Bio-refractory dissolved organic matter and colorants in cassava distillery wastewater: Characterization, coagulation treatment and mechanisms

Development and standardization of spectrophotometric assay for quantification of thermal hydrolysis-origin melanoidins and its implication in antioxidant activity evaluation

Melanoidins are brown recalcitrant polymers originating from the thermal hydrolysis pretreatment (THP) of organic solid waste (OSW). Owing to their various formation pathways and complex structures, there is currently no reliable method to quantify melanoidins. In this study, a spectrophotometric method was developed to determine melanoidins concentration in different OSW. Three typical model Maillard reaction systems (glucose-glycine, glucose/fructose-20 amino acids, and dextran-bovine serum albumin) were used to acquire the characteristic peaks and establish standard curves. The results showed that a standard curve using glucose/fructose-20 amino acids model melanoidins at 280 nm was the optimal quantification method, because it had the best correlation with the physicochemical indicators of melanoidins and semi-quantification results calculated by excitation-emission matrix fluorescence. In addition, the applicability of the proposed method was evaluated using multiple real melanoidins samples extracted from thermally pretreated OSW under different THP conditions and food-derived melanoidins as well, demonstrating its validity and advantages. This study is the first to provide a simple, effective, and accurate method for quantifying THP-origin melanoidins from different sources. Remarkably, as a specific and important application scenario, the proposed quantification method was employed to investigate the concentration dependence of melanoidins antioxidation in thermally pretreated OSW.

Recovery capability of anaerobic digestion from ammonia stress: Metabolic activity, energy generation, and genome-centric metagenomics

Excessive ammonia stresses anaerobic digestion (AD) significantly. Although there has been progress in understanding AD under ammonia exposure, investigations on AD liberated from ammonia exposure are limited. Here, the recovery capability of AD from ammonia stress was evaluated, by examining specific methanogenic activity, energy-conserving capability, microbial community succession, and metabolic pathway reconstruction. The findings demonstrated that ammonia stress relief resulted in < 50% methane recovery, with propionate conversion identified as the critical impediment to AD reactivation. Energy generation could not recovered either. Efforts to mitigate ammonia stress failed to restore acetoclastic methanogens, e.g., Methanothrix soehngenii, and proved futile in awakening propionate oxidizers, e.g., Desulfobulbus. Interestingly, a symbiotic metabolism emerged, prevailing in stress-relieved AD due to its energy-conserving advantage. This study underscores the importance of targeted interventions, including stimulating acetoclastic methanogenesis, propionate oxidation, and energy generation, as priorities for AD recovery following ammonia stress, rather than focusing solely on ammonia level management.

Resource recovery and valorization of food wastewater for sustainable development: An overview of current approaches

The food processing industry is one of the world's largest consumers of potable water. Agri-food wastewater systems consume about 70% of the world's fresh water and cause at least 80% of deforestation. Food wastewater is characterized by complex composition, a wide range of pollutants, and fluctuating water quality, which can cause huge environmental pollution problems if discharged directly. In recent years, food wastewater has attracted considerable attention as it is considered to have great prospects for resource recovery and reuse due to its rich residues of nutrients and low levels of harmful substances. This review explored and compared the sources and characteristics of different types of food wastewater and methods of wastewater treatment. Particular attention was paid to the different methods of resource recovery and reuse of food wastewater. The diversity of raw materials in the food industry leads to different compositional characteristics of wastewater, which determine the choice and efficiency of wastewater treatment methods. Physicochemical methods, and biological methods alone or in combination have been used for the efficient treatment of food wastewater. Current approaches for recycling and reuse of food wastewater include culture substrates, agricultural irrigation, and bio-organic fertilizers, recovery of high-value products such as proteins, lipids, biopolymers, and bioenergy to alleviate the energy crisis. Food wastewater is a promising substrate for resource recovery and reuse, and its valorization meets the current international policy requirements regarding food waste and environment protection, follows the development trend of the food industry, and is also conducive to energy conservation, emission reduction, and economic development. However, more innovative biotechnologies are necessary to advance the effectiveness of food wastewater treatment and the extent of resource recovery and valorization.

Biodecolorization of biogas plant effluent derived from anaerobically digested distillery wastewater by naturally selected Pseudomonas putida

Effluent from biogas plants can contribute to serious environmental issues due to its high organic compound content and its dark color. This study utilizes Pseudomonas putida strains isolated from activated sludge in a wastewater treatment plant to reduce the organic compound content and dark color of biogas plant effluent. The treatment of effluent from the anaerobic digestion of distillery wastewater with P. putida in the best evaluated conditions (sample concentration of 50% v/v, agitation and aeration rates of 250 rpm and 1.0 vvm for 6 days) produced significant decolorization and organic removal efficacies of 34.29 ± 0.87% and 38.94 ± 0.63%, respectively. Bioremediation efficiency was dependent on bacterial growth, and the organic content and dissolved oxygen in the sample during cultivation were key factors in bacterial growth. The naturally selected bacterium could tolerate relatively high levels of organic content and work synergistically with other indigenous microorganisms found in the biogas plant effluent. Therefore, the bioremediation of biogas plant effluent using naturally selected P. putida can feasibly be applied in biogas power plants where sterilization is not necessary.

Chemical and biological combined treatment for sugarcane vinasse: selection of parameters and performance studies

Sugarcane vinasse has been reported as a high strength industrial wastewater that could cause severe environmental pollution due to its complex and bio-refractory compounds. Thus, the combined coagulation and sequencing batch biofilm reactor (SBBR) system was employed for the sugarcane vinasse treatment. This study aims to determine the recommended conditions of various parameters under coagulation and SBBR and investigate the effectiveness of combined processes. First, the approach of the coagulation process could achieve the maximum COD reduction and decolorization efficiencies of 79.0 ± 3.4% and 94.1 ± 1.9%, respectively, under the recommended conditions. Next, SBBR as an integrated biofilm reactor showed excellent synergistic biodegradability, removing 86.6 ± 4.3% COD concentration and 94.6 ± 3.8% color concentration at 3.0 g·COD/L of substrate loading concentration. The kinetic studies of SBBR revealed that the first-order kinetic model was the best fit for COD reduction efficiency. In contrast, the second-order kinetic model was the best fit for decolorization efficiency. The SBBR reaction was further investigated by ultraviolet-visible spectrophotometry (UV-Vis). In the combined processes, SBBR followed by the coagulation process (SBBR-CP) showed greater COD reduction and decolorization efficiencies (97.5 ± 0.3 and 99.4 ± 0.1%) when compared to the coagulation process followed by SBBR (CP-SBBR). This study demonstrated the removal performance and potential application of the combined sequential process to produce effluent that can be reused for bioethanol production and fertigation. This finding provides additional insight for developing effective vinasse treatment using combined chemical and biological processes.

Improving the efficiency of anaerobic digestion of Molasses alcohol wastewater using Cassava alcohol wastewater as a mixed feedstock

Cassava alcohol wastewater (CAW) was utilized as a mixed feedstock to explore whether the addition of CAW could improve the anaerobic digestion of Molasses alcohol wastewater (MAW). The result showed that the rate of removal of the soluble chemical oxygen demand in the M treatment mixed with CAW was 70.13 ± 0.16%, which was significantly higher than that of the C treatment (only MAW), which was 61.23 ± 0.36%. Co-digestion in the M treatment resulted in higher methane production, achieving 23.89% increase in methane yield compared to C treatment. The addition of CAW helps to alleviate the accumulation of volatile fatty acids (397.06 ± 141.82 mg·L^-1), enhance the stability of system and promote the establishment of stable and active microbial communities. Microbial community structure analysis indicated that hydrolytic bacteria such as Bacteroidetes, Firmicutes, and Proteobacteria, and acetoclastic methanogens, including Methanosaeta and Methanosarcina were more abundant in the co-digests.

Effect of genus Clostridium abundance on mixed-culture fermentation converting food waste into biohydrogen

This study examined the effect of various inocula on mixed-culture dark fermentative H₂ production from food waste. Heat-treated and frozen H₂-producing granular sludge (HPG) grown with monomeric sugars showed a higher H₂ yield, production rate, and acidogenic efficiency along with a shorter lag phase than heat-treated methanogenic sludge. Among three different methods of methanogenic sludge inoculation, inoculation after centrifugation showed better H₂ production performance. Propionic acid production and homoacetogenesis were regarded as major H₂-consuming pathways when methanogenic sludge was used, whereas only homoacetogenesis was found in HPG-inoculated fermentation. During fermentation, the abundance of Clostridium increased greater than 48-fold for methanogenic sludge and greater than 108-fold for HPG, respectively. The initial abundance of Clostridium showed a linear relationship with the H₂ production rate and lag-phase time. The use of inoculum with a high abundance of Clostridium is essential for H₂ production from food waste.

Detection and characterization of refractory organic and inorganic pollutants discharged in biomethanated distillery effluent and their phytotoxicity, cytotoxicity, and genotoxicity assessment using Phaseolus aureus L. and Allium cepa L

The color effluent discharged by alcohol distilleries comprises very high pollution loads due to the plethora of refractory chemicals even after anaerobic treatment and causing adverse effects to the environment. The present study aimed to examine the phytotoxic, cytotoxic, and genotoxic potential of the identified refractory organic and inorganic pollutants discharged in bio-methanated distillery effluent (BMDE). Physico-chemical analyses revealed that BMDE retains high BOD, COD, TDS along with heavy metals like Fe (572.64 mg L^-1), Mn (4.269 mg L^-1), Cd (1.631 mg L^-1), Zn (2.547 mg L^-1), Pb (1.262 mg L^-1), (Cr 1.257 mg L^-1), and Ni (0.781 mg L^-1) beyond the permissible limits for effluent discharge. GC-MS analysis revelaed the presence of hexadecanoic acid, TMS ester; octadecanoic acid, TMS ester; 2,3 bis[(TMS)oxy]propyl ester; stigmasterol TMS ether; β-sitosterol TMS ester; hexacosanoic acid; and tetradecanoic acid, TMS ester as major refractory organic pollutants, which are listed as potential endocrine disruptor chemicals (EDCs) as per USEPA. Furthermore, phytotoxicity assessment with Phaseolus aureus L. showed the toxic nature of BMDE as it inhibited various seedling growth parameters, seed germination, and suppression of α-amylase activity in seed germination experiment. Moreover, genotoxicity and cytotoxicity evaluation of the discharged BMDE evidenced in root-tip meristematic cells of Allium cepa L. where chromosomal aberration such as disturbed metaphase, c-mitosis, laggard chromosomes, sticky chromosomes, prolonged prophase, polyploid cells, and apoptotic bodies etc. were observed. Thus, this study's results suggested that BMDE discharged without adequate treatment poses potential risk to environment and may cause a variety of serious health threats in living beings upon exposure.

Removal of refractory organics in wastewater by coagulation/flocculation with green chlorine-free coagulants

Coagulation/flocculation is considered an economical and practical technology to remove refractory organic matter from wastewater. Coagulants containing chlorine may release chloride ions into water, thereby resulting in corrosion. A green chlorine-free coagulant of polyaluminum ferric silicate (PSAF) was synthesized to treat non-oily (e.g., humus wastewater) and oily refractory wastewaters (e.g., lubricating oil wastewater). Results showed that the highest removal efficiency of humus substances in non-oily wastewater achieved 96.0% at pH 7.0 using PSAF alone. When treating oily wastewater, the dosage and addition sequence of PAMALAM significantly affected the coagulation performance. The removal efficiencies of turbidity, chemical oxygen demand, and total nitrogen were increased by 0.3, 1.8, and 5.9 folds, respectively, with the optimal adding sequence of PSAF +0.08% PAMALAM. More fulvic acid-like substances can be removed during this process. The analysis of zeta potential and floc properties revealed that charge neutralization, sweep, and adsorption/entrapment mechanisms existed during the single PSAF coagulation process, and PAMALAM mainly improved the adsorption, bridging, and sweep function.

Current trends for distillery wastewater management and its emerging applications for sustainable environment

Ethanol distillation generates a huge volume of unwanted chemical liquid known as distillery wastewater. Distillery wastewater is acidic, dark brown having high biological oxygen demand, chemical oxygen demand, contains various salt contents, and heavy metals. Inadequate and indiscriminate disposal of distillery wastewater deteriorates the quality of the soil, water, and ultimately groundwater. Its direct exposure via food web shows toxic, carcinogenic, and mutagenic effects on aquatic-terrestrial organisms including humans. So, there is an urgent need for its proper management. For this purpose, a group of researchers applied distillery wastewater for fertigation while others focused on its physico-chemical, biological treatment approaches. But until now no cutting-edge technology has been proposed for its effective management. So, it becomes imperative to comprehend its toxicity, treatment methods, and implication for environmental sustainability. This paper reviews the last decade's research data on advanced physico-chemical, biological, and combined (physico-chemical and biological) methods to treat distillery wastewater and its reuse aspects. Finally, it revealed that the combined methods along with the production of value-added products are one of the best options for distillery wastewater management.

Fungal biodegradation and multi-level toxicity assessment of vinasse from distillation of winemaking by-products

The wastewaters from distilleries of winemaking by-products, a scarcely studied type of vinasse, were treated by white-rot fungal strains from species Irpex lacteus, Ganoderma resinaceum, Trametes versicolor, Phlebia rufa and Bjerkandera adusta. The main objectives of this study were to evaluate fungal performance during vinasse biodegradation, their enzyme patterns and ecotoxicity evolution throughout treatment. Despite all strains were able to promote strong (>80%) dephenolization and reduction of total organic carbon (TOC), P. rufa was less affected by vinasse toxicity and exhibit better decolorization. In batch cultures at 28 °C and pH 4.0, the first phase of P. rufa biodegradation kinetics was characterized by strong metabolic activity with simultaneous depletion of TOC, phenolics and sugars. The main events of second phase are the increase of peroxidases production after the peak of laccase activity, and strong color removal. At the end of treatment, it was observed highly significant (p < 0.001) abatement of pollution parameters (83-100% removal). Since water reclamation and reuse for e.g. crop irrigation is a priority issue, vinasse ecotoxicity was assessed with bioindicators representing three different phylogenetic and trophic levels: a marine bacterium (Aliivibrio fischeri), a freshwater microcrustacean (Daphnia magna) and a dicotyledonous macrophyte (Lepidium sativum). It was observed significant (p < 0.05) reduction of initial vinasse toxicity, as evaluated by these bioindicators, deserving special mention an almost complete phytotoxicity elimination.

Comparison of coagulative colloidal microbubbles with monomeric and polymeric inorganic coagulants for tertiary treatment of distillery wastewater

The flotation using coagulative colloidal gas aphrons (CCGAs) is of great potential in effectively removing the recalcitrant dissolved organic matter (DOM) and colorants from the bio-chemically treated cassava distillery wastewater. As bubble modifier, the monomeric and polymeric inorganic coagulants need to be studied considering their distinct influence on the surfactant/coagulant complex, the properties of colloidal aphrons as well as the process performance and mechanisms. Such studies help to create robust CCGAs with high flotation potential. In this work, the commonly-used monomeric and polymeric Al(III)- and Fe(III)-coagulants were combined with the cationic surfactant - cetyl trimethylammonium bromide (CTAB) to generate CCGAs. The CCGAs functionalized with Al(III)-coagulants (both monomeric and polymeric ones) were featured as small bubble size, strong stability and high air content. Particularly, the monomeric Al(III)-coagulant (AlCl₃ in this work) resulted in low surface tension and high foamability when being mixed with CTAB in the bubble generation solution. Those CCGAs achieved high removal efficiencies of DOM and colorants at low coagulant concentrations. The molecular weight of DOM in effluent was well controlled below 1 kDa by CCGAs. For the flocs obtained from CCGA-flotation, the characteristic Raman band of DOM and colorants showed the layer-by-layer variation of Raman intensity which decreased from the outer layer to the center. In contrast with the conventional coagulation-flotation, the reduction of coagulant dosage by CCGAs was 67% (AlCl₃), 25% (polyaluminum chloride), 60% (Fe₂(SO₄)₃) and 40% (polyferric sulfate). The sludge production could then be largely reduced, and meanwhile, the retention time was shortened by 9.5 min.

Oxygen-rich bismuth oxychloride Bi12O17Cl2 materials: construction, characterization, and sonocatalytic degradation performance

In this study, a series of oxygen-rich bismuth oxychloride Bi₁₂O₁₇Cl₂ samples were prepared at different calcination temperatures and characterized by X-ray diffraction patterns, UV-Vis diffuse reflectance spectra, scanning electron microscope, X-ray energy dispersion spectroscope, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The calcination temperature greatly affected microstructures and band structures of as-prepared samples, further influencing sonocatalytic degradation efficiencies over dye Rhodamine B. Some dependant factors such as ultrasonic power, catalyst dosage, pH value, initial concentration of Rhodamine B, and reaction temperature were systematically investigated and the robust sample Bi₁₂O₁₇Cl₂-550 with a favorable microstructure and band structure provided the best sonocatalytic removal efficiency around 90% at the optimal condition. Based upon reactive species entrapping and hydroxyl radical detection experiments, a primary sonocatalysis mechanism was eventually speculated.

Three-Dimensional Excitation and Emission Fluorescence-Based Method for Evaluation of Maillard Reaction Products in Food Waste Treatment

Hydrothermal treatment (HT) of food waste (FW) can form Maillard reaction products (MRPs), the biorefractory organic matter due to the occurrence of Maillard reaction. However, the integrating qualitative and quantitative approach to assess MRPs is scarce. The goal of this study was to develop a method to characterize and quantify MRPs created by HT of FW. MRPs were identified by molecular weight fractionation, indirect spectrometric indicators, and three-dimensional excitation-emission fluorescence (3DEEM) analysis. The 3DEEM method combined with fluorescence regional integration (FRI) and parallel factor (PARAFAC) analyses was able to differentiate clearly between MRPs and other dissolved organic compounds compared to other approaches. The volume of fluorescence Φ from FRI and maximum fluorescence intensity Fmax from PARAFAC were found to be suitable quantitative parameters for determination of MRPs in the hydrothermal FW system. These two parameters were validated with samples from hydrothermal FW under various operating temperatures and pH.

Using Fe(III)-coagulant-modified colloidal gas aphrons to remove bio-recalcitrant dissolved organic matter and colorants from cassava distillery wastewater

Efficient removal of bio-recalcitrant dissolved organic matter (DOM) and colorants is essential for discharging or reusing the distillery wastewater. The present work adopted a novel microbubble system - Fe(III)-coagulant-modified colloidal gas aphrons (CGAs) in flotation as tertiary treatment of the bio-chemically treated cassava distillery wastewater. Approximately 93% of bio-recalcitrant color and around 79% of dissolved organic carbon (DOC) were removed at the initial pH of 9.0 and 7.1, individually. The modified CGAs exhibited strong ability of complexation and electrostatic attraction of the polyanions of DOM and colorants. But the 1-10 kDa DOM was found to be resistant to the CGA capture. Compared with directly dosing coagulant, the Fe(III)-coagulant-modified CGAs consumed ∼47% and ∼21% less coagulant to achieve the optimum decoloration efficiency and DOC removal, respectively. In the flotation with Fe(III)-coagulant-modified CGAs, the coagulant-dosing system could be omitted while the coagulant utilization was improved.

Enhanced removal of bio-refractory dissolved organic matter from cassava distillery wastewater by powdered activated carbon-ballasted coagulation: Detailed study of separation characteristics and mechanisms

Efficient removal of bio-refractory dissolved organic matter (DOM) and colorants is essential for discharging or reusing the distillery wastewater. An important part of recalcitrant DOM still exists in the effluent of regular coagulation though the ferric coagulant has been found to be effective in decoloration. The present work adopted powdered activated carbon (PAC) as ballasting agent to achieve robust separation effect and efficiency of bio-refractory DOM from the bio-chemically treated cassava distillery wastewater (BTDWW). More than 90% of DOC could be removed at the PAC and Fe(III)-coagulant dosage of 1.40 g/L and 0.84 g/L as Fe when the BTDWW was neutral. PAC should be dosed before coagulant in order to mix well with the DOM in the BTDWW. The analyses of DOM in effluent reveal that PAC facilitated the removal of lignin breakdown products which could not be well eliminated by regular coagulation; the removal of DOM with MW < 5 kDa was mostly enhanced. The characteristics of flocs demonstrate that PAC reinforced the interaction between Fe(III) species and DOM by providing more reaction sites. The sedimentation could be completed within the initial 5 min, and the highest settling velocity was almost 8 times higher than that of the only Fe(III)-involved flocs. The large size and favorable robustness of PAC-involved flocs enabled decent sedimentation even though their stretched structure might not be desirable in regular coagulation. The PAC-ballasted coagulation is recommended as tertiary treatment of BTDWW considering its high efficiency and sound economic feasibility.

Insight into the characteristics, removal, and toxicity of effluent organic matter from a pharmaceutical wastewater treatment plant during catalytic ozonation

Changes in the characteristics, removal efficiency, and toxicity of pharmaceutical effluent organic matter (EfOM) after catalytic ozonation were investigated in this study. After a 90-min treatment with a catalytic ozonation process (COP) in the presence of MnO₂ ceramsite, the total organic carbon (TOC), UV₂₅₄, colority, protein, and humic acid removal rates were 13.24%, 60.83%, 85.42%, 29.36% and 74.19%, respectively. The polysaccharide content increased by 12.73 mg/L during the COP for reaction times between 0 and ~50 min and decreased by 6.97 mg/L between 50 and ~90 min. Furthermore, 64.44% of the total colority was detected in the hydrophobic organic matter (HOM) fraction, and after the COP, and 88.69% of the colority in the HOM was eliminated. Meanwhile, only 59.18% of the colority in the hydrophilic organic matter (HIM) fraction was removed. GC-MS analysis showed that 38 organic pollutant species were completely removed, 8 were partially removed, and 7 were generated. After 90 min of COP treatment, the pharmaceutical EfOM toxicity was effectively reduced based on the higher incubation and lower mortality rates.

Environmental pollution and health hazards from distillery wastewater and treatment approaches to combat the environmental threats: A review

Distillery industries are the key contributor to the world's economy, but these are also one of the major sources of environmental pollution due to the discharge of a huge volume of dark colored wastewater. This dark colored wastewater contains very high biological oxygen demand, chemical oxygen demand, total solids, sulfate, phosphate, phenolics and various toxic metals. Distillery wastewater also contains a mixture of organic and inorganic pollutants such as melanoidins, di-n-octyl phthalate, di-butyl phthalate, benzenepropanoic acid and 2-hydroxysocaproic acid and toxic metals, which are well reported as genotoxic, carcinogenic, mutagenic and endocrine disrupting in nature. In aquatic resources, it causes serious environmental problems by reducing the penetration power of sunlight, photosynthetic activities and dissolved oxygen content. On other hand, in agricultural land, it causes inhibition of seed germination and depletion of vegetation by reducing the soil alkalinity and manganese availability, if discharged without adequate treatment. Thus, this review article provides a comprehensive knowledge on the distillery wastewater pollutants, various techniques used for their analysis as well as its toxicological effects on environments, human and animal health. In addition, various physico-chemicals, biological as well as emerging treatment methods have been also discussed for the protection of environment, human and animal health.