Li, Zhongtian

Zhongtian Li is a lead engineer at Carollo Engineers. Zhongtian has a combined 10 years of experience in engineering consulting and technology development. He is working on engineering design projects in wastewater treatment and solids handling. Zhongtian is leading applied research projects funded by the Water Research Foundation, AWWA, and the DOE ARPA-E program. His primary focus is resource recovery and energy efficiency.

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: Condition-Based Monitoring of Biogas Compressor Using Nonintrusive Sensors and...

Condition-Based Monitoring of Biogas Compressor Using Nonintrusive Sensors and Machine Learning

Abstract

APPLICABILITY 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. The proposed condition-based monitoring approach could provide a low-cost non-intrusive solution for asset management of compressors at water resource recovery facilities. INTRODUCTION Predictive maintenance (PdM) organizes maintenance activities according to the actual health state of machine tools, equipment, and systems [1]. Diagnostic PdM detect detects faults, determines root causes of operation anomalies, and estimates the current health state of a system under investigation to prevent unexpected failures. Condition-based monitoring is an approach for realizing diagnostic PdM as standardized by ISO 17359:2018. Condition-based monitoring can provide significant advantages in relation to product quality, safety, availability, and cost reduction in industrial applications. The recent advent of information and communication technologies and artificial intelligence presents a great opportunity to enhance the practice of data-driven assessment of the operation and maintenance of wastewater infrastructure [2, 3]. The objective of this study is to develop an anomaly detection approach for biogas compressors through vibration analysis for predictive maintenance. To achieve this goal, piezoelectric sensors and edge computing platforms (Raspberry Pi and Arduino board) are deployed on the biogas compressors. Machine learning algorithms are applied for classifying the collected vibration data for anomaly pattern recognition. METHODS The vibration monitoring in this study is implemented for compressor Unit 1 (KAESER) and compressor Unit 2 (SIEMENS) in a biogas facility. A low-power tri-axial accelerometer (model# ADXL345, Analog Devices, Wilmington, MA) is used with serial data communication devices such as Raspberry Pi and Arduino boards to collect vibration data from compressors. The data collection was initiated from the point of time when the compressor operated in normal condition and continued to the occurrence of any failures. The sampling frequency of the accelerometer is 1k Hz for each axis with a measurement interval of 30 minutes. Data are measured and obtained via Inter-Integrated-Circuit (I2C) bus. During the measurement, the sensor collects 10000 data points for each axis, which would take approximately 10 seconds, and is set to idle until the next measurement. The structure of the implemented condition-based monitoring is shown in Figure 1. The raw data includes the time stamp and acceleration data for the x, y, z-axis, and the sampled time for the corresponding sample. Sample x-axis vibration signals are visualized in Figure 2. The machine diagnosis is realized by scoring the anomaly levels of the vibration data, which will increase as failure approaches. Hence, an anomaly scoring model is tested to characterize the different levels of anomalies and provide an informative interpretation of forthcoming failures. The implemented model is inspired by dilated RNN network and Temporal Hierarchical One Class (THOC) network, which contributed to solving complex dependencies and vanishing gradients problems in layers. The THOC network is adopted and modified to develop the anomaly scoring model. The model consists of 3 long-short term memory (LSTM) layers with dilated skip connections. Details of the method implementation could be found elsewhere [6]. The sequential length of the transformed data is 36, and the input batch size is set to 128. In Fig. 3, each node represents a hidden RNN cell. The number of input nodes highlighted as green is determined by the sequential length of input data, which is 36. Similarity score obtained from the score function is translated to loss using the following equation that will be optimized through a training process. Adaptive Moment Estimation (Adam) optimizer is employed as it is known to have good capabilities of reaching global minimum with a high dimensional dataset. The structure of the implemented condition-based monitoring is shown in Figure 1. RESULTS The results of the model are shown in Figure 3. The input data (time-frequency domain) is visualized using power spectrum analysis. It is important to be noted that the Euclidean distance returns the length of a line segment between two vectors. Thus, the test data with a larger distance from the centers in each layer are expected to be assigned higher anomaly scores. As shown in Figure 3, anomaly points are captured when the power spectrum has abnormal patterns or when a peak value pops out from the power spectrum. Also, data points with small anomaly scores are not identified as anomalies, which might be sound as not all anomalies cause machine failures. Thus, a threshold should be carefully determined as it plays a critical role in linking such anomaly information with maintenance strategies. In this study, the threshold value is selected based on the 99.9 percentile in the anomaly scores. Different threshold values are used with an optimal threshold that prevents generating excessive false positives. The results may need to be compared to the actual machine condition such as whether abnormal operations were present while it was monitored. Since Euclidean distance may not be intuitive on a high dimensional dataset, different scoring functions are also tested for comparison. Chebyshev scoring function is adopted and the result is visualized in Figure 4. Chebyshev distance provides the greatest differences between two different vectors along any coordinate dimension. Hence, input data with the highest variance and difference are likely to obtain higher anomaly scores. As shown in Figure 4, the power spectrum with peak values tends to be identified as anomalies. In this case, the warning stage depicted with the orange line was applied with an additional threshold (99 percentile) to demonstrate a warning system that may be applicable to the data-driven maintenance strategy. In this study, the anomaly scoring model has been utilized to detect the abnormal vibration patterns and interpret them into anomaly scores. Based on the results from the proposed anomaly scoring model, a notification strategy can be established for further maintenance scheduling. The operation and maintenance manual or guidelines are provided by manufacturers of the machines. An example of the operation and maintenance manual of a compressor is shown in Table 1. Proper maintenance requires timely tracking of operation hours followed by appropriate actions such as checking oil levels, changing filters, and grease bearings. CONCLUSIONS AND RELEVANCE This study presents a condition-based monitoring approach for biogas compressors as an example of data-driven asset assessment. The test anomaly scores were calculated based on a similarity between unseen data and clusters that are learnable by machine learning algorithms. The study shows that condition-based monitoring using nonintrusive vibration sensors could be a useful asset management tool and providing early failing alarms of equipment embedded in WRRFs. The result of this study suggests that the operator's supervisory control and condition-based monitoring could be integrated for asset management (Figure 5). A combination of preventative maintenance following manufacturer's O&M manual and predictive maintenance guided by condition-based monitoring could lead to adaptive asset management program. Meanwhile, deploying condition-based monitoring solution at WRRFs may add additional responsibilities to the maintenance crew at WRRFs. Future studies are required to understand the operator demand, capital investment, and cybersecurity implications of condition-based monitoring for WRRFs. Attendance at this presentation will benefit operators and design engineers who are interested in data-driven asset management through condition based-monitoring. This study presented a novel application of deploying nonintrusive vibration sensors and edge computing for anomaly detection of biogas compressors. The method developed in this study could be applied in asset monitoring of other rotary equipment in WRRFs.

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

SpeakerLi, Zhongtian

Presentation time

9:30:00

10:00:00

Session time

8:30:00

11:45:00

SessionSession 12: Innovative Processes in Anaerobic Digestion

Session number12

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicResearch & Innovations

Author(s)

Z. Li

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

DOI10.2175/193864718825158801

Volume / Issue

Content sourceResiduals and Biosolids

Word count12

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: Integrated bioenergy recovery, solar power generation, and resource recycling for...

Integrated bioenergy recovery, solar power generation, and resource recycling for municipal sludge and organic waste management

Abstract

APPLICABILITY Toyohashi City Biomass Utilization Center (TCBUC) is Japan's largest composite biomass energy facility that combines co-digestion, combined heat and power (CHP) generation, and solar photovoltaic arrays for an energy neutral facility. It operates as a Public-Private Partnership (P3) between a publicly owned municipal wastewater treatment plant (WWTP) and the adjacent privately owned biomass utilization facility. TCBUC has a sophisticated feedstock pretreatment system that ensures consistent feedstock quality, protecting downstream anaerobic digesters from contaminants, and optimizing biogas production rates. TCBUC also innovatively integrates biogas-fueled combined heat and power (CHP) generation with a large solar photovoltaic array to enhance overall renewable energy production [2], maximizing the facility's energy output and strengthening its energy resilience and flexibility. This case study highlights TCBUC's process design, operational integration, and key lessons learned, and explores the close collaboration and seamless integration between the public and private facilities. This study is partially supported by WRF 5296 Smart and Connected Energy Management.

INTRODUCTION OF THE FACILITY TCBUC is adjacent to the Nakajima WWTP and applies innovative treatment and energy recovery technology, positioning itself as a valuable model for utilities, municipalities, and environmental engineers pursuing sustainable organic waste management aligned with circular economy objectives (Figure 1 and Figure 2). At the heart of the facility is a sophisticated feedstock receiving and preprocessing facility capable of handling heterogeneous inputs through a multi-stage treatment process (Figure 4). Two large mesophilic anaerobic digesters, each with a capacity of approximately 1.32 million gallons (5,000 cubic meters) and operating at a 30-day solids retention time, provide biological treatment for stabilized sludge and organic waste. The biogas-powered CHP system generates approximately 1,000 kW of electricity complemented by 1,995 kW from onsite solar panels-integrated renewables that contribute significantly to the facility's energy self-sufficiency and sustainability (Figure 5 and Figure 6).Both renewable power sources benefit from Feed-in Tariff (FIT) subsidies, which guarantee fixed-price purchase contracts for renewable electricity over 20 years. This provides financial stability and incentives for long-term project success (Figure 3).

DEMONSTRATED RESULTS AND OUTCOMES Over recent years (2021-2023), TCBUC has demonstrated consistent, reliable, and efficient processing of multiple feedstocks, generating substantial renewable energy and carbonized fuel outputs. The performance of the facility is summarized in Table 2, Table 3, and Table 4.
• Feedstock Management: The facility processes an average of approximately 350 to 390 cubic meters per day of public sewage sludge and 140 cubic meters per day of sludge from regional septic systems (excrement purifying chamber sludge). Food waste input remains stable at about 41 to 45 metric tons per day, sourced from local household programs and collection networks, achieved through effective community involvement.
• Energy Generation: Annual renewable electricity production ranges from approximately 7 to 7.5 million kWh, combining CHP output from biogas combustion and solar panel electricity. CHP production is steady around 1,000 kW at full capacity, with solar power generation surpassing this at times during peak solar hours. The energy is sold under the FIT scheme, providing a consistent revenue stream and supporting financial viability.
• Carbonized Fuel Production: Dewatered digested sludge with ~20% total solids are carbonized daily at a throughput of about 6 metric dry tons, yielding over 2,200 metric tons of carbonized fuel annually. This byproduct supports industrial uses, closing the resource recovery loop beyond renewable energy (Figure 7).

RELEVANCE TO AUDIENCE TCBUC represents a robust, scalable, and integrated model for organic waste management that supports municipal sustainability goals and renewable energy mandates. Attendees will gain valuable insights into integrating wastewater treatment, organic waste management, and renewable energy generation for urban sustainability. Key conclusions include:
• Integrated Multi-Feedstock Processing: Combining sewage sludge, septic sludge, and food waste into a single anaerobic digestion system maximizes biogas generation, optimizes resource efficiency, and reduces landfill dependence.
• Synergistic Resource Recovery: Treatment coupling anaerobic digestion with downstream carbonization transforms otherwise waste sludge into a valuable industrial fuel, contributing to material circularity.
• Stable and Efficient Operation: The facility exhibits continuous high-performance operation with minimal maintenance disruption, effective odor mitigation, and efficient logistics and site layouts.
• Effective Public-Private Partnership: The PFI and DBO framework, combined with clear national policy incentives, provides financial sustainability, operational reliability, and alignment with long-term environmental objectives.
• Community Engagement and Social Support: Active citizen participation in waste separation initiatives is crucial for feedstock quality and quantity, underpinning the facility's environmental and economic success.

This paper was presented at WEFTEC 2026 in New Orleans, Louisiana.

Presentation time

11:00:00

11:15:00

Session time

10:30:00

12:00:00

SessionInnovative Approaches to Resource Recovery and Carbon Reduction in Wastewater

Session locationErnest N. Morial Convention Center

TopicBiosolids and Residuals, Circular Water Economy, Energy Production, Conservation, and Management, Resilience, Safety, and Disaster Planning

Author(s)

Li, Zhongtian, Tasser, Christian, Ishida, Cari