Environmental Engineering Reference
In-Depth Information
Chapter 2
L ANDFILL G AS : G ENERATION
M ODELS AND E NERGY R ECOVERY
Lidia Lombardi
Dipartimento di Energetica “Sergio Stecco”
Università degli Studi di Firenze
Via Santa Marta, 3, 50139 Firenze, Italy
A BSTRACT
In this chapter different landfill gas production mathematical models have been
analysed, implemented and compared among themselves and with data collected from
existing landfills. These models will be presented in the chapter. One of these models has
been selected for application to some study cases. The selected model is based on first-
order decay equation and considers as basic inputs the years of landfill operation, the
amount of municipal solid waste landfilled per year, the municipal solid waste
component characterisation and biodegradability. Three different behaviours, in reference
to biodegradation rate, have been considered dividing the material categories into rapidly,
moderately and slowly biodegradable. The model has been used to predict the landfill gas
production of a case-study landfill in order to properly size the energy recovery system.
In particular, reciprocating engines were considered for energy recovery purposes. The
landfill gas energy recovery by means of reciprocating engines is a quite widespread
practice in modern landfills, but the energy recovery system definition and sizing, also in
reference to its economic convenience, is a crucial and tricky issue. For this reason, the
selection of an appropriate combination of engines has been carried out with the aim of
obtaining the maximum profits from selling the produced electric energy. The obtained
configuration for energy recovery was evaluated also from an energetic and
environmental point of view, estimating the overall contribution to Greenhouse Effect
from escaped landfill gas, collected and combusted landfill gas and recovered electric
energy avoided emissions.
Further, in order to investigate the management possibilities to enhance energy
recovery, the behaviour of a landfill where leachate is recirculated was observed,
recording a more concentrated landfill gas production in a shorter time than in
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