Solid wastes agricultural applications

The amount of plastic waste generated is still considerably less than that of plastics produced in numerous applications (building, furniture, appliances) plastics meet longterm requirements before their disposal and therefore do not yet occur in the waste stream in big quantities. The majority of plastic wastes are found in municipal solid waste (MSW), as well as in waste streams arising in distribution, agriculture, construction and demolition, furniture and household ware, automotive, electronic and electrical, or medical applications. For a number of years the APME has ordered studies to be made that compile inventories of on the one hand production figures, on the other waste arising, by resin, country, and application and activity. 

Several firms have developed systems for specialized application such as agricultural residue conversion, wood residue conversion and municipal solid waste disposal. Most of these systems have capacities of less than 50 GJ/h of product gas, i.e., 80-90 oven dried tons per day (ODT/D) of feedstock. Larger systems gasifying more than 100 ODT/D of wood are similar in design to gasifiers developed prior to 1950. 

The simplest type of densification system consists of a shredder followed by an agricultural type "cubing machine. These machines were originally built to produce densified animal feeds, but can be modified easily to produce solid waste fuel cubes. One of the first systems of this type was operated during the early 1970 s in Fort Wayne, Indiana, to produce a solid waste fuel for the city power plant (4). A more recent application of densification was demonstrated by the Papakube Corporation of San Diego, California, which manufactures solid waste cubes as a boiler fuel (5). 

Household and municipal solid waste compost also contains Cd that had its origins in agricultural soil. Composts consist of food wastes that have been microbially degraded. The food wastes contain trace amounts of Cd, most of which originated from the soil (Adriano, 2001). The degradation process results in compost with a much higher Cd concentration than the food wastes that went into it. Just like the farmyard manure, repeated applications of compost onto fields that were not the source of all of the Cd in the compost will result in localized increases in soil Cd concentration. However, the agricultural soils affected by compost application are in the minority, since compost is applied mainly to soils around urban areas. 

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