Chapter 15
Phytoremediation Of Industrial Wastewater
Water is one of the ultimate sinks for various pollutants. The domestic and industrial wastes are discharged in surface water bodies in increasing quantities beyond the natural treatment/buffering potential of fresh water. These wastes include large quantities of organic matter, inorganic nutrients, heavy metals and a variety of organic chemicals, all of which not only lower the water quality but also are toxic to living organisms. Heavy metal pollution of natural water resources is a major environmental problem faced by the modern world. The disposal of heavy metal rich effluents/sewage poses a problem to every large and small scale industry in the country. Several physical, chemical, and biological methods are employed by various industries for waste water treatment such as ion exchange, use of resins, electrodeposition, reverse osmosis etc, but these techniques are much sophisticated and at times costly too, and can not be taken up by small scale/low budget industries. High capital and regeneration cost in these technologies have resulted in increasing search for low cost and efficient systems. Modern researches are emphasizing a shift towards clean, ecofriendly environment, low cost and efficient technology Treatment of effluents/sewage is necessary to bring the concentration of toxic metals to desirable limits before they are discharged or utilized. Recently there has been some research in the use of living and non-living bacteria and algae for the bioremedation and recovery of heavy metals from aqueous streams
In addition, live or dead cultured cells of Datura innoxia, a higher plant can be used to remove Ba +2 from solutions Commercial application of this research is hampered by the high cost of growing pure cultures of cells and microorganisms and by the need of their immobilization or separation from the aqueous stream .
The phytoremedation concept is based on the well known ability of plants and their associated medium to concentrate and/or degrade higher contaminants. These have capability of bioaccumulation. Aquatic plants have the capability to move large amounts of solution in to the plant body through the root and evaporate this water out through transpiration. Nutrients move along with the water uptake. These plants consume a large range of contaminants, mobilize them and accumulate them in the body. The process of bioaccumulation enable the plants to concentrate the toxicant thousand time higher in them than in the soil or waste water. Such plant biomass can further be ashed to reduce its volume and the resulting small volume of material can be processed as an “ore” to recover the contaminant. If recycling the metals is not economically feasible, the relative small amount of ash could be used as a fertilizer in nutrient deficient soils or can be disposed off in an appropriate manner. In case of aquatic plants a regular harvesting can be done and, biomass can be used for making pulp and further processed, for small scale hand paper industries or can also be used for biogas generation.
Phytoremediation is the process of the removal of hazardous substances from soil or ground water contaminated with municipal and industrial wastes by plants. In a study, phytoremediation of copper (Cu), Zinc (Zn) and Iron (Fe) was observed.The purpose of the research work was to remove copper, iron and zinc from industrial wastewater (effluent) by aquatic plants. Aquatic plants have been regarded biofilters and purifiers of small and large water bodies. They are capable of accumulating various contaminants to a concentration several order of magnitude higher than in the surrounding medium. The need for better and efficient system for remediation of wastewater led to the present investigation. An attempt to use few aquatic weeds for wastewater remediation was made.Aquatic higher plants eg. Water hyacinth (Eichhornia crassipes) Water velvet (Azolla pinnata) and (Lemna minor). Have also been regarded as bio-filters and purifiers of ponds and lakes.
Owing to the importance of aquatic plants in the present study an attempt to evaluate the potential for removal of heavy metals from effluents by different aquatic plants, was made. In macrophyte based system shallow ponds, the water flow as surface, or as subsurface. The pollutants are reduced by a complex variety of physical, chemical and biological processes . The macrophytes remove pollutants by;
1. Directly assimilating them into their tissue and
2. Providing surface and suitable environment for microorganism to transform pollutants and reduce their concentration. Oxygen transfer by aquatic plants into the rhizosphere is also a requirement for certain microbial pollutant removing processes to function effectively .In the present study all the test plants that were selected did show a significant removal ability for various heavy metals (Graph: 6-8). The response of various aquatic plant species to different effluent concentration varied. All the plants studied were effective in the effluent treatment, but best resultswere obtained only at lower concentration (10 to 25%). At higher dilution trough the plants could manage to reduce the contamination load but their growth retarted to a great extent. All the test plants showed their differential uptake and were efficient enough to remove considerable amount metals.
The heavy metals Fe and Zn were found to be accumulated more in Hydrodictyon reticulata, followed by Wolffia arrhiza than Hydrilla verticillata. While for Cu, Hydrillawas more effective. All the plants efficiently removed Fe even at 50% effluent dilution, suggesting of its low toxicity. Waste water (effluent) pH, after treatment with plants in all the cases shifted towards alkalinity, which is evident from the decrease in chloride ions. The total dissolved solids decreased significantly in Hydrilla verticillata and Wolffia, followed by Hydrodictyon reticulata sets.The alkalinity also increased after phytoremedation treatment with maximum increase in Hydrilla followed by Wolffia and Hydrodictyon ). The chloride removal was observed in all the plant sets, and the trend was maximum in Hydrilla, Wolffia and Hydrodictyon.The important parameter like oxygen content in the waste-water was found to increase with phytoremedation treatment, the dissolved oxygen of higher dilution after treatment increased significantly. The change in DO was maximum in Hydrodictyon reticulata followed by Wolffia arrhiza and Hydrilla verticillata at 10% effluent concentration . The chemical oxygen demand (COD) reduced significantly in Hydrodictyon reticulata treated sets and efficiently followed by the Wolffia and Hydrilla. It was interesting to note that Hydrodictyon reticulata could decrease COD maximum at higher dilutions . Most of the domestic sewage and small scale industry effluent is poured into some stabilization lagoons. These treatment systems are economical and sufficiently efficient but have their own problems. Use of plant system together with these stabilization lagoons can prove to be far economical and effictive. , Wolffia could be effectively used for waste water treatment. It can bring down the chemical oxygen demand (COD), and Total dissolved solids (TDS), Similar results were obtained in the present investigation too, Wolffia, Hydrodictyon and Hydrilla were sufficiently effective for various metal removal.
According to wetland plants show good phytoremedation potential for trace elements and this could be seen in the present study as well, further the growth rates and harvest potential of the aquatic plants, make them fit for phytoremedationactivities. water hyacinth (Eichhornia crassipes) can remove radio active 137 cs, 90 U from radioactive wastes. It has been reported that phytoremedation is far cheaper, easier and safer than many of the conventional engineering techniques. Even though phytoremedation appears to be quite a promising process for the removal of various contaminants from soil and waste water, but still its scope is limited. More research and an integrated approach is required. A better understanding of the process involved in uptake, transport, acclimatization and reuse is needed.
At this juncture of study it can be said that, more such studies with different effluent and waste water taking various test plants, be done. In order to select a properand efficient system further genetic studies and molecular manipulation be made for improvement in efficiently.
DEVELOPING PHYTOREMEDIATION FOR CHLOROFORM IN A TROPICAL AREA
The study area is an industrial plant situated in the State of São Paulo, Brazil. The groundwater in the area is contaminated with chlorinated solvents, basically chloroform. The remediation approach used different techniques depending the concentration of chloroform. At the source area chemical oxidation with Fenton’s reagent and at the nearby plume, in situ reductive action with molasses and as a polishing system. A phytoremediation system was implemented as a barrier for the eventual contamination of an artificial lake. The goal of the study was to evaluate the effectiveness of the phytoremediation system as a polishing remediation technique and the use of tropical native species to do this. The objective of the phytoremediation system was to create a last barrier for a chloroform contamination plume (up to 16mg/l of chloroform) before the groundwater discharge reaches an artificial lake. The activities started in September of 2000 with 179 plants of 10 native species introduced in a 2175 m 2 area. Four species are from seasonal (mesophytic) and/or tropical rain forests (wet areas) and the other six, from Cerrado (Brazilian savanna). Most of the species are deciduous or semi-deciduous pioneer and secondary species that grow fast and with relatively deep root systems. It were estimated that this system will evapotranspirate in a range from 4 to 170 m 3 /day. The specie with the highest growth rate, Peltophorum dubium (Leguminosae), has grown 1,24 m in 10 months. In August/2001 it was observed an average reduction of 0,15 m of the level of groundwater at the treatment area. The groundwater depth varies from 5,6 m in the upper parts to 1,0m nearby the lake. The groundwater in the area presented a growth in the concentration of dissolved carbon after 6 months, as well as the Fe 2+ concentration. The results for chloroform are preliminary and not yet conclusive, even though a 43% reduction was observed at the wells within the treatment area, and also a metabolite, methylene chloride, appeared in the wells indicating biodegradation.
Phytoremediation acts through two fundamental remediation processes, enhancement of saturated zone in situ biodegradation and phytoextraction .The rhizosphere is the zone in the subsurface Occupied by plants root system. Within therhizosphere plants contribute to enhanced in situ biodegradation through the supply ofcarbonaceous substrate and oxygen transfer. Rhizodeposition is partially the result of thedecay of dead roots and root hairs. Also important are carbonaceous root exudations such as leakage from epidermal cells, secretions resulting from metabolic activity, mucilages from root tips (which act as lubricants for root penetration), and lysates from sloughed cells. Exudates are composed of a wide range of chemicals that include sugars, aminoacids, organic acids, fatty acids, and numerous other compounds. It is estimated that 7% to 27% of the total plant mass is annually deposited as carbonaceous material in the rhizosphere. This carbonaceous material stimulates overall bacterial activity as well as providing substrate to support cometabolic degradation of xenobiotic hydrocarbons. The primary in situ remediation potential of plants for hydrocarbons lies in their capacity to enhance oxidation rates in the subsurface and provide cometabolic substrate.However, plants also have the ability to remove compounds, a process termed phytoextraction, which can be applied to organic or metal contaminants. In the case of hydrocarbons, the compound must be water solubility and have a moderate degree of lipid solubility. Lipid solubility is a function of the octanol-water partition coefficient (Kow) for the compound. The compounds most readily mobilized by plants have log Kow values in the range of 1 to 3. Compounds with values of Kow in this range include BTEXhydrocarbons, chlorinated solvents. (the logKow for chloroform is 1,97). , and other short chain aliphatic hydrocarbons. Once in the interior of the plant the adsorbed hydrocarbons may be: stored via lignification; volatilized; partially degraded through metabolization; orcompletely mineralized. Compounds with values of log Kow higher than 3 such as PNA's are incapable of entering the root, those with log Kow values lower than 1 are rejected by the root membranes.
Site description
The site is near the 22 o S latitude. The phytoremediation system is located downhill between the contamination source area and an artificial lake, where the groundwater discharges . The slope has a 11% gradient, covered only with grass. All the phytoremediation area is within the plant limits, so there is no direct recipients of contamination nearby. According to IAC, 2002, the average monthly temperature in area ranges from 17 o C to 24 o C, and the monthly precipitation from 37 mm rain in July to 238 mm in January. The evaporation ranges from 46,1 mm in June up to 125 mm in January. Geological substratum is characterized by the palaeozoic sediments of the Itararé Group and the mesozoic basalts of the Serra Geral Group. Those rocks originate interbeded soils of silt and sand layers.
Based on the above studies , concluded that: There is a mortality of 15% of total plantings, which indicated that at the concentrations (10 mg/L of chloroform) found there is no observed toxicity._ The most adequate species among those used in this study were canafístula (Peltophorum dubium, Leguminosae) and angico-do-cerrado (Anaderanthera falcata, Leguminosae) that showed higher growth and lower death rates. _ The less adequate were manduirana (Senna macranthera, Leguminosae), pau-terra-mirim (Qualea dichotoma, Vochysiaceae), and ipê-amarelo-do-brejo(Tabebuia umbellata, Bignoniaceae)._ canafístula (Peltophorum dubium, leguminosae) growth 1,24 m in 8 months._ Even with a small period of study, the effect in the groundwater was alreadyobserved with an average drop in groundwater depth of 0,15 m _ The pumping effect was observed also in the change of the soil moisture profile _ Considering the wells in the middle and downstream of the area, it was observed an average reduction of 44% in the chloroform concentration, even though the results are not very conclusive, _ The effect of the plants seems to increase in the dissolved organic carbon which increase the conditions for a reductive decomposition of the chloroform. The increase of TOC, Fe 2+ and the show up of metabolites as methylene chloride are the evidence lines that this could be happening.
FAST-GROWING TREES FOR HEAVY METAL AND CHLORINATED SOLVENT PHYTOREMEDIATION
Recent studies with fast-growing trees in Florida have identified their potential for metal and hydrocarbon phytoremediation Greenhouse studies suggest that 1) baldcypress and castor bean are promising candidates for Cu remediation, accumulating over 15mg/kg in stem biomass, 2) a leaf disk immersion technique may indicate differences among PD clones for As, Cu, and Cr uptake, and 3) of synthetic and biological chelating agents, the combination of EDTA plus histidine increased As concentration in PD by 97% without significantly affecting growth or survival Field studies identify that silvicultural and genetic options impact phytoremediation potential. At a CCA contaminated site near Quincy, FL, although 11 of 97 PD clones had above-average growth and one clone exhibited good growth and high As tissue concentration, growth and survival were low, due primarily to poor site preparation. PD growth and As uptake at a CCA contaminated site in Archer, FL, was superior to that at Quincy but varied with season, plant tissue, and clone (CardellinoEffective phytoremediation of heavy metal or chlorinated solvent contaminated sites by fast-growing trees such as Eucalyptus amplifolia (EA), E. grandis (EG), eastern cottonwood (Populus deltoides, PD), and Salix spp. depends on tree-contaminant interactions and on tree growth as influenced by silvicultural and genetic factors. EA, PD, poplars, and willows tolerated trichloroethylene (TCE) more than baldcypress, and variation within willows was significant. PD growth and arsenic (As) uptake in Archer, FL, varied with season, tissue, and clone. For toluene phytoremediation near St. Augustine, FL, 6” diameter tubes inhibited PD and EA growth, PD and EA were similar in vigor, but an EA progeny was the most productive genotype.
At a TCE contaminated site in Orlando, FL, PD whips stuck 6’ into sandy soil rooted to the base and were up to 18’ tall in six months, with locally adapted clones surpassing a clone widely planted for phytoremediation in more temperate regions. Due to climatic stress at LaSalle, IL, unrooted willow cuttings survived poorly, but several rooted poplar clones all survived and grew rapidly in perchloroethylene (PCE) contaminated clay soil. Non-hyperaccumulating eucalypts, poplars, and willows may phytoremediate while providing an income from energywood, mulchwood, and/or pulpwood.
Effective phytoremediation of heavy metal or chlorinated solvent contaminated sites by fast-growing trees depends on tree-contaminant interactions and on tree growth as influenced by silvicultural and genetic factors. A greenhouse study suggests that young EA, PD, poplars, and willows have similar TCE tolerance, with perhaps useful variation among willow clones. Field studies identified silvicultural and genetic options that impact phytoremediation potential. PD growth and As uptake varied with season, plant tissue, and clone. Small diameter “training” tubes were ineffective in promoting PD and EA root growth, PD and EA were equal in vigor, but an EA progeny was the most productive genotype. PD whips deep planted 6’ into sandy soil effectively rooted to the base of the whip, unless impacted by fluctuating groundwater, and averaged 18’ in height in six months. Locally adapted clones grew more rapidly than a well documented clone planted for phytoremediation purposes in more temperate regions. Unrooted willow cuttings survived poorly compared to rooted poplar cuttings due to late spring freezes, while several poplar clones all survived and grew rapidly in PCE contaminated clay soil. Fast-growing eucalypts, poplars, and willows have phytoremediation potential when superior genotypes are matched with the necessary silvicultural options. As non-hyperaccumulators, they may provide an income to offset cleanup costs.
REFERENCES
Paper F-07, in: V.S. Magar and M.E. Kelley (Eds.), In Situ and On-Site Bioremediation—2003. Proceedings of the Seventh
International In Situ and On-Site Bioremediation Symposium (Orlando, FL; June 2003). ISBN 1-57477-139-6, published by
Battelle Press, Columbus, OH, www.battelle.org/bookstore.Cyro Bernardes Junior (cyrobernardes@ambiterra.com.br), Marcia Sabbag, Cristina
Simonetti, Paula Nogueira, Patrícia Oshiro, and Duva S. Brunelli(AMBITERRA Ltda, São Paulo, Brazil)Dave Vance (ARCADIS, Houston, TX, USA)
Paper F-12, in: V.S. Magar and M.E. Kelley (Eds.), In Situ and On-Site Bioremediation—2003. Proceedings of the Seventh
International In Situ and On-Site Bioremediation Symposium (Orlando, FL; June 2003). ISBN 1-57477-139-6, published by Battelle Press, Columbus, OH, www.battelle.org/bookstore.
D. L. Rockwood, (dlrock@ufl.edu) and R. Cardellino (University of Florida, Gainesville, FL, USA)
G. Alker (WRc, Swindon, UK)
C. Lin and N. Brown (Ecology & Environment, Tallahassee, FL, and Chicago, IL, USA)
T. Spriggs and S. Tsangaris (CH2M Hill, Tampa, FL, USA), J. Isebrands (Environmental Forestry Consultants, New London, WI, USA)
R. Hall (Iowa State University, Ames, IA, USA)
R. Lange (Illinois EPA, LaSalle, IL, USA)
B. Nwokike (Southern Div. Naval Facility Engineering Command, Charleston, SC, USA)