The Subsurface Infiltration Of Wastewater

Essay add: 22-10-2015, 20:34   /   Views: 250

Rapid population growth, urbanization and socioeconomic development are exacerbating the growing water demand (Bakir, 2001). 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.

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