Elsevier

Bioresource Technology

Volume 230, April 2017, Pages 132-139
Bioresource Technology

The impact of silver nanoparticles on the co-composting of sewage sludge and agricultural waste: Evolutions of organic matter and nitrogen

https://doi.org/10.1016/j.biortech.2017.01.032Get rights and content

Highlights

  • Conduct co-composting of sewage sludge, straw, vegetables and bran.

  • Synthesis PVP-AgNPs successfully.

  • Evaluate the impact of PVP-AgNPs on evolutions of organic matter and nitrogen during co-composting process.

  • Less organic matter losses in co-composting pile treated with PVP-AgNPs.

  • AgNPs can reduce the losses of total N but increase losses of mineral N.

Abstract

This study evaluated the influence of silver nanoparticles (AgNPs) on evolutions of organic matter and nitrogen during co-composting of sewage sludge and agricultural waste. Two co-composting piles were conducted, one was treated without AgNPs (pile 1) and the other with AgNPs (pile 2). Results showed that the AgNPs affected the quality of final composts. Less organic matter (OM) losses were determined in pile 2 (57.96%) than pile 1 (61.66%). 27.22% and 30.1% of the initial total organic matter (TOC) was decomposed in pile 1 and pile 2, respectively. The final water soluble carbon (WSC) concentration in pile 2 was 23559.27 mg/kg DW compost which was significantly lower than pile 1 (25642.75 mg/kg DW compost). Changes of different forms of nitrogen in the two piles showed that AgNPs could reduce the losses of TN but increase the losses of mineral N.

Introduction

Composting has been widely applied to dispose many kinds of wastes, such as agricultural wastes, sewage sludge (SS), feces, bio-waste, etc. (Wang et al., 2013, Zhang et al., 2015). It can convert the biodegradable components into nuisance-free, sanitary and humus-like materials, which allows the reuse of the wastes as soil conditioners, fertilizers and soil remediation (Chen et al., 2015, Su et al., 2015). SS is an unavoidable by-product of wastewater treatment plants and it is rich of organic substances and nutrients. Since the technology and capacity of wastewater treatment were improved, SS production increased by more than 50% in EU-15 during 13 years from 1992 to 2005. And by 2020, the production of dry solids from Urban Waste Water Treatment in EU-12 countries will exceed 13 million tons annually (EC, 2006, Léonard, 2011). In China, the SS production of wastewater treatment plants (WWTPS) was about 30 million tons and increased yearly by exceeding 13% during 2007–2015 (Cai et al., 2016). However, approximately 80% SS was disposed improperly (Yang et al., 2015). Since SS usually contains varieties of contaminants (including toxic heavy metal, pathogenic microbes and organic micro-pollutants, etc.), it is thus crucially important to dispose the SS safely before its application to agriculture. Composting has been the most common approach to dispose SS in many countries like Finland, Italy, Spain, etc. (Kelessidis and Stasinakis, 2012) and it has caused more and more attentions (Li et al., 2013, Zhang et al., 2016a).

SS compost is widely applied to agriculture due to the high contents of nutrient elements in it, such as nitrogen and phosphorus. While the high moisture content and low carbon to nitrogen ratio (C/N) provide a favorable environment for ammonia release which leads to losses of nitrogen (Fukumoto et al., 2003), even some times the losses of nitrogen can be up to 80% during composting process (Nakhshiniev et al., 2014). Too many nitrogen losses will reduce the compost fertility and cause air pollution. Hence, it is wise to conduct SS composting with bulking agents or carbon amendments (Ammari et al., 2012). There have been many attempts to conduct co-composting of SS with different bulking agents such as grass waste, sawdust, textures, straw, etc. (Ammari et al., 2012, Su et al., 2015) and these bulking agents can improve the aeration by absorbing the moisture and the final compost quality (Tremier et al., 2005). Lots of studies about SS composting have introduced bulking agents to improve composting conditions. However, the lignocelluloses contained in the bulking agents are difficult to be biodegraded (Yu et al., 2009). To solve this problem, researchers integrated some easily degradable organic wastes (e.g. vegetables) to enhance the composting process and the final compost quality (Ammari et al., 2012).

Nanoparticles, as known, possess comparatively high surface area to volume ratio which leads to higher toxicity than the bulk material (Vance et al., 2015, Xu et al., 2012). Nowadays, silver nanoparticles (AgNPs) have attracted much attention and been applied as antifungal or antibacterial agents to a wide range of consumer products. For instance, AgNPs are frequently discovered in personal-care products, cosmetics, liquid fabric softeners and detergents, coating materials, food storage containers, fabrics and clothing, medical appliances, dietary supplements, and sporting goods (Kim et al., 2010). Studies about the characterization of silver released from textiles showed that approximately 34% to 80% of Ag were released in the form of AgNPs (Lorenz et al., 2012). Other modeling analysis found that Ag+ or AgNPs released from textiles and biocidal plastics accounted for about 15% (Geranio et al., 2009). The manufactured AgNPs in consumer products may be released into the environment during or after their lifetime. At the end of the service life, parts of products are commonly disposed as municipal solid wastes and then AgNPs are released into the solid wastes (Gitipour et al., 2013). Additionally, there were also some AgCl nanoparticles in the waste solution of a laundry (Hassellöv and Kaegi, 2009) and it was found that AgNPs and Ag+ were released into water from socks when washing them (Benn and Westerhoff, 2008). During processes of wastewater treatments, AgNPs may be doped into the sewage sludge by sorption or aggregation and may be enriched with time (Benn and Westerhoff, 2008). With the application of composted sewage sludge to agriculture, AgNPs may also enter into the agricultural wastes. According to Gitipour et al. (2013), 2 mg/kg solid wastes AgNPs was a relatively low concentration that might exist in a real environment. Given the antimicrobial activity of AgNPs, it is important to pay attention to the possible impacts of AgNPs on the composting process of sewage sludge or agricultural wastes.

The aim of this study is to evaluate the impact of AgNPs on co-composting of sewage sludge and agricultural wastes in terms of the evolution of organic matter and nitrogen. The composting materials were composed of sewage sludge, rice straw, vegetables and bran. Two composting piles, one was treated with AgNPs and another was set as blank control, were conducted in laboratory for two months. This research represented the minority studies integrating vegetables as the easily degradable component and bran to adjust the initial C/N. Meanwhile, this study concerned the existence of AgNPs during co-composting of sewage sludge with agricultural wastes.

Section snippets

Synthesis and characterization of AgNPs

In previous researches, it was reported that polyvinylpyrrolidone (PVP) was one of the most common capping agents for AgNPs. The PVP coated AgNPs (PVP-AgNPs) could still maintain stability under high valence background electrolytes condition of high ionic strength solution which was the general environment of a composting system (Gitipour et al., 2013). Therefore, PVP-AgNPs were introduced into this study for evaluating the impacts of AgNPs on co-composting sewage sludge with agricultural

Characterizations of AgNPs

Fig. S1A presents the UV–vis absorbance spectra of the prepared PVP-AgNPs suspensions. The result that the spectra peak appeared at 400 nm indicated the successful synthesis of PVP-AgNPs (Yang et al., 2014). The HDD and zeta potential (ζ) of the suspension were 8.5 nm and −0.7 mV (Fig. S1B) which was similar to other studies (El-Badawy et al., 2010). Though ζ potential may be not enough for electrostatic stabilization, PVP can assist AgNPs in resisting aggregation under complex environmental

Conclusions

The OM contents in two piles dropped rapidly during mesophilic and thermophilic phases, and decreased slowly to 56.1% and 49% for pile 1 and pile 2 at the end of co-composting processing, respectively. Less OM losses was determined in pile 2 indicating that AgNPs could impede the OM decompositions. During the whole co-composting processing, existence of AgNPs could reduce the losses of TN but increase the losses of mineral N which reduced the fertilities of the final composts.

Acknowledgements

This study was financially supported by the National Natural Science Foundation of China (51521006, 51378190, 51409100) and the Program for Changjiang Scholars and Innovative Research Team in University (IRT-13R17).

References (50)

  • A. Kelessidis et al.

    Comparative study of the methods used for treatment and final disposal of sewage sludge in European countries

    Waste Manage.

    (2012)
  • R.H. Li et al.

    Nutrient transformations during composting of pig maure with bentonite

    Bioresour. Technol.

    (2012)
  • Y. Li et al.

    New insights into the interactions between carbon dioxide and ammonia emissions during sewage sludge composting

    Bioresour. Technol.

    (2013)
  • C. Lorenz et al.

    Characterization of silver release from commercially available functional (nano) textiles

    Chemosphere

    (2012)
  • B. Nakhshiniev et al.

    Reducing ammonia volatilization during composting of organic waste through addition of hydrothermally treated lignocellulose

    Int. Biodeterior. Biodegrad.

    (2014)
  • G.A. Ogunwande et al.

    Nitrogen loss in chicken litter compost as affected by carbon to nitrogen ratio and turning frequency

    Bioresour. Technol.

    (2008)
  • L.M. Ren et al.

    Impact of struvite crystallization on nitrogen losses during composting of pig maure and cornstalk

    Waste Manage.

    (2010)
  • R. Riffaldi et al.

    Evaluation of compost maturity by means of chemical and microbial analyses

    Waste Manage. Res.

    (1986)
  • A. Tremier et al.

    A respirometric method for characterising the organic composition and biodegradation kinetics and the temperature influence on the biodegradation kinetics, for a mixture of sludge and bulking agent to be co-composted

    Bioresour. Technol.

    (2005)
  • X. Wang et al.

    Influence of lime on struvite formation and nitrogen conservation during food waste composting

    Bioresour. Technol.

    (2016)
  • P. Xu et al.

    Use of iron oxide nanomaterials in wastewater treatment: a review

    Sci. Total Environ.

    (2012)
  • G. Yang et al.

    Current state of sludge production, management, treatment and disposal in China

    Water Res.

    (2015)
  • X.Y. Yang et al.

    Influence of natural organic matter on transport and retention of polymer coated silver nanoparticles in porous media

    J. Hazard. Mater.

    (2014)
  • M. Yu et al.

    Influence of Phanerochaete chrysosporium on microbial communities and lignocellulose degradation during solid-state fermentation of rice straw

    Process Biochem.

    (2009)
  • G.M. Zeng et al.

    Effects of inoculation with Phanerochaete chrysosporium at various time poits on enzyme activities during agricultural waste composting

    Bioresour. Technol.

    (2010)
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