Downflow sponge biofilm reactor for ammonia removal in raw water treatment / Loi Jia Xing

Loi , Jia Xing (2024) Downflow sponge biofilm reactor for ammonia removal in raw water treatment / Loi Jia Xing. PhD thesis, Universiti Malaya.

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Abstract

High ammonia levels in Malaysian river water poses a challenge for raw water treatment plants (RWTPs) operation. Current RWTPs rely on conventional treatment methods and lack dedicated ammonia removal capabilities, making the introduction of ammonia treatment critical for safe drinking water supply. The biological ammonia removal (BAR) method shows promising potential for RWTPs but requires a comprehensive understanding of local raw water conditions, including its characteristics, due to potential rate limitations at relatively low NH4+-N concentrations, which differs from wastewater BAR. Achieving a high reaction rate necessitates a short hydraulic retention time (HRT). Sporadic ammonia availability in raw water further complicates the compliance accountability of the BAR process. This thesis aims to develop a low-energy, high hydraulic rate, and robust sponge-core BAR system, known as the Downflow Sponge Biofilm (DSB) reactor for raw water treatment. A river water quality assessment was conducted to establish BAR operational guidelines, with DSB system applicability evaluated in lab-scale reactors under varying HRTs and feast-famine conditions. Additionally, microbial community dynamics were investigated to ensure safe and efficient reactor operation. Ammonia levels at the raw water intakes of three major river basins in Selangor, prone to water disruption, ranged from 0 to 6 mg N L−1. The range of ammonia concentrations served as a guideline for DSB reactor operation. Two DSB reactors were operated under short HRTs of 60-, 30-, 20-, and 15-min. The designed ammonia concentrations of DSB-1 and DSB-2 are 5 and 2.5 mg NH4+-N L−1, respectively. Both DSB reactors demonstrated high ammonia removal efficiencies at all four HRTs and their effluents met the recommended raw water quality standards (≤ 1.5 mg NH4+-N L−1). The shortest HRT for effluent compliance was 15 min. The short HRT operation had no adverse effects on the nitrifying microbial communities for safe reactor operation due to excellent biomass retention of the DSB system. The successful enrichment of nitrifiers affiliated with Nitrosomonas and Nitrospira was the key to achieve stable nitrification performance. Further phylogenetic analysis revealed the presence of putative complete ammonia oxidation Nitrospira associated with higher ammonia affinity in DSB-2, operating at low NH4+-N. DSB-2 was continuously operated under a feast-famine regime. Four famine periods were investigated, comprising two 14-days partial famine phases, one 56-day phase involving both partial and complete famine, and one 90-day complete famine phase. Repeated 14-day partial famine phases had no impact on nitrification. A shift from partial to complete famine resulted in a delay in NOx−-N production. After 174 days of famine, the robust DSB reactor successfully restored ammonia and nitrite removal performance in 5 and 29 days, respectively. Under famine conditions, Candidatus Nitrosotenuis predominated while Nitrospira persisted throughout the study. Ca. Nitrosotenius, Nitrosomonas, and Nitrospira co-existed to contribute stable ammonia removal performance. This research demonstrated the DSB system’s potential for highly efficient ammonia removal in raw water treatment, especially under challenging conditions like short HRTs and sporadic ammonia availability. Implementing DSB reactors could alleviate operational strains and ensure the security of water treatment systems.

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