Effects of additives on the co-composting of forest residues with cattle manure
Graphical abstract
Introduction
Forest residues (FR) are renewable resources and are increasingly utilized worldwide (Guo et al., 2020). Composting is a popular way to recycle FR (Zhang and Sun, 2018, Zhang and Sun, 2017). During composting, the organic matter (OM) in FR is degraded and converted into a product that contains a large quantity of humus. The quality of the final compost is closely related to the microbial activity during composting, which is inhibited by the large amounts of refractory organic substances (i.e., lignocelluloses) and the relatively high levels of nitrogen (N) and carbon (C) in FR. Because of these properties, FR composting requires a long time, results in a substantial loss of nutrients, and generates a low-quality final compost; it follows that better ways of composting FR are needed.
Co-composting involves the degradation of two or more kinds of recyclable materials at the same time (Gurmessa et al., 2021). An effective combination of different organic wastes can result in a high quality co-composting product. For instance, co-composting of FR and some organic materials with high nutrient contents increased microbial activity during the initial process (Guo et al., 2020). Cow manure (CM) is an inexpensive and readily available organic waste with a high N content, and is often co-composted with recyclable materials with a low N content. By reducing the C/N ratio, increasing the porosity, and increasing microbial activity (Guo et al., 2022), co-composting of FR with CM accelerates the composting process. Liu et al. (2021) found that addition of CM to the composting of straw provided sufficient nutrients to accelerate the succession of the bacterial community and to shorten the composting period. Zhang and Sun (2017) demonstrated that adding CM to green waste composting promoted N conversions. In addition, CM contains lignocellulose-degrading bacteria that are not found in FR, i.e., CM addition to the composting of organic solid waste can increase the abundance of microorganisms and introduce new microorganisms that increase OM decomposition (Guo et al., 2022). Therefore, using CM as a raw material in the co-composting process is one way to enhance FR composting.
However, there are still some disadvantages in the co-composting of FR with CM, such as a poor N-conversion efficiency, a low rate of OM degradation (Zhang and Sun, 2017), and a final compost product with a poor physical structure and a low nutrient content (Liu et al., 2021). Previous reports have indicated that these disadvantages can be reduced by the use of bone charcoal (BC), pumice (PM), or straw biochar (SB) as additives (Wang et al., 2011, Sun et al., 2016). BC surfaces have many functional groups, which can immobilize volatile organic compounds and heavy metals, and thereby reduce environmental pollution (Dawlet et al., 2013). BC is also rich in phosphorus (Reynel-Avila et al., 2016) and contains many other nutrients. Zhan et al. (2021), who studied the co-composting of kitchen waste and sawdust, found that the addition of P-rich amendments (such as BC or rock phosphate) increased the temperature during composting and reduced the time required to obtain a mature compost. In addition, the structure of PM supports gas exchange and water retention (Yavuz et al., 2008). PM is negatively charged due to the free silica and metal oxides on its surface, resulting in a substantial hydrophilicity and buffering capacity (Yavuz et al., 2008), which helps mitigate the negative effects of changes in the compost environment on microorganisms. Moreover, SB contains a large amount of C and abundant carboxyl, hydroxyl, lactone, and other groups on its surface, and is regarded as a bulking agent in composting (López-Cano et al., 2016). Sun et al. (2016) reported that SB can affect microbial community structure and succession during composting by increasing bacterial abundance and thereby altering the C flux. The addition of SB can also limit the loss of N during composting (Chandra et al., 2020).
Although researchers have shown how addition of BC, PM, or SB affects composting of sewage sludge, livestock manure, and other organic wastes (Sun et al., 2016, Wang et al., 2011), the effects of BC, PM, or SB on the co-composting of FR with CM have not been determined. Previous reports have also concentrated mainly on the effects of BC, PM, or SB on nutrient transformation and microbial succession in composting (López-Cano et al., 2016, Wang et al., 2011) but did not provide a comprehensive assessment of how BC, PM, or SB altered compost properties during the composting and after the composting was complete. The current study evaluated the influences of BC, PM, or SB on the physicochemical and microbial characteristics in the co-composting of FR with CM. The study had three objectives: 1) to investigate the effects of BC, PM, or SB on the physicochemical characteristics during co-composting of FR with CM; 2) to explore the correlations between physicochemical characteristics and microbial community structure in order to find the key factors affecting microbial community structure; and 3) to determine which additive resulted in the product with the highest quality.
Section snippets
Raw materials
FR consisted of residual branches and leaves collected during spring landscape maintenance. The collected materials were mechanically crushed into <2-cm-long pieces before composting. CM was purchased from Qunxuan Breeding Co., Ltd., China. The CM had been air-dried at the breeding farm and crushed into <2-mm pieces before composting. BC (1–4 mm) was obtained from Qingyuan Qumeng Co., Ltd., China. PM (1–4 mm) was obtained from Yunnan Liyintang Commerce Co., Ltd., China. SB (1–3 mm) was obtained
Temperature during composting
During composting, the temperature changes of the four treatments were similar (Fig. 1). Temperature rose quickly at the beginning of the process in all treatments. T3 (with 10 % PM) reached 50.1 °C on day 2 and entered the thermophilic period sooner than the other treatments. T1 (without additives), T2 (with 10 % BC), and T4 (with 10 % SB) all entered the thermophilic period on day 3. If the thermophilic period lasts for ≥3 days, pathogenic microorganisms and weed seeds in the compost are
Conclusion
Addition of 10 % BC, 10 % PM, or 10 % SB improved the co-composting of FR with CM, and the greatest improvements were obtained with addition of 10 % PM. These improvements were associated with changes in physiochemical and microbial properties of compost. Addition of 10 % PM resulted in the highest rate of OM degradation and the shortest composting period (39 days). Additional research is needed on the effects of different ratios of additives on the co-composting. Microbial functional genomics
CRediT authorship contribution statement
Xiaoyu Liu: Conceptualization, Methodology, Writing – original draft. Lu Zhang: Methodology, Writing – review & editing.
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.
Acknowledgements
This study was supported by the Beijing Natural Science Foundation (No. 6222039) and the National Natural Science Foundation of China (No. 32171751; No. 31700537).
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