Current State of Waste Management in Singapore
Being a small, low lying island city-state, Singapore is naturally vulnerable to the impact of climate change. With increasing urban density and limited availability of land, Singapore has to strategize to prepare and adapt early to climate change.
by Chi-Hwa Wang
Singapore contributes to 0.11% of global emissions, and is taking initiatives to reduce carbon
emissions, building on past mitigation efforts. The most significant contributor to the greenhouse gases (GHG) in Singapore is Carbon Dioxide (95.5%), followed by PFCs and N2O. In addition, the combustion of natural gas to generate electricity has been identified to be the main contributor (33.4%) to national GHG emission amongst other contributors including emissions from transportation and industrial activities. Under the Paris Climate change agreement, Singapore pledged to reduce Emissions Intensity (EI) by 36 % from 2005 levels by 2030 and stabilize emissions with the aim of peaking around 2030.
To achieve these ambitious targets, many efforts have been made to promote energy efficiency and environmentally friendly Singapore. Waste management is one of the significant parts to be considered.
HOW DOES WASTE CONTRIBUTE TO CLIMATE CHANGE?
The changes in the climate that the world is witnessing is due to the rising levels of Greenhouse gases in the Earth’s atmosphere. One of the many reasons is the way the waste disposal is managed. The production, distribution, and use of products without effective management of the waste, results in greenhouse gas emissions.
Climate change has accelerated the need to find measures to reduce and manage the waste we create. Reduction, reuse, and recycling can help to mage the waste and reduce pressure on the planet’s natural resources while potentially affecting the GHG emissions created through mass production and consumption of natural resources.
Singapore has been acting to reduce GHG emissions to recover energy from waste. Waste reduction and recycling can reduce GHG emissions from waste incineration. Singapore intends to increase its recycling rate from 59% in 2011 to 70% by 2030, and look in more ways to reduce emissions, such as recycling more plastic waste instead of sending it to incineration. The less waste is generated; the less waste will be burnt, and the less CO2 will be produced.
Research projects in E2S2 aim to provide alternate & sustainable solutions in converting waste to energy by efficient technologies, for instance, it may be a hybrid solution to energy recovery where a particular type of waste is undergone a specific process for making electricity & other by-products useful for industrial purposes, hence offsetting GHG emissions largely from fossil fuels(natural gas) which are used to produce electricity in the present system. This process would also be sustainable in terms of saving space used for landfill of dumping the waste, for instance, Semakau Landfill which is the only landfill in Singapore would be out of space in the next 15 years (in 2035) considering the huge amount of waste and the growth of waste production over past years.
In 2018, 7.70 million tonnes of solid waste was generated in Singapore, which is about 9,000 tonnes less than in 2017. However, the amount of waste recycled also decreased by about 90,000 tonnes to 4.63 million tonnes, and the overall recycling rate decreased from 61 percent (in 2017) to 60 percent (in 2018). Specifically, the quantity of wood waste recycled was dropped from 326,800 tonnes (77% of total wood waste in 2017) to 187,900 tonnes (59% of total wood waste in 2018). On the other hand, the quantity of horticultural waste recycled was increased from 220,700 tonnes (67% of total horticultural waste in 2017) to 370,100 tonnes (77% of total horticultural waste in 2018). Among different recycling approaches, biomass power generation plays an important role in wood and horticultural waste recycling. As shown in the following figure, 350,943 tonnes of biomass fuel has been used for power generation in 2018, which is 62.9% of the total wood and horticultural waste recycled.
In 2018, 763,000 tonnes of food waste was reported, and One-third of domestic waste in 2018 was packaging waste. Every day, about 79% of domestic waste generated will be incinerated at one of the four waste-to- energy (WTE) incineration plants. However, the more waste is incinerated, the higher volume of carbon will be produced. Singapore designated 2018 as the Year of Climate Action – to raise national consciousness and rally businesses, communities and individuals to collectively take climate action. Since then, more and more actions will be taken to conquer this big challenge.
Currently, all food, wood and horticultural waste to energy power plant are based on incineration. However, several gasification projects have already started. For example, the gasification program in Gardens by the Bay, using biomass waste for gasification; the gasification program in Origin chicken farm, using chicken manure for gasification. Whereas AD technologies have successfully been used worldwide like Singapore, China, Europe etc.
In 2005, Singapore created the equivalent of about 0.176kg of carbon dioxide for each GDP dollar. It aims to lower this to 0.113kg per dollar by 2030, a reduction of about 36 per cent. The government has pledged that Singapore's greenhouse gas emissions will peak around 2030 at the equivalent of about 65 million tonnes of carbon dioxide.
Singapore generated more than 50 million tonnes of greenhouse gases in 2014.
The Carbon Pricing Act (CPA) and its accompanying Regulations came into operation on 1 Jan 2019. Industrial facilities emitting 25,000tCO2 equivalent or more annually will have to pay a carbon tax on their GHG emissions. The carbon tax rate will start at SGD 5 (USD3.8) per tonne of GHG emissions, which the government intends to raise to between SGD 10-15 (USD7.6-11.4) by 2030. The tax will cover 80% of the national emissions.
E2S2 RESEARCH ON HOW IT CAN HAVE A POSITIVE EFFECT ON RESPONSE TO CLIMATE CHANGE
Focusing on electricity production from food, wood & horticulture waste, the technologies include Anaerobic Digestion & Gasification:
1. Anaerobic Digestion
Anaerobic digestion is a potential bio-technology to convert organic waste into biogas (methane-rich gas) and digestate. Biogas can be converted into electricity and heat using engine generator. Digestate can be used as fertilizer that can be used for planting or farming. It is a close-loop from food waste to energy and fertilizer. Comparing to fossil fuel, energy from organic waste (food waste) has a positive effect on response to climate change. One of our efforts is to develop novel AD technologies to improve organic waste treatment capacity and energy production. Developing a decentralized AD system to handle organic waste in-situ is also our target. In this case, the CO2 emission during transport of waste will be reduced significantly.
Generally, 1-ton food waste can produce 200-400 kWh electricity depending on the characteristics of food waste and other by-products. The Demo of the decentralized AD system from E2S2 have been completed in NUS canteen. The commercialization of this system is ongoing. Considering the amount in Singapore, 636,900 Tonnes of food waste was disposed in 2018. AD Technology from E2S2 could have converted this disposed waste to 127,380 – 254,760 MWh electricity & other useful by-products like hot water. This amount of electricity generated from food waste is equivalent to 61,780 – 123,558 Tonnes CO2 which would be produced from electricity generated conventionally, considering 0.485 kg CO2 released in producing 1 kWh electricity generated from fossil fuels.
2.Gasification
Gasification is a time-tested and environmentally-sound approach of converting the energy in MSW into useful products such as electricity, fertilizers, transportation fuels, and chemicals. On average, conventional waste-to-energy plants that use mass-burn incineration can convert one ton of MSW to about 550 kilowatt-hours of electricity. With hybrid gasification technology, one ton of MSW can be used to produce up to 1,570 kilowatt-hours of electricity or 1.57 MWh, a much more efficient and cleaner way to utilize this source of energy. Gasification can help the world both manage its waste and produce the energy and products needed to fuel economic growth.
Gasification converts MSW to usable synthesis gas, or syngas. Gasification is a unique process that transforms a carbon-based material, such as MSW or biomass, into other forms of energy without burning it. Instead, gasification converts the solid and liquid waste materials into a gas through a chemical reaction. This reaction combines those carbon-based materials (known as feedstocks) with small amounts of air or oxygen (but not enough to burn the materials), breaking them down into simple molecules, primarily a mixture of carbon monoxide and hydrogen. Besides, the carbon-rich solid residue, derived from gasification, or biochar, has been recognized as an effective carbon abatement tool upon its application to soil. Through converting biomass into biochar for soil application, a significant amount of carbon could be sequestrated, leading to a significant reduction of CO2 emission.
Generally, 1-ton of wood & horticulture waste can produce 1.57 MWh electricity depending on the characteristics of wood & horticulture waste and by-products like biochar and other gases which can be used in industrial purposes. Considering the amount in Singapore, 282,900 Tonnes of wood & horticulture waste was disposed in 2018. E2S2 Hybrid Gasification Technology could have been used in converting this disposed waste into 444.15 GWh of electricity. This amount of electricity generated from wood & horticulture waste is equivalent to 215,412 Tonnes CO2 which would be produced from electricity generated conventionally, considering 0.485 kg CO2 released in producing 1 kWh electricity generated from fossil fuels.
Gasification Technology E2S2 is working on:
a. Solar Gasification
Compared to the conventional gasification (autothermal gasification) of organic solid waste, solar gasification has the merits of minimizing the contamination (mainly composed of CO2) caused by internal combustion of partial feedstock, since concentrated solar radiation provides the high-temperature process heat for gasification. Solar gasification enables to minimizing CO2 production in the gasification process, which is a renewable and CO2-neutral technology. It can upgrade the calorific value of syngas due to solar energy stored into the syngas, thus hugely decreasing CO2 emission per kWh electricity production.
b. Solar/Autothermal hybrid gasification with combined cooling, heat and power (SAHG-CCHP)
So far, non-food organic solid waste is disposed of by using incineration in Singapore, in which electricity is the sole carrier of energy output. The power generation efficiency of gasification-based SAHG-CCHP system is ~25%, which is higher than the net waste-to-electricity (WTE) efficiency of ~23% observed in the MSW incineration plants of Singapore. It is expected that the total energy conversion efficiency of ~80% can be reached in the gasification-based SAHG-CCHP system, thus significantly reducing CO2 emission per kW energy output including electricity, heat, and cooling.
published: , 9|2019