In this thesis, direct application of hollow fiber nanofiltration on surface water is suggested as an efficacious method for surface water treatment. This thesis was carried out as a collaborative effort between Lenntech B.V. and TU Delft. The current research aims to assess the performance of these membranes as a potential solution for surface water treatment and to gain a meaningful understanding of rejection performance and fouling tendencies of these modules through lab-scale experimentation of a low MWCO hollow fiber membrane. Direct application of nanofiltration on surface water was carried out on a lab-scale using the dNF-40 hollow fiber nanofiltration membrane supplied by NXFiltration B.V. Enschede. This membrane is fabricated using a technique called Layer-by-Layer (LbL) polyelectrolyte deposition which consists of an assembly of alternatingly deposited polycationic and polyanionic nanolayers on a polyethersulfone (PES) ultrafiltration support. The dNF-40 membrane is negatively charged at neutral pH. The main objective of the research was to determine the effectiveness of the dNF40 membrane for surface water treatment in terms of three key performance parameters viz. rejection, membrane fouling and concentration polarization. Membrane characterization was carried out by measuring the pure water permeability, Molecular Weight Cut Off (MWCO) of the membrane and rejection of single salt solutions. The pure water permeability of a pristine membrane was 1.53×10^{-14} m. The MWCO was measured using PEG filtration method and was found to be 200 Da. The membrane performance is limited in terms of the flux due to concentration polarization. CP factor was measured experimentally and compared with Sherwood analytical model. Since the flow through the fibers in laminar, high cross-flow velocities are required to reduce CP are high (< 0.5 m/s) due to which hydraulic pressure losses along the feed channel are high. A pressure drop of 0.2 bar was measured for a pristine membrane at a cross-flow velocity of 0.5 m/s. Filtration experiments were carried out with two kinds of surface waters: Delft Schie water and Biesbosch reservoir water. The influence of flux and cross-flow velocity on the rejection of ions were investigated. The removal of Natural Organic Matter (NOM)in both surface waters was between 80 and 85%. The rejection of divalent cations viz. Ca2+and Mg2+was higher at low system recoveries (upto 30%) but a severe drop in rejection was observed at higher recoveries (80%). The final permeate collected at 80% recovery contained 37 mg/L of Ca2+and less than 1 mg/L of NOM. 98%rejection of SO42- was observed irrespective of the feed composition and operating conditions. The dNF-40 membrane exhibited high fouling-resistance during surface water filtration showing no mass transfer coefficient(MTC) decline during 6-hour experimental cycles with surface water. To test for fouling fractions of surface water,additional tests were carried out with model foulant solutions including sodium alginate, humic acid and bovine serum albumin with varying foulant concentrations and ionic strengths; of the three, alginate fouling was most severe in terms of flux decline. Irreversible fouling was observed during the alginate filtration tests. Fiber-blocking was also observed during alginate filtration due to aggregation of alginate and Ca2+. Chemical cleaning with 200 ppm NaOCl solution at pH 12 completely re-stored the permeability. The results presented in this thesis demonstrate that the dNF-40 hollow fiber membrane with the LbL structure can treat surface water with-out pre-treatment. These membranes are ideal for applications such as production of drinking water where partial removal of hardness and complete removal of organic matter is required.

Certain industrial wastewaters have posed a challenge to water treatment systems because of their composition. The bitumen from the reclaimed asphalt process is heated by the BAM Infra Asfalt and produces fumes, which are usually sent to the air filters and then out through the chimney. To recover the heat lost through the fume, it is condensed. The bitumen fume condensate contains aromatic hydrocarbons of petroleum origin and this poses a threat to health and the environment. The removal of these compounds by anaerobic biodegradation was assessed with a mesophilic anaerobic membrane bioreactor (AnMBR). The bitumen condensate contained over 800 compounds, out of which some were p-cresol, o-cresol and 2-napthalenemethanol. The inhibition to the methanogenic activity and toxicity to the biomass of this wastewater on three different inocula were studied under batch-test conditions. A phenol-degrading sludge was less inhibited (IC₅₀= 870 mg COD_bitumen/L) and more resistant to the toxicity than granular sludge from a petrochemical wastewater treatment plant (IC₅₀= 187 mg COD_bitumen/L) and a municipal sludge (sludge from a municipal wastewater treatment plant, IC₅₀= 127 mg COD_bitumen/L). In continuous operation, the bitumen condensate was degraded efficiently with 89%±12% (S.D)COD removal from the influent of the AnMBR. Maximum organic conversion rate of the bitumen condensate was 26.0 mg COD/g VSS.d. This research demonstrated the efficiency of AnMBR technology to degrade bitumen condensate. Further research must be done to improve the organic conversion rate and optimise the technology for large scale implementation.

Resources recovery from wastewater is pursued as it facilitates a circular economy, which a society runs with a minimal environmental impact. Eutectic freeze crystallisation (EFC) has been identified as a potential technology that can assist to achieve such goal. High quality of salt and ice can be retrieved with this treatment with a note of high energy efficiency. In this paper, based on an actual case of a Spanish silica production company, freeze and eutectic freeze crystallisation are found to be applicable to a complex RO concentrate, which involved Na, Mg, Ca, Sr, Ba, SiO2. Quality ice and mirabilite products were also produced, which the impurities attached can be further washed away easily. The influence of the impurities on the eutectic point of sodium sulphate solution is investigated. A conservative recovery rate of 42wt% and 55wt% are obtained respectively for mirabilite and ice. Heat transfer characteristics of the equipment are also conducted, the boundary layers in the working solution and in the coolant have a clear influence on the overall heat transfer. A heat transfer of 404W/K-m2 is obtained for the EFC cooling, which is found to be comparable to past study. Energy consumption for a complete EFC process on the RO concentrate is estimated to be 0.1437 kWh/kg-solution, which is only 22% of the energy consumed in heat crystallisation. Column crystalliser is suggested to be a possible method to resolve impurities accumulation issue. Torque was also identified to indicate nucleation and crystallisation during the process. A crystal size distribution model is developed and can be used to evaluate or predict the performance of an EFC system. During the thesis study, a successful demonstration and training was provided to the staff from Fundació CTM Centre Tecnològic, which is the respondent for the Spanish case and will later perform a EFC experiment in the treatment plant.

Brine that is produced during reverse osmosis (RO) could be further concentrated by another RO step. In the absence of bivalent cations, silica is a limiting factor because a high concentration of silica can cause irreversible fouling of the membranes. To prevent silica scale formation during the further concentration of brine with RO, silica should be removed in a separate process. Silica gel beads have a large specific surface area and can be used to precipitate silica. Previous research on the removal of silica using silica gel beads for solutions with a relatively high silica concentration showed that a removal of 30-60% is possible.
In this research the effect of the dosage of silica gel beads, pH, temperature and the presence of 1 or 10 mg/L of ferric and aluminum on the removal of silica using silica gel beads from a solution with a low silica concentration was investigated. Starting with a silica concentration of 180 mg SiO₂/L a removal up to 30% was obtained after 8 hours (pH 8.5, 21°C).
The removal of silica using silica gel beads was limited, because silica gel dissolved when the solution is unsaturated with regard to silica. The equilibrium concentration was approximately 102 mg SiO₂/L. The difference between the concentration of silica in solution and the equilibrium concentration appeared to be a driver of the removal. The increase in removal efficiency as a result of using a higher dose of silica gel seemed to be limited. Operating at pH 10 instead of 8.5 resulted in a lower removal efficiency. Lowering the pH to 7 or 5 did not result in a decrease of the removal efficiency. Changing the temperature to 10 or 35°C or adding 1 or 10mg/L of ferric or aluminum did not increase the removal efficiency either, but even decreased the efficiency.
The obtained removal efficiency might be too low for direct application of fixed bed column filtration with silica gel beads as interstage silica removal technique in a RO system that is used to concentrate brine. A combination of filtration with silica gel and a technology that can concentrate the brine without scaling to concentrations up to 500 mg SiO₂/L could be an interesting solution to make brine treatment more energy-efficient, because the need for an evaporation step is minimized.

The need to treat waste streams produced during the water treatment processes is becoming a challenge nowadays due to the industries’ disposal expenditures, the limitations imposed by laws and the environmental impacts. The spent regenerant from ion exchange (IEX) processes is an example of such streams. This study investigated the use of Nano-filtration technique for separation as a part of the treatment step for IEX spent regenerant. This research is focused on the parameters such as membrane characteristics, ionic composition and operating conditions that affect the ion rejection of the IEX spent regenerant. This research aims to select a membrane that contributes to a maximum separation of monovalent and divalent ions of the IEX spent regenerant.
During this research six nanofiltration membranes and two reverse osmosis membranes were tested, of which the molecular weight cut-off (MWCO) was measured. Each membrane was placed at a flow Cell unit and fed with artificial water.
The MWCO of the nanofiltration membranes was varied from 115 to 508 Da. The purpose of testing different membranes was to assess how the pore size of the membrane influences the ion rejection of the IEX spent regenerant. In addition, the ion rejection was evaluated in different ionic strengths and different molar ratios. The aim was to investigate how the ionic composition influences the ion rejection. Finally, operating parameters such as permeate flux and temperature were tested to research their impact on the ion rejection of the IEX spent regenerant.
Results showed that the ion rejection of the IEX spent regenerant was strongly affected by the pore size of the membrane as the charge effect was insignificant due to the high ionic strength of the feed solution (1 M). The main exclusion mechanisms were the steric and the dielectric exclusion. Loose membranes with MWCO greater than 500 Da rejected less than 10% of both monovalent and divalent ions. Membranes with pore size from 200 Da to 300 Da rejected 30-60% of Ca2+ and contributed to negative rejections of Na+. NF membranes with MWCO of approximately 150 Da, rejected 90% of Ca2+ and 40% of Na+. Tighter NF membrane and RO membranes rejected more than 95% of divalent ions and more than 70% of monovalent ions.
It was also observed that the ionic composition did not influence the rejection of divalent cations as it remained almost constant in different ionic strengths and molar ratio of the solution. Contrary, the rejection of monovalent cations was greatly influenced by the molar ratio of the solution due to the presence of predominant amounts of ion of higher charge and the need of the ions to maintain electroneutrality. Higher molar ratio resulted in lower rejection of monovalent cations.
The permeate flux affected the ion rejections. Higher fluxes resulted in higher ion rejection and different ion separation. To keep high rejection of bivalent and low rejection of monovalent ions a compromise would be desired. Temperature had a great influence on the ion rejection of the IEX spent regenerant as a 5oC increase in the temperature cased 19% decrease in divalent cation rejection.
TS80, one of the nanofiltration membranes, performed better than other membranes as it rejected 90% of Ca2+ and 40% of Na+. Double Pass NF with TS80 membrane was proposed as the first treatment step of the IEX spent regenerant stream as it resulted in 97% Ca2+ and 45% Na+ rejection.