A laboratory investigation of the effects of water content and waste composition on leachate and gas generation from simulated MSW

摘要

Leachate emitted by landfilled municipal solid waste may cause many and cumulativeudadverse effects ranging from health problems to environmental impacts. South Africa isudone of the few countries in the developing world to have a sound regulatory frameworkudfor waste disposal by landfill. Municipal solid waste, however, is not differentiated byudcontent. It is well established that the characteristics of waste produced by affluentudsuburbs are very different from poor suburbs and informal settlements. The regulatoryudframework for landfilling is presented as a set of the Minimum Requirements thatudspecifies the design of landfills on the basis of the potential to generate leachate and theudtype of waste being disposed. The current study interrogates aspects of the MinimumudRequirements classification system, namely the classification of waste and climatic waterudbalance. The climatic water balance is used as a guiding tool to assess the potential for audlandfill to generate leachate. The end result of this classification is a determination of theudproposed site falls under B+ (water surplus) or B- (water deficient) class. The MinimumudRequirements ensure that all sites which fall under the B+ class must be equipped with anudunderliner owing to the potential for leachate generation, while B- sites do not require anyudunderliner since leachate will be only generated sporadically. However, there is nouddifferentiation on the basis of the content of municipal solid waste from rich and poorudsuburbs. The present study investigates the generation of leachate from landfills situatedudon the borderline between B+ and B- sites, as well as the degradation of refuse having audrange of basic constituents, and representing waste from rich and poor suburbs, as well asuda mixture of the two.udLaboratory lysimeters were filled with synthetic waste consisting of varying proportionsudof paper, putrescible material (grass cuttings) and coal ash (power station fly ash wasudused to ensure consistency). This was intended mimic the waste coming from “poor” andud“rich” suburbs in South Africa. The effect of waste types grading from “poor” to “rich”udon leachate quality was investigated. It has been found that a content of 60 % of ash on auddry mass basis, characterizing poor waste, has a neutralizing capacity which results in audbetter leachate quality than waste with little or no ash, mimicking rich waste. It has beenudalso established that poor waste has lower leachate generation rates than a 1:1 mix ofudpoor and rich waste as well as rich waste alone. A range of water applications was madeudbracketing the climatic divide between B+ and B-. It was also established that poor wasteudis characterized by high degradation owing to the high percentage of ash as compared toudash deficient rich waste. It was also noted that different standards for landfills receivingudeither only poor or only rich waste under the same climatic conditions (B+ and B-) in theudMinimum Requirements may be advantageous. A relaxation of Minimum Requirementsudfor landfills receiving poor waste could significantly reduce the cost of establishing audlandfill under this range of climatic water balance conditions.