Pharmaceutically active compounds 

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Pharmaceutically active compounds

General information on pharmaceutically active compounds

Pharmaceutically active compounds (PhACs), a group of chemicals including analgesics, anti- convulsants, anti-depressants, anti-inflammatories, hormones, antibiotics, etc., are used to maintain the healthy conditions of human and animals. Table 1.1 shows the most commonly prescribed drugs in the U.S. in 2016 (Provided by the ClinCalc DrugStats Database, available online: A large number of PhACs from the different family group are consumed annually throughout the world. Figure 1.1 presents the number of prescription for two commonly used PhACs (diclofenac and propranolol) over time (2006 – 2016) in the U.S.. At present, pollution caused by human and veterinary pharmaceutical substances has become an emerging environmental problem, due to a health risk for humans and ecological system (Bendz et al., 2005; Nikolaou et al., 2007).

Occurrence of PhACs in surface water

A wide spectrum of PhACs and their metabolites have been detected frequently at a low concentration in soils, sediments, surface and groundwater, even in drinking water (Nikolaou et al., 2007; Silva et al., 2011). Table 1.2 shows the residual concentration of common PhACs in surface water based on the reported literature (Dai et al., 2015; Kasprzyk-Hordern et al., 2008; Kim et al., 2007; Silva et al., 2011). The concentration of these PhACs is mainly at the trace level in the ng L-1 and μg L-1 range.
PhACs mainly enter the aquatic environment through: (1) the discharge of sewage treatment plant effluents; (2) the spreading of animal manure; and (3) aquaculture where PhACs are often dispensed with animal feed (EUROPEAN COMMISSION, 2019). Some studies have pointed out that a main source of PhACs in the environment is the discharge of WWTPs effluents. Because wastewater containing many emerging contaminants from houses, hospitals, manufacturing plants, farming and livestock impoundments, are received and assembled in the WWTPs (Bendz et al., 2005; Ganiyu et al., 2015; Kimura et al., 2005).

Occurrence of PhACs in sewage treatment plant effluents

Based on the recent studies, data on the occurrence of the most frequently detected emerging PhACs in the WWTPs influents and effluents are summarized in Table 1.3 (Ashfaq et al., 2017; Blair et al., 2015; Guillossou et al., 2019; Yu et al., 2013). From this table, it is possible to conclude that: (1) the concentration of trace PhACs in the WWTPs influents and effluents is highly variable, ranging from a few ng L-1 to µg L-1. It is linked to some factors, such as metabolism (human and animal excretion), the size of WWTPs, elimination efficacy of WWTPs, etc. (Luo et al., 2014); and (2) treatment technologies in the WWTPs is not sufficient to remove or to degrade most of PhACs from wastewater.
Even though municipal sewer is one of the most important sources of the reclaimed water, the presence of these PhACs and their metabolites in the WWTPs effluents might limit the reclamation of wastewater, due to their potential hazards to the environment and human health even at low concentrations. Kołodziejska et al. (2013) have found that micropollutants can affect reproductive and endocrine system, and have a strongly adverse impact on algae and duckweed as well. Therefore, advanced treatment processes, such as reverse osmosis process (RO) and ozonation, should be established for a higher elimination of trace PhACs, the final aim being to improve water quality for safe reuse.

Reverse osmosis process for wastewater reclamation

General information on reverse osmosis process

RO, a membrane technology, is widely applied in seawater desalination, drinking water production, brackish water treatment and wastewater reclamation, due to high water permeability and salt rejection (Greenlee et al., 2009; Malaeb and Ayoub, 2011). Over the past decades, RO process has gained worldwide acceptance for the reclamation of municipal wastewater due to its high efficiency in rejecting a wide range of organic pollutants, bacteria, dissolved organic matters and inorganic salts (Jacob et al., 2012; Malaeb and Ayoub, 2011; Xu et al., 2005). Figure 1.2 displays three main rejection mechanisms of RO for solutes in wastewater, including size exclusion (steric hindrance effect), charge exclusion, hydrophobic interactions between solutes, solvent and membrane (Bellona et al., 2004; Dolar et al., 2012; Ganiyu et al., 2015; Jacob et al., 2012; Malaeb and Ayoub, 2011).

Rejection capacity of reverse osmosis membrane for micropollutants

Studies with respect to the application of RO process to remove micropollutants from municipal wastewater have been published frequently in recent years (Alturki et al., 2010; Dolar et al., 2012; Jacob et al., 2012; Mamo et al., 2018). Based on the literature published, Table 1.4 summaries the removal efficiencies of RO membrane for micropollutants in wastewater, surface water and groundwater.
It is observed that RO process exhibits a relatively high removal rate for micropollutants present in wastewater, with a removal higher than 90% for most of micropollutants. The higher rejection of micropollutants by RO membrane could be achieved by one or a combination of three basic mechanisms as mentioned above (Ganiyu et al., 2015; Radjenović et al., 2008). The rejection of uncharged micropollutants (such as carbamazepine) by RO membrane is predominantly affected by size exclusion, whereas electrostatic attraction or repulsion force could influence the removal of micropollutants with charge (like diclofenac) by RO membrane (Dolar et al., 2012; Kimura et al., 2005; Radjenović et al., 2008). In addition, hydrophobic adsorption at the membrane-solute interface is a non-neglected role (Mamo et al., 2018). In contrast, the adsorption of hydrophilic micropollutants (such as sulfamethoxazole) to RO membrane is not significant (Alturki et al., 2010).
During the RO filtration process, the rejection rate for micropollutants is affected by membrane properties (pores size, charge), the chemistry of feed stream (pH, ionic strength, organic matters), physicochemical properties of constituents (molecular weight, pKa, charge, and hydrophobic nature), and RO operating conditions (Joo and Tansel, 2015; Mamo et al., 2018; Taheran et al., 2016).

RO membrane fouling

RO membrane fouling is still an inevitable issue as it limits the competitiveness of RO process (Jiang et al., 2017). Membrane fouling is a process resulting in loss of performance of a membrane due to the deposition of suspended or dissolved substances on its external surfaces, at its pore openings, or within its pores (Koros et al., 1996). Membrane fouling is also described as a reduction of permeate flux and of salt rejection because of the accumulation of undesired substances on the membrane surface or inside the membrane pores (Jiang et al., 2017; Malaeb and Ayoub, 2011). RO membrane fouling could reduce water production and the quality of permeate. Moreover, the operating cost increases, which is due to increased energy demand, application of pre-treatment unit, frequent chemical cleaning, shorter membrane lifetime, as well as additional labour for maintenance (Guo et al., 2012; Jiang et al., 2017). Several authors have provided a comprehensive review regarding the major foulants, principal RO membrane fouling mechanisms, and strategies for control RO membrane fouling (Guo et al., 2012; Jiang et al., 2017; Malaeb and Ayoub, 2011; She et al., 2016).
In terms of fouling places, fouling can be classified into external (surface) fouling and internal fouling (Jiang et al., 2017; She et al., 2016). For RO membrane with nonporous nature, external fouling is more frequent compared to internal fouling (Greenlee et al., 2009). Increasing feed water hydrodynamic conditions or chemical cleaning could control external fouling (She et al., 2016). However, in some cases, both external fouling and internal fouling are irreversible, which depends on the compositions of feed water and the interactions between solutes and membrane (Jiang et al., 2017).
In terms of foulants, RO membrane fouling can be categorized into colloidal fouling, inorganic scaling, organic fouling and biofouling (Jiang et al., 2017), as depicted in Figure 1.3. Colloidal/particulate fouling refers to fouling caused by colloids (fine suspended particles) that have a size range from a few nm to a few μm (Schäfer, 2006). Colloids are ubiquitous in the natural water and wastewater, including inorganic compounds (silica, clays, metal oxides and salt precipitates), and organic macromolecules such as polysaccharides, proteins and some natural organic matters (Jiang et al., 2017; Schäfer, 2006). Inorganic scaling, also scale formation or precipitation scaling, is the depositions of inorganic precipitates on the membrane surface or inside the membrane pores (Jiang et al., 2017). As the solubility of some inorganic salts is relatively low or the concentration of some ionic species in the water or wastewater is relatively high, when an ionic product of a sparingly soluble salt exceeds its equilibrium solubility product, the relevant precipitate is formed and then deposits on the membrane surface, resulting in an increase in transmembrane pressure or a decline in permeate flux (Guo et al., 2012; Jiang et al., 2017; Schäfer, 2006). Studies published in the past 10 years shows that calcium sulphate (42%) and calcium carbonate (38%) are two common studied inorganic scalants, and other common scalants include calcium phosphate, barium sulphate, calcium fluoride, etc. (Jiang et al., 2017). Organic fouling is caused by organic matters (humic substances, polysaccharides, proteins, lipids, nucleic acids and amino acids, etc.) (Jiang et al., 2017). In the case of wastewater treatment, effluents organic matters (EfOM, such as humic substances and polysaccharides) could result in membrane fouling by adsorption, surface accumulation or pore blocking (Malaeb and Ayoub, 2011). Biofouling is a process of the accumulation of microorganism on the membrane surface, including deposition, growth and metabolism of bacteria (Guo et al., 2012).
Membrane fouling is also classified into reversible fouling and irreversible fouling based on the attachment strength of solutes to the membrane surface. Some studies state that reversible fouling results from concentration polarization and particle deposit, which is removed by physical means, including relaxation and periodic backwashing (Choi et al., 2005; Huyskens et al., 2008). Irreversible fouling is mainly referred to a strong adherence to the membrane such as adsorption, pore plugging and solute gelation on the membrane (Schäfer, 2006), which is not removed with mechanical means but can be by chemical cleaning, or not at all.


RO membrane fouling mechanisms

As well known, permeate flux membrane lifetime are primarily influenced by concentration polarization and membrane fouling (Sablani et al., 2001). Surface adsorption, pore blocking, inorganic precipitation, gel or cake formation, biological fouling are the main mechanism for membrane fouling (H. Li et al., 2016; Schäfer, 2006). Actually, RO membrane fouling is complicated and caused by complex interactions between fouling constituents and the membrane, and which constituents govern for RO membrane fouling depends on the properties of RO membrane (surface morphology, hydrophobicity, charge and MWCO), the matrix of RO feed (pH, ionic strength, etc.), and RO operating conditions (water recovery, cross-flow velocity, temperature, etc.) (Guo et al., 2012; Jiang et al., 2017).

Concentration polarization / osmotic pressure

Concentration polarization (CP) is a phenomenon that the concentration of solutes or particles (salts and organic matters) near the membrane surface is higher compared to the bulk solution (Figure 1.4), due to the accumulation of solutes/particles at the membrane surface (Guo et al., 2012; She et al., 2016). Retained solutes/particles are brought into the bulk solution by back diffusion. The elevated concentration of inorganic and organic substances at the membrane surface leads to an increase in osmotic pressure, decreasing the effective transmembrane pressure and further reducing the permeate flux. The osmotic pressure of solutes on the side of RO concentrate and RO permeate can be determined by using Van’t Hoff equation and the measured solute concentration on each side (Schäfer, 2006).

Table of contents :

Chapter I Background and Literature Review 
I.1 Pharmaceutically active compounds
I.1.1 General information on pharmaceutically active compounds
I.1.2 Occurrence of PhACs in surface water
I.1.3 Occurrence of PhACs in sewage treatment plant effluents
I.2 Reverse osmosis process for wastewater reclamation
I.2.1 General information on reverse osmosis process
I.2.2 Rejection capacity of reverse osmosis membrane for micropollutants
I.2.3 RO membrane fouling
I.2.3.1 Membrane foulants and fouling type
I.2.3.2 RO membrane fouling mechanisms
I.2.3.3 Fouling behaviour of RO membrane for municipal wastewater reuse
I.2.4 Characteristics and disposal of RO concentrate
I.2.4.1 Characteristics of RO concentrate
I.2.4.2 Occurrence of PhACs in RO concentrate
I.2.4.3 Recirculation of RO concentrate into the biological unit
I.2.4.4 Treatment of RO concentrate by advanced oxidation processes
I.3 Ozonation application for decontamination of PhACs
I.3.1 Ozone decomposition and the formation of hydroxyl radicals
I.3.2 Expected attack site of micropollutants towards ozone
I.3.3 Micropollutants decontamination in wastewater by ozonation
I.3.4 Impact of water matrix on the degradation of PhACs by ozonation
I.3.4.1 Effect of scavengers
I.3.4.2 Impact of organic matters and alkalinity on ozone lifetime
I.3.5 Formation and toxicity of transformation products
I.4 Urine wastewater
I.4.1 Characteristics of source-separated urine
I.4.2 Occurrence of PhACs in source-separated urine
I.4.3 Urine valorisation and treatment of source-separated urine
I.4.3.1 Struvite precipitation
I.4.3.2 Reverse osmosis process
I.4.3.3 Ozonation process
I.5 Summary of literature review
Chapter II Materials and Methods
II.1 Target micropollutants
II.1.1 Properties of the target micropollutants
II.1.2 Preparation of stock solution of the target micropollutants
II.2 Description of RO process
II.2.1 RO membrane used
II.2.2 Dead-end RO cell configuration
II.2.3 Cross-flow RO pilot
II.2.4 RO process parameters
II.2.5 Saturation index calculation
II.3 Semi-batch ozonation
II.3.1 Description of ozonation pilot
II.3.2 Concentration profile of ozone in ultra-pure water and mass balance of ozone
II.3.2.1 Mass balance of ozone in the gaseous and liquid phase
II.3.2.2 Rate constant of ozone self-decomposition
II.3.2.3 Volumetric mass-transfer coefficient
II.3.3 Ozone dose
II.3.4 Ozone solubility in the ionic solution
II.4 Analysis of chemicals
II.4.1 pH and conductivity
II.4.2 Dissolved organic carbon and dissolved inorganic carbon
II.4.3 Chemical oxygen demand
II.4.4 Ions analysis
II.4.5 Ultraviolet absorbance
II.4.6 Size-exclusion high performance liquid chromatography
II.4.7 Polysaccharides and proteins
II.4.8 Micropollutants
Chapter III Combining RO and ozonation process for municipal wastewater reuse: RO membrane fouling and emerging micropollutants removal
III.1 Experimental protocols
III.2 Characteristics of MBR permeate
III.3 RO performance with RO concentrate recirculation to MBR (Set 1)
III.3.1 MBR-RO process with RO concentrate recycling
III.3.2 Characteristics of MBR permeate produced before and during RO concentrate recycling
III.3.3 Influence of RO concentrate recycling on RO retention capacity for NPOC, COD and ions 66
III.3.4 Influence of RO concentrate recycling on RO membrane fouling propensity
III.3.4.1 RO membrane fouling in terms of RO permeate flux decline
III.3.4.2 Impact of osmotic pressure gradient of salts on RO permeate flux decline
III.3.4.3 Scaling potential analysis based on saturation index model
III.3.4.4 Organic fouling potential analysis
III.3.5 Influence of RO concentrate recycling on the retention capacity for PhACs
III.3.6 Conclusions on the impacts of RO concentrate recycling to MBR on RO performance
III.4 Removal of micropollutants by RO process combining ozonation (Set 2)
III.4.1 RO retention capacity for micropollutants
III.4.2 Removal efficiency of PhACs from RO concentrate by ozonation
III.4.3 Removal efficiency of organic matters from RO concentrate by ozonation
III.4.4 Conclusions on performance of RO process + ozonation for PhACs removal
III.5 Conclusions of this chapter
Chapter IV Effect of water matrix on the mechanisms and performance of ozonation for micropollutants removal
IV.1 Experimental protocols
IV.1.1 Preparation of organic matter-free solutions spiked with CBZ and KET
IV.1.2 Real urine collection and pre-treatment
IV.1.3 Ozonation operating conditions
IV.2 Ozonation kinetic regime and ozone mass transfer
IV.2.1 Mass transfer with chemical reactions
IV.2.2 Mass balance of ozone with chemical reactions
IV.3 Investigation of the oxidation mechanism of CBZ and KET
IV.4 Impacts of solution matrix on the efficiency of PhACs removal by ozonation
IV.4.1 Ozonation of CBZ and KET in saline solution and synthetic urine
IV.4.2 Ozonation of CBZ in real urine
IV.4.3 Variation of the concentration of ionic salts and N-NH4+
IV.4.4 Comparison of removal efficiencies of CBZ and KET in the different matrix
IV.5 Effect of water matrix on ozonation consumption and kinetic regimes
IV.5.1 Hatta number and enhancement factor
IV.5.2 Ozone effectiveness yield
IV.6 Conclusions of this chapter
Chapter V A combination process of struvite precipitation, reverse osmosis and ozonation for the reclamation of source- separated urine: nutrient valorisation and micropollutants removal
V.1 Description of the treatment line
V.1.1 Characteristics of urine-based solutions and the target PhACs spike
V.1.2 Struvite precipitation
V.1.3 Dead-end RO filtration
V.1.4 Ozonation experiment
V.2 Recovery of P nutrient from urine-based solutions as struvite crystals
V.2.1 Identification of crystals
V.2.2 Removal of P by struvite precipitation
V.2.3 Removal of organic compounds during struvite precipitation
V.3 RO performance for urine treatment
V.3.1 Retention capacity of RO membrane for target micropollutants
V.3.2 Retention efficiencies for ionic species
V.3.3 Variation of RO permeate flux versus RO permeate volume
V.4 Ozonation of the urine-based solutions
V.4.1 Ozonation efficiencies of real urine
V.4.1.1 Ozonation of HUM-1
V.4.1.2 Ozonation of HUM-2
V.4.1.3 Ozonation of HUM-3 RO concentrate and HUM-3 RO permeate
V.4.1.4 Ozonation of SUM-RO concentrate and -RO permeate
V.4.2 Ozone kinetic regimes and ozone consumption during the ozonation of real urine
V.5 Comparison of P recovery and PhACs removal from source-separated urine by the combination process
V.6 Conclusions of this chapter
Conclusions and Future research


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