# Proof-of-Concept of Spent Mushrooms Compost Torrefaction—Studying the Process Kinetics and the Influence of Temperature and Duration on the Calorific Value of the Produced Biocoal

^{1}

^{2}

^{*}

## Abstract

**:**

^{−1}. The highest calorific value = 17.9 MJ kg

^{−1}d.m. was found for 280 °C (60 min torrefaction time). A significant (p < 0.05) influence of torrefaction temperature on HHV increase within the same group of torrefaction duration, i.e., 20, 40, or 60 min, was observed. The torrefaction duration significantly (p < 0.05) increased the HHV for 220 °C and decreased HHV for 300 °C. The highest mass yield (98.5%) was found for 220 °C (60 min), while the highest energy yield was found for 280 °C (60 min). In addition, estimations of the biocoal recirculation rate to maintain the heat self-sufficiency of MSC torrefaction were made. The net quantity of biocoal (torrefied MSC; 65.3% moisture content) and the 280 °C (60 min) torrefaction variant was used. The initial mass and energy balance showed that MSC torrefaction might be feasible and self-sufficient for heat when ~43.6% of produced biocoal is recirculated to supply the heat for torrefaction. Thus, we have shown a concept for an alternative utilization of abundant biowaste (MSC). This research provides a basis for alternative use of an abundant biowaste and can help charting improved, sustainable mushroom production.

## 1. Introduction

^{−1}to 325 thousand Mg·year

^{−1}, which currently accounts for 24.15% of the total production in the European Union (EU) [1,2]. Poland is the largest grower of mushrooms in Europe and the third in the world. One of the abundant wastes arising during the cultivation of mushrooms is a worn-out substrate—mushroom spent compost (MSC)—which accounts to ~5 kg of MSC per 1 kg of produced mushrooms [3]. This amounts to 5.6 and 1.6 million Mg·year

^{−1}of MSC, in the EU and Poland, respectively [1,4].

^{3}·kg

^{−1}d.m. of biomethane, while corn silage can produce 320 dm

^{3}·kg

^{−1}d.m. [19]. The biogas yield from other available substrates: cattle manure (324 ± 15.5 dm

^{3}·kg

^{–1}d.m.), corn silage (653 ± 28.8 dm

^{3}·kg

^{–1}d.m.), waste fruit and vegetables (678 ± 15.8 dm

^{3}·kg

^{–1}d.m.), sugar beet pulp (634 ± 235 dm

^{3}·kg

^{–1}d.m.), whey (736 ± 15.5 dm

^{3}·kg

^{–1}d.m.) [20], shows that biogas production from MSC is not competitive enough. Another interesting use of MSC is the production of hydrogen, which has already been tested at the lab-scale. Two-step hydrolysis with acid and base resulted in 2.52 moles of H

_{2}·g COD

^{−1}[21].

^{−1}d.m. [3]. MSC’s characteristics (Table 1) do not indicate high profitability of the incineration process [25].

_{2}and flammable substances such as CO, CH

_{4}, or H

_{2}[31]. Depending on process parameters and properties of the substrate, a different ratio of flammable to noncombustible parts may be achieved [28]. The torgas is not an attractive product of torrefaction due to the high content of nonflammable substances [32,33].

^{−1}d.m. and the feedstock should be from solid biomass/waste of vegetable, animal, or biodegradable origin to be considered as a ‘renewable source of energy’ [29].

## 2. Materials and Methods

#### 2.1. The Properties of MSC

#### 2.2. MSC Torrefaction Kinetics Measurements

_{2}was injected with a flow rate of 0.6 mL·min

^{−1}. The tested sample of MSC was located inside the cuvette and placed in the center of the reactor. The cuvette containing the sample was combined with a precise (0.01 g resolution) electronic balance for the determination of the mass drop during the process. The readings (temperature, and mass of the sample) were recorded by PC. Dried samples with a mass of 2.25 g were treated under temperatures in the range from 200 to 300 °C (with an interval of 20 °C) for up to 60 min. The chosen temperatures were in the range of the torrefaction previously used by Bialowiec et al. [37]. The torrefaction rate constant (k) was determined using the first-order equation [42]:

^{−1}, $t$ = time, s.

^{−1}; $R$ = gas constant, 8.314, J·(mol·K)

^{−1}; $T$ = temperature, K.

_{a}was determined with the application of k and the Arrhenius equation, with the assumption that ln(k) is a linear function of 1/T:

#### 2.3. MSC Torrefaction and Torrefied Biomass Generation

_{2}with the flow rate of 10 dm

^{3}·h

^{−1}was used to establish oxygen-free conditions. The process was carried out under temperatures from 200 °C to 300 °C with intervals of 20 °C. For each temperature, torrefaction was carried out with 20, 40, and 60 min retention time. The samples were heated with a heating rate of 50 °C·min

^{−1}from 20 °C to the torrefaction setpoint temperature. Ten grams (± 0.5 g) of the dry mass of the sample was used for the tests. The biocoals were removed from the muffle furnace when the interior temperature was lower than 200 °C (temperature was monitored by an internal thermocouple and visualized on the screen of the furnace). The approximate times of cooling from 300 °C, 280 °C, 260 °C, 240 °C, and 220 °C to 200 °C were 38, 33, 29, 23, and 13.5 min, respectively. The approximate cooling time from 300 °C to room temperature (~20 °C) was around 6 h. Analyses of three replicates were carried out.

- Mass of dry biocoal—mass of (dry) biocoal after the process of torrefaction, g;
- Mass of dried raw MSC—dried mass of MSC used in the process of torrefaction, g;
- 100—conversion to percent;
- HHV of biocoal—higher heating value of biocoal after the process of torrefaction, J∙g
^{−1}; - HHV of raw MSC—higher heating value of dried MSC (raw material) used for torrefaction, J∙g
^{−1}.

#### 2.4. Proximate Analysis

- Moisture content, determined in accordance with [45], by means of the lab dryer (WAMED, KBC-65W, Warsaw, Poland) (Raw MSC and biocoals).
- Volatile solids, determined in accordance with [46], by means of the SNOL 8.1/1100 lab muffle furnace (Utena, Lithuania) (Raw MSC).
- Ash content, determined in accordance with [47], by means of the SNOL 8.1/1100 lab muffle furnace (Utena, Lithuania) (Raw MSC).
- High heating value (HHV), determined in accordance with [48], by means of the IKA C2000 calorimeter (Raw MSC and biocoals).

#### 2.5. Torrefaction Process Models

_{1}) and five regression coefficients (a

_{2–6}) (Equation (9)).

- f (T,t)—the biocoal property obtained under T—temperature, and t—residence time conditions,
- a
_{1}—intercept (-), - a
_{2-6}—regression coefficient (-), - T—temperature, T = 200–300 °C,
- t—residence time, t = 0–60 min.

^{2}) was calculated.

#### 2.6. Torrefaction Mass and Energy Balance Evaluation

- mass of MSC, Mg, assumed 1 Mg,
- moisture content of MSC, %, assumed 65.32% (Table 2),
- torrefaction parameters of temperature and time assumed 280 °C and 60 min, respectively.

- mtb—mass of torrefied MSC after torrefaction process at T, and t conditions, kg, MY—mass yield of biocoal, %/%, mr
_{d}—dry mass of MSC, kg.

- E
_{tb}—chemical energy in torrefied biomass, kJ.

- E
_{w}—heat needed to heat water contained in MSC, kJ - Cp
_{water}—water specific heat, 4.18 kJ·kg^{−1}, - m
_{w}—mass of water in MSC, Mg.

- E
_{ev}—heat needed to vaporization of water contained in MSC, kJ - L
_{h}—latent heat of water vaporization, kJ·kg^{−1}.

- E
_{hw}—heat needed to heat MSC from ambient to torrefaction temperature, kJ - Cp
_{wood}—specific heat of wood (assumed for these calculations), kJ·kg^{−1}.

- E—heat needed to torrefied MSC

_{p}may be calculated:

- μe—the biocoal recirculation rate to obtain the heat self-sufficiency.

## 3. Results

^{−5}s

^{−1}) and the highest (k = 4.6 × 10

^{−5}s

^{−1}) at 300 °C (Table 3). Similar dependence was confirmed by Dhanavath et al. [52]. However, the increase in k in relation to torrefaction temperature was not linear. Significant (p < 0.05) differences between the k values observed for 300 °C and the values obtained in temperatures between 200 and 260 °C; however, no significant increase between 200 °C and 260 °C was observed (Table A1). Torrefaction at 280 °C caused a significant increase of the k value in comparison to 200 °C. The results indicate that the temperature must be >280 °C to achieve significant acceleration of the torrefaction process.

^{−1}, was determined (Table 3). The obtained E

_{a}value is low in comparison with typical woody biomass, where, for example, for beech and spruce, these values are 150 and 155 kJ·mol

^{−1}, respectively [55], for willow from 46 to 152 kJ·mol

^{−1}, [56] pine 131 kJ·mol

^{−1}, and fir 128 kJ·mol

^{−1}[57]. However, these values have been determined by different methods and models. The model used in the present work had a global first-order character, as it was part of the preliminary study. This model allows estimating solid mass yield at a specific temperature and time of the process. Because of the high ash content in MSC and the narrow range of used temperatures, we recommend additional experiments on the kinetics of the process, using more complex models based on first-order kinetics with distributed activation energy models (DAEMs), pseudokinetics, or multicomponent first-order kinetic models.

^{−1}d.m.) (Figure 2). The significantly (p < 0.05) lowest values were noted for temperature 200 °C (all durations) from 14.1 to 14.4 MJ·kg

^{−1}d.m. The best (p < 0.05) fuel properties were noted for biocoals obtained from MSC under 280 °C 16.9–17.9 MJ·kg

^{−1}d.m. In the case of 220 °C, a significant (p < 0.05) influence of torrefaction duration on the increase of HHV was noted (Table A2). On the other hand, the increase of torrefaction time decreased (p < 0.05) the HHV under the temperature of 300 °C, which could be related to organic matter volatilization and mineralization. Additionally, the increase of the temperature from 200 to 280 °C, for the same duration, increased (p < 0.05) the HHV (Figure 2, Table A2). The experiment showed that to achieve the highest HHV of the biocoal, MSC should be torrefied under the temperature of 280 °C for a duration of 60 min.

_{3}, and a

_{6}) were statistically significant (p < 0.05) (Table A3). Such a low fitting degree of the model parameters to existing data could be due to a relatively low number of repetitions (n = 3 for each variant) and/or a low degree of the polynomial. To achieve better results suitable for MSC torrefaction optimization, more sophisticated research with a higher number of repetitions (to reduce the degree of the heterogeneity of the results) with the application of better-fitting models is required.

_{2}, a

_{3}, and a

_{6}) and the intercept (a

_{1}) were statistically significant (p < 0.05) (Table A4).

^{−1}to ~18 MJ·kg

^{−1}. This calorific value of obtained biocoal is comparable with nonagglomerating highly volatile coals (HHV from 17.4 to 23.9 MJ·kg

^{−1}) or lignite coal (HHV below 17.4 MJ·kg

^{−1}) [58]. Our research also showed that the highest efficiency (i.e., the energy yield) was achieved at the temperature of 280 °C for a duration of 60 min.

^{−1}. For these conditions, the estimated biocoal recirculation rate for obtaining the MSC torrefaction heat self-sufficiency was 43.6%. Therefore the 56.4% of produced biocoal (181.6 kg produced form 1 Mg of wet MSC) may be used for heating the mushroom farm (Figure 1) or be sold to external users.

## 4. Conclusions

^{−1}. For these conditions, the estimated biocoal recirculation rate to obtain MSC torrefaction self-sufficiency was 43.6%. The net mass obtained after torrefaction and biocoal recirculation was 0.182 Mg d.m. Second-degree polynomial models for optimization of the torrefaction process were proposed. However, more complex research is required for model calibration and up-scaling. The initial mass and energy balances evaluation showed that MSC torrefaction might be self-sufficient for heat, and therefore feasible. This research provides a basis for alternative use of an abundant biowaste and can help chart improved, sustainable mushroom production.

## Supplementary Materials

## Author Contributions

## Funding

## Conflicts of Interest

## Appendix A

**Table A1.**Calculated values of probability ‘p’ of ANOVA analysis with Tukey’s Test RSD of variable: torrefaction constant rate (k). Highlighted (in bold) differences are significant at p < 0.05000.

Torrefaction Temperature, °C | Calculated Values of Probability ‘p’ | ||||
---|---|---|---|---|---|

200 | 220 | 240 | 260 | 280 | |

200 | |||||

220 | 0.998400 | ||||

240 | 0.976232 | 0.999461 | |||

260 | 0.401048 | 0.618619 | 0.793686 | ||

280 | 0.030215 | 0.058894 | 0.099319 | 0.572968 | |

300 | 0.000291 | 0.000407 | 0.000562 | 0.003267 | 0.051587 |

**Table A2.**Calculated values of probability ‘p’ of ANOVA analysis with Tukey’s Test RSD of variable: Higher Heating Value of biocoal. Highlighted differences are significant at p < 0.05000.

Torrefaction Temperature, °C | Torrefaction Duration, min | Calculated Values of Probability ‘p’ | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

200 | 200 | 200 | 220 | 220 | 220 | 240 | 240 | 240 | 260 | 260 | 260 | 280 | 280 | 280 | 300 | 300 | ||

20 | 40 | 60 | 20 | 40 | 60 | 20 | 40 | 60 | 20 | 40 | 60 | 20 | 40 | 60 | 20 | 40 | ||

200 | 20 | |||||||||||||||||

200 | 40 | 0.9996 | ||||||||||||||||

200 | 60 | 0.9806 | 1.0000 | |||||||||||||||

220 | 20 | 0.9960 | 1.0000 | 1.0000 | ||||||||||||||

220 | 40 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | |||||||||||||

220 | 60 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 1.0000 | ||||||||||||

240 | 20 | 0.1815 | 0.8098 | 0.9680 | 0.9109 | 0.0009 | 0.0012 | |||||||||||

240 | 40 | 0.6147 | 0.9965 | 1.0000 | 0.9996 | 0.0002 | 0.0003 | 1.0000 | ||||||||||

240 | 60 | 0.1425 | 0.7419 | 0.9426 | 0.8636 | 0.0012 | 0.0017 | 1.0000 | 1.0000 | |||||||||

260 | 20 | 0.0004 | 0.0057 | 0.0191 | 0.0105 | 0.3675 | 0.4470 | 0.5434 | 0.1461 | 0.6228 | ||||||||

260 | 40 | 0.0011 | 0.0202 | 0.0621 | 0.0361 | 0.1546 | 0.2009 | 0.8356 | 0.3518 | 0.8887 | 1.0000 | |||||||

260 | 60 | 0.0002 | 0.0004 | 0.0012 | 0.0007 | 0.9386 | 0.9675 | 0.0865 | 0.0124 | 0.1127 | 0.9998 | 0.9862 | ||||||

280 | 20 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0125 | 0.0088 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | |||||

280 | 40 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0012 | 0.0009 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 1.0000 | ||||

280 | 60 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0067 | 0.0632 | |||

300 | 20 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0694 | 0.0509 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.0007 | 1.0000 | 0.9799 | 0.0011 | ||

300 | 40 | 0.6309 | 0.9972 | 1.0000 | 0.9997 | 0.0002 | 0.0003 | 1.0000 | 1.0000 | 1.0000 | 0.1389 | 0.3382 | 0.0116 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | |

300 | 60 | 0.9999 | 1.0000 | 1.0000 | 1.0000 | 0.0002 | 0.0002 | 0.7392 | 0.9909 | 0.6640 | 0.0041 | 0.0146 | 0.0003 | 0.0002 | 0.0002 | 0.0002 | 0.0002 | 0.9924 |

**Table A3.**Statistical parameters of the polynomial model of the influence of torrefaction temperature and process time on the higher heating value of biocoal. Regression analysis used a 2-degree polynomial with a general form, with intercept (a

_{1}) and 5 regression coefficients (a

_{2–6}) (Equation (9)). Highlighted values are significant at p < 0.05000.

Regression Coefficients | Value of Regression Coefficient | Standard Error | T Value, df = 156 | Determined p-Value | Lower Range of Confidence Interval | Upper Range of Confidence Interval |
---|---|---|---|---|---|---|

a_{1} (intercept) | −9.18772 | 8.404435 | −1.09320 | 0.279763 | −26.0860 | 7.710533 |

a_{2} | −0.00025 | 0.000130 | −1.94593 | 0.057531 | −0.0005 | 0.000008 |

a_{3} | 0.16382 | 0.065675 | 2.49436 | 0.016114 | 0.0318 | 0.295867 |

a_{4} | 0.00031 | 0.000687 | 0.45333 | 0.652351 | −0.0011 | 0.001692 |

a_{5} | 0.11483 | 0.080328 | 1.42947 | 0.159347 | −0.0467 | 0.276336 |

a_{6} | −0.00055 | 0.000232 | −2.35809 | 0.022491 | −0.0010 | −0.000081 |

**Table A4.**Statistical parameters of the polynomial model of the influence of torrefaction temperature and process time on the dry mass yield value of biocoal. Regression analysis used a 2-degree polynomial with a general form, with intercept (a

_{1}) and 5 regression coefficients (a

_{2–6}) (Equation (9)). Highlighted values are significant at p < 0.05000.

Regression Coefficients | Value of Regression Coefficient | Standard Error | T Value, df = 12 | Determined p-Value | Lower Range of Confidence Interval | Upper Range of Confidence Interval |
---|---|---|---|---|---|---|

a_{1} (intercept) | 39.01744 | 11.29449 | 3.45455 | 0.004765 | 14.40886 | 63.62603 |

a_{2} | 0.50652 | 0.08826 | 5.73904 | 0.000093 | 0.31422 | 0.69882 |

a_{3} | −0.00105 | 0.00017 | −6.00537 | 0.000062 | −0.00143 | −0.00067 |

a_{4} | 0.16952 | 0.10795 | 1.57039 | 0.142306 | −0.06568 | 0.40473 |

a_{5} | 0.00104 | 0.00092 | 1.12846 | 0.281182 | −0.00097 | 0.00305 |

a_{6} | −0.00122 | 0.00031 | −3.91408 | 0.002057 | −0.00190 | −0.00054 |

**Table A5.**Statistical parameters of the polynomial model of the influence of torrefaction temperature and process time on energy yield value of biocoal. Regression analysis used a 2-degree polynomial with a general form, with intercept (a

_{1}) and 5 regression coefficients (a

_{2–6}) (Equation (9)).

Regression Coefficients | Value of Regression Coefficient | Standard Error | T Value, df = 12 | Determined p Value | Lower Range of Confidence Interval | Upper Range of Confidence Interval |
---|---|---|---|---|---|---|

a_{1} (intercept) | −124.873 | 119.6896 | −1.04331 | 0.317370 | −385.654 | 135.9085 |

a_{2} | 1.681 | 0.9353 | 1.79781 | 0.097396 | −0.356 | 3.7193 |

a_{3} | −0.003 | 0.0018 | −1.55785 | 0.145239 | −0.007 | 0.0011 |

a_{4} | 0.995 | 1.1440 | 0.86967 | 0.401540 | −1.498 | 3.4874 |

a5 | 0.003 | 0.0098 | 0.32266 | 0.752508 | −0.018 | 0.0245 |

a6 | −0.005 | 0.0033 | −1.55290 | 0.146412 | −0.012 | 0.0021 |

## References

- Czop, M.; Kłapcia, E. Termiczne przekształcanie jako sposób zagospodarowania podłoża pieczarkowego po zakończonym cyklu produkcyjnym ‘Thermal transformation as a way of developing a mushroom substrate after a completed production cycle’. Inżynieria i Ochrona Środowiska
**2016**, 19, 67–80. [Google Scholar] [CrossRef] - Kurczewski, R. Odpady Organiczne, Czyli Resztki z Pańskiego Stołu ‘Organic Waste, or Leftovers from Your Table’. Available online: https://sozosfera.pl/ochrona-przyrody/odpady-organiczne-czyli-resztki-panskiego-stolu/ (accessed on 1 June 2019).
- Finney, K.N.; Ryu, C.; Sharifi, V.N.; Swithenbank, J. The reuse of spent mushroom compost and coal tailings for energy recovery: Comparison of thermal treatment technologies. Bioresour. Technol.
**2009**, 100, 310–315. [Google Scholar] [CrossRef] [PubMed] - Singha, A.; Bajara, S.; Bishnoia, N.R.; Singha, N. Laccase production by Aspergillus heteromorphous using distillery spent wash and lignocellulosic biomass. J. Haz. Mat.
**2010**, 176, 1079–1082. [Google Scholar] [CrossRef] [PubMed] - Commission Regulation (EU) 2015/2002 of 10 November 2015 amending Annexes IC and V to Regulation (EC) No. 1013/2006 of the European Parliament and of the Council on shipments of Waste (Text with EEA relevance). Available online: https://publications.europa.eu/en/publication-detail/-/publication/6e580883-8837-11e5-b8b7-01aa75ed71a1/language-en (accessed on 29 May 2019).
- Becher, M. Skład chemiczny podłoża po uprawie pieczarki jako odpadowego materiału organicznego ‘Chemical composition of the substrate after cultivation of the mushroom as waste organic material’. Ekonomia Środowisko
**2013**, 4, 207–213. [Google Scholar] - Kalembasa, D.; Becher, M.; Bik, B.; Makolewski, A. Właściwości materii organicznej podłoża po uprawie pieczarki ‘Properties of the organic matter of the substrate after growing the mushrooms’. Acta Agrophysica
**2012**, 19, 713–723. [Google Scholar] - Regulation (EC) No. 2003/2003 of the European Parliament and of the Council of 13 October 2003 Relating to Fertilisers (Text with EEA Relevance). Available online: http://data.europa.eu/eli/reg /2003/2003/oj (accessed on 28 May 2019).
- Jordan, S.; Mullen, G.; Murphy, M. Composition variability of spent mushroom compost in Ireland. Bioresour. Technol.
**2008**, 99, 411–418. [Google Scholar] [CrossRef] [PubMed] - Wiśniewska-Kadżajan, B. Ocena przydatności podłoża po uprawie pieczarki do nawożenia roślin ‘Evaluation of the suitability of the substrate after cultivation of mushrooms for fertilizing plants’. Ochrona Środowiska i Zasobów Naturalnych
**2012**, 23, 165–176. [Google Scholar] - Majchrowska-Safaryan, A.; Tkaczuk, C. Possibility to use the spent mushroom substrate in soil fertilization as one of its disposal methods. J. Res. Appl. Agric. Eng.
**2013**, 58, 57–62. [Google Scholar] - Garrido, R.; Ruiz-Felix, M.N.; Satrio, J.A. Effects of Hydrolysis and Torrefaction on Pyrolysis Product Distribution of Spent Mushroom Compost (SMC). Int. J. Environ. Pollut. Remediat.
**2012**, 1, 98–103. [Google Scholar] [CrossRef] - Zhou, A.; Du, J.; Varrone, C.; Wang, Y.; Wang, A.; Liu, W. VFAs bioproduction from waste activated sludge by coupling pretreatments with Agaricus bisporus substrates conditioning. Process. Biochem.
**2014**, 49, 283–289. [Google Scholar] [CrossRef] - Song, H.; Yim, G.-J.; Ji, S.-W.; Neculita, C.M.; Hwang, T. Pilot-scale passive bioreactors for the treatment of acid mine drainage: Efficiency of mushroom compost vs. mixed substrates for metal removal. J. Environ. Manag.
**2012**, 111, 150–158. [Google Scholar] [CrossRef] [PubMed] - Asada, C.; Asakawa, A.; Sasaki, C.; Nakamura, Y. Characterization of the steam-exploded spent Shiitake mushroom medium and its efficient conversion to ethanol. Bioresour. Technol.
**2011**, 102, 10052–10056. [Google Scholar] [CrossRef] [PubMed] - Kapu, N.; Manning, M.; Hurley, T.; Voigt, J.; Cosgrove, D.; Romaine, C. Surfactant-assisted pretreatment and enzymatic hydrolysis of spent mushroom compost for the production of sugars. Bioresour. Technol.
**2012**, 114, 399–405. [Google Scholar] [CrossRef] [PubMed] - Sato, N.; Shinji, K.; Mizuno, M.; Nozaki, K.; Suzuki, M.; Makishima, S.; Shiroishi, M.; Onoda, T.; Takahashi, F.; Kanda, T.; et al. Improvement in the productivity of xylooligosaccharides from waste medium after mushroom cultivation by hydrothermal treatment with suitable pretreatment. Bioresour. Technol.
**2010**, 101, 6006–6011. [Google Scholar] [CrossRef] [PubMed] [Green Version] - Jurak, E.; Kabel, M.A.; Gruppen, H. Carbohydrate composition of compost during composting and mycelium growth of Agaricus bisporus. Carbohydr. Polym.
**2014**, 101, 281–288. [Google Scholar] [CrossRef] [PubMed] - Bisaria, R.; Vasudevan, P.; Bisaria, V. Utilization of spent agro-residues from mushroom cultivation for biogas production. Appl. Microbiol. Biotechnol.
**1990**, 33, 607–609. [Google Scholar] [CrossRef] - Żak, A.; Montusiewicz, A. Analiza opłacalności wybranych substratów wykorzystywanych w biogazowniach rolniczych ‘Analysis of the profitability of selected substrates used in agricultural biogas plants’. Acta Sci. Pol. Biotechnol.
**2018**, 17, 5–12. [Google Scholar] [CrossRef] - Ya-Chieh, L.; Shu-Yii, W.; Chen-Yeon, C.; Hsin-Chieh, H. Hydrogen production from mushroom farm waste with a two-step acid hydrolysis process. Int. J. Hydrog. Energy
**2011**, 36, 14245–14251. [Google Scholar] [CrossRef] - Zuwała, J.; Kopczyński, M.; Kazalski, K. Koncepcja systemu uwierzytelniania biomasy toryfikowanej w perspektywie wykorzystania paliwa na cele energetyczne ‘The concept of a biomass biomass authentication system in the perspective of using fuel for energy purposes’. Polityka Energetyczna
**2015**, 18, 89–100. [Google Scholar] - Directive 2009/28/EC of the European Parliament and of Council of 23 April 2009 on the Promotion of the Use of Energy from Renewable Sources and Amending and Subsequently Repealing Directive 2001/77/EC and 2003/30/EC (Text with EEA Relevance). Available online: http://data.europa.eu/eli/dir/2009/28/2015-10-05 (accessed on 27 May 2019).
- Sładeczek, F.; Głodek-Bucyk, E. Badania wykorzystania niskotemperaturowej pirolizy do przetwarzania biomasy odpadowej na biowęgiel w instalacji testowej ‘Research on the use of low-temperature pyrolysis for the conversion of waste biomass into biochar in a pilot-scale installation’. ICiMB
**2017**, 28, 50–60. [Google Scholar] - Koppejan, J.; Sokhansanj, S.; Melin, S.; Madrali, S. Status Overview of Torrefaction Technologies. IEA Bioenergy Task 32 Report. Final Report. Enschede 2012. ISBN 978-1-910154-23-6. Available online: http://task40.ieabioenergy.com/wp-content/uploads/2013/09/IEA_Bioenergy_T32_Torrefaction_review.pdf (accessed on 8 August 2019).
- Białowiec, A.; Micuda, M.; Koziel, J.A. Waste to Carbon: Densification of Torrefied Refuse-Derived Fuel. Energies
**2018**, 11, 3233. [Google Scholar] [CrossRef] - Dębowski, M.; Pawlak-Kruczek, H.; Czerep, M.; Brzdękiewicz, A.; Słomczyński, Z. Technologie produkcji biowęgla- zalety i wady ‘Biochar production technologies—Advantages and disadvantages’. ICiMB
**2016**, 26, 26–39. [Google Scholar] - Kopczyński, M.; Zuwała, J. Biomasa toryfikowana–Nowe paliwo dla energetyki ‘Torrefied biomass–A new fuel for the power industry’. Chemik
**2013**, 67, 540–551. [Google Scholar] - The Act of 20 February 2015 on Renewable Energy Sources (Journal of Laws of 2018, Item 2389, as Amended). Available online: http://prawo.sejm.gov.pl/isap.nsf/download.xsp/WDU20150000478/U/D20150478Lj.pdf (accessed on 27 May 2019).
- Bajpai, P. Pretreatment of Lignocellulosic Biomass for Biofuel Production; SpringerBriefs in Green Chemistry for Sustainability, Springer: Singapore, 2016; Volume 22, pp. 1–24. [Google Scholar]
- Basu, P. Biomass Gasification, Pyrolysis and Torrefaction: Practical Design and Theory, 3rd ed.; Elsevier: Halifax, NS, Canada, 2013; pp. 44–139. ISBN 9780128130407. [Google Scholar]
- Kordylewski, W.; Tatarek, A. Wybrane właściwości toryfikatów z krajowych i importowanych biomas ‘Selected properties of biochars from domestic and imported sources of biomass’. Arch. Spalania
**2012**, 12, 109–116. [Google Scholar] - Jakubiak, M.; Kordylewski, W. Toryfikacja biomasy ‘Biomass torrefaction’. Pol. Inst. Spalania
**2010**, 10, 11–25. [Google Scholar] - Ryu, C.; Finney, K.; Sharifi, J. Pelletised fuel production from coal tailings and spent mushroom compost —Part I Identification of pelletisation parameter. Fuel Process. Technol.
**2008**, 89, 269–275. [Google Scholar] [CrossRef] - Yusup, S.; Ahmad, M.; Melati, U.; Yoshimitsu, R.; Mahari, A.; Azlin Suhaida, A.; Mas Fatiha, M.; Sean Lim, L. Pretreatment Techniques for Biofuels and Biorefineries; Springer: Berlin, Heidelberg, Germany, 2013; pp. 59–75. [Google Scholar]
- Sobolewski, A.; Wasielewski, R.; Dreszer, K.; Stelmach, S. Technologie otrzymywania i kierunki zastosowań paliw alternatywnych otrzymywanych z odpadów ‘Production technologies and applications of alternative fuels derived from waste’. Instytut Chemicznej Przeróbki Węgla
**2006**, 85, 1080–1084. [Google Scholar] - Białowiec, A.; Pulka, J.; Gołaszewski, J.; Manczarski, P.; Stępień, P. The RDF torrefaction: An effect of temperature on characterization of the product—Carbonized Derived Fuel. Waste Manag.
**2017**, 70, 91–100. [Google Scholar] [CrossRef] - Pulka, J.; Manczarski, P.; Koziel, J.A.; Białowiec, A. Torrefaction of Sewage Sludge: Kinetics and Fuel Properties of Biochars. Energies
**2019**, 12, 565. [Google Scholar] [CrossRef] - Dudek, M.; Świechowski, K.; Manczarski, P.; Koziel, J.A.; Białowiec, A. The Effect of Biochar Addition on the Biogas Production Kinetics from the Anaerobic Digestion of Brewers’ Spent Grain. Energies
**2019**, 12, 1518. [Google Scholar] [CrossRef] - Świechowski, K.; Liszewski, M.; Bąbelewski, P.; Koziel, J.A.; Białowiec, A. Fuel Properties of Torrefied Biomass from Pruning of Oxytree. Data
**2019**, 4, 55. [Google Scholar] [CrossRef] - Kopczyński, M.; Plis, A.; Zuwała, J. Thermogravimetric and Kinetic Analysis of Raw and Torrefied Biomass Combustion. Chem. Process. Eng.
**2015**, 36, 209–223. [Google Scholar] [CrossRef] [Green Version] - Bates, R.B.; Ghoniem, A.F. Biomass torrefaction: Modeling of volatile and solid product evolution kinetics. Bioresour. Technol.
**2012**, 124, 460–469. [Google Scholar] [CrossRef] [PubMed] - Syguła, E.; Koziel, J.A.; Białowiec, A. Waste to Carbon: Preliminary Research on Mushroom Spent Compost Torrefaction. 2019. Available online: https://www.preprints.org/manuscript/201906.0189/v1 (accessed on 16 July 2019).[Green Version]
- Zhang, B.; Heidari, M.; Regmi, B.; Salaudeen, S.; Arku, P.; Thimmannagari, M.; Dutta, A. Hydrothermal Carbonization of Fruit Wastes: A Promising Technique for Generating Hydrochar. Energies
**2018**, 11, 2022. [Google Scholar] [CrossRef] - Polish Committee for Standardization. Solid biofuels–Determination of Moisture Content—Drying Method—Part 3: Moisture in a Sample for General Analysis. PN-EN ISO 18134-3:2015-11, 27 November 2015. [Google Scholar]
- Polish Committee for Standardization. Solid Biofuels–Determination of Volatile Matter Content. PN-EN ISO 18123:2016-01, 29 January 2016. [Google Scholar]
- Polish Committee for Standardization. Solid Biofuels—Determination of Ash Content. PN-EN ISO 18122:2016-01, 29 January 2016. [Google Scholar]
- Polish Committee for Standardization. Solid Biofuels—Determination of Calorific Value. PN-EN ISO 18125:2017-07, 12 July 2017. [Google Scholar]
- Świechowski, K.; Liszewski, M.; Bąbelewski, P.; Koziel, J.A.; Białowiec, A. Oxytree Pruned Biomass Torrefaction: Mathematical Models of the Influence of Temperature and Residence Time on Fuel Properties Improvement. Materials
**2019**, 12, 2228. [Google Scholar] [CrossRef] [PubMed] - Brusseau, M.; Walker, D.; Fitzsimmons, K. Physical-Chemical Characteristics of Water. In Environmental and Pollution Science, 3rd ed.; Brusseau, M., Pepper, I.L., Gerba, C.P., Eds.; Academic Press: Amsterdam, The Netherlands, 2019; pp. 23–45. [Google Scholar] [CrossRef]
- Radmanović, K.; Đukić, I.; Pervan, S. Specific Heat Capacity of Wood. Drv. Ind.
**2014**, 65, 151–157. [Google Scholar] [CrossRef] [Green Version] - Dhanavath, K.N.; Bankupalli, S.; Bhargava, S.K.; Parthasarathy, R. An experimental study to investigate the effect of torrefaction temperature on the kinetics of gas generation. J. Environ. Chem. Eng.
**2018**, 6, 3332–3341. [Google Scholar] [CrossRef] - Walkowiak, M.; Bartkowiak, M. The kinetics of the thermal decomposition of the willow wood (Salix viminalis L.) exposed to the torrefaction process. Drewno. Pr. Nauk. Doniesienia. Komun.
**2012**, 55, 37–49. [Google Scholar] - Saddawi, A.; Jones, J.M.; Williams, A.; Wójtowicz, M.A. Kinetics of the Thermal Decomposition of Biomass. Energy Fuels
**2010**, 24, 1274–1282. [Google Scholar] [CrossRef] - Cavagnol, S.; Roesler, J.; Sanz, E.; Nastoll, W.; Lu, P.; Perre, P. Exothermicity in wood torrefaction and its impact on product mass yields: from micro to pilot scale. Can. J. Chem. Eng.
**2015**, 93, 331–339. [Google Scholar] [CrossRef] - Prins, M.J.; Ptasinski, K.J.; Janssen, F.J. Torrefaction of wood. J. Anal. Appl. Pyrolysis
**2006**, 77, 28–34. [Google Scholar] [CrossRef] - Peng, J.H. A Study of Softwood Torrefaction and Densification for the Production of High Quality Wood Pellets, The University of British Columbia. 2012. Available online: https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/BVAU/TC-BVAU-42654.pdf (accessed on 29 June 2019).
- Mandil, C. Energy Statistics Manual. IEA Publications, OECD/IEA/EUROSTAT, Paris. 2004. Available online: http://ec.europa.eu/eurostat/ramon/statmanuals/files/Energy_statistics_manual_2004_EN.pdf (accessed on 29 June 2019).

**Figure 1.**The proposed concept of valorizing mushroom spent compost (MSC) via torrefaction. Resulting biocoal can be renewable fuel, and the process of torrefaction may be self-sufficient for heat due to the reuse of a part of produced biocoal.

**Figure 2.**The mean higher heating value of raw MSC and biocoals produced from MSC in relation to torrefaction temperature and torrefaction duration.

**Figure 3.**The influence of torrefaction temperature and torrefaction time on HHV of biocoals produced from MSC. The mathematical model (Equation (9)) includes parameters and the determination coefficient of the model’s fit to the experimental data (R

^{2}).

**Figure 4.**The dry matter mass yield values of biocoals produced from MSC in relation to torrefaction temperature and torrefaction duration.

**Figure 5.**The influence of torrefaction temperature and torrefaction time on the dry matter mass yield of biocoals produced from MSC. The mathematical model (Equation (9)) includes parameters and the determination coefficient of the model’s fit to the experimental data (R

^{2}).

**Figure 6.**The energy yield values of biocoals produced from MSC in relation to torrefaction temperature and torrefaction duration.

**Figure 7.**The influence of torrefaction temperature and torrefaction duration on energy yield in biocoals produced from MSC. The mathematical model (Equation (9)) includes parameters and the determination coefficient of the model’s fit to the experimental data (R

^{2}).

Parameter | Unit | Values |
---|---|---|

Bulk density | kg·m^{3} | 196.5 |

pH | - | 6.23–7.15 |

Moisture | % | 68.7–56.24 |

Volatile solids | % d.m. | 53.97–65.18 |

Ash | % d.m. | 22.43–38.3 |

Higher Heating Value, HHV | MJ·kg^{–1} d.m. | 4.06–12.98 |

Lower Heating Value, LHV | MJ·kg^{–1} d.m. | 2.03–10.17 |

C | % d.m. | 27.8–40.73 |

H | % d.m. | 3.40–4.86 |

N | % d.m. | 1.80–6.00 |

S | % d.m. | 2.12–2.99 |

Cl | % d.m. | 0.1 |

O | % d.m. | 18.94–26.99 |

P | g·kg^{–1} d.m. | 9.06–18.00 |

K | g·kg^{–1} d.m. | 15.2–20.00 |

C/N | - | 12.3–18.0:1 |

Ca | g·kg^{−1} d.m. | 28–109 |

Mg | g·kg^{–1} d.m. | 3.6–18.0 |

Na | g·kg^{–1} d.m. | 1.60–1.68 |

Lignin | % d.m. | 25 |

Cellulose | % d.m. | 38 |

Hemicellulose | % d.m. | 19 |

Cu | mg·kg^{–1} d.m. | 18.3–54.0 |

Zn | mg·kg^{–1} d.m. | 143.0–168.1 |

Mn | mg·kg^{–1} d.m. | 164.0–336.8 |

Fe | mg·kg^{–1} d.m. | 4.7–4494.5 |

Mo | mg·kg^{−1} d.m. | 1.51–2.13 |

Al | mg·kg^{−1} d.m. | 987 |

B | mg·kg^{−1} d.m. | 12.5–47.7 |

Se | mg·kg^{−1} d.m. | 2.25 |

Li | mg·kg^{−1} d.m. | 3.27 |

Ti | mg·kg^{−1} d.m. | 18.0 |

Pb | mg·kg^{−1} d.m. | 2.47–10.40 |

Cd | mg·kg^{−1} d.m. | 0.089–6.200 |

Cr | mg·kg^{−1} d.m. | 0.21–5.80 |

Ni | mg·kg^{−1} d.m. | 2.75–13.30 |

Parameter | Unit | Mean ± Standard Deviation |
---|---|---|

Moisture | % | 65.32 ± 0.05 |

VS | % d.m. | 71.60 ± 2.31 |

Ash | % d.m. | 28.40 ± 2.31 |

HHV | MJ·kg^{−1} d.m. | 13.79 ± 0.50 |

**Table 3.**The kinetic parameters of MSC torrefaction: torrefaction constant rate (k) for given temperatures (with values of determination coefficients (R

^{2}) for k estimation), Equation (5) parameters, determination coefficient of Equation (5) parameters estimation, and activation energy of MSC torrefaction.

Constant Rate | Temperature, °C | |||||
---|---|---|---|---|---|---|

200 | 220 | 240 | 260 | 280 | 300 | |

k_{1}, s^{−1} | 0.000008 (0.902) | 0.000020 (0.847) | 0.000024 (0.821) | 0.000028 (0.914) | 0.000030 (0.930) | 0.000047 (0.845) |

k_{2}, s^{−1} | 0.000020 (0.891) | 0.000018 (0.823) | 0.000023 (0.901) | 0.000023 (0.953) | 0.000032 (0.957) | 0.000039 (0.942) |

k_{3}, s^{−1} | 0.000022 (0.812) | 0.000017 (0.802) | 0.000012 (0.883) | 0.000024 (0.925) | 0.000034 (0.947) | 0.000052 (0.870) |

Mean ± standard deviation, s^{−1} | 0.000017 ± 7.5 × 10^{−6} | 0.000018 ± 1.5 × 10^{−6} | 0.000020 ± 6.5 × 10^{−6} | 0.000025 ± 2.7 × 10^{−6} | 0.000032 ± 1.7 × 10^{−6} | 0.000046 ± 6.3 × 10^{−6} |

Equation (5) parameters | y = −2678.7 × −5.5 | |||||

Determination coefficient (R^{2}) of Equation (5) parameters estimation | 0.893 | |||||

Activation energy, J.mol^{−1}, | 22271.4 |

Parameter | Symbol | Calculation | Unit |
---|---|---|---|

Mass of torrefied MSC after torrefaction process at T, and t conditions | m_{tb} | $346.8\xb70.928=322.0$ | kg |

Chemical energy in torrefied biomass | E_{tb} | $322.0\xb717900=5763800$ | kJ |

The heat needed to heat water contained in MSC | E_{w} | $653,2\xb74.18\xb7\left(100-15\right)=232082$ | kJ |

The heat needed to vaporization of water contained in MSC | E_{ev} | $653.2\xb72500=1633000$ | kJ |

The heat needed to heat MSC from ambient to torrefaction temperature | E_{hw} | $346.8\xb71.6\xb7\left(280-15\right)=147043$ | kJ |

Total heat needed to torrefied 1 Mg of MSC | E | $232082+1633000+147043=2012125$ | kJ |

The practical heat demand for torrefaction of 1 Mg of MSC | E_{p} | $\frac{2012125\xb7100\%}{80\%}=2515156$ | kJ |

The biocoal recirculation rate | ${\mu}_{e}$ | $\frac{2515156}{5763800}=0.436$ | - |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Syguła, E.; Koziel, J.A.; Białowiec, A.
Proof-of-Concept of Spent Mushrooms Compost Torrefaction—Studying the Process Kinetics and the Influence of Temperature and Duration on the Calorific Value of the Produced Biocoal. *Energies* **2019**, *12*, 3060.
https://doi.org/10.3390/en12163060

**AMA Style**

Syguła E, Koziel JA, Białowiec A.
Proof-of-Concept of Spent Mushrooms Compost Torrefaction—Studying the Process Kinetics and the Influence of Temperature and Duration on the Calorific Value of the Produced Biocoal. *Energies*. 2019; 12(16):3060.
https://doi.org/10.3390/en12163060

**Chicago/Turabian Style**

Syguła, Ewa, Jacek A. Koziel, and Andrzej Białowiec.
2019. "Proof-of-Concept of Spent Mushrooms Compost Torrefaction—Studying the Process Kinetics and the Influence of Temperature and Duration on the Calorific Value of the Produced Biocoal" *Energies* 12, no. 16: 3060.
https://doi.org/10.3390/en12163060