Landfill Gas

Production and use of Biogas in Landfills to produce Energy
Mario Heredia , Abdolrahman Khoshrou Universidad de Aveiro, Aveiro, Portugal, 3810-366

Landfill gas is generated by the biological decomposition of wastes placed in a landfill. The composition of landfill gas is highly variable and depends on a number of site-specific conditions including solid waste composition, density, moisturecontent, and age. The specific composition of landfill gas varies significantly from landfill to landfill and even from place to place within a single landfill but in general we can say that are composed by 50% of CO2 and 50% of methane CH4, the last one gives to the gas a potential heating value that could be used in several ways whit an inherent economically benefit, the environmental benefits arequestionable and are linked to the technical and efficient management of all process implicated, collect, filtration, dispose of contaminants and burn to produce different kinds of energy.

Nomenclature

E th (MW): ṁCH4: LHV CH4 : ℜ : (kWh) :

Thermal energy Flow rate of CH4 (m3/h) Lower heating value of CH4 (MJ/m3) Recovery rate Electrical energy Electrical efficiency

E el

ηel :I.

Introduction

A

LL cities produce waste, the human activity uses a lot of disposable articles, and there is the need of process and disposal these waste. Usually the local governments, has a public or private collection service, that pick up the waste generated in homes and deposit it in a landfill. At the beginning in a lot of countries in ways of developing a landfill is only a hole inthe earth in order to fill it whit waste an then when is full, cover it whit more earth. This activity generates a lot of problems in the landfill situated local, bad smells, vegetation damage, mice and was founded that decomposition of waste generates a leachate, that contaminates the soil and if there are ground water flows also contaminate it. Most of the time this ground water deposits feedwater to the local towns and cities. Another problem that was founded is that the anaerobic decomposition of waste generates dangerous gases at the surface of the landfill, all of those are liberated to the atmosphere and this gas is hardly explosive. So there is the need to have a technical plan in order to minimize the impacts of this landfills taking into account that always the human activitieswill be producing more and more garbage. II. Landfill Structure

The technical management of landfills suggests that we have to insulate the soil from the garbage and the experience dictates that is more efficient and safe to have different levels of insulation.

1

Nowadays there are using two different isolators, natural and artificial isolators (based in polymeric composites). Followingthe excavation of a landfill, we have to stabilize and compact the soil, when the soil is ready, we need` the first layer of natural isolator, most of the times clay is used in this first stage, thereupon is placed a layer of polyethylene waterproofing and another layer of sand. We mention that the decomposition of waste produce a leachate, that is a liquid that sediment at the bottom of thelandfill, in this stage are collocated a pipes grid in order to collect this fluid and transport to an adequate treatment pool. Then we cover this whit a second layer of sand or grave and another layer of soil, finally we are able to deposit the garbage and we have to alternate whit layers of soil at determinate distances.

Figure 1. Schematic of a typical landfill gas collection system We alsomention that the anaerobic decomposition of waste, produce some gases, generally called landfill gas basically composed of CH4 (methane) and CO2 (Carbon dioxide). The actual landfills also consider a structure whit screening pipes in order to collect this gas and prevent the emission to the atmosphere; the deep will depend of the landfill structure because is not desired to break the isolator...