Bioresource Technology xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Nutrient recovery from apple pomace waste by vermicomposting technology Ales Hanc ⇑, Zuzana Chadimova Department of Agro-Environmental Chemistry and Plant Nutrition, Czech University of Life Sciences Prague, Kamycka 129, 165 21 Prague 6, Czech Republic
h i g h l i g h t s Earthworms were able to convert apple pomace waste into a value added product. The addition of straw to apple pomace did not enhance earthworm biomass. The resulting vermicomposts were characterized by slightly acidic to neutral pH. The total content of nutrients increased during vermicomposting.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Apple pomace Earthworms Straw Vermicomposting
a b s t r a c t The present work was focused on vermicomposting apple pomace waste and its mixtures with straw in volume proportions of 25%, 50%, and 75%. The feasibility was evaluated on the basis of agrochemical properties and earthworm biomass. Vermicomposting was able to reduce the weight and volume of the feedstock by 65% and 85%, respectively. The resulting vermicomposts were characterized by slightly acidic to neutral pH (5.9–6.9), and optimal EC (1.6–4.4 mS/cm) and C:N ratios (13–14). The total content of nutrients increased during vermicomposting for all of the treatments with the following average final values: N = 2.8%, P = 0.85%, K = 2.3%, and Mg = 0.38%. The addition of straw to apple pomace did not enhance earthworm biomass, but did increase the available content of nutrients during vermicomposting. The data reveals that vermicomposting is a suitable technology for the decomposition of apple pomace waste into a value added product. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Currently, the world produces 70 million metric tons of apples per year, while the countries of the European Union contribute about 15% of this amount (WAPA, 2013). In the Czech Republic apple trees represent the most important fruit species, and in 2012, 80,000 tons of apple juice was produced. Approximately 1.5–2 tons of apples, depending on their types and age, are required to produce 1 ton of juice, so the utilization ranges from 65% to 50%. The solid material which remains after the extraction of juice is called apple pomace. Apple pomace has been used as a feed for herbivorous animals and as a component in fruit tea. However, the market has been changing, and the livestock population has declined. The proportion of apple pomace in fruit teas
⇑ Corresponding author. Tel.: +420 224382731; fax: +420 224382535. E-mail address: [email protected] (A. Hanc).
has decreased due to higher demand from purchasers for components with better aroma and taste. Thus, apple pomace has become bio-waste. Vermicomposting is one possible solution for handling this feedstock. It is the processes of ingestion, digestion, and absorption of organic waste carried out by earthworms, followed by the excretion of casting through the worm’s metabolic system, during which their biological activities enhance the levels of nutrients in the organic waste (Venkatesh and Eevera, 2008). Compared to the feedstock and conventional compost, vermicompost contains increased and more soluble levels of major nutrients and organic matter with improved quality (Sinha et al., 2010). At this time, there do not appear to be any scientific studies on the vermicomposting of apple pomace waste. Keeping the above facts in mind, the present study was implemented to investigate the feasibility of vermicomposting apple pomace and its mixtures with straw on the basis of agrochemical properties and earthworm biomass.
http://dx.doi.org/10.1016/j.biortech.2014.02.031 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
2
A. Hanc, Z. Chadimova / Bioresource Technology xxx (2014) xxx–xxx
2. Methods 2.1. Feedstocks and their pre-composting Apple pomace obtained from a food-processing company, and shortly chopped wheat straw as a bulking agent to improve structure, enhance aeration, and absorb excess liquids were used in the experiment. For the experiment, dry wheat straw was soaked in water for 1 month to enhance the absorption capacity and thus aid in faster decomposition. Thus, the dry matter content of the straw decreased from 90% to 18%. 2.2. Treatment of bio-waste during the pre-composting process The composition of the feedstocks (in volume proportion) is given below: I II III IV V
Apple Apple Apple Apple Apple
pomace pomace pomace pomace pomace
(50%) + straw (25%) + straw (50%) + straw (75%) + straw (100%).
(50%). (75%). (50%). (25%).
All treatments were pre-composted in 70 L capacity laboratory reactors kept in a room at 25 °C for 14 days. An active aeration device was used to push air through the composted materials from the bottom. The mixtures were batch-wise aerated for 5 min out of each half hour in a volume of 4 L of air min 1. On the basis of their previous experiences, Hanc et al. (2012) found that this aeration level was usually sufficient to achieve the optimal parameters of the composting process.
digests obtained by pressurized wet-ashing (HNO3 + HCl + HF) with microwave heating using an Ethos 1 system (MLS GmbH, Germany). The contents of ammonium nitrogen (N–NH4+), nitrate nitrogen (N–NO3 ), and the available portions of P, K, and Mg were determined in CAT solution (0.01 mol l 1 CaCl2 and 0.002 mol l 1 diethylene triamine pentaacetic acid (DTPA)) at the rate of 1:10 (w/v) according to the International BSI Standard EN 1365, 20011. The N–NH4+ and N–NO3 contents in the extracts were measured colorimetrically using the SKALAR SANPLUS SYSTEMÒ. The element concentrations were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). 3. Results and discussion 3.1. Weight and volume From a practical point of view, changes of weight and volume during vermicomposting are important for planning the amount of processed feedstock and the final product on a given area or space. Weight loss was fairly even during the process. However, the treatment containing 75% straw showed more rapid weight decline, while the treatment containing apple pomace by itself exhibited a slower decrease in weight. On average for the treatments, the weight of the final vermicompost was one third of the initial feedstock. Hanc and Pliva (2013) found that samples consisting of pre-composted kitchen waste with woodchips and paper lost 20% and 55% of their weight, respectively. In this experiment, the volume decreased from 70% to 80% after one month. In the coming months, the volume decreased slightly. Vermicomposting was able to decrease the initial volume overall by 84–89% depending on the addition of straw.
2.3. The vermicomposting process 3.2. Value of pH, EC, and C/N rate Vermicomposting of aerobically pre-composted feedstock was conducted in a specially adapted laboratory with controlled conditions (temperature 22 °C, relative humidity 80%, ventilation for 15 min every 12 h). A 12 L batch of material was manually mixed with 3 L of substrate containing a total of 450 earthworms of the genus Eisenia (treatments II–V). Earthworms were added not alone but in their original beef manure substrate to reduce their initial stress and improve their adaptability to the new environment. In the case of treatment I (control without earthworms), 3 L of substrate was replaced by 3 L of the original pre-composted materials (apple pomace (50%) + straw (50%)). Even after the earthworms had been sorted out, the remaining substrate was not utilized due to the possible presence of cocoons from which new earthworms could hatch and affect the treatment. The mixture was placed into a plastic bowl with a perforated bottom, equipped with irrigation and temperature measurements. Each treatment was carried out in triplicate. Before sampling, the eventual leachate which was captured in a stainless bowl was returned to the vermicomposted material to achieve a closed loop. A sample of 200 g was collected from each bowl each month during the five month study period. The earthworms were sorted out, and the resulting samples were dried at 40 °C to a constant weight and ground to ensure homogeneity. 2.4. Analytical methods Measurements of pH and electrical conductivity (EC) were conducted on samples mixed with deionized water (1:10 w/v dry basis). Organic carbon was determined by dichromate oxidation in sulfuric acid solution and total nitrogen by the Kjeldahl method using a Gerhardt analytical system Vapodest-manager device. Total element contents (P, K, and Mg) were determined in the
Two weeks of pre-composting caused an increase in pH from 4.0 to 6.7 for the treatment containing only apple pomace, nevertheless this was a lower pH than mixtures with straw (up to 7.2). Higher proportions of apple pomace in the mixtures resulted in lower pH values, probably due to the high contents of organic acids (e.g. malic acid). There was a difference between composting and vermicomposting in terms of pH. The pH value in treatment I slightly but gradually increased. This pattern is typical for the composting of source separated household bio-waste as well (Sundberg and Jonsson, 2008). The pH values of mixtures containing a high proportion of apple pomace (50–100%) increased slightly after 1 month of vermicomposting. The increase in pH could be caused by the degradation and consumption of organic acids by microorganisms. Subsequently, a decrease in pH was observed which was directly proportional with the amount of straw in the treatment. The pH values of the final vermicomposts were lower by 0.6 units when compared with the initial mixtures. These differences increased directly with the proportion of straw. The lowest pH was observed in vermicompost containing 75% straw and 25% apple pomace. A decrease in pH (from 8.6 to 7.3) was found in the study conducted by Suthar (2010) who vermicomposted agro-industrial sludge. The decline in pH may be due to the mineralization of the organic compounds, and thus an increase in the contents of organic and humic acids (Suthar and Singh, 2008; Garg et al., 2006). The EC fluctuated around 1 mS/cm in treatment I which did not contain earthworms. The EC gradually increased in all of the treatments with earthworms, which could be explained by the release of bonded elements during earthworm digestion (Garg et al., 2006), and the release of minerals during the decomposition of organic matter in the form of cations in the vermicomposts (Tognetti
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
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A. Hanc, Z. Chadimova / Bioresource Technology xxx (2014) xxx–xxx
Total N content ranged from 1.3% to 1.9% at the beginning of the experiment (Fig. 1a). After 4 months, the content increased by 85% (treatment I) and 58% (average of treatments II–V). The N contents of the final vermicomposts were 12% higher than in composts. Mineral forms of nitrogen are important in terms of fertilizing. At the beginning of the experiment, the N–NH4+ and N–NO3 contents ranged in the same order of magnitude (Table 1). The contents of the individual forms in the final vermicomposts varied markedly. At the end of vermicomposting the increase in the N–NH4+ and N–NO3 contents were 1.5- and 47.1-fold compared to the start, respectively. The increase in the N–NH4+ content can be partially explained by earthworms, because ammonia is a worm excretory product that temporarily reduces the pool of H+ ions. A different situation was observed for treatment I which did not contain earthworms, as there were no significant differences in the N–NH4+ contents between the final compost and the initial mixture. The N–NO3 content increased 2.1-fold in treatment I. It is likely that the presence of earthworms encouraged the nitrification process, and this is evident from a comparison of the N–NO3 contents in the vermicompost and control compost. Vermicomposts contained 23 times more N–NO3 when compared with compost. The N–NO3 content increased directly proportionally to the proportion of straw in the mixtures and made up 2.4% to 11.8% of the total nitrogen in the vermicomposts. The proportion of N–NO3 constituted 7% in vermicompost from kitchen bio-waste prepared by Hanc and Pliva (2013). In this experiment, the increased N–NO3 contents in vermicomposts with increased proportions of straw can be partially explained by a decrease in pH (correlation coefficient R = 0.99). 3.4. Phosphorus, potassium, and magnesium – total and available contents The total contents of macroelements such as P, K, and Mg (Fig. 1b–d) increased during composting and vermicomposting, which was associated with the loss of weight and organic matter (Wani et al., 2013), and no loss of leachate in the closed system. The average ratios of the final and initial total contents of elements increased in the following order: Mg (265%), K (306%), and P (596%). On average, the final vermicomposts contained higher contents of
Total N (mg/kg)
35000 30000 25000 20000 15000 10000 5000 0 I
Total P (mg/kg)
(b)
II
III
IV
V
IV
V
IV
V
IV
V
Treatments beginning end 12000 10000 8000 6000 4000 2000 0 I
II
III Treatments beginning
(c) Total K (mg/kg)
3.3. Total nitrogen and its mineral forms
(a)
end
30000 25000 20000 15000 10000 5000 0 I
II
III Treatments beginning
(d) Total Mg (mg/kg)
et al., 2005). The increase was directly proportional to the increased proportion of straw in the vermicomposted mixture. The values ranged from 1.1–1.5 mS/cm at the beginning, and 1.6–4.4 mS/cm at the end of the experiment. The threshold value of 3 mS/cm for safe agronomical application of the final vermicompost reported by Lazcano et al. (2008) was exceeded only in treatment II which contained the highest proportion of straw. This result could be attributed to the higher EC value in straw than apple pomace, and the soaking of the straw before use. After 1 month of vermicomposting a steep decline in the C/N ratio was observed, and in some cases this was as much as 33%. This result was probably due to microbial respiration and the mineralization of the labile organic compounds, which reduced the weight and volume of the processed mass, and by the concentration effect the Ntot.was increased. Any subsequent decreases observed in the C/N were very slight. The course of the C/N over the duration of the experiment for control treatment I was specific, because 3 L of substrate with earthworms was replaced with straw and apple pomace. This is why a higher initial C/N ratio was achieved for this particular treatment, and this value decreased gradually over time. However, there were no significant differences in the final C:N ratios of the non-vermicomposted and vermicomposted treatments.
end
5000 4000 3000 2000 1000 0 I
II
III
Treatments beginning end Fig. 1. Total contents of N (a), P (b), K (c), and Mg (d) at the beginning and at the end of vermicomposting.
total P and K by 11% and 22% compared to the control compost, respectively. The total Mg content was 9% lower on average, but there was a high standard deviation among the repetitions. The highest contents of P, K, and Mg were in vermicomposts V, IV, and II, respectively. In the study conducted by Pattnaik and Reddy (2010), the contents of N, P, K, and Mg in vermicompost from urban green waste after 60 days of vermicomposting by Eisenia fetida were 1.2%, 0.8%, 0.5%, and 0.8%, respectively. During the transit of materials through the worm gut, some important plant nutrients present in the organic waste are converted into chemical forms which are more available to plants (Garg et al., 2012). In this experiment, the highest ratio of the final and initial content of available elements was found in treatment II (Table 1), where the final vermicompost contained higher contents of the available nutrients than the control compost (by 204%, 117%, and 20% in the case of P, K, and Mg). Similarly, significantly higher contents of the available nutrients in vermicomposts than composts were found in an experiment with urban green waste
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
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A. Hanc, Z. Chadimova / Bioresource Technology xxx (2014) xxx–xxx
Table 1 Available contents of nitrogen (N–NH4+ and N–NO3 ), phosphorus, potassium, and magnesium (mg/kg) determined in CAT extract agent. Element
pressing during the juice production, which adversely affected the amounts of available content determined in CAT.
Treatment
Initial mixture
Vermicompost
3.5. Earthworm biomass
I II III IV V
62 ± 16.2a 45 ± 6.3a 40 ± 4.3a 44 ± 8.4a 38 ± 3.5a
59 ± 11.6a 77 ± 7.8a 49 ± 9.1a 76 ± 20.4a 59 ± 3.0a
I II III IV V
37 ± 25.0a 58 ± 30.5a 49 ± 8.7a 28 ± 3.7a 15 ± 2.0a
78 ± 27.1a 3334 ± 118.7b 1704 ± 460.9c 1543 ± 150.7c 667 ± 315.8a
I II III IV V
365 ± 80.8a 565 ± 131.7ab 553 ± 110.4ab 643 ± 7.7b 576 ± 21.5ab
486 ± 97.5a 1779 ± 177.0b 1643 ± 177.8b 1480 ± 37.0b 1018 ± 27.9c
I II III IV V
3420 ± 417.7a 8113 ± 1185.8b 7734 ± 1460.1b 7398 ± 381.9b 6387 ± 410.4b
6088 ± 599.4a 15878 ± 989.4b 14498 ± 1252.7bc 12588 ± 1141.7c 9899 ± 32.1d
A considerable drop in the earthworm biomass was observed in the first month, and the reduction ranged from 65% to 98%. These results can be explained by the initial stress the earthworms encounter from new environmental conditions (Suthar, 2010). After adaptation, the number and weight of the individual earthworms increased. The maximum biomass was reached at different times depending on the amount of feed. In the case of treatments II, III, IV, and V this peak was after 2, 2.5, 3, and 4 months of vermicomposting, respectively. This implies that apple pomace is a more valuable feed for earthworms than straw. Straw seems to play the role of a bulking agent important for keeping air in the material. Garg et al. (2012) found a maximum worm biomass (Eisenia fetida) between 7 and 10 weeks during vermicomposting of food industry sludges mixed with different organic wastes. In a study conducted by Fernández-Gómez et al. (2010) the maximum individual biomass was recorded after 4 weeks of vermicomposting of vegetable greenhouse waste with the addition of cow dung and straw. In another study, the maximum worm biomass was achieved between the 4th and 5th week of vermicomposting of non-recyclable paper waste (Gupta and Garg, 2009).
I II III IV V
483 ± 65.2ab 394 ± 26.7a 389 ± 36.3a 481 ± 29.8ab 527 ± 10.6b
480 ± 27.3a 787 ± 49.6b 555 ± 34.5a 538 ± 23.0a 435 ± 97.0a
N–NH4+
N–NO3
P
K
Mg
Mean ± SD, n = 3. Mean value followed by different letters indicates a statistical difference (ANOVA, Tukey’s test, p < 0.05).
(Pattnaik and Reddy, 2010). The available content of macroelements in the final vermicompost decreased directly proportionally with the proportion of apple pomace. The resulting vermicomposts were rich mainly in available K (from 9899 to 15878 mg/kg). Additionally, the available content of P was approximately one order of magnitude lower (1018–1779 mg/kg), while the available Mg content ranged from 435 to 787 mg/kg. The available P, K, and Mg contents in vermicomposts constituted approximately 16%, 62%, and 15% of the total contents, respectively, and these values were 60%, 45%, and 25% higher than in the control composts. Hanc and Pliva (2013) found that the available P and K contents in vermicompost from kitchen bio-waste constituted approximately 50% and 5% of the total contents, respectively. Higher available P contents were found in this material with the addition of woodchips than paper. The enhanced number of microflora present in the gut of earthworms in the case of vermicomposting might have played an important role in the release of nutrients. Insoluble P can be converted into soluble forms with the help of P-solubilizing microorganisms through phosphatases present in the gut. Acid production by the microorganisms is the major mechanism for the solubilization of insoluble potassium. The important acids in phosphorus solubilization are carbonic, nitric, and sulfuric (Kaviraj and Sharma, 2003). In regards to magnesium, it is postulated that fungal and micro-algal hyphae, which easily colonize on freshly deposited earthworm casts, contribute to the Mg content in the vermicomposts (Suthar, 2010). In the current study, higher contents of available elements were found in vermicomposts with higher proportions of straw in the initial feedstock. This result could be explained by the soaking of the straw, thereby decomposition and digestibility were enhanced. The treatments containing apple pomace lost large amounts of water-soluble nutrients by
4. Conclusion The study concludes that apple pomace waste is a suitable feedstock for earthworms which are able to convert it into a value added product. The addition of straw to apple pomace did not enhance earthworm biomass but increased the available content of nutrients during vermicomposting. The resulting vermicomposts were characterized by slightly acidic to neutral pH, and optimal EC and C:N ratios. The total content of nutrients increased during vermicomposting which was due to a significant decrease in weight and volume of the processed materials. Acknowledgements Financial support for these investigations was provided by the 7FP Collaborative Project no. 312117 BIOFECTOR. The authors would like to thank Christina Baker for revision of the English text. References EN 13651. Soil improvers and growing media – Extraction of calcium chloride/DTPA (CAT) soluble nutrients. 2001. Fernández-Gómez, M.J., Romero, R., Nogales, R., 2010. Feasibility of vermicomposting for vegetable greenhouse waste recycling. Bioresour. Technol. 101, 9654–9660. Garg, V.K., Gupta, A., Satya, S., 2006. Vermicomposting of different types of waste using Eisenia foetida: a comparative study. Bioresour. Technol. 97, 391–395. Garg, V.K., Suthar, S., Yadav, A., 2012. Management of food industry waste employing vermicomposting technology. Bioresour. Technol. 126, 437–443. Gupta, R., Garg, V.K., 2009. Vermiremediation and nutrient recovery of nonrecyclable paper waste employing Eisenia fetida. J. Hazard. Mater. 162, 430–439. Hanc, A., Pliva, P., 2013. Vermicomposting technology as a tool for nutrient recovery from kitchen bio-waste. J. Mater. Cycles Waste Manage. 15, 431–439. Hanc, A., Szakova, J., Svehla, P., 2012. Effect of composting on the mobility of arsenic, chromium and nickel contained in kitchen and garden waste. Bioresour. Technol. 126, 444–452. Kaviraj, Sharma, S., 2003. Municipal solid waste management through vermicomposting employing exotic and local species of earthworms. Bioresour. Technol. 90, 169–173. Lazcano, C., Gomez-Brandon, M., Dominguez, J., 2008. Comparison of the effectiveness of composting and vermicomposting for biological stabilization of cattle manure. Chemosphere 72, 1013–1019. Pattnaik, S., Reddy, M.V., 2010. Nutrient status of vermicompost of urban green waste processed by three earthworm species – Eisenia fetida, Eudrilus eugeniae, and Perionyx excavatus. Appl. Environ. Soil Sci. 2010, 1–13.
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
A. Hanc, Z. Chadimova / Bioresource Technology xxx (2014) xxx–xxx Sinha, R.K., Agarwal, S., Chauhan, K., Valani, D., 2010. The wonders of earthworms & its vermicompost in farm production: Charles Darwin’s friends of farmers, with potential to replace destructive chemical fertilizers from agriculture. Agric. Sci. 1, 76–94. Sundberg, C., Jonsson, H., 2008. Higher pH and faster decomposition in biowaste composting by increased aeration. Waste Manage. 28, 518–526. Suthar, S., 2010. Recycling of agro-industrial sludge through vermitechnology. Ecol. Eng. 36, 1028–1036. Suthar, S., Singh, S., 2008. Vermicomposting of domestic waste by using two epigeic earthworms (Perionyx excavates and Perionyx sansibaricus). Int. J. Environ. Sci. Tech. 5, 99–106.
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Tognetti, C., Laos, F., Mazzarino, M.J., Hernandez, M.T., 2005. Composting vs. vermicomposting: a comparison of end product quality. Compost Sci. Util. 13, 6–13. Venkatesh, R.M., Eevera, T., 2008. Mass reduction and recovery of nutrients through vermicomposting of fly ash. Appl. Ecol. Environ. Res. 6, 77–84. Wani, K.A., Mamta Rao, R.J., 2013. Bioconversion of garden waste, kitchen waste and cow dung into value-added products using earthworm Eisenia fetida. Saudi J. Biol. Sci. 20, 149–154. WAPA, 2013. The world apple and pear association. (cit. 2013-11-28).
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Nutrient recovery from apple pomace waste by vermicomposting technology Ales Hanc ⇑, Zuzana Chadimova Department of Agro-Environmental Chemistry and Plant Nutrition, Czech University of Life Sciences Prague, Kamycka 129, 165 21 Prague 6, Czech Republic
h i g h l i g h t s Earthworms were able to convert apple pomace waste into a value added product. The addition of straw to apple pomace did not enhance earthworm biomass. The resulting vermicomposts were characterized by slightly acidic to neutral pH. The total content of nutrients increased during vermicomposting.
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Apple pomace Earthworms Straw Vermicomposting
a b s t r a c t The present work was focused on vermicomposting apple pomace waste and its mixtures with straw in volume proportions of 25%, 50%, and 75%. The feasibility was evaluated on the basis of agrochemical properties and earthworm biomass. Vermicomposting was able to reduce the weight and volume of the feedstock by 65% and 85%, respectively. The resulting vermicomposts were characterized by slightly acidic to neutral pH (5.9–6.9), and optimal EC (1.6–4.4 mS/cm) and C:N ratios (13–14). The total content of nutrients increased during vermicomposting for all of the treatments with the following average final values: N = 2.8%, P = 0.85%, K = 2.3%, and Mg = 0.38%. The addition of straw to apple pomace did not enhance earthworm biomass, but did increase the available content of nutrients during vermicomposting. The data reveals that vermicomposting is a suitable technology for the decomposition of apple pomace waste into a value added product. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Currently, the world produces 70 million metric tons of apples per year, while the countries of the European Union contribute about 15% of this amount (WAPA, 2013). In the Czech Republic apple trees represent the most important fruit species, and in 2012, 80,000 tons of apple juice was produced. Approximately 1.5–2 tons of apples, depending on their types and age, are required to produce 1 ton of juice, so the utilization ranges from 65% to 50%. The solid material which remains after the extraction of juice is called apple pomace. Apple pomace has been used as a feed for herbivorous animals and as a component in fruit tea. However, the market has been changing, and the livestock population has declined. The proportion of apple pomace in fruit teas
⇑ Corresponding author. Tel.: +420 224382731; fax: +420 224382535. E-mail address: [email protected] (A. Hanc).
has decreased due to higher demand from purchasers for components with better aroma and taste. Thus, apple pomace has become bio-waste. Vermicomposting is one possible solution for handling this feedstock. It is the processes of ingestion, digestion, and absorption of organic waste carried out by earthworms, followed by the excretion of casting through the worm’s metabolic system, during which their biological activities enhance the levels of nutrients in the organic waste (Venkatesh and Eevera, 2008). Compared to the feedstock and conventional compost, vermicompost contains increased and more soluble levels of major nutrients and organic matter with improved quality (Sinha et al., 2010). At this time, there do not appear to be any scientific studies on the vermicomposting of apple pomace waste. Keeping the above facts in mind, the present study was implemented to investigate the feasibility of vermicomposting apple pomace and its mixtures with straw on the basis of agrochemical properties and earthworm biomass.
http://dx.doi.org/10.1016/j.biortech.2014.02.031 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
2
A. Hanc, Z. Chadimova / Bioresource Technology xxx (2014) xxx–xxx
2. Methods 2.1. Feedstocks and their pre-composting Apple pomace obtained from a food-processing company, and shortly chopped wheat straw as a bulking agent to improve structure, enhance aeration, and absorb excess liquids were used in the experiment. For the experiment, dry wheat straw was soaked in water for 1 month to enhance the absorption capacity and thus aid in faster decomposition. Thus, the dry matter content of the straw decreased from 90% to 18%. 2.2. Treatment of bio-waste during the pre-composting process The composition of the feedstocks (in volume proportion) is given below: I II III IV V
Apple Apple Apple Apple Apple
pomace pomace pomace pomace pomace
(50%) + straw (25%) + straw (50%) + straw (75%) + straw (100%).
(50%). (75%). (50%). (25%).
All treatments were pre-composted in 70 L capacity laboratory reactors kept in a room at 25 °C for 14 days. An active aeration device was used to push air through the composted materials from the bottom. The mixtures were batch-wise aerated for 5 min out of each half hour in a volume of 4 L of air min 1. On the basis of their previous experiences, Hanc et al. (2012) found that this aeration level was usually sufficient to achieve the optimal parameters of the composting process.
digests obtained by pressurized wet-ashing (HNO3 + HCl + HF) with microwave heating using an Ethos 1 system (MLS GmbH, Germany). The contents of ammonium nitrogen (N–NH4+), nitrate nitrogen (N–NO3 ), and the available portions of P, K, and Mg were determined in CAT solution (0.01 mol l 1 CaCl2 and 0.002 mol l 1 diethylene triamine pentaacetic acid (DTPA)) at the rate of 1:10 (w/v) according to the International BSI Standard EN 1365, 20011. The N–NH4+ and N–NO3 contents in the extracts were measured colorimetrically using the SKALAR SANPLUS SYSTEMÒ. The element concentrations were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). 3. Results and discussion 3.1. Weight and volume From a practical point of view, changes of weight and volume during vermicomposting are important for planning the amount of processed feedstock and the final product on a given area or space. Weight loss was fairly even during the process. However, the treatment containing 75% straw showed more rapid weight decline, while the treatment containing apple pomace by itself exhibited a slower decrease in weight. On average for the treatments, the weight of the final vermicompost was one third of the initial feedstock. Hanc and Pliva (2013) found that samples consisting of pre-composted kitchen waste with woodchips and paper lost 20% and 55% of their weight, respectively. In this experiment, the volume decreased from 70% to 80% after one month. In the coming months, the volume decreased slightly. Vermicomposting was able to decrease the initial volume overall by 84–89% depending on the addition of straw.
2.3. The vermicomposting process 3.2. Value of pH, EC, and C/N rate Vermicomposting of aerobically pre-composted feedstock was conducted in a specially adapted laboratory with controlled conditions (temperature 22 °C, relative humidity 80%, ventilation for 15 min every 12 h). A 12 L batch of material was manually mixed with 3 L of substrate containing a total of 450 earthworms of the genus Eisenia (treatments II–V). Earthworms were added not alone but in their original beef manure substrate to reduce their initial stress and improve their adaptability to the new environment. In the case of treatment I (control without earthworms), 3 L of substrate was replaced by 3 L of the original pre-composted materials (apple pomace (50%) + straw (50%)). Even after the earthworms had been sorted out, the remaining substrate was not utilized due to the possible presence of cocoons from which new earthworms could hatch and affect the treatment. The mixture was placed into a plastic bowl with a perforated bottom, equipped with irrigation and temperature measurements. Each treatment was carried out in triplicate. Before sampling, the eventual leachate which was captured in a stainless bowl was returned to the vermicomposted material to achieve a closed loop. A sample of 200 g was collected from each bowl each month during the five month study period. The earthworms were sorted out, and the resulting samples were dried at 40 °C to a constant weight and ground to ensure homogeneity. 2.4. Analytical methods Measurements of pH and electrical conductivity (EC) were conducted on samples mixed with deionized water (1:10 w/v dry basis). Organic carbon was determined by dichromate oxidation in sulfuric acid solution and total nitrogen by the Kjeldahl method using a Gerhardt analytical system Vapodest-manager device. Total element contents (P, K, and Mg) were determined in the
Two weeks of pre-composting caused an increase in pH from 4.0 to 6.7 for the treatment containing only apple pomace, nevertheless this was a lower pH than mixtures with straw (up to 7.2). Higher proportions of apple pomace in the mixtures resulted in lower pH values, probably due to the high contents of organic acids (e.g. malic acid). There was a difference between composting and vermicomposting in terms of pH. The pH value in treatment I slightly but gradually increased. This pattern is typical for the composting of source separated household bio-waste as well (Sundberg and Jonsson, 2008). The pH values of mixtures containing a high proportion of apple pomace (50–100%) increased slightly after 1 month of vermicomposting. The increase in pH could be caused by the degradation and consumption of organic acids by microorganisms. Subsequently, a decrease in pH was observed which was directly proportional with the amount of straw in the treatment. The pH values of the final vermicomposts were lower by 0.6 units when compared with the initial mixtures. These differences increased directly with the proportion of straw. The lowest pH was observed in vermicompost containing 75% straw and 25% apple pomace. A decrease in pH (from 8.6 to 7.3) was found in the study conducted by Suthar (2010) who vermicomposted agro-industrial sludge. The decline in pH may be due to the mineralization of the organic compounds, and thus an increase in the contents of organic and humic acids (Suthar and Singh, 2008; Garg et al., 2006). The EC fluctuated around 1 mS/cm in treatment I which did not contain earthworms. The EC gradually increased in all of the treatments with earthworms, which could be explained by the release of bonded elements during earthworm digestion (Garg et al., 2006), and the release of minerals during the decomposition of organic matter in the form of cations in the vermicomposts (Tognetti
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
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Total N content ranged from 1.3% to 1.9% at the beginning of the experiment (Fig. 1a). After 4 months, the content increased by 85% (treatment I) and 58% (average of treatments II–V). The N contents of the final vermicomposts were 12% higher than in composts. Mineral forms of nitrogen are important in terms of fertilizing. At the beginning of the experiment, the N–NH4+ and N–NO3 contents ranged in the same order of magnitude (Table 1). The contents of the individual forms in the final vermicomposts varied markedly. At the end of vermicomposting the increase in the N–NH4+ and N–NO3 contents were 1.5- and 47.1-fold compared to the start, respectively. The increase in the N–NH4+ content can be partially explained by earthworms, because ammonia is a worm excretory product that temporarily reduces the pool of H+ ions. A different situation was observed for treatment I which did not contain earthworms, as there were no significant differences in the N–NH4+ contents between the final compost and the initial mixture. The N–NO3 content increased 2.1-fold in treatment I. It is likely that the presence of earthworms encouraged the nitrification process, and this is evident from a comparison of the N–NO3 contents in the vermicompost and control compost. Vermicomposts contained 23 times more N–NO3 when compared with compost. The N–NO3 content increased directly proportionally to the proportion of straw in the mixtures and made up 2.4% to 11.8% of the total nitrogen in the vermicomposts. The proportion of N–NO3 constituted 7% in vermicompost from kitchen bio-waste prepared by Hanc and Pliva (2013). In this experiment, the increased N–NO3 contents in vermicomposts with increased proportions of straw can be partially explained by a decrease in pH (correlation coefficient R = 0.99). 3.4. Phosphorus, potassium, and magnesium – total and available contents The total contents of macroelements such as P, K, and Mg (Fig. 1b–d) increased during composting and vermicomposting, which was associated with the loss of weight and organic matter (Wani et al., 2013), and no loss of leachate in the closed system. The average ratios of the final and initial total contents of elements increased in the following order: Mg (265%), K (306%), and P (596%). On average, the final vermicomposts contained higher contents of
Total N (mg/kg)
35000 30000 25000 20000 15000 10000 5000 0 I
Total P (mg/kg)
(b)
II
III
IV
V
IV
V
IV
V
IV
V
Treatments beginning end 12000 10000 8000 6000 4000 2000 0 I
II
III Treatments beginning
(c) Total K (mg/kg)
3.3. Total nitrogen and its mineral forms
(a)
end
30000 25000 20000 15000 10000 5000 0 I
II
III Treatments beginning
(d) Total Mg (mg/kg)
et al., 2005). The increase was directly proportional to the increased proportion of straw in the vermicomposted mixture. The values ranged from 1.1–1.5 mS/cm at the beginning, and 1.6–4.4 mS/cm at the end of the experiment. The threshold value of 3 mS/cm for safe agronomical application of the final vermicompost reported by Lazcano et al. (2008) was exceeded only in treatment II which contained the highest proportion of straw. This result could be attributed to the higher EC value in straw than apple pomace, and the soaking of the straw before use. After 1 month of vermicomposting a steep decline in the C/N ratio was observed, and in some cases this was as much as 33%. This result was probably due to microbial respiration and the mineralization of the labile organic compounds, which reduced the weight and volume of the processed mass, and by the concentration effect the Ntot.was increased. Any subsequent decreases observed in the C/N were very slight. The course of the C/N over the duration of the experiment for control treatment I was specific, because 3 L of substrate with earthworms was replaced with straw and apple pomace. This is why a higher initial C/N ratio was achieved for this particular treatment, and this value decreased gradually over time. However, there were no significant differences in the final C:N ratios of the non-vermicomposted and vermicomposted treatments.
end
5000 4000 3000 2000 1000 0 I
II
III
Treatments beginning end Fig. 1. Total contents of N (a), P (b), K (c), and Mg (d) at the beginning and at the end of vermicomposting.
total P and K by 11% and 22% compared to the control compost, respectively. The total Mg content was 9% lower on average, but there was a high standard deviation among the repetitions. The highest contents of P, K, and Mg were in vermicomposts V, IV, and II, respectively. In the study conducted by Pattnaik and Reddy (2010), the contents of N, P, K, and Mg in vermicompost from urban green waste after 60 days of vermicomposting by Eisenia fetida were 1.2%, 0.8%, 0.5%, and 0.8%, respectively. During the transit of materials through the worm gut, some important plant nutrients present in the organic waste are converted into chemical forms which are more available to plants (Garg et al., 2012). In this experiment, the highest ratio of the final and initial content of available elements was found in treatment II (Table 1), where the final vermicompost contained higher contents of the available nutrients than the control compost (by 204%, 117%, and 20% in the case of P, K, and Mg). Similarly, significantly higher contents of the available nutrients in vermicomposts than composts were found in an experiment with urban green waste
Please cite this article in press as: Hanc, A., Chadimova, Z. Nutrient recovery from apple pomace waste by vermicomposting technology. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.031
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A. Hanc, Z. Chadimova / Bioresource Technology xxx (2014) xxx–xxx
Table 1 Available contents of nitrogen (N–NH4+ and N–NO3 ), phosphorus, potassium, and magnesium (mg/kg) determined in CAT extract agent. Element
pressing during the juice production, which adversely affected the amounts of available content determined in CAT.
Treatment
Initial mixture
Vermicompost
3.5. Earthworm biomass
I II III IV V
62 ± 16.2a 45 ± 6.3a 40 ± 4.3a 44 ± 8.4a 38 ± 3.5a
59 ± 11.6a 77 ± 7.8a 49 ± 9.1a 76 ± 20.4a 59 ± 3.0a
I II III IV V
37 ± 25.0a 58 ± 30.5a 49 ± 8.7a 28 ± 3.7a 15 ± 2.0a
78 ± 27.1a 3334 ± 118.7b 1704 ± 460.9c 1543 ± 150.7c 667 ± 315.8a
I II III IV V
365 ± 80.8a 565 ± 131.7ab 553 ± 110.4ab 643 ± 7.7b 576 ± 21.5ab
486 ± 97.5a 1779 ± 177.0b 1643 ± 177.8b 1480 ± 37.0b 1018 ± 27.9c
I II III IV V
3420 ± 417.7a 8113 ± 1185.8b 7734 ± 1460.1b 7398 ± 381.9b 6387 ± 410.4b
6088 ± 599.4a 15878 ± 989.4b 14498 ± 1252.7bc 12588 ± 1141.7c 9899 ± 32.1d
A considerable drop in the earthworm biomass was observed in the first month, and the reduction ranged from 65% to 98%. These results can be explained by the initial stress the earthworms encounter from new environmental conditions (Suthar, 2010). After adaptation, the number and weight of the individual earthworms increased. The maximum biomass was reached at different times depending on the amount of feed. In the case of treatments II, III, IV, and V this peak was after 2, 2.5, 3, and 4 months of vermicomposting, respectively. This implies that apple pomace is a more valuable feed for earthworms than straw. Straw seems to play the role of a bulking agent important for keeping air in the material. Garg et al. (2012) found a maximum worm biomass (Eisenia fetida) between 7 and 10 weeks during vermicomposting of food industry sludges mixed with different organic wastes. In a study conducted by Fernández-Gómez et al. (2010) the maximum individual biomass was recorded after 4 weeks of vermicomposting of vegetable greenhouse waste with the addition of cow dung and straw. In another study, the maximum worm biomass was achieved between the 4th and 5th week of vermicomposting of non-recyclable paper waste (Gupta and Garg, 2009).
I II III IV V
483 ± 65.2ab 394 ± 26.7a 389 ± 36.3a 481 ± 29.8ab 527 ± 10.6b
480 ± 27.3a 787 ± 49.6b 555 ± 34.5a 538 ± 23.0a 435 ± 97.0a
N–NH4+
N–NO3
P
K
Mg
Mean ± SD, n = 3. Mean value followed by different letters indicates a statistical difference (ANOVA, Tukey’s test, p < 0.05).
(Pattnaik and Reddy, 2010). The available content of macroelements in the final vermicompost decreased directly proportionally with the proportion of apple pomace. The resulting vermicomposts were rich mainly in available K (from 9899 to 15878 mg/kg). Additionally, the available content of P was approximately one order of magnitude lower (1018–1779 mg/kg), while the available Mg content ranged from 435 to 787 mg/kg. The available P, K, and Mg contents in vermicomposts constituted approximately 16%, 62%, and 15% of the total contents, respectively, and these values were 60%, 45%, and 25% higher than in the control composts. Hanc and Pliva (2013) found that the available P and K contents in vermicompost from kitchen bio-waste constituted approximately 50% and 5% of the total contents, respectively. Higher available P contents were found in this material with the addition of woodchips than paper. The enhanced number of microflora present in the gut of earthworms in the case of vermicomposting might have played an important role in the release of nutrients. Insoluble P can be converted into soluble forms with the help of P-solubilizing microorganisms through phosphatases present in the gut. Acid production by the microorganisms is the major mechanism for the solubilization of insoluble potassium. The important acids in phosphorus solubilization are carbonic, nitric, and sulfuric (Kaviraj and Sharma, 2003). In regards to magnesium, it is postulated that fungal and micro-algal hyphae, which easily colonize on freshly deposited earthworm casts, contribute to the Mg content in the vermicomposts (Suthar, 2010). In the current study, higher contents of available elements were found in vermicomposts with higher proportions of straw in the initial feedstock. This result could be explained by the soaking of the straw, thereby decomposition and digestibility were enhanced. The treatments containing apple pomace lost large amounts of water-soluble nutrients by
4. Conclusion The study concludes that apple pomace waste is a suitable feedstock for earthworms which are able to convert it into a value added product. The addition of straw to apple pomace did not enhance earthworm biomass but increased the available content of nutrients during vermicomposting. The resulting vermicomposts were characterized by slightly acidic to neutral pH, and optimal EC and C:N ratios. The total content of nutrients increased during vermicomposting which was due to a significant decrease in weight and volume of the processed materials. Acknowledgements Financial support for these investigations was provided by the 7FP Collaborative Project no. 312117 BIOFECTOR. The authors would like to thank Christina Baker for revision of the English text. References EN 13651. Soil improvers and growing media – Extraction of calcium chloride/DTPA (CAT) soluble nutrients. 2001. Fernández-Gómez, M.J., Romero, R., Nogales, R., 2010. Feasibility of vermicomposting for vegetable greenhouse waste recycling. Bioresour. Technol. 101, 9654–9660. Garg, V.K., Gupta, A., Satya, S., 2006. Vermicomposting of different types of waste using Eisenia foetida: a comparative study. Bioresour. Technol. 97, 391–395. Garg, V.K., Suthar, S., Yadav, A., 2012. Management of food industry waste employing vermicomposting technology. Bioresour. Technol. 126, 437–443. Gupta, R., Garg, V.K., 2009. Vermiremediation and nutrient recovery of nonrecyclable paper waste employing Eisenia fetida. J. Hazard. Mater. 162, 430–439. Hanc, A., Pliva, P., 2013. Vermicomposting technology as a tool for nutrient recovery from kitchen bio-waste. J. Mater. Cycles Waste Manage. 15, 431–439. Hanc, A., Szakova, J., Svehla, P., 2012. Effect of composting on the mobility of arsenic, chromium and nickel contained in kitchen and garden waste. Bioresour. Technol. 126, 444–452. Kaviraj, Sharma, S., 2003. Municipal solid waste management through vermicomposting employing exotic and local species of earthworms. Bioresour. Technol. 90, 169–173. Lazcano, C., Gomez-Brandon, M., Dominguez, J., 2008. Comparison of the effectiveness of composting and vermicomposting for biological stabilization of cattle manure. Chemosphere 72, 1013–1019. Pattnaik, S., Reddy, M.V., 2010. Nutrient status of vermicompost of urban green waste processed by three earthworm species – Eisenia fetida, Eudrilus eugeniae, and Perionyx excavatus. Appl. Environ. Soil Sci. 2010, 1–13.
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