Review Reports

Round 1

Reviewer 1 Report

Congratulations!

The experiment is quite 'simple' but soundness.

I suggest you to reorder the paper's parts to met the usual format: Introduction; Material and Methods; Results; Discussion; Conclusions; Appendix

Author Response

I suggest you to reorder the paper's parts to met the usual format: Introduction; Material and Methods; Results; Discussion; Conclusions; Appendix
Response: We have now rearranged the order so that Materials and Methods comes between the introduction and the Results.

Reviewer 2 Report

Dear Authors,

Firstly let me congratulate you for the effort in putting this study together, it is well presented and easy to follow although the paper is not logically structured. Also, the study was not conducted with rigor and there are important areas you overlooked in the study that undermines its contributions and these should be addressed for your effort to be appreciated.

The title is misleading and does not align with the scheme that was investigated. Using "optical" connotes a technological approach rather than mere colored plastic bags. The title should be changed to reflect the actual scheme.

The materials/methods should come before the results and discussion to improve the fluidity of your narratives.

Also, you should present a brief overview of why the study or the introduction of colored bags is necessary for the city of Kalmar. You can do this by describing the waste recycling/collection performance prior to the introduction of the plastic bags and baseline that performance as a basis for this study. Also, what was the scheme before the colored bags were introduced and how effective is it? I don't see any justification for the study but you need to convince your audience about the need for this study and why it is important.

I want to see a clarity in your methodology including the data collection and analysis approaches. You presented that the optical sorting was introduced in 2014 and yet you conducted a pre-measurement test in 2018, you should reconcile this discrepancy. Why 38 apartments or 2 properties in the whole city for the scheme? If the data were not collected at the point of waste generation, how did you monitor the waste from each property to the recycling center? How confident are you that waste from other properties have not been mixed together? Were the colored plastic bags introduced purposely for this study and how did you monitor the experiment for the period of 4 weeks. All these should be detailed in your study. How many residents did you interviews, how did you select them and what was their experience?

The findings of the interviews should be included in the paper to provide a robust argument about the efficacy of the colored plastic bags in enhancing sorting. 

Author Response

Firstly let me congratulate you for the effort in putting this study together, it is well presented and easy to follow although the paper is not logically structured. Also, the study was not conducted with rigor and there are important areas you overlooked in the study that undermines its contributions and these should be addressed for your effort to be appreciated.
Response: Thank you for the comment!

The title is misleading and does not align with the scheme that was investigated. Using "optical" connotes a technological approach rather than mere colored plastic bags. The title should be changed to reflect the actual scheme.
Response: The title has been changed to “Colored plastic bags for kerbside collection of waste from households – to improve waste recycling”

The materials/methods should come before the results and discussion to improve the fluidity of your narratives.
Response:  We have now rearranged the order so that Materials and Methods comes between the introduction and the Results. We have seen that other articles in Recycling have it in this order.

Also, you should present a brief overview of why the study or the introduction of colored bags is necessary for the city of Kalmar. You can do this by describing the waste recycling/collection performance prior to the introduction of the plastic bags and baseline that performance as a basis for this study. Also, what was the scheme before the colored bags were introduced and how effective is it? I don't see any justification for the study but you need to convince your audience about the need for this study and why it is important.
Resonse: Regarding the necessity specifically for Kalmar, this city has – as all cities with old dense city centers – an infrastructural problem this is firstly described in the last section of the introduction, and then further elaborated on in the method section, where Kalmar is described. Text has been added about the waste collection prior to our study under Materials and Methods (starting with “The lack of space leads to…”). Also text has been added about the lack of studies of the efficiency of waste handling. Also the following section starting with “in Kalmar, optical sorting…” describes the situation as it is/was before our test with introducing bags of additional colors (the green ones have been around since 2014). The data of the pre-measurement phase gives data about the performance, before the test.

I want to see a clarity in your methodology including the data collection and analysis approaches. You presented that the optical sorting was introduced in 2014 and yet you conducted a pre-measurement test in 2018, you should reconcile this discrepancy. Why 38 apartments or 2 properties in the whole city for the scheme? If the data were not collected at the point of waste generation, how did you monitor the waste from each property to the recycling center? How confident are you that waste from other properties have not been mixed together? Were the colored plastic bags introduced purposely for this study and how did you monitor the experiment for the period of 4 weeks. All these should be detailed in your study.
Response:

It was only for food waste optical sorting was introduced in 2014, which was also originally written in the text. However, for clarity, we removed the subordinate clause saying that “,and the use of the system has increased to larger areas”, as this may have been confusing. Further, it is now included in the text that the test was to introduce additional colored bags along with the green ones.

We agree that 38 apartments in two properties constitute a very low sample number which obviously contributes with much uncertainty. However, this was a small pilot study with a budget that did not allow for more.

Regarding the monitoring of waste from each property we have added a sentence that ”All the practical work was carried out in collaboration with the local waste collection company (KSRR) who developed routines for safeguarding that waste from the test properties was kept separated from waste from other properties” and “During the four weeks of sorting (mid-April–mid-May 2018) in colored bags, KSRR collected the waste bags from the properties in marked bins 3 times per week and drove them to a separate space at the recycling centre.”. The description on how we collected the waste has been elaborated.

How many residents did you interviews, how did you select them and what was their experience?The findings of the interviews should be included in the paper to provide a robust argument about the efficacy of the colored plastic bags in enhancing sorting. 
Response:We have now added in the method section that “….all participants were invited to individual  interviews, to evaluate their experience of the new system. As a result, 15 structured interviews were held face to face. One potential sampling issue is that those that said yes to participate in the interview might have been more positive towards using the system”. In addition, we have added a section, 3.3 Participant interviews, in the Results.

Reviewer 3 Report

Overall, the study in the manuscript could be of interest to readers of RECYCLING as optical sorting as a means of improving recycling rates is an emerging technology in the waste industry However I cannot recommend publication of this manuscript in its current form for the following reasons:

The title of the manuscript title is misleading, as there is no optical sorting involved in the study described in the manuscript...just manual sorting in colored plastic bags

The authors are using a mixture of referencing styles, eg name (year), and [6]. The format required by the journal should be used, with the reference number [X] etc at the end of the sentence. This means the work should be re written in the passive tense to avoid statements such as "according to [5]"

The Materials and methods section should be after introduction and before the results.

Line 40, should be very specific with units, eg 440kg per household per year

The manuscript should be proof read for English and grammar.

Line 88, reject phrase is reduced by, not reduced with 

Centre data in table 1 under column headings 

How were the combined numbers for P1 and P 2 pre-measure and sorting period calculated? 

There is more waste (kg/person/week) in sorting period....a better explanation is needed than simply saying there was more packaging in the sorted waste. 

Line 209, be specific about split between Male and female. Including statements such as "was about even" is not scientific.

Details are needed on waste weighing process....type of balance used, accuracy of the balance etc.

There is no reference to any contamination in coloured bags...did residents sort properly? Not necessarily true to say that "The study shows that when a system using coloured bags for kerbside collection of different waste fractions was introduced, the amount of residual waste decreased directly by 15%, and the amount of sorted food waste increased directly by 35%", as contamination does not seem to have been considered. 

No feedback on how easy or otherwise residents found the sorting experience and whether they would continue. 

No details are provided on whether all residents were equally aware and participated in the trial. 

No details are provided on how easy waste collectors found dealing with 7 different bags of waste compared to just two before. What about glass breakages ? Were the waste collectors interviewed for their views on how the system would operate?

In summary, the manuscript reads like an undergraduate study describing a very basic study, with limited scope and with a very limited an unscientific evaluation. 

Author Response

The title of the manuscript title is misleading, as there is no optical sorting involved in the study described in the manuscript...just manual sorting in colored plastic bags
Response: The title has been changed to “Coloured plastic bags for kerbside collection of waste from households – to improve waste recycling”

The authors are using a mixture of referencing styles, eg name (year), and [6]. The format required by the journal should be used, with the reference number [X] etc at the end of the sentence. This means the work should be re written in the passive tense to avoid statements such as "according to [5]"
Response: The references have been changed according to comment. However track-changes was not used when the reference numbers [X] were changed, I thought this would make it easier for the editors with EndNote.

The Materials and methods section should be after introduction and before the results.
Response: We have now rearranged the order so that Materials and Methods comes between the introduction and the Results. We have seen that other articles in Recycling have it in this order.

Line 40, should be very specific with units, eg 440kg per household per year
Response: Text has been changed, also for “180 kg”.

The manuscript should be proof read for English and grammar.
Response: It has been proof read. Also two of three reviewers were satisfied with the language and marked “English language and style are fine/minor spell check required”. Hence, minor changes in the text have been made according to comments from all reviewers.

Line 88, reject phrase is reduced by, not reduced with 
Response: In line 88 there is no work reduced. I assume you mean fell. Changed to fell by, instead of fell with. Made the same change for increase.

Centre data in table 1 under column headings 
Response: Changed according to comment.

How were the combined numbers for P1 and P 2 pre-measure and sorting period calculated?
Response: An average of the two was made. We start the Results section with “The results show that the average amount of residual waste was 2.90 kg/person/week (kg/p/w) in the pre-measurement period, and that the separated food waste amounted to on average 0.55 kg/p/w, see Table 1.“ which indicate that we present average amounts. We have also paid attention to more carefully writing “on average” when we present the results throughout the rest of the paper.

There is more waste (kg/person/week) in sorting period....a better explanation is needed than simply saying there was more packaging in the sorted waste.
Response: Some additional text has been added in section 3.2.

Line 209, be specific about split between Male and female. Including statements such as "was about even" is not scientific.
Response: Text about exact distribution between male and female in the properties has been added.

Details are needed on waste weighing process....type of balance used, accuracy of the balance etc.
There is no reference to any contamination in coloured bags...did residents sort properly?
Not necessarily true to say that "The study shows that when a system using coloured bags for kerbside collection of different waste fractions was introduced, the amount of residual waste decreased directly by 15%, and the amount of sorted food waste increased directly by 35%", as contamination does not seem to have been considered. 
Response: A clarification about the balance has been added in the Material and Methods section. A text has been added about potential missorting in Section 3.2.

No feedback on how easy or otherwise residents found the sorting experience and whether they would continue.
Response: We have added a new section (3.3) to highlight some of the findings from the interview study. Results show that it was positively received while there were still issues that came up.

No details are provided on whether all residents were equally aware and participated in the trial.
Response: All households were aware of the trial through direct communication and posters about the project in the waste room. We could not monitor the involvement in each household and the interviews afterward were with 15 households which had sorted. We did not measure the involvement within the households. This text has been added in Materials and Methods.

No details are provided on how easy waste collectors found dealing with 7 different bags of waste compared to just two before. What about glass breakages? Were the waste collectors interviewed for their views on how the system would operate?
Response: The waste collectors (KSRR) were involved in all the phases of the project, planning, operational and analysis. They were mentioned in the acknowledgment. Now new text has been added that they were involved in the process, also in the regular text. You have a point about the glass fraction, it is not certain in would have been included in a full scale study, also this has been added to the text.

In summary, the manuscript reads like an undergraduate study describing a very basic study, with limited scope and with a very limited an unscientific evaluation. 

Round 2

Reviewer 2 Report

I fail to understand why the qualitative aspect of the research was not discussed and included in great details especially in completing the experimental phase of the study. This would have enhanced the credibility of the study. Also, there is no sufficient gap between the pre-treatment phase and the actual experiment, and no clarity whether the system was discontinued after the pre-treatment and re-introduced at the start of the experiment to examine the participants/residents' behaviour. In addition, the conclusion is generally weak and failed to capture the implications of the study findings.

Author Response

I fail to understand why the qualitative aspect of the research was not discussed and included in great details especially in completing the experimental phase of the study. This would have enhanced the credibility of the study. Also, there is no sufficient gap between the pre-treatment phase and the actual experiment, and no clarity whether the system was discontinued after the pre-treatment and re-introduced at the start of the experiment to examine the participants/residents' behavior. In addition, the conclusion is generally weak and failed to capture the implications of the study findings.
Response: Thank you for your valuable comments (Thank you added now also in acknowledgement). We have further clarified the results of the interviews after the study (see 3.3). The study was pressed in time of financial reasons, the whole study from planning to completion had to be done quickly, that´s the reason for the design of the study. The pre-study was done with the waste handling present in the properties, before the project. We had difficulty to grasp what type of changes you wanted in the conclusion unfortunately. A few changes about the description of the study design has been made in the article. Also, manuscript has in full been proof read again for English by another person, se track changes (by EvaTofvesson Redz).

Reviewer 3 Report

While a number of improvements have been made to the manuscript, I am still of the view that the study is insufficiently rigourous and at a very low scientific level to merit publication. It would really be more suitable as a conference publication. There are many gaps in the analysis as noted in my comments below.

References should be cited in order. Line 84 cites reference [35], which follows on from [19] on line 72.

Manuscript should be proof read for English. For example, line 88 is not grammatically correct and should be “Optical sorting of food waste into green bags has been in operation in Kalmar since 2014”. Furthermore, from what is being described here, the use of the term “optical sorting” ie putting food waste into a green bag, is misleading as this is not optical sorting.

Other examples where English should be corrected is line 96, Correct phrase is “in Kvarnholmen” and not “on Kvarnholmen”; Line 104, “There is no study….” Should be “There was no study…..”; Line 120 is not grammatically correct. The manuscript should be thoroughly proof read for grammar and spelling.

More details are needed on the type of balance used to measure the waste. Simply stating “with three decimal places” is not sufficiently scientific (line 110).

Line 114, the year should also be included.

It is still not clear from the description on line 122 to 124 how the eight different bags were collected, as the authors state there were marked bins, but no indication if a separate marked bin was needed for each different bag, i.e. eight marked bins?

Line 162 use of the term “probably brought” is not scientific. The authors should be able to pin point more accurately why the total amount of waste increased during the sorting period. The absence of such detail and understanding indicates the lack of rigour in the analysis. Another example of the lack of rigour is the use of the phrase on line 186 “most participants thought it worked well”. What is meant by the phrase “most” and what is meant by “worked well”. Both terms are very subjective and not at all scientific, despite the subsequent elaboration on lines 187 to 190.

The caption for Figure 1 is poorly formatted.

Lines 240 to 248 in the discussion should be rewritten as the use of referencing is not correct. Reference numbers should not be the subject of a sentence. Rather the sentences should be written in the passive tense, with the reference number at the end of the sentence (see lines 38-61 as an example of the correct way to write the material).

Reference [36] Brinkmann and Kvale (2015) is not cited in the manuscript and should be deleted from the reference list.

In light of the current world wide emphasis on the use of single use plastics, this project seems to require an exceptional amount of plastic bags. A note should be included in the manuscript about the long term sustainability of this practice.

Author Response

While a number of improvements have been made to the manuscript, I am still of the view that the study is insufficiently rigourous and at a very low scientific level to merit publication. It would really be more suitable as a conference publication. There are many gaps in the analysis as noted in my comments below.
Response: Noted.

References should be cited in order. Line 84 cites reference [35], which follows on from [19] on line 72.
Response: Sorry about this, it has now been changed.

Manuscript should be proof read for English. For example, line 88 is not grammatically correct and should be “Optical sorting of food waste into green bags has been in operation in Kalmar since 2014”. Furthermore, from what is being described here, the use of the term “optical sorting” ie putting food waste into a green bag, is misleading as this is not optical sorting.
Response: Green bags for food waste are sorted with optical sorting since 2014 in Kalmar, so the text is correct. That is why food waste in italic in the text to highlight that it is just the food waste that have been sorted optically so far. The system in place has capacity to sort more colors, that is why this study was valuable to perform, to test the influence with more colors.
Manuscript has in full been proof read again for English by another person, se track changes (by EvaTofvesson Redz).

Other examples where English should be corrected is line 96, Correct phrase is “in Kvarnholmen” and not “on Kvarnholmen”; Line 104, “There is no study….” Should be “There was no study…..”; Line 120 is not grammatically correct. The manuscript should be thoroughly proof read for grammar and spelling.
Response: Changes have been made according to comment. Manuscript has in full been proof read again for English by another person, se track changes (by EvaTofvesson Redz)

More details are needed on the type of balance used to measure the waste. Simply stating “with three decimal places” is not sufficiently scientific (line 110).
Resonse: Portable balances that deal with weights of several kilos are not the kind of high-precision instruments for which information about exact model add much more scientifically to a study – what is relevant, however, is the precision of the balance (decimal places) and that the same balance is used throughout the project. To address this comment we have, however, added information about the model in the manuscript.

Line 114, the year should also be included.
Response: Adjusted according to comment

It is still not clear from the description on line 122 to 124 how the eight different bags were collected, as the authors state there were marked bins, but no indication if a separate marked bin was needed for each different bag, i.e. eight marked bins?
Response: The different colored bags were put in the same bin and were sorted manually afterwards. Text has been added to clarify.

Line 162 use of the term “probably brought” is not scientific. The authors should be able to pin point more accurately why the total amount of waste increased during the sorting period. The absence of such detail and understanding indicates the lack of rigour in the analysis. Another example of the lack of rigour is the use of the phrase on line 186 “most participants thought it worked well”. What is meant by the phrase “most” and what is meant by “worked well”. Both terms are very subjective and not at all scientific, despite the subsequent elaboration on lines 187 to 190.
Response: We cannot change the design of the study. The purpose of the study was to compare residual waste and food waste during prestudy and test period with additional colored bags. The design of the study made that we could only compare the amount of residual waste and food waste in the prestudy and the test period. The amounts of packaging waste taken to recycling center during the prestudy is not known. Changes in the abstract has been made to clarify the purpose.
Changes have been made in text about the perception of the study (line 186 and onwards), now numerical values are given according to suggestion.

The caption for Figure 1 is poorly formatted.
Response: Sorry about this. Changed according to comment

Lines 240 to 248 in the discussion should be rewritten as the use of referencing is not correct. Reference numbers should not be the subject of a sentence. Rather the sentences should be written in the passive tense, with the reference number at the end of the sentence (see lines 38-61 as an example of the correct way to write the material).
Response: Sorry about this. Changed according to comment.

Reference [36] Brinkmann and Kvale (2015) is not cited in the manuscript and should be deleted from the reference list.
Response: Sorry about this. Changed according to comment.

In light of the current world wide emphasis on the use of single use plastics, this project seems to require an exceptional amount of plastic bags. A note should be included in the manuscript about the long term sustainability of this practice
Response: Valuable point! Text about this has been added in the discussion (just above Table 3), that the environmental benefit depends on the material in bags.

Thank you for your valuable comments, this is now added in the acknowledgment!