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Biomedical waste management (BMW) is in the spotlight due to the enormous impact of theCOVID-19 pandemic on public health and hospitals. Further, countries with large populationsgenerate significantly higher amounts and variety of both hazardous and non-hazardous BMW,leading to a need for a comprehensive strategy for effective BMW management. The improper,unscientific disposal of BMW causes environmental pollution and presents a continuing,significant health hazard to the individual and the community. The present study provides acomprehensive assessment of the various types of BMW generated and critiques their currentdisposal strategies. A detailed appraisal of current, in-place BMW management guidelines fromvarious world organisations is presented, and emerging protocols for BMW disposal during theongoing COVID-19 pandemic are assessed. Finally, new state-of-the-art technologies, which canlead to breakthrough improvements in various stages of BMW generation, collection, treatmentand disposal process, are examined. The secondary applications of BMW are highlighted, andrecommendations for enhancing the BMW lifecycle practices are presented.

Excess amounts of phosphorus (P) and nitrogen (N) from anthropogenic activities such as population growth, municipal and industrial wastewater discharges, agriculture fertilization and storm water runoffs, have affected surface water chemistry, resulting in episodes of eutrophication. Enhanced biological phosphorus removal (EBPR) based treatment processes are an economical and environmentally friendly solution to address the present environmental impacts caused by excess P present in municipal discharges. EBPR practices have been researched and operated for more than five decades worldwide, with promising results in decreasing orthophosphate to acceptable levels. The advent of molecular tools targeting bacterial genomic deoxyribonucleic acid (DNA) has also helped us reveal the identity of potential polyphosphate-accumulating organisms (PAO) and denitrifying PAO (DPAO) responsible for the success of EBPR. Integration of process engineering and environmental microbiology has provided much-needed confidence to the wastewater community for the successful implementation of EBPR practices around the globe. Despite these successes, the process of EBPR continues to evolve in terms of its microbiology and application in light of other biological processes such as anaerobic ammonia oxidation and on-site carbon capture. This review provides an overview of the history of EBPR, discusses different operational parameters critical for the successful operation of EBPR systems, reviews current knowledge of EBPR microbiology, the influence of PAO/DPAO on the disintegration of microbial communities, stoichiometry, EBPR clades, current practices, and upcoming potential innovations.

Biogas production from agricultural residue by anaerobic digestion is the most favourable option for providing sustainable energy and reducing the environmental pollution. The experimental methane potential of co-digested rice straw and food waste were measured for different carbon to nitrogen (C/N) ratios in 1 L anaerobic reactor. Co-digesting rice straw with food waste for C/N 25, 30 and 35 almost showed the similar methane yield 294.17 ± 3.78 mL/g-VSadded, with an increase of 134.53 mL/g-VSadded (71.09%) than mono-digestion. After optimizing the C/N ratio for co-digestion, interactive effect of initial pH and food/microorganism (F/M) ratio were also explored in this study using central composite design – response surface methodology (CCD-RSM). Results from the optimization study showed significant interaction, and validation experiment for optimum condition (C/N 30, pH 7.32, F/M 1.87) showed a methane yield of 323.78 mL/g-VSadded (94.41%), 166.54 mL/g-VSadded higher than the mono-digestion (control).

This study emphasizes the use of different thermal pretreatment methods (i.e., hot air oven, hot water bath, autoclave and microwave) on pretreatment of rice straw prior to anaerobic degradation. These pretreatment methods resulted in reasonably high solubilization of recalcitrant biomass. Maximum solublisation was attained by microwave (190 °C; exposure time-4 min) (66.6%) followed by autoclave, hot air oven and hot water bath methods. Accelerated cumulative methane yield of microwave pretreated sample achieved was 367.71 mL/g-VSadded, which was 160.68 mL/g-VSadded higher than the control. Combining this high temperature conditions with lesser exposure time also improved the energy balance of the process. The physicochemical characteristics of pretreated rice straw were investigated by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), FESEM analysis showed the increased porosity of the rice straw, FTIR analysis showed the omission of hemicellulose from the matrix and with XRD analysis reduced value of crystallinity index supports the destruction of the crystalline matrix.

This novel study is focused on estimating the electrohydrolysis pretreatment conditions using DC current (voltage and time) for enhancing the biodegradability of rice straw. The electrohydrolysis pretreatment was performed using graphite electrode with intermittent mode of input voltage fluctuating from 10 to 30 V (voltage study) and in continuous mode for 15–80 min (time study). The result implicated that electrohydrolysis pretreatment with 25 V and 60 min time achieved the maximum solublization (55%). The Batch tests (1 L) were performed to explore the accelerated biomethane production from enhanced solublization and to optimize the food/microorganisms ratio. The different F/M (0.5–3) ratios showed the cumulative methane production ranging from 236 to 319 mL/g-VSadded (control-224.01 mL/g-VSadded). Compositional characterization (FESEM, XRD and FTIR) studies showed the efficacy in disrupting the lignin layer and reducing the cellulose crystallinity of rice straw. The effect of pretreatment on methane production was also kinetically analysed by modified Gompertz, logistic and transference function models.

Anaerobic digestion of lignocellulosic biomass has gained huge attention in current years, especially for degrading agricultural waste (i.e. rice straw, wheat straw etc.). Challenges related to anaerobic digestion of agricultural waste are low biogas yield, poor buffering capacity, low quality end products and potential variability. These inadequacies are either because of low mass transfer (high solid contents, poor nutritional structure) or can be accredited to recalcitrant nature of agricultural residues. To overcome these challenges various techniques exists like pretreatment of feedstock, co-digestion with different substrate and inoculation efficiency have been considered to increase the performance of anaerobic process. This review includes the effect of these techniques on lignocellulosic degradation, synergistic interaction with high C/N ratio feedstock and improving the buffering capacity by inoculum ratio optimization. Furthermore, key parameters influencing the anaerobic digestion are included with proposed future study.

Rice straw is a widely existing lignocellulosic waste with high potential for methane production. However, high carbon/nitrogen (C/N) ratio of rice straw causes the poor process stability for mono-digestion. This study investigated the co-digestion of rice straw and hydrilla verticillata (nitrogen rich co-substrate) at different C/N ratios to enhance biomass degradation. Different C/N ratios revealed notably enhanced process stability and higher volumetric methane yields than mono-digestion (control). C/N-25 (Co-digestion) showed the highest methane productivity with an increase of 40% than the control. This increase was caused by the improvement of the metabolic pathway due to proper nutritional structure (C/N). C/N-15 obtained the lowest methane yield due to ammonia inhibition (315 mg/L). Biodegradation reaction kinetics parameters were also calculated during the digestion process and it showed reasonably good agreement between the experimental and predicted value (R2 > 0.98) for modified gompertz model. The average Rmax of C/N-25 was 2.78% less than Rmax observed in control. The favourable reducing environment established during the degradation stage was represented by low oxidation-reduction potential (−312.8 mV) values. Since no added energy inputs are required for this process, it is highly practicable on farm-scale in contrast to pretreatment.

Lignin modifying or extracellular enzymes secreted by the white rot fungi have the ability of degrading wide range of lignocellulosic substrates and organic pollutants. Lignocellulosic biomass, despite being a renewable source of energy, is difficult to hydrolyse (hydrolysis being rate-limiting stage in anaerobic digestion process). Various pre-treatment techniques like physical, chemical, thermo-chemical and biological to enhance the accessibility of microbes to carbohydrates have been studied. Recently, usage of white- rot fungi in a biological pre-treatment technique have received renewed interest due to its low cost and eco-friendly nature. This review deals with: a) lignocellulosic biomass recalcitrance, b) various pre-treatment techniques and its economic feasibility, c) delignification and hydrolysis mechanism using white-rot fungi, d) factors controlling white-rot fungi pre- treatment process, and e) improvement in methane production through solid-state anaerobic digestion of white-rot fungi pre-treated lignocellulosic biomass. Finally a future perspective is also included.

Biogas has become an alternative clean source of energy. Agricultural residues being renewable and abundant resources could be efficiently used as a feed for methane production. The recalcitrant behaviour of rice straw marks pretreatment an important step to facilitate the transformation into renewable (methane) energy source. Microwave pretreatment has been considered as one of the most effective method, as it can directly (thermal and nonthermal effects) react with the feedstock and destroy its complex matrix. The present study considered the different temperature and exposure time (i.e., 130–230 °C, 2–5 min). Biochemical methane potential was assessed corresponding to the maximum solubilization rate; specific methane yield was obtained as 325.76 mL/g/VS. The total net energy gain of 3288.576 J/g/VS was obtained. The performance parameters were calculated by using different kinetic models. It followed the trend as modified Gompertz > transference function > logistic function models. Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared (FTIR) analysis confirmed the breakdown of lignocellulose structure resulting from the rupture of cuticular surface.

Anaerobic co-digestion is a realistic approach to concurrently manage agriculture residue and harness renewable energy. To achieve the anaerobic degradation requirements and to recompense the nitrogen deficiency of rice straw, it should be digested with another nitrogen-rich co-substrate to advance its characteristics. This study exhibits the necessity of co-digestion to improve physicochemical and biochemical progression compared to mono-digestion. The individual effect of carbon/nitrogen (C/N) ratio, food/microorganisms (F/M) ratio and pH, in addition to their interaction effects on methane yield (mL CH4/g-VSadded) were explored in this study. A central composite design – response surface methodology was used for defining the experimental design for anaerobic co-digestion of rice straw and hydrilla verticillata. Results of this study showed significant interaction of C/N ratio and F/M ratio, and individual response parameters on methane yields. The optimum condition for anaerobic co-digestion (C/N ratio 29.7, F/M ratio 2.15 and pH 7.34) showed methane yield of 287.6 mL CH4/g-VSadded, 1.84 fold (156.32 mL CH4/g-VSadded) higher than mono-digestion (control). Model validation proved the high adequacy of the model and methane yield is good output response variable for co-digestion study and it is necessary to optimize the transient variation in C/N ratio, F/M ratio and pH.

The influence of three different fungal strains—namely, Pleurotus ostreatus (PO), Phanerochaete chrysosposrium (PC), and Ganoderma lucidum (GL)—on pretreatment of rice straw, followed by biochemical methane potential assay was evaluated on the basis of structural (Field Emission Scanning Electron Microscopy, X-ray diffraction etc.) and quantitative (soluble chemical oxygen demand, volatile fatty acids, etc.) analysis. Maximum lignocellulosic degradation was obtained with PC pretreated rice straw (36% more than an untreated sample), followed by PO. Enhancement in the methane yield after 5 weeks of inoculation time was obtained after pretreatment, which was 269.99, 295.91, and 339.31 mL/g VSadded, for PO, GL, and PC, respectively, 1.64–2.22-fold higher than the untreated one. Kinetic modelling of cumulative methane yield showed that modified gompertz model showed the best fit among all analysed models. This study demonstrated the usefulness of fungal species in enhancing the methane yield.