Environmental Engineering Reference
In-Depth Information
Zacharof et al. (2004) developed a mathematical model to simulate the hydrological and
biochemical processes taking place in solid waste landfills. They used a statistical velocity
model to represent the water flow through the waste. The waste biodegradation was assumed
to follow three steps: hydrolysis, acidogenesis and methanogenesis; and employed a
simplified methodology for the rate of biodegradation to reduce the parameter required. The
model was used to simulate case studies. Sensitive analysis showed uncertain results. They
found the model was sensitive to depth of waste, infiltration rate, waste heterogeneity and
biodegradation rate constants. In the end, they concluded that the model could be used as a
tool for modeling landfill processes and that further improvements were required to assess the
model's performance.
Yildiz et al. (2004) proposed a mathematical model to simulate the landfill leachate
behavior, distribution of moisture through the landfill, and methane production. They
assumed that landfills consisted of cells and that each cell consisted of several layers. Also,
they considered each layer as a completely mixed reactor having uniformly distributed solid
wastes, moisture, gases and microorganisms. The model was based on the governing
equations that describe leachate production, solubilization of inorganic and organic matter,
degradation of soluble organic matter, the growth of acidogenic and methanogenic
microorganisms, and their inhibition by acetic acid, and change in pH over time. The
solubilization of inorganic solid waste was assumed to have followed zero order kinetics,
whereas the solubilization of organic solid waste was assumed to be a function of the
concentration difference in leachate and microbial activity. The growth rate of acidogenic and
methanogenic microorganisms were described by the Monod model, and it included an
inhibition terms for acetic acid and pH. The model was solved by the fourth order Runge-
Kulta method and calibrated with real landfill data from the Keele Valley landfill. The values
of the kinetics required for the model were determined by using a trial and error procedure
with the data obtained from the landfill. These values were then compared with the literature.
There was good agreement between the predicted and observed results from the Keele Valley
landfill. They concluded that the model had the potential to be used during the design of the
landfills to estimate the quality and quantity of leachate and methane production for different
operation conditions.
White et al. (2003, 2004)
developed a mathematical model to simulate solid waste
biodegradation and gas generation in landfills. The model included biochemical degradation
of solid waste, and transport of leachate and gas. The biodegradation part was based on the
model proposed by Young (1989) and El-Fadel et al. (1996a) and occurred in three stages:
hydrolysis, acidogenesis and methanogenesis. The Monod kinetics were used to simulate the
growth rate of biomass in all stages. The moisture content and effect of pH inhibition on the
biomass growth rates were included in the model. The required kinetics for the model were
obtained from the literature. The model was used to simulate case studies but was not
calibrated with real data. They concluded that it could be used for laboratory and field tests to
investigate the geotechnical and hydrogeological properties of biodegrading solid waste.
