Advances in Biological Wastewater Treatment Processes: Focus on Low-Carbon Energy and Resource Recovery in Biorefinery Context.

Advancements in biological wastewater treatment with sustainable and circularity approaches have a wide scope of application. Biological wastewater treatment is widely used to remove/recover organic pollutants and nutrients from a diverse wastewater spectrum. However, conventional biological processes face challenges, such as low efficiency, high energy consumption, and the generation of excess sludge. To overcome these limitations, integrated strategies that combine biological treatment with other physical, chemical, or biological methods have been developed and applied in recent years. This review emphasizes the recent advances in integrated strategies for biological wastewater treatment, focusing on their mechanisms, benefits, challenges, and prospects. The review also discusses the potential applications of integrated strategies for diverse wastewater treatment towards green energy and resource recovery, along with low-carbon fuel production. Biological treatment methods, viz., bioremediation, electro-coagulation, electro-flocculation, electro-Fenton, advanced oxidation, electro-oxidation, bioelectrochemical systems, and photo-remediation, are summarized with respect to non-genetically modified metabolic reactions. Different conducting materials (CMs) play a significant role in mass/charge transfer metabolic processes and aid in enhancing fermentation rates. Carbon, metal, and nano-based CMs hybridization in different processes provide favorable conditions to the fermentative biocatalyst and trigger their activity towards overcoming the limitations of the conventional process. The emerging field of nanotechnology provides novel additional opportunities to surmount the constraints of conventional process for enhanced waste remediation and resource valorization. Holistically, integrated strategies are promising alternatives for improving the efficiency and effectiveness of biological wastewater treatment while also contributing to the circular economy and environmental protection.

Hybrid electrosynthesis as non-genetic approach for regulating microbial metabolism towards waste valorization in circular framework.

Biogenic waste (solid/liquid/gaseous) utilization in biological processes has disruptive potential of inclining towards carbon neutrality, while producing diverse products output. Anaerobic fermentation (methanogenesis and acidogenesis) routes are crucial bioprocesses for production of various renewable chemicals (carboxylate platform/organic acids, short/medium chain alcohols, aldehydes, biopolymers) and fuels (methane, hydrogen, hythane, biodiesel and electricity), while individual operations posing process limitations on their conversion efficiency. Advantageous benefit of using the individual bioprocess technicalities is of utmost importance in the context of sustainability to conceptualize and execute integrated waste biorefinery. The opinion article intends to document/familiarize the waste-fed biorefinery potential with application of hybrid advancements towards multiple product/energy/renewable chemical spectrum leading to carbon neutrality bioprocesses. Unique and notable challenges with diverse process integrations along with electrochemical/interspecies-redox metabolites-materials synergy/enzymatic interventions are specifically emphasized on application-oriented waste feedstock potential towards achieving sustainability.

Emerging trends in microbial fuel cell diversification-Critical analysis.

Global need for transformation from fossil-based to bio-based economy is constantly emerging for the production of low-carbon/renewable energy/products. Microbial fuel cell (MFC) catalysed by bio-electrochemical process gained significant attention initially for its unique potential to generate energy. Diversification of MFC is an emerging trend in the context of prioritising/enhancing product output while exploring the mechanism specificity of individual processes. Bioelectrochemical treatment system (BET), microbial electrosynthesis system (MES), bioelectrochemical system (BES), electro-fermentation (EF), microbial desalination cell (MDC), microbial electrolysis cell (MEC) and electro-methanogenesis (EM) are the diversified MFC systems that are being researched actively. Owing to its broad diversification, MFC domain is increasing its potential credibility as a platform technology. Microbial catalyzed electrochemical reactions are the key which directly/indirectly are proportionally linked to electrometabolic activity of microorganisms towards final anticipated output. This review intends to holistically document the mechanisms, applications and current trends of MFC diversifications towards multi-faced applications.

Cathodic selenium recovery in bioelectrochemical system: Regulatory influence on anodic electrogenic activity.

Metal(loid)s are used in various industrial activities and widely spread across the environmental settings in various forms and concentrations. Extended releases of metal(loid)s above the regulatory levels cause environmental and health hazards disturbing the ecological balance. Innovative processes for treating the metal(loid)-contaminated sites and recovery of metal(loid)s from disposed waste streams employing biotechnological routes provide a sustainable way forward. Conventional metal recovery technologies demand high energy and/or resource inputs, which are either uneconomic or unsustainable. Microbial electrochemical systems are promising for removal and recovery of metal(loid)s from metal(loid)-laden wastewaters. In this communication, a bioelectrochemical system (BES) was designed and operated with selenium (Se) oxyanion at varied concentrations as terminal electron acceptor (TEA) for reduction of selenite (Se4+) to elemental selenium (Se0) in the abiotic cathode chamber. The influence of varied concentrations of Se4+ towards Se0 recovery at the cathode was also evaluated for its regulatory role on the electrometabolism of anode-respiring bacteria. This study observed 26.4% Se0 recovery (cathode; selenite removal efficiency: 73.6%) along with organic substrate degradation of 74% (anode). With increase in the initial selenite concentration, there was a proportional increase in the dehydrogenase activity. Bioelectrochemical characterization depicted increased anodic electrogenic performance with the influence of varied Se4+ concentrations as TEA and resulted in a maximum power density of 0.034 W/m2. The selenite reduction (cathode) was evaluated through spectroscopic, compositional and structural analysis. X-ray diffraction and Raman spectroscopy showed the amorphous nature, while Energy Dispersive X-ray spectroscopy confirmed precipitates of the deposited Se0 recovered from the cathode chamber. Scanning electron microscopic images clearly depicted the Se0 depositions (spherical shaped; sized approximately 200 nm in diameter) on the electrode and cathode chamber. This study showed the potential of BES in converting soluble Se4+ to insoluble Se0 at the abiotic cathode for metal recovery.

Self-induced bioelectro-potential influence on sulfate removal and desalination in microbial fuel cell.

This study focused on treatment of sulfate-rich produced water (PW) using microbial fuel cell (MFC) with biotic anode (bAC) and abiotic cathode (aCC) separated by a cation exchange membrane (CEM). MFC was operated under varied circuitry modes - open circuit (OC-without resistance) and closed circuit (CC-applied resistance (1kΩ)) to evaluate and assess the removal of sulfates and salts with simultaneous carbon utilization. The OC and CC operations depicted sulfates removal efficiency of 38% and 56%, salinity removal of 12% and 21% and COD removal of 47% and 58%, respectively. Both OC and CC showed K+ decrement in bAC and increment in aCC with a comparatively higher efficiency of ionic mobility in CC operation. Maximum open circuit voltage (OCV) of 498 mV (OC) was observed with redox catalytic peak currents from cyclic voltammetry [Anode/cathode, 3.5/-4.9 mA (OC); 6.9/-7.9 mA (CC)]. Dominance of Proteobacteria and Actinobacteria with specific enrichment of sulfate reducing bacteria (SRB) and halophiles was observed in bAC at the end of operation.

Concomitant use of Azolla derived bioelectrode as anode and hydrolysate as substrate for microbial fuel cell and electro-fermentation applications.

The potential of deoiled Azolla pinnata biomass (DAB) as electrode and substrate was evaluated for microbial fuel cell (MFC) operation. The anode electrode was fabricated using biochar obtained by subjecting DAB to pyrolysis at 600 °C, while the reducing sugars after hydrolysis of DAB by acid pretreatment was used as substrate. The post pyrolyzed biochar (P-DAB) was characterized for structural and elemental functionalities using SEM, XRD and Raman spectroscopy, whereas the reducing sugar obtained from hydrolyzed DAB (H-DAB) was analyzed for its composition. Experimental results indicated that at a given 3 g COD/L resulted in a voltage of 382 mV with 65.6% of COD reduction in closed circuit (CC) mode of operation. Cyclic voltammetric analysis depicted maximum oxidative and reductive peak currents of 3.42 mA and -4.0 mA. Noticeable peaks were also identified in CC (-0.2 V to +0.2 V and -0.19 V to -0.3 V) and OC (+0.2 V to +0.4 V and -0.1 V to -0.3 V) corresponding to complex IV cytochrome c couples (cytochrome Cox (Cyt Cox)/cytochrome Crd (Cyt Crd)), signifying the participation of electron carriers during electron transfer. The microbiome diversity showed dominance of Proteobacteria, a phylum known for exo-electrogenic bacterial species. The DAB-derived products account to environmental sustainability and support circular bioeconomy in a biorefinery mode.

Modified conductive polyaniline-carbon nanotube composite electrodes for bioelectricity generation and waste remediation.

Anode with good electrocatalytic capabilities is more specifically required to reduce the ohimic losses during microbial fuel cell (MFC) operation. Highly conductive polymers viz., Polyaniline (PANi) and Polyaniline/Carbon nanotube (PANi/CNT) composite were prepared by in situ oxidative chemical polymerization method. Anodes were fabricated independently by coating PANi and CNT/PANi composites on the surface of SSM. The fabricated electrodes were evaluated as anode against stainless steel mess (SSM) as cathode during MFC operation. Maximum bioelectricity generation was observed in SSM-PANi/CNT-anode with power density of 48 mW/m2 and COD removal efficiency of 80% compared with SSM-PANi-anode (38 mW/m2; 65%) and SSM-anode (28 mW/m2; 58%). Bioelectrochemical characterization of the electrode materials using cyclic voltammetry and electrochemical impedance spectroscopy showed high electrocatalytic activity of PANi/CNT composite electrode. The study concluded the efficiency of PANi/CNT composite electrodes as bioanode in operation of MFCs towards achieving increased bioelectricity production along with wastewater treatment.

Microalgae-biorefinery with cascading resource recovery design associated to dairy wastewater treatment.

The potential of microalgae for the treatment of dairy wastewater (DWW) was studied by integrating with bioethanol production. At the end of treatment, organic carbon removal was observed to be 90% with simultaneous removal of nutrients. Biomass concentration increased from 3rd day and reached to a maximum of 1.4 g L-1 by the end of cycle. The biomolecular composition of microalgae comprised of 38% carbohydrates, 15% proteins and 22% lipids. Reducing sugars extracted from deoiled microalgae showed highest percentage of glucose (54.12%) than other monomers. The reducing sugars obtained were utilized for the production of bioethanol via yeast fermentation using Saccharomyces cerevisiae. This resulted in the production of ethanol (3G) upto 116.2 mg g-1 with simultaneous decrease in reducing sugars upto 92 mg g-1. The results obtained indicate potential of microalgae to produce multiple biobased products in a biorefinery framework.

Spatial variation of electrode position in bioelectrochemical treatment system: Design consideration for azo dye remediation.

In the present study, three bio-electrochemical treatment systems (BET) were designed with variations in cathode electrode placement [air exposed (BET1), partially submerged (BET2) and fully submerged (BET3)] to evaluate azo-dye based wastewater treatment at three dye loading concentrations (50, 250 and 500 mg L-1). Highest dye decolorization (94.5 ±â€¯0.4%) and COD removal (62.2 ±â€¯0.8%) efficiencies were observed in BET3 (fully submerged electrodes) followed by BET1 and BET2, while bioelectrogenic activity was highest in BET1 followed by BET2 and BET3. It was observed that competition among electron acceptors (electrode, dye molecules and intermediates) critically regulated the fate of bio-electrogenesis to be higher in BET1 and dye removal higher in BET3. Maximum half-cell potentials in BET3 depict higher electron acceptance by electrodes utilized for dye degradation. Study infers that spatial positioning of electrodes in BET3 is more suitable towards dye remediation, which can be considered for scaling-up/designing a treatment plant for large-scale industrial applications.

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.

Phasic availability of terminal electron acceptor on oxygen reduction reaction in microbial fuel cell.

Oxygen-reduction reactions (ORR) plays a pivotal role in determining microbial fuel cells (MFC) performance. In this study, an attempt to determine the influence of the phasic availability of terminal electron acceptor (TEA) on ORR was made. Two MFCs operated with dissolved oxygen (MFC-DC) and air (MFC-SC) as TEA were constructed and analyzed in continuous mode under open and closed circuit conditions. The bio-electrochemical analysis showed a marked influence of dissolved oxygen resulting in a maximum power density with MFC-DC (769mW/m2) compared to MFC-SC (684mW/m2). The availability of O2 in dissolved phase has lowered the activation losses during the MFC operation as a result of effective ORR. The cyclic voltammetry analysis revealed the TEA dependent biocatalyst activity of NADH and cytochrome complex which enabled electron transfer kinetics and improved substrate utilization. Finally, the study evidenced the critical role of TEA phasic availability to regulate the bio-electrogenic and substrate degradation potential in MFC.

Integrated ecotechnology approach towards treatment of complex wastewater with simultaneous bioenergy production.

Sequential integration of three stage diverse biological processes was studied by exploiting the individual process advantage towards enhanced treatment of complex chemical based wastewater. A successful attempt to integrate sequence batch reactor (SBR) with bioelectrochemical treatment (BET) and finally with microalgae treatment was studied. The sequential integration has showed individual substrate degradation (COD) of 55% in SBR, 49% in BET and 56% in microalgae, accounting for a consolidated treatment efficiency of 90%. Nitrates removal efficiency of 25% was observed in SBR, 31% in BET and 44% in microalgae, with a total efficiency of 72%. The SBR treated effluents fed to BET with the electrode intervention showed TDS removal. BET exhibited relatively higher process performance than SBR. The integration approach significantly overcame the individual process limitations along with value addition as biomass (1.75g/L), carbohydrates (640mg/g), lipids (15%) and bioelectricity. The study resulted in providing a strategy of combining SBR as pretreatment step to BET process and finally polishing with microalgae cultivation achieving the benefits of enhanced wastewater treatment along with value addition.

Multi-pollutant treatment of crystalline cellulosic effluent: Function of dissolved oxygen on process control.

Treatment of crystalline cellulose based wastewater was carried out in periodic discontinuous batch reactor (PDBR). Specific influence of dissolved oxygen on treatment of crystalline cellulosic (CC) wastewater was evaluated in three different microenvironments such as aerobic, anoxic and anaerobic. PDBR-aerobic biosystem documented relatively higher substrate degradation [2.63kgCOD/m(3)-day (92%)] in comparison to PDBR-anoxic [2.12kgCOD/m(3)-day (71%)] and PDBR-anaerobic [1.81kgCOD/m(3)-day (63%)], which is in accordance with the observed DO levels. Similarly, multipollutants viz., phosphates and nitrates removal was observed to be higher in aerobic followed by anoxic and anaerobic operations. Higher nitrate removal in aerobic operation might be attributed to the efficient denitrification carried out by the biocatalyst, which utilizes both nitrates and oxygen as oxidizing agents. Multiscan spectral profiles depicted reduction in color intensity in all three microenvironments that correlated with the substrate degradation observed. Despite the high organic load, PDBR functioned well without exhibiting process inhibition.

GPS and GPRS Based Telemonitoring System for Emergency Patient Transportation.

Telemonitoring during the golden hour of patient transportation helps to improve medical care. Presently there are different physiological data acquisition and transmission systems using cellular network and radio communication links. Location monitoring systems and video transmission systems are also commercially available. The emergency patient transportation systems uniquely require transmission of data pertaining to the patient, vehicle, time of the call, physiological signals (like ECG, blood pressure, a body temperature, and blood oxygen saturation), location information, a snap shot of the patient, and voice. These requirements are presently met by using separate communication systems for voice, physiological data, and location that result in a lot of inconvenience to the technicians, maintenance related issues, in addition to being expensive. This paper presents design, development, and implementation of such a telemonitoring system for emergency patient transportation employing ARM 9 processor module. This system is found to be very useful for the emergency patient transportation being undertaken by organizations like the Emergency Management Research Institute (EMRI).