Date of Graduation
Statler College of Engineering and Mineral Resources
Civil and Environmental Engineering
Development and applications of anaerobic treatment technologies has been discussed as an effective alternative to conventional aerobic processes for removal of nitrogen from wastewaters. With abundance of iron and its high reduction potential, employing ferric reduction-based reaction pathways in engineering processes could be an effective strategy to promote energy efficiency of wastewater treatment. In particular, ferric reduction coupled to ammonium oxidation (Feammox), a novel microbial metabolic function recently found to occur under anaerobic/anoxic condition through iron dosing, can be used for nitrogen pollutant removal. Iron dosing for wastewater treatment could also promote other microbial and chemical reactions that facilitate nutrient recovery and promote sustainability of wastewater treatment. The overarching goal of this research was to investigate the potential of developing an energy efficient iron dosed technology for nitrogen removal from wastewater employing Feammox pathway and to explore use of iron for nutrient recovery from wastewater treatment.
The major research objectives include (1) developing coal mine drainage treatment and sludge disposal guidelines to facilitate production of effective sludge material for their application as iron source for wastewater treatment; (2) identifying the major knowledge gaps in using Feammox for nitrogen removal from wastewater; (3) investigating the effects of organic carbon on Feammox and abundance of Feammox bacteria; (4) examining phosphorus (P) and nitrogen (N) recovery efficiencies from sludge digestates through vivianite precipitation and membrane separation process; and (5) quantifying the efficacy of a novel ferric-dosed upflow sludge blanket bioreactor for nutrient removal and recovery from anaerobic digestates.
An extensive literature review was conducted to develop coal mine drainage (CMD) treatment and sludge management guidelines, that would facilitate iron-rich sludge production with optimum characteristics for different wastewater treatment applications. A comprehensive literature review was also conducted to evaluate the potential of employing Feammox in wastewater treatment. The review identified that there is lack of knowledge regarding the effects of organic carbon or heterotrophic iron reducers (iron reducing bacteria, FeRB) on growth of Feammox microorganisms (autotrophic iron reducers). Two ferric dosed bioreactors were used to treat an ammonium containing wastewater with and without organic carbon over a 270-day period to quantify efficiencies of chemical transformations and to characterize microbial composition for comparisons. The results showed higher ammonium removal (45±5%) from wastewater containing no organic carbon compared to a lower removal efficiency (19±4%) from the wastewater with organic carbon. An increase of Feammox bacteria abundance (Acidimicrobiaceae bacterium A6) of 67% was observed in the reactor without organic carbon enrichment over the operation period. In contrast, their abundance was significantly lower (89%) in presence of organic carbon. Illumina sequencing analysis revealed that relative abundance of Acidimicrobiaceae family containing Feammox bacteria increased in the reactor without organic carbon input. Higher abundance of microorganisms related to denitrifying activity was also observed in this reactor, that is indirect evidence of intensive Feammox activity. These results show that, in presence of significant organic carbon, heterotrophic iron reducers can outcompete autotrophic Feammox bacteria for ferric iron and hinder ammonium oxidation.
Our next research objective was designed to explore the opportunity of nutrient (N and P) recovery from anaerobic sludge digestion liquid (digestate) using ferrous iron and membrane separation. The study identified an optimal condition (Fe/P molar ratio of 2.1 and precipitation pH 7.0) for 100% P recovery from digestate through vivianite (hydrated ferrous phosphate) precipitation, which can be potentially used as fertilizer. Collaborating with Dr. Sanyal’s group in Chemical Engineering, the P-free digestate was further treated with polyelectrolyte-modified nanofiltration (NF) membranes to separate NH4+-N and the organic constituents as a means of N recovery. The surface-modified membranes demonstrated ~2X times higher NH4+-N /organic carbon selectivity than commercial NF membranes. This integrated vivianite precipitation and membrane separation technique showed promising results for recovering phosphorus and ammonium in separate streams of products. This approach is cost-effective because it does not require costly pH adjustment and reduces the energy requirements and CO2 emissions compare to existing approaches.
Our next research objective involved designing and testing an upflow anaerobic sludge blanket (UASB) reactor as a novel iron dosed technology to recover nutrients (N and P) from digestate. Ferric reduction coupled to organic carbon oxidation pathway can facilitate ferrous production in such treatment system and create a scope of P recovery through vivianite precipitation. Significant P removal (90%) has been achieved through precipitation of both ferric phosphate and vivianite as observed from sludge characterization. XPS analysis showed that vivianite was the major P precipitate in the sludge materials collected from the lowest part (bottom) of the reactor. The UASB achieved a high total organic carbon (TOC) removal (85%), resulting in ammonium rich effluent that can be further concentrated using polyelectrolyte-modified NF membrane treatment and used as liquid N fertilizer.
Overall, this research results helped elucidate iron-related biogeochemical reactions that can be incorporated in engineering processes for removal and recovery of nutrients from wastewaters. The research findings are useful for further developing engineering applications of iron-dosed treatment technologies for sustainable wastewater management.
Anwar, Rifat, "Elucidating Biogeochemical Reactions of Iron for Ammonium Removal and Nutrient Recovery from Wastewaters: Moving toward Sustainable Wastewater Management" (2022). Graduate Theses, Dissertations, and Problem Reports. 11399.