Hydrolysis converts the cellulose content of ligno-cellulosic wastes (paper and wood) into fermentable sugars so that methane or ethanol can be produced as alternative fuels. The traditional method is for a high temperature and pressure process, in the presence of acid, to break down the cellulose materials. More recently, enzyme hydrolysis (which is basically the industrialization of the natural processes of degradation from the forest floor) and steam explosion hydrolysis have been receiving significant development interest. However, all hydrolysis processes are sensitive to continuity of feedstock in quality and quantity, which make them unsuitable for mixed wastes and more suitable for agricultural residues such as sawdust, straw, or specially grown crops.

Bio-fermentation

Bio-fermentation is the in-vessel fermentation of the organic parts of waste streams to produce methane (for power generation) and simultaneously stabilize putrescible wastes. This process is receiving renewed interest as a method of pretreating and stabilizing putrescible or organic wastes to recover methane. The residues can then be aerobically composted. The energy recovered is hoped to be enough to run the overall plant. As a volume-reduction technique, only about 7 to 10% of the material in the waste stream will be affected by biodegradation without a prior hydrolysis process to convert the ligno-cellulosic material into fermentable sugars.

WASTE MANAGEMENT RECOVERY THROUGH RESOURCE

The application of recycling, reuse, composting, waste-to-energy or other processes to the recovery of material and energy resources unquestionably provides a substantial alternative supply of raw materials and reduces the dependence on virgin feed stocks. These recovered resources are essentially given another life cycle; however, many recovered materials cannot be readily reused in the identical markets or applications. In order for resource recovery to be effective on a long-term basis, viable markets and alternative uses must be carefully planned to ensure the least waste of resources. Recovered products must meet the fundamentals of market resource security, meaning they should meet the requirements of reliable quality, quantity, and price. This is critical for the end user to make the commitment needed to sustain a reliable market.

The technology of pyrolysis is a form of incineration that chemically decomposes organic materials by heat in the absence of oxygen. Pyrolysis typically occurs under pressure and at operating temperatures above 430°C (800°F). In practice, it is not possible to achieve a completely oxygen-free atmosphere. Because some oxygen is present in any pyrolysis system, a small amount of oxidation occurs. If volatile or semivolatile materials are present in the waste, thermal desorption takes place.

During pyrolysis organic matter is transformed into gases, small quantities of liquid, and a solid residue containing carbon and ash. Off-gases are generally treated in a secondary thermal oxidation unit. Particulate removal equipment such as electrostatic precipitators is also employed.

Fluidized-bed combustion or FBC

Fluidized-bed combustion (FBC) technology has made it possible to significantly increase the utilization of various biomasses and wastes in power and heat generation. The pulp and paper industry served as a forerunner because of the adequate biomass and waste fuel supply and energy demand on site. The range of available biomasses and wastes includes wood-based fuels and residues, such as bark, wood chips, and sawdust, sludge from paper mills and de-inking plants, and other wastes, such as municipal sludges, paper waste, packaging waste. New environmental regulations and taxation of fossil fuels have recently further increased interest in the use of biomasses and wastes in energy generation. In many cases disposal by burning is the only available method of waste treatment. A promising way to fulfill these targets and to utilize energy is to apply co-combustion or gasification of different fuels and wastes. Fluidized-bed combustion has mainly been used in new plants and many grate-fired boilers have been converted to fluidized-bed boilers. Early concepts were based on bubbling fluidized beds (BFB).

BIOMASS-DERIVED RDF

Biomass-derived fuels have been highly successful in Europe. Finland as an example has hundreds of plants which produce heat and power from various types of biomass fuels. Because of the wide variety of fuels, the fuel handling systems are designed to be versatile. The raw feedstock for these systems is typically bark, peat, wood chips, sludge, industrial wood, and various types of combustible waste, including MSW. 

THE COMPOSITION OF MSW or MUNICIPAL SOLID WASTE

Municipal solid waste (MSW) is commonly known as trash or garbage. It comprises everyday items, such as product packaging, grass clippings, furniture, clothing, bottles, food scraps, newspapers, appliances, paint, batteries, and other consumer-related product forms. The composition of MSW depends on a number of factors such as the lifestyles of the population, their relative standards of living, general consumer patterns, and the level of technological advancement of a particular country.