Zero population growth | EPFL Graph Search

Zero population growth, sometimes abbreviated ZPG, is a condition of demographic balance where the number of people in a specified population neither grows nor declines; that is, the number of births plus in-migrants equals the number of deaths plus out-migrants. ZPG has been a prominent political movement since the 1960s. As part of the concept of optimum population, the movement considers zero population growth to be an objective towards which countries and the whole world should strive in the interests of accomplishing long-term optimal standards and conditions of living. The growth rate of a population in a given year equals the number of births minus the number of deaths plus immigration minus emigration expressed as a percentage of the population at the beginning of the given year. For example, suppose a country begins a year with one million people and during the year experiences one hundred thousand births, eighty thousand deaths, one thousand immigrants and two hundred emigrants. Change in population = 100,000 – 80,000 +1,000 – 200 = 20,800 Population growth rate = (20,800 ÷ 1,000,000) x 100% = 2.1% Zero population growth for a country occurs when the sum of these four numbers – births minus deaths plus immigration minus emigration - is zero. To illustrate, suppose a country begins the year with one million people and during the year experiences 85,000 births, 86,000 deaths, 1,500 immigrants and 500 emigrants. Change in population = 85,000 – 86,000 + 1,500 – 500 = 0 Population growth rate = (0 ÷ 1,000,000) x 100% = 0% For the planet Earth as a whole, zero population growth occurs when the number of births equals the number of deaths. The American sociologist and demographer Kingsley Davis is credited with coining the term. However, it was used earlier by George J. Stolnitz, who stated that the concept of a stationary population dated back to 1693. A mathematical description was given by James Mirrlees. In the late 1960s, ZPG became a prominent political movement in the U.S.

Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Anna Minata Cissé

Changing consumption patterns and global population growth lead to ever-increasing waste generation. Human activity and waste generation are irrevocably linked, and the current situation thus calls for a more circular approach to waste management, where wastes become new resources. Industrial ecology offers a variety of waste reduction-favoring concepts. As a first step this project identifies waste-preventing, waste-reducing, end of pipe (EOP) waste management approaches and legislation as classification categories for waste management strategies. Although, according to the waste hierarchy, waste prevention is the most preferable waste management approach, it is the least implemented. To facilitate the identification of waste prevention and reduction potentials, a special waste flow diagram from the waste management perspective is elaborated. The model tends to visualize all waste flows, including by-product valorization along a product's life cycle through the choice of a thematic-geographic system boundary. In a further step the applicability of the waste flow model is tested for concrete-related wastes and phosphorus (P) flows in wastes. The quantification of concrete waste flows for the city of Zurich shows that recycling is well implemented, whereas preferable waste management strategies, prevention and reduction of waste, are hardly put into practice. Scenario modeling is used to show the benefits of these techniques and the comparative LCA for different construction methods and materials identifies waste prevention as most beneficial option. For P, the waste flow model is applied to test its ability to detect P recovery potentials, however no new findings in terms of P-recovery potential are identified. The most compelling result regarding phosphorus is found in the extension to the initial investigation, the mass flow analysis for a wet-chemical and a thermochemical P-recovery procedure from sewage sludge ashes. The analysis shows that for EOP waste technologies, the material output can be bigger than the input due to the extended use of additives. Although all generated by-products can, in this case, be valorized by other industrial activities, this finding highlights the need for more waste prevention-oriented waste management strategies, thus avoiding the necessity to generate high by-product flows in the first place.

2018

Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Anna Minata Cissé

2018