Total Chemical Oxygen Demand Removal Research Articles

Enhanced Organics Removal Using 3D/GAC/O3 for N-Containing Organic Pharmaceutical Wastewater: Accounting for Improved Biodegradability and Optimization of Operating Parameters by Response Surface Methodology

Pharmaceutical industry effluents often contain high concentrations of refractory organic solvents, chemical oxygen demand (COD), and total dissolved solids (TDSs). These wastewaters, including N-containing organic solvents known for their persistence and toxicity, pose significant environmental challenges. The study evaluated the efficacy of 3D/Granular Activated Carbon (GAC)/O3 treatment compared to linear process additions when treating real pharmaceutical wastewater, and revealed a 2.73-fold enhancement in COD mineralization. The process primarily involves the direct oxidation of monoprotic organic acids found in real pharmaceutical effluents, such as acetic and formic acid, crucially influencing mineralization rates. Optimal conditions determined via the response surface methodology were 125 g/L GAC, 30 mA/cm2, and 75 mg/L O3, achieving high total organic carbon (TOC) and COD removal efficiencies of 87.19 ± 0.19% and 89.67 ± 0.32%, respectively (R2 > 0.9), during verification runs. Current density emerged as the key parameter for organic abatement, aligning with the emphasis on direct oxidation at the anode surface. This integrated approach enhances biodegradability (BOD5/COD) and reduces acute toxicity associated with persistent N-containing solvents, demonstrating promising applications in pharmaceutical wastewater treatment.

A novel tubular single-chamber microbial electrolysis cell for efficient methane production from industrial potato starch wastewater

The integration of microbial electrolysis cells (MEC) with anaerobic digestion (AD) shows great promise for enhancing methane production from high-COD wastewater. However, an efficient MEC-AD reactor design remains elusive. Here, a novel tubular single-chamber MEC-AD reactor was constructed to treat potato starch wastewater (COD over 20000mg/L). The concentric and compact design of the stainless-steel cathode and anode reduced internal resistance, resulting in enhanced methane production. Applying -0.2V vs. Ag/AgCl to the anode increased methane production by 1.73 times compared to the open circuit and halved hydraulic retention time. Moreover, the reactor achieved an average methane content of 82.57%, which was 23.89% higher than the open circuit. The reactor showed a total COD removal of 92.2%, which was 24% higher than the open circuit. Additionally, base consumption to maintain pH was reduced to one-sixth of that in conventional AD, preventing volatile fatty acid accumulation. Microbial analysis showed Geobacter (63.4%) and Methanobacterium (96.8%) were highly enriched in the anode and cathode biofilms, respectively. The proportion of fermentative bacteria also increased in the MEC-AD system. These results demonstrate the effectiveness of the tubular single-chamber MEC-AD reactor in enhancing methane production from potato starch wastewater, with strong potential for scale-up applications.

Insight into simultaneous urea hydrolysis and total nitrogen removal in textile printing wastewater: Focus on the impact of sodium sulfate salinity

The textile printing industry discharges large volumes of effluent containing high concentrations of urea and nitrogenous compounds. Anoxic-oxic (AO) treatment is a promising method for treating printing wastewater. However, the effect of sodium sulfate (Na2SO4) salinity on the urea hydrolysis and nitrogen removal simultaneously in the AO process has received little attention. In this study, five batch reactors were used to treat synthetic printing wastewater with high urea and nitrogen concentrations. A strategy was applied to increase the Na2SO4 concentration from 0 to 19 g/L in the anoxic stage of each reactor. The effect of Na2SO4 on urea hydrolysis, total nitrogen removal and COD removal, sludge characteristics, and bacterial community structure were investigated. The findings showed that urea hydrolysis increased with increasing Na2SO4 concentration. The main mechanism of urea removal was intracellular hydrolysis, with a urea removal efficiency (URE%) of approximately 98% in all batch reactors. In addition, under the stress of Na2SO4, the total nitrogen and COD removal performances were partially inhibited. The most significant removal performances after AO treatment were observed at 0 g/L Na2SO4, with nitrogen and COD removal efficiencies of 88% and 95%, respectively. When Na2SO4 concentration reached 19 g/L, the sludge settling performance and compactness were enhanced. The extracellular polymeric substance (EPS) components in the sludge were dependent on their ability of removing organics. Bacterial community diversity analysis revealed that the enrichment of the Proteobacteria, Firmicutes, and Gemmatimonadota phyla in the anoxic stages of batch reactors was related to intracellular urea hydrolysis. Bacteriodota and Chloroflexi were responsible for total nitrogen removal in all anoxic and oxic stages. This research will develop the understanding of Na2SO4 salinity impact on simultaneous urea hydrolysis and nitrogen removal during AO treatment process.

Fe(II)/Fe(III) cycle actuating a novel process to remove organics in waste pit mud from Maotai: Performance and mechanism

In this study, a novel method relying on iron cycle through intermittent aeration was proposed to treat organic matter in waste sealed pit mud from Moutai. Firstly, ferrihydrite was used to verify dissimilatory iron reduction could remove organics from the pit mud; then, the effect of iron cycle induced by intermittent aeration on organics was investigated. The results showed that the removal efficiency of organics was increased by 8.2 % after the addition of ferrihydrite, then intermittent aeration was carried out, Fe(II) content decreased after aeration and increased again after stopping aeration, indicating that iron cycle occurred. Additionally, the total chemical oxygen demand (TCOD) content further decreased by18.8 % in the reactor with intermittent aeration, significantly higher than that in the unaerated group (11.8 %) (p < 0.05). Due to the short aeration time (about once a week, 200–500 mL/min, 30 min for each aeration), aerobic microorganisms were undetected, which further indicated that iron cycle enhanced the removal of organics. Finally, intermittent aeration was conducted in the fermentation system of pit mud without adding iron, and the indigenous iron in the pit mud was also recycled. After 31 days, the TCOD removal efficiency increased by 15.6 % in the aeration group compared with that in the control group. Microbial analysis showed that some microorganism that degraded refractory organics, including iron reducing bacteria, were enriched in the aerated reactors, such as WCHB1–32, ADurb. bin053–1, Lentimicrobium, and Aneurinibacillus, Geobacteraceae. These indicated that organic matter removal can be enhanced by relying on its indigenous iron.

Optimizing hydraulic retention time of high-rate activated sludge designed for potential integration with partial nitritation/anammox in municipal wastewater treatment

The integration of high-rate activated sludge (HRAS), an effective carbon redirection technology, with partial nitritation/anammox (PN/A) is a novel AB treatment process for municipal wastewater. In this study, an airlift HRAS reactor was operated in the continuous inflow mode for 200 d at a wastewater treatment plant. The balance between potential PN/A system stability and peak HRAS performance under decreasing hydraulic retention time (HRT) was optimized. Energy consumption and recovery and CO2 emissions were calculated. The results showed that the optimal HRT suitable with the PN/A process was 3 h, achieving 2–3 g/L mixed liquor volatile suspended solid, 67.8 % chemical oxygen demand (COD) recovery, 81 % total COD removal efficiency, 2.27 ± 1.03 g COD/L/d organic loading rate, 62 % aeration reduction, and 0.24 kWh/m3 power recovery potential. Such findings hold practical value and contribute to the development of the optimal AB process capable of achieving energy autonomy and carbon neutrality.

Elucidating the role of ferric chloride on carbon capture from low-strength municipal wastewater in high-rate activated sludge process: Parameter optimization and crucial mechanism

To enhance organics capture efficiency from low-strength municipal wastewater of China, FeCl3 enhanced high-rate activated sludge (FC-HRAS) process was established in this work. Effects of sludge concentration and FeCl3 dosage on carbon capture in FC-HRAS were investigated. The optimum sludge concentration of 2.0 g/L and FeCl3 dosage of 30 mg Fe/L were obtained, with total COD removal efficiency of 76.8%. Carbon balance analysis showed that FC-HRAS increased organics capture proportion by 91.8% while reducing loss from oxidative metabolism compared to HRAS. The potential mechanism of enhanced carbon capture for FC-HRAS was further explored. Adding Fe(III) caused coagulation of organics by increasing the Zeta potential in wastewater. Impacted by charge neutralization “compression” and coagulation floc “encirclement”, sludge particle sizes decreased, leading to increases of internal surface area and adsorption site of sludge for binding with bacteria; it facilitated the biological flocculation of FC-HRAS. Meanwhile, Fe(III) binding with proteins in EPS induced formation of “protein shell – β polysaccharides kernel” sludge structure and reduction of sludge negative charge, which intensified sludge stability and agglomeration. These factors explained the increase in organics capture proportion. The decrease in metabolism loss of organics could be attributed to the increase in organics transfer resistance in sludge EPS and selective elimination of heteromorphic bacteria (e.g., denitrifiers) in sludge. This work provided guidance for energy-neutral and cost-saving wastewater treatment in China.

Anaerobic Co-digestion of the Liquid Fraction of Food Waste with Waste Activated Sludge

The present study investigated the feasibility of the anaerobic co-digestion (AcoD) of condensate, resulting from drying food waste, with Waste Activated Sludge in a pilot scale continuous stirred tank reactor. Different parameters were assessed in order to enhance the AcoD performance; the condensate potency (condensate A: 13 gCOD/L and condensate B: 4 gCOD/L), the volumetric ratio of condensate to WAS (0–67% v/v) and the hydraulic retention time (HRT) (20, 15 and 12 days). The results showed that increasing the condensate content in the feed from 0 to 67% v/v, enhances the organic load removal (up to 41% increased total COD removal) and the bioenergy production (up to 35% increased biomethane production). Moreover, in the case of condensate A, the reduction of HRT from 20 to 15 days enhanced the bioenergy production (up to 19% increased biomethane production) while the reduction of HRT from 20 to 12 days in the case of condensate B did not significantly affect the reactor’s performance. Overall it is concluded that condensate can be safely introduced in existing facilities for anaerobic digestion, while maintaining a more stable operation and improved effluent quality and bioenergy production in comparison with conventional anaerobic sludge digestion.Graphical

Hydrodynamic behavior and start-up performance in a periodic anaerobic baffled reactor treating traditional Chinese medicine wastewater for different operation patterns

In order to explore the effect of operation pattern on performance, hydrodynamic behavior and start-up performance including molecular weight distribution (MWD) of soluble organic compounds in a periodic anaerobic baffled reactor (PABR) handling traditional Chinese medicine (TCM) wastewater. Residence time distribution test with tap water in the clean PABR was carried out at a certain hydraulic residence time of 48 h in experiments and in computational fluid dynamics (CFD) simulations, both of which were in good agreement for the ‘every second’ (switching period T = 48 h), the ‘clockwise sequential’ (T = 96 h), and the ‘no switching’ (T = ∞) operation pattern. The CFD model output visualized the hydrodynamic-mass transport, which heavily influenced by operation pattern, successfully inside a PABR. The PABRs run in those three operation patterns were subjected to three successive step changes in average organic loading rate at about 1, 2, 4 and 6 kg COD m−3 d−1 for 12, 24, 24 and 6 d, respectively. Pollutants in the TCM wastewater had the longest time to be digested and degraded within PABR run in the ‘every second’ operation pattern, resulting in a most stable performance among the three. Performance of PABR was consistent with the variation in MWD of soluble organic compounds no matter what the operation pattern was. High- MW species (93–130 kDa) broke down into simpler intermediate- MW solutes (7–56 kDa) by the metabolism of anaerobic flocs sludge mostly in the compartment which contributed most to the total COD removal of PABR. Then, intermediate- MW solutes were mineralized step by step into low- MW solutes (100 Da) and biogas in the follow-up compartments in the sequence of flow pattern.

Application of halophiles in UMFC (upflow microbial fuel cell) for the treatment of saline olive oil industrial wastewater coupled with eco-energy yield.

The olive oil industry faces a major problem of treating the wastewater with high organic content and safe disposal. Olive oil industrial wastewater (OOIWW) consists of highly toxic environmental pollutants with high salinity. Saline olive oil industrial wastewater was treated using halophilic consortium in UMFC (upflow microbial fuel cell) mobilized with carbon felt as electrode. Total and soluble COD (chemical oxygen demand), total suspended solids and phenol content removal were studied at different organic loads (0.56, 0.77, 1.05, 1.26, 1.52 and 1.8 gCOD/L). UMFC with OOIWW was optimized at 1.52 gCOD/L for high organic removal and corresponding electricity production. Total COD, soluble COD, TSS and phenol removal were 91%, 89%, 78%, and complete removal of phenol was accomplished at the optimized organic load (1.52 gCOD/L). Correspondingly, the maximum bioenergy yield was 784 mV with 439 mW/m2 (power density) and 560 mA/m2 (current density), respectively. The presence of prominent halophilic exo-electrogens such as Ochrobactrum, Marinobacter, Rhodococcus and Bacillus potently treated the OOIWW and exhibited high energy yield.

Long-term microbiota and performance monitoring of a highly efficient propylene oxide co-production methyl tert-butyl ether production wastewater treatment plant

A wastewater treatment plant (WWTP) was constructed specifically to treat 543,900 m3 wastewater annually generated by a novel propylene oxide (PO) co-production methyl tert-butyl ether (MTBE) petroleum chemical factory in this study. The WWTP consisted of expanded anaerobic granular sludge beds (EGSBs) and aerobic activate sludge tanks (AASTs), which have been operated for 1340 days. The chemical oxygen demand (COD) and petroleum oils of the WWTP influent were 5140 ± 844 mg/L and 70.08 ± 16.57 mg/L, respectively. The overall removal efficiencies for COD petroleum oils were 94.43% ± 2.36% and 93.46% ± 5.95%, respectively. EGSBs account for 41.48% ± 10.52% of the total COD removal, while AAST contributed to 52.95% ± 10.18%. AAST played a prominent role in the removal of petroleum oils. The optimum COD volume loading rate (VLR) of EGSBs during the operation was 1.83 ± 0.10 kg COD/m3/d, whereas the average COD VLR of AAST was 0.45 ± 0.09 kg COD/m3/d. The composition of dominant microorganisms found in EGSBs and AASTs significantly enhance the performance and efficiency of the WWTP. This study underscores the potential of employing a similar approach for long-term and efficient treatment of industrial complex pollutants, while also highlighting the presence of microbiota with exceptional capability to remove petrochemical contaminants.

Sludge floc characteristics and microbial community in high-rate activated sludge and high-rate membrane bioreactor for organic recovery

High-rate activated sludge (HRAS) and high-rate membrane bioreactor (HRMBR) are considered as potential processes for organic recovery through bioflocculation and biosorption of particulate COD and colloidal COD with sludge flocs. In this study, bioflocculation and biosorption, in terms of sludge floc characteristics and microbial community, in HRAS and HRMBR was investigated in relation to organic recovery performance for low strength wastewater treatment. HRAS and HRMBR were operated at two different solids retention times (SRTs) of 2 and 0.8 days. Reducing the SRT of HRAS from 2.0 to 0.8 days resulted in failure in total COD (tCOD) removal efficiency (from 79 ± 2 to 34 ± 13 %) and lowering organic recovery (from 40.8 to 15.7 %). This contrasted with HRMBR, which showed high tCOD removal efficiency (84 ± 2 and 84 ± 1 %) and organic recovery (43.4 and 46.3 %) at both SRTs of 2.0 and 0.8 days. Analysis of sludge floc characteristics showed that the lower organic recovery of the HRAS operated at an SRT of 0.8 days could be associated with poor bioflocculation and biosorption, as evidenced by relatively larger floc size, higher extracellular polymeric substance, higher protein/polysaccharide ratio, and higher zeta potential value of the sludge. These characteristics were in contrast to the HRMBR operated at an SRT of 0.8 days, that exhibited the highest organic recovery among the reactors studied. The microbial taxa Bdellovibrio, Clostridium sensu stricto 9, Hyphomicrobium, and Ideonella could play a role in the poor bioflocculation and biosorption in HRAS. Rhodanobacter, Enterobacter, Terrimonas, Nakamurella, and Mizugakiibacter may be associated with bioflocculation and biosorption and organic recovery in HRMBR. The results of this study enhanced our understanding on the relationships between the microbial community, sludge floc characteristics, and organic recovery performance of HRAS and HRMBR for future optimization of the systems.

Experimental study on the water purification performance of carbonated recycled aggregate pervious concrete

By carbonation treatment, the disadvantages of recycled aggregates (RAs), such as a high porosity, high crushing index and weak interface transition zone, can be improved to some extent. However, the purification performance of carbonated recycled aggregate pervious concrete (CRAPC) remains unknown. In this study, the purification performance of three types of pervious concrete prepared from natural aggregates (NAs), RAs and carbonated recycled aggregates (CRAs) was investigated. High-throughput sequencing of microorganisms was carried out as well. The results reveal that pervious concrete has a significant purification capacity, and the pervious concrete prepared by RAs and CRAs can further improve the ability to remove pollutants. Compared with natural aggregate pervious concrete (NAPC), recycled aggregate pervious concrete (RAPC) and CRAPC were more favourable for pollutant adsorption and microorganism growth due to their special pore structure. Furthermore, although the purification capacity of CRAPC was slightly inferior to that of RAPC, its mechanical properties and alkalinity were improved. In addition, the purification mechanism of pervious concrete mainly includes adsorption and microorganism degradation. The total COD removal amounts of NAPC, CRAPC and RAPC were 87.00 mg/L, 104.00 mg/L and 108.00 mg/L, respectively. The adsorption amounts were 10.00, 12.50, and 16.75 mg/L, and the microorganism degradation amounts were 77.00, 91.50 and 91.25 mg/L, respectively. Compared with adsorption, microorganism degradation plays a major role in total pollutant removal. Furthermore, a water purification model for pervious concrete is proposed.

Effect of coupling primary sedimentation tank (PST) and microscreen (MS) to remove particulate organic carbon (POC): a study to mitigate energy demand in municipal wastewater treatment plants

Particulate Chemical Oxygen Demand (COD) removal is one of the first and foremost steps in a wastewater treatment plant (WWTP). It is a highly essential step that supports subsequent biological steps to achieve discharge limits. However, the energy demand for subsequent biological steps is significant due to the requirement of physical processes such as aeration. As a part of the project: WWTP of the future, it was expected that by coupling primary sedimentation tank (PST) and microscreen (MS) as advanced primary treatment (APT), around 60 to 70% removal of total COD and more than 90% of total suspended solids could be achieved which can replace such energy-intensive steps. To achieve this, a pilot plant set up including two different types of rotatory drum sieves (8 and 20 μm) was coupled with a PST in the WWTP Büsnau, Stuttgart, Germany, and the efficiency of APT was undergone for deeper investigations. The results showed that applying APT processes is an innovative and robust approach for removing more solids in municipal WWTPs so that retrofitting treatment plants comes true with a marginal footprint. However, the long-term performance of the APT system demonstrated that the system’s ability to remove solids is highly limited by MS capacity and strength of produced flocs/filter-cakes inside the MS against shear forces, which makes it easier for flocs to be detained by MS. Therefore, additional auxiliary steps like flocculation are recommended to be synchronized with APT system to enhance its efficiency. Additionally, applying a middle mesh size sieve, for instance, a 15 μm, along with changing the backwashing regime, could be considered the next alternative.

Overall evaluation of a multi-stage reverse electrodialysis reactor series system for organic wastewater treatment and power generation

A multi-stage reverse electrodialysis reactor (REDR) series system for organic wastewater treatment and power generation is proposed in this paper. An energy evaluation method is developed for the first time by analyzing the electrical energy and oxidative degradation energy conversion efficiencies of the system. The influences of the current and feed solution velocity on the overall performances of the system are investigated by experiments. Results demonstrate that a high current can enhance the gross output power but reduce the net output power and total energy conversion efficiency. A peak value of the total COD removal can be obtained at an appropriate current. A low feed solution velocity can improve the performance of the system except for the lower net output power. Although the electrical energy conversion efficiency reduces as the serial number of REDR increases, the oxidative degradation energy conversion efficiency increases significantly, which results in the total energy conversion efficiency enhancement. Under the given experimental conditions, the maximal values of the net output power, total COD removal and total energy conversion efficiency are 1.05 W, 450.98 mg·L−1, and 11.41%, respectively.

Effect of operational parameters on the performance of an anaerobic sequencing batch reactor (AnSBR) treating protein-rich wastewater

Treating protein-rich wastewater using cost-effective and simple-structured single-stage reactors presents several challenges. In this study, we applied an anaerobic sequencing batch reactor (AnSBR) to treat protein-rich wastewater from a slaughterhouse. We focused on identifying the key factors influencing the removal of chemical oxygen demand (COD) and the settling performance of the sludge. The AnSBR achieved a maximum total COD removal of 90%, a protein degradation efficiency exceeding 80%, and a COD to methane conversion efficiency of over 70% at organic loading rates of up to 6.2 g COD L−1 d−1. We found that the variations in both the organic loading rate within the reactor and the hydraulic retention time in the buffer tank had a significant effect on COD removal. The hydraulic retention time in the buffer tank and the reactor, which determined the ammonification efficiencies and the residual carbohydrate concentrations in the reactor liquid, affected the sludge settleability. Furthermore, the genus Clostridium sensu stricto 1, known as protein- and lipids-degraders, was predominant in the reactor. Statistical analysis showed a significant correlation between the core microbiome and ammonification efficiency, highlighting the importance of protein degradation as the governing process in the treatment. Our results will provide valuable insights to optimise the design and operation of AnSBR for efficient treatment of protein-rich wastewater.

Study on the Efficiency of a Hydroponic Treatment for Removing Organic Loading from Wastewater and Its Application as a Nutrient for the “Amaranthus campestris” Plant for Sustainability

The investments needed for treating the wastewater produced by an ever-growing population has raised serious concerns regarding the environmental upkeep of many cities across the world. The concept of the circular economy in this context, i.e., the reuse of partially treated water to produce hydroponic plants, is the central idea of this paper. Usage of partially treated (secondary treated) wastewater for the growth of Amaranthus campestris is investigated. The many benefits here are the cost reduction in the treatment process, the reuse of water for commercial plants, the use of treated water, and no pressure on soil all address sustainable development goals such as zero hunger, no poverty, clean water, and sanitation. This study focuses on the degree of pollutant removal using Amaranthus campestris, a local green widely used in India. Secondary-treated domestic wastewater was fed to the hydroponic medium through batches by using an aerobic process, and the hydraulic retention time was maintained for 10 days. In addition to wastewater, a commercial hydroponic solution was added. This study was carried out to verify the reduction in organic loading in wastewater and the growth of plants in comparison with commercial hydroponic solutions. The total COD and BOD removal was significant (p &lt; 0.0009), ranging from 58.5% to 72.5% and 80% to 82.5%, respectively, from the 0th day to the 50th day. After treatment, the lowest nitrogen, potassium, and phosphorus values in DWW were 2.4 mg/L, 5.4 mg/L, and 0.41 mg/L, found on the 20th, 30th, and 40th days of the experiment, respectively. It was also proven that the treated wastewater from the outlet of the hydroponic reactor was within the standard limits and safe to discharge into water bodies. Based on these results, it is encouraging to implement this method at a large scale in small local communities at a lower cost because of its simplified design in promoting a water-based circular economy, which has been proven to reduce carbon footprints, thus supporting a green environment.

Performance of a pilot-scale EGSB-Bardenpho process treating fresh leachate from municipal solid waste incineration plant

The fresh leachate of municipal solid waste incineration plant (FLIP) has different characteristics from that of sanitary waste landfill plant (LSL), so attention should be paid to the development of FLIP treatment technology. This study proved that EGSB-Bardenpho process with massive effluent reflux could achieve better COD and TN removals. Through the reflux, the effluent organic matter (EfOM) and dissolved organic nitrogen (DON) could be further removed, thus improving the effluent quality. The effluent reflux effectively overcame the inhibition of ammonia nitrogen, and increased the COD removal of the process by about 7.8%, which was attributed to the additional 73% removal of EfOM. The average methane yield of EGSB reactor was 309 N ml·(g COD removed) −1 but the methane production did not timely reflect the state of the reactor. The inhibition threshold of total ammonia nitrogen (TAN) and free ammonia nitrogen (FAN) on the expanded granular sludge bed (EGSB) reactor was 250–360 and 7–10 mg N·L−1, respectively. 20% of the total influent entering the Bardenpho system could provide the carbon source enough for the denitrification when the TN removal rate was about 98%. In the case of 80% of the FLIP treated by the EGSB reactor, its contribution to the total system COD removal was approximately 71%. The presence of TAN appeared to promote the formation of cocci-dominated granular sludge in EGSB reactor.

Long-term effect of free ammonia pretreatment on the semi-continuous anaerobic primary sludge digester for enhancing performance: Towards sustainable sludge treatment

Primary sludge (PS) is one of the major sludge sources for anaerobic digesters in wastewater treatment plants. Although the impact of free ammonia (FA) pretreatment on methane production from anaerobic PS digestion was previously investigated using batch biochemical methane potential tests, these tests could not fully represent the continuous/semi-continuous anaerobic digestion that is currently used in practice. This study comprehensively evaluated the impact of FA pretreatment on the performance of anaerobic PS digestion for the first time using semi-continuous systems that run for over 120 days. FA pretreatment (560 mg NH3-N/L, 24 h) improved the volatile solids (VS) removal of PS by 12.2 % from 60.5 % to 67.9 %, with a similar improvement in total chemical oxygen demand removal of 14.9 % and methane production of 16.1 %. FA pretreatment increased the biomass-specific hydrolysis rate of digesters by 23.5 %. Model-based analysis revealed that the enhanced anaerobic digestion performance may be due to both the increased apparent hydrolysis rate (increased by 26.7 %) and the enhanced degradability extent (increased by 9.5 %) of PS, caused by FA pretreatment. The dewaterability of digested sludge was enhanced by 14.0 % due to FA pretreatment, which is also supported by the reduced capillary suction time from 15.1 s to 10.9 s. Removals of Fecal Coliform and E. Coli were enhanced by 0.6 and 1.4 log Most Probable Number/g vS by FA pretreatment. This study firstly manifested that FA pretreatment is a favourable approach to improve the performance of anaerobic PS digestion with extra benefits in pathogen removal and dewaterability.

Dual utilization of aloe peel: Aloe peel-derived carbon quantum dots enhanced anaerobic co-digestion of aloe peel

Carbon materials have been widely used in anaerobic digestion (AD), but the role of zero-dimensional carbon quantum dots (CQDs) in anaerobic co-digestion (AcoD) has not yet been reported. In this work, the effect of aloe peel-derived CQDs (AP-CQDs) on the AcoD system of aloe peel and dairy manure was investigated. The addition of AP-CQDs accelerants increased the cumulative CH4 yield from 201.14 to 266.92–339.64 mL/g VS and increased total chemical oxygen demand removal efficiency from 34.72 % to 48.77–57.87 %. The use of a digestate with 0.36 wt.% of AP-CQDs resulted in a thermogravimetric mass loss of 47.15 % and a promising total nutrient content of 46.65 g/kg. The excellent electron exchange capacity of AP-CQDs may facilitate direct interspecies electron transfer during the AD process. Moreover, the use of AP-CQDs can enrich methanogenic microorganisms (Methanosarcina and Methanobacterium). These findings provide a viable strategy for improving methane production and create awareness regarding the dual use of biomass waste.

Retrofitting a full-scale multistage landfill leachate treatment plant by introducing coagulation/flocculation/sedimentation and ultrafiltration process steps.

Considering that landfilling still remains among the most commonly used methods for the confrontation of solid wastes, effective methods should be applied to treat the leachate generated, due to its recalcitrant nature. In this work, a full-scale system consisting of two SBRs operating in parallel (350 m3 each) and two activated carbon (AC) columns operating in series (3 m3 each) was retrofitted by introducing a coagulation/flocculation/sedimentation (C/F/S) unit of 7.8 m3 and an ultrafiltration (UF) membrane of 100 m2 to effectively treat landfill leachate. The raw leachate was characterized by high COD and NH4+-N concentration, i.e., 3095 ± 706mg/L and 1054 ± 141mg/L respectively, a BOD/COD ratio of 0.22, and high concentrations of certain heavy metals. Leachate processing in this retrofitted multistage treatment system resulted in total COD removal efficiency of 89.84%, with biological treatment, C/F, UF, and AC contributing 46.31%, 4.68%, 15.98%, and 22.87% to the overall organic content removal. The retrofitted scheme achieved an overall NH4+-N and TKN removal of 92.03% and 91.75% respectively, attributed mostly to the activity of an effective nitrifying community. Color number (CN) was reduced by 26.96%, 10.29%, 15.94%, and 5.39% after the activated sludge, the C/F, the UF, and the AC adsorption process respectively, corresponding to a 58.91% overall decrease. Regarding heavy metal removal, all elements examined, apart from Ni, i.e., effluent As, Cd, Co, Cr, Cu, Hg, Mg, Mn, and Pb, were below the legislative limits set by the national authorities for restricted or unrestricted irrigation. Lastly, total operating expenses (OPEX) were estimated as equal to 72,687 €/year or 6.64 €/m3.