Remediation of soils contaminated with heavy metals and toxins

Remediation of soils contaminated with heavy metals and toxins

This is one of the most challenging tasks in land restoration. The main rule isFirst, determine the type of contamination, and only then choose a strategy. Metals and organic toxins behave completely differently.

There are four main strategies:

Isolatepollution.

Connectpollutants so that they do not enter plants and water.

Destroypollutants (if these are organic compounds).

ExtractSoil contamination (phytoremediation or soil removal).

Step 1. Diagnostics

Without analysis, it is impossible to determine a safe recovery method.

It is necessary to investigate:

Heavy metals

lead (Pb);

cadmium (Cd);

mercury (Hg);

arsenic (As);

nickel (Ni);

copper (Cu);

zinc (Zn);

chromium (Cr).

Organic pollutants

petroleum products;

petrol;

diesel;

polycyclic aromatic hydrocarbons (PAHs);

pesticides;

herbicides;

PCB;

dioxins;

solvents.

Also determine:

pH;

humus content;

granulometric composition;

depth of contamination;

groundwater level.

Step 2: Immediate stabilization

Before you start cleaning, it is important to stop the spread of contamination.

Necessary

cover bare soil;

prevent erosion;

prevent dust transfer;

do not grow food crops;

do not use the area as pasture.

The first plants should primarily perform a protective function.

Step 3. If there is heavy metal contamination

Metals are practically indestructible.

Therefore, the task is either:

extract them;

or make them less accessible.

Method 1. Immobilization

The safest strategy.

Add to the soil:

compost;

mature humus;

biochar;

zeolite;

clay minerals;

phosphate;

lime (if the soil is acidic).

These materials:

reduce the solubility of metals;

reduce their intake by plants;

increase the activity of microorganisms;

improve soil structure.

Particularly effectivebiochar, which has a very large internal surface area and is capable of adsorbing some pollutants, while simultaneously improving moisture capacity and conditions for soil microflora.

Method 2. Phytoremediation

Some plants are able to extract metals.

For cadmium and zinc

Some types are suitable:

mustard;

cruciferous;

hyperaccumulators of the genusNoccaea (previously Thlaspi).

For lead

Extraction is much more difficult.

Most commonly used:

sunflower;

mustard;

some willows.

However, lead is generally immobile, so it is often bound rather than extracted.

For nickel

They use specialized hyperaccumulators, for example some species of the genusAlyssum.

For copper

Certain types of willows, poplars and grasses help.

After collecting the plants

This is very important.

If plants have accumulated metals:

❌ They cannot:

compost;

use as mulch;

feed to animals;

burn without a special cleaning system.

They are disposed of as contaminated biomass in accordance with local environmental requirements.

If there is pollution by oil products

The situation here is much better.

Organic compounds can be broken down by microorganisms.

For this purpose, use:

Bioremediation

Add:

oxygen;

organic matter;

moisture;

nitrogen;

phosphorus.

Then the development of bacteria is stimulated.

Main groups:

Pseudomonas;

Rhodococcus;

Bacillus;

Arthrobacter.

They gradually decompose:

petrol;

diesel;

oils;

some solvents.

Mushrooms

A very promising direction.

Some wood fungi are capable of breaking down complex organic pollutants.

Used by:

oyster mushroom;

some tinder fungi;

mushroom mats;

wood mulch.

This method is calledmycoremediation.

Helper plants

After the toxicity level has been reduced, the following can be administered:

Cereals

fescue;

rump;

ryegrass;

soup.

Their task:

close the soil;

reduce erosion;

develop the root system.

Legumes

After toxicity reduction:

clover;

alfalfa;

sainfoin;

lotus.

They:

accumulate nitrogen;

increase humus;

nourish the soil microflora.

Trees

After the area has been stabilized, tree species are planted.

At the first stage the following are suitable:

Willows

Advantages:

rapid growth;

huge root system;

high transpiration;

good soil stabilization.

Poplars

Used for:

oil product contamination;

groundwater protection;

soil strengthening.

Birch

Suitable for:

restoration of poor lands;

gradual accumulation of humus;

creating a microclimate.

Alder

Especially valuable:

fixes nitrogen through symbiosis withFrankish;

grows quickly;

improves soil structure.

Pine

Used by:

on sandy contaminated lands;

to secure slopes;

to restore ecosystems.

Biochar

For the DREVO project, this is a particularly promising technology.

Biochar:

binds metals;

retains water;

increases carbon content;

improves aeration;

serves as a substrate for microorganisms;

has been working for decades.

If produced from local wood and plant residues, it can simultaneously produce a renewable resource for soil restoration.

Zeolite

Natural zeolite is capable of:

bind ammonium;

retain heavy metals;

improve air exchange;

reduce the migration of pollutants.

It is especially useful when combined with compost and biochar.

Compost

High-quality mature compost:

increases humus;

stimulates bacteria;

improves structure;

reduces the availability of a number of metals.

But it can be usedonly clean compostContaminated compost will only make the problem worse.

Microorganisms

Without them, recovery is almost impossible.

Useful:

mycorrhizal fungi;

nitrogen-fixing bacteria;

cellulose-destroying bacteria;

phosphate-mobilizing microorganisms.

As their toxicity decreases, they gradually restore the soil ecosystem.

Stages of recovery

Stage 1

Diagnostics.

Stage 2

Stopping erosion.

Stage 3

Binding of contaminants:

biochar;

zeolite;

compost;

liming if necessary.

Stage 4

Phytoremediation.

Used by:

mustard;

sunflower;

willows;

hyperaccumulators.

Stage 5

Microbiological restoration.

Add:

organics;

wood chips;

mushroom cultures;

mycorrhiza.

Stage 6

Transition to protective plants:

cereals;

clover;

shrubs;

trees.

Stage 7

Only after re-analysis can one proceed to growing food crops.

When you can't grow food

Before receiving the test resultsfood plants should not be grownin areas where contamination is known or suspected:

near former factories;

near smelting plants;

at old landfills;

near battery production facilities;

on the territories of old gas stations;

near railroad ties treated with creosote;

near major highways with old accumulated pollution.

Even if plants appear healthy, some metals can accumulate in leaves, roots, or fruits without any noticeable external signs.

WOOD concept

A multi-stage system can be used to restore contaminated lands:

1 year

diagnostics;

surface protection;

sowing perennial grasses.

2–4 years

biochar;

zeolite;

compost;

phytoremediation;

microremediation.

5–8 years

willow;

alder;

birch;

shrubs;

humus restoration.

8–15 years

mixed forest;

soil quality monitoring;

preservation of areas with protective vegetation.

After security confirmation

lick;

fruit trees;

wild boar;

vegetable crops.

This approach combinesenvironmental safety, restoration of soil life and gradual return of the territory to economic circulationwithout exposing people and animals to unnecessary risk.