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Ammoniacal nitrogen (NH₄-N) can accelerate eutrophication in rivers and lakes and thus needs to be removed from domestic wastewater before discharging the effluent into a fresh water or a seawater. Currently, biological processes are used to oxidise the reactive nitrogen into N2, but these processes are highly energy intensive and have difficulties to reach the required effluent concentrations lower than 1 mg L⁻¹. Zeolites have the ability to selectively remove NH₄+ ions even in the presence of competing species such as calcium. This thesis investigated and compared the properties of natural and synthetic zeolites to determine their suitability for removing nitrogen in a tertiary treatment. Overall the synthetic zeolite MesoLite showed the highest capacity (4.6 meq g⁻¹) and selectivity towards NH₄+ when compared to other zeolites. Dynamic experiments also showed MesoLite to achieve the highest operational capacity at 27 mg g⁻¹, while other commonly used zeolites like Mordenite and US-linoptilolite achieved 25 and 22 mg g⁻¹ respectively. One of the most prominent knowledge gaps in literature concerns regeneration of zeolites. Regeneration is the biggest obstacle to wide spread use of zeolite based wastewater treatment on full scale in a way that is economically feasible. The results showed that when the regeneration occurs at pH 12, brine reuse was possible for 5 consecutive cycles. Brine reuse was also found to be one of the key factors determining overall economical feasibility of the process. Specifically, operational expenses were found to be reduced by 50 % when the brine was reused during three consecutive cycles. When the whole life cycle was compared to a solution based on a Nitrifying submerged Aerated Filter (N-SAF) the process became cheaper for empty bed contact times (EBCT) of 1, 2.5 and 4 min for a 20,000 popular equivalent (PE) business case and for 1, 2.5, 4 and 8 min EBCT for a 2,000 PE business case. The option of recovering reactive nitrogen through a hollow fibre membrane was considered for the 20,000 PE business case. This last setup was found to be more economical than a solution based on the N-SAF process for every one of the tested EBCT (1, 2.5, 4, 8 and 15 min EBCT). In summary, this thesis identified configurations of zeolites and process parameters that were shown to be effective at removing ammoniacal nitrogen from both synthetic and real wastewater and economical analysis showed that zeolite based processes can compete with state of the art approaches. PhD in Water |
