**1. Introduction**

148 Management of Organic Waste

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In 2009, the United States generated 243 million tons of municipal solid waste equaling 1.97 kg per person per day. Approximately 54% or 131.9 million tons of municipal solid waste was landfilled, with a similar percentage in 2008 and 2007, which is equivalent to a net per capita landfilling rate of 1.07 kg per person per day. Municipal solid waste includes commercial waste but does not include industrial, hazardous, or construction waste (US EPA, 2010). Therefore, approximately 7.6 million additional tons of industrial wastes are disposed of in landfills in the United States each year (EPA, 2011a). In 2003, New Jersey (a state located in the Northeast of the United States) alone generated 19.8 million tons of solid waste, with 9.5 million tons sent for disposal (NJDEP, 2006).

Landfills are the ultimate disposal of waste after recovery (i.e. recycling and reuse) and combustion, and the most acceptable and used form of solid waste disposal in the United States and throughout the world due to low costs in terms of exploitation and capital costs (Renou et al, 2008). However, municipal, commercial, industrial, hazardous, and construction materials contain nonhazardous and hazardous waste such as cleaning fluids and pesticides. Hazardous waste is harmful to the health of humans and the environment, exhibiting one of the following characteristics: toxicity, reactivity, ignitability, or corrosivity (EPA, 2011b). Nonhazardous waste includes all materials thrown in the garbage, sludge from wastewater, water, and air treatment plants, and wastes discarded from industrial, commercial, community, mining, and agricultural activities (EPA, 2011a). In the early 20th century, nonhazardous and hazardous wastes were regularly burned (Hansen & Caponi, 2009) and/or placed in unlined landfills coming into direct contact and polluting the air, water, and surrounding land (Duffy, 2008). To remedy the pollution caused by landfilling, appropriate remediation options should be performed. The most common methods for the remediation of landfills include excavation to recover recyclable materials, capping to reduce leachate generation, air sparging and soil vapor extraction to capture and remediate gases, and pump-and-treat of the leachatecontaminated plume. In contrast, modern landfills minimize the amount of landfill contamination cause through liner systems, leachate collection, and caps. The government controls landfills to ensure that they are properly operated, maintained, designed, closed, and monitored (Environmental Industry Association, 2011).

<sup>1</sup> Corresponding Author

Landfill Management and Remediation Practices in New Jersey, United States 151

the hydrosphere (particularly groundwater) and lithosphere (i.e. soil), while the landfill gases connect solid wastes to the atmosphere. Therefore, it is vital to understand that landfill

Typically, solid waste within landfills undergoes four stages of decomposition: an initial aerobic phase, an anaerobic acid phase, an initial methanogenic phase, and a stable methanogenic phase. The initial aerobic phase lasts only the first couple of days as oxygen in the voids is quickly depleted without any replenishment when the waste is covered. Therefore, an aerobic biodegradation of organic fraction of solid waste solely occur during a very short period, in which carbon dioxide is produced as a product and the temperature of the waste is increased. Leachate produced during this phase comes from direct precipitation or released from the moisture content of the waste itself (Kjeldsen et al, 2002). With the depletion of oxygen, the landfills quickly become anaerobic, and aerobic microbes dominate within the landfills, allowing fermentation to take place. Therefore, in the following anaerobic acid phase, the complex organic molecules are mostly degraded to volatile fatty acids, leading to a pH decrease. The initial methanogenic phase begins when methanogenic microorganisms grow in the waste, further transforming the volatile fatty acids to methane and carbon dioxide (Renou et al, 2008). The consumption of the organic acids raises the pH of the waste. During the stable methanogenic phase, the pH continues to increase. Methane production peaks and then declines as the amount of soluble materials decreases. The remaining waste is mainly refractory, non-biodegradable compounds like humic-like substances. The overall decomposition rates can be accelerated by a high moisture content

During different organic waste decomposition phases, landfill leachate and landfill gases may exhibit different characteristics. When volatile organic compounds dominate in the acid phase, leachate pH is typically at 3.0-4.0, under which heavy metals, such as calcium, magnesium, iron, and manganese, largely exist in leachate. Meanwhile, a huge number of biodegradable organic compounds are present in leachate, and 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand (COD) may reach a few tens of thousands of mg/L. And the organics are highly biodegradable characterized by a high BOD5/COD (typically > 0.6). However, with the further decomposition into methangoenic phase and subsequent reduction in the concentration of organic acids, the leachate pH is raised to a neutral range, and the leachate organic content is significantly reduced. COD may drop to a few hundreds or thousands of mg/L, and the organic compounds are refractory with a low BOD5/COD (typically < 0.3). And the concentrations of heavy metals in leachate greatly decrease as a result of precipitation more readily occurring at a high pH. When the landfill condition transform from aerobic to anaerobic condition, sulfate may be microbiologically reduced to hydrogen sulfide, so that the sulfate level is decreased with the landfilling time. Chloride, sodium, and potassium do not show a significant change in their concentrations throughout the decomposition, thus exhibiting an inert behavior. Ammonia-nitrogen concentrations remain high during all phases of decomposition, and thought to be the largest issue in landfill management for the long term. In leachate, monoaromatic hydrocarbons (e.g., benzene, toluene, ethylbenzene, and xylenes) and halogenated hydrocarbons are the most common xenabiotic organic compounds found. They are relatively recalcitrant. The concentrations of xenabiotic organic compounds vary broadly

engineered sites have a potential to pollute more than one of the Earth's spheres.

**2.1.2 Decomposition of solid waste in landfills** 

and an initial aeration of the waste (Kjeldsen et al, 2002).

As the human population, along with the industrial, municipal, and commercial sectors, continues to grow exponentially, the amount of waste generated will significantly increase over the years (Renou et al, 2008). The number of municipal landfills and amount of waste landfilled have declined combined with an increase in recycling and composting rates over the past 40 years in the United States (EPA, 2010). However, the majority of waste is already located in landfills (Environmental Industry Association, 2011) and landfills are still the most common form of waste disposal in the United States (EPA, 2010). As of 2003, approximately 21.3 years of landfill capacity remained in the United States, and less than ten years of capacity left in New Jersey (Hansen & Caponi, 2009).
