Ammonia partitioning and recovery from industrial wastewater - exploring precipitation, stripping, and sorption technologies

Abstract

Jefferson, Bruce - Associate SupervisorCircular economy in wastewater management is increasingly applied, with ammonia recovery playing a critical role. Established ammonia partitioning technologies, being precipitation, typically as struvite, stripping and scrubbing, and sorption, have been predominantly applied to manure, anaerobic digestate, urine and municipal wastewater. Industrial effluents also hold potential for ammonia recovery and have been increasingly targeted by research. These effluents comprise a wide category of wastewaters with diverse physicochemical characteristics, generated by different sectors, including food/drink processing, mining, agro-industrial processes, manufacturing, metallurgy, etc. Some of these effluents contain high ammonia loads alongside significant concentrations of ions, metals, and recalcitrant organic compounds, contributing to complex chemical compositions that can pose challenges for conventional recovery technologies. Despite the increasing focus on industrial wastewaters, there remains limited understanding of how to effectively select and operate recovery technologies, based on the effluent composition and desired recovery outcomes. This research aimed to advance the understanding of how several physicochemical factors impact the mechanisms enabling ammonia partitioning into gas, liquid and solid phases, in order to establish optimum transfer pathways. The key knowledge gaps addressed in this research were i) determination of main criteria for ammonia recovery technology selection for a range of industrial wastewaters, ii) understanding the feasibility and recovery performance of struvite precipitation and ammonia stripping at demonstration scale from distillery wastewater, iii) understanding and quantifying the impact of transition metals and acidic organic compounds on ammonia stripping, iv) assessment and comparison of ammonia separation performance via ion and ligand exchange media and influence of operation parameters (e.g. pH, buffer capacity, metal load, N concentration). The findings are utilised to generate an informed decision process for technology/strategy selection and the operational requirements and potential challenges posed by selected factors, with relevance for industry stakeholders, technology providers, and consultants. A specific focus was placed on distillery wastewater as a case study, a sector concerned with ammonia management and potentially suitable for recovery, particularly in Scotland. A review of the literature found that struvite precipitation is the most widely implemented method with industrial effluents, yet stripping and sorption processes may be preferred for their ability to deliver versatile, ammonia-rich solutions. The identified technology-selection criteria included the feed concentration of ammonia and competing cations, and the struvite formation potential. Based on the practical recommendations developed in this study, an ammonia recovery strategy for distillery wastewater was established, integrating anaerobic digestion with chemical precipitation and ammonia stripping coupled with scrubbing. The performance of this treatment train had never been tested before for filtered digestate of distillery effluent, addressing a key gap in understanding for full scale applications. Demonstration scale trials allowed to understand how the expected performance translated with real digested distillery wastewater and to validate its feasibility. The results demonstrated its technical viability, achieving 76% N removal and 80% P removal, while generating high- quality struvite and ammonia sulphate solution. Moreover, the findings highlighted the critical impact of pH and addressed operational challenges, improving readiness for full-scale application. Beyond distillery effluents, this thesis examined broader challenges in industrial wastewaters treatment, addressing gaps identified in the literature review, relevant for a range of industrial wastewaters, including from metallurgy and agro/food processing. Specifically, the impacts of species found in some of these effluents, such as transition metals (as Ni, Cu, Zn) and organic, acidic compounds (as humic acids), on the stripping process were investigated. Results showed that elevated levels of such species can reduce ammonia availability for stripping, via complex formation and electrostatic interactions. This highlighted the need for mitigation strategies to maintain stripping efficiency with these streams. Additionally, the metal-ammonia bond potential was further explored to assess ligand exchange (LEX) sorption mechanism as alternative to ion exchange (IEX), a mechanism often limited by high concentrations of ammonia and competing cations. Although various media have been tested in literature, comparative studies on their performance under different conditions are lacking, along with insights on how factors such as pH, transition metal and cations load can impact their mechanisms and effectiveness. In this study, two zinc-hybridised sorption media were tested and benchmarked against IEX media, in synthetic and real wastewaters (distillery, municipal). The results showed effective removal, although limited by self-inhibiting pH changes, with a zinc-hybridised media matching or exceeding IEX resin’s performance only when pH 9-10 was maintained (75 meq N/g). pH, buffer capacity and Zn/Na loads were demonstrated to be critical factors to enable or limit IEX and LEX mechanisms. The findings established operational requirements for hybridized sorption media and provided research directions for further improvement. Overall, this work advanced knowledge on the impact of key species on ammonia recovery technologies, with implications for industrial effluents treatment in general and distillery wastewater management in particular. The findings contributed to developing recommendations for selection and operation of ammonia partitioning strategies, optimizing metal-hybridized sorption media, and improving process feasibility for full-scale implementationPhD in Wate