After reading this article you will learn about:- 1. Characterization of Wastewater 2. Sources of Wastewater 3. Environmental Problems 4. Treatment 5. Recent Trends.
Characterization of Wastewater from Coffee Processing Industry:
Preparation of washed coffee requires pulping; washing equipment’s and adequate quantities of clean water. The approximate water requirement for the production of one tonne of clean coffee is 85,085 L for Arabica and 93,000 L for Robusta while using conventional pulper and washer.
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Although the levels of contamination of wastewater vary from region to region according to quantity of water and type of technology used in the process, in general coffee effluents are acidic- low pH (Refer Table 1.0) containing high concentration of suspended and dissolved organic solids (refer Table) and less dissolved oxygen.
The pollution load measured in terms of BOD ranges from 8500-10,260 mg L_1. Coffee factory wastewaters contain high concentration of organics such as sugars, peptides phenols and pectines. Nutrient concentrations in pulpery wastewater have low values of Nitrogen Phosphorus and Sulphur (Refer Table 1.0).
The biodegradability of this water can be measured as a function of COD constituted by BOD oscillating between 33 and 83%. Table 1.0 shows various Physicochemical parameters present in wastewater and their values along with tolerance limits prescribed by the Central Pollution Control Board, New Delhi.
Sources of Wastewater:
The various sources of wastewater from wet processing include wastewater from pulping, fermentation (or demucilaging) and washing operations. The effects of these waters when discharged into water courses without proper treatment.
The following Water Balance Diagram (Fig. 2) indicates the quantity of water used in various processing units. Utilized water during the process emanates as process wastewater.
Environmental Problems of Wastewater from Coffee Processing Industry:
Coffee is processed in two ways:
(a) Wet Processing by which plantation or parchment coffee is prepared.
(b) Dry Processing by which cherry coffee is prepared.
Preparation of parchment coffee involves pulping, washing and demucilaging and finally drying. Pulping and washing operations require adequate quantities of clean water. The resultant wastewater, when released directly or after a brief lagooning, causes pollution of perennial water sources in the vicinity of plantations. Further, coffee harvesting and processing coincide with dry season when the natural water resources are at low ebb which aggravates pollution problems.
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The coffee effluents are acidic, containing high amount of suspended and dissolved organic solids. Their pollution load measured in terms of BOD ranges from 2.5 to 12 g per litre. These effluents also impart undesirable colour and foul odour to waters into which they are discharged.
Colour is considered to be very important from the stand point of aesthetics as is stated as ‘visible pollutant’. The characteristic dark brown colour of the effluent is primarily due to the presence of vegetable extracts like tannin, humic acid and humates from the decomposition of lignin.
The other by-products of wet processing of coffee include coffee pulp. Waste products include parchment husk and coffee husk. Giving due consideration to these waste products from coffee processing, it becomes mandatory to have an effective environmentally friendly treatment and disposal methods.
Treatment of Wastewater from Coffee Processing Industry:
Closing or relocating the factory isn’t the solution to waste management problems. Hence treatment methods are very essential as an environmental solution to coffee waste water. Apart from applying the dry process, there are other options which can help reduce the wastewater load by wet process.
Water Recycling:
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It is one of the efficient and economical method by which the quantity of wastewater generated at the source can be reduced. Subsequent modifications in processing machinery like recycling pump and introduction of recycling system can reduce water usage by 90% compared to conventional wet processing. Also reduction in quality of water is one of the most important aspect in reducing the size of treatment plant and investment cost.
Fig. 3 and Fig. 4 illustrate the flow chart of water recycling process and diagram of water recycling mechanism respectively.
Conventional Treatment Methods:
In general, coffee effluents can be treated by aerobic/anaerobic or a combination of both aerobic and anaerobic methods. The anaerobic method is the biological treatment which is by far the most commonly employed method to treat biological wastes.
It is a process to coagulate and remove non-settable solids and to stabilize the organic matter by biological means. This process of coagulation and degradation of organic matter is carried out by anaerobic bacteria. Surveys have also revealed that the two stage biological method i.e., anaerobic followed by aerobic treatment is also efficient for treating coffee effluent. The Karnataka State Pollution Control Board accepts NEERI method for treating coffee effluents as shown in Fig. 5.
It has 3 tanks:
1. Equalization tank.
2. Anaerobic tank.
3. Aerobic tank.
Equalization Tank:
The effluents from different sections viz., pulping, washing and soaking will be let into the equalization tank for homogenizing the pollution load with the addition of lime (0.5 g/L). The capacity of this tank will be equivalent to quantity of wastewater generated per day.
Anaerobic Tank:
Water from equalization tank now moves into aerobic tank which is filled up to 10% of its total capacity with cow dung slurry. As a result, high strength organic wastewater containing high quantity of solids is degraded. For every 100 kg BOD, add 4.5 kg urea and 2.6 kg superphosphate daily to hasten the process of degradation. This tank must have the capacity to hold the effluent generated in 21 days.
Aerobic Tank:
The supernatant liquid from anaerobic tank is fed into aerobic tank. The wastewater may be aerated by fixed or floating aerator of suitable oxygenation capacity for 48-50 hours so as to bring down the BOD load to nearly 30 mg/L. In case of small growers sector, instead of aeration, water from anaerobic lagoon is diluted at 1:10 fresh water and utilised only for agricultural purposes.
Recent Trends for Coffee Processing Industry:
(a) Coffee Processing Effluent for Production of Biogas:
Such a treatment system of coffee wastewater is located at Tlapexcatl Processing plant, Verzeuz, Mexico. This plant aims at treating the wastewater as well as generating biogas as to byproduct. In this wastewater treatment system, physical and chemical treatment operations (sedimentation and neutralization) are combined with biological (anaerobic and aerobic) operations.
Fig. 6 illustrates the treatment system of coffee wastewater.
The wastewater from depulping and washing the coffee are conveyed into a Setting Tank (1) where a large part of the solids settle and removed as Sludge (2). The wastewater is treated with neutralizers to accelerate the process of acidification. Once the water has been acidified and neutralized (pH 7 ± 0.3), it is conveyed to the Flow Regulation Tank (3).
The water then passes through the Heater (4) where its temperature is revised from approximately 18-23°C in order to provide a more appropriate medium for bacterial growth and activity. The warm water is conveyed to a Biodigester (5) which in case of Tlapexcatl is a 13 m3 hybrid upflow type. As the water rises it comes in contact with methanogenic bacteria in the sludge bed which treat the wastewater. The primary metabolite of the process is biogas (primarily a mixture of CH4 and CO2) which is evacuated from the top of the bio digester to a Gasometer (6).
The treated water flows into the post treatment system, where a series of Sprinklers (7) promote volatilization of short chain volatite fally acid and at the same time oxygenation of treated waste. The water falls onto a Pordus Bed (8) where it receives aerobic polishing treatment. The water is then stored in Recirculation Tank (9) from which it could potentially be recirculated to the processing plant, but is currently discharged into the river.
(b) Coffee Pulp as Fertilizer and Soil Conditioner:
The most efficient method of composting coffee pulp has been described by Adams et al, (1980 and 1981). This involves aerobic wind row composting wherein the material is piled into long heaps about 1 m high and 1 m wise at the top and 1.5 m at the base.
Aeration is maintained by curing the heap at-least once in a day which can either be done mechanically or manually. The complete operation takes around 4-10 weeks and is indicated by a pH of 10, C/N ratio of 1: 10 and no further rise in temperature. Coffee pulp compost has been shown to have beneficial effects to many crops and no observable adverse effects have been reported.
(c) Coffee Pulp as an Animal Feed:
The use of coffee pulp as an animal feed ingredient has been extensively investigated in various coffee growing regions of the world. Investigation by Ceevarghese et al, (1981) and other reports concluded that up to 20% coffee pulp can profitably be incorporated in the concentrate mixture for dairy cows for economic milk production. Coffee pulp can also be used as a suitable matrix for growing mushrooms.
(d) Coffee Pulp for Ethanol, Wine and Vinegar Production:
Adams (1981) found that the alcoholic fermentation of juice from fresh pulp by yeast gives a solution containing 2.5-5 percent w/v ethanol. It is estimated that a factory producing 1 tonne of clean coffee each day would produce about 2 tonnes of pulp which would yield at most between 34-55 liters of anhydrous alcohol per day. The production of vinegar from coffee pulp appears to have been successful Brazil.
