When we think of compost, we usually imagine the pile in the backyard, dedicated composting facility, or the use of it. Unless we know the industry, we rarely think of utilizing compost in landfills.
And, many people compost because they don’t want their solid wastes end up in landfills and damage the environment.
However, a new study from North Carolina State University may change our perception. It finds that there can be significant environmental benefits associated with using compost at landfills.
Corresponding author James Levis said, “There are an increasing number of composting programs out there, and many of them are required to use the resulting compost ‘beneficially’,
“A lot of state and local regulations don’t recognize ‘alternative daily cover’ as a beneficial use. But our work shows that using compost as alternative daily cover at landfills is competitive, and often superior, to the use of compost as a soil amendment in terms of its environmental benefits.”
So far, landfills have applied a layer of daily cover each day. They do that to reduce odors, win-blown debris, and keep vermin out. US Federal regulations currently require six inches of soil as a daily cover.
Most of USA’s yard waste has become compost. A small but rapidly growing percentage of its food waste is in the compost too. However, compost from food waste often contains broken glass and other contaminants. That makes it unsuitable for composting and amending gardens or agricultural fields.
Removing contaminants using technologies is feasible and available, but the cost of composting will increase. Also, there is not always a sufficient local market for all of the available compost.
Using compost on landfills
With his collaborators, Levis wanted to know if it’s environmentally beneficial to use compost as a daily cover replacement. He also wants to know if the benefits are comparable to the benefits of using compost to amend soil.
Therefore, the researchers made a complex computational model. It predicted the overall environmental impact of two defined cases: the use of compost to amend soil and as a daily cover in landfills.
The model ran simulations evaluating the entire life cycle of each case. For instance, they looked at greenhouse gases from the compost. Not only that, they also looked at emissions from the equipment that applies compost at landfill facilities as well.
Simulations from the model also accounted for decreases in emissions. For example, reduced emissions related to fertilizer use when growers use compost in their soil instead of conventional fertilizers.
There are 5 environmental impacts that the model looked at. First, global warming potential or warming effect that the greenhouse gases released in the two cases.
Second, acidification. It looked at the extent to which each case contributes to acidification of the hydrological system like acid rain. Third, eutrophication, meaning the amount of nutrients released to ground and surface water by each case.
Fourth, cumulative energy demand. The model looked at the amount of fossil fuel resources that each case needs and offsets.
Fifth, abiotic resource depletion potential. It means the amount of any non-biological, non-renewable resource that each case needs to perform and the amount that each case can offset. For example, phosphorus in compost reduces the need for mined phosphorus in fertilizers.
Simulations and findings
The researchers ran a range of simulations. The purpose is to account for both uncertainty and the wide variety of different circumstances.
They found that using compost as daily cover outperformed its use as a soil amendment in almost 100% of the simulations. Additionally, daily cover also did more to reduce acidification in 77% of simulations and reduced global warming potential 63% of the time.
On the other hand, soil amendment was better at limiting abiotic resource depletion potential in 96% of the simulations. Also, it was better in terms of cumulative energy demand about 94% of the time, primarily due to the reduction of peat use.
First author Mojtaba Sardarmehni said, “ur work also highlights the circumstances that make one process more environmentally attractive than the other,
“For example, our work shows which variables are relevant when determining whether using compost as daily cover in a landfill will reduce global warming potential, as compared to using compost to amend soil.”
Levis added, “We are not suggesting that compost should necessarily be used as alternative daily cover instead of to amend soil. But we think this work highlights the fact that there are environmental benefits associated with using compost as daily cover at landfills—and we need decision-makers to consider that.”
Airborne bacteria from burning and burying garbage
Maybe landfill facilities should use compost as a daily cover soon. New finding states that this could be problematic for us humans.
Trash in municipal solid waste usually includes plastic, food scraps, lawn clippings, and other things that go into garbage bins and don’t get recycled. Most facilities bury or incinerate this type waste.
May seem okay, but researchers show that this method of disposal can lead to disadvantageous effect. Turns out, municipal solid waste can be an important source of antibiotic-resistance genes in the air.
How does this happen? Well for one, residual antibiotics from discarded medications and other products can end up in municipal solid waste. So, some microbes in the garbage are resistant to those antibiotics. They can spread those resistance genes to other bacteria, allowing them to survive in the presence of these drugs.
Scientists hadn’t studied about the waste treatment through incineration or landfilling. That is, they hadn’t examined if waste treatment releases these bacteria and genes into the air where animals and humans can inhale them.
Sampling and analyzing
The researchers wanted to investigate the bacterial community. They also wanted to find out about associated antibiotic-resistance genes in the municipal solid waste treatment system of Changzhou, China.
So Yi Luo, Xiangdong Li, and colleagues collected air samples from several locations. They took air from a landfill site, a municipal solid waste incinerator, and two transfer stations where they deliver and process garbage.
Air from municipal incinerator and landfill site had higher levels of particulate matter and bacteria. Meanwhile, upwind locations had less of them. The team identified 16 antibiotic-resistance genes in the air samples and tracked their source to municipal solid waste and leachate in the system.
Unsurprisingly, the genes were a lot more in air downwind from the facilities than upwind.
Consequently, the results suggest that municipal solid waste treatment systems could be a source of antibiotic resistance genes. Since it’s airborne, it can transmit easily to nearby residents or animals who breathe the air.