Review
Lignocellulosic crop residue composting by cellulolytic nitrogen-fixing bacteria: A novel tool for environmental sustainability

https://doi.org/10.1016/j.scitotenv.2020.136912Get rights and content

Highlights

  • The present study explores lignocellulosic crop residue (LCCR) composting by cellulolytic nitrogen-fixing bacteria (CNFB).

  • Findings of the study suggest that CNFB may enhance the LCCR composting and quality of the compost.

  • The methods for isolation of CNFB from various environmental sources have been summarized.

  • Methods for pre-treatment of LCCR for the composting process have been critically reviewed.

  • The applications of compost for agronomic and environmental benefits have been also discussed.

Abstract

Lignocellulosic crop residue (LCCR) composting is a cost-effective and sustainable approach for addressing environmental pollution associated with open biomass burning and application of chemical fertilizers in agriculture. The value-added bio-product of the composting process contributes to the improvement of the soil properties and plant growth in an environment-friendly way. However, the conventional process employed for composting LCCRs is slow and becomes an impediment for farmers who plant two or three crops a year. This concern has led to the development of different techniques for rapid composting of LCCRs. The use of cellulolytic nitrogen-fixing microorganisms for composting has emerged as a promising method for enhancing LCCR composting and quality of the compost. Therefore, this review addresses the recent progress on the potential use of cellulolytic nitrogen-fixing bacteria (CNFB) for LCCR composting and discusses various applications of nutrient-rich compost for sustainable agriculture to increase crop yields in a nature-friendly way. This knowledge of bacteria with both cellulose-degrading and nitrogen-fixing activities is significant with respect to rapid composting, soil fertility, plant growth and sustainable management of the lignocellulosic agricultural waste and it provides a means for the development of new technology for sustainability.

Introduction

Lignocellulosic crop residues (LCCRs) are produced in large quantities worldwide and are effective carbon-rich materials for the production of soil conditioners. However, in many countries, LCCRs are frequently burnt after harvest to facilitate land preparation, which causes massive environmental pollution and loss of plant nutrients (Kim Oanh et al., 2018). The incorporation of LCCRs into soil reduces the amount of plant-available nitrogen as the microbial biomass which develops during decomposition of the lignocellulosic plant material needs more nitrogen than the amount that is provided by the substrate and the final breakdown products of LCCRs tend to be phytotoxic (Ocio et al., 1991).

In most developing countries, LCCRs are commonly used as a part of feeding ingredients for the ruminants. However, they have a low nutritional value due to their poor digestibility, nitrogen deficiency and high levels of anti-nutritional components (lignin and silica) (Van Soest, 2006; Aquino et al., 2020). The most commonly used practice to increase the nutritive value of LCCRs is treatment of the LCCRs with chemicals such as urea, ammonia or sodium hydroxide (Aquino et al., 2020), with sodium hydroxide being recommended by the Food and Agriculture Organization (FAO) (2008). However, these chemicals are expensive and hazardous, and can cause a variety of environmental effects such as sodium contamination of the soil coupled with air pollution and water pollution (Liu et al., 1999).

The search for cost-effective, fast, and sustainable alternative processes for the better management of LCCRs to solve environmental issues is therefore of paramount importance and one of the greatest challenges in agriculture. Aerobic composting has been extensively studied and the results have shown that it can be an eco-sustainable green approach for LCCR treatment and agricultural development. The bulk of research on aerobic composting can be found on the Web of Science Core Collection database (Fig. 1). This natural bioprocess enhances the long-term sustainability of agriculture by converting agriculture wastes into nutrient-rich compost (Kausar et al., 2016). Furthermore, the compost can be applied as a soil conditioner, organic fertilizer, and plant growth stimulator, thus reducing dependence on chemical fertilizers for crop production. The results of recent research on compost application have shown the positive effects of compost use on the environmental resilience and climate adaptation, that has been observed as improved plant growth, stabilization of soils, and reduced air pollution and water pollution (Lim et al., 2016; Xia Guo et al., 2019). The compost should be highly mature and stable in order to be used safely in agriculture without adverse effects on plants. Immature compost may produce phytotoxic compounds that may disrupt seed germination and plant growth (Makan, 2015).

The ordinary composting of LCCRs is intensely dilatory due to the low nitrogen content of the carbon-rich LCCRs. This limitation can be overcome by using microorganisms with both nitrogen-fixing and cellulose-degrading properties (Yu et al., 2017). Numerous nitrogen-fixing bacteria such as Azomonas agilis, Stenotrophomonas spp., Bacillus spp., Streptomyces spp., Pseudomonas spp., Paenibacillus azotofixans, and Gluconacetobacter spp. (Table 2) produce lignocellulolytic enzymes (Leschine et al., 1988; Kyaw et al., 2018; Latt et al., 2018). Furthermore, the inoculation of two cellulolytic nitrogen-fixing Bacillus strains in composting of rice straw has been shown to reduce the composting time by 40%–43% and increased the levels of total nitrogen, phosphorus, and potassium in the compost (Abdel-Rahman et al., 2016). Additionally, the application of different bacterial agents with both cellulolytic and nitrogen-fixing properties has been shown to boost lignocellulose degradation by increasing the activities of key enzymes during straw composting (Wei et al., 2019).

Unlike a fungal consortium, cellulolytic nitrogen-fixing bacteria (CNFB) do not need a nitrogen (N2) source partner as they have the ability to satisfy their nitrogen requirements through fixation of atmospheric N2 (Leschine and Canale-Parola, 1989). The completion of a composting process and subsequent use of the compost as a soil conditioner are extremely reliant on the capacity of the microflora present during the composting process. The addition of CNFB to the composting material showed several benefits in different domains like agriculture and waste management (Wei et al., 2019; Kausar et al., 2011; Abdulla, 2007).

Despite large number of past reviews on organic waste composting, this study is the first to present a detailed and comprehensive review of the potential application of CNFB in LCCR composting. Thus, various studies on CNFB, including screening of the microorganisms and methods for essays on the enzyme activity, have been reviewed. In addition, the effectiveness of compost application in sustainable agriculture has been discussed.

Section snippets

Worldwide production of lignocellulosic crop residues

LCCRs refer to the plant biomass such as rice straw, wheat straw, sorghum, corn stover, sugarcane bagasse, etc. Driven by agricultural industrialization and an increasing demand for food worldwide, billions of tons of LCCRs are produced every year and constitute the most abundant biomass on earth (Zheng et al., 2014).

Worldwide availability of LCCRs varies based on the plant species and this availability is different among countries and regions. Sugarcane is the leading agricultural plant in the

Carbon-rich components of the lignocellulosic agricultural residues

Lignocellulosic biomass predominantly consists of a complex mixture of three natural carbohydrate biopolymers - cellulose (30%–50%), hemicelluloses (20%–40%), and lignin (10%–30%), that are closely linked by physical forces and chemical forces. The amount of cellulose, hemicelluloses, and lignin in dry crop residues varies from species to species (Table 1) and also depends on the cultivation conditions, the geographical location and the age of plants (Pérez et al., 2002). In addition, cellulose

Pre-treatment of the lignocellulosic crop residues for composting

Lignocellulosic biomass is resistant to microbial degradation due to its inherent complexity and heterogeneity. Therefore, enhancement of LCCR composting requires pretreatment of LCCRs, which disrupts the tightly packed structure of the lignocellulosic biomass and exposes cellulose and hemicelluloses to enzymatic attack (Agbor et al., 2011).

We can classify the major pre-treatment methods for LCCR composting into three different categories: physical methods, chemical and biological approaches.

Microbial degradation of lignocellulosic crop residues

Several microorganisms have the ability to decompose lignocellulose, which is ultimately converted into carbon dioxide and water under aerobic conditions, and into carbon dioxide, methane, and water under anaerobic conditions. Most of the lignocellulolytic microorganisms are bacteria or fungi, but anaerobic lignocellulose-degrading protozoa have also been identified in the rumen (Gupta et al., 2012; Béguin and Aubert, 1994).

Based on an intensive research on the lignocellulolytic system of the

Definitions

CNFB are a group of microorganisms that produce cellulases to break down the cellulose molecules into simple sugars, and produce nitrogenase to catalyze the conversion of atmospheric nitrogen (N2) to fixed nitrogen (NH3). Such species are helpful in transforming lignocellulosic and other cellulosic resources into commodities and fertilizers with increased nutritional quality of carbohydrates and higher levels of assimilable nitrogen (Hardy and Wiley, 1990).

Waterbury et al. (1983) were the first

Definitions

Composting is the microbial transformation of different biodegradable materials into nutrient-rich products that can enhance the soil health, the soil productivity, and the soil's ability to absorb and retain water and crop nutrients. The composting process is controlled by physicochemical factors, physiological factors and microbiological factors. This ancient practice has long been used to treat solid wastes so that the organic material can be easily degraded through the natural process of

Lignocellulosic crop residue composting by CNFB

Studies have revealed that key microorganisms involved in nitrogen transformation during the composting process are mostly cellulose-decomposing bacteria. Nitrogen-fixing bacterial genera, such as Stenotrophomonas, Xanthomonas, Pseudomonas, Klebsiella, Alcaligenes, Achromobacter, and Caulobacter, isolated from the compost materials (Pepe et al., 2013), have been previously described to be involved in organic matter degradation during composting (Insam and de Bertoldi, 2007). While composting

Some applications of compost in sustainable agriculture

Compost is the final product of aerobic microbial decomposition of biodegradable materials. While chemical fertilizers improve the soil only by adding nutrients, the use of mature compost in agriculture improves the soil's organic matter content, resistance to soil erosion, groundwater keeping ability, carbon sequestration, nutrient content, and plant disease resistance (Pergola et al., 2018).

Compost is a natural, safe and environment-friendly option for the recovery of organic fertility in the

Conclusions and future perspectives

Inoculation of compost materials with CNFB has been shown to be the most environment-friendly and the quickest way to recycle lignocellulosic biomass back into the soil and enhance the physicochemical properties and the biological properties of the soil. Bacteria with both cellulolytic and nitrogen-fixing traits reduce the overall time required for composting, and accelerate the composting performance of the lignocellulosic waste by decreasing the C/N ratio, reducing odors and adding more value

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This project was funded by the national first-class discipline program of the Light Industry Technology and Engineering (LITE2018-11). The authors wish to thank our all laboratory colleagues for their constructive advice and help.

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