A. Naresh Kumar

Integrating sequencing batch reactor with bio-electrochemical treatment for augmenting remediation efficiency of complex petrochemical wastewater

The present study evaluates the sequential integration of two advanced biological treatment methods viz., sequencing batch reactor (SBR) and bioelectrochemical treatment systems (BET) for the treatment of real-field petrochemical wastewater (PCW). Initially two SBR reactors were operated in aerobic (SBR(Ae)) and anoxic (SBR(Ax)) microenvironments with an organic loading rate (OLR) of 9.68 kg COD/m(3)-day. Relatively, SBR(Ax) showed higher substrate degradation (3.34 kg COD/m(3)-day) compared to SBR(Ae) (2.9 kg COD/m(3)-day). To further improve treatment efficiency, the effluents from SBR process were fed to BET reactors. BET(Ax) depicted higher SDR (1.92 kg COD/m(3)-day) with simultaneous power generation (17.12 mW/m(2)) followed by BET(Ae) (1.80 kg COD/m(3)-day; 14.25 mW/m(2)). Integrating both the processes documented significant improvement in COD removal efficiency due to the flexibility of combining multiple microenvironments sequentially. Results were supported with GC-MS and FTIR, which confirmed the increment in biodegradability of wastewater.

Regulation of acidogenic metabolism towards enhanced short chain fatty acid biosynthesis from waste: metagenomic profiling

Short chain carboxylic (volatile fatty) acid (VFA) production in mixed microbiomes is majorly limited by the prevalence of methanogenic bacteria and the availability of substrate from waste to the biocatalyst during the fermentation process. To enhance the VFA production from food waste, the present study evaluates a strategy for selective enrichment of the biocatalyst by exposing it to acid-shock, followed by operation under alkaline conditions (pH 10). A comprehensive system based analysis was carried out during the bio-based platform chemical synthesis from waste, in conjugation with microbial profiling and bio-electrochemical analysis. After the selective enrichment of the biocatalyst, enhanced VFA synthesis was conducted with pretreated biocatalyst (PT; 11.1 g L−1) and compared with untreated parent biocatalyst (UT; 6.1 g L−​1). In both systems biohydrogen was the co-product. Variations in the VFA profiles were documented with respect to the biocatalyst used, which influenced the degree of acidification (DOA – PT: 37% and UT: 11%). A high fraction of acetic acid (6.9 g L−1) was observed, followed by butyric acid (2.6 g L−1) and propionic acid (1.3 g L−1) in PT operation, contrary to the control system (acetic acid, 3.9 g L−1, butyric acid, 1.6 g L−1; propionic acid, 0.9 g L−1). Specifically, the PT system showed the biosynthesis of iso-valeric acid: 0.15 g L−1 (C5) and caproic acid: 1.9 g L−1 (C6), which indicates the possibility for chain-elongation through the selective enrichment of the microbial community. The PT system showed Epeak at −0.415 V on the cyclic voltammogram, which corresponds to the involvement of the redox couple, H+/H2, correlating with the enhanced acidogenic process, unlike UT. Tailoring of the parent inoculum (pretreatment) resulted in the enrichment and enhancement of the capabilities of the biocatalyst in secreting the redox mediators, which were not detected in the UT system. Acidogenic firmicutes (spore formers) and fatty acid producing bacteroides were enriched in the PT system along with saccharolytic and proteolytic bacteria (Bacillus cellulosilyticus (alkalophile), Soehngenia saccharolytica, etc.). The presence of Clostridium autoethanogenum and Propionibacterium freudenreichii in the PT system supports effective utilization of complex carbohydrates, facilitating acidification.

Retrofitting hetrotrophically cultivated algae biomass as pyrolytic feedstock for biogas, bio-char and bio-oil production encompassing biorefinery.

Algal biomass grown hetrotrophically in domestic wastewater was evaluated as pyrolytic feedstock for harnessing biogas, bio-oil and bio-char. Freshly harvested microalgae (MA) and lipid extracted microalgae (LEMA) were pyrolysed in packed bed reactor in the presence and absence of sand as additive. MA (without sand additive) depicted higher biogas (420 ml/g; 800 °C; 3 h) and bio-oil (0.70 ml/g; 500 °C; 3 h). Sand addition enhanced biogas production (210 ml/g; 600 °C; 2 h) in LEMA operation. The composition of bio-gas and bio-oil was found to depend on the nature of feedstock as well as the process conditions viz., pyrolytic-temperature, retention time and presence of additive. Sand additive improved the H2 composition while pyrolytic temperature increment caused a decline in CO2 fraction. Bio-char productivity increased with increasing temperature specifically with LEMA. Integration of thermo-chemical process with microalgae cultivation showed to yield multiple resources and accounts for environmental sustainability in the bio-refinery framework.

Biomineralization of azo dye bearing wastewater in periodic discontinuous batch reactor: Effect of microaerophilic conditions on treatment efficiency

The present study illustrates the influence of microaerophilic condition on periodic discontinuous batch reactor (PDBR) operation in treating azo dye containing wastewater. The process performance was evaluated with the function of various dye load operations (50-750 mg/l) by keeping the organic load (1.6 kg COD/m(3)-day) constant. Initially, lower dye operation (50mg dye/l) resulted in higher dye [45 mg dye/l (90%)] and COD [SDR: 1.29 kg COD/m(3)-day (92%)] removal efficiencies. Higher dye load operation (750 mg dye/l) also showed non-inhibitory performance with respect to dye [600 mg dye/l (80%)] and COD [1.25 kg COD/m(3)-day (80%)] removal efficiencies. Increment in dye load showed increment in azo reductase and dehydrogenase activities (39.6 U; 4.96 μg/ml; 750 mg/l). UV-Vis spectroscopy (200-800 nm), FTIR and (1)H NMR studies revealed the disappearance of azo bond (-NN-). First derivative cyclic voltammogram supported the involvement of various membrane bound redox shuttlers, viz., cytochrome-C, cytochrome-bc1 and flavoproteins (FAD (H)).

Relative performance of biofilm configuration over suspended growth operation on azo dye based wastewater treatment in periodic discontinuous batch mode operation

Functional role of biofilm and suspended growth bioreactor configurations in response to the treatment of azo-dye (C.I. Acid Black 10B) bearing wastewater was evaluated in periodic discontinuous batch mode operation at varying dye concentrations. The biofilm system depicted higher dye removal efficiency (93.14%) compared to suspended mode (84.29%) at 350 mg dye/l operation. Both the reactor configurations did not show much process inhibition at higher dye loads studied. Azo reductase and dehydrogenase enzyme activities showed significant variation indicating the different metabolic capabilities of the native-microflora, stable proton shuttling between metabolic intermediates and differences in the delivery of reducing powers from the substrate metabolism towards dye removal. Voltammograms visualized marked variations in electron discharge properties with the function of reactor configuration, time intervals and dye load. Higher redox catalytic currents, lower Tafel slopes and polarization resistance showed good correlation with enzyme activities and dye removal.

Food waste biorefinery: Sustainable strategy for circular bioeconomy

Enormous quantity of food waste (FW) is becoming a global concern. To address this persistent problem, sustainable interventions with green technologies are essential. FW can be used as potential feedstock in biological processes for the generation of various biobased products along with its remediation. Enabling bioprocesses like acidogenesis, fermentation, methanogenesis, solventogenesis, photosynthesis, oleaginous process, bio-electrogenesis, etc., that yields various products like biofuels, platform chemicals, bioelectricity, biomaterial, biofertilizers, animal feed, etc can be utilized for FW valorisation. Integrating these bioprocesses further enhances the process efficiency and resource recovery sustainably. Adapting biorefinery strategy with integrated approach can lead to the development of circular bioeconomy. The present review highlights the various enabling bioprocesses that can be employed for the generation of energy and various commodity chemicals in an integrated approach addressing sustainability. The waste biorefinery approach for FW needs optimization of the cascade of the individual bioprocesses for the transformation of linear economy to circular bioeconomy.

Waste derived bioeconomy in India: A perspective

Environmental and climatic change issues, population explosion, rapid urbanisation, depletion of fossil reserves, need for energy security, huge waste generation, etc. are some of the inherent issues associated with the fossil based linear economy which need greater attention. In this context, the world is gradually transforming from fossil-based economy to a sustainable circular bio-economy. The biogenic waste which is generated in enormous quanties in India can be considered as potential feedstock for structuring the bio-based economy. This communication depicts the need for developing waste derived bioeconomy in the Indian perspective. Waste is now being perceived as a resource with value and believed to supplement petroleum feedstock to a great extent if properly utilized. The necessity to introduce waste as the core element for the future economic models which also allows sustainable development is discussed. The review also establishes drivers for the bioeconomy and structures the waste derived bioeconomy in a sustainable format to address the futuristic needs, scope and opportunities envisaged in the business and economic realm. The enabling technologies/processes that can be applied for biogenic wastes valorisation are elaborated. Circularizing the economy in a waste biorefinery model for the production of biobased products including bioenergy is discussed.

Functional behavior of bio-electrochemical treatment system with increasing azo dye concentrations: Synergistic interactions of biocatalyst and electrode assembly.

Treatment of dye bearing wastewater through biological machinery is particularly challenging due to its recalcitrant and inhibitory nature. In this study, functional behavior and treatment efficiency of bio-electrochemical treatment (BET) system was evaluated with increasing azo dye concentrations (100, 200, 300 and 500mg dye/l). Maximum dye removal was observed at 300mg dye/l (75%) followed by 200mg dye/l (65%), 100mg dye/l (62%) and 500mg dye/l (58%). Concurrent increment in dye load resulted in enhanced azo reductase and dehydrogenase activities respectively (300mg dye/l: 39.6U; 4.96μg/ml). Derivatives of cyclic voltammograms also supported the involvement of various membrane bound redox shuttlers, viz., cytochrome-c, cytochrome-bc1 and flavoproteins during the electron transfer. Bacterial respiration during BET operation utilized various electron acceptors such as electrodes and dye intermediates with simultaneous bioelectricity generation. This study illustrates the synergistic interaction of biocatalyst with electrode assembly for efficient treatment of azo dye wastewater.

Metabolic phasing of anoxic-PDBR for high rate treatment of azo dye wastewater

The treatment of azo dye wastewater was studied in a periodic discontinuous batch reactor (PDBR) at high loading condition (1250mg/l) under anoxic microenvironments. PDBR performance was evaluated by varying the time period of aerobic microenvironment during the cycle operation [before multiphasing (BMP; Control), 0.014; after multiphasing (AMP): AMPI, 0.84; AMPII, 0.73; AMPIII, 0.65]. Induction of air in anoxic-PDBR facilitated the simultaneous oxidation and reduction conditions and thus resulted higher dye removal efficiency with AMPIII strategy (65%) followed by AMPII (59.4%) and AMPI (54.4%) than the corresponding control operation (BMP: 49.4%). Relatively higher azo reductase enzyme activity was documented with AMP than corresponding BMP operation correlating well with azo dye decolorization. UV- UV-Significant transformational changes of azo dye peaks (618nm) were documented before and after multiphase operations. Cyclic voltammogram profiles depicted increment in redox catalytic currents during AMPIII operation and also supports the involvement of reducing equivalents towards the dye removal. Derivatives of voltammograms illustrated the involvement of various redox mediators viz., cytochrome-C, quinones, Fumarate/Succinate, Fe(CN)63-/Fe(CN)64-, and flavoproteins. Flexibility in phasing the multiple microenvironments in single bioreactor (PDBR) provides new insights in embodying the required capabilities to treat the recalcitrant azo dye wastewater especially at higher dye load operations.

Waste Remediation Integrating with Value Addition: Biorefinery Approach Towards Sustainable Bio-based Technologies

The perpetual increase in the environmental pollution and the diminution of fossil fuels are forcing mankind towards the usage of sustainable and eco-friendly technologies to build a green and global future. Similarly, increase in human population is eventually resulting in the discharge of huge quantities of waste that need serious attention. If the waste is managed aptly, the negatively valued waste would absolutely result in the generation of a definite value-added product. A multifaceted approach is needed to alleviate the energy crisis in an interdisciplinary way by integrating waste remediation towards bioenergy generation. Diverse forms of energy, viz. biohydrogen, bioelectricity, biodiesel and bioplastics could be produced by utilizing waste/wastewater as substrate by the catalytic action of bacteria. The inherent potential of the diverse bacteria present in wastewater can be effectively exploited for the generation of bioenergy along with the recovery of value-added products in a green and integrated approach. In this context, sustainable, green and eco-friendly technologies were described in this chapter to exploit the potential of waste/wastewater in the framework of biorefinery.