Analysis of Current Status and Regulatory Promotion for Incineration Bottom Ash Recycling in Taiwan

Round 1

Reviewer 1 Report

Conclusions

The paper lacks any significant conclusions

Author Response

Q1. The paper lacks any significant conclusions

Reply: As suggested by the reviewer, the significant findings have been added to the Conclusions. 

 

“Under the authorization of the Waste Management Act, the bottom ash derived from 24 large-scale MSW incineration plants with total design treatment capacity of around 8 million metric tons per year has been considered as one of “mandatory” recyclables by the Taiwan EPA for the production of recycled aggregate in the concrete and construction applications.  Regarding the trend analysis of operation performances for Taiwan’s MSW incineration plants over the past decade (2010-2019), it indicated an increased power generation, growing from 0.485 kWh/kg in 2010 to 0.530 kWh/kg in 2019.  In 2019, 2,738 GWh power was sold to the Taipower for electricity grid connection, gaining the income of about NT$ 5,089,383,000 (≈ US$ 172,520,000) at an average rate of 1.86 NT$/kWh (0.063 US$/kWh).  On the other hand, the ratios of IBA generation to incinerated refuse decreased from 17% to 14%.   It can be attributed to the increased operation efficiencies of MSW incineration plants by waste segregation, combustion upgradation and heat recovery revamping.

On 18 May 2020, the Taiwan EPA announced the revised regulation (“Management Methods of Municipal Solid Waste Incinerator Bottom Ash Recycling”), which was based on leaching scenarios and their control purposes when the recycled aggregate from IBA was used in the environment.  This approach by replacing natural mineral resources with recycled aggregate from IBA will gain both benefits by reducing the mining of non-renewable resources and saving the space of sanitary landfills.  More importantly, the regulation on IBA recycling will promote the supply chains of sustainable building materials, thus forming a special material flow under the circular economy policy in Taiwan.  However, the price of recycled aggregate from IBA is higher than unsustainably sourced raw materials in Taiwan.  We recommend the government to provide subsidies for deflating the price of recycled aggregate, so that its true value can be reflected in the price.  In addition, the government must take care to not only review the legislation, but to also conduct more stringent audits for IBA recycling treatment facilities across the country.”

Reviewer 2 Report

The paper shows novel findings that are important for environmental scientists. Using IBA is interesting which has a negative impact on the environment after incineration. The study needs some changes before publication.

The major problem of this paper is referencing which needs major changes. There are many references in which the access link is not given in the reference list. line 67: do not cite the many references like this. more than three is nit suggested. What is the source of Tabel 4?
Any update for the reference 28? is there any changes after the year 2007? How the authors missed this reference (Tsai, W. T. (2019). Promoting the circular economy via waste-to-power (WTP) in Taiwan. Resources, 8(2), 95.)? Please remove all the old references and replace them with the new ones. Every fact and statement needs references such as (lines 300-308 when you discussing related the resolution in any specific country).

The location of the sampling is not clear.

Figure 2: why the CA amount is too high? any reason for that? Add more explanation regarding Figure 2 in the text.

Why the heating rate is 10 in figure 1? is there any reason?

Figure 3 is your results or from the other sources?

What about the economic aspects of using IBA in these years (2010-2019)? Is the trend of income is increasing or decreasing?

The author's suggestion should be added and will be useful for the industries which have a direct and indirect connection with IBA.

 

Author Response

Q1. The major problem of this paper is referencing which needs major changes. There are many references in which the access link is not given in the reference list.  line 67: do not cite the many references like this.  more than three is nit suggested.  What is the source of Tabel 4?  Any update for the reference 28? is there any changes after the year 2007? How the authors missed this reference (Tsai, W. T. (2019). Promoting the circular economy via waste-to-power (WTP) in Taiwan.  Resources, 8(2), 95.)?  Please remove all the old references and replace them with the new ones.  Every fact and statement needs references such as (lines 300-308 when you discussing related the resolution in any specific country). 

Reply: As suggested by the reviewer, we removed all the old references and replaced them with the new ones. 

 

Q2. Regarding the IBA’s characteristics in the measurements, the following items should be clarified

• The location of the sampling is not clear.
• Figure 2: why the CA amount is too high? any reason for that? Add more explanation regarding Figure 2 in the text.
• Why the heating rate is 10 in figure 1? is there any reason?

Reply: The corresponding replies were given below:

• The IBA sample was obtained from the central Taiwan MSW incineration plant (Taichung City, Taiwan).
• The significant content of Ca in the IBA was due to the removal of acidic air pollutants (i.e., sulfur oxides and hydrogen chloride) by slurry lime addition.
• The heating rate at 10℃/min matched the TGA specifications and also simulated oven heating conditions.

 

Q3. Figure 3 is your results or from the other sources? 

Reply: The data in Figure 3 (i.e., Figure 1 in the revised manuscript) were calculated from the official database, which has been referred in the revised manuscript.

 

Q4. What about the economic aspects of using IBA in these years (2010-2019)? Is the trend of income is increasing or decreasing?

Reply: As IBA undergoes a rigorous treatment process before it can be recycled as construction materials, the price of IBA is higher than unsustainably sourced raw materials in Taiwan.  However, the market price of IBA doesn’t reflect the environmental benefits of recycled aggregates by saving sanitary landfill space and preventing the depletion of non-renewable resources.  

 

Q5. The author's suggestion should be added and will be useful for the industries which have a direct and indirect connection with IBA. 

Reply: As suggested by the reviewer, some suggestions have been added to the second paragraph of the Conclusions. 

“…………  However, the price of recycled aggregate from IBA is higher than unsustainably sourced raw materials in Taiwan.  We recommend the government to provide subsidies for deflating the price of recycled aggregate, so that its true value can be reflected in the price.  In addition, the government must take care to not only review the legislation, but to also conduct more stringent audits for IBA recycling treatment facilities across the country.”

Reviewer 3 Report

English use needs improvement bu a professional editor.

The paper must be restructured. The experimental part id you do not add a leaching test and a few other samples is useless and can be deleted.

Better organizing the information on IBA and their use in Taiwan can make a decent paper.

The information however must be better organized

Have also a look on the suggestions on the enclosed file

Comments for author File: Comments.pdf

Author Response

Q1. English use needs improvement by a professional editor (a look on the suggestions on the enclosed file). 

Reply: As suggested by the reviewer on the enclosed file, the paper has been clarified.  In addition, the rhetorical writings and English grammar in the revised manuscript have been carefully checked.

 

Q2. The paper must be restructured.  The experimental part id you do not add a leaching test and a few other samples are useless and can be deleted.

Reply: As suggested by the reviewer, the paper has been restructured for clarity.  Regarding the experimental part (including the findings), we incorporated it into the “Results and Discussion” concisely.

 

Q3. Better organizing the information on IBA and their use in Taiwan can make a decent paper.  The information however must be better organized.

Reply: As suggested by the reviewer, the information on IBA and their recycling percentage in Taiwan has been highlighted in Sec. 3.3.

Round 2

Reviewer 3 Report

I think English is still questionable.

In the introduction you must clarify the role of energy recovery and the concept of GHG relevant/non-relevant carbon. In addition the issue of the GHG landfill emissions must be introduced. Normally if MSW is not incinerated it is landfilled

Comments for author File: Comments.pdf

Author Response

Q1. Based on the enclosed file, you must clarify the role of energy recovery and the concept of GHG relevant/non-relevant carbon in the introduction.  In addition, the issue of the GHG landfill emissions must be introduced.  Normally if MSW is not incinerated it is landfilled

Reply: As suggested by the reviewer on the enclosed file, the first paragraph in the Introduction has been clarified.

 

“Besides recycling and reuse, incineration may be the most commonly used management option for the treatment of municipal solid waste (MSW) and industrial waste in the developed and developing countries [1].  The combustion process is not only proved as an effective way to reduce waste volume, but also provides an electricity or superheated steam by the heat exchange.  Therefore, the waste-to-energy (WTE) or energy recovery from MSW incineration plants has been considered as one of biomass energy sources.  Therefore, the emissions of greenhouse gases (GHG) from waste management have shown a string decrease due to the development of WTE and other recycling processes, especially in methane emissions from landfills [2-6].  On the other hand, MSW incineration can prevent groundwater and surface water pollution as compared to the waste disposed of in sanitary landfills.  However, it should be noted that MSW incineration plants require well-operated control systems for flue gas cleaning and residual ash (i.e., bottom ash and fly ash) treatment, which can contaminate the environment if not handled appropriately and efficiently [7-11].”

Author Response File: Author Response.doc