Performance assessment of improved composting system for food waste with varying aeration and use of microbial inoculum

doi:10.1016/j.biortech.2017.03.023

Bioresource Technology

Volume 234, June 2017, Pages 167-177

https://doi.org/10.1016/j.biortech.2017.03.023 Get rights and content

Highlights

•
The modified composting systems resulted in matured and non-phytotoxic compost.
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Addition of microbial inoculum reduced active decomposition period significantly.
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Compost yield improved in the modified drum with microbial inoculum.
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Humic and biological substances were reduced significantly in modified drums.
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Waste mass and volume reductions were up to ∼75% and 50% after composting.

Abstract

Wet waste recycling at generation point will alleviate burden on the overflowing waste dumpsites in developing nations. Drum composting is a potential treatment option for such waste at individual or community level. The present study was aimed to produce compost from wet waste (primarily comprising food waste) in composting drums modified for improved natural air circulation. Effect of microbial inoculum and waste turning on composting process was also studied. The final results showed the production of matured and stable compost in the modified drums. Addition of the microbial inoculum resulted in thermophilic phase within a week time. The self-heating test and germination index (>80%) showed the production of non-phytotoxic and mature compost in the modified drums after 60 days. The change in microbial population, humic substances and biological parameters (lignin, cellulose and hemicellulose) during the study is discussed. Moreover, the reduction in waste mass and volume is also reported.

Graphical abstract

Introduction

Composting is considered a preferable recycling option worldwide due to its ability of aerobic microbial conversion of the biodegradable fraction of municipal solid waste (MSW) in an oxidized and innocuous product. The usage of composting reduces greenhouse gas (GHG) emissions, and eutrophication of natural water bodies (Mu et al., 2017). In addition, it adds nutrients to the soil. The biodegradable fraction mainly comprised of food waste (FW) and garden waste (GW) and it is ∼50% (by wt.) of the total MSW (Annepu, 2012). For efficient composting process, carbon to nitrogen ratio (i.e., C/N) should be 20–40 while the moisture content of input feed need to be maintained between 40–60% (Garg and Tothill, 2009). In developing nations, the waste dumping sites are overburdened due to the uncontrolled disposal of mixed MSW (Jara-Samaniego et al., 2016). Apart from this, open burning of waste leads to the release of undesired emissions having extremely negative impacts on the surrounding environment in countries like India. To overcome this situation, several efforts for encouraging composting of the biodegradable fraction at the source of its generation are ongoing in the urban cities of developing nations. Decentralized composting facility offers several tangible and intangible benefits. For example, the need for waste transportation is avoided and the bio-transformed material can be recycled locally as a soil conditioner. Generally, the decentralized composting systems require long duration (up to 3 months or so) for waste stabilization (Zurbrugg et al., 2004). Additionally, odour nuisance has been reported as a major issue since anaerobic conditions are developed due to insufficient turning and inadequate ventilation in the composting systems. Therefore, a research study was planned to develop a naturally ventilated household based community drum which could generate good quality compost out of FW in a shorter duration.

For decentralized systems, different configurations of composting drums or vessels exist in the market but the technical information regarding the design, methodology and final product quality is lacking (Karnchanawong and Suriyanon, 2011). A few researchers have studied application of the decentralized composting systems for kitchen waste in Bangladesh and Thailand (Moqsud et al., 2010, Karnchanawong and Suriyanon, 2011). In Moqsud et al. (2010) study, the steel barrel (∼197 L) was modified by making holes (diameter: 12.5 mm) throughout the barrel whereas in Karnchanawong and Suriyanon (2011) study, rectangular holes (50 mm × 100 mm) were made on the periphery of polyethylene bins (200 L) for passive aeration. In the modified drums, the active phase of composting (during which temperature change is expected), was completed in 6 to 8 weeks. Moreover, the overall volume reductions were of the order of ∼60–70% in the modified bins/ drums compared to 40% obtained in control systems with no holes. The above studies evaluated the effect of modification on composting process by observing the changes in conventional parameters like temperature, pH, C/N ratio and moisture content which may assist in rapid assessment of the process. For instance, pH and temperature are reported to be among the most influencing parameters for diversity of denitrifiers during the composting process (Chen et al., 2014).

Though composting occurs with naturally developing microbial biota, addition of lignocellulolytic inoculum in the beginning can result substantial enhancement in waste degradation rate (Zhang et al., 2014). There are three types of inoculum namely, EM (effective microbes) agents, Avermectin fermentation and VT bacteria which have been used commonly for composting. Among these, effective microbial inoculum (EM1) was widely been used for composting (Huang et al., 2012, Jusoh et al., 2013). In a recently published review paper, the use of microbial inoculum during composting, and compost maturity testing by more than one test are emphasized (Onwosi et al., 2017). Apart from the above, a thorough information on the change in lignocellulosic compounds and production of humic substances with composting time has not been reported.

In the view of above challenges, the present study was aimed to investigate the effect of microbial inoculum, and waste turning on the performance of batch composting process on a mixture of FW and GW in modified plastic drums. Moreover, the change in lignocellulosic compounds and humic substances were also determined during composting process along with other conventional parameters. Besides, two maturity tests (i.e., self-heating test and germination index) were also performed to assess the compost quality.

Section snippets

Waste samples and inoculum

FW comprised of bread and cooked waste which was collected from a student mess located at IIT Bombay campus while GW containing grass trimmings, leaves and small plants was also collected from the campus. Around 200 kg of FW and 100 kg of GW were properly mixed (2:1 by weight) to prepare mixed waste (MW).

A widely used commercially available microbial inoculum (EM1) which contains lactic acid bacteria, yeast and phototrophic bacteria (Jusoh et al., 2013), was procured from 3R Enviro Solutions

Characterization of raw waste

Fig. 2 shows the percentage of individual as well as mixed samples retained in the meshes of different pore openings. It was found that the percentage of samples retained on sieves with pore openings 15–100 mm were added to approximately 84%, 95% and 83% of the total FW, GW and MW, respectively. Moreover, around 30% and 25% of the total MW were in the size range of 30–50 mm and 50–100 mm, respectively. The particle size range of larger than 50 mm is recommended for passive aeration systems (

Conclusions

The present study demonstrated the performance of modified composting drums for treating mess waste. The provisions for natural air ventilation and turning resulted in the completion of active decomposition period in 54 days while the addition of inoculum reduced this period to 36 days. Lignocellulosic compounds were also degraded at faster rate in the presence of microbial inoculum (i.e., in drum 3). Two maturity tests confirmed the production of stable product after 60 days of process. Finer

Acknowledgements

We are thankful to Sophisticated Analytical Instrument Facility (SAIF), IIT Bombay for helping in the analysis of waste samples. The first author is grateful to Ministry of Human Resources and Development (MHRD), New Delhi, India for providing him the fellowship to carry out the research work for his doctoral degree.

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¹: Adjunct Faculty at CESE, IIT Bombay.

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Performance assessment of improved composting system for food waste with varying aeration and use of microbial inoculum

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Waste samples and inoculum

Characterization of raw waste

Conclusions

Acknowledgements

Waste Manage.

Bioresour. Technol.

Bioresour. Technol.

Waste Manage.

J. Hazard. Mater.

Process Biochem.

Geoderma

Bioresour. Technol.

Bioresour. Technol.

Bioresour. Technol.

Resour. Conserv. Recy.

Waste Manage.

Waste Manage.

Bioresour. Technol.

Waste Manage.

J. Environ. Manage.

Process Saf. Environ.

Int. Biodeter. Biodegr.

Bioresour. Technol.

Chemosphere