Coffee, Cocoa, Coconut, Rubber: waste characteristics, management, value addition

Globally, coffee is the second largest commodity and produces an estimated 0.5 and 0.18 t of coffee pulp (CP) and husk (CH) respectively per tonne of fresh coffee and six million tonnes of spent coffee grounds (SCG) per year. According to the International Coffee Organization, annual coffee production increased from 140 to 152 million 60 kg bags since 2010, thus minimizing coffee by-products presents a serious challenge. Utilizing these by-products as a base or substrate for value adding applications is an effective way to minimize their wastage as landfill. Current value adding applications include biofuel, mushroom, and fertiliser production, along with enzyme, dietary fibre, and bioactive compound extraction. The feasibility of by-products for particular applications can be limited due to their composition. The presence of phenolic compounds such as caffeine and tannins limits their use in animal feeds due to their anti-nutritional properties. Similarly, the presence of chlorogenic acid limits their application as a plant fertiliser as it is phytotoxic. Furthermore, there is mounting evidence that these bioactive compounds are of ecotoxicological concern. Developmental, behavioral and morphological abnormalities have been observed in a variety of aquatic organisms due to exposure to caffeine and tannins, including algae, sea urchin and fish. Chlorogenic acid has negative effects on seed germination and plant growth.

Bioremediation using solid-state fermentation (SSF) and submerged fermentation are potential methods for detoxifying coffee by-products while producing value added products such as enzymes. However, these methods can be costly, require technical expertise and infrastructure for operation. Composting and vermicomposting offer a simple and low-cost solution for detoxifying byproducts that maximize their utilization. A study comparing bioaugmented and control mixtures of SCG showed that compost inoculated with a fungal strain (Tinea versicolor) displayed a reduction in volatiles, along with an increase in C and N. Similarly, a strain of Aspergillus sp. had high efficiency in caffeine degradation in culture, demonstrating the high potential of microbes in the detoxification process. There is an urgent need for applications that obtain maximum utilization of coffee by-products, and given the chemical composition of these by-products, this is highly feasible.

Coffee by-products

Coffee cherries are the fruit from coffee plants or shrubs, which belong to the family Rubiaceae. There are two commercially explored species of coffee plants, including Coffea arabica (Arabica) and Coffea canephora (Robusta), which account for 75% and 25% respectively, of the world’s coffee production. The coffee process begins with removal of the external components of the coffee cherry, either through dry or wet methods, leaving only green coffee beans. The dry method is commonly used for Robusta and produces a husk, while the wet method is mainly used for Arabica and produces pulp as a by-product. The external components include the skin, pulp/ husk and silver skin with silver skin being the main by-product of the roasting process.

Coffee pulp and husk (CP and CH) Depending on the processing method, either wet or dry, coffee pulp and husk are the first by-products of the industrial process, and account for 29% and 12% of the overall coffee cherry (dry weight). The amount of coffee pulp and husk produced for a single tonne of fresh coffee is 0.5 and 0.18 t respectively. Pulp and husk are rich in carbohydrates, mineral and proteins, however they also contain organic compounds such as tannins, chlorogenic acid and caffeine.

Coffee silver skin (CSS)

The second by-product, coffee silver skin, is produced during the roasting process. The CSS is the integument of the coffee bean, and although it accounts for only a small fraction of the total coffee berry (1–2%), it is high in total dietary fibre, antioxidant activity and phenolic compounds. The composition of CSS indicates dietary fibre and antioxidant adjuncts for food industries as potential value adding applications.

Spent coffee grounds (SCG)

The coffee bean accounts for approximately 50% of the coffee cherry dry weight and produces spent coffee grounds as the final byproduct of the coffee industry. SCG are generated during the production of solubilized instant coffee, whereby roasted, ground coffee beans are heat or steam treated to produce a coffee extract for consumption. The residue remaining after extracting is referred to as SCG. Annually, an estimated six million tonnes of SCG is produced worldwide, with one tonne of green coffee producing 650 kg of SCG. As urban SCG is often separated at the point of drink preparation from other wastes, it is feasible to prevent this from reaching landfill by developing coffee waste removal infrastructure.

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Chemical composition (%) of raw and processed coffee by-products

Component	Raw fruits			Processed fruits
	Pulp	husk	Silver skin	Spent coffee grounds
Carbohydrates	44-50	58	44	82
Cellulose	63	43	18	8.6
Hemicellulose	2.3	7	13	36.7
Moisture	81	12	10-59	12
Lipids	2.5	1.5-2.0	2.2	6.0
Total fibre	18.0–21.0	31.9	62.4	60.5
Ash	8.9	6	4.7-7.0	1.6
Protein	10.0–12.0	9.2	16.2–18.6	13.6
Nitrogen	3.2	1.8	3	2.3
Caffeine	1.25–1.3	1.2	1.4	0.4
Tannins	1.8–8.6	4.5–9.3	0.02	0.02
Chlorogenic acid	10.7	12.59	15.82	11.45

Mushrooms

Coffee by-products have been of interest as substrates for mushroom cultivation for nearly three decades. The initial by-product of interest for the cultivation of Flammulina velutipes was SCG. Later research expanded to the use of other by-products, such as coffee husk and pulp, which is also rich in organic content, with some studies reporting biological efficacy between 125 and 138%. A  mixture of SCG, coffee cherry waste and coffee leaves had a bioconversion efficacy of 152%. Furthermore, the protein content of CH and SCG increased after the cultivation F. velutipes, as did the fibre content of CH. Caffeine and tannin content is also reduced without any evidence of their presence in the fruiting body of the fungi, suggesting it is degraded in the cultivation process. Detoxification of coffee husk has important implications as these compounds limit its application in livestock feed and bioprocesses. Approximately 73% of the substrate will be utilised during mushroom cultivation, the remaining substrate can be further used as compost to produce a fertiliser for soils

Enzymes Two methods, solid-state fermentation (SSF) and submerged fermentation (SmF), dominate industrial enzyme production. The solid supports found in SSF can be inert materials such as industrial residues like coffee by-products. SSF is advantageous in the cultivation of fungi as the residues used can act as a carbon source for the production of enzymes. A recent study explored the feasibility of SCG as a substrate for cellulase production by Paenibacillus chitinolyticus and achieved 71% yield under optimal conditions using a batch-adsorption system. Similar studies have investigated feasibility and extraction optimisation on enzymes such as tannase, xylanase, pectinase, and β-fructofuranosidase.

Biofuels

Coffee by-products have excellent potential for ethanol production. Treated SCG with acid hydrolysis and fermented the hydrolysate with Saccharomyces cerevisiae has a 50% yield. A similar experiment on CH yield only 8.5% (dry basis), possibly due the higher concentrations of caffeine and tannins. The potential of CP was further improved using an acid hydrolysis method, followed by fermentation with Pichia anomala achieved 78% yields of ethanol. The concentration of ethanol produced from CP (6.12 g/L) was more successful than poultry manure (5 g/L), but not as efficient as banana peels (9.8 g/L) or sugarcane (10.2 g/L). These high yields suggest coffee by-products are viable substrates for ethanol production. Similar studies on the feasibility of coffee waste for biodiesel and biogas production have yielded promising results. Oil has been extracted from SCG and converted to biodiesel with a 10–15% yield, where 100% of this oil was converted to biodiesel. More recent studies have returned similar findings of biodiesel yields up to 16% using SCG and suggested an estimated 700,000 t of biodiesel could be produced from the 5,817,500 t of SCG waste annually.

Organic acids

          Organic acids such as citric and gibberellic acid (plant hormone) have been produced using coffee by-products as a substrate. SSF with Aspergillus niger produced an 82% yield of 1.5 g citric acid/10 g dry CH. SSF was also used in the production of gibberellic acid from Gibberella fujikuroi. A mixture of CH and cassava bagasse obtained optimal results with 492.5 mg/kg of dry CH.

Dietary fibre

Dietary fibre (DF) promotes gastrointestinal health, reduces the risk of cardiovascular disease and obesity, with the recommended fraction ratio of 1:2 soluble/insoluble dietary fibre. DF includes a variety of non-starch polysaccharides such as cellulose, hemicellulose and lignin. SCG and CSS both have high proportions of DF (60.46 and 54.11% w/w), consisting of nearly five-fold more insoluble DF (IDF) than soluble DF (SDF).

Composting and vermicomposting

Composting and vermicomposting provide a low-cost solution to agro-industrial waste, which create nutrient-rich fertilisers for increased plant productivity. Currently, CP is considered the most time efficient using conventional turning methods and will compost in three weeks. Other materials, such as SCG have decomposition times of ninety days or more possibly as a result of the roasting process.

Vermicomposting of SCG following a twenty one day pre-treatment of composting, there was an increase in nutrient elements such as nitrogen and potassium, demonstrating their potential as a high-quality fertiliser. Microorganism inoculation is a novel approach to increase the speed and quality of SCG composting. Inoculation of compost with the white-rot fungus, Trametes versicolor, resulted in a mature final compost with reduced phenolic compounds that produced a germination index of 120% for barley in less than 20 weeks.

Cocoa

These by-products are usually considered as “waste” and left to rot on the cocoa plantation, which can cause environmental problems, such as producing foul odors or propagate diseases (e.g., pod rot, because they are not composted)

Cocoa Pod Husk (CPH), Cocoa beans and Shells

Cocoa  meal,  cocoa  bean  shells  and  pod  husks  all  have  nutritive  value  and  can  be considered as animal feed materials but their use is severely restricted by the theobromine content which is toxic to livestock.  Dried fresh CPH can be fed to cattle up to 7 kg per day without toxic effects and up to 2 kg per day to pigs without toxic symptoms.  Up to 0.8 kg of cocoa shells (a good source of vitamin D) are acceptable to cows but they are more dangerous  to pigs and poultry.  Cocoa products  can be rendered  harmless if the theobromine is removed by cooking in water for 1½ hours, filtering and drying.  Up to 25% of the treated product can be included in rations for pigs without reduction in weight gain or feed efficiency. It should be noted that  animals fed  on a  CPH  diet tend  to consume  more water  than normal due to a high sodium (Na+) content and the fact that the adsorption of water in the

small  intestines  is  proportional  to  the  rate  of  sodium  chloride  (NaCl)  adsorption. 

Additionally, animals fed on a CPH diet tend to have a leaner body for marketing.  In chickens,  if  the diet  of  CPH  exceeds  10%,  laying  hens  produce  darker  yolks,  while broilers obtain larger gizzards, both of which are preferred in most countries.   

 

          Cocoa pod husk and cocoa beans shells have relatively high potassium contents and may be used to manufacture fertilisers or composts.    Cocoa pods  husks can  be used as  a compost or mulch if left to rot in the fields on cocoa estates where they recycle nutrients back into the soil as manure and also serve as a breeding ground for midges.  Midges are the chief pollinators of cocoa and increasing the amount of midges enhances pollination efficiency and ultimately pod yields.

          Cocoa  pod  husks  may  also  be  burnt  and  the  ash  used  to  manufacture  a  potassium containing fertiliser.  In parts of West Africa CPH is burnt and the ash used as a source of potassium carbonate for the manufacture of soft soap.

 

Waste cocoa beans and cocoa bean shells can be used as a source of theobromine which is then either used directly in medicinal preparations or converted to caffeine.  However, these products might have difficulty competing in price with synthetic theobromine and caffeine.  

 

Cocoa  bean  shells  when  used  as  mulch  contains  approximately  2.5%  nitrogen,  1% phosphate and 3% potash as well as a natural gum that is activated when watered.  This enables the cocoa shell mulch to slow soil moisture loss through evaporation as well as retarding weed growth.  The texture of the cocoa shell also deters slugs and snails to help prevent plant damage. 

Cocoa pods

The possibility of using cocoa pods as  a cheap source of pectin has been investigated. Pectin  is  a  gel  forming  material,  which  frequently  occurs  in  fruits  and  has  many applications in the food, pharmaceutical and textile industries.  The husks of immature cocoa pods are found to contain 25 to 30 % crude pectin (dry weight basis) and mature pod husks 6 to 12 % pectin.  Freshly harvested pods must be processed immediately after removal of the cocoa beans to prevent deterioration of the pectin.  Sun drying the CPH before extraction of the pectin reduces both the yield and gelling  power of  the pectin. 

The costs of transportation of pod  husks  and oven drying needs to be investigated to ensure that this could be an economically viable proposition.  

Pulp/Juice

Pectin is also present in  cocoa pulp and  juice and in many cocoa producing  countries spin-off industries  have been created utilizing the pulp and juice of cocoa.  In Brazil, research work initiated by the Cocoa Research Centre of CEPLAC, Ilheus, Bahia use the juice which is extracted by pressing the beans just before they are fermented to produce a range of jams and jellies.  The pulp and juice is also fermented to give a good quality wine and liqueur.  Cocoa sweatings have also been used to provide alcohol, vinegar and other products. Success in this area relies on proper harvesting protocol and removal of any diseased beans before pressing.  Also the area where pressing is done must be clean for hygienic extraction of the juice and pulp.  This is often very difficult to achieve on a large  scale  but  is  feasible.    Recent  analysis  of  cocoa  sweatings  before  and  after fermentation indicated  that alcohol/vinegar production  might be economically feasible. 

Unfermented cotyledon

The unfermented cotyledon has limited food use but can be ground and pressed or passed through an expeller to extract cocoa butter.  Cocoa butter has a range of commercial uses in the food, cosmetic and pharmaceutical industries.  It is the most valuable product that can be extracted from the cocoa bean and accounts for up to 55% of mass of the bean. 

The press cake from unfermented beans can be used as a feedstock but may be too bitter and unpalatable to some animals.  The press cake is also used as manure.

 

Options After Primary Processing for Adding Value to Cocoa

Fermented cotyledon

The fermented cotyledon offers the widest range of value added uses for the cocoa bean. 

 

The  dried,  fermented  cocoa bean  is  the  main  ingredient used  in  the  manufacture  of chocolate.  It is also used to make several products of interest to the confectionery and cosmetic industries, such as cocoa butter and cocoa powder.

Coconuts are produced in 92 countries worldwide on about more than 10 million hectares. Indonesia, Philippines and India account for almost 75% of world coconut production with Indonesia being the world’s largest coconut producer. A coconut plantation is analogous to energy crop plantations, however coconut plantations are a source of wide variety of products, in addition to energy. The current world production of coconuts has the potential to produce electricity, heat, fiberboards, organic fertilizer, animal feeds, fuel additives for cleaner emissions, health drinks, etc.

The coconut fruit yields 40 % coconut husks containing 30 % fiber, with dust making up the rest. The chemical composition of coconut husks consists of cellulose, lignin, pyroligneous acid, gas, charcoal, tar, tannin, and potassium. Coconut dust has high lignin and cellulose content. The materials contained in the casing of coco dusts and coconut fibers are resistant to bacteria and fungi.

Coconut husk and shells are an attractive biomass fuel and are also a good source of charcoal. The major advantage of using coconut biomass as a fuel is that coconut is a permanent crop and available round the year so there is constant whole year supply. Activated carbon manufactured from coconut shell is considered extremely effective for the removal of impurities in wastewater treatment processes.

Coconut Shell

Coconut shell is an agricultural waste and is available in plentiful quantities throughout tropical countries worldwide. In many countries, coconut shell is subjected to open burning which contributes significantly to CO₂ and methane emissions.  Coconut shell is widely used for making charcoal. The traditional pit method of production has a charcoal yield of 25–30% of the dry weight of shells used. The charcoal produced by this method is of variable quality, and often contaminated with extraneous matter and soil. The smoke evolved from pit method is not only a nuisance but also a health hazard.

Coconut Husk

Coconut husk has high amount of lignin and cellulose, and that is why it has a high calorific value of 18.62MJ/kg. The chemical composition of coconut husks consists of cellulose, lignin, pyroligneous acid, gas, charcoal, tar, tannin, and potassium. The predominant use of coconut husks is in direct combustion in order to make charcoal, otherwise husks are simply thrown away. Coconut husk can be transformed into a value-added fuel source which can replace wood and other traditional fuel sources. In terms of the availability and costs of coconut husks, they have good potential for use in power plants

Total world coconut area in 1996 was estimated at 11 million hectares and around 93 percent is found in the Asian and Pacific region. The two biggest producers Indonesia and the Philippines have about 3.7 million ha and 3.1 million ha respectively. India is the third largest producer. In the South Pacific countries, Papua New Guinea is the leading producer. In Africa, Tanzania is the largest producer while in Latin America Brazil accounts for more than one half of the total coconut area of that region.

The two main types of waste generated by the processing company are coconut skin, after the dehusking of raw coconut and coconut shell after the removal of the inner part (kernel), which is also called deshelling. Currently, both waste types are sold for manufacturing charcoal. Yet, this practice generally is not in line with the target to reduce GHG emissions. Therefore, alternatives which ensure a more environment friendly approach need to be implemented.

Rubber industrial waste

Physicochemical and microbiological properties of liquid wastes from rubber processing factories Proteins, sugars, lipids, carotenoids, inorganic and organic solids of latex, various chemicals added for processing and water used for processing constitute the effluent from natural rubber processing factories. These nutrient rich effluents containing fairly large amount of dissolved organic and inorganic solids, besides suspended solid particles support a large number of general and indicative bacteria. The fast growth of microorganisms causes depletion of the oxygen content in the effluent and receiving water bodies.

Latex concentrate effluent (LCE) contained more suspended solids, dissolved solids, total solids (TS) and volatile solids (VS) which resulted in substantial growth of microorganisms resulting in high BOD and COD. They have confirmed that dissolved solids play a significant role in the salinity of the effluent. The high BOD and COD values of the LCE indicate that the TS in the effluents are mainly organic, especially fine particles of rubber hydrocarbon, with high oxygen requirements for their oxidation. The enhanced BOD and COD in LCE may be due to the high concentration of proteins, sugars, lipids, inorganic and organic salts in addition to high ammonia nitrogen.

The LCE is highly acidic. The addition of sulphuric acid for recovery of rubber by its coagulation from the skim portion of latex resulted in the reduction of pH of the effluent. Sulphuric acid also contributes to the sulphate content of the effluent. Phosphate content in the effluent is also high due to the addition of diammonium phosphate in the latex. Highly acidic effluent loaded with salts adversely affect plant growth and causes corrosion of structures in river

The LCE contains large amount of total and ammoniacal nitrogen. The addition of substantial quantity of ammonia in the preservation of latex contributes to this. Ammonia is toxic to fishes and also encourages algal bloom. So the discharge of such effluents to water—ways is discouraged

It is found that the population of different groups of microorganisms in the LCE was less when compared to that in the effluent from other processes. Pelczar gt al. (1993) recorded low counts of bacteria in nutrient rich medium and which he attributed to low pH. Pollution by sheet processing effluent (SPE) was less than LCE, but was more than other effluents. Even though the effluents from large scale RSS factories adversely affect the environment, small units spread out in the rubber tract do not cause noticeable impact on the quality of the environment. The pollution by large units, however, should be treated on par with that of latex concentrate factories. During RSS processing, addition of formic or acetic acid causes reduction in pH of the effluent. This effluent causes very high levels of BOD and COD, indicating that the TS are mainly of organics with high oxygen requirements for their oxidation. SPE contained all the different groups of bacteria in large number. The yeast population in the effluent was very high compared to other effluents. Enhanced microbial activity including yeasts in SPE has already been reported. The optimum pH required by yeasts for its growth is 4 to 5 and obviously the RSS effluent favoured its proliferation

Though the pollution load in crumb processing effluent (CPE) and crepe rubber effluent (CRE) was comparatively less, the environmental impact would be much higher due to the discharges of high volume. TSR and CR processing factories generate 26.3 and 24.5 l of effluent respectively per kg of processed rubber, which ultimately reach and pollute water bodies

Effluent from agroindustries is reported to contain considerable quantities of suspended and dissolved solids as well as organic acids, which are good substrates for biomethanation. The present study revealed that the wastes from natural rubber and rubber wood processing contain high levels of valuable substrates for biogenesis of methane

Physicochemical properties of solid wastes

The quantity of TS, VS, carbon, nitrogen, phosphorous, potassium, cellulose, hemicellulose and lignin was high in the solid wastes from rubber based industries. The C:N ratio of optimum range in these solid wastes suggests their usefulness as a raw material for methane production. Crumb waste (cw) is mainly composed of bark remnants rich in cellulose and such sludge from crumb factories with C:N ratio 33:1 was ideal for biogas production.

Low nitrogen content in sawdust is overcome by addition of urea or bio—degradation of lignocellulosic materials by cellulolytic fungi. The presence of organic and inorganic nutrients at optimum level makes sawdust biodigesteable, even though the nitrogen level is poor. The degradation by cellulolytic fungi brought down the C:N ratio from 90:1 to 40:1 which is within the minimum required limit for biomethanation.