An assessment of environmental factors involved in the management of garden waste

Eades, Paul (2007) An assessment of environmental factors involved in the management of garden waste. University of Southampton, Doctoral Thesis.

Abstract

Using Hampshire as a case-study (approximately 800,000 households in 2020), a total of 12 potential scenarios for the management of green municipal waste was devised in order to identify which option performed best in respect of minimising environmental impacts.  For each scenario an output was created consisting of energy consumption, global warming potential, acidification potential, eutrophication potential, fuel consumption, compost production, and distance that material was transported.  These outputs were then normalised and assessed against decision-making criteria.  The scenarios were then ranked according to their desirability.

The most preferential option consisted of a combination of techniques, in which 53.8% of material would be processed through anaerobic digestion, 40% would be processed through home composting, and 6.2% would be incinerated.  The material would be recovered through household waste recycling centres, the kerbside collection of source segregated material and the commingled collection of materials.  This scenario would be expected to produce 41,025 GJ of energy per annum.  In addition it would have a global warming, acidification, and eutrophication potential of 92,262 tonnes of CO₂ equivalent, -80.1 tonnes of SO₂ equivalent, and 4.5 tonnes P₄O₅ equivalent per annum respectively.  This scenario would produce 70,500 tonnes of compost and consume 1,503,462 litres of diesel and 332,685 litres of gasoline per annum.

Four of the six most preferential options used anaerobic digestion as the predominant method of processing material.  This outcome was predominantly due to the recovery of energy through the combustion of biogas and the production of a high-grade fertiliser.  In addition, three of the four most preferential options used home composting to a large extent, in which 40% of the material was processed in this manner.  These scenarios were made increasingly preferential as no energy or emissions were expended through the collection and transportation of material.  This indicated that a combination of anaerobic digestion and home composting was desirable in terms of minimising environmental impact.  This was demonstrated through the scenario that was considered most preferential.  No economic or practicality analyses were however performed as this was not within the remit of this research.

The scenario outputs were also assessed against LATs targets.  Those scenarios that landfilled waste directly or used MBT were least preferential as a large proportion of the waste would be landfilled directly, or landfilled after partial stabilisation.  Conversely, those scenarios where only rejects or process residues were landfilled were most preferential in terms of achieving LATs targets.  It could be however be identified whether or not LATs targets would be achieved with the implementation of these scenarios as other waste streams would need to be taken into consideration through the process of integrated waste management.

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