Nitrogen (N) removal is one of the key tasks for every wastewater treatment plant under the growing pressure of environmental protection. Prevailing applied N treatment technologies are mostly energy-intensive. This dilemma triggers a rethinking of the way to approach N management. “N2kWh-From pollutant to power” is a project that aims at creating an energy-positive 푁 treatment system by exploiting the energy potential stored in reduced N compounds. Both thermal and electrical energy needed in this scheme will be provided by Solid Oxide Fuel Cell (SOFC) using the ammonia recovered from wastewater. To guarantee a proper function of the SOFC a minimum of 5 wt% of ammonia in the gas mixture is a prerequisite, whereas, the reject water of anaerobic digester only typically contains 0.15 wt%. Therefore, selectively stripping NH3 in waste streams is the main technical bottleneck of this project.This study aims at contributing to the understanding of selective transport of NH3 by pervaporation. A comprehensive literature study indicates silica-based ceramic membrane is able to perform this selective transport. Therefore, the task of this research was to test the feasibility of selective transport of NH3 by commercially available silica-based pervaporation membranes (hydrophobic PDMS and hydrophilic Hybrid Si AR). The objective was to find the optimum operating condition for maximizing the selective transport of NH3 by silica-based ceramic pervaporation membrane. To this end, the impact of flow regime (laminar and turbulent flow), temperature (35 oC and 45 oC), presence of additional salt (NaCl and Na2CO3) and TAN concentrations (total ammonium nitrogen; 1.5, 12.0 and 20.0 g TAN·L-1, respectively) was assessed through a series of systematic experiments.It was found that the PDMS membrane was unable to selectively transport NH3 from liquid solution because both H2O and NH3 are polar molecules while the hydrophobic PDMS was nonpolar. Besides, the PDMS membrane tested was not stable under solutions used in this study.The results of Hybrid Si pervaporation membrane showed that the optimum operating conditions for selective transport of NH3 was 35 oC, Re=2,400, 20.0 g TAN·L-1 ammonium bicarbonate solution (pH adjusted to 10). For these conditions, the highest perm-selectivity (ratio of mass transfer coefficients of NH3 and H2O) was 0.5 indicting NH3 was less selectively transported than H2O.The impact of flow regime on selective transport of NH3 was related to polarization effects and depended on TAN concentration in feed solution. In the tested temperature and TAN concentration range, perm-selectivity was independent on both parameters. In addition, the effect of both temperature and TAN concentration on the ammonia was mainly due to the driving force, so their influence on the perm-selectivity was limited. Presence of salt seemed to have a positive impact on the perm-selectivity. Although salt has little impact on the mass transfer coefficient of NH3, it decreased the mass transfer of H2O resulting in a better selective transport of NH3.As for energy consumption, it was inversely related to TAN content. At the optimum operating condition 7 MJ·kg-1 - N was consumed by pervaporation in this study. Compared with the energy consumption of air stripping, pervaporation is a promising technology for NH3 recovery.

Water scarcity emphasizes the necessity of water recovery from saline sources, which are plentifully available. Nanofiltration (NF) is widely implemented in water reclamation treatment particularly in industrial field. However, the presence of silica hinders the possibility of obtaining a high recovery in a NF membrane system. In this work, the effect of silica concentration on the scaling of a NF membrane was investigated. Three types of feed water (demineralized water, water with 100 mg L-1 and 300 mg L-1 of SiO2) were fed to a single stage nanofiltration element. All cases were carried out at room temperature, pH values ranged 7 - 8 and a constant recovery of 11±1% for 24 hours continuously. The mass transfer coefficient (MTC) was used as method to determine the scaling of the membrane module. Results showed that no silica scaling occurred during the system runtime. Nonetheless, for all cases, an initial decrease in MTC could be detected. On the one hand, based on some literature reports, it is likely that a part of silica (mainly colloid) had precipitated on the membrane surface forming a more porous layer than the precipitation of polymerized monomeric silica. But to verify this argument, a further autopsy method is demanded. On the other hand, concentration polarization may also contribute to the initial decline in mass transfer coefficient. But the reason for the decrease for demi-water case remains unknown. In brief, Nanofiltration membrane can operate at a silica concentration up to 300 mg L-1 for 24 hours in lab-scale. The guideline (120 mg SiO2 L-1) suggested in the industrial standard (ASTM, D4933-08) was judged to be relatively conservative. For more practical purpose, further study is needed.

Traditionally, industrial processes produce wastes that, even though often containing useful materials, are discarded, contributing to environmental pollution and depletion of natural resources. An example of such wastes are brines, flows of concentrated salts, produced in water treatment processes, which are now routinely discharged into receiving water bodies. Brines however can also be considered as flows of reusable materials which should be recovered, and the Zero Brine cooperation project aims to develop processes for that purpose. For a demineralized water production plant in the port of Rotterdam (the Netherlands), a closed water processing cycle was proposed to treat the large volume of spent Ion Exchange (IEX) regenerant brine which, apart from recovering demineralized water, is also intended to produce magnesium (Mg2+) and calcium (Ca2+) salts, with the highest purity possible, from the otherwise discharged brine. The process scheme includes nanofiltration (NF) for separating mono- and multivalent ions, followed by sequential chemical precipitation of Mg2+ and Ca2+ ions from the NF concentrate, and production of demineralized water by evaporation of the NF permeate. The concentrate of monovalent ions produced in the evaporator, essentially a concentrated sodium chloride solution, in its turn might be reused for IEX regeneration. Part of the supernatant of the sequential precipitation may be fed to the evaporator as well, but bleeding the other part of this supernatant is essential in order to maintain process stability, avoid accumulation of minor pollutants, and reduce scaling. In this study, various scenarios to operate the process were modeled, using PHREEQC and Excel. According to the simulation results, recovery of ≈97% of Mg2+ and Ca2+ is possible, the latter with a higher purity than the former. The main factors affecting the results are the concentration of carbonate present in the spent IEX regenerant, as well as characteristics of the NF membrane and the dosing of sodium hydroxide in the sequential precipitation steps. The results of the simulations were used for the design and operation of a pilot plant, comprising all mentioned process steps.@en