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Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dagnew, Martha

Abstract

There has been an increased interest in alternative wastewater treatment systems to improve nutrients removal and energy consumptions while achieving acceptable discharge limits. Wastewater treatment plants (WWTP) have shifted their interest in treating the sidestream wastewater; a reject liquid post anaerobic digestion, rich in ammonium-nitrogen. A dedicated sidestream wastewater treatment unit has become an attractive option with the finding of a relatively new species of bacteria, anaerobic ammonium oxidizers (anammox), able to convert ammonium and nitrite into nitrogen gas. However, anammox bacteria are sensitive in environmental changes, and in combination with their low growth rate, it is challenging to establish a robust activity. Several technologies have been applied to develop partial nitritation, and anammox process. This study investigated sidestream wastewater treatment using Membrane Aerated Biofilm Reactors (MABRs). MABR is an innovative technology that enables capacity expansion in existing tanks in WWTP, providing better plant performance with a cost-effective solution. To date, limited studies have been published reporting the partial nitritation anammox (PNA) process using MABR technology for the treatment of sidestream wastewater streams.

This research was conducted to investigate start-up strategies and characterize the performance of the sidestream PNA process in two lab-scale MABRs. Three start-up phases were studied, and a two-step PNA development was examined to assess the potential of the PNA process development in MABR systems. The first start-up strategy considered prioritizing selective growth of anammox bacteria on the membrane surface over aerobic organisms, which requisite turning the membrane process air off. During this period, ammonium and nitrite accumulation inside the MABRs were observed that were indicative of anammox bacteria inhibition. The results showed that process startup under this configuration was affected by several conventional MABR operating conditions and slow attachment of the anammox granule to the membrane surface. The MABR pH levels were often high, and pH control was found crucial during the start-up period. The observed elevated pH levels were identified to be associated with the pure nitrogen gas used for mixing purposes. All the parameters that negatively affected the process were carefully studied and applied in the subsequent PNA process startup that was successfully developed in MABRs. In the second approach, the startup strategy involved selective growth of aerobic ammonia-oxidizing bacteria, followed by an introduction of the anammox bacteria in the pilot MABRs. The MABR partial nitritation and PNA process were developed under continuous and intermittent aeration mode. The results showed that MABRs had a partial nitration capacity up to 4 g N/m2.d at a hydraulic retention time (HRT) of 24 hours, removing up to 80% of the influent NH4-N. A subsequent PNA study showed higher ammonia and total nitrogen removal rates. The intermittent and continuous aeration modes showed maximum ammonium removal rates of 10.7 g N/m2.d and 6.8 g N/m2.d, respectively and total nitrogen (TN) removal rates of 5.2 g N/m2.d and 4.8 g N/m2.d, respectively, This study identified important MABR operating parameters for the successful startup of the PNA process for sidestream wastewater treatment with higher ammonium-nitrogen removal capacity.

Summary for Lay Audience

In aquatic systems, nitrogen occurs primarily as ammonia, ammonium, nitrate, and nitrite. Ammonia can be harmful to aquatic organisms, while ammonium is harmless and nitrate levels in drinking water are related to infant methemoglobinemia. Microorganisms though, and environmental conditions can lead to changes between these forms of nitrogen. Due to those negative effects, some nitrogen compounds have on human and aquatic life, regulations have been instituted to protect the aquatic environments, animals’ and humans’ health and life. Different types of microorganisms have been studied during the years for biological nitrogen removal. However, a recently discovered one, able to consume ammonium and nitrite and produce nitrogen gas in the absence of oxygen, called anaerobic oxidizing bacteria (anammox), and its consistence with aerobic oxidizing bacteria (AOB), bacteria which convert ammonium to nitrite, is still investigated. The Partial Nitritation – Anammox (PNA) process, as it is called, has been studied in separate as well as in one-stage reactors for the ammonium removal of highly concentrated wastewaters, called sidestream, but still, there are questions to be answered regarding its successful performance. Membrane Aerated Biofilm Reactors (MABR) is a new and promising technology, as it can be installed in existing wastewater treatment plants’ (WWTP) tanks, increasing the area for bacterial growth while supplies oxygen to the microorganisms by diffusion. In our research, we examined the potential of the PNA process for sidestream wastewater treatment in MABR, studying the start-up phases, the difficulties during this period as well as the development of the process in the MABR systems.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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