Frederick G. Pohland

In situ nitrogen management in controlled bioreactor landfills

Abstract The characteristics of leachate from landfills vary according to site-specific conditions. Leachates from “old” landfills are often rich in ammonia nitrogen due to the hydrolysis and fermentation of the nitrogenous fractions of biodegradable substrates, with decreases in concentration mainly attributable to leachate washout. At landfills where leachate containment, collection and recirculation is practiced to accelerate decomposition of readily biodegradable organic constituents, leachate ammonia nitrogen concentrations may accumulate to higher levels than during conventional single pass leaching, thereby creating an ultimate leachate discharge challenge. Landfill leachate treatment options include complex and often costly sequences of external physical–chemical and biological processes for removal of high-strength organics and inorganics, including nitrogen. Therefore, this paper focuses on investigations with bioreactor landfill simulations to demonstrate the potential for in situ nitrogen removal in dedicated nitrification/denitrification zones. Using leachate recirculation, associated system modifications provided separate aerobic and anoxic zones for ammonia nitrogen transformations to nitrate and nitrogen gas, respectively. Results from the three simulated optional stages of methanogenesis, nitrification and denitrification indicated that nitrogen conversion and removal was dependent on the operational stage. Both separate and combined reactor operation with internal leachate recycle provided 95% nitrogen conversion. In contrast, combined reactor operation with single pass leaching provided a conversion efficiency per cycle ranging between 30–52% for nitrification and 16–25% for denitrification, thereby indicating the efficacy of using the landfill itself for attenuation of leachate ammonia nitrogen concentrations to levels acceptable for ultimate discharge.

The assimilation of organic hazardous wastes by municipal solid waste landfills

SummaryCo-disposal of 12 compounds representing major organic classes (aromatic hydrocarbons, halogenated hydrocarbons, pesticides, phenols, and phthalate esters) with shredded municipal solid waste was tested using a laboratory-scale column and pilot-scale lysimeter to characterize transport and transformation phenomena including sorption, volatilization and bioassimilation. Leachate and gases emitted from the lysimeters were examined for identifiable products of biotransformation. The results of this investigation provided a mechanistic evaluation of the attenuating and assimilative capacity of municipal solid waste landfills for specific organic compounds. Physical/chemical organic compound characteristics were related to refuse characteristics and composition to predict compound fate. Such knowledge is useful in developíng landfill management and operational strategies consistent with the need for control of pollutant releases.

Calculation of residence time distribution from tracer recycle experiments

This note develops a procedure that can be used to calculate the single pass residence time distribution in a reactor system, such as a landfill, operated with recycle, from pulse tracer studies. An equation relating the effluent tracer concentration and residence time distribution (“E curve”) is derived, and a numerical technique to solve such an equation is presented and applied to data obtained from experiments on a laboratory-scale reactor. The significance of the procedure developed to biological reactors is discussed.

Effects of Elevated Hydrogen Partial Pressures on Anaerobic Treatment of Carbohydrate

The theory of interspecies hydrogen transfer (Wolin and Miller, 1982) is now nearly two decades old, and is considered the biochemical cornerstone of methanogenesis in all natural and man-made habitats (soils, sediments, intestines; anaerobic digesters and treatment systems). Therefore, it is surprising that only a handful of engineering studies (Table 1) have focused on the production and effects of hydrogen during continuous treatment of various waste substrates. A review of this information reveals: 1) a lack of consensus on the inhibitory effects of hydrogen, and 2) an insufficiency of information to allow generalization of interspecies hydrogen effects under all possible treatment scenarios (i.e., all combinations of reactor configuration and wastewater type).

In situ Groundwater Remediation Using Treatment Walls

Development of treatment wall technology for the clean up of contaminated ground-water resources has expanded in the past few years. The main perceived advantage of this technology over ex situ and other in situ ground-water remediation approaches is reduced operation and maintenance costs. Since the first commercial application of zero-valent iron using a funnel-and-gate system for the removal of chlorinated hydrocarbons in February, 1995, several field- and pilot-scale studies are evaluating the feasibility of this technology for treatment of both organic and inorganic contaminants.