Introduction

That a country’s environment—the air its people breathe, the water they drink and so on—will have a profound effect on its overall economic performance hardly seems surprising (Wang et al. 2015). A variety of studies have documented the long- and short-term effects of air pollution on respiratory and cardiovascular illness and the associated effects on morbidity and mortality. Human beings should therefore be motivated and directed to creating a sustainable way of the life (Klemeš 2015). Although agriculture only accounts for a small share of GDP, existing studies have underlined the impact of climate change on the value of farmland and agricultural productivity (Chen et al. 2015). However, despite repeated efforts (Jain 2005), neither consumers nor the regulatory authorities are not fully informed about managerial value orientations; the production technology setup (Walker and Mercado 2015) and the environmental or ethical impacts (Maroušek 2013a). A central issue in environmental and climate policy is the economical assessment of the technological reengineering of unregulated carbon-generating sectors (Bento et al. 2015). The development and effective use of natural resources is essential for meeting crucial societal needs and for the economic development of a nation (Jain 2015). There is always speculation whether current corporate carbon management practices are really reducing corporate carbon emissions (Doda et al. 2015; Sikdar 2003a). If we assume that they do, such measures have the potential to substantially reduce the overall economic costs of climate change mitigation programmes (Fell et al. 2012; Sikdar 2003b). Pulp and paper mills generate, dependent on the level of technology, various quantities of energy-rich biomass as waste, pulp and paper grades and wood quality. These waste products are produced at all stages of the process: wood preparation, pulp and paper manufacture, chemical recovery, recycled paper processing and wastewater treatment. The recovery of energy from these waste products has become a generally accepted alternative to their disposal. The pulp and paper industry has expressed an interest in adapting and integrating advanced biomass energy conversion technologies into their mill operations. The adoption of these new technologies by the industry has the potential to make it more efficient by driving down capital costs and ensuring greater operational safety than conventional operations that burn fossil fuels (Gavrilescu 2008). Today, an increasing number of companies are also disclosing their environmental and social performance (Alberici and Querci 2015). JIP—Papírny Větřní, a. s., which has a history that goes back almost 450 years, is the biggest paper mill in South Bohemia (Czech Republic). Numerous papers have traced the mill’s efforts to improve its technology (Sládeček 1967; Zahradník et al. 1983) and minimize its environmental impacts (Havlínová et al. 2009). Lime mud is the solid waste produced as part of the process (result of the causticization reaction in the alkali recycling process) that turns wood chips into pulp for paper. The major component of lime mud is calcium carbonate (CaCO3). It is estimated that about 0.47 m3 of lime mud is generated for every tonne of pulp produced (Wirojanagud et al. 2004).

The hypothesis for this work is that it is possible to process the mixture of fibre residues from the paper thickener and lime mud into a reasonable product without a disproportionately expensive investment, low processing costs and a positive or at least neutral impact on the environment.

Materials and analytical methods

The mixture of fibre residues from the paper thickener and lime mud was stored indoors for approximately 15 years. This resulted in a solid, grey-coloured fibrous and homogenous material (see Fig. 1). Samples of this material were taken for analysis. The dry weight (DW) of the mixture was 22.2 % (analysed at 105 °C), pH = 7.2 and conductivity 38.8 mS m−1. The analyses of heavy metals was carried out externally by ALS Czech Republic, s.r.o. (Praha, Czech Republic) in accordance with Acts 294/2005 Sb. and 383/2001 Sb. (Ministry of Environment of the Czech Republic). The analyses revealed BTEXs (sum of benzene, toluene, ethylbenzene and xylenes); PAHs (sum of polyaromatic hydrocarbons); EOX (extractable organic halogen); C10–C40 (sum of aromatic hydrocarbon compounds which contain between 10 and 40 carbon atoms); PCB congeners (the sum of congeners of polychlorinated biphenyls) and other hazardous substances. The results are presented in Table 1. A detailed analysis of the individual hazardous substances present (BTEXs; PAHs; EOX; C10–C40 and PCB congeners) are given in Table 2. The analytical methods used were I–11885—atomic emission spectrometry with inductively coupled plasma according to the EPA 200.7 and ISO 11885 standards; Č–465735—Hg analysis by atomic mass spectrometry according to the ČSN 465735 and TNV 75 7440 standards; EPA–601—volatile organic compounds analysis according to the EPA–624 standard; EPA–610—PAH analysis according to the EPA–3550 standard; D06 07 025—EOX analysis according to the DIN 38409–H8 and DIN 38414–S17 standards; E–14039—analysis of C10–C40 by gas chromatography with flame ionization detector and EPA–8082—analysis of PCB congeners according to the DIN 38407 standard. Acute toxicity tests were carried out three times on seven fish Poecilia reticulata (22 ± 2 °C; 4 months old; 100 mL of sample per fish; exposure time 96 h; no aeration and no feeding) according to the ČSN EN ISO 7346–2 standard (see Tables 3, 4, 5, 6). Further three biotoxicity tests were carried out on 20 individuals of Daphnia subspicatus (21 ± 2 °C; 10 mL of waste per individual; exposure time 48 h; individuals 24 h old; no aeration and no feeding) according to the ČSN EN 8692 standard (see Tables 3, 4, 5, 6). Three verification tests on metabolism inhibition were carried out on Desmodesmus subspicatus freshwater algae (initial concentration 10 k cells mL−1; 23 ± 2 °C; exposure time 72 h; no aeration; continual gentle agitation) according to the ČSN EN 8692 standard (see Tables 3, 4, 5, 6). Phytotoxicity analysis was carried out on Sinapis alba seeds (20 ± 2 °C; 10 mL of waste in a Petri dish of 14 cm diameter; 30 seeds per dish; 72 h in biological thermostat). The results are given in Tables 3, 4, 5, 6. The pools of carbon (labile pool 1:0 %; labile pool 2:4.1 %) were determined by the acid hydrolysis (H2SO4) approach according to Rovira and Vallejo (2002) as modification by Shirato and Yokozawa (2006) using an automatic high sensitive N/C analyser (NC–90A, Shimadzu, Tokyo, Japan). The heating values (10.709 MJ kg−1) were analysed using an auto-calculating bomb calorimeter (CA–4AJ, Shimadzu, Tokyo, Japan). The TriStar 3000 surface area analyser (Micromeritics Ltd., Tokyo, Japan) was used for the analysis of microporosity (see Table 7) after 10 h of degassing at 150 °C and 24 h of degassing at 200 °C. A JSM 7401F electron microscope (JEOL, Japan) was used for analytical scanning. The quantity and quality of biogas production (gaseous CH4, CO2, O2 and H2S) obtained by anaerobic fermentation were analysed by a GA3000 infrared-based biogas analyser (Chromservis Ltd., Praha, Czech Republic) as described in Maroušek et al. (2012). Solid biofuels were analysed according to norms set by the European Committee for Standardization: 14961; 16127; 14774–1; 14774–2; 14774–3; 14775; 14918; 15103; 15210–1; 15290; 15104; 15289; 15105; 15290; 15296 and 15370–1 as detailed by Mardoyan and Braun (2015). Enzymatic mixtures of Accellerase XC (complex xylanase/cellulase enzyme designed to supplement the other whole cellulases to improve both xylan and glucan conversion of lignocellulosic biomass, endoglucanase activity 1134 carboxymethyl cellulose units g−1, xylanase activity 3609 acid birchwood xylanase units (ABXU) g−1 , optimal pH 3.7–4.2); Accellerase BG (accessory β-glucosidase to supplement whole cellulases deficient in β-glucosidase to achieve high glucan conversion, 3557 para-nitrophenyl- β-d-glucopyranoside units g−1, optimal pH 5–6) and Accellerase XY (complex xylanase enzyme to synergistically enhance various polysaccharide conversions, 26909 ABXU g−1) were provided by Genencor International oy (Hanco, Finland). Barley germination tests were performed according to (Busch et al. 2012). A detailed breakdown of the costs of the technology (not stated) can be found in Maroušek et al. (2012) and through the providers of the equipment. Financial analyses were carried out on the basis of net cash flow according to standard methods (Maroušek et al. 2015a). Unless indicated otherwise, analyses were carried out according to standard laboratory and statistical procedures.

Fig. 1
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Screen shot of the “raw” waste from an electron microscope scan (where by A—fibre residues from the paper thickener, B—lime mud)

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Table 1 Data presented in mg kg−1 DW with 95 % confidence interval
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Table 2 Data presented in mg kg−1 DW with 95 % confidence interval
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Table 3 Acute toxicity to fish Poecilia reticulata
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Table 4 Acute toxicity to fish Daphnia magna
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Table 5 Acute toxicity to freshwater algae Desmodesmus subspicatus
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Table 6 Phytotoxicity to Sinapis alba
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Table 7 Analysis of microporosity (whereby “raw”, “pyrolyzed” and confidence interval are as in Table 1
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Technological setup

The mixture of the lime mud and cellulose fibre residues from the paper mill (hereinafter referred to as the “waste”) was techno-economically assessed under eight alternative technological setups (as presented in Table 8). Anaerobic fermentation was assessed four times with increasing intensity of waste pre-treatment (AF1–AF4). The waste was also combusted in its raw form combustion trials (CB). Pyrolysis was assessed three times: for energy provision (PE), soil improver (PB) and composting (PC). In Table 8, UHWM stands for Under-hot-water-maceration by the M2 under-hot-water phytomass macerator (95 °C; 200 s; BiomassTechnology a.s., Czech Republic). SE stands for steam explosion under a high-pressure reactor with expansion tourniquet (single 0.3 L explosion from 1.2 MPa into atmospheric pressure performed at 0.11–0.09 s after a hydraulic retention time of 20 min) as described by Maroušek (2013b). EH stands for enzymatic hydrolysis of the mixture of Accellerase XC, Accellerase BG and Accellerase XY under a weight ratio of 1:1:1 at 5 g kg−1 DW of the waste. AF stands for the final step of the anaerobic fermentation. In this step, the waste was inoculated by percolate from the Nedvědice 1 biogas station to achieve the final DW of 10 % and subsequently subjected to a battery of fully automatically monitored semi-continuous batch reactors (biochemical analysis of the percolate as well as a detailed description of the reactor can be found in Maroušek et al. 2012). CB were performed to analyse whether the mixture of lime mud and cellulose fibre residues fulfils the European norms (European Committee for Standardization, as stated in Mardoyan and Braun 2015). The pyrolysis step was carried out using continuous apparatus (horizontally placed pyrolysis chamber equipped with a slowly rotating helix) for biochar production (Maroušek 2014) which utilizes waste flue gases from the biogas cogeneration unit for the pyrolysis (410 °C, hydraulic retention time of 10 min). For the PE, the solid pyrolysis residue was pelleted using a Falach 50 briquette press with a custom-made adapter (FALACH s.r.o., Czech Republic) operating at 50 kg h−1 as described in Maroušek et al. (2015b). This step was followed by an analysis of the European norms (European Committee for Standardization, as stated in Mardoyan and Braun 2015). The unpelleted solid pyrolysis residue (PB) was also analysed for its soil-improving abilities (Lehmann and Joseph 2009). Assessment of its use for composting (PC) was carried out by mixing it with sunflower stalks (biochemical analysis as described in Maroušek 2013b) to achieve a final bulk density of 500 kg m−3 to comply with the additional requirements of COMPO technology (Compost Systems, GmbH, Austria) that is used at the composting plant (KOBRA Údlice, s.r.o., Czech Republic).

Table 8 Setup of the experiment (whereby horizontally—assessment methods; vertically—pre-treatment and processing steps; X marks the performance of the process; interest rate = 8.5 % p.a.)
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Results and discussion

At first, it should be reminded that biochar production from the paper mill waste and its impact on agronomic performance are already somehow traceable in the literature (van Zwieten et al. 2010). However, despite the fact that so far this has been tested only in the greenhouse, the study presented here respects all the commercial-scale aspects and therefore techno-economically assesses 8 alternatives of technology setup. There are many techno-economic similarities (Sun et al. 2013; Rongyue et al. 2013) between the mixture of lime mud and cellulose fibre residues from JIP—Papírny Větřní, a.s. (Czech Republic) when compared to those for similar mills elsewhere in the world (see Tables 1, 2, 3, 4, 5, 6, 7). This initial observation is positive because the results subsequently obtained could gain more general application. The greatest concern aroused from the presence of heavy metals; however, in a good agreement with Hossain et al. (2010), its bioavailability was found to be far below the corresponding maximum. Despite the analytical similarities, it should be pointed out that according to the analysis carried out by gas chromatography with a flame ionization detector according to the EN 14039 standard, the waste exceeds the limits on C10–C40 (sum of aromatic hydrocarbon compounds which contain between 10 and 40 carbon atoms) by almost 37 % and therefore, in its unprocessed state, does not comply with Act 294/2005 Sb. (Ministry of Environment of the Czech Republic). This implies that the waste cannot be put into a landfill site or used directly on soil surfaces. This conclusion may be unjustified when one considers the fact that the waste in its unprocessed state stimulated (by almost 63 %) the Sinapis alba seeds. This is in contrast to the results of C10–C40 analysis which imply that there should be some inhibition. The barley germination tests carried out according to (Busch et al. 2012) showed that the waste has some phytotoxicity potential (phytomass weight decreased by 27 % in comparison to the control sample). It would therefore be economically viable to plough the waste deeper into soil provided that there were to be a reasonable financial profit from the combustion of the biogas obtained from its anaerobic fermentation. From the management point of view, the generated income should cover not only the deeper ploughing-in of the waste itself but also of the other fermentation residues. In addition, it should be noted that the wastes’ co-fermentation will result in additional costs linked to additional dilution, the warming up of the fermentor, the increased costs of ploughing, etc. Although the list of additional procedural casuistries (additional costs linked with processing) cannot be considered as all encompassing, they can be considered to be relatively accurate because the trials were carried out on an almost commercial scale. The biogas yields from anaerobic fermentation are directly interpreted as income from electricity sales (Maroušková and Braun 2014) as stated in Table 8. The cost analysis indicates that none of the pre-treatment methods is economically viable. The poor economic results are directly related to the following technological issues: the amount of organic matter is relatively low; and the origin and previous processing history makes the wastes’ lability to fermentation processes low. This is probably the reason why the amount of biogas produced, respectively methane, even with an increasing intensity of pre-treatments, almost does not increase. Detailed calculations also show that the variable costs increase very fast. This makes the anaerobic fermentation of the waste economically unattractive. The same mechanism was observed by (Méndeza et al. 2009), who state that the crystallinity of the cellulose plays the key role. The high water content also hampers the direct combustion of the raw waste (CB) due to the high energy demands for drying and its relatively low heating value. Flue gas combustion is also not favourable (see Table 9). Due to this, the waste has to be co-fired with solid fuels with a higher heating value. This observation is not surprising, and the data obtained are very much in line with the analyses undertaken by (Gavrilescu 2008). Following on from the above, it must be pointed out that the processing of the waste by the pyrolysis unit was only made possible when the pyrolysis reactor that was used in the techno-economic assessment was run on externally sourced energy. The results of the analysis into the PE of the pyrolysis residue are given in Tables 1, 7 and 9. The economical assessment was based on a comparison of the wastes’ heating value; however, this practice is difficult to defend from an ethical point of view (Lehmann and Joseph 2009). What is economically viable is to process the waste into products for soil improvement (PB) (Lehmann and Joseph 2009) which increase microporosity (see Table 7; Fig. 2). Unfortunately, its selling price is volatile due to a lack of awareness of the product. The most attractive option in terms of ethics and the environment is the composting of the pyrolysis residue (PC). The only disadvantages of this option are the long processing times and the high cost of the technology involved (see Table 8).

Table 9 Analysis of combustion flue gases (mg m−3) in relation to EC Directive 2000
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Fig. 2
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Screen shot of the “pyrolyzed” waste from an electron microscope scan (whereby C—increase in size of micropore at the opening of the cellulose crystal, D—increase in surface area due to liberation of lignocellulose fibres

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Conclusion

A large number of biotechnological analyses and a deep literature review show that the mixture of residues from paper thickener and lime mud originating in the JIP—Papírny Větřní a.s. paper mill do not significantly vary to those from other paper mills worldwide. Further analyses reveal that, regardless of the wastes’ agrochemical value (caused by CaCO3) and its stimulation of some flowers in the short term, the waste may after a while also act phytotoxically. The cause of this is the level of aromatic hydrocarbon compounds that contain between 10 and 40 carbon atoms. The results obtained from the anaerobic fermentation of the waste on an almost commercial scale show that the processing of the waste is senseless from both the technological and economical points of view. The levels of biogas production remain weak regardless of the pre-treatments undertaken. This is probably due to a combination of inhibition factors and the high resistance of the organic matter to enzymatic hydrolysis (high level of cellulose crystallinity). A secondary factor may be the relatively low percentage of organic matter in the waste. The high water content of the waste was also shown to make the combustion of it financially unviable due to the energy requirements for drying and the costs associated with co-combustion with other fuels with higher heating values. This issue can be significantly remedied by pyrolysis. Results indicate that combustion of the charcoal obtained may represent an interesting investment, particularly if the technology used for the pyrolysis process is run using external waste heat. However, business ethics should also be considered. The incorporation of the carbon-based pyrolysis residue (biochar) into the soil may represent a more environmentally and socially friendly option. This option may also be the most profitable, but for the fact that the market for biochar is still not fully established and the resulting calculations may therefore be very inaccurate. When weighing-up all the issues, the application of the solid carbon-based pyrolysis residue into compost may represent the best compromise alternative.