Phytoremediation, an Option for Tertiary Treatment of Sewage

Dr. Arvind Kumar MungrayChemical Engineering Department,

SVNIT, Surat

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INTRODUCTION

Water pollution is one of the most serious problems of today’s civilization.

Major impact on the Rivers, Lakes, Oceans by Deforestation of Riparian zones, Inundating fields with Fertilizer, Faulty septic systems or Poorly designed waste water overflow systems.

If drastic efforts in water protection are not made by year 2025, 2.3 billion people will live in areas with chronic water shortage (WHO, 2005).[1]

Wastewater treatment is classified in two basic groups: Conventional methods and Alternative methods.

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Conventional Methods

The method involves:- Primary, Secondary, & Tertiary, or Advanced

Stages.

Primary treatment removes of about 30-50% of the Suspended Solids in raw wastewater by Sedimentation.

The organic matter is extracted by Biological Secondary treatment processes using activated-sludge processes, trickling filters, or rotating biological contactors to meet effluent standards.

Figure 1:- Sewage Treatment

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Tertiary Treatment

The final stage of the treatment involves, 1. Nitrogen Reduction, 2. Phosphorus Reduction &3. Disinfection.

• Disinfection is done for the removal of the pathogens and is usually done by either chlorination, ultra- violatilization, or ozonation.

Figure 2:- Chlorination tank

Figure 3:- The Advanced Tertiary Treatment.

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Where the Method Fail…..• The treatment fails in satisfying all demands of ecologically aware

societies. • Do not enable Reclamation and Reuse of water and nutrients, • Generated effluent not up to the standards, • Harmful to environment and people.• Unable to handle storm water.

• In Boston, often beaches are closed as bacteria levels reach hazardous levels due to untreated raw sewage and urban water runoff enters the river and bay. Another city headed toward a parallel scenario was Chicago and its relationship with adjacent Lake Michigan. [2]

• Huge algal blooms in the Mississippii River and it’s tributaries, cultural Eutrophication leads to oxygen-poor situations, making it difficult for aquatic life to continue.[2]

Beachwood beach in U.S.

Source: abc news 09/08/2007

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Continued……..

• Higher quality of effluent employs additional technologies results in increased costs of construction, operation, and maintenance, resulting in ignorance of this step.

• Water is often dumped directly into neighboring lakes or rivers, which bear the burden of dealing with these excess pollutants. Pollutants such as organic matter, suspended particulates, micropollutants, nutrients (phosphorus and nitrogen) or heavy metals.

• EFFECTS:-[2]

• High concentrations of Nitrates & Phosphates leads to Infant methemoglobinemia [blue baby syndrome].

• Chlorine combined with nitrate or phosphate forms a carcinogenic compound.

• High Phosphate levels in streams attributed to algal blooms.

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Alternatives…

Phytoremediation Bio-remediation

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PHYTOREMEDIATION

• Phytoremediation is an emerging ‘green bioengineering technology’ that uses plants to remediate environmental problems.

• Green plants (both aquatic and terrestrial) have the wonderful properties of environmental restoration, such as decontamination of polluted soil and water. [3]

• They are aesthetically pleasing, passive, solar-energy driven and pollution abating nature’s (green) technology meeting the same objectives conventional technology and thus becoming a cost-effective, non-intrusive, and a safe alternative.

• They thrive in very harsh environmental conditions of soil and water; absorb, tolerate, transfer, assimilate, degrade and stabilise highly toxic materials (heavy metals and organics such as solvents, crude oil, pesticides, explosives and polyaromatic hydrocarbons) from the polluted soil and water.[3]

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Phyto-volatilization

Figure 5: Phyto-volitilization of organic compounds [4]

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Phytodegradation

Figure 6: Phytodegradation of organic & inorganic compounds [4]

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Phytoaccmulation

Figure 7: Phytoaccumulation of organic compounds [4]

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Rhizodegradation

Figure 8: Rhizodegradation of organic compounds [4]

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Phytostabilization

Figure 9: Phytostabilization of organic & inorganic compounds [4]

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How they achieve it….

• The symbiotic relationships between their basic components, aquatic plants, microorganisms, algae, substrates and water they have the ability to remove organic and inorganic matter, nutrients, pathogens, heavy metals and other pollutants from wastewater in a completely natural way.[3]

• The plants species like, cattails, bulrushes, reeds and aquatic plants like water hyacinths, pennywort, and duckweed were found useful.

Figure 10: Pathway of Contaminants through the Plant [6]

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Inside the Plant Cell-wall….

Figure 11: Pathway of Contaminants inside the Plant Cell wall [6]

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Type and Contaminants…..

Mechanism Media Typical contaminants Plants Types

Phytostablization Soils, sediments, Sludges. As, Cd, Cr, Cu, Pb, Zn Herbaceous species, grasses, trees, wetland species.

Rhizodegradation Soils, sediments, sludges, groundwater.

Organic compounds (TPH, PAHs, BTEX) pesticides,

chlorinated solvents,(PCBs)

Herbaceous species, grasses, trees, wetland species.

Phytoaccumulation Soils, sediments,

sludges

Metals: Ag, Au, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni. Pb. Zn.

Herbaceous species, grasses, trees, wetland species.

Phytodegradation Soils, sediments, sludges, groundwater, surface water

Organic compounds, chlorinated solvents,

phenols,pesticides,munition

Algae, herbaceous species, grasses, trees, wetland species

Phytovolatization Soils,sediments,

sludges,groundwater

Chlorinated solvents,MTBE,some

inorganics

(Se,Hg&As)

Herbaceous species,grasses,trees,wetland

species

Evapotranspiration Groundwater,surface,stormwater

Water soluble organic & inorganics

Herbaceous species,grasses,trees,wetland

species

Table 1:- Summary of Phytotechnology Applications [4]

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Efficiency results of a UASB reactor coupled with a Duckweed pond

Parameter Treatment unit

UASB Duckweed ponds efficiency Overall efficiency

Summer (%) Winter (%) Summer (%) Winter (%) Summer (%) Winter (%)

COD % removal

79 ± 5 70 ± 1.8 64 ± 17 72 ± 1.3 93 ± 4 92 ± 0.4

BOD % removal

82 ± 5 73 ± 2 73 ± 12 75 ± 3 95 ± 2 93 ± 1

Ammonia N% removal

4 ± 14 19 ± 3 98 ± 4 44 ± 7 98 ± 3 39 ± 10

TKN % removal

26 ± 9 15 ± 5 80 ± 6 45 ± 5 85 ± 4 53 ± 7

Total P% removal

20 ± 9 28 ± 5 73 ± 8 40 ± 8 78 ± 7 57 ± 7

TSS % removal

83 ± 7 73 ± 3 43 ± 21 63 ± 6 91 ± 5 91 ± 2

Faecal coliform %

removal

63 73 99.93 99.7 99.998 99.94

Table 2:- Efficiency of treatment system as % removal [9]

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Duckweed pond Efficiency…

Parameter Concentration (mg/l) Removal efficiency(%)

Influent (%) Effluent (%)

BOD total 23 ± 13 8 ± 5 60 ± 32

BOD filtered 13 ± 6 4 ± 2 65 ± 25

BOD suspended 10 ± 8 4 ± 4 67 ± 26

COD total 126 ± 81 49 ± 20 54 ± 24

COD filtered 54 ± 37 29 ± 20 41 ± 37

COD suspended 72 ± 62 20 ± 20 65 ± 33

TSS 35 ± 30 11 ± 4 57 ± 29

NH4-N 48 ± 18 26 ± 12 46 ± 26

NO3-N Negligible 2 ± 1 -

N-Organic 6 ± 9 Negligible 100

PO4-P 16 ± 3 11 ± 4 33 ± 29

pH 7.4 ± 7.9 7.3 ± 8.3 -

Table 3:-Characteristics of pond system influent (UASB reactor effluent) and effluent, and removal efficiencies [10]

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Efficiency results of a UASB reactor coupled with a Water hyacinth (WH) pond

Type ph Alkali

(mg/l of CaCO3 )

COD

(mg/l)

TSS

(mg/l)

ECOD

%

ETSS

%

Influent 8.15 618 465 154

Effluent

UASB

8.05 635 162 41 65 73

Effluent

(WH)

8.00 620 90 12 81 92

Table 4:- Efficiency of the USAB and Water Hyacinth pond [10]

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Comparison of Cost & Time….

Type Of Treatment Cost/m3 ($) Time Req

(months)

Additional factors/expense Safety Issues

Land filling 100-400 6-9 Long term monitoring Leaching

Soil extraction, leaching 250-500 8-12 5,000m3 minimum Chemical recycle

Residue disposal

Phytoremediation 15-40 18-60 Time /land commitment Residue disposal

Table 5:- Cost Advantage of Phytoremediation [4]

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Advantages & Disadvantages…

Advantages 1. Natural

2. Green, growing

3. Aesthetically pleasing

4. Cost-effective for large land areas where other technologies are not feasible

5. Sensible, appropriate, sustainable technology

Disadvantages 1. Long clean-up times

2. Uncertain performance

3. Not for every site (deep wastes, anaerobic soils, etc)

4. Regulatory hurdles

[8]

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To Apply Phytoremediation…..

• Wetlands offer an unlimited potential for the phytoremediation of toxins and pollutants.

• Wetlands are shallow (typically less than 0.6 m (2 ft)) bodies of slow-moving water in which dense stands of water tolerant plants such as cattails, bulrushes, or reeds are grown. In manmade systems, these bodies are artificially created and are typically long, narrow trenches or channels.[5]

They offset the cost of chemical treatments and are an alternative to regions too remote, too small, or too economically disadvantaged to support standard waste water treatment plants.

Figure 12: A Constructed Wetland

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Types of Wetlands Treatment system are:

Natural Wetlands.

Constructed Wetlands.1. Free Water Surface

System,2. Subsurface Flow

Systems.

Aquatic Plant Systems.1. Floating Plant

Systems, 2. Submerged Plant

Systems.[5]

Figure 13: Treatment Wetlands

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Treatment Wetlands

Figure 14: A Treatment Wetland depicting the various methods of Phytoremediation [4]

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Alternative Methods

Figure 15: A proposed Step for Wastewater treatment using Phytoremediation [7]

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CONCLUSIONS

The 'green technologies' are more appropriate for water clean up as:-• Decompose organic pollutants to non-toxic low molecular

substances,• Do not introduce additional chemical substances into the

environment,• Are relatively easy to manage and easily adopted to the local

needs,• Do not require large investment to be practically introduced,• Are able to remove several pollutants in combination,• Can be applied at a small as well as at a large scale.

Is a sustainable & inexpensive process is fast emerging as a viable alternative to conventional remediation methods, and will be most suitable for a developing country like India.

In India commercial application of Phytoremediation of soil heavy metal or organic compounds is in its earliest phase.

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References….

1. "WHO, Water Resource Quality." http://www.who.int/ (11/17/05).2. Loeffler R. 2001. A Study of Three Aquatic Plant Species and Their Effectiveness at

Removing Nitrates and Phosphates from a Nutrient Enriched Aqueous Solution, Sewanee,University of the South, Ecology 210.

3. Sinha R.K., Heart S. and Tandon P.K. 2007. Phytoremediation: Role of Plants in Contaminated Site Management, Environmental Bioremediation Technologies, Chapter 14, pp 315-318.

4. ITRC, April 2001, “Phytotechnology Technical and Regulatory Guidance Document”, Interstate Technology and Regulatory Cooperation Work Group, Phytotechnologies Work Team, Columbia, U.S.

5. Terry N., Banuelos G.S. 2000. Phytoremediation of Contaminated Soil and Water, Chapter 2, pp 13-18.

6. Schnoor J.L, 1997 “Phytoremediation”, Ground-Water Remediation Technologies Analysis Center (GWRTAC), Technology Evaluation Report, pp 11.

7. Peter Schröder, Juan Navarro-Aviñó, Hassan Azaizeh, Avi Golan Goldhirsh, Simona DiGregorio, Tamas Komives, Günter Langergraber, Anton Lenz, Elena Maestri, Abdul R. Memon, Alfonso Ranalli, Luca Sebastiani, Stanislav Smrcek, Tomas Vanek, Stephane Vuilleumier & Frieder Wissing. December 2006, “Using Phytoremediation Technologies to Upgrade Waste Water Treatment in Europe”, Phytoremediation Technologies, Env Sci Pollut Res 14 (7) 490 – 497 (2007), pp 496.

8. B. Van Aken, J. M. Yoon, C. L. Just, S. Tanake, L. Brentner, B. Flokstra & J.L. Schnoor, April 2005, “Phytoremediation: From the Scale Molecular to the Field”, Presented at the International Phytotechnologies Conference April 20 2005, pp 8.

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References

9. Saber A. El-Shafai, Fatma A El-Gohary, Fayza A.Nasr. , N. .Peter van der Steen, Huub J. Gijzen, March 2006, “Nutrient recovery from domestic waste water using a UASB-duckweed pond system”. Bioresource Technology 98 798–807.

10. Peter Van Der Steen ,Asher Brenner ,Joost Van Buuren and M Gidoen Oron, June 1998, “Post-Treatment Of UASB Reactor Effluent In An Integrated Duckweed And Stablization Pond System”, Wat. Res. Vol. 33, No. 3, pp. 615-620.

QUESTIONS???

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