Zhang, Xueyao

Xueyao Zhang is a PhD candidate in Environmental Engineering at Virginia Tech, specializing in waste valorization and resource recovery. She earned...

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About Zhang, Xueyao

Xueyao Zhang is a PhD candidate in Environmental Engineering at Virginia Tech, specializing in waste valorization and resource recovery. She earned a Masters degree in Environmental Engineering from the University of Southern California and a Bachelors degree in Environmental Science from Beijing University of Civil Engineering and Architecture. Committed to practical solutions, she works with diverse teams to tackle global water and waste management challenges.

Zhang, Xueyao

Titles from this speaker

Alternate: Bioplastic Production from Salty Food Waste

Abstract

1.Introduction High salinity food wastes management has been a challenge because it is inhibitory to conventional biological processes such as anaerobic digestion or composting [1]. Haloferax mediterranei (HM) is a hyperhalophilic microorganism capable of producing polyhydroxyalkanoate (PHA) from wastewater with salinity in the range of 7-30% [2]. Such a high salinity environment also protects HM from culture contamination by other indigenous organisms that came with the wasted materials [3]. Moreover, the high osmotic pressure in HM cells also allow the cell wall to burst in fresh water and thus offer low energy and chemical free PHA recovery [4]. Hence, this study demonstrated an innovative pathway enabling the bioconversion of high salinity food wastes to PHA by taking advantage of HM. The outcomes of this study include: (1) confirmed the positive effect of high salinity food waste on volatile fatty acids (VFAs) production; (2) verified that unrefined VFAs can be directly used as feedstocks for high PHA productivity; (3) proved that by fresh water can be used to open the cell walls of HM for high PHA recovery without chemical addition. Key words: Haloferax mediterranei; Polyhydroxyalkanoate; Volatile fatty acid; Food waste 2.Materials and Methods VFA production Although HM does not require VFAs to provide PHA, the PHA yield is always higher when VFAs were used as a feedstock [2]. For that reason, dark fermentation (DF) was employed to ferment high salinity food waste collected from Quasar Energy Group [5]. The inoculum was collected from an anaerobic DF reactor running over one year at University of Maryland, College Park. The food waste to inoculum ratio was 1:2 or 4:1 (by VS). The fermenter was operated with 20-day retention time at 35 ±1oC with pH adjustment of 7. PHA production The wild-type strain HM (ATCC 33500) was used throughout the study. The cells were firstly activated in ATCC 1176 medium [6]. Batch reactors were cultivated in an incubator shaker controlled at 37 oC and 150 rpm. After 48 hours incubation, the cell density measured at optical density (OD) 600 nm reached 0.5 in the triplicate flasks. The activated culture was distributed into 30, 5 ml sterile tubes with 15% glycerol (v/v) for long term storage at -80 °C. To check if there is any contamination, activated culture was spread in triplicate agar plates and incubated for another 144 hours at 37 °C. Only the characteristic pink colonies of HM strain grew in the plates (Figure 1), which confirmed there was no contamination during the HM activation process. To understand the optimized conditions for HM strain to produce PHA using VFAs as carbon source in high salinity digestate, activated HM strain was inoculated in high salinity digestate. OD and suspended solid (SS) were tested to evaluate cell growth. The culture was cultivated in the incubator shaker until the OD reached a plateau. 30 45 ml culture was collected for PHA extraction and quantified by gas chromatograph (GC) [7]. 3.Results 3.1 VFA production from high salinity food waste Food waste with salinity ranging from 0 to 150 g/L were inoculated with food to inoculum ratio of 1:2 and 4:1(by VS) to understand the effects of salinity and inoculum ratio on VFA yields. As can be seen from Figure 2, VFA yield increased with food waste salinity and increased with the food to inoculum ratio. The greatest VFA yield of 43 g/L was achieved in food waste with salinity as high as 150 g/L and food to inoculum ratio of 4:1. Therefore, it is important discovery from this experiment that high salinity food waste actually favors VFA production probably due to its inhibition of methanogenesis as reported previously [1]. 3.2 PHA production from high salinity digestate DF digestates were diluted for 2, 2.5, 3, 4.5, and 9 times with DI water to investigate the dilution effect on PHA yield when salinity was maintained at 156 g/L NaCl. As can be seen from Figure 3, the greatest PHA yields of 60% PHB and 5% PHV were obtained at 2 times dilution when digestate COD was around 9 g/L. In contrast, HM did not grow in raw digestate probably because of inhibition. Further dilution of the digestate proportionally decreased PHA yield, which is expected because of the loading rate decrease. The PHA yields of 65% from HM were much higher than from mixed culture (e.g. 30%) [8]. Moreover, PHV yields of 5% from HM higher than that in mixed culture ( ‰ˆ0% PHV) makes it more commercially valuable since higher HV content results in more elasticity of the plastic material [7, 9]. 3.2 PHA recovery in fresh water HM cells were harvested in centrifuge and then soaked in fresh water for 48 hours for PHA recovery, during which the water was refreshed for 10 times. A comparison was made between two groups with and without stirring. Results showed that the PHA recovery efficiencies 94 % and 95%, respectively, with and without stirring. Hence, it can be concluded that stirring is not important for PHA recovery in fresh water. 4.Conclusions It was concluded from this study that high salinity in food wastes actually favor VFA production in DF. HM cells can effectively utilize VFAs in the two times diluted digestates for PHA production. Soaking HM cells in fresh water can offer PHA recovery efficiency as high as 95% without chemical addition.

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

SpeakerZhang, Xueyao

Presentation time

8:30:00

11:15:00

Session time

8:30:00

11:15:00

SessionSession 19: Resource Recovery

Session number19

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicSustainability and Resource Recovery

Author(s)

X. Zhang

Author(s)X. Zhang1, N. Amradi2, A. Hassanein3, S. Lansing4, Z. Wang5,

Author affiliation(s)Virginia Tech1; University of Maryland2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158789

Volume / Issue

Content sourceResiduals and Biosolids

Word count8

Description: Long-term effects of cycle time and volume exchange ratio on...

Long-term effects of cycle time and volume exchange ratio on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from food waste digestate by Haloferax mediterranei cultivated in sequencing batch reactors

Abstract

Introduction The problem of food waste accumulation, combined with the pollution of petroleum-based plastic, presents a significant environmental challenge (Atiwesh et al., 2021, Paritosh et al., 2017). Converting food waste into bioplastics offers a potential solution to these issues by reducing landfilled food waste and replacing traditional plastics with biodegradable alternatives. Haloferax mediterranei (HM), a halophilic microorganism, is notable for its ability to produce the bioplastic poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) while thriving in high-salinity environments, which inherently reduces contamination risks (Meereboer et al., 2020). Previous studies have demonstrated that HM can produce PHBV from food waste in single-batch reactors, yet these systems are inefficient for large-scale industrialization (Wang and Zhang, 2021). The sequencing batch reactor (SBR) system addresses these limitations by enabling semi-continuous production, thereby enhancing economic feasibility and scalability (Allman, 2024). Despite these advantages, research on the long-term stability and operational optimization of SBRs for PHBV production remains limited. This study aims to fill this knowledge gap by investigating the effects of cycle time and volume exchange ratio (VER) of SBR on PHBV production performance. This work presents an opportunity to address both food waste management and plastic pollution challenges in one approach, contributing to a more sustainable and environmentally friendly future. Materials and Methods The food waste used as a substrate in the experiment was processed into digestate through arrested anaerobic digestion, which breaks down complex molecules into simpler, more digestible forms. The digestate was prepared with controlled composition, including organic acids and other nutrient sources, and was diluted to minimize substrate inhibition. The arrested anaerobic digestion was conducted at 35°C with a hydraulic retention time of 12 days and maintained a consistent organic loading rate of 2.5 g volatile solids (VS)/L-day. The PHBV production process was conducted in a 500 mL SBR, with a working volume of 400 mL (Figure 1). Each cycle included phases of feeding, reaction, and discharging, with the cycle time and VER as key variables. The SBR operated at 37°C with aeration and maintained high salinity (156 g/L NaCl) to support HM's growth while minimizing contamination risks. The cycle time was systematically increased from 1 to 12 days in the initial phase, while the VER remained constant at 0.5 (Figure 2). In the subsequent phase, the VER was adjusted from 0.3 to 0.5, with the cycle time determined by HM growth. The experiment included a 450-day continuous operation, making it one of the longest durations reported for HM fermentation. To assess HM growth, total organic carbon (TOC) reduction, and PHBV production, samples were collected at regular intervals and analyzed using various analytical techniques. Cell density was monitored with OD600nm, and PHBV content was measured using gas chromatography following a series of extraction and purification steps. Results 1.Optimal Dilution and TOC Utilization: HM demonstrated substrate inhibition with undiluted food waste digestate, showing no growth or PHBV production. A dilution factor of 2, with an initial TOC concentration of 7 g/L, achieved optimal PHBV yield, maintaining approximately 70% PHBV content and 6% 3-hydroxyvalerate (HV) fraction in the cellular biomass. This condition was chosen for subsequent SBR operations. 2.Growth and Substrate Utilization: Stable HM growth was observed over the 450 days, with optimal cell concentrations achieved at low VERs due to higher retention of HM cells in the reactor (Figure 3A). Substrate utilization showed a direct correlation with cell growth; however, around 2 g/L TOC remained unutilized, which was hypothesized to be linked to product inhibition (Figure 3B). 3.\PHBV production performance: PHBV cellular content stabilized at around 65% for over 450 days without contamination (Figure 4A). The HV fraction in PHBV remained consistently near 15%, aligning with commercial application standards. PHBV titer followed the same trend as HM growth (Figure 4B). PHBV yield declined as VER decreased, likely due to product inhibition (Figure 4C). PHBV productivity followed organic loading rate (OLR) trends, demonstrating that higher OLR increases PHBV production rate (Figure 4D). Discussion The study demonstrates that SBRs provide a viable solution for long-term PHBV production from food waste, maintaining stable production and minimizing contamination risks due to HM's halophilic nature. However, substrate inhibition from food waste digestate and product inhibition in the SBR pose limitations to production titer and yield. The relationship between PHBV productivity and OLR suggests that increasing OLR can enhance productivity, while controlling VER can mitigate inhibitor accumulation, optimizing yield and titer. These findings underscore the importance of managing cycle time and VER to balance microbial growth, product accumulation, and inhibitory effects. This research offers insights into scaling PHBV production sustainably, aligning with industry goals to reduce reliance on petroleum-based plastics. Conclusion This study successfully demonstrates the feasibility of long-term, stable PHBV production by HM using food waste digestate in SBRs over 450 days. By optimizing operational parameters such as cycle time and VER, the study presents a scalable approach for converting food waste into bioplastics, addressing environmental concerns associated with food waste and plastic pollution. Future research should focus on mitigating substrate and product inhibition to enhance industrial applications of this bioplastic production method, contributing to more sustainable waste management and plastic reduction efforts.

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerZhang, Xueyao

Presentation time

11:05:00

11:25:00

Session time

10:45:00

11:45:00

SessionAcademic Advancements in Digestion and Fugitive Greenhouse Gas Emissions

Session number2

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Anaerobic Digestion, Biogas, Biogas Production, Energy recovery, food waste, Greenhouse Gases, Membrane bioreactor, Nitrous oxide, Resource Recovery, Sustainability And Social Responsibility

Author(s)

Zhang, Xueyao, An, Zhaohui, Wang, Jiefu, Lansing, Stephanie, Amradi, Naresh Kumar, Haque, Md Sazzadul, Wang, Zhiwu

Author(s)X. Zhang1, Z. An J. Wang 1, S. Lansing2, N. Amradi2, M. Haque Z. Wang1

Author affiliation(s)Virginia Tech, 1University of Maryland, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159768

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count25

Salty Food Waste Conversion to Bioplastics

Abstract

High salinity food wastes management has been a challenge because it is inhibitory to conventional biological processes such as anaerobic digestion or composting [1]. Haloferax mediterranei (HM) is a hyperhalophilic microorganism capable of producing polyhydroxyalkanoate (PHA) from wastewater with salinity in the range of 7-30% [2]. Such a high salinity environment also protects HM from culture contamination by other indigenous organisms that came with the wasted materials [3]. Moreover, the high osmotic pressure in HM cells also allow the cell wall to burst in fresh water and thus offer low energy and chemical free PHA recovery [4]. Hence, this study demonstrated an innovative pathway enabling the bioconversion of high salinity food wastes to PHA by taking advantage of HM. The outcomes of this study include: (1) confirmed the positive effect of high salinity food waste on volatile fatty acids (VFAs) production; (2) verified that unrefined VFAs can be directly used as feedstocks for high PHA productivity; (3) proved that by fresh water can be used to open the cell walls of HM for high PHA recovery without chemical addition.

This study explores using Haloferax mediterranei (HM), a hyperhalophilic microorganism, to convert high salinity food waste into polyhydroxyalkanoate (PHA). The authors demonstrate that high salinity food waste promotes the production of volatile fatty acids (VFAs) and verifies that unrefined VFAs can be directly used as feedstocks for high PHA productivity. They also show that soaking HM cells in freshwater enables high-efficiency PHA recovery without chemical additives.

SpeakerZhang, Xueyao

Presentation time

09:00:00

09:20:00

Session time

08:30:00

10:00:00

SessionFood and Aquaculture Wastewater Treatment

Session locationRoom S501d - Level 5

TopicIntermediate Level, Nutrients, Research and Innovation, Sustainability and Climate Change

Author(s)

Zhang, Xueyao

Author(s)X. Zhang 1; N. Amradi 2 ; A. Hassanein 2; S. Lansing 2; Z. Wang 1; X. Zhang 1;

Author affiliation(s)Department of Biological Systems Engineering, Virginia Tech 1; Department of Environmental Science and Technology, University of Maryland 2 ; Department of Environmental Science and Technology, University of Maryland 2; Department of Environmental Science and Technology, University of Maryland 2; Department of Biological Systems Engineering, Virginia Tech 1; 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159148

Volume / Issue

Content sourceWEFTEC

Word count7

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Zhang, Xueyao

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