Elsevier

Journal of Cleaner Production

Volume 129, 15 August 2016, Pages 410-416
Journal of Cleaner Production

Anaerobic digestion of chrome-tanned leather waste for biogas production

https://doi.org/10.1016/j.jclepro.2016.04.038Get rights and content

Highlights

  • The technical viability of biogas production using chromed leather waste was evaluated.

  • Waste biodegradation using strict and non-strict anaerobic seeds was possible.

  • The biogas and methane yield decreased with increasing the chromium concentration.

  • The adoption of destabilization processes can increase the biogas yield (66–74%).

  • The highest biogas yield (162 mL g−1) was produced in times between 3 and 36 days.

Abstract

The introduction of cleaner technologies through the reuse of wastes, producing a clean fuel (biogas) and its utilization for energy recovery, can improve the environmental performance of the tannery industry. The degradability assessment of collagenic substrates (tanned or not) is necessary to evaluate the possibility/need of using prior treatments or mixtures of tannery wastes before its use as a growing substrate for anaerobic degradation processes. In this work, the biodegradation mechanism was studied by comparing collagenous substrates containing different concentrations of chromium (tanning degree) which helps the comprehension of the interrelation effect between microorganisms and substrate. This work presents the results from assays carried out in biorreactors to generate biogas by protein-based substrates at bench scale under controlled conditions. In the bioreactors, four substrates (soybean meal, hydrolyzed collagen, hide powder and wet-blue leather shaving) were inoculated with three different biological sludges collected from wastewater treatment plants (sewage anaerobic sludge, slaughterhouse anaerobic sludge and tannery aerobic sludge). The mole fractions of methane, carbon dioxide, nitrogen and oxygen in the generated gases were evaluated by gas chromatography. The experiments showed a previous adaptation of some of the tested inocula (seeds) and allowed to visualize and discuss the effect of the Chromium III concentration in the substrates over the rate and total biogas production for each of the inocula. The rising of chromium concentration in the substrate significantly reduced the biogas and methane yield. The maximum rate of biogas production for chrome leather shaving occurred in periods between 3 and 36 days, reaching a biogas yield of 162.2 mL g−1 and methane fraction of 73.7%. Better results were obtained using slaughterhouse and tannery sludges due to its preadaptation to collagen based protein substrates. The results indicated a considerable gain in biogas production (74–181%), if the leather substrate is treated or mixed with readily degradable materials prior to its use as substrate for anaerobic digestion (destabilizing the chrome–collagen complexes, increasing of the water dispersion and lowering the stability of chrome–collagen complexes).

Introduction

The leather making process generates substantial quantities of solid waste (cuts of hides and skins, fats, shavings and trimmings, buffing dust and sludge from wastewater treatment plants) and wastewater (Cooper et al., 2009, Gutterres and Aquim, 2013). Several works reported alternatives to improve the environmental performance of the leather industry through the adoption of clean and innovative approaches in processes, effluent treatment and solid waste (Menikpura et al., 2013, Kanagaraj et al., 2015). By definition, chrome leather is the raw hide stabilized using chromium salts (Cr (III)). Wet-blue is the wet leather after chrome tanning stabilization which is held in wet state prior to the wet end (deacidulation, retanning, fatliquoring and dying), drying and finishing steps, thus wet-blue trimmings and wet-blue shavings (chrome shavings) represent typical chrome-tanned leather wastes. The quantities of chrome shavings were reported to be of 8.8% (Thangamani and Parthiban, 2011), 24.7% (Sundar et al., 2011) and 24.8% (Stoop, 2003) of the overall tannery waste production. The most common way to manage these solid wastes is by disposing them off at landfill sites (Yılmaz et al., 2007).

The challenge related to leather waste processing is the conversion/oxidation of Cr (III) to Cr (VI). Cr (VI) compounds are more toxic than Cr (III) due to the mobility of the former, which can cross the cellular membranes and react with intracellular biomolecules. Some biological processes have stimulated the growth of Cr (III) concentrations up to 15 mg L−1 (above which it is inhibited), with lethal doses above 160 mg L−1. For Cr (VI), toxic effects appear at concentrations above 5 mg L−1, with the lethal dose identified as approximately 80 mg L−1 (Vaiopoulou and Gikas, 2012). Furthermore, Cr (VI) results in human systemic toxicity to the kidneys and when combined in the forms of calcium or magnesium chromate, it becomes a carcinogenic agent (Kolomaznik et al., 2008, Dettmer et al., 2012).

The most explored processes for biological degradation of tannery wastes employ fleshings and trimmings from rawhides or after the liming step together with tannery effluents (Ravindranath et al., 2015, Kameswari et al., 2014). Chrome shavings, wet-blue trimmings and sludge from tannery wastewater treatment plants proved to be degradable by microorganisms. Analytical results of methane fractions in biogas generated at bench scale experiments and landfill gases exhibit such behavior (Dhayalan et al., 2007, Priebe et al., 2011). Therefore, a more environmentally friendly alternative to landfilling disposal is the controlled degradation of waste using microorganisms focused on biogas production. This is not a simple practice for leather wastes because these residues are essentially non-putrescible (Hu et al., 2011). Thus, prior practices, such as the preparation of the substrate and/or use of pre-adapted microorganisms (to leather mineralization agents) must be studied (Dixit et al., 2015). The use of these substrates (leather wastes), rich in carbonaceous matter, requires the establishment of efficient and economically viable biological degradation technologies (Basak et al., 2014, Pati and Chaudhary, 2014).

The main advantages of anaerobic treatment applied to solid wastes are: lower energy consumption because forced aeration is not required; the organic matter of the substrate is converted into biogas that can be used as an energy source; and a lower amount of biomass is remained, resulting in lower costs for sludge disposal (Di Berardino and Martinho, 2009, Ravindran and Sekaran, 2010). This final sludge can also be used as a source of organic matter and nutrients for agricultural activity (Parawira et al., 2005). Biogas comprises 55–70% methane (CH4), 30–45% carbon dioxide (CO2) and traces of other gases. The energy content of biogas is 6.0–6.5 kWh m−3 and the fuel equivalent is 0.60–0.65 L of oil m−3. Thus, the use of energy from biogas proves to be energetically and environmentally interesting for heat/power generation and for the reduction of environmental impacts (Deublein and Steinhauser, 2008, Priebe and Gutterres, 2012).

The first reports drawing attention to the potential for energy recovery from tannery wastes (through anaerobic digestion) were in the 1980s (Cenni et al., 1982). This work was followed by a sequence of studies in this field published by other authors (Lalitha et al., 1994, Urbaniak, 2006, Zupancic and Jemec, 2010; and Kameswari et al., 2012). The potential for biogas production presented in these mentioned papers varied between 145 and 829 mL per gram of volatile solids. Other studies (Yang et al., 2006, Hilligsmann et al., 2011; and Pillai and Archana, 2012) showed data related to the biodegradability of leather wastes employing various sources of microorganisms. These works employed strictly anaerobic biota as inoculum, obtained from anaerobic treatment processes, mainly sewage sludge. Practices widely used are the co-digestion of solid wastes and effluents in order to enhance the anaerobic processes by the mixture of wastes with different characteristics, adjusting the substrate composition (López et al., 2015, Kanchinadham et al., 2015).

This work aims to contribute to the state of art of biological degradation/digestion of leather wastes. The evaluation relied on the ability of the available microorganisms to degrade/metabolize different types of substrates by comparing the cumulative biogas generation and methane fractions. These observations allow the discussion of a range of issues related to the biodegradation process; the influence of the source of the microorganisms over the biological process; the feasibility of using an aerobic biota as a seed for anaerobic processes; the influence of chromium concentration over the process stability/efficiency; the choice for better-adapted microorganisms; the need for prior treatments of the substrates containing chromium (e.g., hydrolysis); the establishment of a routine to assess different seeds for anaerobic processes; and the influence of the origin of the microorganisms over the digestion/degradation effectiveness (pre-adaptation). Furthermore, such a collection of information can contribute to the introduction/development of anaerobic processes of solid waste treatment in tanneries located in regions that are characteristically diverse.

Section snippets

Experiment

The experiments were assembled to compare three different biotas (sludges used as seed) collected from: 1) an anaerobic municipal sewage treatment plant (anaerobic digester sludge); 2) an anaerobic wastewater treatment plant of a slaughterhouse (anaerobic pond sludge); and 3) an aerobic wastewater treatment plant of a tannery (activated sludge reactor). The activated sludge was collected in a tannery that employs chromium salts as a tanning agent. These inocula were used for biological

Results and discussion

This section shows the results of substrates characterization, the results associated with the anaerobic degradation processes using different substrates and inocula and the evaluation of the effect of the chromium concentration over the biological process. The results of the biodegradation processes are presented in terms of biogas generation and methane fraction in biogas. The different behaviors are discussed based on the interrelation of the parameters: specific characteristics of the

Conclusion

The experimental work and results described in this paper prove the feasibility of applying microorganisms (inocula) from different sources to perform the anaerobic degradation of chrome tanned leather wastes, especially processes designed for the treatment of wastewaters containing protein-based materials. Furthermore, the work points to the viability of using non-strict anaerobic biota to produce biogas.

The slaughterhouse sludge (SHS experiment) and the aerobic sludge (AS experiment)

Acknowledgments

The authors thank the National Council for Research and Innovation – CNPq/Brazil for the financial support through public notices MCT/CNPq nº 014/2010 – Universal and MCT/CNPq CTAgro nº 505822/2008-3. The authors are also grateful to the tanneries Fridolino Ritter Ltda. and Kern-Mattes S.A., DMAE – Porto Alegre and Frigorífico Costa da Serra Ltda. for offering their facilities and providing samples whenever necessary.

References (44)

  • W. Parawira et al.

    A study of industrial anaerobic treatment of opaque beer brewery wastewater in a tropical climate using a full-scale UASB reactor seeded with activated sludge

    Process Biochem.

    (2005)
  • P. Pillai et al.

    A novel process for biodegradation and effective utilization of chrome shavings, a solid waste generated in tanneries, using chromium resistant Bacillus subtilis P13

    Process Biochem.

    (2012)
  • B. Ravindran et al.

    Bacterial composting of animal fleshing generated from tannery industries

    Waste Manag.

    (2010)
  • M.L.M. Stoop

    Water management of production systems optimised by environmentally oriented integral chain management: case study of leather manufacturing in developing countries

    Technovation

    (2003)
  • E. Vaiopoulou et al.

    Effects of chromium on activated sludge and on the performance of wastewater treatment plants: a review

    Water Res.

    (2012)
  • W. Wu et al.

    Cultivation of anaerobic granular sludge in uasb reactors with aerobic activated sludge as seed

    Water Res.

    (1987)
  • H. Yang et al.

    Continuous bio-hydrogen production from citric acid wastewater via facultative anaerobic bacteria

    Int. J. Hydrogen Energy

    (2006)
  • O. Yılmaz et al.

    Conversion of leather wastes to useful products

    Resour. Conserv. Recycl.

    (2007)
  • G.D. Zupancic et al.

    Anaerobic digestion of tannery waste: semi-continuous and anaerobic sequencing batch reactor processes

    Bioresour. Technol.

    (2010)
  • M. Alves et al.

    Reactors for anaerobic treatment

  • S.R. Basak et al.

    Anaerobic digestion of tannery waste by mixing with different substrates

    Bangladesh J. Sci. Ind. Res.

    (2014)
  • M. Cooper et al.

    Environmental developments and researches in Brazilian leather sector

    J. Soc. Leather Technol. Chem.

    (2009)
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