Solving a friendly dispute re dog poo bags.
December 7, 2010 9:48 AM   Subscribe

Who is the greenest of them all? Solving a friendly dispute re dog poo bags.

My significant other and I have two dogs together. We are having a friendly dispute about dog poo bags and being green. We have two dogs together. We live in a city, San Francisco, that has banned plastic bags in most stores.

My view: In our jurisdiction, dog poo picked up by urban dog owners using plastic bags goes into regular garbage aka landfill. Therefore it is not essential to purchase biodegradable dog poo bags. It is okay to use any type of plastic bag, and okay to buy and use non-biodegradable dog poo bags. And, best to use a plastic bag that has already been created -- e.g. a plastic bag from a loaf of bread, a plastic bag from a store. Buying a box or roll of dog poo bags is okay, but better to use a bag that already exists so as not to "waste" the energy creating new bags.

Her view: A person shouldn't use the plastic grocery bags to pick up poo. The plastic grocery bags should be returned to the grocery stores for them to deal with via their recycling program. A plastic bag that is already destined for landfill -- that is not eligible to be brought back to a store's recycling program -- can be used to pick up dog poo. And, when buying dog poo bags, best to buy biodegradable bags, as this is better for the landfill situation.

My reply: I'm not sure how effective those grocery store plastic bag "return here" programs are -- it seems better for me to just immediately re-use the bag for dog poo. Also now that SF has banned plastic bags I'm not sure if there's an easy place to return plastic grocery bags (though honestly I have not really looked).

Disclaimers: This is totally non-important, but we've been going back and forth, and it seemed fun to see what AskMe had to say. Also, my side has more "ink" here -- I tried to get my SO to write her side but she told me to write it.
posted by ClaudiaCenter to Science & Nature (23 answers total) 4 users marked this as a favorite
I'm no expert but I think I agree with you. I doubt a grocery store plastic bag can be recycled effectively enough to make up for the creation of a whole new bag for poo.
posted by ghharr at 9:53 AM on December 7, 2010

Datapoint: the Castro Safeway still has a bin for plastic bag recycling.

I would tend to side with you, though.
posted by needs more cowbell at 9:59 AM on December 7, 2010

Re-using is always better than recycling, and re-using is always manifestly better than buying new. Nothing biodegrades in the landfills of today, they are plastic-lined anaerobic cells.

Her view would win hands-down if the dog poo were being composted, but as it's not, reusing old bags that were already created and used for something else saves the energy of making a new (biodegradable) bag.
posted by ldthomps at 10:00 AM on December 7, 2010 [2 favorites]

regular garbage aka landfill

Things that are biodegradeable will biodegrade within landfills, too. It may take longer, it may not be as "green" as recycling. But it's not an either/or proposition.

IMO, use the plastic bags after you have used them to carry home groceries and then toss them.

* You're using the bag twice. Score!
* They will biodegrade.
* Recycling centers are not set up well to handle animal waste; it's not their purpose.
posted by Cool Papa Bell at 10:00 AM on December 7, 2010

I see it like this:

If you're recycling one bag, and making another bag, that's two extra energy expenditures that don't occur if you just use the bag you were going to recycle. The waste problem is the inverse problem though, as eventually with the recycle and buy a bag, there's no waste at all (one bag recycles, the other bag degrades, and so does the poop), and with the use the bag you have option, there's a ratty bag that may never break down.

I guess if you can justify the extra energy expenditure to save the bag, that's cool and all, but I'd rather just trash the bag I had.
posted by deezil at 10:01 AM on December 7, 2010

I think both of your points have merit, but working only within the scenario you painted, I think reusing plastic bags is better than buying new biodegradable ones. I agree that in our effort to live greenly, it is important that consider not only the material itself, but the (energy) cost of production and transportation. However, if you didn't have plastic bags lying around to begin with, using biodegradable bags is probably better because they'll still degrade faster in the landfill. I know this isn't what you're asking, but a better solution might be to minimizing getting any plastic bags at all by carrying your own canvas bags, and then using biodegradable poo bags.
posted by lacedcoffee at 10:10 AM on December 7, 2010

Yeah, we don't have many plastic grocery bags lying around anymore, due to the bag ban and our using canvas bags. But we have a few.

I also reuse zip lock plastic bags that seem too skanky for food re-use. Don't know if those can be recycled or how they affect landfill.

From SO: I guess the question is the harm caused by sending to landfill a non-biodegradable bag that could potentially be recycled versus the harm/pollution/byproducts caused by the manufacturing of the biodegradable/compostable dog poo bags.
posted by ClaudiaCenter at 10:24 AM on December 7, 2010

There's a reason the old rallying cry is "Reduce, Reuse, Recycle" is in the order it is. They represent a "best-better-good" relationship. Reducing is preferable to re-using which is in turn preferable to recycling.

Well, generally at least. I don't have any grasp on the science behind this specific question, which would be interesting to see. It would seem the benefit numbers for the shopping bag recycling would need to be outstandingly high to make up manufacturing new bags though.

We use canvas grocery bags pretty extensively in our house, but still accumulate plenty of bread bags, newspaper sleeves and whatnot to handle our dog's doo.
posted by Dano St at 10:32 AM on December 7, 2010

The "simple" solution is not to send the bag to the landfill after one use, no matter what bag you use - flush the waste, wash the bag (in toilet water) and reuse/recycle it.
posted by muddgirl at 10:33 AM on December 7, 2010

Not so simple, muddgirl! Water treatment has a pretty high energy cost--15% of total energy consumption of the state of California. Assuming non-green sources, that might have a higher environmental impact than disposing of a used bag. It all gets pretty complicated...
posted by hydrophonic at 10:58 AM on December 7, 2010

Well, for one, it depends on how much embodied energy is in the new, biodegradable bags you're buying. The plastic bags have been made once and used twice (minimum). The biodegradable bags are used once. As long as the energy used to make them is half or less of the plastic bag, you've used the same or less resources. From a (year) 2000 article, that may not be the case, but hopefully things have changed:
"In our most recent study, completed this past spring, we and our colleagues found that making one kilogram of PHA from genetically modified corn plants would require about 300 percent more energy than the 29 megajoules needed to manufacture an equal amount of fossil fuel-based polyethylene (PE). To our disappointment, the benefit of using corn instead of oil as a raw material could not offset this substantially higher energy demand. "

They both go in the landfill, and either the biodegradable bag doesn't degrade (which is what I tend to believe about landfill, as they are generally jammed so tightly with stuff that there is little oxygen or water,and few decomposing microorganisms of either the aerobic or anaerobic variety), or it does and releases greenhouse gasses. Plus feedstocks (resources) for making biodegradable materials use land that could be used for growing food, or require land that once was habitat. So I would go with re-using plastic bags if you have enough of them. That could change if dog waste in compostable bags goes into a biogas generator. Some municipalities are starting to look into these.
posted by oneirodynia at 11:01 AM on December 7, 2010

Will flushing dog waste significantly contribute to one family's use of water treatment? I suspect if they are using the "if it's yellow, let it mellow" technique and are conscientious about multiple-stage poops, it will not impact a family waste water budge the way it impacts their plastic bag budget.
posted by muddgirl at 11:03 AM on December 7, 2010

Things that are biodegradeable will biodegrade within landfills, too. It may take longer, it may not be as "green" as recycling. But it's not an either/or proposition.

No, but it's worth considering the fact that when discussing plastic bags "biodegradable" should be in scare quotes. Their breakdown is dependent on sun & other elements abrading them; I'd wager the difference between them and "non-degradable" bags when sealed in a claypit is minimal.

I believe, mudgirl, that hydrophonic's point is the introduction of more solid waste into the waste processing system than would otherwise have been added.

I suspect that the largest impact you will have here will be in the "reduce" portion of things. The energy & material investment involved in creating a roll of bags will always pale in comparison to the energy costs involved in packaging, handling & shipping. You would probably have a bigger impact using the most recycle-unfriendly bags you could lay your hands on if you simply avoid purchasing another consumer good you otherwise would not have.
posted by phearlez at 11:16 AM on December 7, 2010

I'm with the camp that says reusing bags is the best option. Most things you have to buy are non-green. Not buying stuff is generally greener.

Another option. Take newspaper, pick up poo, fold neatly and deposit in bin. (Dog poo and newspaper can be composted, but the compost generally should not be used on food.)
posted by Mom at 11:47 AM on December 7, 2010

The costs of landfilling the dog crap moot the difference between your differing plastic bag regimes. Your share of having the refuse collected, driven around town, barged across the bay to Oakland, loaded onto railcars, pulled 130 miles to Yuba County, and then unloaded is much, much greater than any savings that you might incur using one or the other of your plastic bag regimes.

Right now, San Francisco is nearing the end of a contract that landfills its refuse in the Altamont landfill, in Alameda County. It's been trucking the city refuse to that landfill for 30 years. The upside is that the methane from that landfill powers a fleet of 350 garbage trucks (by fueling their engines!). The downside is that those trucks do not operate in San Francisco. Recology states that they are using b-20 biodiesel in their collection and transfer trucks, and have a handful (about 13 out of 385 vehicles) running on liquified natural gas.
posted by the Real Dan at 11:49 AM on December 7, 2010

I asked this question previously re: kitty litter disposal and got some interesting answers.
posted by analog at 12:11 PM on December 7, 2010

Greenest scenario I can think of is to bring along a little digging tool and bury the poo when possible. I'm not sure if that's legal or not.
posted by Bonzai at 12:29 PM on December 7, 2010

I don't clean up my dogs business. Its going to degrade far faster if left out in the open air then putting it in to a wasteful plastic container that prevents it from decomposing properly.
posted by ShootTheMoon at 1:19 PM on December 7, 2010

I don't clean up my dogs business. Its going to degrade far faster if left out in the open air then putting it in to a wasteful plastic container that prevents it from decomposing properly.
According to recent research, non-human waste represents a significant source of bacterial contamination in urban watersheds. Genetic studies by Alderiso et al. (1996) and Trial et al. (1993) both concluded that 95 percent of the fecal coliform found in urban stormwater was of non-human origin. Bacterial source tracking studies in a watershed in the Seattle, Washington area also found that nearly 20% of the bacteria isolates that could be matched with host animals were matched with dogs. This bacteria can pose health risks to humans and other animals, and result in the spread of disease. It has been estimated that for watersheds of up to twenty-square miles draining to small coastal bays, two to three days of droppings from a population of about 100 dogs would contribute enough bacteria and nutrients to temporarily close a bay to swimming and shellfishing (US EPA, 1993).
There is a reason we pay the high cost of treating dirty water before returning it to our water system.
posted by muddgirl at 1:25 PM on December 7, 2010 [1 favorite]

Can you not compost dog waste? I can't find a clear answer from my garbage service's website... seems like something that they should address.
posted by jeffamaphone at 1:30 PM on December 7, 2010

Just to be clear, we are not permitted to put dog poo, whether in newspaper or compostable bags, in the general San Francisco green bin composting system.

There has been periodic buzz about setting up dog poo composters at dog parks in San Francisco, but I have never actually seen one. That sounds like the best option, once it's available.
posted by ClaudiaCenter at 1:31 PM on December 7, 2010

There are dog poop bags specifically designed for flushing. They make a compelling argument for that approach on the Flush Doggy web site.

Another possibility for people with a yard is the Doggie Dooley, which is sort of a mini septic tank for dog poop.

I've never used the flushable bags, but I used to have a doggie dooley and it worked surprisingly well. I suspect that either one of these methods would be better than sending the poop to landfill -- even if it's in a biodegradable bag.
posted by rhartong at 2:00 PM on December 7, 2010

Can you not compost dog waste? I can't find a clear answer from my garbage service's website... seems like something that they should address.

Not really. Ensuring that all the pathogens are killed would require pretty careful monitoring of the compost pile temperature.

The plans for a DIY composter are really for something more like a septic tank, which probably isn't a great idea either. Depending on the permeability of your soil, location of the water table and whether there's nearby bodies of water, you still risk contaminating ground- or surface water.

Muddgirl has the right idea. Use the wastewater treatment system for what it's designed.
posted by electroboy at 11:09 AM on January 4, 2011

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