Publications by authors named "April Gu"

This paper thoroughly examines how policy incentives impact the economic and environmental sustainability of anaerobic digestion (AD) systems. It uses techno-economic and life cycle analyses, along with real industry data, to explore the entire AD process-from feedstock acceptance to digestate disposal. It evaluates the effects of various U.

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  • Regulations use THM4 and HAA5 to measure health risks from disinfection byproducts (DBPs), assuming these metrics reflect toxicity levels.
  • A study found that while increasing chlorine contact time raised THM4 and HAA5 levels, it actually decreased overall cytotoxicity, suggesting these metrics may mislead regulatory focus.
  • Alternative methods, like granular activated carbon followed by chlorine, were shown to significantly reduce cytotoxicity, indicating the need for better toxicity-correlating metrics to enhance consumer safety in water distribution systems.
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Air pollution is a leading environmental health risk factor, and in situ toxicity assessment is urgently needed. Bacteria-based bioassays offer cost-effective and rapid toxicity assessments. However, the application of these bioassays for air toxicity assessment has been challenging, due to the instability of bacterial survival and functionality when directly exposed to air pollutants.

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  • The study focuses on understanding the microdiversity of Polyphosphate Accumulating Organisms (PAOs) in side-stream enhanced biological phosphorus removal (S2EBPR) systems, which improve stability compared to traditional methods.
  • Researchers used an advanced technique called oligotyping analysis on 16S rRNA gene sequencing to identify subgenus-level PAO profiles in activated sludge from 12 different water resource recovery facilities (WRRFs).
  • The findings suggest that significant differences exist at the sub-genus level across different facilities and highlight the potential of oligotyping and network analysis for identifying links between PAO diversity and the performance of EBPR/S2EBPR systems.
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  • The study introduces a new system called A-B-S2EBPR for efficient nitrogen removal from low-strength municipal wastewater by promoting nitrite accumulation.
  • Researchers achieved significant nitrite levels (5.5 mg N/L) and high removal efficiency of total inorganic nitrogen (TIN at 84.9%) through a combination of biological processes.
  • The findings highlight a shift in microbial communities that favor partial denitrification over conventional nitrification, with specific microorganisms utilizing carbon sources during the process.
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Drinking water security in Puerto Rico (PR) is increasingly challenged by both regulated and emerging anthropogenic contaminants, which was exacerbated by the Hurricane Maria (HM) due to impaired regional water cycle and damaged water infrastructure. Leveraging the NIEHS PROTECT (Puerto Rico Testsite for Exploring Contamination Threats) cohort, this study assessed the long-term tap water (TW) quality changes from March 2018 to November 2018 after HM in PR, by innovatively integrating two different effect-based quantitative toxicity assays with a targeted analysis of 200 organic and 22 inorganic pollutants. Post-hurricane PR TW quality showed recovery after >6-month period as indicated by the decreased number of contaminants showing elevated average concentrations relative to pre-hurricane samples, with significant difference of both chemical and toxicity levels between northern and southern PR.

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Woodchips are widely used as a low-cost and renewable organic carbon source for denitrifying biofilms in passive nutrient removal systems. One limitation of wood-based biofiltration systems is their relatively poor removal of phosphorus (P) from subsurface drainage and stormwaters, necessitating the use of additional filter media when co-treatment of nitrogen (N) and P is required. Here, we show that anoxic-oxic cycling of woodchip media, which enhances nitrate (NO) removal by increasing the mobilization of organic carbon from wood, also improves orthophosphate (P) uptake onto woodchips.

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Titanium dioxide nanoparticles (nTiO) have been considered a possible carcinogen to humans, but most existing studies have overlooked the role of human enzymes in assessing the genotoxicity of nTiO. Here, a toxicogenomics-based in vitro genotoxicity assay using a GFP-fused yeast reporter library was employed to elucidate the genotoxic potential and mechanisms of nTiO. Moreover, two new GFP-fused yeast reporter libraries containing either human CYP1A1 or CYP1A2 genes were constructed by transformation to investigate the potential modulation of nTiO genotoxicity in the presence of human CYP enzymes.

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Class A biosolids from water resource recovery facilities (WRRFs) are increasingly used as sustainable alternatives to synthetic fertilizers. However, the high phosphorus to nitrogen ratio in biosolids leads to a potential accumulation of phosphorus after repeated land applications. Extracting vivianite, an FeP mineral, prior to the final dewatering step in the biosolids treatment can reduce the P content in the resulting class A biosolids and achieve a P:N ratio closer to the 1:2 of synthetic fertilizers.

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A novel integrated pilot-scale A-stage high rate activated sludge, B-stage short-cut biological nitrogen removal and side-stream enhanced biological phosphorus removal (A/B-shortcut N-S2EBPR) process for treating municipal wastewater was demonstrated with the aim to achieve simultaneous and carbon- and energy-efficient N and P removal. In this studied period, an average of 7.62 ± 2.

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We piloted the incorporation of side-stream enhanced biological phosphorus removal (S2EBPR) with A/B stage short-cut nitrogen removal processes to enable simultaneous carbon-energy-efficient nutrients removal. This unique configuration and system conditions exerted selective force on microbial populations distinct from those in conventional EBPR. Interestingly, effective P removal was achieved with the predominance of Acinetobacter (21.

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While the adsorption/bio-oxidation (A/B) process has been widely studied for carbon capture and shortcut nitrogen (N) removal, its integration with enhanced biological phosphorus (P) removal (EBPR) has been considered challenging and thus unexplored. Here, full-scale pilot testing with an integrated system combining A-stage high-rate activated sludge with B-stage partial (de)nitrification/anammox and side-stream EBPR (HRAS-P(D)N/A-S2EBPR) was conducted treating real municipal wastewater. The results demonstrated that, despite the relatively low influent carbon load, the B-stage P(D)N-S2EBPR system could achieve effective P removal performance, with the carbon supplement and redirection of the A-stage sludge fermentate to the S2EBPR.

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Side-stream enhanced biological phosphorus removal process (S2EBPR) has been demonstrated to improve performance stability and offers a suite of advantages compared to conventional EBPR design. Design and optimization of S2EBPR require modification of the current EBPR models that were not able to fully reflect the metabolic functions of and competition between the polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) under extended anaerobic conditions as in the S2EBPR conditions. In this study, we proposed and validated an improved model (iEBPR) for simulating PAO and GAO competition that incorporated heterogeneity and versatility in PAO sequential polymer usage, staged maintenance-decay, and glycolysis-TCA pathway shifts.

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Granular activated carbon treatment with postchlorination (GAC/Cl) and chlorination followed by chloramination (Cl/NHCl) represent two options for utilities to reduce DBP formation in drinking water. To compare the total cytotoxicity of waters treated by a pilot-scale GAC treatment system with postchlorination (and in some instances with prechlorination upstream of GAC (i.e.

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Enhanced biological phosphorus removal (EBPR) is an economical and sustainable process for phosphorus removal from wastewater. Despite the widespread application of EBPR for low-strength domestic wastewater treatment, limited investigations have been conducted to apply EBPR to the high-strength wastewaters, particularly, the integration of EBPR and the short-cut nitrogen removal process in the one-stage system remains challenging. Herein, we reported a novel proof-of-concept demonstration of integrating EBPR and nitritation (oxidation of ammonium to nitrite) in a one-stage sequencing batch reactor to achieve simultaneous high-strength phosphorus and short-cut nitrogen removal.

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The integration of biological phosphorus removal (bio-P) and shortcut nitrogen removal (SNR) processes is challenging because of the conflicting demands on influent carbon: SNR allows for upstream carbon diversion, but this reduction of influent carbon (especially volatile fatty acids [VFAs]) prevents or limits bio-P. The objective of this study was to achieve SNR, either via partial nitritation/anammox (PNA) or partial denitrification/anammox (PdNA), simultaneously with biological phosphorus removal in a process with upstream carbon capture. This study took place in a pilot scale A/B process with a sidestream bio-P reactor and tertiary anammox polishing.

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Micron-size spherical polystyrene colloidal particles are mechanically stretched to a prolate geometry with desirable aspect ratios. The particles in an aqueous medium with specific ionic concentration are then introduced into a microchannel and allowed to settle on a glass substrate. In the presence of unidirectional flow, the loosely adhered particles in the secondary minimum of surface interaction potential are easily washed off, but the remnant in the strong primary minimum preferentially aligns with the flow direction and exercises in-plane rotation.

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Wastewater treatment plants (WWTPs) have been regarded as an important source of antibiotic resistance genes (ARGs) in environment, but out of municipal domestic WWTPs, few evidences show how environment is affected by industrial WWTPs. Here we chose Hangzhou Bay (HZB), China as our study area, where land-based municipal and industrial WWTPs discharged their effluent into the bay for decades. We adopted high-throughput metagenomic sequencing to examine the antibiotic resistome of the WWTP effluent and coastal sediment samples.

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Among ubiquitous phosphorus (P) reserves in environmental matrices are ribonucleic acid (RNA) and polyphosphate (polyP), which are, respectively, organic and inorganic P-containing biopolymers. Relevant to P recycling from these biopolymers, much remains unknown about the kinetics and mechanisms of different acid phosphatases (APs) secreted by plants and soil microorganisms. Here we investigated RNA and polyP dephosphorylation by two common APs, a plant purple AP (PAP) from sweet potato and a fungal phytase from .

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Article Synopsis
  • Advanced analytical methods, like single-cell technologies, provide a deeper understanding of microbial ecology, but challenges exist in determining the right sample size due to community complexity and limited resources.
  • We developed and validated a computational protocol using a metric called kernel divergence, which allows for the assessment of sample sizes without prior knowledge or human intervention, accommodating both linear and nonlinear data relationships.
  • This method was successfully tested on Single-cell Raman Spectroscopy data from multiple biological communities and aims to standardize sampling size optimization, making experiments more comparable and reproducible in complex environmental studies.
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Loss of basic utilities, such as drinking water and electricity distribution, were sustained for months in the aftermath of Hurricane Maria's (HM) landfall in Puerto Rico (PR) in September 2017. The goal of this study was to assess if there was deterioration in biological quality of drinking water due to these disruptions. This study characterized the microbial composition of drinking water following HM across nine drinking water systems (DWSs) in PR and utilized an extended temporal sampling campaign to determine if changes in the drinking water microbiome were indicative of HM associated disturbance followed by recovery.

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Polyphosphate (polyP) accumulating organisms (PAOs) are the key agent to perform enhanced biological phosphorus removal (EBPR) activity, and intracellular polyP plays a key role in this process. Potential associations between EBPR performance and the polyP structure have been suggested, but are yet to be extensively investigated, mainly due to the lack of established methods for polyP characterization in the EBPR system. In this study, we explored and demonstrated that single-cell Raman spectroscopy (SCRS) can be employed for characterizing intracellular polyPs of PAOs in complex environmental samples such as EBPR systems.

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Candidatus Accumulibacter phosphatis (CAP) and its clade-level micro-diversity has been associated with and implicated in functional differences in phosphorus removal performance in enhanced biological phosphorus removal (EBPR) systems. Side-stream EBPR (S2EBPR) is an emerging process that has been shown to present a suite of advantages over the conventional EBPR design, however, large knowledge gaps remain in terms of its underlying ecological mechanisms. Here, we compared and revealed the higher-resolution differences in microbial ecology of CAP between a full-scale side-stream EBPR configuration and a conventional A2O EBPR process that were operated in parallel and with the same influent feed.

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The mass production of graphene oxide (GO) unavoidably elevates the chance of human exposure, as well as the possibility of release into the environment with high stability, raising public concern as to its potential toxicological risks and the implications for humans and ecosystems. Therefore, a thorough assessment of GO toxicity, including its potential reliance on key physicochemical factors, which is lacking in the literature, is of high significance and importance. In this study, GO toxicity, and its dependence on oxidation level, elemental composition, and size, were comprehensively assessed.

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Polyphosphate-accumulating organisms (PAOs), which can store high levels of phosphate (P) in the form of polyphosphate (polyP), are employed to engineer enhanced biological P removal (EBPR) from wastewaters. Co-localization of Mg and K in polyP granules of PAOs has been reported, and higher abundance of Mg-polyP granules relative to other metal complexes was correlated positively with EBPR performance stability. However, the underlying mechanism remains unknown.

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