Sequenced Bioleaching and Bioaccumulation of Phosphorus ...€¦ · Bioleaching and Bioaccumulation...

739

Bioleaching and Bioaccumulation of Phosphorus from Sludge Combustion

Sequenced Bioleaching and Bioaccumulation of Phosphorus from Sludge Combustion

– A New Way of Resource Reclaiming –

Wolfgang Dott, Maxime Dossin and Petra Schacht

1. Bioleaching .........................................................................................................739

2. Biological phosphate enrichment ...................................................................741

3. Combination of bioleaching and biologically induced phosphate recovery .......................................................743

4. Abstract ..............................................................................................................749

5. Bibliography .......................................................................................................749

Reutilization of heavy metal contaminated solids, incineration ash in particular, is being increasingly problematic, since the use of ash in agriculture or construction industry is often not possible, due to its potential toxicity. Methods of bioleaching, known from ore extraction, may be used as an alternative remediation concept for heavy metal depletion in contaminated solids. The bioleaching bacteria of Acidithiobacillus species oxidize metal sulfides into soluble metal ions, which are then brought in solution. At the same time, sulfur compounds are oxidized by these bacteria in sulfuric acid: acid-soluble heavy metals are thereof brought in solution. In this work, contaminated solids are treated with the bioleaching process: focus is made on depletion of heavy metals in ash and their sub-sequent fixation, to prevent any pollution of groundwater. In addition, a selective recovery of phosphorus is achieved.

Phosphorus is an absolute essential element for life, without any possible substitution through other element. This irreplaceable compound presents limited reserve, which are unequally spread in the world. It is found in marine-sedimentary deposits (approximately 90 % of inventories) and in igneous rocks (10 %) [1]. The marine-sedimentary deposits are concentrated in North Africa (Tunisia and Morocco), China and in the southeastern United States. The magmatic deposits are located mainly in Russia and Brazil. Most of the phosphate is used in agriculture in the form of phosphatic fertilizer. With the increasing world population, demand for fertilizers will continue to increase. A responsible use of phosphate would go through a recovery of this element, where it is lost up to now, namely in sewage sludge or sewage sludge ash.

1. BioleachingThe bioleaching has experienced a drastic development during the last 20 years: from un-controlled leaching of copper out of piles, to a developed biotechnological process branch [2]. With a part of up to 25 % for the mining of copper in Chile, Canada and the USA, bioleaching is now a strong economic field. The technical application of the process is the

Wolfgang Dott, Maxime Dossin, Petra Schacht

740

conversion of insoluble copper, zinc and uranium ores in water-soluble metal sulfates, which are recovered after drainage, precipitation and evaporation. The development of commercial bioleaching process has made great steps in recent years.

The advantages of bioleaching over conventional metal extraction are followings:

• economicalleachingoflowconcentratedorunpurifiedores,

• leachingproceedsatlowtemperaturesandatmosphericpressure,

• theadditionofexpensivechemicalsiseliminatedbythebiogenicproductionofsulfuricacid,

• processingiseasy,

• noemissionofCO2(lowenergyinput,microorganismsfixCO2)

The leaching potential of Acidithiobacillus is based on two reactions, represented in Figure 1. Both reactions lead to a release of an important part of the heavy metals contained in the ash. The basis of bioleaching is the utilization by sulfur-oxidizing bacteria of inorganic electron donors, mainly compounds with reduced form of sulfur or elementar sulfur, which are used for energy production [4]. For bacteria, it concerns Acidithiobacillus species for example, a group of aerobic, gram-negative, chemolithotrophic bacteria that are capable of producing sulfuric acid through oxidation of reduced metal sulfides. Metals are then brought in solution. Through the biogenic production of sulfuric acid, most of phosphorus is also brought in solution into the form of phosphate anion.

Table 1 summarizes the metal content of various contaminated solids (mainly incineration ash) implemanted before (left) and after (right) the leaching process. Values exceeding the German limits are highlighted. A massive decontamination of heavy metals is obtained.

Figure 1:

Reaction A: oxidation of metal sulfides (MS) by microorga-nisms (MO), release of heavymetals and thiosulfate, oxidation of thiosulfate to sulfuric acid. Reaction B: proton attack by sul-furic acid on the metal sulfides, release of heavy metals, oxidati-on of reduced sulfur compounds to sulfuric acid.

Source: Hollender, J.; Dreyer, U.; Kron-berger, L.; Kämpfer, P.; Dott, W.: Selective enrichment and characterization of a phosphorus-removing bacterial con-sortium from activated sludge. Applied Microbiology and Biotechnology, 2002, 58, 106-111

Fe3+

H SO

MO

MO MS2O

2+Fe

Fe , O3+

2

S O2 32-

S O , S2-

6n 8

2 4

MO Fe , O3+

2

Reaction A: thiosulfate mechanism

Fe3+

MO

MS

2+Fe

Fe , O3+

2

+ H S (H S )2

H S2 n

MO Fe , O3+

2

H+

2 2

SO +2-4 H+

MO 2O

M 2+ +2+M

Reaction B: polysulfide mechanism

741


2. Biological phosphate enrichmentPhosphate removal in sewage treatment plants takes place mainly through chemical pre-cipitation with iron and aluminum salts. This leads to an increase of the salinity of treated water and an increase of metal loading in waste sludge. To reduce these effects, biological phosphate removal is now used in an increasing extent. With this process, phosphate is eliminated from wastewater without any addition of coagulant. Phosphate is fixed in the biomass, which form flakes that settle in the sewage sludge. Essential mechanism of the biological removal is the ability of certain bacteria to save phosphate under the form of polyphosphate. The biological phosphate elimination is known as EBPR [6] (Enhanced Biological Phosphorus Removal) and is applied in wastewater treatment since 2000.

Table 1: Metal content before (left) and after (right) in bioleaching mg/kg

Metal

content EOS WS RA ZA EA AS BS EOS WS RA ZA EA AS BS

of ash

As 17.4 14.5 25.2 10.0 36.4 19.6 4.4 8.2 8.5 11.7 3.8 3.0 0.3 4.4

Cd – – 0.1 13.7 93.5 – 0.3 – – – 1.6 3.2 – 0.3

Cr 4,723 288 119 35 47 92 281 2,858 219 66 19 47 55 136

Cu 121 135 120 95 305 291 37 102 44 39 23 122 36 29

Pb 4.5 201.6 1.3 29.3 431.0 171.7 2.4 5.2 100.1 1.3 19.0 431.0 43.8 2.2

Ti 0.05 0.15 0.01 1.30 17.90 0.12 – – 0.04 0.01 0.70 17.59 0.03 –

V 935.4 717.6 31.2 29.1 25.1 35.3 – 910.3 21.0 – – – 25.3 –

Zn 198 5,647 38 876 13,434 1,420 180 209 784 13 153 270 146 –

fat: Exceeding the limits LAGA ZO/Z1.1

EOS:electricfurnaceslag,WS:rollingmud,RA:bottomash,ZA:cycloneflyash,EA:electrostaticflyash,AS:digestedsludge,BS:Sittard´ssoil

Source: Dott, W.: Metalllaugung von Verbrennungsaschen, 2010

EPS: extracellular polymeric substance PHF: Poly(hydroxy fatty acid)

anaerob aerob

Acetat PHF

Poly-P

EPSEPS

P

PO43-

PHF

Figure 2: Mechanism of storage of carbon and polyphosphate in EBPR under aerobic and anaerobic conditions


742

Figure 2 presents the nechanism underlying the biological phosphate elimination. Under anaerobic conditions (left), microorganisms use acetate as carbon source, and convert it to acetyl coenzyme A (Acetyl-CoA). During this process, the consumed adenosine tri-phosphate (ATP) is restored through a transfer of phosphate molecule from intracellular polyphosphate. During the hydrolysis of intracellular polyphosphate chains, inorganic phosphate is also released out of the cell into the surrounding solution. The Acetyl-CoA molecules are condensed and stored under the form of poly(hydroxy fatty acids).

When switching to aerobic conditions (right), poly(hydroxy fatty acids) are then used as a source of energy. Phosphate in the surrounding solution is then incorporated by the bacteria and stored as intracellular polyphosphate. Bacteria take more phosphate than they would need, a phenomenon called luxury uptake [7, 8, 9, 10]. Identity of the phosphate-storing microorganisms as well as the underlying mechanism, circumstances and reasons for the luxury uptake are discussed again and again.

Figure 3 shows an example of the phosphate incorporation by a special culture named RSAS. The concentration of inorganic phosphate is measured during sequential aerobic and anaerobic phases. These results are a clear representation of the phosphate incorporation under aerobic condition and the phosphate release under anaerobic conditions.

20 30 40

70

60

50

40

30

20

10

phosphatemg/L

10

0

80

acetatemg/L

50 60 70 80

2.500

2.000

1.500

1.000

500

0

3.000

addition of acetate

0

time h

aerob anaerob aerob

Figure 3: Concentrations of inorganic phosphate and acetate in solution with the special culture RSAS. 72 h of fumigation with change between aerobic and anaerobic conditions every 24 h.

Source: Schacht, Petra: Mikrobiologische Gewinnung von langkettigen Polyphosphaten, 2011

Figure 4 gives an overview of the protein content of the solution, it means the quantity of biomass. A continuous growth of the biomass is observed.

743


Figure 5 gives a representation of yield and composition of polyphosphate chain lengths obtain with for three different special crops, which were cultivated under similar conditions. Extraction and determination of the distribution of the polyphosphate chains were done following the method from Clark et al.[12].

3. Combination of bioleaching and biologically induced phosphate recovery

Goal of the work is to find a biotechnological process that would perform a selective recovery of phosphate after a bioleaching of heavy metals contaminated solids. In presented process, the dissolution of phosphorus from the ash, and subsequent removal of dissolved phosphate is performed in one step. A schematic representation of the mechanism is given on Figure 6.

The AEDS culture (Acidithiobacillus enriched digested sludge) is used in this work. The bacterial population consists of several bacterial species/genera, whose distribution of population is represented on Figure 7.

16S rRNA gene sequence analysis and FTIR spectroscopy were used for the identification of microorganisms in the AEDS solution, and to study their activity.

Figure 4: Time course of protein content of the special culture RSAS during sequential change between aerobic and anaerobic phases


20 30 40

800

700

600

500

400

200

100

protein contentmg/L

10

0

50 60 70

addition of acetate

0

time h

aerob anaerob aerob

300

80


744

6

5

3

2

1

polyphosphatemg

0

4

6

5

3

2

1

polyphosphatemg

0

4

6

5

3

2

1

polyphosphatemg

0

4

6

5

3

2

1

polyphosphatemg

0

4

Phosphate residues: Long-chain (250-750) Medium-chain (20-250) Short-chain (< 20)

RSAS BSKN BPSB

147,6 mg acetate (1 x acetate) 442,73 mg acetate (3 x acetate) 885,45 mg acetate (6 x acetate)

Figure 5: Composition of polyphosphates for different chain lengths (short chains: chain length <20 phosphate residues, medium: chain length of 20-250 phosphate residues, long chain: chain length of 250-750 phosphate residues) in the special crops RSAS, BSKN and BPSB with one-, three-time and six-time acetate addition


745


Figure 6: Mechanism of microbial phosphate storage (left) and heavy metals from solution (right)

Source: Dott, W.: Metalllaugung von Verbrennungsaschen, 2010

Figure 7: New synthrophe bacterial population for the acid recovery of phosphorus from sewage sludge ash

EPS: extracellular polymeric substances; Me2+: metal ion

Polyphosphateaccumulating bacteria

e.g. Acinetobacter Iwoffii,Pseudomomas spp.

14 %

Acidithiobacillus ferrooxidans

52 %

New genus Fulvimonas

19 %

New genus Rhodanobater

8 %

Iron oxidizing bacteria

6 %


746

The process of selective phosphorus recovery can be described in three points: • BioleachingbyAcidithiobacillusferrooxidansofphosphorusandheavymetalsfrom

sewage sludge ash and release of these elements in solution. • Phosphorusaccumulationbypolyphosphate-storingmicro-organismsoftheclassAc-

tinobacteria.• MicrobialinducedFe(III)-phosphateprecipitationbyAcidithiobacillusferrooxidans.The resulting product is a phosphate-rich solid, which consists of Fe(III)-phosphate and polyphosphate.The experiments were first conducted in a laboratory-scale bioleaching reactor, schematizes on Figure 8. The bacterial suspension is sprinkled on the ash in a lysimeter: most heavy metals and phosphate dissolve. The bioleaching solution is then collected through a glass frit. The process is repeated several times in order to obtain sufficient phosphate and metal concentrations in the bacterial solution. During the continuous sprinkling of the solution, a biofilm forms on the ash.

AerationPump

Bioleachingmedium:

pH 1.9

• Disolved metals • Disolved phosphate

Mixed culture of

leachingbacteria

pH: 2.0-1.5

Bioleachingpercolator

With sewagesludge ash on

glas frit

Probes for analytics

Figure 8: Schematic representation of bioleaching reactors

Figure 9 represents concentrations of phosphate and some heavy-metals in the bacterial solution during the whole process. The first part of curves shows that phosphate and hea-vy metals are leached from the sewage sludge ash and released in the bacterial solution. The second part of curves show that phosphate is then incorporated in the biomass and removed from the solution: its concentration declines rapidly. During the incorporation of phosphate, heavy metals remain in solution: concentrations stay quasi constant und don’t decline like for phosphate. The phosphate is then removed from the solution, and is found in the biomass. This process combines succesfully a simultaneous release of phosphate and heavy-metals from sewage sludge ash, following by a selective fixation of phosphate in the biomass. This solid biomass, poor in heavy metal, can be easily separated by sedimentation and filtration.

747


Figure 9: Phosphate and heavy metal concentration during the process of selective recovery of phosphate from sewage sludge ash. The results shown were obtained for 6 experiments.

Source: Dott,W.;Zimmermann,J.:Recoveryofphosphorusfromsewagesludgeincinerationashbyfractionatedbioleachingand fate of heavy metals, 12th international symposium of microbial ecology, ISME 12, Cairns, Australia, August 17-22, 2008

Figure 10 gives a schematization of the process in a technical scale. Same kind of results were obtained in technical scale during the leaching of several kilograms of ash.

1 3 4

70

60

50

40

30

20

10

Leaching%

0 days

0

80

2 5

Al Cu Zn Mn PO4

1. AEDS-production 2. Phosphate and heavy metal release

3. Phosphate recovery and heavy metal separation

Phosphateindustry

agriculture

P-enrichedproduct

Figure 10: Schematisation of the presented P-recovery process in technical scale


748

Figure 11 presents the ratio of phosphorus and metals in the combustion ash (left) and in the P-enriched biomass (right). Proportion of Metals is drastic reduced in the P-enriched sludge in comparison to raw ash.

* sum of the metals Al, Ca, Mg, Pb, Cu, Cr, Zn

AEDS P-product

70

60

50

40

30

20

10

Ratio of phosphorus and metals%

Incineration ash

Metals* Phosphorus

0

80

90

100

Figure 11:

Ratio of phosphorus and metals in the incineration ash (left) and P-enriched biomass (right)

350

300

250

200

150

100

50

mg/l

00

1 2 3 4 5 6 7 8 9 10 11 12days

Fe P

Organic phosphateaccumulation 30 %

Iron-phosphatePrecipitation70 %

Figure 12: Evolution of the concentration of iron and phosphate in the bioleaching medium

749


Iron plays an important role in the metabolism of Acidithiobacillus species: micororganisms win energy through the oxidation of Fe2+ in Fe3+. Therefore, it is presumed that iron plays an important role in the fixation of phosphate, beside the formation of polyphosphates, as can be seen on figure 12. The evolution of the concentrations of iron and phosphate in AEDS solution are represented. In the first days, evolutions of iron and phosphate con-centrations show that phosphate is incorporated in the biomass. Then, a precipitation of iron-phosphate is observed.

The ratio between polyphosphate and iron-phosphate is simplified on Figure 13.

Organic P(polyphosphate)

26 %

FePO4

74 %

4. AbstractThe recovery of phosphorus from sewage sludge incineration ash as well as the separation of heavy metals from ash was investigated by using the biotechnological process of bioleaching and bioaccumulation of released phosphorus by newly developed syntrophic population of bioleaching bacteria, Acidithiobacillus spec. strains, and polyphosphate (poly-P) accumu-lating bacteria, the AEDS-population (Acidithiobacillus spec. enriched digested sludge). The biologically performed solubilization of phosphorus from sewage sludge incineration ash is accompanied by the release of toxic metals. Therefore a combined process to sepa-rate phosphorus from heavy metals by achieving a plant available phosphorus-enriched product and a metal depleted ash was designed. Leaching experiments were conducted in leaching reactor containing a bacterial stock culture of Acidithiobacillus spec. Following step was the enhancement of P-recovery in combining bioleaching with simultaneous bio-P-accumulation by AEDS-population. The uptake of phosphorus in biomass reaches up to 66 % of the mobilized phosphorus by bioleaching. The combined biologically performed technology of phosphorus leaching and separation from toxic metals by simultaneous bioaccumulation developed in this work is a promising economical and ecological process for the recovery of phosphorus from waste solids.

5. Bibliography[1] Wellmer, F. W.; Becker-Platten, J. D.: Mit der Erde leben, Beiträge Geologischer Dienste zur

Daseinsvorsorge und nachhaltigen Entwicklung. Berlin Heidelberg: Springer-Verlag, 1999, S. 129-13

[2] Olson,G.J.;Brierley, J.A.;Brierley,C.L.:BioleachingreviewpartB-Progress inbioleaching:Applications of microbial processes by the mineral industries. Applied Microbiology and Bio-technology, 2003, 63: 249-257

Figure 13:

Ratio of polyphosphates and iron-phosphate in the bioleaching medium


750

[3] Hollender, J.; Dreyer, U.; Kronberger, L.; Kämpfer, P.; Dott, W.: Selective enrichment and cha-racterization of a phosphorus-removing bacterial consortium from activated sludge. Applied Microbiology and Biotechnology, 2002, 58, 106-111

[4] Silverman, M.; Lundgren, D.: Studies on the chemoautotrophic iron bacterium Ferrobacillus ferrooxidans – I. An improved medium and a harvesting procedure for securing high cell yields. Journal of Bacteriology, 1959, 77: 642-647

[5] Dott, W.: Metalllaugung von Verbrennungsaschen, 2010

[6] Oehmen,A.;Lemos,P.C.;Carvalho,G.;Yuan,Z.;Keller,J.;Blackall,L.L.;Reis,M.A.M:Advancesin enhanced biological phophorus removal: From micro to maccro scale. Water Research, 2007, 41: 2271-2300

[7] Bark, K.; Kämpfer, P.; Sponner, A.; Dott, W.:Polyphosphate-dependent enzymes in some cory-neform bacteria isolated from sewage sludge. FEMS (Federation of European Microbiological Societies) Microbiology Letters, 1993, 107: 133-138

[8] Bark,K.:EnzymedesPolyphosphatstoffwechselsunterschiedlicherBakterienimZusammen-hang mit der biologischen Phosphateliminierung aus Abwasser. Dott, W.; Rüden, H. (Hrsg.): Veröffentlichungen aus dem Fachgebiet Hygiene der Technischen Universität Berlin und dem Institut für Hygiene der Freien Universität Berlin 10. Berlin, 1992

[9] Hoffmeister, D.; Weltin, D.; Dott, W.: Untersuchungen zur bakteriellen Phsophateliminierung. GWF Wasser Abwasser. 1990, 131(5): 270-277

[10] Hoffmeister D., Dynamik der extra- und intrazellulären Phosphorverbindungen bei der biologi-schen Phosphatelimination. Dott, W.; Rüden, H. (Hrsg.): Veröffentlichungen aus dem Fachgebiet Hygiene der Technischen Universität Berlin und dem Institut für Hygiene der Freien Universität Berlin 16. Berlin, 1993

[11] Schacht, Petra: Mikrobiologische Gewinnung von langkettigen Polyphosphaten, 2011

[12] Clark et al., 1986

[13]Dott,W.;Zimmermann,J.:Recoveryofphosphorusfromsewagesludgeincinerationashbyfractionated bioleaching and fate of heavy metals, 12th international symposium of microbial ecology, ISME 12, Cairns, Australia, August 17-22, 2008

Sequenced Bioleaching and Bioaccumulation of Phosphorus ...€¦ · Bioleaching and Bioaccumulation...

Documents

Transcript of Sequenced Bioleaching and Bioaccumulation of Phosphorus ...€¦ · Bioleaching and Bioaccumulation...