Wednesday, April 24, 2013

Bag Job

Cherry picking is a econometric sport, and figuring out the cost of things is often not as simple as a bunny might wish.  Brian had a few posts on fluoridation discussing the fact that there are not only pros, but also cons, and coming to the conclusion that on balance, and with care in application, the pros win.  Eli's attention was drawn to the question of are non-reusable or reusable bags better, and if so which sort and on what basis.  This, as Eli said, is not as straightforward as a bunny might wish.

There is an obvious part of the answer, the more times a bag is used, the cheaper it is, but how many more times is a good question and what are the problems with reusing a bag is another.

The last has an interesting answer, if you put meat, fish, and milk products into a bag, you have to worry about bacteria, and some of the bacteria, E. coli, for example can be nasty.  Well, you can wash the bags (something Eli has never done, but might start) and doing so reduces the risk of contamination, but increases the amount of water and electricity used.

So what is a Rabett to do?  Well Google is a friend and a quick search turned up Life Cycle Assessment of Reusable and Single-use Plastic Bags in California by Joseph Greene from Cal State Chico.  Besides his own life cycle analysis, Greene presents the results of several others, which pretty much agree with his, each within their own limits. 

The first step is to figure out what bags one is talking about and how to compare them.  On the non-reusable side the running is pretty much made by High Density Polyethylene (HDPE) and paper, on the reusable side we got woven Low Density Polyethylene (LDPE) and non-woven polypropylene (PP) and cotton.  To compare all of these, the general agreement is to look to carrying capacity, in which case you need about 1500 HDPE bags to carry about the same amount as 1000 of the others.  Of course, HDPE, bags being very thin often spill the carrots.

Impact indicator
1500
HDPE single- use
bag
1000
Reusab le PP non-
woven
single- use
1000
Reusable
PP non- woven 8
times
1000
Reusable
PP non- woven 52
times
1000
Reusable LLDPE bag with
40% PCR
single- use
1000
Reusable LLDPE with 40%
PCR bag
8 times
1000
Reusable LLDPE with 40%
PCR bag
52 times
1000
Paper bag
single
-use
Non-renewable energy, GJ
763
3736
467
72
2945
368
57
2620
GHG emissions, CO2 eq
0.04
0.262
0.033
0.005
0.182
0.023
0.003
0.08
Solid Waste, kg
7.0
34.3
4.29
0.7
34.1
4.3
0.7
34
Fresh water consumption, gal
58
426
85
216
250
40
57
1000
Mass, g
6
42
42
42
44
44
44
52


The amount of water includes that used in washing and manufacture.

While the number of times a bag is used is the major issue, such things as the amount of recycled materials, the cost of disposal, the cost of transportation,  biodegradeability, litter and the effects on fauna and flora are also significant in any decision to tax or eliminate different types of bags. It turns out that  cotton or canvas bags are not a good choice because of their weight and the energy needed to grow the cotton and make the bags.  HDPE bags can be recycled and, with a bit of luck, used one or two times, in Eli's experience maybe 1.5 (breaks the other .5). 

So, on balance, multiple use woven bags made from LDPE with 40% recycled polyethylene are the best choice.

13 comments:

bill said...

I live in a state - South Australia - that not only pioneered container deposit legislation (initially 5c, currently 10c; we have the cleanest roadsides in the country - by a mile! - but the other states are still in the dark ages due to packaging and retail industry alarmism), but a couple of years back we also banned single-use plastic shopping bags!

That was in '08, the '12 review results are available here.

Now the state government tended to only look at the - considerable and positive - impact on the waste stream, but the ACT government bought a similar ban in in 2011, and their review in November 2012 tackled the other greenhouse and environmental factors, including citing a major study from the UK, and they concluded that the woven plastic reuseable bags adopted in Australia were indeed the least-impact technology.

These box-construction bags with a plastic bottom 'stiffener' insert are bloody handy for transporting gear when car, or even bike, camping, I might add. Everyone uses them!

PS - Scrotum rides again...

bill said...

D'oh! ACT Government Plastic Bag Ban review report.

bill said...

What the?! I give up - I have no idea why that link gets referred back here to blogger; ah, it doesn't have the magic url prefix, does it? So it's either here, or here it is ready for the old Ctrl+C Ctrl+V shuffle:

www.environment.act.gov.au/__data/assets/pdf_file/0004/260752/12-26082_Plastic_bag_review_report.pdf

Brian said...

Reuseables do better than I thought. I had heard a figure of about 30 reuses to make them better. Maybe that was cotton.

And of course there's the issue of clogging creeks and mucking up the ocean food web.

Anonymous said...

And then, of course, there are the bottles.

Gazillions of them, especially all those plastic water bottles.

And only ten of the states have bottle bills , which really DO make a huge difference, between 30% and 70% recycled.

That is how far we have not come in recent decades and does not bode well for the future.

We have been having these conversations about bags and bottle laws FOREVER.

These things (whether to use multiuse bags or throwaways and whether to recycle bottle and cans) are really no brainers. You don't need a detailed "analysis" to figure them out.

By and large, we are a country of people who like to talk (and blog), but that's about it.

PS: if you live in a state that does not have a bottle law, you share responsibility for getting one passed.

~@:>

Anonymous said...

I have to echo and emphasis Brian's point about plastics.

Not included in the energetic cost is the environmental cost, which is wide-ranging and complex. I could wax lyrical about it, but it's easier to link to:

http://www.jenniferlavers.org/plastic-pollution/

Entanglement, suffocation, gut impaction, chemical adsorption and concentration... there are many ways that plactics and the environment do not mix. If we followed the 'seven generations' philosophy, we'd probably be much more steam punk than melamine-and-styrene.


Bernard J.

[I think, therefore I am not a robot.

QED]

Anonymous said...

Plastic bags and bottle are just the tip of the iceberg.

Here's an uplifting video about the environmental impacts of plastic.

We are literally choking the life out of the planet.

~@:>

Hank Roberts said...

> ... what bags one is talking about
> ...
> So ...

Mmmm, I'll wait to see how may of -those- show up in the category of "what bags one is talking about" -- which would be:

snagged on bushes around every hight water line.

Watch that space, in a year or two or ten, and see how fast that stuff shows up, while the blooming plastic harvest we get now diminishes.

Look at we get now, any creekbank after high water accumulates plastic bags like dandruff.

Anonymous said...

Further to the video mentioned at 25/4/13 7:40 AM, there are a number of other documentaries about this not-so-sleeping problem:

http://www.plasticoceans.net/the-documentary/

http://www.plasticizedthemovie.com/

http://www.intothegyre.com/

http://www.crypticmoth.com/plastic.php

http://www.javafilms.fr/spip.php?article268

I'd say "enjoy" but there's really nothing to enjoy about the message embodied by these productions...


Bernard J.


[I think, therefore I am not a robot.

QED]

Anonymous said...

If only Mr. McGuire in the movie "The Graduate" had said "Hemp!" instead of "Plastics!" we wouldn't even be having this conversation.

~@:>

Anonymous said...

Wow, I've been recycling plastic bottles ever since there were deposits on them, and return the plastic bags I occasionally get to the recycling container at the store. I use paper bags multiple times until they tear or the handles wear off.

My main complaint about reusables is most are not as tall as a paper bag. The few that are I could only buy online, and were much more expensive.

Anonymous said...

And when the LDPE bags' carrying days are over we fill'em with straw and compost and grow potatoes in them.

one_iota

Angliss said...

What about canvass bags? I prefer those because they're stronger, hurt my hands less to carry, and they don't disintegrate in the sun and heat of my car.