Tomonori Ishigaki

The degradability of biodegradable plastics in aerobic and anaerobic waste landfill model reactors

Degradabilities of four kinds of commercial biodegradable plastics (BPs), polyhydroxybutyrate and hydroxyvalerate (PHBV) plastic, polycaprolactone plastic (PCL), blend of starch and polyvinyl alcohol (SPVA) plastic and cellulose acetate (CA) plastic were investigated in waste landfill model reactors that were operated as anaerobically and aerobically. The application of forced aeration to the landfill reactor for supplying aerobic condition could potentially stimulate polymer-degrading microorganisms. However, the individual degradation behavior of BPs under the aerobic condition was completely different. PCL, a chemically synthesized BP, showed film breakage under the both conditions, which may have contributed to a reduction in the waste volume regardless of aerobic or anaerobic conditions. Effective degradation of PHBV plastic was observed in the aerobic condition, though insufficient degradation was observed in the anaerobic condition. But the aeration did not contribute much to accelerate the volume reduction of SPVA plastic and CA plastic. It could be said that the recalcitrant portions of the plastics such as polyvinyl alcohol in SPVA plastic and the highly substituted CA in CA plastic prevented the BP from degradation. These results indicated existence of the great variations in the degradability of BPs in aerobic and anaerobic waste landfills, and suggest that suitable technologies for managing the waste landfill must be combined with utilization of BPs in order to enhance the reduction of waste volume in landfill sites.

Biodegradation of a polyvinyl alcohol-starch blend plastic film

Attempts were made to elucidate the degradation mechanism of a polyvinyl alcohol (PVA)-starch blend plastic. A part of the starch fraction of this plastic was dissolved into an aqueous phase in a control test. Treatment with a PVA-degrading bacterium or enzyme gave a maximal weight loss of approximately 70% and film breakage occurred. Since this plastic contains 40% PVA, it is apparent that not only the PVA fraction but also a considerable portion of the starch fraction was lost from the film by treatment with the PVA-degrading enzyme. As the PVA-degrading bacterium and enzyme used here showed no starch-degrading activity, loss of the starch fraction seems to depend on its dissolution with degradation of the PVA fraction. These experimental results indicated that the degradation of the PVA fraction is an important requisite for complete degradation or decomposition of this plastic film.

Abundance of polymers degrading microorganisms in a sea-based solid waste disposal site.

In order to assess the degradability of plastics in solid waste disposal landfill sites, microbial populations capable of degrading five kinds of plastic‐constituting polymers, poly ε‐caprolactone (PCL), poly‐lactic acid (PLA), polyethylene glycol (PEG), poly‐β‐hydroxybutyrate (PHB) and cellulose acetate (CA), in a sea‐based solid waste disposal site were investigated. Enumeration of aerobic and anaerobic polymers‐degrading microorganisms (PDMs) was performed against to total 8 leachate samples, which were seasonally collected from the facultative pretreatment pond and the aerated lagoon. Both aerobic and anaerobic PDMs for natural polymers, PHB and CA, were found in all of the samples, while those for chemically‐synthesized polymers, PCL, PLA and PEG, could not be always detected. In most cases, the ratios of the PHB‐ and CA‐degraders to the heterotrophic bacterial population were more than 0.1%. On the other hand, the ratios of PCL‐, PLA‐ and PEG‐degraders were often much lower. These data indicate that the plastics degradation potential is commonly present in the studied disposal site, and that the degradation potential for plastics composed of chemically‐synthesized polymers is inferior to that of natural polymers. Population sizes of the PDMs correlated to those of heterotrophic bacteria, and the counts of aerobic heterotrophic bacteria and PDMs in the aerated lagoon tended to be higher than those of anaerobic ones, indicating that the aeration of the leachate resulted in the activation of growth of whole aerobic microbial community including the PDMs.

Enzymatic degradation of cellulose acetate plastic by Novel degrading bacterium Bacillus sp. S2055

Cellulose acetate (CA)-degrading bacteria were isolated from samples obtained from environments at a population size of 6.7 x 10(1) to 1.0 x 10(8) halo-forming cfu/ml-water or g-solid, suggesting their ubiquitous presence. The classification of 35 isolated strains of CA-degrading bacteria into 15 genera indicates that CA-degrading activity is over a wide range of taxonomical groups. From these isolates, Bacillus sp. S2055 was found to be the most efficient CA-degrading bacterium, and its CA-degrading enzyme(s) was partially characterized. The weight loss of CA plastic film (degree of substitution (DS)=1.7) in the culture of S2055 was less than 12% after a 35-d culture while that in the crude enzyme solution extracted from the culture supernatant reached 62% after the same period. Lipase and cellulase activities were detected in the culture supernatant of strain S2055. The crude enzyme solution contained three major protein fractions that have different mean molecular weights (MWs). Fraction I with the highest MW exhibited both lipase and cellulase activities, while fraction II and III exhibited only lipase activity. Fraction I significantly deacetylated CA (DS 1.5) and fragmented CA plastic film into pieces while the other fractions failed to do so even when used in combination with commercially-available cellulases and lipases. The lipase activity of fraction I against various substrates differed considerably from those of known lipases. It was thus suggested that deacetylation of CA mediated by an enzyme with such a peculiar lipase-like activity is a requisite for the efficient biodegradation of CA plastics.

Effect of UV irradiation on enzymatic degradation of cellulose acetate

The effect of UV irradiation on enzymatic degradation of highly substituted cellulose acetate (CA) was investigated. The degradability of CA by cellulase decreased with increasing the degree of substitution (DS) of CA. Combination of the deacetylating enzyme (lipase or esterase) and cellulase did not promote the degradation of CA with DS 2.4. On the other hand, the UV-irradiated CAs that were suspended in the sterilized buffer and cellulase solution showed 23% and 60% of weight loss, respectively. UV irradiation resulted in the decrease of molecular weight of CA and did not affect DS. Observation by atomic force microscope confirmed that UV irradiation increased the surface area of CA film. Wash-out of depolymerized component from UV-irradiated CA film would increase the surface area and the contactability with cellulase. These results suggested that degradation of CA by cellulase would be positively influenced by UV irradiation under the natural environment.

Water reduction by constructed wetlands treating waste landfill leachate in a tropical region

One of the key challenges in landfill leachate management is the prevention of environmental pollution by the overflow of untreated leachate. To evaluate the feasibility of constructed wetlands (CWs) for the treatment of waste landfill leachate in tropical regions, water reduction and pollutant removal by a CW subjected to different flow patterns (i.e., horizontal subsurface flow (HSSF) and free water surface (FWS)) were examined in both rainy and dry seasons in Thailand. A pilot-scale CW planted with cattail was installed at a landfill site in Thailand. With HSSF, the CW substantially removed pollutants from the landfill leachate without the need to harvest plants, whereas with FWS, it only slightly removed pollutants. Under both flow patterns, the CW significantly reduced the leachate volume to a greater extent than surface evaporation, which is regarded as an effect of the storage pond. Additionally, water reduction occurred regardless of season and precipitation, within the range 0-9 mm d(-1). In the case of low feeding frequency, water reduction by the CW with HSSF was lower than that with FWS. However, high feeding frequency improved water reduction by the CW with HSSF and resulted in a similar reduction to that observed with FWS, which exhibited maximum evapotranspiration. In terms of water reduction, with both HSSF in conjunction with high frequency feeding and FWS, the CW provided a high degree of evapotranspiration. However, pollutant removal efficiencies with HSSF were higher than for FWS. The present study suggested that CWs with HSSF and high frequency feeding could be useful for the prevention of uncontrollable dispersion of polluted leachate in the tropical climate zone.

Microorganisms in landfill bioreactors for accelerated stabilization of solid wastes

Landfill bioreactors (LBRs) with management of leachate and biogas have presented numerous advantages such as accelerated stabilization of solid wastes, reduced amount of leachate, and in situ leachate treatment. Such advantages have minimized environmental risks, have allowed extension of the useful life of the landfill site, and have fostered cost reduction. LBRs of three types have been developed using both anaerobic and aerobic modes: anaerobic, aerobic, and hybrid. Microorganisms in landfills cause various reactions related with organic fractions and heavy metals. Such functions have been stimulated in LBRs by recirculation of leachate with or without aeration. To date, most studies of microorganisms in LBRs have analyzed bacteria and archaea based on 16S rRNA genes and have analyzed fungi based on 18S rRNA genes from a taxonomical viewpoint. Indicator genes for specific functions in LBRs such as nitrification, denitrification, and methane production have also been monitored. The population dynamics of microorganisms in LBRs have been partially clarified, but the obtained data remain limited because of highly heterogeneous features of solid wastes inside LBRs. Systematic monitoring of microorganisms should be established to improve LBR performance.

Removal of heavy metals from synthetic landfill leachate in lab-scale vertical flow constructed wetlands

Synthetic landfill leachate was treated using lab-scale vertical flow constructed wetlands (CWs) in sequencing batch modes to assess heavy metal removal efficiencies. The CWs filled with loamy soil and pumice stone were unplanted or planted with common reed (Phragmites australis) (Reed-CW) or common rush (Juncus effusus) (Rush-CW). Synthetic leachate contained acetate, propionate, humate, ammonium, and heavy metals. Common reed grew almost vigorously but common rush partly withered during the 8-month experiment. The CWs reduced the leachate volume effectively by evapotranspiration and removed easily degradable organic matter, color, and ammonium. Furthermore, the CWs demonstrated high removal amounts for heavy metals such as Zn, Cr, Ni, Cd, Fe, and Pb, but not Mn from leachate. The metal removal amounts in the CWs were low for high-strength leachate (influent concentration increased from one time to three times) or under short retention time (batch cycle shortened from 3days to 1day). The Rush-CW showed slightly lower removal amounts for Cr, Ni, Mn, and Cd, although the Reed-CW showed lower Mn removal amounts than the unplanted CW did. However, Cd, Cr, Pb, Ni, and Zn were highly accumulated in the upper soil layer in the planted CW by rhizofiltration with adsorption compared with unplanted CW, indicating that the emergent plants would be helpful for decreasing the dredging soil depth for the final removal of heavy metals. Although the emergent plants were minor sinks in comparison with soil, common rush had higher bioconcentration factors and translocation factors for heavy metals than common reed had.

Effect of increasing salinity on biogas production in waste landfills with leachate recirculation: A lab-scale model study

Highlights • Effects of accumulation of complex salts with leachate recirculation on anaerobic waste degradation and microbial communities were evaluated.• A high salt concentration, 80 mS cm−1 EC, inhibited not only CH4 and CO2 generation, but also the degradation of organic compounds.• High salinity exerted selective pressure on bacterial communities, resulting in a change in bacterial community structure.• Concentration of ammonium is a key inhibitor of anaerobic waste degradation in landfills when leachate recirculation.• Quality control, especially of ammonium levels, is essential for the promotion of waste degradation in landfills with leachate recirculation.

Greenhouse Gas Emission from Solid Waste Disposal Sites in Asia

1.1 Difficulties in estimating GHG emission from solid waste disposal sites (SWDSs) in Asian countries From the viewpoint of sustainable development, appropriate waste management is crucial for conserving the local and global environments. Improvement of waste management in developing countries is directly related to preventing environmental pollution and expanding public health services. Appropriate waste management contributes to reducing not only the emission of water/atmospheric pollutants and odors, but also the emission of greenhouse gases (GHGs). Those involved in international cooperation via technology transfer should take into consideration the potential for shared benefits in terms of “co-benefit” of waste management and climate change. The recent framework of Nationally Appropriate Mitigation Actions (NAMAs) indicated in the Bali Action Plan requires measurability, reportability, and verifiability of emission reduction in mitigation action. Therefore, researchers in the waste management field have focused on finding precise and practical methods for estimating GHG emissions. Solid waste disposal sites (SWDSs) that include both managed landfills and unmanaged dump sites were recognized as major GHG emission sources in developing countries. Although the Intergovernmental Panel on Climate Change (IPCC) released guidelines for estimating GHG emissions, there is still considerable uncertainty regarding emissions from SWDSs in Asian countries, because of the lack of data about the precise emission behavior and waste degradation kinetics, especially at waste disposal sites. In this chapter, authors are going to describe the current situation of the GHG emission estimation and mitigation action in the waste management field in Asia.