Further description:-  Recycling/reuse 

Glossary Entry
Minimizing waste generation from site remediation by recovering and reprocessing usable products 
that might otherwise become waste
Further description: Recycling, Reuse

Further description: Recycling, Reuse

 

Recycling/Reuse in this chapter covers the treatment or processing of materials which are directly or indirectly involved in remediation techniques to treat (in a wider sense) contaminants.

 

Further Information

 

1. General approach

Recycling/Reuse in this chapter is dealing with aspects of the treatment or the processing of materials which are directly or indirectly involved in remediation techniques. It is focused on reactive materials.

During the remediation measures hazardous substances might be accumulated within medias which are an integrative part of treatment as a reactive or within technical elements.

Examples for this are:

1.      reactive medias whenever they are exchangeable

2.      reactive medias, accumulators or filter materials within treatment facilities

The life cycle of such medias mostly is limited in time and intake capacity.

The main questions are:

          How to eliminate these accumulated contaminants from the reactive medias or from the technical elements?

          What are the conditions for reuse of recycled medias ( regarding capacity and operating lifetime)?

          Cost comparison between disposal and treatment/reuse of such materials

          It is feasible to recycle these medias/materials from the technical as well as from the economic point of view ?

          Are there substitutes which will reach a better performance regarding intake and recycling?

It is essential how to monitor the accumulation with contaminants and how to proceed the removal und exchange of this medias as well as the recycling process for reuse.

These materials should be selected and applied after a case specific investigation. In practice a trial investigation can help to optimise the effectiveness and capacity for such medias with could be materials, substances or mixtures. May be other alternatives are also practicable with lower costs or prices for recycling.

 

2. Media and materials

 

2.1 Reactive medias for PRB

 

In permeable reactive barriers as well as in several in-situ remediation techniques the selection of reactive materials is one of the key questions. This decision will have an significant influence to functionality, time scale, costs and environmental sustainability.

 

The selection of the reactive media is based on the following criteria (Gavaskar et al. 1997):

Reactivity. The reactivity of the material is quantitatively evaluated by the required residence time or the reaction rate constant. It is desirable to have low residence times and high reaction rates in order to keep the barrier’s thickness within acceptable limits.

Stability. The material is expected to remain active for long periods of time because its replacement is not easily achieved. Stability in changes of pH, temperature, pressure and antagonistic factors is also required.

Availability and cost. The amount of reactive material required for the construction of a reactive barrier is large enough and therefore it is essential to have considerable quantities in low prices.

Hydraulic performance. The hydraulic conductivity of the material depends on its particle size distribution and its value must be greater or equal to the value of the surrounding soil. However, an optimum particle size that would provide appropriate permeability and sufficient contact time must be determined. 

Environmental compatibility. It is important that the reactive media does not form any by products when reacting with the contaminants and that it is not a source of contamination itself by solubilisation or other mobilization mechanisms.

Safety. Handling of the material should not generate any risks for the workers health.

In accordance with research results and practical experiences the following table gives an overview what kind of reactive/media is appropriate for which kind of contaminants.

 

Table 1: Summarised data on permeable reactive barrier applications

 

REACTIVE MATERIAL

TREATABLE CONTAMINANTS

Fe0 

Iron sponge

Pd, Ni, Cu coated Fe

Fe0, O

Fe0, sand, concrete mixture

Zero-valent iron pellets

Organic materials: 

1,1,1-trichloroethane, 

1,1,2-trichloroethane, 

1,1-dichloroethane, tetrachloromethane, trichloromethane, dichloromethane, tetrachloroethylene, trichloroethene, 

cis-1,2-dichloroethene, 

trans-1,2-dichloroethene, 

1,1-dichloroethene, vinyl chloride, 

1,2-dichloropropane, Freon 113, benzene, toluene, ethylbenzene, hexachlorobutadiene, 1,2-dibromoethane, 

N-nitrosodimethylamine

 

Inorganic materials:

Cr, Ni, Pb, U, Tc, Fe, Mn, Se, Cu, Co, Cd, Zn, SO4, NO3, PO4, As, Hg

REACTIVE MATERIAL

TREATABLE CONTAMINANTS

Organic carbon containing materials:

leaf, peat, sewage sludge, manure, sawdust, wood waste, composted leaf mulch, pine mulch, pine bark

NO3, SO4, Cd, Pb, Co, Cu, Ni, Zn

Limestone, hydrated lime

Cr, U, As, Mo, PO4, Se

Phosphates

U, As, Mo

Ferrous sulfate

Cr, U, As, Mo

Natural zeolites:

clinoptilolite, mordenite

Surfactant modified zeolite (SMZ)

Sr, Ba, Cr, PCE

Iron oxide, Basic oxygen furnace oxide (BOF), amorphous ferric oxide (AFO)

U, As, PO4, Sr

Activated alumina

As, PO4, Sr

Organic polymers: 

Cyclophane I, II

Halogenated hydrocarbons (e.g. chloroform) aromatic compounds (e.g. benzene)

Sodium dithionite

Cr

REACTIVE MATERIAL

TREATABLE CONTAMINANTS

Activated carbon

Alpha-hexachlorobenzenes (BHC), beta-BHC, DDD, DDT, xylene, ethylbenzene, lindane, methyl parathion

Microorganisms:

G. matallireducens, A. putrefaciens

Tertiary butyl ether (MTBE), U, Ag, Cd, Co, Cu, Fe, Ni, Pb, Zn

 

The long-term efficiency of a PRB is a matter of great concern especially when the contaminants are persistent for several decades. The concentration of inorganic constituents like Ca, Mg, and Na determines the formation and deposition of inorganic precipitates on the surface of the reactive medium thus inducing its performance. A change in the hydraulic conductivity of the barrier due to clogging of the iron surface can alter the flow of the plume, which either dips further down the aquifer or passes around the barrier.

 

 

2.2  Activated carbon as reactive material for other remediation techniques and within technical elements

Activated carbon is characterized through a high porosity and the associated high specific internal surface of up to 2000 m2/g. A multiplicity of macro -, meso- and micropores makes possible the material transfer by the extensive cavity system for the activated carbon, and within the crystal lattice structure changed by the production process the actual adsorption processes take place at so-called active centers (= lattice defects). In these lattice defects the activated carbon is chemically not saturated. This is the cause for a particularly high reactivity and thus the ability to bind certain materials/contaminants. For the adsorption effect of volatile pollutants from soil air is mainly the physical adsorption of importance. The material transfer with adsorption processes consists of a diffusion and the actual adsorption. In the gaseous phase due to the high mobility of the molecules for the adsorption a time of contact of approx.. 0,1- 2.0 seconds is sufficient. In the liquid phase a time of contact of approx.. 1- 3 min is needed to bind the molecules to the activated carbon. For this reason smaller adsorbent units can be used than with the adsorption made of groundwater for the adsorption from soil air. Both with soil air and with groundwater the load capacity of the activated carbon rises with rising of pollutant concentration. For the comparative evaluation of activated carbon the following manufacturer data are suitable:

 

adsorption isotherm,

water content when packaging,

-          porosity and gap volume,

-          ash content,

-          specific internal surface,

-          granulation (sieve analysis),

-          apparent weight,

-          hardness (e.g. ball mill test),

-          flow resistance,

-          acid resistance.

The load capacity of the selected adsorbent depends also considerably on the humidity content of soil air. Those pollutants which can be adsorbed compete within the contact with the activated carbon with oxygen and hydrogen atoms around the free charge places at the lattice defects. Due to the polarity of the oxidic surfaces of the activated carbon in landfill gas atmosphere strengthens water vapour adsorbed, whereby the purposeful admission of other steams or gases with according to contained pollutants is obstructed.

 

3 Removal and recycling

 

In Europe a recycling of PRB reactive medias in practice does not exist. There are any open questions which needs a solution in advance:

          How to dismantle the medias out of existing PRB (construction works, geotechnical problems etc.)

          Are they any kind of In situ recycling methods feasible?

          How long a reactive media will be effective (long term experiences in most cases are still missing)?

In general contaminants will be bound to the reactive medias. This means that the concentration particular on this reactive medias would increase. The common practice is to dump such materials on waste disposal sites.

For activated carbons recycling processes are in common use. But the recycling ratio is  definitely lower as for disposal. This is also true for reactive materials within remediation installations as well as for filters.

At the end of pipe the contaminant will not to blow over. New solutions regarding recycling of such materials should consider the life cycle assessment as well. This will generate technical and economic criteria for future developments.

 

4 Author

 

 Jörg Frauenstein, German Federal Environmental Agency, http://www.umweltbundeamt.de

 

 

5 Acknowledgement

 

Extracted from

http://www.perebar.bam.de/PereOpen/pdfFiles/Review_Reactive_Materials.pdf

http://www.rubin-online.de/english/introduction/index.html

 

 

Authors
Jörg Frauenstein
German Federal Environmental Agency, Germany

Who does what?