Gupta, Rashi

Rashi is Carollo Engineers Wastewater Practice Director after having led the firms solids practice for 8 years. She is a licensed civil engineer in...

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About Gupta, Rashi

Rashi is Carollo Engineers Wastewater Practice Director after having led the firms solids practice for 8 years. She is a licensed civil engineer in multiple states and obtained her Bachelors degree in Civil Engineering from UC Davis, and her Masters from UT Austin. She is the incoming Vice-Chair of the WEF RBC, a past-Chair of the Solids Separation Focus Group and a member of the Bioenergy Focus Group. Rashi co-authored the thickening chapter of WEFs MOP 8 and has contributed to a number of thickening and dewatering fact sheets produced by the Solids Separation Focus Group.

Gupta, Rashi

Titles from this speaker

Description: Application of Non-intrusive Sensors and Edge Computing for Condition-based...

Application of Non-intrusive Sensors and Edge Computing for Condition-based Monitoring of Biogas Compressors

Abstract

The reliability of manufacturing equipment is critical for ensuring the productivity and energy efficiency of a manufacturing facility. An unexpected machine breakdown may lead to unexpected downtime, disruption of the process schedule, lower production efficiency, and higher operation and maintenance cost. The recent development in machine learning and artificial intelligence enables data-driven Predictive Maintenance (PdM) by means of perceiving the dynamics of manufacturing systems and abstracting them into learnable features to provide a better interpretation of machine failures or unplanned downtimes. Often, vibration is used as a proxy for an early indicator of impending failure. In this study, tri-axial acceleration data collected from biogas compressors are utilized. PdM-based strategies for machine condition monitoring and smart scheduling of equipment maintenance using an anomaly scoring model are discussed. This study exploresincorporating smart manufacturing concepts into Water Resource Recovery Facilities (WRRFs) by implementing non-intrusive sensors and edge computing.

The objective of this work is to develop an anomaly detection approach for biogas blowers using nonintrusive vibration sensors for machine conditions and health management. High-frequency vibration signals are collected from a tri-axial accelerometer installed on the exterior of the biogas blower casing. Long short-term memory (LSTM) artificial neural network algorithm is applied for signal classification.

SpeakerLi, Zhongtian

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionAdvances in Preventative Maintenance

Session locationRoom S504c - Level 5

TopicAsset Management, Intermediate Level

Author(s)

Li, Zhongtian

Author(s)Z. Li 1; R. Gupta 1 ; W. Wasfy 1; Z. Li 1;

Author affiliation(s)Carollo Engineers 1; Carollo Engineers 1 ; Carollo Engineers 1; Carollo Engineers 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159204

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Comprehensive Assessment of Co-Digestion Capacity, Costs, Impacts, and Operational...

Comprehensive Assessment of Co-Digestion Capacity, Costs, Impacts, and Operational History in California

Abstract

Recent legislation in California aims to reduce short-lived climate pollutants like methane released from decomposing organic material in landfills. One potential alternative to landfilling this organic material is to co-digest it at municipal wastewater treatment plants and beneficially use the biogas generated. This study conducted on behalf of the California State Water Resources Control Board assesses the feasibility of co-digesting food waste in existing anaerobic digesters across California. This study quantifies the costs and benefits to co-digestion and estimates the amount of food waste that could be diverted and the amount of methane emissions that could be reduced. Six case studies are also presented of wastewater treatment plants who have implemented or plan to implement food waste co-digestion to understand their lessons learned through this process. The full results of the study will be documented in a comprehensive report to be published soon by the California State Water Resources Control Board. As such, this paper provides a preview and short summary of key results.

SpeakerGupta, Rashi

Presentation time

08:50:00

09:10:00

Session time

08:30:00

10:30:00

SessionOpportunities, Challenges, and Impacts of Co-digestion with Source Separated Organics

Session number519

Author(s)

R. GuptaR. Gupta

Author(s)R. Gupta1; R. Gupta1;

Author affiliation(s)Carollo Engineers, CA1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157473

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Dewatering Technology Selection for the "2nd Most Difficult-to-Dewater...

Dewatering Technology Selection for the "2nd Most Difficult-to-Dewater Sludge in the World"

Abstract

The City of Bend, Oregon, and Carollo Engineers, Inc. worked together to select a new dewatering technology to replace the City’s aging, poorly performing belt filter press. While the selection process included economic and non-economic analyses, the project team also assessed solids dewaterability through testing by third-party experts and incorporated criteria specific to the City’s Water Reclamation Facility (WRF) to identify the most suitable technology for the plant. The WRF’s digested solids are extremely difficult to dewater so dewaterability testing was used to determine the underlying reasons for poor dewaterability and the realistically achievable performance from different technologies. Belt filter presses, screw presses, centrifuges, and drying beds were considered, and centrifuges were ultimately selected as the most appropriate technology for the City’s Water Reclamation Facility (WRF). In-person site visits and telephone surveys of operating facilities allowed staff to hear about different equipment directly from other operators and maintenance personnel, which proved essential in building consensus around technology selection. Performance criteria and ultimate design features were based on the plant’s specific O&M needs and the results of the third-party dewaterability testing and on-site pilot tests.

SpeakerGupta, Rashi

Presentation time

10:30:00

10:50:00

Session time

10:30:00

11:30:00

SessionOvercoming Dewatering Difficulties

Session number520

TopicBiosolids and Residuals, Facility Operations and Maintenance

Author(s)

R. GuptaR. Gupta

Author(s)R. Gupta1; R. Gupta1;

Author affiliation(s)Carollo Engineers, CA1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157542

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Going the Extra Mile in Evaluating Digester Mixing Technologies for Existing...

Going the Extra Mile in Evaluating Digester Mixing Technologies for Existing Digesters

Abstract

APPLICABILITY Optimized mixing improves digestion stability and increases digestion capacity. Our objectives were to evaluate nine mixing technologies for installation on existing digesters at a California WRRF, determine what retrofit modifications would be required and associated costs, and ultimately select a mixing technology for the digesters. Understanding available mixing options for existing digesters and how to evaluate them in a manner that defines retrofit requirements allows for better feasibility assessment and cost estimates than typical evaluations. DEMONSTRATED RESULTS/CONCLUSIONS Introduction The mixing systems for two existing digesters at a California WRRF were the gas lift 'eductor tube' type system which have been working well for the plant since initial installation. However, the utility wanted to determine if changing to a different mixing technology could reduce energy consumption while maintaining good digestion and the costs to implement such a change. Nine mixing technologies were considered in a phased evaluation that began with a technology screening/initial cost comparison to identify the three most beneficial options for the utility followed by a detailed structural analysis to finetune understanding of retrofit requirements and overall costs for those three options. The digesters are prestressed concrete tanks with column-supported concrete covers, so the tanks have unique structural constraints relative to retrofitting. Therefore, a finite element analysis (FEA) was performed on the three screened technologies to better assess feasibility, understand the extent of structural modifications required for installation, and the costs to implement the mixing system at the WRRF. Nine mixing technologies were considered in a phased evaluation that began with a technology screening/initial cost comparison to identify the three most beneficial options for the utility followed by a detailed structural analysis to finetune understanding of retrofit requirements and overall costs for those three options. The digesters are prestressed concrete tanks with column-supported concrete covers, so the tanks have unique structural constraints relative to retrofitting. Therefore, a finite element analysis (FEA) was performed on the three screened technologies to better assess feasibility, understand the extent of structural modifications required for installation, and the costs to implement the mixing system at the WRRF. Methodology The nine technologies and associated representative system manufacturers that were considered for the initial screening and cost comparison are listed below: Gas Recirculation: - Lance type (manufacturer supporting technology not identified/responsive). - Bottom mounted diffusers (Enviromix). - Gas lift 'Eductor Tube' (Walker Process). - Gas piston 'Bubble Gun' (Suez/Veolia). Mechanical: - Submersible high solids axial impeller mixers (Anaergia). - Vertical shaft agitators (Philadelphia Mixing Solutions). - Linear motion (LM) mixing (Ovivo). - Hydraulic draft tubes - externally mounted and roof mounted (Ovivo). Hydraulic: - Pumped mixing systems (Vaughan). Equipment proposals solicited from the vendors included the recommended number of mixing units for each digester, system layout, cut sheets, motor sizes, ancillary equipment needed, installation lists, and costs. Screening level evaluation criteria included the following factors: —Economic o Conceptual Level Capital Costs o Operation & Maintenance Costs o 20-Year Life Cycle Costs — Non-Economic: o Footprint o Performance o Number of installations o Operating history o Retrofit requirements and feasibility o Constructability o O&M requirements o Sensitivity to debris o Suitability for co-digestion o Position relative to industry trends Based on the initial evaluation, the following systems were deemed infeasible: lance type gas mixing due to outdated technology and externally mounted hydraulic draft tubes and pumped mixing systems due to large penetrations required in the pre-stressed digester walls. The remaining technologies were then considered relative to the non-economic criteria, capital costs, and life cycle costs. The cost estimates at this stage of the evaluation were high level and included base assumptions regarding retrofit requirements for implementation. From that analysis, four more technologies were screened out due to high life cycle cost. The three remaining technologies included: gas lift mixers (similar to existing), submersible axial impellers, and LM mixers. Advantages, disadvantages, and the initial 20-year life cycle cost for each of these three technologies following the screening level evaluation are displayed in Table 1. The cost for the gas lift system assumed replacement in-kind of existing eductor tubes but maintaining existing compressors which remain in good condition. Each of these remaining technologies involve elements that are fully or partially roof-mounted. The axial impeller and LM mixer technologies would impart new static and dynamic loads on the roof structure and the axial impellers would require new, large openings to be cut into the roofs. Furthermore, while the axial impellers can be supported off the walls and floor, the LM mixers are usually supported entirely by the roof. Both digesters have column-supported concrete roofs with heavy rebar reinforcement along the column line grid as indicated in yellow and green in Figure 1. Equipment installed in the blue areas of the figure would be most feasible. However, additional structural analysis was necessary to truly assess impacts for the axial impellers and LM mixers and their associated static and dynamic loads. To understand and fully vet feasibility and implementation cost of these technologies, FEA was performed for both digesters. In addition, the vendor-recommended number of axial impellers was lower for each digester than on other studies for similar applications. The vendor reassessed their recommendation, adding one more mixer on each tank. The technology evaluation and cost estimates were then updated with the more refined assessment of structural and electrical impacts and equipment proposals. Results An example of the FEA results for the LM mixer for both digesters is shown in Figure 2. These results showed that the loads imparted by this mixing system, would require significant structural upgrades including additional bracing and concrete beams between columns. The FEA for the axial impeller option indicated a need for additional reinforcement at new roof openings, but no more significant modifications. However, with the increased mixing units, this technology's capital and power costs increased. Previously assumed modifications were found to be unnecessary for the gas lift option, reducing the technology's capital costs. After updating the cost estimates, the previous initial results changed, making gas lift mixing the most economical option. Table 2 shows the final life cycle cost estimates for the three technologies. Conclusions The phased evaluation with detailed structural assessment confirmed that the existing gas lift technology is the best option for this utility even though it consumes higher power than other options. Results for other WRRFs with differently constructed digesters, power costs, or drivers for change may vary. Investigating the potential impacts on existing digesters from changing technologies can yield different conclusions than typical evaluations that stop at the initial step described above. CONSEQUENCES Our results show that technology evaluation requires thorough vetting and consideration of impacts on existing tanks. The mechanical, electrical, and structural requirements for implementation should be investigated to thoroughly assess option feasibility and cost. Furthermore, energy savings alone may not warrant change if the existing system is effective and well-functioning. RELEVANCE To reduce costs and improve performance, WRRFs are focused on optimization and fully leveraging existing infrastructure. While newer, efficient technologies are promising, thoroughly evaluating options against a utility's specific drivers and investigating the impacts of various technologies on existing infrastructure is essential to defensible decision-making. There is no one-size-fits-all solution.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerGuo, Xiaolun

Presentation time

10:45:00

11:15:00

Session time

08:30:00

11:45:00

SessionAdvancing Anaerobic Digestion

Session number12

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicMixing, Retrofit, Technology Comparison

Author(s)

Guo, Xiaolun

Author(s)X. Guo1, R. Gupta1

Author affiliation(s)Carollo 1; Carollo1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159461

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count13

Description: Impacts of Various Hydraulic and Solid Loading Conditions on Process Capability of...

Impacts of Various Hydraulic and Solid Loading Conditions on Process Capability of Sludge Thickening with Thickening Centrifuges

Abstract

Solids thickening is an indispensable unit process for process intensification of biosolid s treatment. The fluctuations of feed sludge characteristics often impact the stability of the thickening process, reduce process capability, and increase operation and maintenance costs. Often, the optimization of sludge thickening is focused on meeting performance requirements as detailed in specifications. This study expands the assessment of sludge thickening by including both thickening equipment and its up- and downstream infrastructure from a process capability perspective. The presentation will benefit engineers and utility operators in better design and troubleshooting of sludge thickening processes with designed thickened sludge solids total equal to or higher than 6%. The presentation will provide practical suggestions for improving the process capabilities of sludge thickening, including pumping improvement, pipe flushing using digested sludge, and improvements on sensors.

This study documented the impact of sludge characteristics on the performance of thickening and subsequent sludge transfer. The significant increase of sludge viscosity when thickened from 4% to 6% TS requires a design of higher discharge pressure of thickened sludge transfer well. The findings of this study suggested that special attention is needed in the design of the process piping, pumping, and process controls to realize the capability of thickening equipment.

SpeakerLi, Zhongtian

Presentation time

14:00:00

14:20:00

Session time

13:30:00

15:00:00

SessionUpgrading and Optimizing Thickening and Dewatering

Session locationRoom S401a - Level 4

TopicIntermediate Level

Author(s)

Li, Zhongtian

Author(s)Z. Li 1; R. Gupta 1 ; Z. Li 1;

Author affiliation(s)Carollo Engineers 1; Carollo Engineers 1 ;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159233

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Process Capability Assessment of Centrifugal Sludge Thickening Under Various...

Process Capability Assessment of Centrifugal Sludge Thickening Under Various Operating Conditions

Abstract

APPLICABILITY Solids thickening is an indispensable unit process for process intensification of biosolids treatment. The fluctuations of feed sludge characteristics often impact the stability of the thickening process, reduce process capability, and increase operation and maintenance costs. Often, the optimization of sludge thickening is focused on meeting performance requirements as detailed in specifications. This study expands the assessment of sludge thickening by including both thickening equipment and its up- and downstream infrastructure from a process capability perspective. The presentation will benefit engineers and utility operators in better design and troubleshooting of sludge thickening processes with designed thickened sludge solids total equal to or higher than 6%. INTRODUCTION The practice of wastewater treatment is evolving to transform wastewater treatment plants into WRRFs with the adoption of advanced wastewater treatment and solids handling equipment, processes, and systems. Enhanced sludge thickening plays an important role in achieving footprint reduction, chemical and energy efficiency, and process control of solids handling [1]. Several studies have suggested that enhancing sludge thickening plays an important role in achieving energy self-sufficiency [2]. Studies showed that improvements in primary sludge (PS) and waste activated sludge (WAS) thickening significantly increased biogas production [3]. Thickened sludge with higher than 4% total solids could be sufficient for achieving a positive energy balance in two-step AD processes. Sludge thickening is taking an increasingly important role in process intensification in biosolids treatment, either through pass-through thickening prior to sludge digestion or recuperative thickening integrated with digestion processes. Centrifugal thickening is one approach to achieving high-rate sludge thickening. The control of the thickened sludge total solids (TS) usually involves the control of Relative Centrifugal Force (G-force), solids retention time, differential rotation speed between centrifuge bowel and screw, and polymer dosage. The application of an in-line density meter or pressure-indicating transmitter could provide control signals for optimizing the performance of centrifugal thickening through mechanical adjustment of the size of thickened sludge outlet [4] or adjustment of the specific gravity of thickened sludge through air injection [5]. Feed sludge characteristics have a significant impact on the performance of thickening centrifuges. The variables of the sludge characteristics include hydraulic loadings, solids loadings, and the mixing ratio between PS and WAS. The fluctuation of feed sludge characteristics could negatively affect the performance of thickening centrifuges and interrupt subsequent operations of biosolids processes. At the same time, fluctuations in feed sludge characteristics are expected and should be accommodated in the design of sludge thickening. The objective of this study is to investigate two cases of centrifugal thickening installations, respectively equipped with GEA and Centrisys thickening centrifuges. This study will provide practical recommendations for mitigating potential bottlenecks in achieving 6% TS of thickened sludge. This study will introduce the use of process capability assessment as a tool for O&M. METHODS Collection and organizing of site information. One challenge for thickening improvement is to systemically document and organize the site information associated with sludge thickening. This study investigates the design and operation of thickening centrifuges and the immediate upstream and downstream unit processes of the thickening centrifuges at two water resource recovery facilities (WRRFs). The design conditions of the two thickening centrifuges systems are summarized in Table 1. The process capability of sludge thickening is affected by both performance of the thickening centrifuges and the performance of up and downstream infrastructure, including wet wells, sludge transfer pumps, the design of process piping, and flow measurement devices. In this study, we developed a check list for a detailed documentation of the thickening unit process as well the immediate upstream and downstream processes, as shown in Table 2. Process capability assessment. Process capability assessment is a manufacturing tool to gain process performance knowledge by analyzing a measurable property of a process to the specification [6]. In this study, an easy-to-use process capability assessment tool is developed for operators to document the thickening performance as a record for understanding process performance and preventative & predictive maintenance of the thickening equipment on a monthly basis. RESULTS A scoring matrix is developed based on the assessment checklist (Table 2) for the evaluation of the positive and negative factors impacting efficient thickening for the two WRRFs. The scoring matrix is used as a survey and communication method to collect opinions from operating crew, maintenance crew, and engineers. Figure 1 shows an example of the scoring matrix. The scoring matrix will be further developed to document the progressive process improvement of sludge thickening. As it is not practical to adjust feed sludge TS in a controlled approach at WRRFs, the impact of solids loading on the performance of sludge thickening is evaluated through time series analysis and histogram analysis of feed and thickened sludges. Figure 2 shows the time series analysis of the feed sludge and thickened sludge TS. As illustrated in Figure 3, histogram analysis of the same set of data reveals the process operation in respective to specified performance (Table 1). Hydraulic loading of thickening centrifuges could be readily adjusted by throttling feed pump. The impact of hydraulic loading is evaluated in terms of solids recovery ratio under different thickened solids TS. As shown in Figure 4, a trade-off exists between hydraulic loading and the solids recovery under the same thickened sludge TS. The results of Figure 4 is based the WRRF 2. A similar curve will be developed for WRRF 1 for this study. Figure 5 shows the change of apparent viscosity as sludge is thickened to TS of 2.5%, 4.5%, 6.0%, and 8.5% respectively. The significant increase in thickened sludge viscosity leads to a higher transfer pump discharge pressure. Depending on different process piping design, the thickened sludge transfer pump's discharge pressure varies 90-110 PSI for WRRF 1 and 70-100 PSI for WRRF 2. It is necessary to size the thickened sludge transfer pump appropriately to minimize process interruption due to insufficient pumping capacity. Figure 6 provides an example of the developed process capability assessment method for monthly evaluation of the performance of thickening centrifuges. The assessment serves as a standard approach to understand the process stability and capacity in related to specified performance requirements. CONCLUSIONS This study documented the impact of sludge characteristics on the performance of thickening and subsequence sludge transfer. The significant increase of sludge viscosity when thickened from 4% to 6% TS requires a design of higher discharge pressure of thickened sludge transfer well. The findings of this study suggested that special attention is needed in the design of the process piping, pumping, and process controls to realize the capability of thickening equipment. The process capability assessment tool applied in this study provides plant operators with means to document and understand the performance of thickening centrifuges. The method developed in this study could be applied to the process capability assessment of other types of thickening technologies beyond thickening centrifuges in WRRFs. This method can serve as a communication tool between the operation and maintenance crews/departments, as the results addressed both process performance and equipment conditions. With the adoption of more advanced and sophisticated solids handling equipment, developing comprehensive process capability assessment tools for respective unit processes may lead to improved performance and reduced life cycle costs of solids handling at WRRFs. This study adopts process capability assessment in evaluating the performance of sludge thickening based on two types of centrifugal thickening machines with different control mechanisms. Attendance at this presentation will benefit design engineers interested in designing centrifugal thickening as part of the process intensification of solids handling in WRRF. The presentation will provide practical suggestions for understanding the process capability of installed thickening equipment for performance improvement.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerGupta, Rashi

Presentation time

10:45:00

11:15:00

Session time

10:45:00

11:45:00

SessionSession 04: Process Case Studies in Dewatering

Session number04

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicThickening & Dewatering

Author(s)

R. Gupta

Author(s)Z. Li1, R. Gupta2, 3, 4,

Author affiliation(s)Carollo Engineers1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158812

Volume / Issue

Content sourceResiduals and Biosolids

Word count12

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