Soluble Chemical Oxygen Demand Research Articles

Enhanced degradation and methane production of food waste anaerobic digestate using an integrated system of anaerobic digestion and microbial electrolysis cells for long-term operation.

The integrated system of anaerobic digestion and microbial electrolysis cells (AD-MEC) was a novel approach to enhance the degradation of food waste anaerobic digestate and recover methane. Through long-term operation, the start-up method, organic loading, and methane production mechanism of the digestate have been investigated. At an organic loading rate of 4000mg/L, AD-MEC increased methane production by 3-4 times and soluble chemical oxygen demand (SCOD) removal by 20.3% compared with anaerobic digestion (AD). The abundance of bacteria Fastidiosipila and Geobacter, which participated in the acid degradation and direct electron transfer in the AD-MEC, increased dramatically compared to that in the AD. The dominant methanogenic archaea in the AD-MEC and AD were Methanobacterium (44.4-56.3%) and Methanocalculus (70.05%), respectively. Geobacter and Methanobacterium were dominant in the AD-MEC by direct electron transfer of organic matter into synthetic methane intermediates. AD-MEC showed a perfect SCOD removal efficiency of the digestate, while methane as clean energy was obtained. Therefore, AD-MEC was a promising technology for deep energy transformation from digestate.

Impact of tannery wastes on anaerobic co-digestion: enhancing biogas production and process efficiency

The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry.Graphical

Microwave facilitated bacterial liquefaction of sago biomass for efficient biomethane production: Energy and Cost assessment

Sago has been considered to be a major staple food throughout the world for centuries. Thus, the sago processing industry also contributes to economic growth. However, waste disposal from this industry is an environmental concern and is addressed in this study. The generated solid waste sago is a starchy-rich substrate that is underutilized and can be exploited for bioenergy production. The present study focused on improving the hydrolytic potential of sago biomass during anaerobic digestion by implementing the combined microwave and bacterial pretreatment techniques. The microwave liquefaction yields the maximum solubilization of 11% at the microwave power of 720 watts and the time of 11min. Incorporation of bacterial pretreatment significantly enhances COD solubilization from 11 to 31.6%. This combined pretreatment of sago biomass shows the biomethane generation of 0.223L/gCOD compared to the microwave (0.106L/gCOD) and control sample (0.044L/gCOD). Energy and cost analysis of combinative pretreatment shows a positive net energy of 0.97 kWh/kg and a net cost of 1.63 USD/ton. Thus, this combined pretreatment can be effectively adapted on an industrial scale.

Electrochemistry promotion of Fe(Ⅲ)/Fe(Ⅱ) cycle for continuous activation of PAA for sludge disintegration: Performance and mechanism

In this study, electrochemistry was used to enhance the advanced oxidation of Fe(Ⅱ)/PAA (EC/Fe(Ⅱ)/PAA) to disintegrate waste activated sludge, and its performance and mechanism was compared with those of EC, PAA, EC/PAA and Fe(Ⅱ)/PAA. Results showed that the EC/Fe(Ⅱ)/PAA process effectively improved sludge disintegration and the concentrations of soluble chemical oxygen demand, polysaccharides and nucleic acids increased by 62.85%, 41.15% and 12.21%, respectively, compared to the Fe(Ⅱ)/PAA process. Mechanism analysis showed that the main active species produced in the EC/Fe(Ⅱ)/PAA process were •OH, R–O• and FeIVO2+. During the reaction process, sludge flocs were disrupted and particle size was reduced by the combined effects of active species oxidation, electrochemical oxidation and PAA oxidation. Furthermore, extracellular polymeric substances (EPS) was degraded, the conversion of TB-EPS to LB-EPS and S-EPS was promoted and the total protein and polysaccharide contents of EPS were increased. After sludge cells were disrupted, intracellular substances were released, causing an increase in nucleic acids, humic acids and fulvic acids in the supernatant, and resulting in sludge reduction. EC effectively accelerated the conversion of Fe(Ⅲ) to Fe(Ⅱ), which was conducive to the activation of PAA, while also enhancing the disintegration of EPS and sludge cells. This study provided an effective approach for the release of organic matter, offering significant benefits in sludge resource utilization.

Insights into the effects of cobalt ferrite nanoparticles activated peroxymonosulfate on waste activated sludge dewaterability during ciprofloxacin degradation

This research delved into the effect of cobalt ferrite nanoparticles activated peroxymonosulfate (CoFe2O4/PMS) treatment on sludge dewaterability during the ciprofloxacin (CIP) degradation in waste activated sludge (WAS). When the dosage of CoFe2O4 was 80 mg/g TSS and PMS was 60 mg/g TSS, the water content (Wc) of sludge was reduced from 80.84% to 66.33% while the capillary suction time (CST) of sludge descended from 82.6 s to 55.2 s. Considering cost and follow-up operations, the favorable pH for sludge dewatering was 6.9 additionally. During the process, the sludge disintegration brought out the dissolution of organic substances and the destruction of extracellular polymer substances (EPS). The results showed that both of soluble chemical oxygen demand (SCOD) and total nitrogen (TN) dissolved in the supernatant had a remarkable positive correlation with the sludge dewaterability. The strong oxidative free radicals SO4∙- (63.6%), ∙OH (28.2%), and ·O2- (6.3%) produced by CoFe2O4/PMS destructed the EPS structure, accompanied with proteins and polysaccharides oxidization as well as the bound and intracellular water release. There was also a significant positive relationship between polysaccharide ratio to protein and sludge dewatering (CST and Wc), which was consistent with that polysaccharide is more hydrophilic than protein. At last, a mechanism involving oxidization and re-aggregation has been presented, which is beneficial to the dewatering performance of sludge. This research underlines the potential of CoFe2O4/PMS as a promising technology for enhancing the sludge dewatering efficiency and degrading CIP, with significant implication for environmental protection.

Electro-assisted anaerobic digestion of waste activated sludge for biomethane production enhanced by hyperosmosis of sodium chloride: Characteristics and microbial mechanisms

This first-attempted study explored the hyperosmosis of sodium chloride (NaCl) for enhancing methane production from waste activated sludge (WAS) via electro-assisted anaerobic digestion. The 0.6–0.9 g/g TS levels of sodium chloride caused an obvious WAS solubilization with ca. 104.7–110.3 mg/L of soluble chemical oxygen demand (SCODMn) release within 96-h (including 132.56–158.34 mg/L of soluble protein and 55.67–66.36 mg/L of soluble carbohydrates). The NaCl addition increased conductivity and current density positively, but decreased microbial biodiversity, community evenness and archaeal metabolic activities negatively in the electro-assisted anaerobic digestion process. The proper use of NaCl for enhancing methanogenesis of WAS should seek a balance between such positive and negative impacts, which was at ca. 0.6 g/g TS adding level and maintained a good-cooperation between acidogens and methanogens. Acidogens of Acrobacter, Mesotoga, Mesoaciditoga, Candidatus-cloacamonas, Bacteroidales, Bacteroidetes, Anaerolineaceae, Treponema and Fusibacter contributed to VFAs generation, while Methanobacterium, Methanomassiliicoccus and Methanothrix were responsible for methanogenesis positively under NaCl-hyperosmosis circumstances. Finally, a mechanistic illustration for depicting biomethane conversion in electro-assisted anaerobic digestion with sodium chloride addition was proposed. The results obtained might shed lights on this efficient and low-cost strategy for WAS treatment and resource recovery.

Improved biohydrogen production by co-fermentation of corn straw and excess sludge: Insights into biochemical process, microbial community and metabolic genes

The global climate change mainly caused by fossil fuels combustion promotes that zero-carbon hydrogen production through eco-friendly methods has attracted attention in recent years. This investigation explored the biohydrogen production by co-fermentation of corn straw (CS) and excess sludge (ES), as well as comprehensively analyzed the internal mechanism. The results showed that the optimal ratio of CS to ES was 9:1 (TS) with the biohydrogen yield of 101.8 mL/g VS, which was higher than that from the mono-fermentation of CS by 1.0-fold. The pattern of volatile fatty acids (VFAs) indicated that the acetate was the most preponderant by-product in all fermentation systems during the biohydrogen production process, and its yield was improved by adding appropriate dosage of ES. In addition, the content of soluble COD (SCOD) was reduced as increasing ES, while concentration of NH4+-N showed an opposite tendency. Microbial community analysis revealed that the microbial composition in different samples showed a significant divergence. Trichococcus was the most dominant bacterial genus in the optimal ratio of 9:1 (CS/ES) fermentation system and its abundance was as high as 41.8%. The functional genes prediction found that the dominant metabolic genes and hydrogen-producing related genes had not been significantly increased in co-fermentation system (CS/ES = 9:1) compared to that in the mono-fermentation of CS, implying that enhancement of biohydrogen production by adding ES mainly relied on balancing nutrients and adjusting microbial community in this study. Further redundancy analysis (RDA) confirmed that biohydrogen yield was closely correlated with the enrichment of Trichococcus.

Degradation of organic compounds by a novel Bacillus cereus BX16 in starch waste

Starch wastes are organic pollutants that have a negative impact on the environment. Bacillus cereus BX16, a newly isolated strain with the capacity to exclusively digest starch, was separated and purified using food waste (FW). The efficiency of starch breakdown by Bacillus cereus BX16 was greatly influenced by operational parameters, such as organic load rates (OLRs), pH and temperature. According to the findings, Bacillus cereus BX16 degraded more effectively at the starting starch concentration of 20 g/L. Further optimization resulted in approximately 90% and 99% removal of soluble chemical oxygen demand (SCOD) and polysaccharides, over a wide range of settings (pH 5.0–9.0, 25 °C to 37 °C). In addition, when starch was effectively degraded, 90% of the residual SCOD (<5000 mg/L) consisted mainly of proteins and volatile fatty acids (VFAs). In contrast, in the absence of active Bacillus cereus BX16, the residual polysaccharide and glucose concentration jumped to 20,000 mg/L. Ultimately, the unique biological method of treating starch waste with Bacillus cereus BX16 also proves the effectiveness of microbial treatment.

Magnetic iron oxide nanoparticle enhanced microwave pretreatment for anaerobic digestion of meat industry sludge

Our study investigates the effects of iron oxide (Fe3O4) nanoparticles combined microwave pretreatment on the anaerobic digestibility and soluble chemical oxygen demand (SCOD) of meat industry sludge. One of our main objectives was to see whether the different microwave-based pretreatment procedures can enhance biogas production by improving the biological availability of organic compounds. Results demonstrated that combining microwave irradiation with magnetic iron oxide nanoparticles considerably increased SCOD (enhancement ratio was above 1.5), the rate of specific biogas production, and the total cumulative specific biogas volume (more than a threefold increment), while having no negative effect on the biomethane content. Furthermore, the assessment of the sludge samples’ dielectric properties (dielectric constant and loss factor measured at the frequency of 500 MHz) showed a strong correlation with SCOD changes (r = 0.9942, R2 = 0.99), offering a novel method to evaluate pretreatment efficiency.

Carbon-ferrous-sulfur mixotrophic denitrification driven by polyferric sulfate (PFS)-conditioned recovered sludge fermentation liquor enhanced nitrogen removal in woolen wastewater

Reducing pollution and carbon emissions synergistically in wastewater treatment is an important part of carbon neutralization. Recycling carbon sources (CSs) in sludge to refeed denitrification has been considered a promising sustainable pathway, but it is limited by CSs purification and recovery. This study evaluated the effects of polyferric sulfate (PFS), polyaluminum chloride (PAC), and polyacrylamide (PAM) conditioning on fermentation CSs recovery and denitrification efficiency. Results indicated PFS-conditioned recovered fermentation liquor showed higher denitrification efficiency for woolen wastewater. CSs recovery test showed that PFS conditioning improved the purity of high-bioavailability CSs by depleting fewer short-chain fatty acids (SCFAs) and removing more total nitrogen (TN), total phosphorus (TP), and humic acids. Under the 0.05 g/gTSS PFS conditioning and recovery, the preservation of soluble chemical oxygen demand (SCOD) and SCFAs were 71.00 % and 84.36 %, respectively, and the nitrate degradation rate achieved 3.19 mgNO3−·h−1·gVSS−1. Importantly, Fe(III) dissociated from PFS oxidized the S2− from woolen wastewater, and generated Fe(II) and S0, which composed a synergistic electron donor system together with SCFAs. They constituted a mixotrophic denitrification dominated by heterotrophic denitrification and reinforced by ferrous and sulfur-autotrophic denitrifications, which contributed 69.56, 17.72, and 12.72 % to nitrogen removal, respectively. In addition, the refeeding of PFS-conditioned recovered fermentation liquor promoted the proliferation of microorganisms involved in iron/sulfur autotrophic denitrification and the abundance of denitrification functional genes, especially the napA, nirS, cnorB, qnorB, and nosZ, forming an efficient Carbon-Ferrous-Sulfur hybrid denitrifiers community to enhanced nitrogen removal from woolen wastewater.

Multiomics study on co-fermentation of chemically enhanced sludge and waste activated sludge to produce volatile fatty acids under different temperatures and pHs

This study examined the effects of different temperatures (37°C and 45°C) and pH (uncontrolled, 8 and 10) on the co-fermentation of FeCl3, anionic polyacrylamide (a-PAM) settling chemical enhanced primary sedimentation (CEPS), and waste activated sludge (WAS) to produce volatile fatty acids (VFAs), which analyzed through characterization, microbial community, and untargeted metabolic pathways. Further, to investigate the interacting effects, temperatures of 37°C, 45°C, and pHs of 8 and 10 were chosen, with a sludge ratio of 7.5. The hydrolysis of sludge was aided by the concentration of soluble chemical oxygen demand (SCOD) rising as temperature and pH rose. Nevertheless, elevated SCOD concentrations failed to materialize into benefits for acid production. Therefore, considering practical applications, the optimal conditions for acid production were determined to be 37°C and pH 10, with a concentration of 3411.17 ± 119.92 mg COD/L. A thorough investigation of correlations between microbial communities, differential metabolites, and environmental factors was carried out, highlighting the significance of pH in relation to microbial and acid production performance. That instance, the pH affects acid generation efficiency more so than temperature parameters. Within the microbial community, there is a considerable positive correlation between several distinct metabolites and Steptococcus, Trichococcus, and Tepidimimicrobium. These metabolites are intimately associated with the materials and energy needed for biological cell production and metabolism. This could be as a result of how environmental influences alter the distribution of microbial populations, which influences various metabolites and ultimately the process of producing acid.

Application of environmentally friendly technologies for the management of nanofiltration concentrate from landfill leachate

In this study, the treatability of leachate nanofiltration (NF) concentrate using the modified Fenton process was investigated. The modified Fenton process employs an environmentally friendly oxidant (sodium percarbonate, SPC), an environmentally friendly catalyst (Fe2+), and environmentally friendly activators (electrooxidation-ultraviolet, EO-UV). The study aimed at enhancing the biological degradability of leachate NF concentrate and was conducted in two stages. In the first stage, the process variables of the SPC/Fe2+ process were optimized. In the second stage, combined processes were applied under optimum conditions. With the SPC/Fe2+ process under optimum conditions (pH: 5, SPC dose: 10 mM, Fe2+ concentration: 50 mM, reaction time: 60 min, pre-catalyst dosing), removal efficiencies of 53.5%, 47.1%, and 61.6% were obtained for chemical oxygen demand (COD), UV254, and color, respectively. After optimizing the operational parameters of the SPC/Fe2+ process, combined processes of EO/SPC/Fe2+ and UV/SPC/Fe2+ were applied, and higher pollutant removal efficiencies were achieved with the EO/SPC/Fe2+ process. Under optimum conditions, removal efficiencies of 75.3%, 80.5%, and 85.6% were achieved for COD, UV254, and color, respectively. The first-order reaction rate constant was 0.022 1/min for the EO/SPC/Fe2+ process. The biochemical oxygen demand (BOD)/COD, which increased from 0.040 to 0.080 with the SPC/Fe2+ process, reached 0.455 with the EO/SPC/Fe2+ process. Additionally, with the EO/SPC/Fe2+ process, the biologically degradable COD ratio of leachate NF concentrate increased from 16.7% to 83.5%, and the soluble COD fraction increased from 72.7% to 89.5%.

Energy efficient biohydrogen production from waste activated sludge through a novel phase separated pretreatment

Disintegration of sludge by microwave irradiation is considered an energy-intensive pretreatment as it demands more significant energy input to achieve the desirable solubilization. Extracellular polymeric substance (EPS) present in the floc matrix of sludge limits the extent of sludge solubilization. Hence, this study attempted to disrupt the EPS with potassium peroxymonosulphate (PPMS) before microwave (MW) pretreatment to attain maximal solubilization in an energy-efficient way. A maximal EPS disruption was achieved at 0.009 g/g TS of PPMS dosage and treatment time of 36 min. The outcome of the phase-separated pretreatment shows that PPMS induced MW pretreatment (PPMS-MW) obtained a maximum chemical oxygen demand (COD) solubilization of 35.67 % at a specific energy input of 8795 kJ/kg TS. In contrast, the MW pretreatment achieved only 22.41 % at a specific energy input of 21973 kJ/kg TS. When comparing both PPMS-MW and MW pretreatments, an ample amount of energy was saved by PPMS-MW than MW. The biohydrogen production potential assay showed that PPMS-MW obtained an increased biohydrogen production of 79.76 mL/g VS compared to MW (50.10 mL/g VS). Thus, this phase-separated PPMS-MW pretreatment was considered efficient compared to MW pretreatment.

Extracellular Polymeric Substance Composition Effects on Biosorption for Primary Carbon Diversion

This paper characterizes the composition of extracellular polymeric substances (EPSs) in different types of activated sludge (AS) processes and analyzes the biosorption of soluble organics when waste AS (WAS) is mixed with raw wastewater for primary carbon diversion. The fraction of AS organics identified as EPSs was 26% in a membrane bioreactor (MBR), 54% in conventional AS (CAS), and 51% in a trickling filter/solids contact (TF/SC) process. EPSs were found to be approximately 15% carbohydrates, 40% proteins, 40% humics, and 5% uronics in CAS and MBR AS. Biosorption was not correlated to the organic portion (VSS) of the WAS; however, statistically significant correlations were found for the total amount of EPSs (for TF/SC and CAS) and the protein fraction (for TF/SC and MBR) in the VSS. EPSs from different types of AS biosorbed the same amount of soluble organics, removing 1.43 ± 0.15 (n = 16) mg of soluble chemical oxygen demand (sCOD), and 1.20 ± 0.18 (n = 16) mg of truly soluble COD (ffCOD), per mg of cation exchange resin (CER) total extracted EPSs. Utilizing multiple extraction methods in series (CER–base–sulfide) increased EPS extraction yields by nearly 100% relative to CER alone and indicated different EPS fractionization for CAS (a smaller fraction of carbohydrates and a larger fraction of humics).

A novel additive for enhancing biomass energy production from agro-industrial wastes: synthesis of hydrophobic nanoporous silica aerogel and its effect on methane production

AbstractAnaerobic digestion (AD) is one of the most preferred processes for the treatment of organic waste. However, additional processes such as co-digestion, pretreatment, and additive addition continue to be explored to remove the limits on the applicability of AD. This study investigated the effects of hydrophobic nanoporous silica aerogel (NpSA) synthesized from waste rice husks on the anaerobic co-digestion (AnCD) of the mixture consisting of sewage sludge and fruit processing industry wastes. All bioreactors containing NpSA-free, 0.1 g, 0.2 g, 0.5 g, and 1 g NpSA (0.03–0.3 gNpSA/gVSadded) were operated in a mesophilic-batch process. Biogas and methane yields increased from 346 mL/gVS (NpSA-free) to 387 mL/gVS and from 231 mL/gVS (NpSA-free) to 288 mL/gVS, respectively, with 0.1 g NpSA addition. NpSA additive increased biogas production in all bioreactors compared to the blank. However, biogas production rate and methane content increased faster at lower doses of NpSA. Maximum soluble chemical oxygen demand (sCOD), protein, carbohydrate, and volatile solid (VS) reductions were between 45–71%, 35–54%, 44–65%, and 34–91% for NpSA added mixtures, respectively. The hydrophobic NpSA additive was effective in improving the AnCD performance and biogas/methane production. Experimental results fit the kinetic models frequently preferred in such AD processes. In addition, the possible energy and financial potential of the produced methane were also discussed, and it was determined that the direct sale of methane gas produced by the addition of NpSA in the global market could provide 1.4 $/Lmixture more financial gain than the mixture NpSA-free. Graphical Abstract

Cultivation of Microalgae in Liquid Digestate to Remove Nutrients and Organic Contaminants

AbstractThe goal of this research was to assess the efficiency of the liquid digestate treatment conducted with algal, environmental isolates illuminated entirely with sunlight. The photobioreactor was exposed to natural conditions and evaluated based on the reduction of chemical oxygen demand (COD), nitrogen compounds, and soluble phosphates. Microalgal and bacterial communities growing during the treatment process were studied. A high removal rate of soluble COD (= 91%) and nutrients (= 86%) was achieved. The average concentrations of nitrogen, phosphates, and COD in the reactor effluent were 95 mgN/L, 49 mg/L, and 735 mg O2/L, respectively. The overall algae-bacteria biomass productivity of 22 mg/L/d, calculated on the total suspended solids (TSS) basis, was recorded. The microbial analysis revealed the dominance of Tetradesmus obliquus followed by Microglena sp. in the first 14 weeks of the experiment. At the end of the experimental run, Chlorella sorokiniana cells appeared as a result of illumination intensity changes. The dominating bacteria belonged to Firmicutes (26.31%), Patescibacteria (17.38%), and Actinobacteriota (14.86%) and could have been responsible for the transformation of nitrogen and oxidation of organic contaminants. The research demonstrated that natural sunlight can successfully be used for efficient liquid digestate treatment with the algae-bacterial community.

Optimised start-up strategy for bioelectrochemical systems operating on hydrolysed human urine

Key nutrients, such as nitrogen measured as total ammonium nitrogen (TAN), could be recycled from hydrolysed human urine back to fertiliser use. Bioelectrochemical systems (BESs) are an interesting, low-energy option for realising this. However, the high TAN concentration (> 5 g L–1) and pH (> 9) of hydrolysed urine can inhibit microbial growth and hinder the enrichment of an electroactive biofilm at the anode. This study investigated a new strategy for bioanode inoculation by mixing real hydrolysed urine with thickened waste activated sludge (TWAS) from a municipal wastewater treatment plant at different volumetric ratios. The addition of TWAS diluted the high TAN concentration of hydrolysed urine (5.2 ± 0.3 g L–1) to 2.6–5.1 g L–1, while the pH of the inoculation mixtures remained > 9 and soluble chemical oxygen demand (sCOD) at 5.6–6.7 g L–1. Despite the high pH, current generation started within 24 h for all reactors, and robust bioanodes tolerant of continuous feeding with undiluted hydrolysed urine were enriched within 11 days of start-up. Current output and Coulombic efficiency decreased with increasing initial hydrolysed urine fraction. The anodes inoculated with the highest sCOD-to-TAN ratio (2.1) performed the best, which suggests that high organics levels can protect microbes from inhibition even at elevated TAN concentrations.

Thermophilic self-fermentation of chicken manure for enhanced soluble metabolite products and bio‑hydrogen production

Treating chicken manure (CM) through anaerobic digestion encounters a hurdle due to its high nitrogen content, leading to volatile fatty acid accumulation and methanogenesis disruption. To overcome this, redirecting the process to yield soluble metabolite products (SMPs) and hydrogen is proposed. Mesophilic (30 °C) and thermophilic (55 °C) acidogenesis were employed, utilizing self-fermentation and sludge augmentation at various total solids (TS) concentrations ranging from 2.5 % to 20 %. SMP production showed direct proportionality to TS concentration. Optimal conditions were observed in thermophilic self-fermentation at 15 % TS, yielding 0.20 ± 0.01 g SMPs/g volatile solid. Moreover, the mass balance analysis revealed 46.68 g of SMPs, equivalent to 53.82 g of soluble chemical oxygen demand (SCOD) solubilized in the total SCOD of 63.56 g in the effluent. Although thermophilic bioaugmentation enhanced hydrogen production, its impact on SMPs was insignificant. This study underscores the potential of CM self-fermentation, highlighting its organic matter and microorganism-rich characteristics.

Insightful Analysis and Prediction of SCOD Component Variation in Low-Carbon/Nitrogen-Ratio Domestic Wastewater via Machine Learning

The rapid identification of the amount and characteristics of chemical oxygen demand (COD) in influent water is critical to the operation of wastewater treatment plants (WWTPs), especially for WWTPs in the face of influent water with a low carbon/nitrogen (C/N) ratio. Given that, this study carried out batch kinetic experiments for soluble chemical oxygen demand (SCOD) and nitrogen degradation for three WWTPs and established machine learning (ML) models for the accurate prediction of the variation in SCOD. The results indicate that four different kinds of components were identified via parallel factor (PARAFAC) analysis. C1 (Ex/Em = 235 nm and 275/348 nm, tryptophan-like substances/soluble microbial by-products) contributes to the majority of internal carbon sources for endogenous denitrification, whereas C4 (230 nm and 275/350 nm, tyrosine-like substances) is crucial for readily biodegradable SCOD composition according to the machine learning (ML) models. Furthermore, the gradient boosting decision tree (GBDT) algorithm achieved higher interpretability and generalizability in describing the relationship between SCOD and carbon source components, with an R2 reaching 0.772. A Shapley additive explanations (SHAP) analysis of GBDT models further validated the above result. Undoubtedly, this study provided novel insights into utilizing ML models to predict SCOD through the measurements of the excitation–emission matrix (EEM) in specific Ex and Em positions. The results could help us to identify the degradation and transformation relationship between different kinds of carbon sources and nitrogen species in the wastewater treatment process, and thus provide a novel guidance for the optimized operation of WWTPs.

Enhancing biogas production from palm oil mill effluent through the synergistic application of surfactants and iron supplements

In this study, the effects of various surfactants on the soluble chemical oxygen demand (COD) fraction and biogas production from palm oil mill effluent (POME) were investigated. A cationic surfactant (cetyltrimethylammonium bromide, CTAB) and a nonionic surfactant (Tween 80; TW80) were found to adsorb onto the particulate matter from POME, markedly reducing the soluble COD, unlike an anionic surfactant (sodium dodecyl sulfate, SDS). The mechanism underlying this phenomenon might be the adsolubilization of oil on particulate matter induced by the adsorbed surfactants. In terms of biogas production, 0.1 % w/v SDS and CTAB dramatically reduced the biogas yield, while 0.1 % w/v TW80 did not have this negative effect. A synergistic effect was observed when TW80 (0.1 % w/v) was combined with FeSO4 (400 mg/L), resulting in a 17 % greater biogas yield than that achieved with treatments using TW80 or FeSO4 alone. Moreover, the combination of TW80 and FeSO4 increased the biogas production rate. Surprisingly, the water-soluble iron fraction remained consistent across all treatments, suggesting that the adsorption of TW80 on particulate matter may limit micelle formation. Importantly, the proportion of methane in the generated biogas remained stable in all the treatments. Microbial community analysis revealed that the introduction of TW80 and FeSO4 had no discernible impact on the microbial community of the system. Pretreatment with TW80 and an iron supplement significantly enhanced biogas production and reduced the retention time of the anaerobic digestion (AD) system while maintaining the biogas quality and microbial community stability.