of fresh water (as in many plantationstoday), this water is recovered and recycled for 2–5 days inthe pulping process. In India three main types of pulpers areused—the drum, disc and slotted types (Chellamuthu et al.,2000). At a few locations, modified designs use screwconveyers to carry the skin and pulp and therefore do not have a significant pulp water stream. The seeds at this stagecarry a mucilage layer that is removed in the next step.

Washing (removal of mucilage)Freshly pulped coffee seeds are covered with a highly

slippery mucilaginous layer approximately 1.5 mm thick and translucent. There are five methods of removing this muci-lage (Ranganna, 2002) namely, natural fermentation, chemi-cal methods, warm water soaking, enzymatic fermentationand attrition. The most popular methods combine fermenta-tion and attrition. The beans, still enclosed in a sticky inner mucilage and parchment wrapper, are soaked for 4–72 h infermentation tanks. This fermentation loosens the remainingmucilage through a series of enzymatic reactions. It is then‘washed’ away in a combination of the processes of washingand attrition (mostly by a machine called a ‘washer’).Fermentation time is controlled to achieve the right qualityof beans. The resultant coffee is termed ‘parchment coffee’.

Sometimes coffee fruits are washed and sorted as in thewashed method, but are not placed in fermentation tanks.Instead they are set out to dry. This also results in parchment coffee called semi-washed coffee. The washed coffee, with amoisture content of 55%, is dried in the sun to a moisturecontent of 15%. The dried coffee is later hulled to removethe parchment and the silver skin. The overall sequence of operations typical for a South Indian plantation is given inFigure 2. Note that for robusta most Indian plantationsfollow the dry processing method.

Secondary processing Dried green beans are subjected to mechanical removal of

the parchment layer from the bean. The beans are thengraded according to size, shape, weight, colour and unifor-mity. The beans are then roasted to give them a dark browncolour and the strong aroma and taste that are usuallyassociated with coffee. Roasting represents the largest frac-tion of value addition. Secondary processing has lessenvironmental impact and near zero impact on water resources. The air emissions perhaps are the only aspect that needs to be considered. Very little secondary processingis carried out in producer countries except for internalconsumption or bulk soluble coffee.

Tertiary processing

Coffee powder may be subjected to different processes todevelop product varieties. Instant coffee manufacture and


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decaffeinated coffee are two main products from tertiarytreatment steps. The production of instant coffee generateslarge volumes of high-strength particle-bearing wastewater.The waste is also discharged at high temperature (70C).Wastewater treatment aspects of tertiary processing havereceived much more attention and these activities take placemostly in developed countries (Dinsdale et al., 1996, 1997;Fernandez and Forster, 1994; Kostenberg and Marchaim,1993).

Environmental Impacts of Primary

Coffee Processing

The arabica is usually subjected to wet processing. Thusfrom an environmental impact review it is wet processingwhich merits attention. This is schematically shown inFigure 3. On average, 5 tons of fruits are processed to get 1 ton of parchment coffee. On a mass basis this is 3 tonnes of organic waste load directly from the fruit and 1 tonne of moisture left in the bean (sun-dried). The organic load coming from the pulper and washer streams is mixed withsignificant quantities of water used in the process. The fruit skin is, however, removed as a solid waste stream. Theamount of water used varies significantly with location and hence there is significant variation in the strength of waste-

water generated. Two or three wastewater streams can beidentified—wastewater from pulping and washing operations

(the first wash operation carries mechanically separated mucilage fractions; the second wash is the post-fermentationwash).

Water consumption and concomitant wastewater dis-charged range from 1.5 to 23 m3 per tonne of fruit processed. No water is consumed by the process. Wet processing with itssignificant quantities of liquid effluent has received much

attention, although international good practices are still wellshort of optimum. Adams and Dougan (1987) reviewed thewaste products from coffee processing. Wet processing isattractive as it yields a superior quality product and countriesthat carry out dry processing of coffee are interested inswitching to wet processing to increase their incomes. The pollution resulting from 1 tonne of clean processed coffee isestimated at being equivalent to 273 m3 of crude domesticsewage. This corresponds to daily sewage from a populationof approximately 2000 persons (Calzada et al., 1989).Coulthard (1979) reported an average water consumption of 8.4m3 per tonne of fruit processed. Water usage for coffee processing by Indian coffee estates varies from 2.25 to 23 m3

per tonne of fruit processed (ASTRA, 2002a). Field observa-tions suggest that low water use in most cases is due to water shortages in the pulping season or where estates make aneffort not to discharge any wastewater. The constituents of thethree streams of effluents (pulper, washer and secondarywash) are predominantly organic and biological in nature.They rapidly ferment to produce organic acids, lowered pH,eutrophication of receiving water bodies and malodours.Currently the effluents are treated in anaerobic—aerobiclagoons. Groundwater pollution from faulty lagoons is alsoa concern.

Characteristics of coffee effluents

The characteristics of wastewater derived from analysis of several Indian estates are given in Table 4 (ASTRA 2002a).Coffee effluent is acidic and has a high content of suspended and dissolved organic matter. Coffee wastewater is rich insugars and pectins and is thus amenable to rapid biodegra-dation. The high BOD=COD (biological=chemical oxygendemand) ratio is also an indication of the suitability for biological treatment. Field studies have determined coffee processing to discharge up to 45 kg COD per tonne of fruit processed. Their concentration in wastewater varies inver-sely according to the quantity of water used in the process(ASTRA, 2002a). Table 5 presents wastewater characteris-tics from Kenyan and Mexican studies and is presented for comparison.

ASTRA studies indicate wastewaters of higher strengths.As the processing material is essentially the same,

Figure 2. Primary processing of coffee (block arrows indicate steps that yield wastewater).

Figure 3. Block diagram of an Indian pulping operation.




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this suggests that Kenyan and Mexican situations used significantly higher quantities of processing water, thusdiluting the waste stream.

Environmental Management in PrimaryCoffee Processing

From the preceding discussions on coffee processing as asource of environmental concerns, the following overall processing needs emerge:

reduction of water usage leading to reduction in thevolume of wastewater generated;

alternative uses for ‘by-products’ of coffee processing; appropriate methods of wastewater treatment and

resource recovery technologies.

Field observations by ASTRA suggest that primary produ-cers of coffee carry out limited wastewater treatment.Burdened with adverse market conditions, inadequate tech-nology support and service providers, the plantations focus

primarily their production activities. Wastes receive muchless attention in spite of plantation owners’ concerns and conscious efforts to avoid environmental damage. In theliterature, of the two main liquid streams, pulp waste hasreceived more attention as it is easier to address. The washwater, however, has a higher load of suspended and dissolved organic matter.

Reducing Water Used andWastewater Generation

From data presented in Table 4 (range of concentration), it is seen that there is potential to reduce water use—from anexcessive 23 to just 1.5 l per kg of fruit processed. This is animportant first step in any situation. Reduction in water used has also arisen from a few other causes. An increase in thenumber of plantations carrying out wet processing hasresulted in water shortages, at least towards the end of the pulping season (end January to early March). In addition, adrought prevailing over the last three years, lower water

quality in streams resulting from lean-flow and high wastedischarges, etc., have aggravated the water shortage. Thisreduction is an important first step in controlling investment in treatment and has been a learning step, especially in places where plantations had to choose between expensivelagoons or less expensive bioreactors. The following steps,leading to reduced water use, have been adopted by somecoffee processing units:

reuse of pulp water for a few cycles prior to discharge; deployment of new machinery that use less water; and eliminating a few fermentation steps.

However, these voluntary efforts at water use reductionalways carry a fear that reducing water use will sacrifice

quality and sale price.In traditional processing practices (23 l per kg of fruit

processed), about 20% of the wastewater originates from the pulping process and the rest comes from various conveyanceand washing processes. Baseline studies on water use and quality of waste water (ASTRA, 2002b) have suggested that,when water has to be obtained from sources other than free-flowing natural streams, usage reduces from the above highvalue to about 6–8 l per kg of fruit processed, and sometimes below this level. Net water consumption has also beenreduced by reuse of water used in transportation of fruit tothe pulper machines (pulp water). Field estimates revealed that a 66% reduction in water use was achieved in some

Table 4. Physico-chemical characteristics of coffee effluents (range,ASTRA, 2002a).

Parameter UnitsPulpwater

Wash water (semi-washed

coffee)Secondarywash water

Plantations involved with partial anaerobic treatment and partial control on water use

pH 4–7 4–6 4–4.5Total

solids (TS)g l1 4–10 1.2–44 5.6–13.4

COD g l1 1.5–9 1.2–41.7 4.3–9.8BOD=COD 0.5–0.86 0.5–0.9 0.5–0.7Total sugars g l1 0.8–6 1–36.7 3.9–7.2Reducing

sugarsg l1 0.05–1.8 0.2–22.2 0.8–2.6

Acidity g l1 0.1–0.8 0.07–1.3 0.18–1.2

Plantations using bioreactors and exercising control on water use in wet processing. pH 3.9–6.9 4–6.3 N.A.Total

solids (TS)g l1 3.1–30.8 16.4–70 N.A.

COD g l1 2.6–25.8 15.5–65 N.A.BOD=COD 0.37–0.97 0.5–0.9 N.A.

Total sugars g l1

2.3–23 14.3–53 N.A.Reducing

sugarsg l1 0.8–6 5.3–30 N.A.

Acidity g l1 0.1–1.6 0.2–1.9 N.A.

Table 5. Physico-chemical characteristics of coffee pulping wastewater effluents.

Kenya (Gathuo, 1995;Gathuo et al., 1991)

Parameter UnitsWith

recirculationWithout

recirculationMexico (Bello-Mendoza and

Castillo-Rivera, 1998)a

pH — 4–5 4–5 5.4 (0.74)Total Solids mg l1 1950–4800 2200–4600Total dissolved solids=total solids % 50–90COD mg l1 1650–2800 850–1750 2480 (1158)BOD mg l1 1200–3000 1400–3900 1443 (483)Total alkalinity g l1 0.039 (0.027)

a The standard deviation for each sample in parentheses.


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estates for water used in conveying fruit. A significant reduction was also achieved for pulper water, brought about by reusing pulp water for a period ranging from 3to 5 days. Field measurements have shown that it is possibleto bring down water used for pulping to about 0.5 l per kg of fruit processed. Similarly a large reduction in wash water has been achieved, leading to a discharge of 0.7 l wash water

per kg fruit processed (ASTRA, 2002a). This level of overall reduction in water use translates into a nearly 20-fold reduction in wastewater volume and an equivalent increase in organic strength of the effluent (Table 4). Work-ing with processing plant operators, it has been found that it is possible to bring down the water use to less than 1.5 l per kg of fruit processed with existing machinery and operatingskills (ASTRA, 2002a).

Efficient Machinery and AlternativeUses for Effluents

So far, the need to show low concentration of organics inthe coffee effluents (‘non-polluting’), and a fear of sacrifi-cing parchment quality by recovering concentrated effluent (inadequate mucilage removal), have deterred voluntaryefforts of reduction in water usage by coffee planters(personal communication). A significant contribution fromCenicafe is the development of a new pulper device toreduce water usage in on-farm processing from about 8 to


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Figure 4 provides a block diagram of this NEERI processsuggested for coffee plantations in India.

The Karnataka State Pollution Control Board web site(www.kspcsb.karnic.in) states that the coffee estates mainlyuse (unlined) ‘Kutcha’ pits instead of the recommended stone-lined, acid-proof masonry structures. Major advan-tages of the stabilization ponds are the low initial costs and ease of operation. Some disadvantages include odour

problems and mosquito breeding (public health issues),loss of cultivable area, unsatisfactory treatment, potentialfor groundwater contamination and low loading rates. Under normal ponding conditions every hectare of plantation willneed 230 m2 pond area (10 tonnes of fruit per ha, 23 m3

water per tonne of fruit, 1 m pond depth). Ponds and lagoonsalso have inherent low conversion rates. For example typicallagoons have loading rates as low as 0.05–0.2 kg VS m3 day(under field conditions) (VS¼ volatile solids). Typical cattledung plants in India operate at a conversion rate of 0.5 kgVS m3 day (Rajabapaiah et al., 1979). When these rates arecorrected for low ambient temperatures (10–15C), low N-nutrition, low methanogen recycle, etc., the conversionrates are expected to be very low, leading to long retention

times. With increased enforcement leading to a switch tostone-lined, acid-proof cement-based lagoon construction,the cost advantage has also disappeared. With a gradualincrease in the cost of land, a decrease in water use (higher effluent concentration), stricter pollution laws, the pondsand lagoons have lost viability and alternative and appropriate technologies and processes are required. Lower valueaddition at the producer level and the need for change intechnologies require alternative environment management strategies.

Field observations and data presented in Table 4 reveal that the organic strength of coffee wastewater is gradually rising.As a result of this high strength, the lagoon system is subject

to significant overloading. Lagoons receive effluents at 10–20 times the normal loading rates (i.e. 0.05–0.07 kgCOD or VSm3 day1). This inevitably leads to processfailures, low pH levels, a


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an anaerobic system (lagoon, bioreactors, UASB, etc. that remove over 90% COD in one step). Field observations revealthat secondary treatment by oxidative lagoons were veryrarely being operated to meet best practices and artificialaeration was almost non-existent in these plantations.

Anaerobic Digesters (AD) with Biogas RecoverySystems

Anaerobic digestion whereby the dissolved and suspended organic carbon of wastewater is converted to biogas is an extremely effective way of handling a high-strength effluent. The process has a positive energy balanceand as such is a resource recovery method of waste treat-ment. The earliest reported AD for coffee is from Kenya,where the use of 150 units has been reported for batchdigestion of coffee pulp (Aagaard, 1961; Maheshwaran,1988; Anonymous, 1967). Coffee pulp has proven to be agood biogas producer when mixed with cattle manure to buffer the medium against pH changes arising from the

rapid catabolism of soluble sugars. A Mexican researchgroup has reported similarly using a semi-continuous process with a mixture of 84% pulp with 16% manurewith a retention time of 20 days and a loading rate of 3.6 kgvolatile solids m3 day1 (Monteverde and Olguin, 1984).In some instances old pulp has been digested without theuse of manure. The absence of manure from animalhusbandry, especially cow dung which is a ready sourceof methanogens, has surfaced as a problem (Papua NewGuinea, Calvert, 1997). In many of the coffee plantations inSouth India, coffee processing water (concentrated washwater) has been used in place of cattle dung in existingsmall-scale semi-continuous cattle dung-type biogas plants

during the pulping season (personal communication). Asignificant level of R&D as well as field trials has beenreported on conversion of coffee wet processing wastes to biogas and compost. In spite of such efforts, the adoption of such technologies has been rather slow. Thus it is seen that,while R&D reports are many, field trials and long-termstudies have been few. Many laboratory studies with respect to coffee pulp had been reported (Calle, 1957, Boopathy,1987, 1988; Boopathy et al., 1986; Boopathy and Mariap- pan, 1984). These studies are summarized in Table 7,although a comprehensive summary is not an objectivehere. Adams and Dougan (1987) in their review consider anaerobic digestion to be an attractive concept for thetreatment of coffee waste due to the virtues of assisting

the disposal of both pulp and wastewater with a useful yield of gaseous fuel (potentially around 66 m3 per ton of pulp).The unreliability of the process, the requirement for skilled attention and the high capital costs are cited as reasons whyselection of the technology is unjustified.

Anaerobic digestion technologies seem to be driven bythree different approaches namely:

low cost, slow and rugged technologies requiring lowskills of operation exemplified by stabilization ponds,anaerobic–aerobic lagoons, etc.;

recourse to advanced technologies for faster and efficient conversion to biogas exemplified by UASB, PBRs,diphasic=two-stage digestion, etc.;

multiple use and multi-feed reactors for year-round operation with coffee and local wastes.

These technologies carry varying investment costs, oper-ating skills, operating costs and environmental branding.These also lead to different strategies in environment management by coffee producers. For a long time inIndia, anaerobic–aerobic lagoons have been the only tech-nology accepted by most stakeholders. As argued earlier inthe text, due to the poor water situation and the number of

estates involved in pulping, this technology needs to begradually phased out. This technology in its current formsolves only the earlier kind of environmental problems.Further, this end-of-pipe approach is not conducive for backward integration of best practices and environmentalconsciousness. On the other hand large numbers of existing biogas=anaerobic digester technologies are being adapted tocoffee effluents as primary feedstock. Many of them func-tion well and would require operation and management strategies just like those followed in industrial wastewater treatment systems. The high initial investment costs, theminimum economic size-based bottom-line, high skillsneeded for operators, etc., are conducive for adoption by

large plantations but not small and medium size plantationsthat dominate the Indian coffee cultivation scenario. Thisalso is an end-of-the pipe solution and is unlikely tosignificantly influence the backward integration of best practices. The majority of Indian coffee plantations fallin the small and medium categories processing under 10 tonnes fruit per day, and the strategy must accommodatethe seasonal nature of the process.

This situation is conducive for a third kind of anaerobicreactors that can function with multiple feed stock—bothsolid and liquid wastes generated on the coffee plantation— throughout the year. A variant of downflow whole cellimmobilized reactor (Chanakya et al., 1998; currentlycalled the ASTRA bioreactor) has been functioning in

15 locations for periods of up to 4 years (see for examplewww.ginimao.com). The reactor functions like a plug-flowreactor using various biomass feed stocks found on thecoffee plantation. In this mode it is made to accumulate partially digested herbaceous biomass on which high popu-lations of methanogens remain adhered. During the pulpingseason, biomass feeding is stopped and coffee effluents(COD >2 5 g l1) is passed horizontally through the metha-nogen rich biomass bed. Over 90% COD is removed (Table7). As this system can accept a high concentration effluent,reactors built are small, occupying only 5% of the spaceoriginally allocated to anaerobic lagoons, and plantationsalso reduce their water needs for processing by about 90%.

The bioreactors are built as 60 m

3

modules by plantationsusing largely local materials and skills. It costs US$1200 per module. Each module has a peak overall loading rate(OLR) of 2 kg BOD m3 day1 arising from pulping 1–2tonnes of fruit per day when operated at 15–20C. Theresource recovery concept embodies the extraction of usefulenergy, trapping of excess dissolved and suspended plant nutrients and re-use of the wastewater on-farm for irrigation.The digested biomass support is extracted as compost (soilconditioner) for the plantation. The bioreactor treated efflu-ent has 0.6–1.0 g l1 BOD and requires a short stay in anaerobic lagoon before reuse on land for irrigation. In thefuture, as more, of the small plantations take to wet proces-sing, there will be need to use even more best practices

integrated resource recovery systems—avoiding environ-mental stresses with process modifications rather than




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Table 7. Summary of R&D and field trials on anaerobic digestion of coffee waste water.

Authors Year CountryScale of operation

Type of reactor

Feed ratekg m3 d 1

Conversion(% or kgm3 day1 H

Calle 1957 Spain Laboratory Batch 60 kg of pulp and 5 kg of cow dungin 182l of water

NA 60

Maheswaran 1988 Kenya Batch Review of work in Kenya—the only successful biogas incoffee pulp (uses a masticated mixture)

Calzada et al.(diphasic)

1984 Guatemala Laboratory Acid phase and methane phase

22 kg COD 57–71 % CODreduction

2

Calzada et al.(packed bed reactor)

1984 Guatemala Laboratory PBR (PUF) 9–22 kg VSm3 day7 1

40–47% conversionof sugars

1–

Gathuo (pulp) 1995 Kenya Bench NA 7.2 kg DM 90 4–Gathuo et al.

(wastewater)1991 Kenya Bench NA 6.5 kg COD 90 4–

BTG(www.btgworld.com)

1999 Costa Rica= Netherlands

Demonstrationand 250 m3

UASB 2000–3000 kg COD 75–80% COD 1–

Calvert 1997 PNG Bench UASB Inlet feed—8–10 g BOD 80% BODremoval

Bello-Mendozaand Castillo-Rivera

1988 Mexico Pilot UASB-filter 1.89 kg COD 77% 0

Boopathy et al.(1986)

1986 India Laboratory Bottle C: N ration study for satisfactory AD of coffee pulp—30

Boopathy 1988 India=Italy Laboratory 2.5 l batch Metabolism of protein, carbohydrates and lipid of coffeewas found to be higher compared with a cow dung di

Boopathy 1987 India=UK Laboratory Cow dung was identified as the best innoculum material fsubstrate

Boopathy 1987 India Laboratory CSTR Boopathy and

Mariappan1984 India Laboratory CSTR Coffee pulp at 25% total solids concentration produced

Chanakya et al. 1998 India Laboratory BIBR 8–10 kg TS 85% 0ASTRA 2002b India Field BIBR 2–3 kg COD 90% 7–

CSTR, completely strirred tank reactor (often unstirred); PBR, packed bed reactor; UASB, upflow anaerobic sludge blanket; PUF, polyurethane foam; BIBR, biom basis; DM, dry matter; VS, volatile solids.

Tr an s I Ch e mE ,P ar t B ,P r o c e s s S a f e t y a n d E n v i r o n m e n t a

l P r o t e c t i o n ,2 0 0 4 , 8 2 ( B4 ) : 2 9 1 – 3 0 0


10/10

attempting end-of-pipe treatment. Large quantities of biogas produced are used on-farm for running machinery, domesticcooking, yard lighting, etc., saving wood and fossil fuelsand thereby significantly reducing the environmental footprint.

CONCLUSIONS

The review shows that there are significant problemsfacing the producer countries and the situation is steadilydeteriorating further. The additional environmental burden is perceived to be high. There is no one solution, although asolution which will bring in environmental protectionwith resource-recovery will help significantly. Cenicafe’s pulping system, ASTRA’s plug flow type bioreactor system, composting and vermi-composting methods appear to significantly benefit in impact reduction in primary proces-sing. ASTRA’s design overcomes the limitations listed by thereview of Adams and Dougan. The significance is that it canhandle both the solid and liquid waste streams together inaddition to being a system of lower operating and mainte-nance cost. Financing appears to be a major hurdle inimplementing wastewater treatment in primary producingcountries. In India external subsidy via an international donor programme has sparked the ASTRA implementation of atechnology that had been pursued for a while. In Costa Rica it appears that climate change convention had found a partner in implementing a government directive on pollution control.

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ACKNOWLEDGEMENT

The authors would like to express their gratitude to Indo-NorwegianEnvironment Program (INEP) for the financial support, which provided thefoundation for this work.

The manuscript was received 23 July 2003 and accepted for publication22 March 2004.



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