Anaerobic membrane bioreactor (AnMBR) for the treatment of lipid-rich dairy wastewater

Abstract

The ongoing growth of the global population has led to increased resource consumption, particularly in the realm of water resources, resulting in potential shortages and environmental concerns. The surge in industrialization has intensified the demand for freshwater, consequently causing significant contamination of global water sources through the discharge of industrial wastewater. This wastewater contains harmful contaminants, such as heavy metals and organic compounds, which pose significant threats to both aquatic ecosystems and human health (Corcoran, 2010). To effectively address this issue, it is imperative to strengthen regulatory measures, promote industrialized initiatives for wastewater reduction and treatment, and foster technological
advancements in wastewater management.
Lipids within wastewater systems present both opportunities and challenges. Their high energy content holds promise for bioenergy conversion, yet they can also disrupt anaerobic wastewater treatment processes. Consequently, it is often advisable to extract lipids before commencing biological treatment processes (Alves et al., 2009). Lipids are commonly referred to as fats, oils, and grease (FOG) (Cavaleiro et al., 2008). At the core of FOG composition are triglycerides, formed through the esterification of glycerol with long-chain fatty acids (LCFA) (Alves et al., 2009). Within lipid-rich wastewaters, the prevailing LCFAs identified include palmitic acid (C16:0) and oleic acid (C18:1), as highlighted by Hwu et al. (1996). Anaerobic digestion (AD) plays a central role in advancing various sustainable development objectives by seamlessly integrating energy and resource recovery from organic residues and wastewater, all while effectively managing pollution. AD's ability to produce renewable gaseous energy, recycle essential nutrients, and minimize excess sludge production, combined with an enhanced understanding of microbiology and ecophysiology, has propelled AD technologies to the forefront. These technologies now serve as environmentally friendly treatment options for a wide range of wastes and wastewaters, as evidenced by their widespread adoption at the global level (van Lier et al., 2020). Sustainable and efficient conversion of these waste lipids into methane within anaerobic reactors is met with impediments including adsorption, sludge flotation, washout, and inhibition. However, these complications can be circumvented through feeding protocols, optimized mixing, and adept solid separation methods, underpinned by cutting-edge reactor designs and operational methodologies. More recently, developments such as the anaerobic membrane bioreactor (AnMBR) and flotation-based bioreactors have emerged as solutions tailored for lipid-intensive wastewater treatment (Cavaleiro et. al., 2008). AnMBR, a nexus of anaerobic digestion and membrane filtration, has proven particularly adept for dairy wastewater treatment. It alleviates the challenges tied to gravity-based separation, yielding effluents devoid of suspended solids and of superior quality (Judd, 201).
The central focus of this research centered on the assessment of solids retention time (SRT) and its critical role in the operational parameters of AnMBR. This was accomplished by studying sludge filterability and membrane filtration performance. Additionally, we investigated how the acclimatization of biomass impacted the transformation of longchain fatty acids (LCFA) in lipid-rich wastewater. Initial evaluations emphasized the role of SRT on AnMBR efficiency during the treatment of synthetic dairy wastewater laden with lipids. Employing two distinct AnMBR configurations with SRTs of 20 and 40 days, both systems manifested approximately 99%efficiency in waste removal at an organic loading rate of 4.7 g COD L-1 d-1. Significantly,lipid sedimentation was absent, facilitating their continued anaerobic degradation. LCFAaccumulation was minimal in both systems, with the 40-day SRT configuration showing slightly enhanced biological conversion and stability. Subsequently, the study delved into the effects of SRT on the filtration efficacy of AnMBR using lipid-rich synthetic dairy wastewater. When confronted with 40-day SRT, the system encountered elevated pressures and resistances, presumably due to escalated contaminant levels, including fats, oils, and LCFAs. While both systems showcased analogous filterability, the 20-day configuration exhibited superior membrane performance, suggesting potential membrane operational refinements for the 40-day SRT. Lastly, the influence of LCFA on anaerobic sludge processes was investigated. Trialing three distinct sludge samples—two lipid-acclimated and one non-acclimated—they were exposed to varying oleic and palmitic acid concentrations, ranging between 50 to 600 mg COD/L. Oleic acid showed superior degradation capabilities compared to palmitic acid across all samples, with heightened methane production. Lipid-acclimated sludges demonstrated augmented LCFA degradation potential. However, upon reaching LCFA concentrations beyond 400 mg/L, degradation of both acids into intermediate products was inhibited, albeit without affecting methane production. Intriguingly, specific bacterial taxonomies associated with LCFA degradation were identified in lipid-acclimated sludge samples, underscoring the potential of sludge adaptation strategies in enhancing anaerobic treatment of lipid-rich effluents.
In this doctoral research, we elucidated the prospects and challenges associated with the utilization of AnMBR for treating lipid-rich dairy wastewater. We highlighted the critical importance of Solid Retention Time (SRT), a key operational parameter that exerts a profound influence on both the biological and membrane aspects of the system.
Furthermore, our study underscored the paramount role played by the two most prevalent Long-Chain Fatty Acids (LCFAs), namely oleic and palmitic acid, within the domain of anaerobic digestion.