Innovative Multistage Co-Liquefaction of Lignocellulosic Biomass and Wastewater Sludge for Enhanced Middle Distillate Biocrude Production

The global pursuit of sustainable energy solutions necessitates the exploration of alternatives to traditional fossil fuels, with hydrothermal liquefaction (HTL) emerging as a promising technology for converting diverse feedstocks into biocrude. HTL’s efficiency in processing wet waste, such as wastewater sludge (WWS) with its high moisture content (70-95%), is particularly advantageous as it bypasses energy-intensive drying processes. Bangladesh, facing significant challenges in managing the substantial amounts of WWS generated annually (including fecal sludge (FS) and sewage sludge (SS)), alongside the large volumes of agricultural residues like rice husk (RH) and industrial byproducts such as sawdust (SD), presents a compelling case for exploring HTL. Currently, these biomasses are often disposed of through environmentally detrimental methods like incineration and landfilling, contributing to pollution and greenhouse gas emissions.  

WWS, rich in proteins, lipids, and carbohydrates, is inherently suitable for HTL conversion due to its high moisture content. Simultaneously, lignocellulosic biomass (LB) like RH and SD contains significant amounts of cellulose, hemicellulose, and lignin, along with metal oxides that can act as natural catalysts in thermochemical conversion processes. Preliminary research suggests that HTL of SD can yield biocrude with a high proportion of heavy fractions, and SS and SD contain notable amounts of iron oxide, which has shown promise in increasing asphaltene content in biocrude derived from FS. The co-liquefaction of LB with WWS is hypothesized to enhance biocrude yield by increasing volatile content while maintaining energy efficiency. Initial pilot trials by the S2Asphalt and SOIL research groups have indicated the potential to produce distinct biocrude fractions – a lighter fraction from FS and a heavier, asphaltene-rich fraction through the co-liquefaction of RH and FS. This dual output could potentially address the growing demands for both lighter fuels (like octane and gasoline) and heavier products (like bitumen).  

Given Bangladesh’s reliance on diesel-fired power plants and the widespread use of diesel in transportation and industry, the production of middle distillates (such as kerosene and diesel) from alternative sources is crucial. A novel approach proposed in this research is the multistage co-HTL of WWS and LB. This innovative method involves applying stage-wise heating with varying retention times to optimize the different chemical reactions (hydrolysis, decarboxylation, deoxygenation, etc.) that occur at different temperature ranges during HTL. This controlled process aims to enhance the production of middle-grade biocrude fractions. To the authors’ knowledge, this study represents the first attempt to explore multistage co-HTL of WWS (FS/SS) and LB (RH/SD) to produce a wider spectrum of distillate fractions in biocrude, offering a unique opportunity to optimize biocrude production across multiple grades. The overarching aim of this research is to develop an integrated biocrude fraction, with a specific focus on middle distillates, through multistage co-HTL of WWS and LB in varying ratios. This endeavor holds the potential to provide a sustainable alternative energy source for Bangladesh, reducing its dependence on fossil fuels and contributing to the achievement of SDGs 6 (clean water and sanitation), 7 (affordable and clean energy), and 11 (sustainable cities and communities).

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The primary and most significant anticipated result of this research is the Successful Development of a Multistage Co-Hydrothermal Liquefaction (HTL) Process for the Production of High-Quality Biocrude, Enriched with Middle Distillate Fractions, from Wastewater Sludge (WWS) and Lignocellulosic Biomass (LB) in Bangladesh. This key outcome is characterized by the following critical achievements:

  • Demonstrated Potential of Local Feedstocks: The study will establish the viability of using WWS (from Dasherkandi Sewage Treatment Plant and FS) and LB (RH/SD) as effective feedstocks for co-HTL conversion.
  • Optimized Multistage Co-HTL Process: The research will identify the optimal multistage heating parameters (temperature ranges and retention times at each stage) for the co-HTL of WWS and LB to maximize the yield and quality of biocrude, particularly the middle distillate fractions.
  • Characterized Biocrude Quality: The produced biocrude will be comprehensively analyzed to determine its yield, chemical composition (using GC-MS and FTIR), heavy fraction content (using TGA), elemental composition (CHNS), and overall quality as a potential fuel source, with a specific focus on the properties relevant to middle distillates.
  • Established Effect of Retention Time: The study will elucidate the impact of varying retention times at each stage of the multistage co-HTL process on the characteristics and yield of the resulting biocrude.
  • Techno-Economic and Energy Balance Assessment: A preliminary evaluation of the techno-economic feasibility and energy balance of the proposed multistage co-HTL technology will be conducted to assess its potential for practical implementation in Bangladesh.
  • Contribution to Sustainable Development Goals: The research will provide a pathway for sustainable waste management and the establishment of an alternative energy source, directly contributing to Bangladesh’s efforts to achieve SDGs 6, 7, and 11.

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Socially sustainable WASH integrated spatial model for informal settlement

Ensuring adequate Water, Sanitation, and Hygiene (WASH) services in urban informal settlements, home to a significant portion of the global urban poor, remains a critical challenge. The dense populations, substandard infrastructure, and limited access to essential services in these areas exacerbate public health risks and environmental degradation. Research efforts are increasingly focusing on developing sustainable WASH systems that address both the physical infrastructure and the social needs of these vulnerable communities. The spatial arrangement of WASH infrastructure (water points, sanitation facilities, waste management) directly influences its accessibility, usability, and overall effectiveness. Irregular layouts and dense housing in informal settlements often hinder the placement of WASH facilities in safe and accessible locations for all residents. Studies highlight a misalignment between the design and spatial arrangement of services and the socio-spatial patterns of residents, leading to inequalities in service distribution and longer travel distances for essential WASH access.

The high population density, lack of formal infrastructure, and insecure land tenure further complicate WASH service provision in these settlements. Socio-spatial approaches emphasize integrating not only the physical location of services but also the social practices, behaviors, and cultural norms that shape residents’ engagement with WASH infrastructure. This underscores the need for improved spatial planning that considers these factors to enhance the living conditions and quality of life in these areas. Research emphasizes the importance of designing services that align with community preferences, including cultural, gender, and safety considerations. While technical advancements in WASH infrastructure are important, overlooking socio-cultural aspects can limit the effectiveness and long-term use of these facilities. Engaging communities in the design process has been shown to increase satisfaction and promote sustainability.

This proposed research builds upon these advancements by integrating spatial analysis with user preference evaluation to develop a conceptual framework for a socially sustainable WASH model. It aims to evaluate both the spatial efficiency and user satisfaction with existing WASH systems, bridging the gap between technical and social sustainability. Current literature highlights the necessity of considering socio-spatial factors in WASH planning and implementation in informal settlements. However, research on spatial models that prioritize social sustainability, including user preferences and satisfaction, remains limited. This research aims to address this gap by developing a socially sustainable WASH integrated spatial model that optimizes the placement and design of WASH services in informal settlements while ensuring community acceptance and effective use. The focus is on creating WASH systems that are not only functional but also aligned with the specific needs and preferences of the community.

The rationale for this research is particularly relevant to Khulna, the second-largest division in Bangladesh, which faces significant WASH challenges in its informal settlements, home to over 130,000 people. The unplanned layouts of these settlements complicate the effective placement of WASH facilities, forcing residents, especially women and children, to travel long distances for basic services, increasing overcrowding and the risk of waterborne diseases. Cultural norms and gender roles further influence the use of WASH services, with women often avoiding communal toilets due to safety and privacy concerns. A socio-spatial model is crucial for combining the physical layout of facilities with the social practices of the community, allowing for the design of technically viable, culturally acceptable, and socially relevant solutions. This research aims to create a tailored socio-spatial WASH integrated model for Khulna’s informal settlements, assessing socio-spatial characteristics and improving their arrangement based on user satisfaction. The expected outcomes include better living conditions, improved access to WASH services, and an enhanced overall quality of life for residents. By providing a robust framework for government agencies and NGOs, this research seeks to enhance their impact in these vulnerable urban areas.

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On-Site Rapid Anaerobic Digestion of Faecal Sludge with Suitable Agents in the Conventional Latrine

The burgeoning challenge of managing faecal sludge (FS) in emerging nations, driven by rapid urbanization and population growth, poses significant environmental and public health risks. A substantial portion of the population in low- and middle-income countries relies on on-site sanitation systems like pit latrines and septic tanks, where effective FS management is often lacking due to the absence of sewer networks and centralized treatment facilities. Current approaches to anaerobic digestion (AD), a well-established method for stabilizing organic waste and producing bioenergy, face limitations when applied to FS. These limitations include the slow and incomplete degradation of complex organic matter, the physical and chemical barriers erected by the intricate microbial floc structure of FS, and other factors such as improper organic loading, nutrient imbalances, unfavorable microbial communities, and suboptimal ambient conditions. Furthermore, conventional AD struggles with efficient pathogen removal and presents scalability challenges when transitioning from laboratory to full-scale applications, often encountering issues with long hydraulic retention times, maintaining optimal environmental conditions, inconsistent microbial activity due to temperature fluctuations, and high operational costs.

To address these shortcomings, significant research has focused on pre-treating sludge before AD to enhance the accessibility of the substrate to anaerobic bacteria, thereby accelerating digestion, improving degradation, and reducing the final sludge volume. Various pre-treatment methods have been explored, including mechanical disintegration, ultrasonic treatment, chemical treatment using strong acids or alkalis, and thermal pre-treatment (thermal hydrolysis). Enzymatic pre-treatment, involving the addition of specific industrial enzymes like cellulases, lipases, proteinases, and hydrolases, offers an environmentally friendly approach to improve the breakdown of biopolymers, leading to faster hydrolysis, increased product formation, and better dewaterability. However, enzymatic pre-treatment faces hurdles related to high costs, scalability, and enzyme sensitivity. Anaerobic co-digestion, which involves combining sludge with other organic wastes to improve nutrient balance and enhance microbial activity, also presents limitations such as feedstock compatibility, operational complexity, potential contamination, and increased infrastructure costs.

Recognizing the potential synergies, the integration of enzymatic pre-treatment and anaerobic co-digestion presents a promising avenue for enhanced sludge management. This combined approach can improve process stability, optimize nutrient balance, reduce retention times, and mitigate feedstock variability, potentially leading to a more cost-effective, scalable, and efficient solution. However, careful optimization and monitoring are crucial to address potential challenges such as inconsistencies in microbial activity, enzyme costs, and inhibitory effects.

This research proposal outlines the development of a novel product, Quick Digestant of Faecal Sludge (QDFS), which aims to overcome the limitations of conventional AD and the challenges associated with combined pre-treatment methods. QDFS will be formulated by integrating enzymatic pre-treatment with anaerobic co-digestion principles and will include deodorants and disinfectants to provide a comprehensive on-site FS treatment solution. The intended benefits of QDFS include efficient organic matter degradation, pathogen elimination, odor control, and improved scalability compared to traditional AD methods. Laboratory tests and pilot experiments will be conducted to validate the effectiveness of QDFS in addressing scalability issues and its potential to improve public health and reduce environmental impacts. The rationale for this research stems from the urgent need for sustainable FS management solutions in emerging nations, particularly in low-income communities where existing sanitation infrastructure is inadequate. Challenges identified through key informant interviews include the underutilization of mechanized emptying services due to cost and accessibility issues, improper disposal practices, and the prevalence of manual pit emptying. The development of QDFS is envisioned as a cost-effective and efficient on-site solution that can reduce septic tank cleaning frequencies, eliminate odors, and control pathogens. QDFS will be a carefully formulated mixture of seed organisms, deodorants, anti-pathogenic agents, suitable substrates, and essential nutrients, designed to create favorable environmental conditions for rapid and efficient anaerobic digestion. The seed organisms will provide an ideal microbial consortium, while deodorants will target odor-producing chemicals, and anti-pathogenic agents will eliminate disease-causing bacteria. The inclusion of suitable substrates will support the growth of diverse microorganisms capable of producing a range of hydrolytic enzymes. The application of QDFS is expected to stabilize organic matter, reduce sludge volume, simplify disposal, prevent improper waste disposal, lower cleaning costs, and improve public health outcomes. By optimizing microbial activity and reducing hydraulic retention times, QDFS aims to address the scalability challenges associated with conventional AD, potentially reducing the need for extensive infrastructure and enzyme purchases, thereby facilitating a smoother transition from pilot to full-scale industrial applications.

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January 2025 to ongoing

Biogas Production Optimization Approach through Anaerobic Co-digestion of Tannery Fleshing and Fecal Sludge

The increasing demand for sustainable waste management solutions has spotlighted the potential of anaerobic co-digestion (ACoD) as an innovative approach to address environmental and public health concerns. In particular, the improper disposal of fecal sludge (FS) and tannery fleshing (TF) — two high-risk waste streams — presents serious environmental challenges, especially in industrial zones like the Savar Tannery Estate in Bangladesh. This research explores an integrated ACoD approach using TF and FS to produce biogas, reduce waste volumes, and recover valuable nutrients, thereby offering a sustainable alternative to current unsystematic waste disposal practices.

Tannery fleshing, rich in proteins and lipids, and fecal sludge, containing microbial biomass and organic compounds, both possess significant biogas potential under anaerobic conditions. Their co-digestion can enhance microbial activity, balance carbon-to-nitrogen (C/N) ratios, and stabilize the digestion process, resulting in improved methane yields. While previous studies have explored ACoD involving either FS or TF with other wastes, limited attention has been paid to the combined treatment of these two specific streams. This research seeks to fill that gap by examining their synergies in biogas production through experimental and statistical optimization.

The methodology involves a series of detailed steps: sample collection and characterization, laboratory-scale biogas unit setup, substrate and inoculum ratio optimization, flowability and temperature variation studies. Through regression-based statistical analysis, the study aims to determine the optimal operational conditions to maximize methane yield.

Given the substantial volume of tannery waste generated in Bangladesh’s leather sector and the growing urban sanitation burden, the application of this ACoD model could significantly contribute to sustainable waste-to-energy systems. The proposed framework could help industries shift toward more circular, energy-efficient operations and ensure environmental compliance. Ultimately, this study not only explores a practical biogas solution but also provides a scientific foundation for scaling up waste treatment innovations in developing economies.

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November 2024 to ongoing