Biomass based biochar production approaches and its applications in wastewater treatment, machine learning and microbial sensors

Biochar is a stable carbonaceous material derived from various biomass and can be utilized as adsorbents, catalysts and precursors in various environmental applications. This review discusses various feedstock materials and methods of biochar production via traditional as well as modern approaches. Additionally, the biochar characteristics, HTC process, and its modification by employing steam and gas purging, acidic, basic / alkaline and organo-solvent, electro- and magnetic fields have been discussed. The recent biochar applications for real water, wastewater and industrial wastewater for the abstraction of environmental contaminants also reviewed. Moreover, applications in machine learning and microbial sensors were discussed. In the meantime, analyses on commercial and environmental profit, current ecological concerns and the future directions of biochar application have been well presented.

Techno-economic optimization of phosphorous recovery in an algal-based sewage treatment system

Previous reports have documented the technical viability of an algal pathway for treating primary effluent and recovering its phosphorus-content (P) via hydrothermal liquefaction (HTL) of the resulting biomass. In this pathway, leaching P from HTL-derived biochar was found as the critical step impacting the economics of P-recovery. As such, a process model was developed in the current study to optimize P leaching from biochar as a function of five parameters. Model predictions under various conditions agreed well with measured data (r² = 0.93; n = 184). The validated process model was then integrated with a cost model to establish the following conditions as optimal for leaching P from biochar: batch leaching time of 72 h; eluent NaOH concentration of 0.5 M; eluent-to-biochar ratio of 20; temperature of 60 °C; and provision of mixing. Under these conditions, 73.5% of P from biochar could be recovered at $5.98/kg P.

Symbiotic integration of bioprocesses to design a self-sustainable life supporting ecosystem in a circular economy framework

Climate change, resource depletion and unsustainable crop productivity are major challenges that mankind is currently facing. Natural ecosystems of earth's biosphere are becoming vulnerable and there is a need to design Bioregenerative Life Support Systems (BLSS) which are ecologically engineered microcosms that could effectively deal with problems associated with urbanization and industrialization in a sustainable manner. The principles of BLSS could be integrated with waste fed biorefineries and solar energy to create a self-sustainable bioregenerative ecosystem (SSBE). Such engineered ecosystems will have potential to fulfil urban life essentials and climate change mitigation thus generating ecologically smart and resilient communities which can strengthen the global economy. This article provides a detailed overview on SSBE framework and its improvement in the contemporary era to achieve circular bioeconomy by means of effective resource recycling.

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 C_ox (Cyt C_ox)/cytochrome C_rd (Cyt C_rd)), 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.

Algal biorefinery models with self-sustainable closed loop approach: Trends and prospective for blue-bioeconomy

Microalgae due to its metabolic versatility have received a focal attention in the biorefinery and bioeconomy context. Microalgae products have broad and promising application potential in the domain of renewable fuels/energy, nutraceutical, pharmaceuticals and cosmetics. Biorefining of microalgal biomass in a circular loop with an aim to maximize resource recovery is being considered as one of the sustainable option that will have both economical and environmental viability. The expansive scope of microalgae cultivation with self-sustainability approach was discussed in this communication in the framework of blue-bioeconomy. Microalgae based primary products, cultivation strategies, valorization of microalgae biomass for secondary products and integrated biorefinery models for the production of multi-based products were discussed. The need and prospect of self-sustainable models in closed loop format was also elaborated.

Municipal solid waste-derived biochar for the removal of benzene from landfill leachate

The potential of biochar, produced from fibrous organic fractions of municipal solid waste (MSW), for remediation of benzene, one of the frequently found toxic volatile organic compounds in landfill leachate, was investigated in this study based on various environmental conditions such as varying pH, benzene concentration, temperature and time. At the same time, landfill leachate quality parameters were assessed at two different dump sites in Sri Lanka: Gohagoda and Kurunegala. MSW biochar (MSW-BC) was produced by slow temperature pyrolysis at 450 °C, and the physiochemical characteristics of the MSW-BC were characterized. All the leachate samples from the MSW dump sites exceeded the World Health Organization permissible level for benzene (5 µg/L) in water. Removal of benzene was increased with increasing pH, with the highest removal observed at ~pH 9. The maximum adsorption capacity of 576 µg/g was reported at room temperature (~25 °C). Both Freundlich and Langmuir models fitted best with the equilibrium isotherm data, suggesting the involvement of both physisorption and chemisorption mechanisms. Thermodynamic data indicated the feasibility of benzene adsorption and its high favorability at higher temperatures. The values of [Formula: see text] suggested physical interactions between sorbate and sorbent, whereas kinetic data implied a significant contribution of chemisorption. Results obtained from FTIR provided clear evidence of the involvement of functional groups in biochar for benzene adsorption. This study suggests that MSW biochar could be a possible remedy for benzene removal from landfill leachate and at the same time MSW can be a potential source to produce biochar which acts as a prospective material to remediate its pollutants while reducing the volume of waste.

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.