What is Bioremediation? - Compost for Soils

ocompost for soilsSoil RemediationOpportunitiesfor the use ofRecycled Organicsin theBioremediationIndustryThis is the first in a series of Fact Sheetsdescribing emerging markets thatadd value to the recycled organicsindustry. The target audience includesrecycled organics processors, regulators,environmental consultants andremediation contractors.There are significant opportunitiesfor the use of recycled organicsand composting techniques in thebioremediation industry. This FactSheet gives a general overview of thebioremediation process with a particularemphasis on the use of recycledorganics products.Benzo (a) PyreneIntracellularbacterialdegredationpreventedby moleculesize/ low watersolubilityWhat is Bioremediation?Bioremediation refers to the use ofbiological treatments to clean uphazardous materials in the environment.These biological treatments generallytake advantage of the naturalmetabolic processes of plants (termed‘phytoremediation’) or micro-organismsto stabilise or degrade environmentalcontaminants.FungusO==OExtracellularEnzymeRleasede.g. 6,12 - Benzo (a) Pyrene Quinone(water soluble degredation product)Micro-organisms involved inbioremediation processes include:• Bacteria - these generallyuse organic compounds (e.g.hydrocarbons) as an energy sourceand in the process convert themto innocuous by-products andultimately into CO2 and H2O.• Fungi – these generally produceenzymes that can breakdown largerorganic compounds (eg. lignin inwoody material) into smaller byproducts that can be processed bybacteria.• Actinomycetes – a type of bacteriacharacterised by the presence of finefilaments. They are typically found insoil and give it its ‘earthy’ smell.BacteriaCO2 + H20Figure 1: An example of how adiverse community of microorganismsbreaks down the organiccontaminant benzo-(a)-pyrene.

BenefitsBioremediation offers the followingadvantages over other remediationmethods:• Generally cheaper than traditionalphysical and chemical remediationtechnologies;• Environmentally friendly (convertsmost contaminants to water, carbondioxide and innocuous by-products);Contaminated Soil• Environmentally sustainable(treated soil can often be reusedon-site avoiding landfill disposal);• The process harnesses the highlyspecific and efficient metabolicprocesses of naturally occurringorganisms.LimitationsBioremediation has the followinglimitations:• Certain poly aromatic hydrocarbons(e.g. benzo-(a)-pyrene) andchlorinated compounds (e.g.Polychlorinated biphenyls) arerecalcitrant to biodegradation.Inorganic contaminants such asheavy metals are not degraded bybioremediation (even though it canassist to ‘lock them up’);• Bioremediation is a relatively slowprocess generally taking from severalmonths to several years to complete;• Sometimes contaminants are not‘bio-available’ which mean that theyare so strongly bound to the soilstructure that they are not accessibleto micro-organisms;• Extreme environmental conditions(e.g. salt, pH, nutrients) or highconcentrations of contaminants canbe toxic to micro-organisms.Target ContaminantsBioremediation can effectively degrade or stabilise a wide range ofcontaminants. These are summarised in the table below:Chemical ContaminantPAH (Poly Aromatic Hydrocarbons)PCP (Pentachlorophenol)Total PhenolsHeavy Metals (stabilisation)TPH (Total PetroleumHydrocarbons)BTEX (benzene, toluene, ethylbenzene,xylene)TNT (Trinitrotoluene)Common SourcesGas works, wood treatments (eg.creosote), industrial byproductsBiocides used in wood treatments, oilsand paintsWood treatments, general industryDiverse industries, metal works,tanneries, refineries, smelters, miningPetroleum products, service stations,refineries, waste oilPetroleum products, service stations,refineriesExplosives, mining and defenceindustriesExample of the ma

BioremediationTechnologiesThere are a number of differentbioremediation technologies used toclean up contaminated sites. Theseinclude:• Bioreactors (or bioslurry)– treatment of a contaminatedsubstance in a tank containingorganisms or enzymes;• Bioventing – involves the venting ofoxygen through soil to stimulate thegrowth of natural and introducedbioremediation organisms;• Co-Composting – generally involvesmixing contaminated materialswith either mature compost or freshrecycled organics. The mixtures areformed into turned windrows orengineered biopiles (see below);• Biopiles – specially engineeredstatic piles of mixed contaminatedsoil and remediation amendmentsusually involving a network ofpumps and pipes for forced aeration;• Landfarming – the use of farmingtilling and soil amendmenttechniques to encourage the growthof bioremediation organisms in acontaminated area.Using RecycledOrganics forBioremediationRecycled organics are used extensivelyin bioremediation and in many casesunderpin the basic requirementsof the process. Often referred toas ‘co-composting’, the process issimilar to commercial compostingwhere windrows are constructed andtechnical parameters are monitoredto ensure that optimal conditions forbiodegradation are maintained.Recycled organics provide a numberof benefits when utilised in thebioremediation process:• A complex microbial communitywith a wide range of metaboliccapabilities;• Macro nutrients such as nitrogen,phosphorus and potassium;• Trace elements essential formicrobial growth;• High porosity for the supply ofoxygen and diffusion of air;• Increased water holding capacity;• Buffering capacity (particularly forhigh or low pH soils);• Heat generation allowingincreased bio-availability of somecontaminants.Extracting contaminated soilIn bioremediation processes whereforced aeration is used (e.g. biopiles,bioventing) a ‘biofilter’ is oftenemployed to mitigate the emissionof volatile compounds. Recycledorganics (normally mature compostand coarse woodchips) are often a keycomponent of the biofilter medium.chinery used in the bioremediation process