Ryan Holloway - Academia.edu (original) (raw)

Papers by Ryan Holloway

A majority of wastewater plants in the United States use conventional activated sludge (CAS) in t... more A majority of wastewater plants in the United States use conventional activated sludge (CAS) in their treatment process. While CAS is a common practice, it is not without faults. One of its drawbacks is the difficulty in maintaining the process, as it is often prone to bulking, which is caused by an undesired build up of filamentous bacteria and results in sludge that does not settle. Additional drawbacks include limited space for WWTPs to expand and the energy costs required for aeration during CAS treatment. Because CAS infrastructure is so common, optimizing this technology is crucial for the prevention of water pollution. Some solutions for these problems have been developed including aerobic granulation, which allows the plant to have a smaller footprint; however, these advanced wastewater technologies are not easily implemented in existing WWTPs.

SSRN Electronic Journal, 2021

Separation and Purification Technology, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Water Research, 2019

Recent advancements in data-driven process control and performance analysis could provide the was... more Recent advancements in data-driven process control and performance analysis could provide the wastewater treatment industry with an opportunity to reduce costs and improve operations. However, big data in wastewater treatment plants (WWTP) is widely underutilized, due in part to a workforce that lacks background knowledge of data science required to fully analyze the unique characteristics of WWTP. Wastewater treatment processes exhibit nonlinear, nonstationary, autocorrelated, and co-correlated behavior that (i) is very difficult to model using first principals and (ii) must be considered when implementing data-driven methods. This review provides an overview of data-driven methods of achieving fault detection, variable prediction, and advanced control of WWTP. We present how big data has been used in the context of WWTP, and much of the discussion can also be applied to water treatment. Due to the assumptions inherent in different data-driven modeling approaches (e.g., control charts, statistical process control, model predictive control, neural networks, transfer functions, fuzzy logic), not all methods are appropriate for every goal or every dataset. Practical guidance is given for matching a desired goal with a particular methodology along with considerations regarding the assumed data structure. References for further reading are provided, and an overall analysis framework is presented.

Proceedings of the Water Environment Federation, 2018

Stochastic Environmental Research and Risk Assessment, 2016

Multivariate statistical methods for online process monitoring have been widely applied to chemic... more Multivariate statistical methods for online process monitoring have been widely applied to chemical, biological, and engineered systems. While methods based on principal component analysis (PCA) are popular, more recently kernel PCA (KPCA) and locally linear embedding (LLE) have been utilized to better model nonlinear process data. Additionally, various forms of dynamic and adaptive monitoring schemes have been proposed to address time-varying features in these processes. In this analysis, we extend a common simulation study in order to account for autocorrelation and nonstationarity in process data and comprehensively compare the monitoring performances of static, dynamic, adaptive, and adaptive–dynamic versions of PCA, KPCA, and LLE. Furthermore, we evaluate a nonparametric method to set thresholds for monitoring statistics and compare results with the standard parametric approaches. We then apply these methods to real-world data collected from a decentralized wastewater treatment system during normal and abnormal operations. From the simulation study, adaptive–dynamic versions of all three methods generally improve results when the process is autocorrelated and nonstationary. In the case study, adaptive–dynamic versions of PCA, KPCA, and LLE all flag a strong system fault, but nonparametric thresholds considerably reduce the number of false alarms for all three methods under normal operating conditions.

Journal of Membrane Science, 2016

Forward osmosis membrane performance and fouling was studied during 100 days of continuous activa... more Forward osmosis membrane performance and fouling was studied during 100 days of continuous activated sludge treatment. The purpose of the study was to compare the performance and fouling of commercial cellulose triacetate and newly developed polyamide thin film composite membranes that treated high salinity and low salinity activated sludge from two membrane bioreactors. Water flux, reverse salt flux, and specific reverse salt flux were measured to evaluate the performance of virgin and fouled membranes. Membrane autopsy was used to investigate foulant composition and compare physicochemical membrane properties before and after fouling. The results indicated that both membrane types attained steady-state water flux over 100 days, characterized by an initial decline and subsequent steady-state period. Biofouling and organic fouling caused overall water flux decline, in which foulants were identical between membrane and activated sludge types. Water flux results were similar for the two activated sludge types and demonstrated that FO membrane performance and fouling was independent of total dissolved solids, calcium, and mixed liquor suspended solid concentrations. Lastly, virgin membrane properties (i.e., hydrophilicity and surface roughness) did not contribute substantially to membrane fouling. Cellulose triacetate membranes outperformed thin film composite membranes, with lower fouling propensity, higher water flux, lower reverse salt flux, and lower specific reverse salt flux.

Proceedings of the Water Environment Federation, 2016

Environmental Science & Technology, 2016

20-day and 5-day SRTs, with inset graphs showing rDNA abundance scale between 0 and 1.2 % relativ... more 20-day and 5-day SRTs, with inset graphs showing rDNA abundance scale between 0 and 1.2 % relative abundance. (B) Relationship between rRNA and rDNA frequencies of bacterial OTUs at 20-day and 5-day SRTs. The points are paired rRNA and rDNA frequencies for each individual OTU and time points that correspond to redox conditions: anaerobic(10-min)/oxic(60-min)/anoxic(108-min) for 20-day and anoxic(10min)/oxic(60-min)/anoxic(108-min) for 5-day. The solid line is the x=y line and the dotted vertical line delineates rare (<1% relative abundance) and abundant taxa (≥1% relative abundance). A. B. Nitrospira Sp hin go ba cte ria les Str am en op iles

ACS Symposium Series, 2013

Cities worldwide are facing a growing water crisis with challenges from climate change, populatio... more Cities worldwide are facing a growing water crisis with challenges from climate change, population growth, and deteriorating infrastructure that threatens economic development, social welfare, and environmental sustainability. New strategies are needed for water/wastewater treatment and distribution that will reduce the need to pump water over long distances and provide opportunities to reuse wastewater locally. A full-scale pilot hybrid sequencing batch membrane bioreactor (SBMBR) wastewater treatment system serving 400 residential units at Colorado School of Mines (Colorado) was used as a case study to assess the technical feasibility of using the SBMBR process as a sustainable approach for onsite water reclamation and reuse of domestic wastewater effluents. The system was first tested in its capability to produce an effluent quality adequate for landscape irrigation applications. Further, the authors examined the applicability of the SBMBR as a decentralize treatment technology in terms of local water demand, infrastructure requirements, energy consumption and environmental impact. The technical challenges related to the operation of the SBMBR were also evaluated. Findings

Water Research, 2015

In this study we investigated the removal of viruses with similar size and shape but with differe... more In this study we investigated the removal of viruses with similar size and shape but with different external surface capsid proteins by a bench-scale membrane bioreactor (MBR). The goal was to determine which virus removal mechanisms (retention by clean backwashed membrane, retention by cake layer, attachment to biomass, and inactivation) were most impacted by differences in the virus surface properties. Seven bench-scale MBR experiments were performed using mixed liquor wastewater sludge that was seeded with three lab-cultured bacteriophages with icosahedral capsids of~30 nm diameter (MS2, phiX174, and fr). The operating conditions were designed to simulate those at a reference, fullscale MBR facility. The virus removal mechanism most affected by virus type was attachment to biomass (removals of 0.2 log for MS2, 1.2 log for phiX174, and 3 log for fr). These differences in removal could not be explained by electrostatic interactions, as the three viruses had similar net negative charge when suspended in MBR permeate. Removals by the clean backwashed membrane (less than 1 log) and cake layer (~0.6 log) were similar for the three viruses. A comparison between the clean membrane removals seen at the bench-scale using a virgin membrane (~1 log), and the full-scale using 10-year old membranes (~2e3 logs) suggests that irreversible fouling, accumulated on the membrane over years of operation that cannot be removed by cleaning, also contributes towards virus removal. This study enhances the current mechanistic understanding of virus removal in MBRs and will contribute to more reliable treatment for water reuse applications.

Environmental Science: Water Research & Technology, 2015

The osmotic membrane bioreactor (OMBR) is a hybrid biological-physical treatment process for wast... more The osmotic membrane bioreactor (OMBR) is a hybrid biological-physical treatment process for wastewater treatment and water reuse.

Journal of Membrane Science, 2015

Reverse salt flux (RSF) of ions from the draw solution (DS) to the feed is a major drawback of fo... more Reverse salt flux (RSF) of ions from the draw solution (DS) to the feed is a major drawback of forward osmosis (FO). RSF is reduced when divalent ion salts such as MgCl 2 and MgSO 4 that have larger hydrated radius are used instead of salts with monovalent ions only (e.g., NaCl). However, using divalent ion DSs comes with a costnamely lower water flux compared to NaCl DS at similar osmotic pressures. The objective of this study was to enhance FO by lowering RSF while maintaining high water flux by adding low concentrations of divalent ions or organic ions to NaCl DS. We have demonstrated that water flux was similar for pure NaCl DS and mixed salts DS having low concentrations of divalent or organic ions at the same osmotic pressure of pure NaCl DS. Simultaneously, the average RSF was lower for all mixed salts DSs tested compared to pure NaCl DS. Results from a student t-test comparing the average RSF of the mixed salts DSs to the pure NaCl DS revealed that although the average RSF was lower for all the mixed DSs tested, only the mixed salts DS containing MgCl 2 has RSF significantly lower than the pure NaCl DS.

Water Research, 2007

The nutrient-rich liquid stream produced during the dewatering of digested biomass (i.e., the cen... more The nutrient-rich liquid stream produced during the dewatering of digested biomass (i.e., the centrate) is commonly mixed with the influent raw wastewater at wastewater treatment facilities. This increases the nitrogen and phosphorus loading on biological processes, increases operating costs, and in some cases, results in increased nutrient concentrations in the final effluent. Forward osmosis (FO) is a membrane treatment process that was investigated at bench scale to determine its feasibility to concentrate centrate under both batch and continuous operating conditions. The continuous bench-scale system used FO as pretreatment for reverse osmosis (RO). Results demonstrated that high water flux and high nutrient rejection could be achieved. The combined FO/RO process exhibited sustainable flux over an extended time period. A mathematical model was developed in order to determine the specific energy, power, and membrane area requirements for a larger-scale centrate treatment process. Modeling results indicated that to optimize power and membrane area requirements, the system should be operated at approximately 70% water recovery.

Environmental science & technology, Jan 16, 2014

A hybrid ultrafiltration-osmotic membrane bioreactor (UFO-MBR) was investigated for over 35 days ... more A hybrid ultrafiltration-osmotic membrane bioreactor (UFO-MBR) was investigated for over 35 days for nutrient and trace organic chemical (TOrC) removal from municipal wastewater. The UFO-MBR system uses both ultrafiltration (UF) and forward osmosis (FO) membranes in parallel to simultaneously extract clean water from an activated sludge reactor for nonpotable (or environmental discharge) and potable reuse, respectively. In the FO stream, water is drawn by osmosis from activated sludge through an FO membrane into a draw solution (DS), which becomes diluted during the process. A reverse osmosis (RO) system is then used to reconcentrate the diluted DS and produce clean water suitable for direct potable reuse. The UF membrane extracts water, dissolved salts, and some nutrients from the system to prevent their accumulation in the activated sludge of the osmotic MBR. The UF permeate can be used for nonpotable reuse purposes (e.g., irrigation and toilet flushing). Results from UFO-MBR inve...