Vertical flow constructed wetlands for the treatment of inorganic ...

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chemisorption. Cation exchange involves the physical binding of cations to the surface of clays and organic matter. Once metals are adsorbed on to humic or clay colloids they will remain there as metal atoms, their speciation however may change with time as the conditions in the sediment change, (Sheoran and Sheoran, 2006; Wiebner et al., 2005). The cation exchange capacity of soils is directly proportional to its organic matter and clay contents. Chemisorption represents a stronger a more permanent form of bonding than cation exchange. More than 50 % of the metals can be easily adsorbed onto particulate matter in a wetland and thus be removed from the water component by sedimentation. Lead and copper tend to be adsorbed most strongly whereas zinc, nickel and cadmium are usually held weakly and hence likely to be more labile or bioavailable (Alloway, 1990). Oxidation and hydrolysis of metals: Iron, aluminium and manganese can form insoluble compounds through hydrolysis and/or oxidation that occur in wetlands, such reactions lead to the formation of oxides, oxyhydroxides and hydroxides. Iron removal depends on pH, redox potential and presence of various anions (ITRC, 2003). Aluminium removal is governed by pH, it can precipitate as aluminium hydroxides at pH close to 5 (Hedin et al., 1994). Manganese removal can be accomplished by oxidation, which takes place at a pH close to 8. Bacteria play an important role in accelerating the oxidation of Mn 2+ to Mn 4+ (Stumm and Morgan, 1981). Precipitation and co-precipitation: Precipitation and co-precipitation are important adsorptive mechanisms in wetland sediments. The formation of insoluble heavy metal precipitates is one of many factors limiting their bioavailability in aquatic ecosystems. Precipitation depends on the solubility product Ksp of the metal, pH of the wetland and concentration of metal ions and anions involved (Sheoran and Sheoran, 2006). Co-precipitation: heavy metals co-precipitate with secondary minerals in wetlands. Copper, nickel, zinc, chromium and manganese are co-precipitated in Fe oxides. Cobalt, iron and also nickel and zinc are co-precipitated in manganese oxides. Alkaline conditions are necessary for co-precipitation of cationic metals such as copper, zinc nickel and cadmium (Stumm and Morgan, 1981). 32
Metal carbonates: When the concentration of bicarbonate in water is high heavy metals may form carbonates, which although not being as stable as sulphides, can still play an important role in initial trapping of metals (Sheoran and Sheoran, 2006). Metal sulphides: Anaerobic conditions and appropriate substrate may promote the growth of sulphate reducing bacteria which generate hydrogen sulphide. Most heavy metals react with hydrogen sulphide to form highly insoluble metal sulphide solids that precipitate (Stumm and Morgan, 1981). 2.4.4.3 Biological processes Plant uptake: The most widely recognised biological process in wetlands for metal removal is plant uptake. In emergent and surface floating wetland plants the main route for metal uptake is through roots, in the case of plants with completely submerged leaves or both floating and submerged leaves take up is through leaves and roots (Sheoran & Sheoran, 2006). Bacterial metabolism: It is the bacterial metabolic processes that play the most significant role in removal of metals. Reduction of metals to non-mobile forms by microbial activity in wetlands has been reported. Metals like chromium, uranium, selenium and copper are removed through reduction by bacterial activity (Sheoran & Sheoran, 2006). 2.5 Treatment of saline wastewaters Many industrial wastewaters are characterised by high salinity. Industries related to the production of chemicals, fertilisers and pharmaceuticals, food pickling, cheese manufacturing, seafood processing, tanning, oil and gas recovery and mining usually produce high inorganic salt and heavy metal concentrations in their wastewaters (Moussa et al., 2006, Lefebvre and Moletta, 2006). 33
Page 1: Vertical flow constructed wetlands
Page 4 and 5: 1. Journal articles: Items derived
Page 6 and 7: Berryman and Frances Brigg provided
Page 8 and 9: The feasibility of using carbon ric
Page 10 and 11: Table of Contents Items derived fro
Page 13 and 14: 1.1 Industrial wastewaters Chapter
Page 15 and 16: eneficial as long as the water is t
Page 17 and 18: 1.4 Scope of this thesis The main r
Page 19 and 20: Chapter 8 describes the design rati
Page 21 and 22: similar to aerobic ponds, usually s
Page 23 and 24: 2.3 Common uses of constructed wetl
Page 25 and 26: These systems favour settling of su
Page 27 and 28: Total organic carbon (TOC) determin
Page 29 and 30: organically bound N is called ammon
Page 31 and 32: Biochemically equation 2.11 is subd
Page 33 and 34: oxidised. External carbon sources s
Page 35 and 36: 2009) in FWS wetlands, and also oxy
Page 37 and 38: intensive (Reed et al., 1995). Harv
Page 39 and 40: limited because they only allow the
Page 41 and 42: whose distribution followed a clear
Page 43: The concentration of heavy metal io
Page 47 and 48: and 8.3g Na2SO4/L. The authors attr
Page 49 and 50: therefore were selected for a 97 da
Page 51 and 52: Chapter 3: Salinity impact on nitri
Page 53 and 54: associated with the reduced number
Page 55 and 56: 2000). The theoretical HRT is the a
Page 57 and 58: 3.2.3 Water sampling and analysis W
Page 59 and 60: Table 3.1: Sediment sampling dates
Page 61 and 62: threshold calculation suggested by
Page 63 and 64: 18 days. The plants in T2 wetlands,
Page 65 and 66: Even though known amounts of sea sa
Page 67 and 68: 3.3.3.1 Ammonia removal Ammonia rem
Page 69 and 70: NH 3-N (mg/L) 160 140 120 100 80 60
Page 71 and 72: attempted to be answered in one of
Page 73 and 74: During Phase I, the overall average
Page 75 and 76: NH3-Nconcentration out (mg/L) Figur
Page 77 and 78: to the literature, some peaks have
Page 79 and 80: 3.3.5.2.1 Control wetland TRFLP ana
Page 81 and 82: % of total peak area 100 90 80 70 6
Page 83 and 84: % of total peak area 100 90 80 70 6
Page 85 and 86: 3.4 Discussion 3.4.1 Plant health S
Page 87 and 88: ones reported by Kantawanichkul et
Page 89 and 90: Chen et al. (2003) observed nitrite
Page 91 and 92: Ward et al. (2000) found that in th
Page 93 and 94: Chapter 4: Nitrification and denitr
Page 95 and 96:
Figure 4.1: Experimental set up dem
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of sediment was performed through t
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4.2.7 Data analysis Microsoft Excel
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4.3.2.2 NO3-N Effluent nitrate conc
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The load vs concentration chart pre
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Because the influent pump did not d
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increased during the first two week
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clear seasonal variation in nosZ ge
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4.4 Conclusions The unplanted semi
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Fick 1997; Ingersoll and Baker, 199
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Both systems were planted with nati
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A B C Figure 5.2: A. Containers hol
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5.3.1.1 Implications of storage for
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NO 3-N (mg/L) 100 90 80 70 60 50 40
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COD (mg/L) 600 500 400 300 200 100
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Chapter 6: Heavy metals in a constr
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Figure 6.1: Photo of the constructe
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potassium, phosphorus, sulphur and
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Table 6.2: Mean (standard deviation
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values are comparable to the Aqua R
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On a dry weight basis, macrophyte r
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Chapter 7: Nitrogen removal and amm
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etween the sand surface and 0.3m ab
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profiles were analysed using Genema
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Table 7.1: Monthly total flows, ave
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clones S8-sludge and S9-sand which
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specific 119bp OTU. Even though N.
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Chapter 8: Design and monitoring of
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VF wetlands operated in parallel in
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8.2.1.1.4 Distribution/collection p
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Figure 8.4: Wetland cell 1 on the f
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Figure 8.7: Cell 2 being tested at
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on Figure 8.7. Within a year vegeta
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NH3-N Load (kg/d) 900 800 700 600 5
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The same strong positive correlatio
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construction and planting costs, in
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Considering the findings and limita
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Brant A.H., Jagoe C.H., Kelsey-Wall
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Crites, R., Tchobanoglous, G. (1998
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Gorra, R., Coci, M., Ambrosoli, R.
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Kadlec, R.H., Bastiaens, W.V. and U
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eactors. WEFTEC 79th Annual Technic
Page 179 and 180:
16S rRNA and amoA sequence analysis
Page 181 and 182:
Sun, G. and Austin, D. (2007). Comp
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Wu, Y., Tam, N.F.Y. and Wong, M.H.
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Figure A2: Permeability of the sand
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Treatment 1 wetland Dec-08 Mar-09 A
Page 189 and 190:
Comparison of Surface samples from
Page 191 and 192:
Treatment 1 wetland Mar-09 Figure B
Page 193 and 194:
Appendix C. Complementary results f
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