Micropollutant removal and nutrient recovery for sustainable management of urban wastewater

Abstract

The continuous discharge of nutrients and micropollutants such as pharmaceutically active compounds (PhACs) potentially create a threat to urban aquatic environment and water safety. This issue is extremely important for some metropolitans that rely on the renewable/reclaimable water resources such as Singapore. This study explores new approaches to improve the current wastewater management practice particularly in terms of nutrient recovery and micropollutant mitigation from both scientific and engineering perspectives. In Chapter 2, this study first reviewed the current research on nutrient recovery and micropollutant removal from wastewaters. Cytostatic drugs were selected as target micropollutants, whose environmental occurrence and behaviors, source contributions, and potential ecotoxicity were summarized. Source separation strategy promises to improve the current wastewater management practice, especially in terms of nutrient/energy recovery and separate treatment of pharmaceutical residue. The benefits, limitations, and trends of development of different approaches to address the ‘emerging’ contamination issue are covered for urine source-separation strategy, membrane bio-reactor, reverse/forward osmosis (RO/FO) and advanced oxidation processes. Promising alternatives may essentially lie on the state-of-the-art treatment technologies based on urine source-separation strategy; it deserves further comprehensive evaluation from the technological, social-economical and administerial perspectives. In Chapter 3, the feasibility and potential limitations of applying urine source separation system in a tropical urban setting was evaluated by systematically investigating urine hydrolysis process (i.e., enzymatic ureolysis, spontaneous mineral precipitation, odor emission issue) and different nutrient recovery approaches (i.e., seawater-induced struvite precipitation and ammonia stripping). The results demonstrated that an effective and automated urine source separation system could be achieved. The entire process can be accurately monitored by measuring conductivity as a timesaving and cost-efficient indicator. Approaches were suggested to cope with pipe clogging and odor emission issues from an engineering perspective. This study also demonstrated that seawater can be used as a cost-effective magnesium source to recover phosphorus from hydrolyzed urine. Structural characterization of the precipitates confirmed struvite crystals (slow-releasing fertilizer) as the main product with certain magnesium calcite or calcite as co-precipitates. Air stripping process can be further applied to effectively recover ammonia from source-separated urine and the experimental parameters provided certain guidelines for the development of N-recovery process in industrial-scale. In Chapter 4, the feasibility of applying FO dewatering process for nutrient recovery from source-separated urine was further investigated under different conditions, using seawater or desalination brine as a low-cost draw solution. The filtration process…