USING GREEN CHIMNEY AS A STRATEGY FOR CARBON SEQUESTRATION AND URBAN FOOD PRODUCTION

Abstract

The build-up of carbon dioxide (CO2) and other greenhouse gases in the Earth’s atmosphere has caused concern about possible global climate change (IPCC, 2007) which combustion of fossil fuels for electricity generation is one of the major contributors to GHG emissions, accounting 22% of global GHG emissions in 2004(IEA, 2007; IPCC, 2007). This elevated CO2 and associated climate change may greatly affect agricultural production worldwide (IPCC, 1995), especially on food safety and security. Moreover, the fast-growing urbanization may results in cities facing problems of increasing food demand from a burgeoning urban population and decreasing food supply from displacement of farmlands by built-up areas (WHO, 2009) as well as exerting large ecological footprints on the global environment (Rees, 1992) as energy resources are consumed with concomitant carbon emissions for importing food (Sim et al., 2007) which in turn contributes back to global warming. These problems of increasing GHG emission, food safety and security are especially vital to land scarce urbanized country like Singapore. In this research, a new technology-Green Chimney was proposed to reduce CO2 emission produced from power generation and attempt to facilitate urban agriculture. First a laboratory experiment using “stepping down approach” was conducted to determine the optimum starting CO2 level for the proposed photosynthesis agent, Ipomea aquatic Forssk, which is 5000ppm. Then rooftop experiment was conducted where flue gas from a portable electric generator that contained CO2 was channeled into photobioreactor up to 5,000ppm of CO2 as starting level. Four different conditioned specimens, namely two main categories of single and periodic dosage of CO2 which CO2 was re-pumped whenever it fell below atmospheric level; and two subcategories of open containment which the photobioreactor was open during the 12-hours darkness period and sealed containment which the photobioreactor was sealed throughout the duration of the rooftop experiment. Results shows that periodic dosage specimens (PO & PS) remove more CO2 than single dosage specimens (SO & SS); and open specimens (SO & PO) were more efficient than sealed specimens (SS & PS). Using the data collected and a few assumptions, it shows that a 4000m3 green chimney has a maximum CO2 removal rate of 12 tons per year (equivalent to 2373 trees/155,702m2 of forestland). However the dosed specimens were not of saleable appearance upon the roof experiment even though no lead or cadmium was detected in the stems of the dosed specimens but with adjustment(s) to the condition(s), there is possibility of using Green Chimney for both carbon sequestration and urban agriculture.