Sanin, Dilek

Prof. F. Dilek Sanin received her PhD from Duke University in USA. She is currently working in Department of Environmental Engineering at Middle East...

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About Sanin, Dilek

Prof. F. Dilek Sanin received her PhD from Duke University in USA. She is currently working in Department of Environmental Engineering at Middle East Technical University, Turkey as a full-time faculty. She is also serving as an executive board member of IWA Specialist Group on Sludge Management. Dr. Sanin is the co-author of one book and over 60 research articles published in peer reviewed journals. She has more than 2500 citations made to her work. Her interest areas are beneficial use of sludge, energy from sludge and emerging contaminants and microplastics in wastewater and sludge.

Sanin, Dilek

Titles from this speaker

Bio-aging of Polyethylene And Its Impact on Sorption of Organics

Abstract

Introduction Microplastics (MPs) are plastic debris resulting from plastic waste fragmentation or direct emissions of micro- and nano-sized plastics from a variety of sources. Recently, MPs were added to the list of global threats because they are ubiquitous and may pose a risk to the food chain as a result of their interaction with organic contaminants (OCs) and heavy metals (Y. Wang et al., 2022; Zhou et al., 2022). Hence, understanding the interaction mechanisms of OCs with MPs is essential for evaluating the impact of MPs on the environment. Wastewater treatment plants receive a high quantity of MPs from a variety of sources. These MPs accumulate in sludge and this, together with the sorption potential for OCs, some of them endocrine disruptors (EDCs), on MPs cause a special concern for land application of biosolids. Furthermore, MPs also undergo aging in treatment processes and in environment, which may in turn affect their interaction with OCs. MPs subjected to UV aging have been widely studied in the literature, however, their biological aging of them are not equally investigated (Zafar et al., 2022). Especially bioaging during sludge digestion which is applied right before land application was not investigated. Additionally studies indicated that MPs not only simply bio-age during digestion but also inhibit the microbial community and may lower methane production levels when present in high doses which also creates additional concern for the environment as the doses of MPs keep increasing (Wei et al., 2019). This study aims to investigate the bioaging potential of polyethylene (PE) MPs in mesophilic anaerobic digesters operated as BMP reactors. Study also examines the comparative sorption of two OCs, one of them an EDC, on pristine (PE0) and bio-aged polyethylene (PE1) collected from anaerobic digesters. For this purpose, biotic and abiotic anaerobic reactors (BMP test bottles) containing a high dose of PE MPs (200 mg/g TS) were operated together with reactors containing no MPs. Following digestion bio-aged and pristine MPs are characterized using FTIR and SEM to compare the changes in PE's physical and chemical properties. Sorption of two OCs, namely 2,3,6-trichlorophenol and triclosan (an EDC) are investigated. Methane production is monitored in biotic and abiotic reactors to see the effect of MPs on digestion process to check whether there is inhibition on the microbial community. Materials and Methods Three sets of reactors were designed: biotic (B), abiotic (A), and seed control (S). BMP reactors were set-up using waste activated sludge (WAS) and digested sludge (seed) collected from a conventional WWTP with a capacity of 765,000 m3/d (4 millon design population equivalent). In reactors F/M ratio was 1, TS was adjusted to 2% and VS/TS ratio was 0.59. Details of reactor sets including the number of replicates are explained in Table 1. Biogas volumes in reactors were measured using a water displacement set-up. A gas chromatography (GC) device equipped with a thermal conductivity detector (TCD) was used to measure the biogas methane content. When the reactors are terminated full analysis of parameters shown in Table 2 will be conducted. PE used in reactors had particle size range of 425-500 µm; which were sieved, washed, and ultrasonicated before added to the reactors. The initial characteristics of PE were such that the density was 0.935 g/cm3, the crystallinity (by DSC) was 49.4% and melting temperature (Tm) was 126 °C. Sorption tests with pristine PE (PE0) showed a maximum sorption capacity of 1.0 mg/g for 2,3,6-trichlorophenol (TCP) and 6.9 mg/g for triclosan (TCS). Bioaging may affect sorption onto MPs favorably or unfavorably, depending on the type of changes that happen on PE (e.g., oxidation, peeling, etc.) affecting sorption mechanisms. Results and Discussion Table 2 demonstrates the initial reactor characteristics. The initial VS/TS ratio is higher for biotic and abiotic reactors, on the other hand it is lower in seed control, indicating that seed is more stable as expected. pH values of the samples are as expected as well; with seed having a little higher pH due to being digested compared to the sample. The COD value in abiotic reactors showed to have a wider range and higher values than any other set due to the effect of HgCl2, added to suppress the microorganisms and inhibit biotic activity. On the other hand, seed control showed the lowest COD content because it is stable and there is no WAS in the reactor so total organic content is almost half of the other reactors. The cumulative biogas volume was measured for 45 days (data not shown). Biotic reactors with no MPs addition showed higher biogas production than those with MPs, which, could be due to inhibition caused by high quantity of MPs. Reactors kept producing biogas but at lower amounts as time went on. Seed control reactors produced much smaller amount of biogas. Figure 1 shows the cumulative methane production in mL up to 45 days. Corresponding to increasing biogas volume, methane content also increased within all the biotic reactors. Similar to biogas production, methane production slowed down with time. B0 reactors showed the highest amount of methane, suggesting inhibition effect of MPs. S0 reactors produced much smaller amount of methane since they already reached a stable state before reactor set-up. Abiotic reactors produced no gas, with some days having negligibly small amount of gas production. Interestingly, in the reactors that contain MPs, although methane volume, parallel to the biogas volume, was less than those that did not contain MPs, the percent methane in the biogas was not necessarily less. With our experience we know that biogas and methane production decrease as the organic content in sludge is consumed; which corresponds to a time long before 60 days. Operating reactors for 60 days is with the expectation that 60 days is long enough to see some effect of bio-aging on the plastics. At the reactor termination, full characterization of the reactors will be done. MPs will be manually sieved and picked up from sludge then washed and left to dry. In an earlier trial to analyse the recovery of MPs from the sludge samples, it was found that 84% recovery by wt was achieved with MPs in the size range used here. Recovered MPs will be used for further analysis where, a sample of the abiotic-aged and biotic-aged MPs will be sent to FTIR analysis and SEM imaging. At the same time sorption tests will be conducted on the obtained MPs, for sorption potential of TCP and TCS as model OCs. Based on the level of aging and preliminary results, new reactors will be set for further studies. Results of sorption studies with bio-aged MPs will be included in the full-text manuscript. Conclusion Presence of PE in the digesters affected biogas production negatively, showing discernible difference when compared to the control reactors. Interestingly, in the reactors that contain MPs, although methane volume, in parallel with the biogas volume, was less than those that did not contain MPs, the percent methane in the biogas was not necessarily less. Experimental results currently indicate that the biogas volume in biotic reactors started decreasing each day, demonstrating that sludge is stabilized and the experiment is coming to an end. Once the reactors are taken down, the plastics will be isolated from the reactor content, examined for bio-aging and will be used for sorption of TCP and TCS. Acknowledgements This study was supported by TUBITAK Project No: 220N044.

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

SpeakerSanin, Dilek

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionSession 15: New Research in Anaerobic Digestion

Session number15

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicEmerging Issues (PFAS, Microplastics, Covid, etc.)

Author(s)

F. Sanin

Author(s)F. Sanin1, M. Dassouki Dit Tahan2, Ä. Ä°mamoÄŸlu3, 4,

Author affiliation(s)Middle East Technical University1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158842

Volume / Issue

Content sourceResiduals and Biosolids

Word count11

Thermophilic Digestion is Enhanced in The Presence of Polyamide Microplastics

Abstract

INTRODUCTION Despite the fact that MPs can be removed from wastewater with an efficiency of up to 90 %, still 105108 microplastics (MPs) are released from WWTPs each day (HatinoÄŸlu & Sanin, 2021). Indeed, more than 90% of the removed MPs accumulate in sludge during treatment (Okoffo et al., 2019) reaching an abundance varying from 510 to 495,000 MP particles/g DS (HatinoÄŸlu & Sanin, 2021). Studies reveal that MPs have harmful impacts on organisms; they may act as a vector of hazardous pollutants such as pharmaceuticals and heavy metals with an absorption mechanism onto their surfaces. Moreover, they provide sustainable surfaces for pathogens to colonize and form biofilm. Even though pathogens can be removed by WWTPs to a great extent, MPs can offer a safe environment for them to survive during the treatment process. MPs themselves, together with the hazardous chemicals and pathogens they can accumulate on their surfaces, pose a new concern for the land application of biosolids. Anaerobic digestion (AD) is a sustainable stabilization system with renewable energy generation and good-quality biosolids production for land application. Thermophilic digestion (TAD) is well known to be more effective in stabilization compared to mesophilic AD (MAD) due to its effective pathogen inactivation and Class A biosolids generation. Recent studies have shown that the presence of MPs can affect AD, and in addition, MPs themselves seem to be affected during the process. Yet, all these studies investigating MPs in AD are conducted under mesophilic conditions. TAD has not been investigated so far to reveal the fate and effect of MPs during the process. Polyamide (PA) (nylon) with amide groups (-CO-NH-) having the strength and fatigue resistance is one of most commonly encountered type of MP in sludge (El Hayany et al., 2022). Its high abundance and leaking potential of its monomer caprolactam (CPL) during MAD (Chen et al. 2021) creates interest for PA6. This study aims to comparatively investigate the effect of PA6 on methane production with MAD and TAD while evaluating this MPs' fate during these processes. This work is unique for identifying the behavior of MPs in TAD and specifically evaluating the fate and effects of PA6 comparatively in MAD and TAD processes. MATERIAL & METHOD For the simulation of MAD and TAD, biochemical methane potential (BMP) test was conducted at 35oC and 55oC, respectively. Waste activated sludge (WAS) (substrate) and anaerobically digested sludge (ADS) (inoculum) were sampled from a conventional WWTP designed for a population equivalent of 4 million with a capacity of 765,000 m3/day. The seed was used as sampled for MAD BMPs but was acclimated for the TAD study. As PA6, a fishline with a diameter of 0.5 mm was cut into sizes in the 425-500 µm range and used. Each mesophilic and thermophilic BMP tests had 13 sets of triplicate reactors comprising biotic, abiotic control and seed control groups. Each biotic and abiotic set included six different PA6 doses in reactors, 0, 10, 30, 60, 100, and 200 MPs/g TS. Reactor TS values were adjusted to 2% with an F/M of 1 (g VS of WAS/g VSS of seed). All reactors were purged with 99% nitrogen gas, and were incubated for 60 days. Biogas volume was measured routinely with water displacement and its composition was determined by Gas Chromatography (GC) with a thermal conductivity detector (TCD). Solids were measured using Standard Methods and COD was measured with the US EPA-approved digestion method. Mass, size, and morphology of PA6 before and after digestion were evaluated with scanning electron microscope (SEM), fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC) to comparatively assess the changes in MPs during digestion. RESULTS & DISCUSSION The cumulative methane productions of MAD and TAD reactors are shown in Figure 1 and Figure 2, respectively. In both groups, methane production started immediately and increased steadily as time went on. In the thermophilic reactors different than the mesophilic reactors, methane volume increased in two distinct steps; second step coming about 10 days after the first. In both mesophilic and thermophilic reactors, the highest methane production has been observed in the reactors containing the highest dose (200 PA6/g TS), with the lowest dose, 10 PA6/g TS, following. However, for the mesophilic group, reactors with all other doses of PA6 produced lower methane than the control set (R0M). Even though one-way ANOVA test showed a significant difference between the sets (p<0.05), a further test of post hoc (TUKEY test) demonstrated that the significant difference was only between the R30M and R200M sets. As a consequence, when compared to the control set, PA6 addition seemed to have no effect on methane production. In TAD reactors however, while no pattern between dose and methane production is seen (Figure 2), the outstanding results reveal that all PA6-added reactors produced significantly higher methane than the control set (R0T), as validated by One-Way ANOVA results (p<0.05). Additionally, the post hoc test (TUKEY test) found that except R100T, all the PA6 added sets have significantly different methane production compared to the control set (R0T), indicating PA6 affected methane production positively in TAD. This is thought to be due to leaching of monomer CPL. Chen et al., (2021) claims that CPL attaches to enzyme molecules, changing the enzyme's active site and other conformations, increasing the enzyme's affinity for the substrate and catalytic activity. The distinct second step of increase in methane production may hint the leaching of CPL providing additional affinity for enzyme-substrate system, which is currently under investigation. SEM images were captured to examine the changes in the shape and surface of PA6 during the MAD and TAD processes. Figure 3 depicts the SEM results of biotic and abiotic controls from the mesophilic BMP test. Images exhibit minor changes on the borders of PA6 after digestion. In order to better understand the changes experienced by PA6, FTIR and DSC analyses for both mesophilic and thermophilic reactors are currently underway. ACKNOWLEDGEMENT This study is supported by METU-BAP with a grant number of BAP-GAP-311-2021-10613.

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

SpeakerSanin, Dilek

Presentation time

14:30:00

15:00:00

Session time

13:30:00

16:45:00

SessionSession 06: Microplastics and other Emerging Contaminants

Session number06

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicEmerging Issues (PFAS, Microplastics, Covid, etc.)

Author(s)

F. Sanin

Author(s)F. Sanin1, Ä. ÅžimÅŸek2, 3, 4,

Author affiliation(s)Middle East Technical University1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158850

Volume / Issue

Content sourceResiduals and Biosolids

Word count11

Base text size -

Sanin, Dilek

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