Reclamation of Landfills and Household Waste Dumps

Today landfills to which 90 to 95% of all municipal solid wastes (MSW) are dumped are the most used dumping sites in Russia. Such landfills are extremely hazardous in terms of both immediate and future environmental impact.

The environmental impact of such landfills is really huge – according to different scientific estimates, they pollute the atmosphere, ground, subterranean waters and soils penetrating for more than 20 m into it. At the same time, scientists have found that infiltrated waters are a source of pollution with heavy metals, ammonia, nitrates and chlorine.

Thus, arrangement of efficient insulating layers (e.g., those of aquitard soil, including clays and loams with poor filtering capacity) is one of the most important tasks to accomplish in construction and maintenance of the landfills. More often than not constructors either fail to arrange such insulating layers or arrange them of materials not suited for the purpose.

Using substrates (e.g., dehydrated wastewater sediments) enriched with active humates based on AViTA® agent is one of the possible solutions to this issue. It has been proven that use of such substrates as an insulating material facilitates binding of heavy metals and destruction of organic ecotoxicants. Therefore, our technique of activation of the humus component in MSW compost is topical.

We have developed the technique taking into account the fact that depending on molecular weight, humic substances play a dual role in heavy metal migration:

1. On one hand, mobile low-molecular fulvic acids and humic acids react with metals forming water-soluble chelates and, thus, play the key role in heavy metal mobilization and migration.
2. On the other hand, when heavy metals interact with high-molecular humic substances steadily bound in the mineral component of soil (humates), heavy metals settle down. With regard to the aforesaid, action of humic substances as a geochemical barrier for heavy metal migration should be enhanced, and formation of water-soluble metal-humate complexes should be prevented. This can be achieved by removing the most mobile low-molecular humic substances from compost before activation. Since such humic substances are the most physiologically active substances, it would be reasonable to use these activation side products as humic fertilizers to facilitate plant growth.

Arrangement and Maintenance of MSW Landfills

Waste dumping is the simplest, cheapest and most used waste disposal method, but it causes great damage to the environment. The disadvantages of this method include:

• ineffective use of land resources;
• impossibility of waste recycling;
• high expenses on after-operation maintenance.

However, analysis of tendencies in MSW disposal in Russia shows that in the nearest future waste dumping will become an integral part of the sanitation system of populated areas.

Analysis of MSW dumping practices suggests that such dumping sites are a source of long-standing negative environmental impact.

Mixed filtrates forming in dumps in the process of interaction between wastes and infiltrating precipitation is the most hazardous component at such sites. Filtrates contain multiple products of decomposition of organic and mineral substances. First of all, filtrates pollute ground water.

Possible Solutions

1. Loam Underlay

There are several options of underlying layers that can be arranged to prevent penetration of filtrates into ground water. Loam underlay is the most commonly used solution. However, it has some essential disadvantages, including:

• If such underlay is arranged on a vast site, the arrangement is too labour-intensive – layer-by-layer arrangement, wetting and soil compaction require thousands of cubic meters of soil and, thus, development of soil pits;
• This method is rather inefficient, since such underlay does not provide for complete sealing and gets loose with the passing of time.
2. Polyethylene Film Underlay

Arrangement of polyethylene film underlay is another option. It is more efficient than the abovementioned method as it almost completely prevents infiltration. Furthermore, it does not require development of high-quality soil pits. However, this solution also has a few disadvantages ‒ the film used to arrange such underlay must be high-quality and, therefore, it must be expensive. This method, therefore, is more cost-intensive than the previous one, depending of the scope of works to be carried out. Furthermore, it requires thorough surface planning and leveling.

3. Unused Compost Underlay

In order to avoid labour-intensive clay mining and complex and cost-intensive arrangement of polymer film underlay, we suggest arranging underlay of unused municipal solid waste compost treated with AViTA® agent.

Such treatment:

• provides for removal of mobile humic substances intensifying heavy metal migration in the environment;
• reduces water permeability of compost due to soaking of its particles;
• transforms inactive humic substances into active ones making them similar to heavy metal ions and, thus, intensifying irreversible absorption of heavy metals and improving quality of infiltrate.

Time of penetration of one liter of water into compost by 7 cm:

Studies have shown that cation exchange capacity of compost after activation with AViTA® agent increases by 6 to 120%. Such increase depends on organic substance content in compost, its maturity, and the activating agent:

• If compost is activated with 2% AViTA® solution, the increase is 27.5 to 120%.
• If compost is activated with humified organic substances in high concentrations (Lot I), its total cation exchange capacity increases 2.2 to 2.5 times (if compost is treated with AViTA® agent).
• If compost is activated with poorly humified organic substances in low concentrations (33.4%; Lot III compost), its cation exchange capacity is only 1.3 times higher in comparison to the initial capacity.

Effectiveness of Heavy Metal Binding

If activated compost is used to arrange underlay, its heavy metal binding capacity is of a great importance. Activated compost absorbs plenty of heavy metals – their concentration may reach 11 to 33 g/kg of wet weight. Hence, such compost can absorb and irreversibly transform all mobile fractions of copper and 3-valent chrome into inactive forms.

Thus, it has been proven by experiments that activated MSW compost can act as a barrier preventing heavy metal migration into soil and water. The thicker the underlay, the more efficient it is. It becomes even more obvious if we take into account the fact that actual heavy metal concentrations in waste are hundred and thousand times lower than those we used to perform the experiments detailed above. To increase absorption of MSW, it is important to use MSW with highly humified activating organic substances. Practice shows that 90 to 99% of copper, nickel and 3-valent chrome are absorbed by activated compost and cannot be removed from it even after irrigation. Taking into account the fact that mostheavy metals are micronutrients essential for plant growth, their presence in humic substance solutions is rather advantageous than not.

Conclusion

The studies performed have proven feasibility of MSW compost activation. Such activation results in formation of two products which can be utilized:

• Solid phase – activated compost – can be used as an interlayer at solid waste landfills. Filtering capacity of such compost is low, and it actively absorbs heavy metals. Activated compost is able reduce heavy metal concentrations in dumped waste filtrates, even if such concentrations in the initial wastes are high. Taking the said properties into account, underlay thickness can be reduced from the standard 25 cm to 15-20 cm.
• Liquid phase, i.e. humic substance solutions enriched with nutrients and micronutrients. Such solutions can be used as agents facilitating plant growth and in reclamation of abandoned landfills and currently used industrial waste dumping sites. Furthermore, such agents inhibit pathogenic microflora and removes stinking of decomposing organic substances. AViTA® agent has great commercial prospects as a solution to issues in arrangement and maintenance of MSW landfills.