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. 2026 Apr 17;105(7):106954. doi: 10.1016/j.psj.2026.106954

Disinfection of poultry processing wastewater using advanced oxidation processes

Seth Adesope a, Mark Carlson b, Nikolay Barashkov b, Casey Owens a, Tomi Obe a,c,⁎
PMCID: PMC13142115  PMID: 42066406

Abstract

Given the increasing demand of poultry products, poultry processing continues to generate a large volume of wastewater rich in diverse foodborne pathogens that require effective treatment to support safe reuse. This study evaluated the disinfection rate of photo-electrochemical (PEC) treatment, which combines electrochemical (EC) and photochemical (PC) treatments for poultry processing wastewater. Wastewater from the scald and inside-outside bird washer (IOBW) units were treated using independent 7 L and 30 L PEC reactors operated at 70 V and 100 V EC with a fixed 1.6% curcumin for PC. Treatment was conducted for 300 minutes with aliquots collected every 30 minutes for quantification of aerobic bacteria (AC), Enterobacteriaceae (EB), coliforms (CC), and E. coli, on Petrifilm™. Furthermore, samples at 0, 150 and 300 minutes were selectively enriched and plated on Campylobacter agar and xylose lysine tergitol-4 for Campylobacter and Salmonella detection, respectively. Microbial reductions were reported as log10 CFU/mL and analyzed using linear mixed-effects model on R software (p ≤ 0.05) with a limit of detection of 1 CFU/mL. Across all wastewater types and reactor scales, PEC treatment at 70 V and 100 V achieved substantial reductions in AC, reducing initial loads of 5.4 - 6.2 log CFU/mL to 2.0 - 2.9 log CFU/mL within 300 minutes. Specifically, treatments at 100 V reduced AC to below the regulatory threshold of 500 CFU/mL (2.70 log CFU/mL) for wastewater reuse. EB, CC, and E. coli were completely inactivated, with faster disinfection generally observed at 100 V (120-180 minutes) compared to 70 V (180-210 minutes). Although differences between pathogen reductions were insignificant between 70 V and 100 V (p> 0.05), disinfection at 100 V showed a trend of quicker and greater microbial reduction across all microorganisms tested. Furthermore, Campylobacter and Salmonella were consistently eliminated within 150 minutes across all treatments. Overall, these findings demonstrate PEC as a viable, sustainable disinfection strategy which effectively reduced microorganisms including Campylobacter and Salmonella in processing wastewater, supporting safe reuse while reducing environmental impact.

Keywords: Poultry processing wastewater, Advanced oxidation processes (AOPs), Electrochemical process, Photochemical treatment, Foodborne pathogens

Introduction

The poultry industry relies on water as an essential resource, shaping every phase of production from the moment chicks are placed on the farm to final packaging of processed meat products (Avula et al., 2009; Edge et al., 2025). While the pre-harvest stage requires generous use of water for maintaining bird hydration, feed preparation, and environmental management such as cleaning and sanitation of barns, the post-harvest phase has also witnessed a substantial increase in water consumption over the years (Manning et al., 2007; Meiramkulova et al., 2021; Mustedanagic et al., 2023). Birds on arrival at the processing plant undergo several stages that demand substantial water input during post-harvest operations that include stunning, bleeding, scalding, defeathering, evisceration, inside-outside bird washing (IOBW), and chilling. In scalding, for example, carcasses are immersed in hot water at a continuous temperature of 50-60°C to loosen feathers and maintain hygienic standards (Finstad et al., 2012; Xiao et al., 2019). At the IOBW stage following evisceration operation, high-pressure sprays are used to remove organic contaminants from both the internal and external parts of the carcass (Dogan et al., 2021; Flôres et al., 2024). Research shows that poultry processing facilities in the United States utilize 15-30 L of clean water on each bird processed, which results in the generation of hundreds of thousands of gallons of processing wastewater daily from operations that handle one million birds per week (Fatima et al., 2021). The enormous use of portable water in poultry processing creates both challenges and opportunities. While managing the high-volume wastewater generated can be challenging, effective treatment and recycling create an opportunity to reduce overall water demand (Burton and Tinker, 2008; IDRA, 2025).

Poultry processing wastewater (PPW) is highly rich in organic matter, making it a microbiological hotspot for microorganisms originating from live birds and processing equipment (Ishak et al., 2022). Pathogens such as Campylobacter species and Salmonella enterica appear commonly in scald and IOBW wastewater (Dogan et al., 2021; Guergueb et al., 2020; Savin et al., 2021). Globally, these pathogens have been recognized as leading causes of foodborne illness in humans when ingested in contaminated foods such as poultry products–a significant vehicle for transmission (Furukawa et al., 2017). In addition to these target pathogens, poultry processing wastewater harbors various microorganisms, including aerobic bacteria (AC), Enterobacteriaceae (EB), coliforms (CC), and generic E. coli that could serve as indicators of fecal contamination and hygiene status (González-Miret et al., 2006; Lansini et al., 2017; Savin et al., 2020). Although scalding temperatures have the potential of reducing pathogen counts, soft scald tanks still create conditions for bacterial survival along with proliferation because they provide warm and nutrient-rich conditions (Dogan et al., 2021; Rimet et al., 2019). Likewise, the mechanical actions of IOBW sprays help release bacteria from surfaces into wastewater (Savin et al., 2021). From regulatory point of view, untreated or improperly treated wastewater poses dual threats to environmental safety and public health. The release into surface water without proper disinfection will contaminate recreational water bodies and drinking water sources (Naidoo and Olaniran, 2014). Also, the reuse of PPW during processing or for sanitation will require microbial standards compliance, most especially if the water comes into direct or indirect contact with carcasses (Flôres et al., 2024).

The poultry industry now faces rising demands to adopt sustainable water management practices. The combination of climate-related uncertainties and local droughts alongside growing water resource competition has made conservation efforts increasingly vital (El-Hendawy et al., 2019; Greve et al., 2018). Water reuse presents an immediate solution with processing wastewater treatment to meet microbiological and chemical standards, enabling processing plants to substantially decrease their potable water consumption (Fallah et al., 2025). The USDA Food Safety and Inspection Service (FSIS) permits PPW reuse under certain conditions, which must be included in the plant’s Hazard Analysis and Critical Control Point (HACCP) plan and meet established microbial quality standards (Russell, 2010; USDA FSIS, 2005). Poultry wastewater requires maintenance or zero tolerance of non-detectable Campylobacter, coliforms, E. coli, Enterobacteriaceae, and Salmonella, with an actionable limit of 500 CFU aerobic bacteria (Micciche et al., 2018).

Traditionally, chemical oxidants such as chlorine are the standard method for wastewater disinfection (Sohaib et al., 2015). While this controlled-pathogen reduction method delivers effective results, over time, they also present multiple limitations in practice. The process of disinfection of microorganisms becomes less effective when organic matter and suspended solids shield them from contact (Chen et al., 2014). Furthermore, the process of chlorination could lead to the generation of trihalomethanes together with other harmful disinfection by-products (Dąbrowska, 2019). Other conventional treatment methods utilize aerobic and anaerobic treatment mechanisms (Chan et al., 2008; Sangoremi et al., 2025). However, these conventional treatments further created challenges of cost and sustainability due to high-energy requirements needed for treatment procedures and escalating chemical expenses with expanded water treatment operations (Calise et al., 2020; Rijo et al., 2024). These established boundaries highlight the need for alternative approaches that provide both robust performance in complex matrices and economically viable at different plant scales (Dada et al., 2023).

Advanced oxidation processes (AOPs) present a promising alternative with the potential to overcome limitations associated with conventional treatment methods. AOP treatments disinfect bacteria through in-situ generation of reactive oxygen species (ROS), which include hydroxyl radical (•OH), hydrogen peroxide (H2O2), singlet oxygen (1O2), and superoxide anion (O2⁻•) (Garrido-Cárdenas et al., 2019). These short-lived, strong oxidizing agents are non-specific and effectively inactivate diverse microbial populations as well as organic pollutants (Samet et al., 2012). The advanced oxidation method targets and damages the microbial cell wall, aiding the release of water tightly bound within cells or attached to organic compounds, and facilitating the removal of micropollutants (Yanfeng et al., 2023).

Common AOPs include electrochemical, photochemical, Fenton, and ozone-based processes. Electrochemical-based processes generate hydroxyl radicals through electrochemical reactions at the anode and cathode electrodes when a voltage is applied in the presence of an electrolyte (Kim et al., 2025; Zhang et al., 2023). Photochemical reactions utilize natural photosensitizers (Ps) like curcumin or synthetic ones such as Tetraphenyl porphyrin to produce singlet oxygen in the presence of light (Abrahamse and Hamblin, 2016; Oskolkova et al., 2024; Ossila, 2024), while the Fenton process generates additional hydroxyl radicals via ferrous ion-activated hydrogen peroxide (Zhang et al., 2019; Zhou et al., 2020). These AOPs have proven their effectiveness in treating industrial wastewater, including those from food processing, pharmaceutical production, and textile dye operations (Chan et al., 2011; Collivignarelli et al., 2020; Naderi et al., 2017). The method delivers broad-spectrum effectiveness and produces little to no dangerous residues while operating at ambient temperatures. However, the high turbidity and organic content with complex chemical makeup of PPW present efficiency limitations for using individual AOP treatments (Amor et al., 2019). The combination of two or more oxidative processes in hybrid AOPs resolves this challenge via improved ROS generation, disinfection rate, and expanded treatment windows (Berdejo et al., 2019).

PEC AOPs that combine photochemical, electrochemical, and Fenton processes offer special appeal (Adesope et al., 2026; Cheruvu et al., 2025). Cheruvu et al. (2025) reported disinfecting >5 log CFU/mL non-typhoidal Salmonella serotypes in simulated wastewater (pathogen-contaminated water) within 140 minutes of treatment. Adesope et al. (2026) demonstrated the complete disinfection of ∼ 6 log CFU/mL Campylobacter species individually and in combination with Salmonella Typhimurium within 120 minutes of treatment at 70 V EC and using curcumin as a photosensitizer. To test these PEC processes in poultry processing wastewater in the current study, we evaluated the microbial disinfection of poultry wastewater from scald and IOBW stages of poultry processing using PEC treatments at 70 V and 100 V EC levels in combination with fixed 1.6% curcumin concentration for PC. We assessed the effectiveness of PEC treatments in both 7 L and 30 L systems to reduce AC, EB, CC, and E. coli as well as the disinfection of Campylobacter and Salmonella.

Materials and methods

Photo-electrochemical treatments

The combined processes follow similar mechanisms reported by Adesope et al. (2026). Here, however, the system was upscaled to a 30 L unit and the larger volume moved through upscaled electrochemical and photochemical chambers in a recirculating loop before the solution returned to a positive-displacement pump (Fig. 1). For all timed experiments, the system flow rate was 2.2 L/s. As confirmed in Adesope et al. (2026), ROS such as singlet oxygen were generated in the photochemical reactor while simultaneously, hydrogen peroxide and hydroxyl radical were generated in the electrochemical reaction chamber (Fig. 1).

Fig. 1.

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A photo-electrochemical (PEC) reactor apparatus for reactive oxygen species (ROS; hydroxyl radicals (•OH), hydrogen peroxide (H2O2), and singlet oxygen (¹O₂)) generation, integrating 1) alternating-current (AC) power supply for 2) an electrochemical reaction cell with stainless steel electrodes in presence of 0.2% ammonium sulfate ((NH4)2SO4) electrolytes and 3) a photochemical reaction cell with buoyant spheres coated with photosensitizer (curcumin-containing polymer film) that is radiated by 4) a low-intensity visible LED sheet lamp. The system circulates wastewater through the two reaction cells and then back to 5) a positive-displacement pump at 2.2 liters per second.

The electrochemical reaction chamber consists of stacked-screen electrodes made from stainless steel which provide both large contact surfaces and adjustable spacing between electrodes. The system used alternating current (60 Hz) which operated within the 70-100 voltage range during experiments. The system also used 0.2% ammonium sulfate electrolytes to maintain conductivity and 9 ppm ferrous iron as a Fenton’s reagent for additional hydroxyl radical generation.

The PC reactor consisted of a transparent acrylic tube that optimized exposure of wastewater samples to light and ensured contact between liquid and photosensitizer-coated spheres. The buoyant styrofoam spheres were coated with the photosensitive polymer film (ethyl cellulose:shellac, 25:75 w/w) containing curcumin (Curcuma longa) at 1.6% concentration. The spherical shape and porous surface of the carrier enabled better coating exposure while enhancing the surface adhesion. A LED sheet lamp operated at low intensity with peak output between 410 and 450 nm was attached to the PC to drive the production of singlet oxygen through Type II photochemistry. The chosen pumping rate kept fluorescent spheres immersed and suspended in the wastewater to boost light absorption and singlet oxygen generation during each trial.

Experimental design

Scald and IOBW wastewater representing the first (dirty) and second (cleaner) stages of primary poultry processing, respectively were used in this study. Following the findings from our previous study (Adesope et al., 2026), both PPW were exposed independently to EC at 70 V and 100 V combined with a fixed PC level at 1.6% curcumin concentration (Fig. 2). Both types of PPW were disinfected independently by both PEC reactors – the 7 L laboratory prototype and 30 L pilot scale capacities (Fig. 2). In the 7 L reactor, both PPW were treated at 70 V in four biological replicates with each run in two technical duplicates (n = 8 per PPW type). Scald wastewater, being the dirtier of the two, was additionally treated at 100 V in three biological replicates (n = 3) without technical duplication. However, in the 30 L reactor, both PPW were treated at 70 V (n = 4 per PPW type) and 100 V (n = 8 per PPW type) in two and four biological replicates, respectively, each with two technical duplicates (Fig. 2). To minimize batch effect, the experiment was structured as a randomized complete block design (RCBD) with wastewater batch/collection as the block factor, and technical duplicates included to minimize run-to-run variability. Voltage comparisons were performed within each reactor volume independently for scald and IOBW wastewater.

Fig. 2.

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Experimental setup for photo-electrochemical (PEC) treatment of poultry processing wastewater. Two PEC reactor volumes, 7 L and 30 L, were used independently in the disinfection of scald and inside–outside bird washer (IOBW) using electrochemical (EC) treatment at 70 V and 100 V combined with a fixed 1.6% photochemical (PC) concentration of curcumin that serve as the photosensitizer. Each experiment included biological replicates, with each replicate consisting of two technical duplicates, except for the scald treatments at 100 V in the 7 L capacity and scald and IOBW treatments at 70 V in the 30 L capacity.

Wastewater sample collection

The wastewater samples were collected from two different processing stages in a small-scale commercial poultry processing plant with an average of 3000 birds processed per day. Independent collections regarded as biological replicates were obtained on different processing days to capture the natural variation in microbial and organic matter in the processing plant. In contrast, collections for technical replicates consisted of batches of wastewater collected from several flocks processed the same day to reflect the average wastewater characteristics for that production day. Scald wastewater was collected from the scald effluent tank, while the IOBW was obtained from an outlet directly beneath the IOBW cabinets. Collections for both PPW went through physical preliminary filtration using a sterile sieve (>0.6 mm hole size) to remove large debris such as feathers, fat lobes or solid fecal matter. The filtered samples were collected in sterile polypropylene containers and transported to the laboratory for treatment. All samples were refrigerated and processed within 24 h of collection.

Disinfection of poultry processing wastewater using photo-electrochemical set-up

The 7 L PEC disinfection system, previously described in Adesope et al. (2026), operated using 14 curcumin-coated spheres positioned in the PC chamber. In this system, 14 g of ammonium sulfate and 0.3 g of ferrous sulfate were dissolved in 0.5 L of deionized (DI) water and introduced into the unit through the sample inlet. Processing wastewater (6.5 L) was then introduced to fill up the 7 L unit, and the solution was homogenized throughout the unit by using a pump. The 30 L upscaled system followed the same driving disinfection mechanism by utilizing 45 curcumin-coated spheres in the PC chamber. To ensure that the component solute concentrations matched those of the 7 L system, the 30 L unit utilized 60 g of ammonium sulfate and 3.5 g of ferrous sulfate dissolved in 2 L of DI water. Processing wastewater (28 L) was then introduced to fill up the 30 L unit, after which the pump was switched on for 3-5 minutes to homogenize the solution throughout the unit. The first sample was then collected at time zero (T0) for baseline microbial levels. Subsequently, the disinfection process was initiated by activating the EC reactor with a transformer set to the required voltage demand and illuminating the PC chamber using the LED light sheet. Circulation was maintained throughout the trial, and 10 mL treated samples were collected every 30 minutes throughout a 300-minute operating period. Samples collected from T0 (zero minutes) to T10 (300 minutes) were serially diluted in phosphate-buffered saline (Corning, REF 21-040-CV) and plated on AC, EB, CC and E. coli Petrifilm™ plates. The plates were incubated at 37°C for 48 h to determine reduction in bacterial population following disinfection. Bacterial counts were recorded, log transformed and reported as log CFU/mL of the wastewater disinfected.

Separately, 100 mL treated PPW samples were collected at time zero (T0), middle of treatment (150 minutes, T5), and upon completion of treatment (300 minutes, T10) for further analysis. This analysis includes the detection of Campylobacter and Salmonella. Briefly, 10 mL of treated samples were added to 10 mL of sterile Bolten’s broth (Hardy Diagnostics, CM0983) in whirl packs and incubated at 42°C for 48 h under microaerophilic conditions. The enriched samples were plated on Campylobacter agar (Oxoid, CM0689B) plates that were incubated under microaerophilic conditions at 42°C for 48 h to detect Campylobacter. For Salmonella detection, 30 mL of each sample was pre-enriched in 30 mL buffered peptone water (Hardy Diagnostics, C5322) and incubated at 37°C for 24 h, after which, 10 mL from the incubated cultures was enriched in tetrathionate broth (Hardy Diagnostics, C7061) and further incubated at 37°C for 24 h. The enriched samples were streaked on xylose lysine tergitol-4 (Hardy Diagnostics, C7322) plates incubated at 37°C for 24 h.

Statistical analysis

The microbial count data was log transformed (log CFU/mL), while AC data was also expressed in CFU/mL to align with the reporting standards used by the USDA. The log transformed microbial counts were used to conduct independent statistical studies using R Version 4.5.0 (R Core Team, 2024) to assess the effect of different EC voltage levels on treatment of scald wastewater in the 7 L reactor and both scald and IOBW in the 30 L scale reactor using a linear mixed-effects model (LMM; Carnoli, 2024) with voltage, time, and their interaction as fixed effects; and replicate as a random effect with an autoregressive (AR (1)) covariance structure to account for repeated measures. Significance of voltage effects was assessed at p ≤ 0.05 using restricted maximum likelihood (REML) estimation. With a detection limit of 1 CFU/mL, the time at which microorganisms reached the threshold dose (TD) was determined over the 300-minute treatment period. The figures were expressed as reduction (i.e., the difference between the microbial log count recovered at time zero (T0) and the log counts at each sampling times (T1, T2, T3, …, T10) in log CFU/mL.

Results

Disinfection of scald wastewater

The PEC treatment at both 70 V and 100 V EC and 1.6% curcumin for PC decreased microbial populations for all bacteria evaluated in the scald wastewater samples. At 70 V, 6.15 log CFU/mL (1,412,500 CFU/mL) AC at start of treatment was reduced to 2.86 log CFU/mL (724 CFU/mL) in 300 minutes of treatment in the 7 L reactor (Table 1), which did not meet the USDA required limit of 500 CFU/mL AC population for wastewater reuse. Concurrently, there was a complete disinfection of EB (2.63 log CFU/mL), CC (2.51 log CFU/mL), and E. coli (1.57 log CFU/mL) at 210, 210, and 180 minutes, respectively. Treatments in the 30 L unit followed the same pattern. There was a 2.92 log CFU/mL (830 CFU/mL) reduction of AC by the end of the 300-minute treatment, which also did not meet the USDA limit while EB (2.78 log CFU/mL), CC (2.53 log CFU/mL), and E. coli (1.70 log CFU/mL) were completed disinfected within 210, 210, and 180 minutes, respectively (Table 1).

Table 1.

Bacteria reduction counts (log10 CFU/mL) during the 300-minute PEC treatment of scald poultry wastewater.

EC (V) Aerobic bacteria (AC)
 Enterobacteriaceae (EB)
 Coliform (CC)
 E. coli
70 V 100 V 70 V 100 V 70 V 100 V 70 V 100 V
Time (mins) 7 L 30 L 7 L 30 L 7 L 30 L 7 L 30 L 7 L 30 L 7 L 30 L 7 L 30 L 7 L 30 L
0 6.15 5.87 5.76 5.42 2.63 2.78 4.35 3.80 2.51 2.53 3.02 4.12 1.57 1.70 3.05 2.98
300 2.86 2.92 2.09 2.01 – – – – – – – – – – – –
TD 210 240 210 210 120 150 210 210 120 150 180 180 90 150
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TD is the time to reach USDA limit of AC at ≤ 500 CFU/mL; EB, CC, E. coli at 0 CFU/mL, and blanked when the required standard was not achieved within 300 min of treatment.

For 100 V in the 7 L reactor, AC had an enhanced disinfection from 5.76 log CFU/mL (753,333 CFU/mL) to 2.09 log CFU/mL (103 CFU/mL) within 300 minutes, meeting the USDA regulatory benchmark at 210 minutes. The corresponding acceleration was observed in other microorganisms tested including complete disinfection of 4.35 log CFU/mL EB, 3.02 log CFU/mL CC, and 3.05 log CFU/mL E. coli in 120, 120, and 90 minutes, respectively. Similarly, there was a substantial disinfection of 5.42 log CFU/mL (263,713 CFU/mL) AC in the 30 L reactor, also meeting the regulatory limit in 300 minutes (2.01 log CFU/mL or 103 CFU/mL), and achieved the 500 CFU/ml benchmark at 240 minutes, while EB (3.80 log CFU/mL), CC (4.12 log CFU/mL), and E. coli (2.98 log CFU/mL) were completely disinfected in 150 minutes. Campylobacter and Salmonella were not detected at mid (150 minutes) and end of the treatment (300 minutes) at all PEC treatment levels.

Disinfection of bird washer wastewater

The disinfection pattern of microorganisms in IOBW wastewater followed a similar trend as observed in scald wastewater. Campylobacter and Salmonella were completely disinfected as observed previously. In the laboratory prototype (7 L) unit at 70 V, an average of 5.75 log CFU/mL (568,000 CFU/mL) AC was reduced to 2.79 log CFU/mL (618 CFU/mL) during the 300-minute treatment period, which did not meet the USDA reuse limit (Table 2). Furthermore, there was a complete elimination of EB (3.47 log CFU/mL) and CC (4.08 log CFU/mL) within 210 minutes, while E. coli (2.93 log CFU/mL) was attenuated in 150 minutes. Exposing the IOBW wastewater to the same treatment levels in the 30 L pilot scale capacity resulted in disinfection of AC from 5.77 log CFU/mL (585,750 CFU/mL) to 2.77 log CFU/mL (583 CFU/mL) within 300 minutes and complete disinfection of 2.28 log CFU/mL EB (210 minutes), 2.64 log CFU/mL CC (210 minutes), and 1.30 log CFU/mL E. coli within 90 minutes. Overall, E. coli exhibited the quickest attenuation due to its low initial microbial count while a quicker/moderate disinfection time was observed for EB and CC, whereas AC required the highest exposure time for disinfection (Table 2). Increasing the voltage to 100 V in the 30 L unit showed a decrease in disinfection time of microorganisms compared to 70 V. Within 300-minute treatment, 5.67 log CFU/mL (468,500 CFU/mL) AC reduced at TD as early as 180 minutes and a final count of 1.84 log CFU/mL (69 CFU/mL) in 300 minutes. Also, there was complete disinfection of EB (4.27 log CFU/mL), CC (4.30 log CFU/mL), and E. coli (3.10 log CFU/mL) within 150, 180, and 120 minutes respectively.

Table 2.

Bacteria reduction counts (log10 CFU/mL) during the 300-minute PEC treatment of IOBW poultry wastewater.

EC (V) Aerobic bacteria (AC)
 Enterobacteriaceae (EB)
 Coliform (CC)
 E. coli
70 V 100 V 70 V 100 V 70 V 100 V 70 V 100 V
Time (mins) 7 L 30 L 30 L 7 L 30 L 30 L 7 L 30 L 30 L 7 L 30 L 30 L
0 5.75 5.77 5.67 3.47 2.28 4.27 4.08 2.64 4.30 2.93 1.30 3.10
300 2.79 2.77 1.84 – – – – – – – – –
TD 180 210 210 150 210 210 180 150 90 120
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TD is the time to reach USDA limit of AC at ≤ 500 CFU/mL; EB, CC, E. coli at 0 CFU/mL, and blanked when the required standard was not achieved within 300 min of treatment.

Comparison of electrochemical levels for scald wastewater disinfection in 7 L reactor capacity

Comparisons between the 70 V and 100 V EC levels were made based on bacterial reduction in log CFU/mL. This was calculated as the difference between the log microbial count at time zero (0 minute) and the log count at successive sampling times (30 - 300 minutes). At 70 V, AC reduced by 3.21 log CFU/mL over the 300-minute of treatment and the final count failed to meet regulatory standards, whereas treatment at 100 V achieved a comparable 3.67 log CFU/mL reduction, with a final count of 2.09 log CFU/mL reaching the USDA limit of 500 CFU/mL within the same duration (Fig. 3A). The rate of reduction between both voltages was not statistically significant (p = 0.44), however looking at the slope of the reduction curve, 100 V demonstrated a greater reduction in the last 90 minutes of treatment (210 - 300 minutes) compared to 70 V that had a slightly better reduction in the first 180 minutes. EB showed a maximum reduction of 2.63 log CFU/mL at 70 V after 210 minutes, whereas 100 V achieved a greater reduction of 4.35 log CFU/mL within 120 minutes (Fig. 3B). Although complete elimination of EB occurred approximately 90 minutes earlier at 100 V compared to 70 V, the difference in log reduction was not statistically significant (p = 0.075). A similar 90-minute quicker voltage-driven trend was observed for CC (Fig. 3C), which reduced by 3.02 log CFU/mL in 120 minutes (p = 0.105) at 100 V compared to 70 V (2.51 log CFU/mL) within 210 minutes. For E. coli, disinfection was enhanced by 90 minutes at the higher EC voltage with a 3.05 log CFU/mL reduction compared to 1.57 log CFU/mL after 180 minutes of treatment at 70 V (Fig. 3D). This illustrated greater E. coli inactivation at 100 V in half the treatment time required at 70 V.

Fig. 3.

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Microbial disinfection (log CFU/mL) of scald wastewater at 70 V and 100 V electrochemical (EC) treatment levels combined with 1.6% curcumin for photochemical (PC) treatment in a 7 L reactor capacity over 300 minutes of disinfection for (A) Aerobic bacteria (AC), (B) Enterobacteriaceae (EB), (C) Coliforms (CC), and (D) E. coli. The data presented were the mean with error bars representing standard error of the mean (SEM).

Comparison of electrochemical levels for scald and bird washer wastewater disinfection in 30 L reactor capacity

Treatments in the 30 L PEC capacity followed similar trend observed in the 7 L reactor capacity. EC at 70 V successfully reduced AC in scald (2.73 log CFU/mL) and IOBW (2.82 log CFU/mL) wastewater during the 300-minute disinfection but failed to meet the USDA wastewater reuse standard (Fig. 4A and 5A). However, increasing the EC to 100 V resulted in AC reducing to the USDA standards within 240 minutes for scald and 180 minutes for IOBW (Table 1, Table 2). Interestingly, using the 500 CFU/mL benchmark, a 60-minute quicker disinfection difference was observed between both wastewater types. While EB, CC, and E. coli were completely disinfected at 70 V EC treatment level, optimization to 100 V showed a faster reduction rate (time to complete disinfection) of these microorganisms in both wastewater types. Specifically in scald wastewater, treatment at 100 V exhibited quicker disinfection of EB, CC, and E. coli by 60, 60, and 30 minutes, respectively, than treatment at 70 V (Fig. 4B-D). The corresponding rate of disinfection in IOBW treatment followed 60-minutes and 30-minutes faster rate for EB and CC, respectively, while TD for E. coli required an additional 30 minutes for the 100 V (TD = 120 minutes) treatment possibly due to its significantly higher initial microbial load compared to the 70 V (TD = 90 minutes) treatment (Fig. 5B-D). Although the differences in pathogen-disinfection between 70 V and 100 V were not statistically significant (p > 0.05), a marked reduction in microbial counts and a noticeably faster rate of disinfection trend were observed at 100 V across all tested bacteria. Furthermore, there was significant interaction between EC levels and time (p < 0.05), indicating the effect of EC treatment varied across time points.

Fig. 4.

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Microbial disinfection (Log CFU/mL) of scald wastewater at 70 V and 100 V electrochemical (EC) treatment levels combined with 1.6% curcumin for photochemical (PC) treatment in a 30 L reactor capacity over 300 minutes of disinfection for (A) Aerobic bacteria (AC), (B) Enterobacteriaceae (EB), (C) Coliforms (CC), and (D) E. coli. The data presented were the mean with error bars representing standard error of the mean (SEM).

Fig. 5.

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Microbial disinfection (Log CFU/mL) of IOBW wastewater at 70 V and 100 V electrochemical (EC) treatment levels combined with 1.6% curcumin for photochemical (PC) treatment in a 30 L reactor capacity over 300 minutes of disinfection for (A) Aerobic bacteria (AC), (B) Enterobacteriaceae (EB), (C) Coliforms (CC), and (D) E. coli. The data presented were the mean with error bars representing standard error of the mean (SEM).

Discussion

In previous studies (Adesope et al., 2026; Cheruvu et al., 2025), we demonstrated using spectrometric and microbial analysis, the effective generation of ROS from PEC treatment and its potential in disinfecting common foodborne pathogens. The combined function of hydroxyl radicals and singlet oxygen generated via electrochemical oxidation at the anode, light-driven excitation of curcumin and Fenton reaction as illustrated in Fig. 1 resulted in a synergistic oxidative effect that effectively inactivated pathogens. This current research further showed that PEC treatment with ranging voltages combined with optimum curcumin concentration enabled a wide-range microbial elimination in PPW. Both scald and IOBW wastewater showed multi-log reductions of AC, EB, CC, and E. coli. The complete removal of Campylobacter and Salmonella within the first 150 minutes for all treatment levels in scald and IOBW wastewater was consistent with our previous work, where combined PEC treatments achieved complete disinfection of ∼ 6 log CFU/ mL of Campylobacter jeujni and Salmonella Typhimurium in bacterial contaminated water that simulated wastewater (Adesope et al., 2026). A limitation of our previous study was that the effectiveness of PEC treatment was accessed in pathogen-contaminated water with an open question of its effectiveness under complex wastewater conditions with organic loads that may interfere with pathogen inactivation. This current study resolves this limitation, and the results validate the efficacy of PEC treatments in disinfecting pathogens regardless of the presence of organic load.

A 1.6% curcumin concentration was fixed for PC and regarded as the optimal level in this study based on previous findings which showed no significant difference in disinfection time between 0.8% and 1.6% in pathogen-contaminated water disinfection (Adesope et al., 2026). Furthermore, increasing photosensitizer concentration beyond appropriate range has been revealed in other studies to create photo-saturation, interference, and radical self-quenching conditions, which interferes with and decreases ROS generation (Sabbahi et al., 2010; Thandu et al., 2015). The study by Yang et al. (2023) on the removal of antibiotic-resistant bacteria in wastewater by emission photosensitizer revealed that photosensitizers have a concentration quenching effect, and reduction of singlet oxygen generation usually occurs at high concentration, which hinders their application. In this study, although the overall main effect of EC levels did not differ statistically, a significant voltage and time interaction indicated the pattern of reduction over time differed between the EC levels. Bacteria inactivation was faster with higher voltage treatments regardless of the wastewater type, reactor and bacterial load. Disinfection time was quicker (30 to 60 minutes) in EB, CC, and E. coli at 100 V even in conditions with higher initial microbial load compared to respective treatments at 70 V. Moreover, 100 V treatment reduced the AC to below the USDA action limit of 500 CFU/mL within the 300-minute treatment window used in this study. It is important to note that this disinfection treatment window was primarily chosen based on findings from our previous studies (Cheruvu et al., 2025 and Adesope et al., 2026) and showed to have worked for the current study. Increasing the electrochemical parameters of the treatment has also been shown to increase ROS generation rates (Adesope et al., 2026). Ji et al. (2019) reported that more hydroxyl radicals are produced at higher voltage levels with emphasis that the net increase in ROS generation resulted in increased cell death and reduced treatment time. Increasing voltage from 50 V to 70 V produced a 30-minute faster inactivation of Campylobacter species and greater generation of ROS (Adesope et al., 2026), highlighting a main driving force of disinfection is enhanced ROS generation.

Notably, variability in the rate of inactivation was observed among the microorganisms tested in the same treatment conditions. An obvious influence is varying starting microbial counts and makeup of the microorganisms from different flocks processed on each processing day that wastewater was collected. The AC group likely needed the longest exposure time because they had the highest initial population size and diversity. Ramm et al. (2025) indicated that pathogen disinfection in wastewater may be less effective within practical treatment timeframes due to high bacterial load which will cause extended treatment durations to achieve adequate inactivation. Differences in cellular structure and physiological resilience among microbial groups may also contribute to this variability. According to Zarei et al. (2017), a study on microbial physiology reveals that different microbial species demonstrate different levels of resistance against oxidative stress. Furthermore, part of the variability could be explained by differences in wastewater composition since our result showed that IOBW wastewater exhibited 60-minute quicker reduction pattern of AC disinfection compared to scald wastewater. While scientific studies confirm organic compounds absorb ROS to protect microbial cells from damage (Ngobeni et al., 2022), higher organic loads or organic compounds also serve as scavengers and compete with microorganisms for the oxidants produced by AOPs (Khare, 2016). Similar studies stated that radical-driven AOP reactions become significantly slower because of scavenging effects which demand either higher oxidant dosages or longer treatment durations to reach the desired outcomes (Chiha et al., 2010; Zhang et al., 2025). This competition means that some proportion of the oxidants will be consumed by organic matter rather than targeting and inactivating microorganisms, ultimately decreasing disinfection performance.

The 100 V EC treatment level exhibited rapid reduction of all microorganisms tested with AC disinfection meeting the required standards within 300 minutes of treatment. Although we observed that 70 V treatments failed to meet regulatory standards for AC within 300 minutes, longer treatment periods beyond 300 minutes would likely achieve the limit. However, 100 V treatment proved more practical for industrial use because it achieved compliance within a shorter time and lesser operational demands. The successful scale-up from laboratory prototype (7 L) to pilot scale (30 L) that could be suitable for small-scale processing demonstrates the feasibility of transitioning a PEC-AOP technology for practical implementation. However, a large commercial processor would require an industrial unit with higher volume capacity and microbial disinfection validation. Overall, our finding suggests that combined effects of controlled PC dosing and optimized EC in both reactors showcased successful disinfection of microorganisms meeting the USDA microbial wastewater reuse standards.

Conclusion

This study evaluated and reported the utility of combined AOP in disinfecting key microorganisms in poultry wastewater. The findings further evaluate the successful scale-up to pilot level, presenting PEC as a strategic approach to poultry wastewater recycling with promising potential for reuse at optimal EC and PC treatment levels. Overall, the adoption of PEC as a tertiary treatment could enhance cost saving for poultry processors who want to reuse wastewater while maintaining USDA reuse limits.

CRediT authorship contribution statement

Seth Adesope: Writing – original draft, Validation, Methodology, Formal analysis. Mark Carlson: Writing – review & editing, Methodology, Funding acquisition, Data curation. Nikolay Barashkov: Writing – review & editing, Project administration, Funding acquisition. Casey Owens: Validation, Methodology, Funding acquisition. Tomi Obe: Writing – review & editing, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Data curation, Conceptualization.

Disclosures

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the USDA–NIFA SBIR program (Grant No. 2023-70439-39189). The authors also acknowledge the managers of the processing plant who supported the validation of the pilot scale unit and members of the Applied Food Safety Microbiology and AMR lab at the University of Arkansas’ Poultry Science Department for their valuable assistance throughout the study.

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