Remediation Measures

Coffee processing involves large volumes of water and wastewater. Coffee growing estates draw water for pulping from huge natural and man-made water bodies. These water bodies in turn feed the down stream lakes or streams. Coffee effluent, which is rich in sugars, pectin, phenolics, etc, are biodegradable, contains a high BOD/COD load. Coffee effluent poses significant threat to man-made and natural lake ecosystems. An organic load of 35kg BOD/tonne of fruit processed is released to natural and man-made water bodies. The large effluent volume is resorted to because of the absence of appropriate methods to treat high strength waters as well as the high costs of treatment. If water use in processing is reduced, a thick and concentrated effluent is produced, which is difficult to treat in the conventional lagoon systems. Conventional lagoon systems often improperly operated results in only < 50% BOD removal and a load of 10-18 kg BOD/ tonne fruit is let into water bodies inadvertently. This paper proposes management of this pollution through the use of biomass immobilized bioreactors (an appropriate technology solutions) coupled to aerobic lagoons > 95% BOD is removed and < 1kg BOD enters the water bodies for every ton of fruit processed. The reduction in operating costs and gaseous fuel is an attractive bonus especially to small and medium plantations dispersed around 4 districts of Karnataka. This paper discusses results of a few field trials with bioreactor technology and pollution management.

Water is very important for coffee fruit processing - where the pulp portions surrounding the coffee bean is squeezed out and washed thoroughly with copious quantities of water drawn from the nearest tank or streams that feed these tanks. Coffee processing takes place after the monsoon fades away and there is little flow of water in the various streams arising from the Western Ghats. To overcome this shortage, water from natural and man-made lakes and water bodies are pumped out and the resultant spent water, treated only partially, becomes the main source of water to the next water body (usually another lake /tank) downstream. There are very few coffee plantations that have the capability to remove all undesirable organics and minerals from the coffee effluents before they reach various water bodies downstream. Sometimes the problem is so severe that in many towns downstream, drinking water pumped from natural tanks possess a deep purple shade - characteristic of partly treated coffee effluents reaching these water bodies. Today, coffee cultivation has gradually spread from the wetter hill slopes of the Western Ghats to the adjoining drier rolling lands where natural and manmade water bodies are important water reservoirs. Coffee processing has now created a great demand for water stored in these reservoirs and is adding a new dimension to this problem.

Karnataka is the largest coffee growing and coffee pulping state in India accounting for about 72% of total coffee produced. More than 3000 coffee estates located in the districts of Chikkamagalur, Kodagu, Hassan and Mysore carry out pulping (wet processing that needs huge quantities of water as well as discharge equally large quantities of water). It is estimated that nearly half the coffee grown here (40‑50%) is processed by wet pulping method to yield a ‘superior' quality product compared to the dry processing option also available. However, wet processing produces a BOD /COD rich effluent. The coffee wastewater is rich in simple organic matter such as sugars, pectin and primary cell walls released during the pulping process (removal of skin) and washing (removal of mucilage layer surrounding the coffee bean). A significant part of the wastewater enters the riverine systems while an equally large quantity is held in man-made and natural water tanks posing a significant water pollution threat. It is estimated that every tonne of coffee produced releases 80,000 litres of wastewater (Damodaran, 1998; Coffee Board, 2000). The figures for this discharge are at an average concentration of 1000 mg/l BOD discharged with around 80,000 litres per tonne of coffee produced, and at an annual production of about 300,000 tonnes coffee spread over three months. The nature of the stream flow and man-made water bodies are shown in Figures 1 and 2.

Figure 1: River pollution due to coffee effluents

Figure 2: Water bodies converted to Anaerobic lagoons on a coffee estate

The nature of the problem may directly be related to the absence of appropriate conservation and remediation measures and technologies. Firstly it is important to find ways of reducing the water consumed for processing. By reducing the water used it is possible to conserve water. There are simple ways to reduce the water usage in processing (from 80 ‑ 93 m 3 /t of clean coffee) to about 6m 3 /t coffee (Damodaran 1998). If an attempt is made merely to reduce water used and generating a thick and concentrated effluent, the main product (pulped coffee bean) is considered slightly inferior while on the other the effluent is too concentrated to be treated by conventional anaerobic lagoons or let into normal water bodies by dilution or simple treatment processes - a classic chicken and egg problem. There is therefore a disincentive to conserve and this barrier needs to be overcome.

The recommended treatment process of using "anaerobic and aerobic" lagoons is not suitable for high strength wastewater that comes from adopting water conservation measures. Concentrated effluents cannot be treated in conventional lagoons and thus do not satisfy the stipulated standards for wastewater discharge. Hence it is not attractive to conserve water in processing. In addition to this, these lagoons are often overloaded and thus the microbial process breaks down releasing partially treated (20-30% BOD removal) effluent. A major disincentive to adopt remediation measures is the large area of land that needs to be assigned for making water treatment lagoons. Thus the nature of the problem may simply stated to be

i. the absence of an appropriate water conservation strategy during wet coffee processing and

ii. the absence of a suitable technology that can handle concentrated effluents with smaller demand on land and resources.

Further, it may also be stated that the important site of remedial action needs to be at each of the dispersed generation points (organic load). Remedial action for water bodies should therefore focus on management and conservation.

Coffee processing is done during the dry period of the year (November ‑ March). The partially treated coffee wastewater containing sugars and sugar derivatives (sucrose, fructose and pectin), when let into the water bodies during lean flow /low storage periods, have the potential to result in rapid eutrophication and pose a great danger to the receiving waters. In the event that a 90% reduction in demand for process water is achieved, it will be a great help to the coffee growers especially in areas where water is in short supply or ends up in lakes and tanks. As a consequence of reduction in water use by 90%, water discharged will also be reduced in the same range. Such drastic reduction in water use can be achieved in a combination of practices as described in the following text. Water in coffee processing is used in two major steps

• washing (attrition and washing off the mucilage adhering to the coffee beans).

Recycling of water for the pulping operations e.g. berry floatation and skin conveying processes reduces 70‑80% of water usage.

Wash water is rich in sugars and pectic material in the range of 60-120g/l but owing to its high viscosity it cannot be recovered at this high concentrations. The need to remove this mucilage completely compels processing units to use a lot of water in this step (80%). Wash water is therefore not usually recycled. Pre‑fermentation of pulped beans reduces the effluent production by 35% (Ramprasad, 1997). This results in easy and complete removal of mucilage with lower water use (Shanmukhappa, et al ., 1998) and the volume for wastewater to be treated becomes smaller.

In this way coffee effluent has polluted the Hirekolale tank situated at the bottom of the Chikkamagalur hill range. This is the drinking water source for Chikkamagalur town. Most of the estates have their own man made huge lakes/tanks for the storage of water for pulping activities as well as for effluent storage. Under provision of the existing law it is an offence to discharge untreated effluents however, there is little clarity on the threats if the very same effluent is held in an earthen lined tank for over 4-6 months. Further, the water body is usually within a private property. Also, there is no discharge and therefore no "cognizable" offence. Many coffee plantations situated in Chikkamagalur district utilise about 18‑23m 3 water for pulping. In order to meet this requirement they have a huge water tank that stores fresh water from run-off (tanks /lakes) for pulping operations. Finally the wastewater is discharged from anaerobic lagoons to another ground level large water tank. In times of drought this nutrient rich water is itself sprinkled on the crop as irrigation water. This is possible if the water has been subjected to about four months of natural treatment in this system of ponds and tanks. There is little understanding of the impact of impounding large volumes of water in natural and man-made water bodies. Second, the resultant sludges are usually washed off in subsequent rainy seasons; there is little understanding of this also.

• To propose a strategy to manage water quality threats to water bodies from coffee processing activities.

• To show that (for coffee processing systems), with a combination of simple conservation measures, appropriate technology interventions and remediation /reuse strategies water body and water quality degeneration can be kept in check minimising ecological damage to receiving water bodies.

Water quality measurements were made on site at various coffee plantations with and without lagoon /bioreactor based wastewater treatment systems. Water samples in these cases were collected at random, stored in ice and subsequently frozen at the receiving laboratory till various physico-chemical analyses were carried out. Water samples were collected from the coffee plantation at four points by random sampling on a weekly basis. These sampling points were

The physico‑chemical parameters analysed were pH, total solids (TS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total carbohydrates, reducing sugars, titrable acidity and volatile fatty acids (VFA).

A flow chart is prepared using actual field data of a situation where the water body is polluted by coffee processing unit. The data from a functioning bioreactor is used along with this to show the extent of organic matter that could be removed from the water (Figure 3).

The properties of the main pollutant, namely the wash water is presented in Table 1. This is characterized by a pH generally lower than <6.0. It is also seen from the Table that the COD, total sugar and total solid contents were of similar magnitude compared to each other. This indicated that the major organic pollutant was organic in nature and generally saccharic in nature. The COD/BOD ratio is the indicator of biodegradability of the wastewater. The COD/BOD ratio was found to be 2 and BOD/reducing sugar ratio was 1 indicating that not all the total sugars (mono and poly saccharides) were degraded in a span of 5 days at 20°C. In this case the VFAs produced during the fermentation of sugars contributed to the total titrable acidity. The total titrable acidity was 0.73g/l (average). Such values suggest that incompletely decomposed acid intermediates may be expected.

Table 2 shows the characteristics of pulp water sample. Pulp water pH was <5.0 due to the fermentation of sugars. Pulp water constitutes about 20% of the total water pollution load generated during the coffee process. Pulp water effluent thus had contributed 12kg BOD/tonne of coffee fruit processed. From Table 2 it is clear that COD, TS, total sugar contents were less.

Figure 3. Schematic representation of the coffee processing and effluent treatment

The combined discharge of the two effluents, the wash water and pulp water, is discharged into a man-made water body. Table 3 shows the quality of water in this tank. This water is used to store water for pulping purposes and also for coffee processing effluent. During periods of drought or March-April this water is used for "sprinkler irrigation" in order to induce flowering. The pH of wastewater in this tank was <5.0 indicates accumulation of VFAs in the form of acids (which is supported by the values of total titrable acidity). The accumulation of acids suggests that inefficient conversion of acids in the anaerobic lagoons even after 21 day retention time. As a result of dilution with water present in the water body, the water quality does not meet standards for discharge into water bodies down stream. However, after dilution the COD, total solids and total sugar content were significantly less. At this stage the COD/BOD ratio was still 2. From the COD/BOD ratio and the total carbohydrates present, it appears that the effluent will need further treatment. The reducing sugar value was quite low suggesting the conversion of sugars to acids. The fermentation of sugars to acids is supported by the high titrable acidity (>1g/l) and low pH values. The concentration of COD and BOD of the wastewater was found to be too high to be directly used in conventional anaerobic‑aerobic lagoons. The existing treatment facilities (anaerobic-aerobic lagoons) were over loaded and the process was not functioning satisfactorily. As a result the effluent flowed through the treatment plant without much change in its characteristics. Accumulation of VFAs increases the acidity. This further inhibits conversion of COD and BOD (Ikbal et al ., 1994). Our results clearly indicate inadequate treatment of coffee processing effluents reaching water bodies and causing pollution. It must be noted that these water bodies are within private properties and often mis-used.

Table 3. Water quality of a man-made water body, which is used to store the coffee processing effluent.

Total Solids (g/l) 1.5

A plug flow bioreactor (PFBR) system developed at astra (Jagadish et al., 1997) employed in treatment of wastewater showed significant reduction in organic pollutants (Figure 4). Results of a bioreactor operation are given in Table 4. There is visible improvement in the effluent as shown in Figure 5.

Figure 4. Bioreactor to treat coffee effluent. Figure 5. Treated effluent, Wash and Pulp water (L-R).

Also noted had been the ability of the PFBR to handle significantly higher organic loadings and still perform satisfactorily. As such the performance of the PFBR compared to the lagoon systems is far superior.

Wet processing of coffee is water intensive, using between 80-100,000 litres water per tonne coffee processed. The wastewater even after under going an anaerobic treatment (21d HRT) and an aerobic treatment (7d HRT) under normal conditions existing in the field still contains high levels of COD, BOD, total solids and sugars. It is characterised by a low COD conversion efficiency of 30-60% and a BOD conversion efficiency of less than 30%. This effluent usually causes eutrophication of the receiving water bodies and often large water tanks that serve as drinking water sources to small towns in Karnataka. The wastewater either mixes with run-off during the subsequent monsoon season. A part of this water is used to irrigate (sprinkler) the coffee plantations to induce flowering. This process recycles a part of the inorganic pollutants (potassium and phosphate, etc.). The presence of organic acids however is expected to lead to the acidification of the soil. There is potential to reduce water used for processing with simultaneous discharge of a high concentration effluent. By deploying a bioreactor such high strength effluents can still be degraded to a tune of 98% (COD basis) before discharge. The effluents discharged from such bioreactors are much smaller in volume and can be stored separately in small earthen tanks for recycle as irrigation by sprinkling. In this scheme of things there is little water body pollution and ecological damage.

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