Rapid population growth, urbanization and socioeconomic development are exacerbating the growing water demand. Furthermore, pollution of water sources, uneven distribution of water resources and global weather change are exerting severe effect on water demand (Asano and Cotruvo, 2004) Therefore, to sustain the water crises many treatments technologies and purification techniques are adopted to meet required guidelines (Kennedy, 2010). Advanced water treatment technologies have high capital and operation costs and require operators with high expertise (Westerhoff and Pinney, 2000). One of the reasonable water engineering solutions to cope with water shortage is to use reclaimed wastewater effluents, storm water or surface water through a natural filtration system considered as a soil aquifer treatment (SAT) (Asano and Cotruvo, 2004).
SAT is used for the subsurface infiltration of wastewater or other reused water passing through soil percolation barrier to the ground water aquifer. That is to say, it is a technology which helps to manage recycles water to recharge into aquifer zone under certain controlled conditions with later withdrawal (Houston et al., 1999). SAT is one of managed aquifer recharge (MAR) systems. MAR has many schematic designs such as SAT, aquifer storage and recovery (ASR), aquifer storage, transfer and recover (ASTR), infiltration ponds and others (Authority, 2005). Also MAR can serve as a barrier against saltwater or other contaminants entering soil aquifer (Leviston et al., 2006).
The main idea of SAT as a natural filtration system is the attenuation and the removal of the contaminations from reused water containing all kind of contaminations especially endocrine disrupting compounds (EDCs) specified as chemicals, pharmaceutically active compounds (PhACs), different range of industrial chemicals, agricultural and domestic polluted elements as well as dissolved organic carbon DOC (Amy and Drewes, 2007; Rice and Bouwer, 1984).
SAT is considered as one of the conspicuous technologies used in the unsaturated and in the saturated zone of the aquifer to improve water quality of wastewater effluent (Cha et al., 2004). Several investigations conducted at laboratories level and field studies during which was SAT was operated using different wastewater quality, soil type, residence time, hydraulic loading rate aerobic and anoxic conditions as well as wetting drying cycle revealed its effectiveness in remiving a wide range of contaminants (Sharma et al., 2008). Nevertheless, the removal process of organic matter as well as EDCs during the SAT is still not completely comprehensible due to the absence of complete information about mechanism of removal in underground hidden layers, effect of temperature variations as well as attenuation level of EDCs.
EDCs are considered as an anthropogenic chemicals that could have adverse effect on endocrine system of fish, wildlife as well as humans (Health, 2010). Moreover, EDCs include almost 87,000 chemicals produced worldwide. Institute of Environmental and Health in UK listed 966 known potential EDCs.
The fate and the removal mechanisms of EDCs during soil passage mostly depend on many parameters of SAT such as characteristics of soil type (Bouwer, H. 2002) , infiltration rate applied catabolic activities of microorganisms living in that certain type of soil (Fox et al., 2001), redox conditions during drying cycle of soil (Pescod, 1992), temperature of soil, organic matter and the trait of EDCs (Amy and Drewes, 2007).
It is urgent to investigate and to understand clearly the procedure of the biodegradation, sorption, activation and transport of EDCs during the SAT passage under different temperature conditions (Maeng et al., 2010).
1.2 Problem identification
SAT is a sustainable process for reduction of EDCs and dissolved organic carbon (DOC) (Fox et al., 2005). However the effect of ground water recharge techniques such as SAT and subsurface injection evaluate the fate and the transport of EDCs (Heberer, 2002). Moreover the estrogenic activity is detected in ground water where wastewater effluent is recharged (Conroy et al., 2005).
EDCs are mostly accumulated in suspended solids or in sediments. Depend on seasonal temperature variations EDCs intrusion in ground water aquifer through soil possible. Hence, based on researches degradation of EDCs depend on many factors such as redox conditions, temperature, travel distance, pH of the soil, dissolved and suspended solid and organic matter content (Gomes et al., 2003).
EDCs appear in the environment from different sources and pathways. It may appear in aquatic environment by means of sewage leakage, or run off from industrial wastes, agricultural one as well as natural hormones and steroid drugs used to promote the growth in livestock (Birkett and Lester, 2002). In general, the wastewater treatment plants are considered as the main primary sources for the EDCs appearance in the environment. Furthermore EDCs have been detected in surface water as well as in drinking water (Desbrow et al., 1998).
The EDCs formed natural synthetics of estrogens and the contact with activated sludge during aerobic batch experiments showed the reduction of 17β-estradiol (E2) during wastewater treatment (Ternes et al., 1999). The biodegradability of estrone E1, E2 under aerobic condition is much higher than anaerobic one (Ying et al., 2004). However the complete biodegradation of EDCs is still remaining a concern for the water engineers. In general, the investigation shows that the biodegradation under aerobic condition of redox is a primary factor. However the biodegradation in anaerobic redox conditions still need more scientific investigations. Moreover, to evaluate the degradability under different redox conditions for the estrogenic and for the androgenic hormones is ongoing research procedure (Westerhoff et al., 2005).
Only limited number of studies has been carried out to probe the influence of temperature and redox conditions on the fate and transport of EDCs and individual steroids during SAT. Further no information is available on the rate of EDCs in primary effluent during soil passage (Nema et al., 2001).
Goal and Objectives
The main goal of this study is to investigate the fate and the removal level of EDCs passing through the SAT during the temperature change and redox operating conditions in unsaturated and in saturated system respectively using laboratory-based soil columns and batch reactors.
The particular objectives of this study are the following:
To study the impact of properties of EDCs on their removal in SAT system.
To investigate the effect of temperature variation on removal of EDCs during unsaturated SAT.
To probe the influence of redox conditions on removal of EDCs during SAT.
To explore the effect of retention time (HLR) on attenuation of EDCs during saturated as well as unsaturated SAT.
LITERATURE REVIEW.......................................................................
Endocrine disrupting compounds (EDCs)........................................................
2.1.1 Introduction....................................................................................................
Endocrine systems are hormone systems found in human and any other types of living organisms (Wikipedia). The production of hormones is carried out by glands located through the human body. Produced hormones released into bloodstream and served as chemical messengers. They joint with cells and receptors which carry out the hormones instructions to change proteins existing in cell as well as to produce automatically genes that will build a new protein. The biological process of body regulates by endocrine system which includes development of brain, nervous system, the function and the growth, process of metabolism, the level of blood sugar (Colborn et al., 1993). Shortly the endocrine system controls the biological growth of body starting from adulthood to the old age. Therefore the appearance of strange (artificial) EDCs, defined as chemicals, in living body will have adverse consequences by changing the endocrine functions of that body (by disruption of their artificial synthesis and metabolism) effects on fish. However, concerning to human it still needs to investigate scientifically (Kavlock et al., 1996). In addition this is reminds the similarity with bacteriophages.
Figure 2.1.1 http://en.wikipedia.org/wiki/Endocrine_system
Endocrine-disruptor-graphic - Report images - toxicants that interfere with the endocrine system - (http://www.google.com/)
2.1.2 Origin and emission routes of EDCs in the environment
In common EDCs found in environment have not high toxicity rather than being hormonally active and to be able to change normal physiology or biological function of the host organism as soon as they are in living body (Zacharska et al., 2010).
The main environmental EDCs compounds are various members of separate chemical groups such as the E1, E2, estriol (E3), 17α-ethynylestradiol EE2, Bisphenol A (BPA), and 4-tert-octylphenol (4 - t - OP). The members group of E1, E2 and E3 consider as natural one. These hormones occurring in nature derived from female hormones very important for maintaining reproductive tissues. The group of EE2, BPA and 4 - t - OP in the rage of synthetic estrogens (Desbrow et al., 1998). The steroids have significant endocrine disruption potential. They are mostly estrogens and contraceptive and including (E2), (E1), (E3), (EE2) and mestranol (MeEE2) (Ying et al., 2002). Moreover (E2), (E1) based on their tetracycline molecular structure they include distinguishing aromatic A-ring (Sarmah et al., 2006).
Figure 2.1.2.
Molecular structures of natural estrogen 17h-estradiol, its derivatives (estrone and estriol) and the synthetic analogue, 17aethynylestradiol (The letters and numbers indicate the ring assignments and carbon numbers, respectively). (Sarmah et al., 2006; Ying et al., 2002).
2.1.3 Classification and physical-chemical properties of EDCs
EDCs are classified as chemicals. EDCs found in aquatic environment have various structural forms as well as physical and chemical properties. Physicochemical properties of EDCs are pointed out mostly their molecular weight, solubility, vapor pressure, bio-concentration (log KOW) and pKa equilibrium constant (dissociation constant in aqueous solution). Based on their parameters such as water solubility, adsorption coefficient (log KOC), bio-concentration (log KOW), Henry's law constant the fate and the behavior of EDCs are different (Rahman et al., 2009).
In general many of EDCs have low solubility degree with high or moderate log KOC (organic carbon-referenced sorption coefficients or organic carbon-normalized partition coefficient (cm3g-1 of organic carbon). Hence the insoluble mass of EDCs eventually is finished in organic compounds. It can be ab/adsorbed or can be sediment. This process of division into organic fractions is baffled in the log Kd (respective or linear sorption coefficient (cm3 g-1 or dm3 kg-1) values. Even in digested sludge the value of Kd remain high. In the sediments the biological attenuation is reflected to less or more active forms of degradation or transformation. Possibility is that especially more soluble predecessors of EDCs are detected in groundwater and in drinking water due to high pH or the formation of EDCs' molecular aggregates of colloidal size (Campbell et al., 2006). In case of synthetic EDCs; the synthetic BPA is less estrogenic. After aerobic biodegradation it sorbs solids degradation products which are more estrogenic than BPA itself (Council).
The solubility of synthetic estrogenic steroids is lower. EE2 has 0.3 mg/l and mestranol 0.3 mg/l (Lai et al., 2000). Moreover the range of vapor pressures fluctuated from 2.3 x 10 -10 to 6.7 x 10-15 (mm Hg) (shown in Table 1). The table of these steroids illustrates that estrogens belong to hydrophobic organic compound with low volatility. Consequently the expectation that factors such as sorption on soil or sediment is significant to reduce in aqueous phase concentrations.
Table 2.1.3
Chemical name
Molecular
weight
Water
solubility
(mg/l at 20 jC)
Vapour
pressure
(mm Hg)
log
Kowb
Estrone
(E1)
270.4
13
2.3 x 10-10
3.43
17h-Estradiol
(E2)
272.4
13
2.3 x 10-10
3.94
Estriol
(E3)
288.4
13
6.7 x 10-15
2.81
17a-Ethynylestradiol
(EE2)
296.4
4.8
4.5 x 10-11
4.15
Mestranol
(MeEE2)
310.4
0.3
7.5 x 10-10
4.67
Phsycochemical properties of steroids (Lai et al., 2000) (Lai KM).
b Octanol- water partition coefficient.
The observations show that the natural E1, E2, E3 and the synthetic EE2 estrogens have different biodegradable level (highest to lowest). E3 is the heist one > E2 > E1 > EE2. Aerobic conditions rapidly oxidize E2 to E1. The fate and the degradation level of by-products such as EE2, E3 and E1 are still unknown (Figure 2). However the degradation level in freshwater (6 to 10 days) is higher than the inlet of the sea where the salt and the freshwater mixed to combine as estuarine waters (14 to 49 days). In case of the higher temperature the more rapid microbial degradation will occur (Jurgens et al., 1999).
EE2 - is the major ingredient of contraceptive pill. It may have even higher estrogenic activity comparing with their natural duplicates. However E2 also may have 5-1000 greater activity than oestrone and oestriol (Lee et al., 2003). Bothe natural and synthetic groups have variable degradation steps based on aerobic and anaerobic conditions (Jurgens et al., 1999). Consequently not completely degraded estrogens' appearance in groundwater aquifer is a major anxiety for the future.
Figure 2.1.3
Estrogen Degradation, Biodegradation of estrogens E1, E2, E3 and EE2, (Porter and Hayden, 2002).
2.1.4 Fate of EDCs in wastewater treatment plants (WWTPs)
EDCs are invisible threat to humans and to environment. The wastewater treatment technologies are not so developed to remove EDCs chemicals in wastewater treatment plant. Consequently these chemicals escape from treatment phase and appeared in environment spreading evil in surrounding wildlife. Many studies have investigated the percentage and the mechanisms of estrogen elimination in wastewater treatment plants (Andersen et al., 2003; Clara et al., 2005; Johnson and Sumpter, 2001; Joss et al., 2004). During the preliminary treatment impossible to remove EDCs compounds. However during the primary and secondary clarifier treatment procedure thanks to sorption process the removal of estrogen is significant in liquid phase (Pauwels et al., 2008). According to Clara (Clara et al., 2005) the high pH influence the desorption of E2 and EE2 from sludge.
The EDCs removal strategy has three steps such as A) physical removal, B) biodegradation as well as C) chemical advance oxidation (CAO) (Liu et al., 2009).
As a physical removal the activated carbon (AC) is used. AC applied with two forms such as powder activated carbon (PAD) and in granular form (GAC) in packed bed filters. The researches have been done to show the effectiveness of both PAC and GAC during the removal of trace organic elements from water (Asada et al., 2004; Matsui et al., 2002; Westerhoff et al., 2005). Moreover the test with AC in laboratory conditions on pilot and full-scale plants shows that AC has capability to remove some range of EDCs (Fukuhara et al., 2006; Iwasaki et al., 2001; Snyder et al., 2004; Zha and Wang, 2005).
All these studies were focused on removal efficiency and the influence of physicochemical properties on EDCs as well as the finding the best type of material for AC productions. In studies of Abe (Abe, 1999) there were calculated about 70 EDCs removed by AC based on their chemical structures and activation time. With increasing activation time the volume of micro - pores and the specific surface area increasing as well (Iwasaki et al., 2001). The EDCs for three compounds such as Bisphenol A, amitrol and nonylphenol were investigated by GAC with fixed bed on lab-scale. The EDCs with high Kow (octanol-water partition coefficient) values removed effectively based on AC types and service life. Moreover the coal-based carbon type was found the most effective because of its larger pore volume (Choi et al., 2005). Meanwhile E1 and E2 were used to value the absorption capacity of removal performance. It was studied that the basic environmental parameters such as the concentration of adsorbent, pH and salinity of water, the presence of humic acid as well as surface-active agent had obvious effect. Moreover the adsorption capacity of AC is decreased as soon as the adsorbent concentration increased. The presence of the surface-active agent and the humic acid is influenced negatively on adsorption of AC as well (Zhang and Zhou, 2005).
The amount of E2 that adsorbed simultaneously in river water and in the secondary effluent was one-thousandth of that in pure water solution. Besides the higher deterioration of adsorption capacity had been found in the effluent of wastewater treatment plants (WWTPs) (Snyder et al., 2004).
B) EDCs removal by biodegradation
Conventional wastewater treatment system is designed to remove organic substances and other contaminations which are very easy biodegradable. However the last researches for EDCs discovered that during the activated sludge processes the EDCs decreased definitely. The main process for EDCs diminution was biodegradation rather than chemical precipitation, aeration or sludge absorption (Andersen et al., 2003; Braga et al., 2005; Svenson et al., 2003). Based on research data it was clear that EDCs were not completely removed in WWTPs. The effluent water contains EDCs which had less but not enough percentage than the influent wastewater. Probably it was connected to poor operation or inadequate sludge activation. However the studies for EDCs removal by activated sludge processes were carried out in Germany, Canada and Brazil starting from 1999. It shows the effectiveness of removal E1, E2 and EE2. The data were fluctuated from 83%, 99.9% and 78 % (Ternes et al., 1999). Some researches in Sweden show that estrogenic compounds were removed better in activated sludge 81%, for trickling filters it was 28% and the chemical precipitation methods made only 18% (Svenson et al., 2003).
E1, E2 and EE2 were investigated in one German WWTP and it was found more or less the same results. E1, E2, was above 98% comparing EE2 that had lower value. However the degradation procedure of EE2 started only in nitrifying tank (Andersen et al., 2003). Later on the same result discovered (Yi and Harper Jr, 2007) showing the relationship between the biotransformation rate of EE2 with the biotransformation rate in a series of batch experiment of NH3-N. Some investigations had been done to remove of biomass catalyzes through organic micro pollutants though bio-oxidatin (co-metabolism). The effluent of pharmaceutically active compounds (PhACs) sample were collected on the day of 60 and then was calculated the removal efficiency (Abel 2009).
Two controversial ideas about the solids retention time (SRT) on removal of EDCs appeared. According to Clara (Clara et al., 2005) SRT is an appropriate data for design parameters of removal EDCs. However (Servos et al., 2005) came to the result that SRT has not a strong relationship with the removal of EDCs especially when SRT measured by chemical analyzes and by biomass.
The biotransformation of E2 into E1 (Johnson et al., 2005) is the result of high E1 in the effluent than E2. The environmental conditions such as dissolved oxygen on removal of EDCs considered as an important factor as well. Therefore the removal efficiency of EDCs in aerobic condition remain higher comparing with anaerobic one (Furuichi et al., 2006).
The measurement have been carried out by using GC-MS analysis and E-screen and chemical derived values in range of 0.1% - 1340% to compare the influent and the effluent outcome of two WWTPs ( (endocrine et al.). The result from two WWTPs were suggested that chemically derived estrogenic activities were 1.2 - 83.8% measured by ER ligand competitive binding chemical probe (Esperanza et al., 2007). The Bioassays method for information about activated EDCs has low cost and has capability of throughput for large - scale mounting. However to evaluate the pollution index in wastewater plant the Chemical Oxigen Demand (COD) and Biological Oxygen Demand (BOD) is used rather than bioassay one.
The chemical advance oxidation methods used for removal of EDCs as well. The mineralization of pollutants in wastewater to CO2 used by Chemical Advanced Oxidation (CAO) mechanisms. Moreover to transfer pollutants to any other metabolite products is carry out by strong oxidizers as well through oxidation reduction reactions. For the CAO method it is important to choose the main oxidizers. For some wastewater treatment plant as oxidizers (such as FeO4) are listed for the redox potentials. In general for the strength order for the redox potential suggested FeO4-2 > O3 > S2O42- > H2O2 > Cl2 ClO2. For removal of EDCs some combinations are used; UV/O3, UV/H2O2 (hydrogen peroxide) or UV/ Fenton. All these methods used from hydroxyl radical (OH) generations and with the redox potential 2.80V and higher to get better results (Basile et al., 2011).
The three categories are essential during the removal EDCs by CAO. 1) To optimize the operational conditions for the removal efficiency of CAO. 2) Degradation dynamics. 3) Degradation pathways. The results of the research based on artificial sewage carried out by (Jiang et al., 2005).
The most common disinfectant such as chlorine is used for disinfection of effluent water in wastewater treatment plants and the removal of BPA and E2 (Hu et al., 2002). However the result had been evaluated that the reaction by chlorination was incomplete. Moreover for BPA the estrogenic activity was not decreased after chlorination (Hu et al., 2003).
O3, UV/H2O2 and other combination methods provided more effectiveness than chlorination one. The removal efficiency of UV/H2O2 for BPA, E2 and EE2 were above 90% (Rosenfeldt and Linden, 2004). The combination of UV/H2O2 was proved by Chen (Chen et al., 2006) as well (Chen et al., 2007).
Some investigations show the concentration of estrogenic compounds after wastewater treatment by conventional methods. In table 3 the data are given (Desbrow et al., 1998).
Compound
Concentration range
17b-oestradiol (E2)
1-50 ng l-1(a,b) up to 64 ng l-1(c)
17a-ethinyloestradiol (EE2)
0.2-7 ng l-1(a,b) up to 42 ng l-1(c)
Table 2. Examples of concentration ranges of estrogenic compounds in sewage treatment
works (STWs) effluent.: (Desbrow et al., 1998).
Removal of EDCs from effluents.....................................................................................
The EDCs removal from effluent water starts in primary sedimentation tank in WWTPs. The mechanism is known as adsorption. The degree of removal of micro-pollutants is based on the hydrophobic capability of hormones, the reaction time and the surface loading rate. The lipophilic compounds such as fats, oils and greases have larger adsorption rate for adsorption of hydrophobic compounds as well as endocrine disruptors. The fact is that estrogens are hydrophilic, polar and show low adsorption. The concentration ratio between organic liqud and water log Kow for E1,E2, E3 is 3.4, 3.1, 2.7. E1 removal research in Norway WWTPs and Canada E2 and E1 occurred only in primary treatment (Koh et al., 2008).
Secondary treatment is the main process of biological treatment to remove most of estrogenic activities. The fast and effective removal of microorganisms as well as EDCs is carried out under aerobic conditions through catabolic pathways (Mills and Chichester, 2005).
The steroid hormones can be removed by membrane bioreactors. It has an advantage and more flexible during the operation at higher solids retention time (SRT). The integration with biological degradation of waste product and membrane filtration is prospective development for WWTPs. The removal rate of steroids hormones is higher than 90% in membrane bioreactors with nitrification and gentrification (SRT 12-15d) (Jones et al., 2007).
The removal of EDCs by flocculation, adsorption, oxidation and chlorination makes 90%. However some endocrine disruptors can be removed only partially. Consequently the treatment methods depend on the individual structure of the EDCs (Gros et al., 2006).
Advantages and disadvantages of EDCs (removal)...............................................................
Activated sludge and membrane Bioreactor Processes is used for removal of EDCs. The conventional activated sludge (CAS) is biological process where aerobic biodegradation of suspended solids and dissolved organics are combined in wastewater. This procedure is effective and efficiency makes higher than 50%. The development of removal efficiency needs to be investigated (Radjenovic et al., 2007).
Reverse Osmosis
Membrane based treatment process. The separation of contaminants from water is taking place through membrane under pressure. Dissolved contaminates are separated from water when water passes through membrane. It effectively removes micro constituents. This process is a physical one which effectively removes contaminations. During RO the high loss of product water are lost. It consumes high energy due to high pressure. The large volume of waste increases disposal cost (Comerton et al., 2007).
Activated Carbone based on adsorption of micro constituents by GAC and PAC. It is an effective adsorbent. It removes many dissolved compounds existing in water. Removal efficiency of EDCs is high. The disadvantages of AC are the high cost, the lifetime as well as the material of the carbon (Abe, 1999).
Oxidation and advance oxidation processes (AOPs) can be used for removal of EDCs as well. It includes the removal by chemical distraction procedures. The consequence of the AOPs is to oxidize the toxic organic compounds into carbon dioxide, water as well as mineral acids (Abbaszadegan et al., 2008). It comprises three types of oxidation processes such as chemical oxidation, advance oxidation and oxidation photolysis. The removal efficiency of EDCs UV/H2O2 makes 90% (Rosenfeldt and Linden, 2004). Most of conventional combinations are not effective due to lower oxidant concentrations and less powerful oxidants are required to destroy the trace concentrations of the micro constituents (Andreozzi et al., 2004).
Different Methods to remove EDCs.................................................................................
Soil aquifer treatment (SAT)
2.2.1 Introduction
Soil aquifer treatment (SAT) is a treatment technology when application of wastewater effluent through percolation basins can renovate the wastewater quality equal to the level of drinking water quality standards (Amy and Drewes, 2007). During the passage through soil matrix the wastewater is influenced by processes such as physical and biochemical. Therefore the treatment technology is considered as a cost effective. The worldwide application of SAT is a profitable treatment especially in developing countries even though SAT is used in developed countries as well (Sharma, 2007). SAT system is very common to use for primary (Nema et al., 2001) as well as secondary and tertiary (Drewes et al., 2003) wastewater effluents degradation and treatment procedures (Fox et al., 2001). The design and operation of SAT system depend on several factors such as pretreatment degree of wastewater before SAT, type of percolation basins, depth of soil percolation zone, the wet/dry operational schedule of soil infiltration zone of SAT, mixture and travel distance of biodegraded water through ground water flow to the recovery wells (Fox et al., 2001).
Figure 2.2.1
Schematic of soil-aquifer treatment (Fox et al., 2001).
Table 2.2.1.1
Process/parameter
Infiltration interface
Soil percolation
Groundwater transport
Treatment mechanisms
Filtration,
biodegradation
Biodegradation,
adsorption
Biodegradation,
adsorption, dilution
Transport
Saturated
Unsaturated
saturated
Residence time
Minutes
Hours to days
Months to years
Travel distance
Inches/centimeters
10-100 ft/3-30 m
Variable
Mixing
No
No
Yes
Oxygen supply
Recharge water
Unsaturated zone
Regional groundwater
Biodegradable carbon
availability
Excess
Excess/limiting
limiting
Redox conditions
Aerobic
Aerobic to facultative
(denitrifying)
Aerobic to anaerobic
Comparison of typical SAT zones (Amy, 2006b).
Factors influencing SAT operation
The most important parameter during the SAT passage for reclaimed water is the quality of wastewater applied to SAT. In the soil water interface surface the total oxygen is being utilized due to biological activities of effluent water. Finally the anoxic water flows through saturated zone (Pescod, 1992). Other parameters are temperature (Amy and Drewes, 2007) and redox reactions (Pescod, 1992). The redox reactions can be result of gaining or loosing electrons which finally will be the consequence of reduction and oxidation of the ions. For example (Fe) can reduced to soluble (Fe2+) ferrous form or oxidize (Fe 3+) which will precipitate as Fe (OH)3 ferric form (Nelson, 2002).
Influence on temperature and redox conditions on SAT performance
Temperature
The temperature is the most important parameter for all processes during the SAT such as physical and chemical reactions as well as reaction rates, adsorption and degradation. Moreover the high temperature can promote the growth of water plants or fungus in wastewater (Metcalf and Eddy, 2004). The parameters such as temperature, pH, oxygen concentration as well as electrical conductivity affecting the processes developed during the SAT. Consequently with increase of temperature the dissolved organic carbon (DOC) increases as well. Fast biodegradation process starts based on microbial activity (Sharma, 2007). The numerical predictions proved that after the influence of the temperature on surface tension, it will be assumed, the capillary rise occurred under the influence of the temperature of soil water pressure head. The hydraulic conductivity depend on temperature expressed
KTs (h) = α*k KTref (h)
where KTs and KTref mark the hydraulic conductivity at the certain temperature T oC and at the soil temperature oC
α*k is the temperature scaling factor for the hydraulic conductivity which is depend on some parameters such as density ρ [M/L3] and viscosity µ [ M/TL] of soil water at the temperatures of Ts and Tref
α*k = (μTref / µTs ) x (ρTs / ρTref)……. infiltration rate affected by temperature (Bouwer, 2002). The decrease of infiltration rate can cause physical and biological clogging in recharge basins. Consequently similar to chain reaction the retention time and the DOC removal depend on infiltration rate as well (Drewes and Fox, 1999). The infiltration rate keeps the ground water table to be changed. In case if the ground water table more than 1 m from the bottom of the recharge basins the infiltration rate remains independent from the water levels. In case if ground water table less than 1m from bottom of the recharge basins than infiltration level decreases linearly by decreasing depth of water level (Bouwer, 2002). The water level based on infiltration rate changes with seasonal variations as well. Cool water viscosity is high and winter the infiltration rate is less comparing with summer. The low viscosity based on the high temperature creates greater van der Waals forces. This temperature dependent phenomenon is increasing the removal efficiency of contaminations during the SAT. The optimal temperature for nitrification was investigated at the lab conditions make (20 - 30) oC (Malhi and McGill, 1982).
The temperature affecting on metabolic activities of microorganisms as well as gas-transfer rates for adjustment of the biological solids are essential as well (Mulkerrins et al., 2004). For the biological activities during the SAT the proper temperature is in the range of (25 - 30) oC. At the 50 oC aerobic digestion is stopped. Inactivation of the methane-producing bacteria starts 15 oC, the function of autotrophic-nitrification is ceased at the temperature 5 oC. Moreover, when temperature drops to 2 oC chemo-heterotrophic bacteria using carbonaceous are becoming latent (Metcalf and Eddy, 2004). The temperature dependant biological process can be expressed through the fallowing equation:
KT = K20 x θ T-20
Where the
KT is the reaction rate coefficient at certain T temperature, oC
K20 is the reaction rate coefficient at 20 oC
θ is the Temperature activity coefficient
T is the temperature, oC.
Redox
The organic and inorganic conditions develop the process of biodegradation (conversion of organic carbon to inorganic one) by changing the oxidation state of inorganic compounds with activation of microbes mediating oxidation/reduction (redox) reactions between electron donor and respectively electron acceptors (Lovley et al., 1994). In redox reaction the hydrogen ions are involved. Consequently, the influence of pH is occurs as well as changes of carbonate alkalinity. Moreover as soon as the oxidation state of inorganic compounds is change it can bring about a) anoxic conditions, b) removal of nitrate and others c) precipitation of solid phases and d) modification in the toxicity of many hazardous metals (Abrams et al., 1998).
The redox zones in aquifers can be developed by several ways (Baedecker and Back, 1979; Barcelona et al., 1989; Champ et al., 1979; Edmunds et al., 1984; Jackson and Patterson, 1982). The studies suggest five development zone of redox condition: 1) oxegen reduction zone, 2) de-nitrification as well as manganese reduction zone, 3) iron reduction zone, 4) sulfate reduction zone and 5) methane production zone. In this each zone the oxidation of organic matter to oxidant will occur. During this oxidation steps to oxidize per mol of organic carbon will allow the free energy change with the greatest capacity (Champ et al., 1979; Froelich et al., 1979) .
According to the U.S. Geological Survey (Cape Cod research site in Massachusetts) oxic, suboxic and anoxic redox zone identified had been identified within sewage effluent (LeBlanc, 1984).
Figure 2.2.1
Conceptual illustration of redox zones in a vertical slice down the long profile of the plume at the Cape Cod site, oriented along a hypothetical flow plane (LeBlanc, 1984).
The suboxic zone is applied for the de-nitrification and for the manganese reduction as well as iron one due to the presence of small concentrations of dissolved oxygen (Kent et al., 1994) .
The three main redox conditions during the filtration of wastewater effluent duaring the SAT are 1) aerobic 2) anaerobic and 3) anoxic.
Aerobic
The presence of oxygen in unsaturated zone is main controlling factor of redox condition during the SAT (Massmann et al., 2006). The oxygen concentration 2-6.3 mg/L in reclaimed water shows the efficacy of unsaturated vadose zone which helps biochemical processes to be finished during passage through aerobic conditions (Nema et al., 2001). The attenuation of EDCs occurred in this zone is the highest compearing with anaerobic one (Furuichi et al., 2006) and the domination of aerobic condition in subsurface zone will continue as long as oxygen will be present (Boulding and Ginn, 2003). Mostly the development of the aerobic conditions happened in subsurface 0.5-1.5 m of vadose zone in the end of the drying cycle of percolation basins (Fox et al., 2001).
Anaerobic
The dissolved oxygen consumed during the water percolation through the vadose zone which makes redox potential to decrease. Followed by iron and manganese after the decrease of redox potential the nitrate becomes electron acceptors for the next oxidation step. As soon as the presence of nitrate is finished the sulfate-reducing condition developed (Fox et al., 2001).
The investigation in anaerobic redox for biotransformation of EE2 and E2 under methanogenic, sulfate-, iron- and nitrate-reducing conditions shows that anaerobic degradation of EE2 absence. Concerning to E2 it was transformed to E1 under all four above mentioned anaerobic conditions. Moreover the oxidation of E2 was not inhibited even though the E1 was present (Chang et al., 2005).
Anoxic
Denitrification starts as soon as redox potential decreased under anoxic conditions in limited anaerobic parts in the aerobic zone (Idelovitch et al., 2003). The development of anoxic condition can start with long term primary or high-strength wastewater effluent into percolation basin. The soil clogging will developed anaerobic conditions in the underneath of the recharge basin (Van Cuyk et al., 2001).
The observation for E2 compounds in anoxic ground water shows very low degradation rate compairing with aerobic one (Ying et al., 2004; Ying et al., 2003).
They also observed that only E2 degraded in anoxic groundwater, although this degradation rate was significantly slower than under aerobic conditions (Ying et al., 2003, 2004). In these studies low EDCs biodegradation may have been limited based on two factors, those are; the lack of sufficient nutrients for complete biodegradation process and the usage of old samples of aquatic material (Ying et al., 2008).
Removal of contaminants in SAT systems
SAT has a great capability to remove various categories of contaminants through physic-chemical processes taking place in vadose as well as following saturated zone based on simple operation and cost effective procedures (Amy and Drewes, 2007).
SAT filtration based on biotic and abiotic mechanisms before recharging it into ground water system (Xue et al., 2009). Moreover, SAT as a natural filtration system mainly depend on wastewater effluents quality. During the percolation procedures through unsaturated zone several the mechanisms are taking place such as biodegradation, reduction oxidation, chemical precipitation, adsorption followed by saturated zone the nitrification and denitrification which finally end up with mixing groundwater flow (Amy and Drewes, 2007). Consequently these mechanisms can influence not only degradation of organic compounds but also attenuation of natural or anthropogenic estrogenic compounds such as EDCs(Ying et al., 2003).
Table 2.2.4.1
Parameter Typical range DOC (SE) 10-94% DOC (PE) 12-62% Total Nitrogen 25-90% Phosphorous 70-99% Pathogens 4-6 log removal NH4-N >98% NO3-N 20-70%
Typical removal efficiency of SAT systems for different contaminants. Sources: (Sharma et al. 2007; Fox et al. 2001; Idelovitch et al 2003)
Removal of EDCs during SAT........................................................................................
Studies for SAT and experiments with EDCs such as 17β-estradiol (E2) degradation under aerobic conditions showed that this system is one of the reliable technologies for removing EDCs chemicals (Ying et al., 2003). Therefore SAT system is used for reuse of direct influent of wastewater. Some studies had been carried out in the shallow depth of 1.5 m of soil and the presence of E2 with low concentration appeared (Mansell et al., 2004). Also biological degradation of Estrone (E1), E2, Estriol (E3), 17α-ethynylestroidiol (EE2) were much more better during soil passage (Snyder et al., 2004). Moreover the concentration of alkylphenolpolyethoxy carboxylates (APECs) decreased by 95% throughout 3m of SAT.
Table 2.2.5.1
Compound
Abbrev
MW
EE2 equivalents (Mol EE2/mol)
17a-ethinylestradiol
EE2
296.39
1.000000
17a-estradiol
E2a
272.37
0.8403
17b-estradiol
E2b
272.37
0.8403
Estrone
E1
270.35
0.319328
Estriol
E3
288.37
0.002017
4-n-Octylphenol
4nOP
206.32
0.0006975
4-tert-Octylphenol
4tOP
206.32
0.0006975
4-Octylphenol monoethoxylates
OP1EO
250.36
0.0000070
4-Octylphenol diethoxylates
OP2EO
294.42
0.0000070
4-Nonylphenol
NP
220.34
0.0001429
4-Nonylphenol monoethoxylates
NP1EO
264.39
0.0000017
4-Nonylphenol diethoxylates
NP2EO
290.43
0.0000021
Bisphenol A
BPA
228.29
0.0005628
Bis(2-ethylhexyl) phthalate
DEHP
390.56
0.0000210
Diethylstilbestrol
DES
268.34
0.924000
Fifteen most estrogenically important compounds, their abbreviations, molecular weight (MW) and their estrogenic potencies relative to the estrogen 17α-ethinylestradiol (EE2), the oral contraceptive (Teske, 2009).
The behavior and the fate of EDCs may modify based on temperature and the matrix where they are present. Consequently, the persistence the rate of breakdown point are different in the water soil or air. Even the removal rate of EDCs during the sewage treatment depend on factors such as chemical nature of the compounds, the technology of the treatment plant as well as climate variations (Schäfer et al., 2003).
The organic contaminates move in soil depend on the soil characteristics such as pH, the organic matter of the soil, clay and silt contents of the soil and others. Based on this the fate and the behavior of the EDCs will be different. The most important thing is not only chemical structure and properties but also the climate and soil physiochemical properties (Kookana et al., 2003).
Table 2.2.5.2
Parameter
17 -estradiol
-sitosterol
bisphenol A
4-nonyl- phenol
endosulfan
Potency (relative to estradiol)
1
1/220,000
1/15,000
1/5000
1/5,000,000
Environmental
concentration reported (g/L)
<0.010
20-50
< 1
0.2-200
<5
Mobility (Koc, L/kg)
<5000
unknown
<1000
60000
10000
Half-life
<week
unknown
<month
days
months
Bioconcentration factor
2000
unknown
200
10,000
5000
Some indicative parameters for the environmental fate and behaviour of EDCs (estimated or compiled from various sources in the literature) (Kookana et al., 2003).
Effect of other contaminants on EDCs removal during SAT....................................
.
Removal mechanisms of EDCs in SAT
The major concern connected with EDCs compounds during the SAT is the percentage of effective removal. The attenuation of the certain EDCs are based on adsorption, biodegradation (Mansell et al., 2004), dilution or dispersion (Nema et al., 2001).
Adsorption
Based on log Kow the 4-tertoctylphenol's the organic carbon and water partition coefficient (KOC) can be calculated. Based on Kwo Koc estimated by Episuite version 4.1(EPISUITE, 2011) which shows the high tendency adsorption at organic material. Some studies had been done to investigate the sorption of the 4-tert-octylphenol in different river sediments based on laboratory batch techniques (Johnson et al., 1998). The study shows that the highest quantities of 4-tert-octylphenol adsorbed by sediments had the higher level of total organic carbon. Moreover the proportion of the clay and silt particles had the greatest proportion. Therefore Koc experiment and calculation withdraw a point that soil, sludge and sediment can strongly adsorb the 4-tert-octylphenol (Brooke and Britain, 2005). The study shows that 4-tert-octylphenol is a weak acid and the pH influence on the adsorptive behavior probably. That means that pKa considered around 10. Therefore the substance has un-dissociated and hydrophobic form in the environment (Calafat et al., 2008).
Biodegradation
SAT is very useful system for removal of especially endocrine disrupting compounds (EDCs) as well as anthropogenic contaminates from wastewater (Fox et al., 2001). During the passage from SAT the most three phenomenon processes are considered such as biodegradation, sorption as well as volatilization (Bouwer et al., 1981). These three main processes is affecting in attenuation of EDCs. The biodegradation attenuate organic compounds after which probably the volatilization of trace compounds removed by transferring liquid to gaseous phase by simultaneous sorption which prevent the trace compound to move fast in soil matrix (Bouwer et al., 1981). According to Mansell (Mansell et al., 2004) the attenuation of EDCs' movement during the SAT mostly depend on biodegradation and adsorption. Some researchers showed the importance of the vadose zone as main layer for degradation of EDCs during the SAT (Mansell et al., 2004).
Dilution
Dilution considered as a physical mixing process rather than removal one. Therefore dilution can serve for lowering the weight of solids. Moreover after percolation through vadose and saturated zone the reclaim water diluted with ground water. However for dilution procedure the concentration of the contaminants in surface water must be higher than in the ground water (Ray et al., 2002).
Dispersion
Typical permeability values of the various soils (Bouwer, 2002). Other treatment mechanisms are dilution, dispersion and filtration.
