Utilization of carbon-based nanomaterials for wastewater treatment and biogas enhancement: A state-of-the-art review

The management of environmental pollution and carbon dioxide (CO2) emissions is a challenge that has spurred increased research interest in determining sustainable alternatives to decrease biowaste. This state-of-the-art review aimed to describe the preparation and utilization of carbon-based nanomaterials (CNM) for biogas enhancement and wastewater contaminant (dyes, color, and dust particles) removal. The novelty of this review is that we elucidated that the performance of CNMs in the anaerobic digestion (AD) varies from one system to another. In addition, this review revealed that increasing the pyrolysis temperature can facilitate the transition from one CNM type to another and outlined the methods that can be used to develop CNMs, including arc discharge, chemical exfoliation, and laser ablation. In addition, this study showed that methane (CH4) yield can be slightly increased (e.g. from 33.6% to 60.89%) depending on certain CNM factors, including its type, concentration, and feedstock. Temperature is a fundamental factor involved in the method and carbon sources used for CNM synthesis. This review determined that graphene oxide is not a good additive for biogas and CH4 yield improvement compared with other types of CNM, such as graphene and carbon nanotubes. The efficacy of CNMs in wastewater treatment depends on the temperature and pH of the solution. Therefore, CNMs are good adsorbents for wastewater contaminant removal and are a promising alternative for CO2 emissions reduction. Further research is necessary to determine the relationship between CNM synthesis and preparation costs while accounting for other factors such as gas flow, feedstock, consumption time, and energy consumption.

Analyzing the Impact of Physicochemical Factors on Chlorella vulgaris Growth Through Design of Experiment (DoE) for Carbon Capture System

The CO2 emission is increasing every year and threatening both humans and the ecosystem. Carbon capture technological innovations have emerged as a potential solution to mitigate this emissions. Due to its high capacity of photosynthetic activity, CO2 sequestration by microalgae, such as Chlorella vulgaris has attracted much attention as a carbon capture system. The growth of this microalgae is influenced by various physicochemical factors. By designing the Design of Experiment (DoE) with Response Surface Methodology (RSM), the effect of several independent factor can be evaluated to optimize Chlorella vulgaris growth condition and CO2 conversion. This study aims to identify the most impact factors affecting C. vulgaris growth through investigating the variations in physicochemical factors of aeration, initial pH, dark light regime, saline, and substrates concentration using DoE. In this study, C. vulgaris was cultivated in batch culture for 10 days with 8 experiments that were designed under various conditions as per experimental run. Biomass growth was observed using optical density and analyzed by first order regression. The result shows that aeration parameters was statistically significant affect microalgae growth, evidence by p-value below 0.05 at all observation points. Runs with aeration treatment showed a prolonged exponential growth phase and delayed onset of the deceleration phase. Additionally, this study also found that the initial pH level also significantly affects growth at the last day of cultivation. Cultures with a higher initial pH reached the stationary phase earlier than those with a lower pH. Thus, the growth of C. vulgaris can be optimized by adding aeration treatment into culture media and regulating initial pH around 8 to enhancing carbon fixation and biomass yield.

Bioengineering strategies of microalgae biomass for biofuel production: recent advancement and insight

Algae-based biofuel developed over the past decade has become a viable substitute for petroleum-based energy sources. Due to their high lipid accumulation rates and low carbon dioxide emissions, microalgal species are considered highly valuable feedstock for biofuel generation. This review article presented the importance of biofuel and the flaws that need to be overcome to ensure algae-based biofuels are effective for future-ready bioenergy sources. Besides, several issues related to the optimization and engineering strategies to be implemented for microalgae-based biofuel derivatives and their production were evaluated. In addition, the fundamental studies on the microalgae technology, experimental cultivation, and engineering processes involved in the development are all measures that are commendably used in the pre-treatment processes. The review article also provides a comprehensive overview of the latest findings about various algae species cultivation and biomass production. It concludes with the most recent data on environmental consequences, their relevance to global efforts to create microalgae-based biomass as effective biofuels, and the most significant threats and future possibilities.

Pineapple core from the canning industrial waste for bacterial cellulose production by Komagataeibacter xylinus

To address the high production cost associated with bacterial cellulose (BC) production using the Hestrin-Schramm (HS) medium, alternative agricultural wastes have been investigated as potential low-cost resources. This study aims to utilize pineapple core from pineapple canning industry waste as a carbon source to enhance the bacterial growth of Komagataeibacter xylinus and to characterize the physical and mechanical properties of the resulting BC. To assess growth performance, commercial sugar at concentrations of 0, 2.5, and 5.0 % (w/v) was incorporated into the medium. Fermentation was conducted under static conditions at room temperature for 5, 10, and 15 days. The structural and physical properties of BC were characterized using SEM, FTIR, XRD, and DSC. With the exception of crystallinity, BC produced from the pineapple core medium exhibited comparable characteristics to BC produced in the HS medium. These findings highlight the potential of utilizing pineapple core, a byproduct of the canning industry, as an economically viable nutrient source for BC production.

Micro and macro analysis of restaurant wastewater containing fat, oil, grease (FOG): An approach based on prevention, control, and sustainable management

The number of restaurants is increasing day by day in almost all the developing countries, causing the increase in the generation of restaurant wastewater. Various activities (i.e., cleaning, washing, and cooking) going on in the restaurant kitchen lead to restaurant wastewater (RWW). RWW has high concentrations of chemical oxygen demand (COD), biochemical oxygen demand (BOD), nutrients such as potassium, phosphorus, and nitrogen, and solids. RWW also contains fats, oil, and grease (FOG) in alarmingly high concentration, which after congealing can constrict the sewer lines, leading to blockages, backups, and sanitatry sewer overflows (SSOs). The paper provides an insight to the details of RWW containing FOG collected from a gravity grease interceptor at a specific site in Malaysia, and its expected consequences and the sustainable management plan as prevention, control, and mitigation (PCM) approach. The results showed that the concentrations of pollutants are very high as compared to the discharge standards given by Department of Environment, Malaysia. Maximum values for COD, BOD and FOG in the restaurant wastewater samples were found to be 9948, 3170, and 1640 mg/l, respectively. FAME and FESEM analysis are done on the RWW containing FOG. In the FOG, palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9c), linoleic acid (C18:2n6c) are the dominant lipid acids with a maximum of 41, 8.4, 43.2, and 11.5%, respectively. FESEM analysis showed formation of whitish layers fprmed due to the deposition of calcium salts. Furthermore, a novel design of indoor hydromechanical grease interceptor (HGI) was proposed in the study based on the Malaysian conditions of restaurant. The HGI was designed for a maximum flow rate of 132 L per minute and a maximum FOG capacity of 60 kg.

Advancement of biochar-aided with iron chloride for contaminants removal from wastewater and biogas production: A review

The use of fossil fuels, emission of greenhouse gases (GHG) into the atmosphere, and waste pose a problem to the environment and public health that urgently needs to be dealt with. Among numerous chemical activating agents that can be added to anaerobic digestion (AD) to enhance nutrient removal and increase the quality and quantity of biomethane, iron chloride (FeCl₃) is the one that has the lowest cost and is the most environmentally friendly. This state-of-the-art review aims to revise the influence of FeCl₃ on the Brunauer-Emmett-Teller (BET) surface area of biochar and its ability to increase methane (CH₄) yield and remove contaminants from biogas and wastewater. The novelty of the study is that FeCl₃, an activating agent, can increase the BET surface area of biochar, and its efficacy increases when combined with zinc chloride or phosphoric acid. Regarding the removal of contaminants from wastewater and biogas, FeCl₃ has proven to be an effective coagulant, reducing the chemical oxygen demand (COD) of wastewater and hydrogen sulfide in biogas. The performance of FeCl₃ depends on the dosage, pH, and feedstock used. Therefore, FeCl₃ can increase the BET surface area of biochar and CH₄ yield and remove contaminants from wastewater and biogas. More research is needed to investigate the ability of FeCl₃ to remove water vapor and carbon dioxide during biogas production while accounting for a set of other parameters, including FeCl₃ size.

Haitians' perceptions of biogas produced via human excreta: An approach to the democratization of energy systems

The utilization of organic matter (OM) to produce biogas is an attractive alternative for promoting sustainable development, addressing energy shortages and waste disposal problems, creating jobs, and investing in sanitation systems. Thus, this alternative is becoming increasingly important in developing countries. This study investigated the perceptions of residents in Delmas district, Haiti, regarding the use of biogas produced via human excreta (HE). A questionnaire containing closed- and open-ended questions was administered for this purpose. Sociodemographic aspects had no influence on locals' willingness to use biogas produced via different types of OM. The novelty of this research is that democratization and decentralization of the energy system are possible in the Delmas district using biogas produced from various organic wastes. Socio-characteristics of the interviewees did not influence their willingness towards a possible adopt biogas-based energy from several types of degradable organic matter. The results showed that more than 96% of the participants agreed that HE could be used to produce biogas and reduce energy shortages in their locality. In addition, 93.3% of the interviewees thought this biogas could be utilized for cooking food. However, 62.5% of respondents argued that using HE to produce biogas could be dangerous. Bad smell and fear of biogas produced via HE are the major concerns of users. In conclusion, this research could guide stakeholders' decisions to better address the problems of waste disposal and energy shortages and to create new jobs in the target study area. The research findings could help decision-makers better understand the willingness of locals to invest in household digester programs in Haiti. Further research is required to investigate farmers 'willingness to use digestates from biogas production.

Remediation techniques for elimination of heavy metal pollutants from soil: A review

Contaminated soil containing toxic metals and metalloids is found everywhere globally. As a consequence of adsorption and precipitation reactions, metals are comparatively immobile in subsurface systems. Hence remediation techniques in such contaminated sites have targeted the solid phase sources of metals such as sludges, debris, contaminated soils, or wastes. Over the last three decades, the accumulation of these toxic substances inside the soil has increased dramatically, putting the ecosystem and human health at risk. Pollution of heavy metal have posed severe impacts on human, and it affects the environment in different ways, resulting in industrial anger in many countries. Various procedures, including chemical, biological, physical, and integrated approaches, have been adopted to get rid of this type of pollution. Expenditure, timekeeping, planning challenges, and state-of-the-art gadget involvement are some drawbacks that need to be properly handled. Recently in situ metal immobilization, plant restoration, and biological methods have changed the dynamics and are considered the best solution for removing metals from soil. This review paper critically evaluates and analyzes the numerous approaches for preparing heavy metal-free soil by adopting different soil remediation methods.

An integrated biorefinery strategy for the utilization of palm-oil wastes

Each year, the palm oil industry generates a significant amount of biomass residue and effluent waste; both have been identified as significant sources of greenhouse gas (GHG) emissions. This issue poses a severe environmental challenge for the industry due to the possibility of long-term negative effects on human well-being. The palm-oil industry must invest significantly in the technology that is required to resolve these issues and to increase the industry's sustainability. However, current technologies for converting wastes such as lignocellulosic components and effluents into biochemical products are insufficient for optimal utilization. This review discusses the geographical availability of palm-oil biomass, its current utilization routes, and then recommends the development of technology for converting palm-oil biomass into value-added products through an integrated biorefinery strategy. Additionally, this review summarizes the palm oil industry's contribution to achieving sustainable development goals (SDGs) through a circular bioeconomy concept.