Incinerators and plastics in PH, 1

TRY BURNING all sorts of plastic. You’ll find out that most of them (except most notably PVCs) burning quickly and cleanly, with almost no smoke and no ash.

Why you might ask? It’s because plastics are mostly composed of carbon and hydrogen. They burn cleanly to produce carbon dioxide and water.

So why not just incinerate them? Sounds like a good idea. And it truly is. Plastics probably compose most of the hard-to-degrade material in garbage.

Yet…

The Philippines is the only country in the world to have an absolute ban on incinerators for waste disposal. This in spite of the pressing need to replace the ever-growing volumes of trash landfills.

What stupidity. Only in the Philippines.

Regarding heavy metals, these consist only a small part of wastes, and can be segregated away.

Again, if plastics are the main concern, consider that burning plastics mostly produce only carbon dioxide and water.

Lawmakers, please take note!

Specifically, look at the composition of plastics. (Based mainly on Wikipedia articles.)

1. Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene) – It is the most common plastic in use today.

Chemical formula: (C2H4)n

Polyethylene plastic contains only carbon and hydrogen. Burning it produces only carbon dioxide CO2 and water H2O.

Example: Plastic syringe. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, etc.). As of 2017, over 100 million tons of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.

Many kinds of polyethylene are known, with most having the chemical formula (C2H4)n. PE is usually a mixture of similar polymers of ethylene, with various values of n. It can be low-density or high-density: low-density polyethylene is extruded using high pressure (1000–5000 atm) and high temperature (520 kelvins), while high-density polyethylene is extruded using low pressure (6–7 atm) and low temperature (333–343 K). Polyethylene is usually thermoplastic, but it can be modified to become thermosetting instead, for example, in cross-linked polyethylene.

Polyethylene, like other synthetic plastics, is not readily biodegradable, and thus accumulates in landfills. However, there are a number of species of bacteria and animals that are able to degrade polyethylene.

In May 2008, Daniel Burd, a 16-year-old Canadian, won the Canada-Wide Science Fair in Ottawa after discovering that Pseudomonas fluorescens, with the help of Sphingomonas, can degrade over 40% of the weight of plastic bags within six weeks. He later guessed that it would be gone after six more weeks.

The thermophilic bacterium Brevibacillus borstelensis (strain 707) was isolated from a soil sample and found to use low-density polyethylene as a sole carbon source when incubated together at 50 °C. Biodegradation increased with time exposed to ultraviolet radiation.

Acinetobacter sp. 351 can degrade lower molecular-weight PE oligomers. When PE is subjected to thermo- and photo-oxidization, products including alkanes, alkenes, ketones, aldehydes, alcohols, carboxylic acid, keto-acids, dicarboxylic acids, lactones, and esters are released.

In 2014, Jun Yang, a Chinese researcher, discovered that Indian mealmoth larvae could metabolize polyethylene from observing that plastic bags at his home had small holes in them. Deducing that the hungry larvae must have digested the plastic somehow, he and his team analyzed their gut bacteria and found a few that could use plastic as their only carbon source. Not only could the bacteria from the guts of the Plodia interpunctella moth larvae metabolize polyethylene, they degraded it significantly, dropping its tensile strength by 50%, its mass by 10% and the molecular weights of its polymeric chains by 13%.

In 2017, researchers reported that the caterpillar of Galleria mellonella eats plastic garbage such as polyethylene. (To be continued)/PN