Sulphur-driven anammox systems for nitrogen removal from wastewater

Abstract

This thesis explored sulphur-driven Anammox systems as a potential solution for removing nitrogen from wastewater. It focused on using sulphur compounds as electron donors to drive the Anammox process, aiming to reduce energy requirements and costs compared to conventional methods. The thesis provided an overview of existing nitrogen removal techniques in wastewater treatment plants, highlighting the limitations of conventional methods and the potential of Anammox as an alternative. The theoretical framework of sulphur-driven Anammox systems was discussed, emphasizing their advantages in terms of energy efficiency, carbon footprint reduction, and cost-effectiveness. The study examined the principles and significance of the Anammox process in wastewater treatment, where anaerobic microorganisms convert ammonium and nitrite into nitrogen gas, thereby eliminating nitrogen pollution. By harnessing the power of sulphur-driven Anammox processes, this study aimed to address these environmental challenges and develop innovative and sustainable wastewater treatment technologies. The research investigated the potential of sulphur compounds, such as sulphide (S2-), sulphate (SO4 2-) and elemental sulphur (S0), as electron donors in Anammox systems. These compounds serve as alternative sources of reducing equivalents, enabling the Anammox bacteria to carry out the conversion process efficiently. The performance and microbial dynamics of sulphur-driven Anammox systems were extensively analyzed. Various parameters, such as nitrogen removal efficiency, sulphur compound dosage, pH and temperature, are evaluated to optimize system performance. The study also investigated the microbial community composition and metabolic pathways involved in sulphur-driven Anammox, shedding light on the key micro-organisms and their functional roles. The combination of partial nitrification (PN) and anaerobic ammonium oxidation was investigated as a promising technology for nitrogen removal from wastewater. Strategies such as intermittent aeration, pH shocks and sulfide addition were studied for PN start-up and suppression of nitrite-oxidizing bacteria (NOB). Intermittent aeration with low dissolved oxygen (<5 mg/L) suppressed NOB activity, resulting in a 93% nitrite accumulation rate (NAR). Low pH (5) reduced both ammonia oxidising bacteria (AOB) and NOB activity while raising it to pH 7.5 increased AOB activity (84% NAR) but kept NOB suppressed. Adding sulfide (up to 25mg/L) without pH control raised NAR from 63% to 85%. These factors affect nitrite accumulation in our system. The study provided insights into establishing PN in a sequential batch system and highlighted the sensitivity of nitrite oxidation to sulfide. The incorporation of sulphur into carbon and nitrogen removal processes in a wastewater treatment plant was explored in this study. A dosage of 15 mgS/L of sodium salt of sulphide combined with 2-3 mg/L dissolved oxygen, established PN effectively in synthetic and real wastewater. PN was established when pH naturally rose due to sulfide hydrolysis, suppressing NOB activity. Long-term operation achieved a nitrite accumulation ratio of 70 ± 19%, with ammonia and nitrite concentrations of 19 ± 4 mgN/L and 18 ± 4 mgN/L, respectively. NOB communities diminished during stable PN but returned when sulfide dosing stopped, indicating the need for continuous sulfide dosing.The study emphasized the continuous adoption of this strategy for sustained PN and its potential application in nitrogen removal from domestic wastewater. This study explores the intriguing sensitivity of Anammox bacteria to sulfide, revealing captivating insights into their unique response to this compound. The short-term negative effect of sulfide on Anammox performance was observed but quickly recovered under low sulfide stress. Reducing or removing sulfide in the influent is suggested to accelerate the recovery of Anammox performance. The stoichiometric ratio was identified as an indicator of Anammox performance and consortium development. The study highlighted the importance of environmental conditions and sulfide concentration control in optimizing Anammox processes and nitrogen removal in wastewater treatment systems. The study extensively examines the performance of the sulfide-driven Anammox (SPDA) process, specifically focusing on the impact of various hydraulic retention times (HRTs) and external sulfide dosing. The objective was to understand how variations in HRTs and the addition of external sulfide influence the efficiency and effectiveness of the SPDA process in removing nitrogen from wastewater. To gain a deeper understanding of the microbial communities involved in the SPDA process, next-generation high-throughput sequencing techniques were employed. These advanced sequencing methods allow for a comprehensive analysis of the structural and functional dynamics of the microbial communities present in the SPDA system. By analyzing the genetic material of these micro-organisms, it becomes possible to identify and quantify their abundance, diversity and potential functional roles in the nitrogen removal process. The findings from this study are expected to provide valuable insights into optimizing the performance of the SPDA process. By examining the effects of different HRTs and external sulfide dosing, researchers can determine the most favorable conditions for achieving efficient nitrogen removal. Additionally, by evaluating the microbial communities' dynamics, the study aimed to uncover the relationships between specific microorganisms and their contributions to the SPDA process. Ultimately, the results obtained from this investigation can contribute to the development of improved strategies for nitrogen removal from wastewater using the SPDA process. This knowledge can inform the design and operation of wastewater treatment systems, leading to enhanced performance, reduced energy consumption and increased cost-effectiveness in the treatment of nitrogen-rich wastewater.