J.P.A. Hettiaratchi

Effect of enzyme additions on methane production and lignin degradation of landfilled sample of municipal solid waste

Operation of waste cells as landfill bioreactors with leachate recirculation is known to accelerate waste degradation and landfill gas generation. However, waste degradation rates in landfill bioreactors decrease with time, with the accumulation of difficult to degrade materials, such as lignin-rich waste. Although, potential exists to modify the leachate quality to promote further degradation of such waste, very little information is available in literature. The objective of this study was to determine the viability of augmenting leachate with enzymes to increase the rate of degradation of lignin-rich waste materials. Among the enzymes evaluated MnP enzyme showed the best performance in terms of methane yield and substrate (lignin) utilization. Methane production of 200 mL CH(4)/g VS was observed for the MnP amended reactor as compared to 5.7 mL CH(4)/g VS for the control reactor. The lignin reduction in the MnP amended reactor and control reactor was 68.4% and 6.2%, respectively.

Waste degradation and gas production with enzymatic enhancement in anaerobic and aerobic landfill bioreactors.

The presence of lignin is the limiting factor at later stages of biodegradation of municipal solid waste under aerobic or anaerobic conditions. Supplying enzymes into the system could facilitate lignin degradation, thereby aiding anaerobic and aerobic waste degradation processes. A comprehensive set of laboratory experiments were conducted under both anaerobic and aerobic conditions to evaluate the feasibility of using enzymes in accelerating lignin-rich waste degradation. After 30 days of anaerobic operation, MnP and LiP enzyme treated reactors produced 36 and 23 times higher cumulative methane (CH4), respectively, compared to that of the control reactor devoid of enzyme treatments. The carbon dioxide (CO2) yield of MnP enhanced aerobic reactor showed more than two-fold increase.

Enhancing Gas Production in Landfill Bioreactors: Flow-Through Column Study on Leachate Augmentation with Enzyme

AbstractLandfill bioreactors have many advantages relative to conventional dry-tomb sanitary landfills. Leachate augmentation with enzymes (prior to its recirculation) to enhance waste degradation and gas production in landfill bioreactors is a relatively new concept and very little is known about its applicability. The research reported in this paper was undertaken to determine the viability of enzymatic augmentation of leachate to enhance waste-degradation rates at later stages of anaerobic bioreactor operation. There was a five-fold increase in the cumulative methane production in enzyme-added flow-through columns compared with the control column. This observation is attributed to an increase in the fraction of waste being degraded, as indicated by the increasing levels of dissolved organic carbon and decreased lignin levels in the waste.

Inhibitory effects of acidic pH and confounding effects of moisture content on methane biofiltration

This study focussed on evaluating the effect of hydrogen sulfide (H2S) on biological oxidation of waste methane (CH4) gas in compost biofilters, Batch experiments were conducted to determine the dependency of maximum methane oxidation rate (Vmax) on two main factors; pH and moisture content, as well as their interaction effects. The maximum Vmax was observed at a pH of 7.2 with decreasing Vmax values observed with decreasing pH, irrespective of moisture content. Flow-through columns operated at a pH of 4.5 oxidized CH4 at a flux rate of 53g/m2/d compared to 146g/m2/d in columns operated at neutral pH. No oxidation activity was observed for columns operated at pH 2.5, and DNA sequencing analysis of samples led to the conclusion that highly acidic conditions were responsible for inhibiting the ability of methanotrophs to oxidize CH4. Biofilter columns operated at pH 2.5 contained only 2% methanotrophs (type I) out of the total microbial population, compared to 55% in columns operated at pH 7.5. Overall, changes in the population of methanotrophs with acidification within the biofilters compromised its capacity to oxidize CH4 which demonstrated that a compost biofilter could not operate efficiently in the presence of high levels of H2S.

Reaction mechanisms and rate constants of waste degradation in landfill bioreactor systems with enzymatic-enhancement

Augmenting leachate before recirculation with peroxidase enzymes is a novel method to increase the available carbon, and therefore the food supply to microorganisms at the declining phase of the anaerobic landfill bioreactor operation. In order to optimize the enzyme-catalyzed leachate recirculation process, it is necessary to identify the reaction mechanisms and determine rate constants. This paper presents a kinetic model developed to ascertain the reaction mechanisms and determine the rate constants for enzyme catalyzed anaerobic waste degradation. The maximum rate of reaction (Vmax) for MnP enzyme-catalyzed reactors was 0.076 g(TOC)/g(DS).day. The catalytic turnover number (k(cat)) of the MnP enzyme-catalyzed was 506.7 per day while the rate constant (k) of the un-catalyzed reaction was 0.012 per day.

Interaction effects of metals and salinity on biodegradation of a complex hydrocarbon waste.

Abstract The presence of high levels of salts because of produced brine water disposal at flare pits and the presence of metals at sufficient concentrations to impact microbial activity are of concern to bioremediation of flare pit waste in the upstream oil and gas industry. Two slurry-phase biotreatment experiments based on three-level factorial statistical experimental design were conducted with a flare pit waste. The experiments separately studied the primary effect of cadmium [Cd(II)] and interaction effect between Cd(II) and salinity and the primary effect of zinc [Zn(II)] and interactioneffect between Zn(II) and salinity on hydrocarbon biodegradation. The results showed 42–52.5% hydrocarbon removal in slurries spiked with Cd and 47–62.5% in the slurries spiked with Zn. The analysis of variance showed that the primary effects of Cd and Cd–salinity interaction were statistically significant on hydrocarbon degradation. The primary effects of Zn and the Zn-salinity interaction were statistically insignificant, whereas the quadratic effect of Zn was highly significant on hydrocarbon degradation. The study on effects of metallic chloro-complexes showed that the total aqueous concentration of Cd or Zn does not give a reliable indication of overall toxicity to the microbial activity in the presence of high salinity levels.

Towards developing a representative biochemical methane potential (BMP) assay for landfilled municipal solid waste - A review

The applicability of slurry-based (semi-liquids) BMP assay in determining biodegradation kinetic parameters of landfilled waste is critically reviewed. Factors affecting the amount and rate of methane (CH4) production during anaerobic degradation of municipal solid waste (MSW) and optimal values of these factors specific to landfill conditions are presented. The history of conventional BMP, and some existing procedures are reviewed. A landfill BMP (LBMP) assay is proposed that manipulates some of the key factors, such as moisture content, particle and sample size, that affects the rate of CH4 production and the CH4 generation potential of landfilled MSW (LMSW). By selecting proper conditions for these factors, a representative BMP assay could be conducted to ensure accurate determinations of CH4 potential and the kinetic parameters k; first order rate coefficient and Lo; methane generation potential.

Enhanced performance of the aerobic landfill reactor by augmentation of manganese peroxidase

The aim of the work discussed in this article was to determine the ability of an MnP augmented aerobic waste cell to reach stable conditions rapidly in terms of gas production, nutrient content and cellulose and hemicellulose to lignin ratio (C+H/L). Two types of experiments were conducted; small batch and laboratory scale lysimeter experiments. Results from batch experiments showed that enzyme added treatments have the capability to reach a stable C+H/L and lower gas production rates, faster than the treatments without enzyme addition. Enzyme enhancement of the lysimeter increased the rate of biodegradability of the waste; gas production increased more than two times and there was clear evidence of increase in nutrients (nitrogen, dissolved carbon, biological oxygen demand) in the lysimeter ​leachate.

A model for assessment of energy utilisation within an urban centre

This paper presents development of a model for analysis of energy and exergy utilisation within an urban centre of Calgary, Canada. The analysis began with the detailed assessment of energy resource utilisation patterns and energy flows across six different energy consuming sectors, namely energy generation, residential, commercial, industrial, transportation and agricultural. For each sector, the energy and exergy efficiencies were determined. Calgarys overall energy and exergy efficiencies were found to be 40.9% and 15.7%, respectively. Thereafter, the developed model was used to identify energy and exergy losses in different sectors and potential areas for improvement. It was determined that, by switching coal with natural gas by 50%, the CO2 emissions can be reduced by 24.3%. In addition, as much as 31.5% reduction in emissions is also possible by reducing the electricity usage up to 50%.

Leaf composting in cold climates: a theoretical and an experimental evaluation

There are many factors influencing the process of composting organic waste. This paper provides an experimental and theoretical evaluation of the leaf composting process to elucidate the importance of these various factors during composting of leaves. The analysis is performed specifically for the environmental conditions encountered in cold climates. Theoretical models are developed to evaluate the changes of temperature profile of a windrow composting operation because of atmospheric temperature and compost windrow height. The theoretical model was validated using field data. The results indicate that the leaf composting process analysed does not satisfy the Canadian Compost Council criteria for a successful composting process. Windrow height and moisture content are found to be the most influential parameters for leaf composting.