Microbes Can Save the World! Biocementation: Making the Mining Industry Greener with Microbes!

Good morning class! Welcome to another lecture on how we microbes can help the Giants fix the mess they have made of our home! It's no secret their mining industry isn't the greenest industry on the planet. They produce copious amounts of waste and are huge contributors to greenhouse gases, not to mention they have had their fair few environmental disasters in the past few years. But mines also supply the Giants with many of the things they love most. If it can't be grown in the ground, odds are it was mined.

According to Laura Cole at the BBC:

If you live in a middle-income country, every year you use roughly 17 tons of raw materials – equivalent to the weight of three elephants and twice as much as 20 years ago. For a person in a high-income country, it is 26 tons – or four and a half elephants' worth.

So, while mining may be highly toxic to the earth, it's a process the Giants cannot live without. However, because it is a huge global industry, a little solution can go a long way. Let's talk about cement, which is a powder of alumina, silica, lime, iron oxide, and magnesium oxide - all of which have to be mined - burned together in a kiln and finely pulverized and used as an ingredient of mortar and concrete. It is used to bind materials together and form structures that the Giants construct to live and work in, drive on and many other uses. Raw materials employed in the manufacture of cement are extracted by quarrying in the case of hard rocks such as limestones, slates, and some shales, with the aid of blasting when necessary. Some deposits are mined by underground methods. Softer rocks such as chalk and clay can be dug directly by excavators. All of this mining causes damage and waste that are contributing to the destruction of our planet. But we microbes can once again come to the rescue!

And today we will highlight our 'little' solution, actually microscopic, it is called biocementation, which is the process of using microbes to create cement which can help make the mining industry greener! This process is sometimes referred to as microbial induced (calcium) carbonate precipitation or MICP.

Wait what?? We can do that?

That's right Anna. There is so much diversity within our microbial world, there are even microbes that can create cement.

I don't get it? What the petri dish is what ever you just said?

Excellent Question Psydney but before we get into how they do it. Let me tell you about some of our microbial friends that can do it!

Which Microbes Can Contribute to MICP?

There are 4 main groups of bacteria that are capable of this process. There are cyanobacteria and algae which are photosynthetic organisms. As an added bonus, these microbes can also convert CO2 into oxygen, just

like plants. So not only can they help create biocement but they can reduce greenhouse gases.

Another group of bacteria that can contribute to microbially induced carbonate precipitation is sulfate-reducing bacteria. A third group is microbes that are involved in denitrification. As the name suggests, these microbes are important contributors to other earth-balancing cycles like the carbon, sulfur, and nitrogen cycles.

One of the most popular groups for MICP is urealytic bacteria. These microbes have a special tool called the urease enzyme that helps them in forming the biocement.

While there are many more of us than the giants have found that have this special superpower, there are a handful that the Giants frequently study for use in biocementation including:

• Pseudomonas

• Sporosarcina

• Bacillus

• Myxococcus

• Halomonas

• Thalassospira

• Lysinibacillus

• Sphigopyxis

But I don't get it? What do the giants need so much cement for? Is this even useful?

Ah-ha! Good thinking Larry! Everything must have a purpose. So let me tell you some of the ways the giants are partnering with our microbial world to help heal the earth!

Uses Of MICP

Anywhere there is a wall that needs to remain unbroken is a place that MICP can be used. Walls are not limited to the Giants'-made structures that box them in at night. No, walls can be many different types of environmental surfaces that can protect and contain all kinds of things! For example, in mines where they dig into the earth to extract materials, they might store all the waste generated in a big pond and the giants will create a dam, a cement wall, to contain it. Portland cement, the most commonly used cement type, is the current standard for closing off mining and contaminated sites from disturbing ecosystems. The irony however is that about 10% of the total anthropogenic CO2, which is causing so many environmental issues, is due to cement production! This is a prime area the Giants can use MICP biocement to reduce environmental impacts. But there are many other areas as well including:

• Riverbank erosion

• Soil erosion

• Beach erosion

• CO2 sequestration (CO2 capturing)

• Restoring old monuments

But what about my question. What the petri dish are we talking about?!?

Right, yes let's talk about the MICP process.

The MICP Process

While I told you there are four groups of microbes that can do this. Let's discuss how one of these groups actually does this. Let's talk about ureolytic microbes.

These microbes have an enzyme called Urease which breaks down urea, forming carbonate and ammonium. Now calcium ions can react to this to form calcium carbonate. And when there are also other toxic ions like heavy metals (think lead and zinc) then the calcium carbonates can immobilize these free toxics trapping them into a nontoxic metal complex, making them safer.

So we are:

1. Trapping waste and toxic elements leads to detoxification.

2. Decreasing permeability through biocementation, aka, stabilizing the potentially hazardous sites

3. Reducing leachability of toxic waste in mine sites through solidification

If this is such a superpower why aren't the giants using it to solve all their dumb problems that they created?

Anna, I think we could have phrased that a little nicer.

Why? It's not like they ever try to understand us!

Advantages and Disadvantages of Biocementaiton (MICP)

Just like all of us, MICP microbes require certain conditions. They won't work for nothing, they must be provided livable wages and not be overworked to perform their best.

This includes providing them with optimal :

• Temperature

• microbes/enzymes present <- particularly of urease and carbonic anhydrase

• pH

• Surrounding substrates/elements

And while there are several advantages to this process:

• Easily permeates the soil

• Naturally occurring

• Biobased

• Eco-friendly

• Low-carbon footprint

• Low energy consumption

• Can be pretty effective

• Immobilizes mine waste

There are also a handful of disadvantages the giants have yet to figure out how they can deal with including:

• Ammonium is a byproduct

• Doesn’t happen uniformly

• How to deploy

• In some instances, microbes might be too big

So have they figured it out? I'd be terrified if this was my job. It's so much pressure!

Yes! There are a few success cases that Giants have that give them hope to keep researching.

How MICP Has Been Used in the Giant's World!

Salifu and colleagues applied the bacteria Sporosarcina pasteurii to soil to see the biocementation effects during tidal cycles. They found calcite produced by the bacteria, filled 9.9% of the soil pore space and was thus effective at controlling erosion for 30 tidal cycles.

In another study, Dubey and Colleagues isolated soil from a riverbank and showed there was a number of MICP bacteria including Sporosarcina spp that had biocementation potential.

That's all tod-

Wait I have a question!

Of course, what is it?

I was reading ahead and I was confused about biostimulation and bioaugmentation isn't that sort of like prebiotics and probiotics for the earth?

Ahhhh Excellent question, Mia! Yes you are on the right track.

Biostimulation vs. BioAugmentation

Biostimulation is modifying an existing environment to promote native communities to do the thing you want, here MICP. So like bribing the microbes.

BioAugmentation is adding the actual bacteria that perform the function of interest. So this might involve screening for a microbe, isolating that microbe, perhaps enhancing that microbe to perform that function better, and then deploying that microbe into a space that needs that function. Very much like probiotics.

Alright that's all for now. Goodbye class!