Helene Hilger

Microbial methane oxidation processes and technologies for mitigation of landfill gas emissions

Landfill gas containing methane is produced by anaerobic degradation of organic waste. Methane is a strong greenhouse gas and landfills are one of the major anthropogenic sources of atmospheric methane. Landfill methane may be oxidized by methanotrophic microorganisms in soils or waste materials utilizing oxygen that diffuses into the cover layer from the atmosphere. The methane oxidation process, which is governed by several environmental factors, can be exploited in engineered systems developed for methane emission mitigation. Mathematical models that account for methane oxidation can be used to predict methane emissions from landfills. Additional research and technology development is needed before methane mitigation technologies utilizing microbial methane oxidation processes can become commercially viable and widely deployed.

A New Planning and Design Paradigm to Achieve Sustainable Resource Recovery from Wastewater

To employ technologies that sustainably harvest resources from wastewater (for example struvite granules shown here), new perceptions and infrastructure planning and design processes are required.

Biotic systems to mitigate landfill methane emissions

Landfill gases produced during biological degradation of buried organic wastes include methane, which when released to the atmosphere, can contribute to global climate change. Increasing use of gas collection systems has reduced the risk of escaping methane emissions entering the atmosphere, but gas capture is not 100% efficient, and further, there are still many instances when gas collection systems are not used. Biotic methane mitigation systems exploit the propensity of some naturally occurring bacteria to oxidize methane. By providing optimum conditions for microbial habitation and efficiently routing landfill gases to where they are cultivated, a number of bio-based systems, such as interim or long-term biocovers, passively or actively vented biofilters, biowindows and daily-used biotarps, have been developed that can alone, or with gas collection, mitigate landfill methane emissions. This paper reviews the science that guides bio-based designs; summarizes experiences with the diverse natural or engineered substrates used in such systems; describes some of the studies and field trials being used to evaluate them; and discusses how they can be used for better landfill operation, capping, and aftercare.

Methane oxidation and microbial exopolymer production in landfill cover soil

Abstract In laboratory simulations of methane oxidation in landfill cover soil, methane consumption consistently increased to a peak value and then declined to a lower steady-state value. It was hypothesized that a gradual accumulation of exopolymeric substances (EPS) contributed to decreased methane uptake by clogging soil pores or limiting gas diffusion. This study was conducted to detect and quantify EPS in soil from columns sparged with synthetic landfill gas and from fresh landfill cover cores. Polysaccharide accumulations were detected with alcian blue stain. EPS was observed adhering to soil particles and as strands associated with, but separate from soil grains. Glucose concentrations in laboratory soil columns averaged 426 mg kg−1 dry soil, while in a column sparged with air the average glucose concentration in a horizon was 3.2 mg glucose kg−1 dry soil. Average glucose concentrations in two of four cores sampled from a closed landfill ranged from 600–1100 mg kg−1 dry soil, while control cores averaged 38 mg glucose kg−1 dry soil. Viscosity due to EPS was measured by comparing filtration rates of soil suspensions. Soil extracts from the upper horizons of laboratory columns sparged with landfill gas filtered at about one-third the rate of extracts from the lower horizons, and the landfill core with the highest glucose content also produced highly viscous extracts. Breakthrough curves measured in columns before and after methane exposure were similar, so that short-circuiting due to clogging was not occurring. The data support the hypothesis that EPS impeded oxygen diffusion to an active biofilm and limited the extent of methane oxidation.

BIOTIC LANDFILL COVER TREATMENTS FOR MITIGATING METHANE EMISSIONS

Landfill methane (CH4) emissions have been cited as one ofthe anthropogenic gas releases that can and should be controlledto reduce global climate change. This article reviews recent research that identifies ways to enhance microbial consumptionof the gas in the aerobic portion of a landfill cover. Use of these methods can augment CH4 emission reductions achievedby gas collection or provide a sole means to consume CH4 atsmall landfills that do not have active gas collection systems.Field studies indicate that high levels of CH4 removal can be achieved by optimizing natural soil microbial processes. Further, during biotic conversion, not all of the CH4 carbonis converted to carbon dioxide (CO2) gas and released to theatmosphere; some of it will be sequestered in microbial biomass.Because biotic covers can employ residuals from other municipalprocesses, financial benefits can also accrue from avoided costsfor residuals disposal.

Development of a Wireless Sensor Network for Monitoring a Bioreactor Landfill

Recent studies of aerobic bioreactors have demonstrated their success in expediting stabilization of municipa l solid waste (MSW), reducing or eliminating treatment and disposal costs of leachate, and increasing landfill capacity. Such aerobic decomposition is highly dependent on maintaining optimum distribution of moisture and air throughout the highly heterogene ous waste for the duration of the stabilization process. This requires distributed monitoring of the temperature and moisture in the bioreactor. This work presents the development and implementation of an autonomous monitoring system using an array of wire less sensors (motes). Each mote is equipped with embedded microprocessor, flash memory, and a wireless transceiver. Networked data collection along with 3D interactive visualization tools are developed for efficient assessment of the conditions in the bior eactor.

Engineering behavior of biofilm amended earthen barriers used in waste containment

Purpose – The purpose of this paper is to evaluate the influence of a mixture of nutrient solution, bacteria and biofilm on the consolidation, unconfined compression and desiccation characteristics of two soils that could be used in waste containment applications.Design/methodology/approach – Experimental work was conducted to investigate the influence of biofilm on the desiccation, strength and consolidation characteristics of two barrier soils. The soils were evaluated with water alone and with a biofilm solution composed of nutrients, bacteria and exopolymeric substances (EPS). These solutions were mixed with a locally available clay (“red bull tallow” (RBT)) as well as a mix of 65 percent sand and 35 percent bentonite (65‐35 Mix).Findings – Reductions in strength and increases in ductility are observed with biofilm amendment for two soil types. The shear strength was reduced from 413 to 313 kPa and from 198 to 179 kPa for RBT and 65‐35 Mix, respectively. Desiccation tests reveal an increase in moistur...

BUILDING MATERIALS RECLAMATION PROGRAM

This report describes work conducted on the Building Materials Reclamation Program for the period of September 2008 to August 2010. The goals of the project included selecting materials from the local construction and demolition (CD five materials were selected for more detailed investigations. In the Engineering Feasibility and Dissemination Phase, a conceptual study for a regional (Mecklenburg and surrounding counties) collection and sorting facility was performed, an engineering feasibility project to demonstrate the viability of recycling or reuse schemes was created, the literature review was extended and completed, and pedagogical materials were developed. Over the two-year duration of the project, all of the tasks and subtasks outlined in the original project proposal have been completed. The Final Progress Report, which briefly describes actual project accomplishments versus the tasks/subtasks of the original project proposal, is included in Appendix A of this report. This report describes the scientific/technical aspects (hypotheses, research/testing, and findings) of six subprojects that investigated five common C&D materials. Table 1 summarizes the six subprojects, including the C&D material studied and the graduate student and the faculty advisor on each subproject.

A novel long-term undergraduate research team experience

This paper describes the establishment and management of an undergraduate research team. The team includes representatives from each year of the undergraduate curriculum, and new members are recruited from the second-semester freshman class. Members agree to stay through their senior year. Students are paid for 10 h/wk as research assistants, except in their senior year, when each conducts an independent research project for course credit. Leadership is shared by graduate students who benefit from the research assistance provided. Weekly meetings provide a forum for research reports and topic sessions. Marked increases in student confidence and interest in independent learning have been reported and observed. Success has required careful shaping and guidance of graduate student expectations and leadership skills. Other benefits and lessons learned after the first full academic year cycle are described.