Anaerobic digestion of recalcitrant textile dyeing sludge with alternative pretreatment strategies

Strategies for energy conversion from sludge to methane through pretreatment coupled anaerobic digestion: Potential energy loss or gain

Anaerobic digestion (AD) of wasted activated sludge from wastewater plants is recognized as an effective method to reclaim energy in the form of methane. AD performance has been enhanced by coupling various pretreatments that impact energy conversion from sludge. This paper mainly reviewed the development of pretreatments based on different technologies reported in recent years and evaluated their energy benefit. Significant increases in methane yield are generally obtained in AD with pretreatments demanding energy input, including thermal- and ultrasound-based methods. However, these energy-intense pretreatments usually gained negative energy benefit that the increase in methane yield consumed extra energy input. The unbalanced relationship counts against the goal of energy reclamation from sludge. Combined pretreatment consisting of multiple technologies normally outcompetes the single pretreatment, and the combination of energy-intense methods and chemicals potentially reduces energy input and simultaneously ensure high methane yield. For determining whether the energy reclamation from sludge via AD contribute to mitigating global warming, integrating greenhouse gas emission into the evaluation system of pretreated AD is further warranted.

Comprehensive Meta-Analysis of Pathways to Increase Biogas Production in the Textile Industry

The textile industry is one of the largest environmental polluters in the world. Although waste management via anaerobic digestion (AD) is a sustainable strategy to transform waste into clean energy and water recovery, the efficiency of the AD process is reduced by the presence of recalcitrant materials, chemicals, and toxic contents. This study aims to investigate the performance of several chemical, physical, and biological pretreatments applied to improve the biodegradability of textile waste. We performed a meta-analysis with 117 data extracted from 13 published articles that evaluated the efficiency of pretreatments applied to textile waste prior to AD to increase biogas production measured as methane (CH4) yield. Even though the majority of the studies have focused on the effect of chemical and physical pretreatments, our results showed that the application of biological pretreatments are more efficient and eco-friendlier. Biological pretreatments can increase CH4 yield by up to 360% with lower environmental risk and lower operating costs, while producing clean energy and a cleaner waste stream. Biological pretreatments also avoid the addition of chemicals and favor the reuse of textile wastewater, decreasing the current demand for clean water and increasing resource circularity in the textile industry.

Genotoxicity assessment of textile waste contaminated soil and characterization of textile dye degradation by a novel indigenous bacterium Ochrobactrum intermedium BS39

The harmful effects of textile wastewater irrigation practices on the crop productivity and soil nutrient levels are primarily related with the accumulation of recalcitrant azo dyes in the soil. Therefore, toxicity assessment of the textile waste contaminated soil along with the development of a powerful soil bioremediation strategy is a challenging task for the researchers. Present study aimed to evaluate potential toxicity of the textile wastewater irrigated soil collected from Panki industrial site 5, Kanpur, India employing Ames Salmonella/mammalian microsome test, Escherichia coli DNA repair defective mutation assay and Allium cepa chromosomal aberration assay. The results of the Ames test and DNA repair defective mutation test showed that all the organic extracts of the contaminated soil samples induced different degrees of DNA damage, indicating the existence of mutagenicity and genotoxicity. Additionally, in A. cepa root cells, the contaminated soil altered mitotic index and caused chromosomal abnormalities. Results of the study demonstrated potential health risks related with the irrigation of textile wastewater. Keeping in view of the above scenario, the study led to the isolation and characterization of a novel indigenous bacterium capable of tolerating very high concentration of reactive black 5 dye (500 μg-mL^-1) and salt (20 gL^-1) with concurrently high efficiency of the dye degradation i.e., 93% decolorization at temperature of 37 °C and in pH range of 5-9. Based on the 16S rRNA gene sequencing, the bacterium was identified as Ochrobactrum intermedium. Further, dye degradation products were identified as sodium-2-hydrosulfonylethyl sulphate and sodium-3-aminonaphthalene-2-sulfonate by Gas Chromatography-Mass spectrometry; and this isolate can be exploited for bioremediation of textile waste contaminated soils.

Anaerobic co-digestion of textile dyeing sludge: Digestion efficiency and heavy metal stability

Anaerobic co-digestion (AcoD) has become an important mean for the stabilization and recycling of textile dyeing sludge (TDS). Using the soybean okara byproduct (SOB) as a co-digestion substrate, the effects on AcoD performance and heavy metal stability were studied. The results indicated that the optimal mixing ratio was 1:1 (calculated by total sloid). Under this condition, the SCOD removal efficiency was 64% (that of TDS alone and SOB alone were 47% and 48%, respectively) and the cumulative methane production field was 503 L CH₄/kg VS (that of TDS alone and SOB alone were 435 L CH₄/kg VS and 408 L CH₄/kg VS, respectively). At the same time, the addition of SOB could also enhance the stability of heavy metals (Zn, Cu, Cr and Ni) in TDS. Remarkably, that could increase the steady state content nickel from 47.98% to 57.21%, while anaerobic digestion of TDS caused no increase but a decrease (only 42.13%). According to the risk assessment code analyses, the AcoD of TDS by SOB can significantly reduce the ecotoxicity risk caused by Ni, Zn and Cr.

Biodegradation of azo dye-containing wastewater by activated sludge: a critical review

The effluent from the textile industry is a complex mixture of recalcitrant molecules that can harm the environment and human health. Biological treatments are usually applied for this wastewater, particularly activated sludge, due to its high efficiency, and low implementation and operation costs. However, the activated sludge microbiome is rarely well-known. In general, activated sludges are composed of Acidobacteria, Bacillus, Clostridium, Pseudomonas, Proteobacteria, and Streptococcus, in which Bacillus and Pseudomonas are highlighted for bacterial dye degradation. Consequently, the process is not carried out under optimum conditions (treatment yield). Therefore, this review aims to contextualize the potential environmental impacts of azo dye-containing wastewater from the textile industry, including toxicity, activated sludge microbiome identification, in particular using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as a novel, rapid and accurate strategy for the identification of activated sludge microbiome (potential to enhance treatment yield).

A comprehensive review on the integration of advanced oxidation processes with biodegradation for the treatment of textile wastewater containing azo dyes

The threat of dye contamination has achieved an unsurpassed abnormal state lately due to their massive consumption in several enterprises including textile, leather, cosmetic, plastic, and paper industries. This review focuses on the integrations of various advanced oxidation processes (AOPs), such as Fenton, photocatalysis, and ozonation, with biodegradation for the treatment of textile azo dyes. Such integrations have been explored lately by researchers to bring down the processing cost and improve the degree of mineralization of the treated dyeing wastewater. The review refers to the basic mechanisms, the influence of various process parameters, outcomes of recent works, and future research directions. All the three AOPs, independently, demonstrated substantial color reduction of 54–100%. The ozonation process, stand-alone, showed the most efficient decolorization (of 88–100%) consistently in all reviewed research works. In contrast, all three AOPs independently offered varied and inadequate COD reduction in the range of 16–80%. The AOPs, after getting integrated with biodegradation, yielded an additional reduction (of 11–70%) in the COD-levels and (of 16–80%) in the TOC-levels. Further, the integration of AOPs with biodegradation has potential to significantly reduce the treatment costs. The review suggests further research efforts in the direction of sequencing chemical and biological routes such that their synergistic utilization yield complete detoxification of the textile azo dyes economically at large-scale.

Biochar as an Eco-Friendly and Economical Adsorbent for the Removal of Colorants (Dyes) from Aqueous Environment: A Review

Dyes (colorants) are used in many industrial applications, and effluents of several industries contain toxic dyes. Dyes exhibit toxicity to humans, aquatic organisms, and the environment. Therefore, dyes containing wastewater must be properly treated before discharging to the surrounding water bodies. Among several water treatment technologies, adsorption is the most preferred technique to sequester dyes from water bodies. Many studies have reported the removal of dyes from wastewater using biochar produced from different biomass, e.g., algae and plant biomass, forest, and domestic residues, animal waste, sewage sludge, etc. The aim of this review is to provide an overview of the application of biochar as an eco-friendly and economical adsorbent to remove toxic colorants (dyes) from the aqueous environment. This review highlights the routes of biochar production, such as hydrothermal carbonization, pyrolysis, and hydrothermal liquefaction. Biochar as an adsorbent possesses numerous advantages, such as being eco-friendly, low-cost, and easy to use; various precursors are available in abundance to be converted into biochar, it also has recyclability potential and higher adsorption capacity than other conventional adsorbents. From the literature review, it is clear that biochar is a vital candidate for removal of dyes from wastewater with adsorption capacity of above 80%.

Decolorization of azo and anthraquinone dyes by crude laccase produced by Lentinus crinitus in solid state cultivation

White-rot basidiomycetes such as Lentinus crinitus produce laccases with potential use in dye biodegradation. However, high productivity and enzymes with specific properties are required in order to make viable laccase production. We aimed to produce laccase from Lentinus crinitus grown in sugarcane bagasse for dye decolorization. Solid state cultivation medium had sugarcane bagasse added with a nutrient solution of 10 g/L glucose, 1 g/L KH₂PO₄, 0.5 g/L MgSO₄, 0.001 g/L FeSO₄, 0.01 g/L ZnSO₄, and 0.01 g/L MnSO₄. The addition of different nitrogen sources (peptone, urea, or peptone plus urea) and different nitrogen concentrations (0, 0.4, 0.6, 0.8, 1.0, and 1.2 g/L) were evaluated. Enzymatic extract was used in the decolorization of azo dyes, reactive blue 220 (RB220) and reactive black 5 (RB5), and anthraquinone dye, Remazol brilliant blue R (RBBR). The greatest laccase activity (4800 U/g dry mass) occurred when the peptone and urea mixture was added to the solid state cultivation medium. When the nitrogen concentration was 1 g/L, the laccase activity increased to 6555 U/g dry mass. The laccase activity peak occurred on the 10th day, and the maximum decolorization within 24 h was observed with enzymatic extracts obtained on different cultivation days, i.e., 6th day for RB220, 10th day for RB5, and 9th day for RBBR. Manganese and lignin peroxidases were not produced when nitrogen was added to the cultivation medium. The crude enzymatic extract was more effective in the decolorization of azo dyes (RB220 and RB5), more than 90% of decolorization, than anthraquinone dye with 77% decolorization.

Carbon and nitrogen metabolic pathways and interaction of cold-resistant heterotrophic nitrifying bacteria under aerobic and anaerobic conditions

In this study, both the carbon and nitrogen metabolisms of two heterotrophic nitrification bacteria were investigated under aerobic and anaerobic conditions at 2 °C. Similar catabolism and anabolism trends were observed for the two bacteria in stable experimental systems under aerobic and anaerobic conditions. Based on the nitrogen and carbon balance analysis and adenosine triphosphate (ATP) calculation, we proposed the following metabolic pathways: i) aerobic: except for microbial assimilation, the carbon and nitrogen sources were removed through respiration and nitrification, which provided energy for cell synthesis; and ii) anaerobic: the nitrification process almost stopped and most of the carbon sources decomposed into inorganic carbon, which dissolved in the medium. Based on our proposed metabolic pathways, we speculated that the nitrifying process almost stopped under anaerobic conditions and the nitrification bacteria would degrade more carbon contaminants to produce energy and maintain the cell growth. Furthermore, these bacteria may decompose the non-readily biodegradable carbon through anaerobic degradation. To verify these hypotheses, experiments with two types of synthetic wastewater were conducted: i) synthetic wastewater rich in carbon and poor in nitrogen, and higher carbon removal efficiencies of strain J and strain P (∼25%) were obtained under anaerobic conditions compared with aerobic conditions (∼19%); and ii) synthetic wastewater with recalcitrant carbon sources, and carbon removal efficiencies under anaerobic conditions were higher than those under aerobic conditions. The results of the synthetic wastewater experiments were consistent with the hypotheses and thus validated the metabolic pathways proposed for carbon and nitrogen.

Performances of Pichia kudriavzevii in decolorization, biodegradation, and detoxification of C.I. Basic Blue 41 under optimized cultural conditions

The aim of this study was to evaluate the performances of Pichia kudriavzevii CR-Y103 yeast strain for the decolorization, biodegradation, and detoxification of cationic dye C.I. Basic Blue 41, a toxic compound to aquatic life with long-lasting effects. Under optimized cultural conditions (10.0-g L^-1 glucose, 0.2-g L^-1 yeast extract, and 1.0-g L^-1 (NH₄)₂SO₄), the yeast strain was able to decolorize 97.86% of BB41 (50 mg L^-1) at pH 6 within 4 h of incubation at 30 °C under shaken conditions (12,238.00-μg h^-1 average decolorization rate) and 100% within 12 h. The UV-Vis spectral analysis, high-performance liquid chromatography (HPLC), and Fourier-transform infrared spectroscopy (FTIR) analysis confirmed the complete decolorization and degradation of the BB41 dye by P. kudriavzevii CR-Y103. Also, other seven yeast strains, isolated from soil, as P. kudriavzevii (CR-Y108, CR-Y119, and CR-Y112), Candida tropicalis CR-Y128, Cyberlindnera saturnus CR-Y125, and Candida solani CR-Y124 have shown a promising decolorizing potential of azo-dye BB41 (99.89-76.09% decolorization). Phytotoxicity, cytotoxicity, and genotoxicity assays on Trifolium pratense and Triticum aestivum seedlings confirmed the high toxicity of BB41 dye (500 ppm), with inhibition on germination rate (%), root and shoot elongation, decreasing of mitoxic index value (with 34.03% in T. pratense and 40.25% in T. aestivum), and increasing the frequency of chromosomal aberrations (6.87 times in T. pratense and 6.25 times in T. aestivum), compared to control. The same biomarkers indicated the nontoxic nature of the BB41 degraded metabolite (500 ppm) obtained after P. kudriavzevii CR-Y103 treatment. Moreover, the healthy monkey kidney cells (Vero cells) had a low sensitivity to BB41 biodegraded products (250 μg mL^-1) (MTT cell viability assay) and revealed minor DNA damage (comet assay) compared to BB41 dye treatment. These findings show that P. kudriavzevii could be used in eco-friendly bioremediation technologies, applicable for reducing the toxicity of basic azo-dyes containing wastewaters.

Degradation of organophosphate esters in sewage sludge: Effects of aerobic/anaerobic treatments and bacterial community compositions

In this study, the degradation of organophosphate esters (OPEs) in sewage sludge with aerobic composting and anaerobic digestion was investigated. The total concentrations of six OPEs (ΣOPEs) in the whole treatment process reduced in the order of anaerobic digestion combined with pig manure (T3) > aerobic composting combined with pig manure (T1) > aerobic composting (T2) > anaerobic digestion (T4). The addition of pig manure significantly enhanced the removal rate of OPEs in both aerobic and anaerobic treatments. The abundance and diversity of bacterial community reduced after the treatment process. Shannon index, principal component analysis, network analysis, and heat map further confirmed the variation of bacterial community compositions among different treatments. Five genera (i.e., Flavobacterium, Bacillus, Alcaligene, Pseudomonas, and Bacillus megaterium) might be responsible for the degradation of OPE compounds in sewage sludge.

Recent advancements in bioremediation of dye: Current status and challenges

The rampant industrialization and unchecked growth of modern textile production facilities coupled with the lack of proper treatment facilities have proliferated the discharge of effluents enriched with toxic, baleful, and carcinogenic pollutants including dyes, heavy metals, volatile organic compounds, odorants, and other hazardous materials. Therefore, the development of cost-effective and efficient control measures against such pollution is imperative to safeguard ecosystems and natural resources. In this regard, recent advances in biotechnology and microbiology have propelled bioremediation as a prospective alternative to traditional treatment methods. This review was organized to address bioremediation as a practical option for the treatment of dyes by evaluating its performance and typical attributes. It further highlights the current hurdles and future prospects for the abatement of dyes via biotechnology-based remediation techniques.

Understanding azo dye anaerobic bio-decolorization with artificial redox mediator supplement: Considering the methane production

Artificial redox mediators (ARM) have been proven to accelerate the azo dye anaerobic bio-reduction (ADAB) but the mechanisms involved are still unclear. Previous studies do seldom focus on the production of methane during the ADAB, particularly if supplemented with ARM. Our studies revealed that the supplement of ARM could significantly accelerate the decolorization rate, recover the inhibited methanogenesis and decrease extracellular polymeric substance secretion in an ADAB system. Supplement of an ARM only enhanced the pre-existing metabolic pathway of the ADAB system. Significant differences in metabolic pathway and microbial community were found between traditional methanogenic system and ADAB system by high-throughput sequencing technique. The ADAB system performed an "over-requirement for electron donor" phenomenon and the requirement amount can be altered by regulating ARM dosage. Response surface methodology was then successfully employed to optimize the dosage of ARM and possible additional electron donor required for ADAB under different conditions.

Effect of low temperature of thermal pretreatment on anaerobic digestion of textile dyeing sludge

The minimization and methane production of textile dyeing sludge (TDS) can be simultaneously attained via anaerobic digestion (AD). However, the possible toxicity and complex recalcitrant organic matters involved in limited the hydrolysis of TDS. Therefore, the low-temperature of thermal pretreatment (LTTP) lasting for 1h at temperatures from 60 to 100°C was employed to accelerate the hydrolysis and subsequent methane generation of TDS. The results showed that LTTP with temperatures higher than 70°C obviously improve the AD performance of TDS. Highest accumulative methane production was achieved for 100°C pretreated TDS and from thermal analysis point of view it was due to the disintegration of some recalcitrant macromolecules in TDS. Nevertheless, 90°C pretreated TDS did not perform favorable methane yield as expected, attributing to the inhibited acetogenesis as well as the hindered methanogenesis which was simultaneously competed by dye reducer for electrons.