Investigation of used cooking oil on the formation of FOG deposits in sewer line clogging

Influence of improper disposal on FOG deposition: Rheological behaviour and pumping power requirements in sewer systems

Residents often perceive kitchen sinks and toilets as convenient disposal points for substances like leftover food particles, used cooking oil (UCO), tissues, wet wipes, and other sanitary products. However, this practice significantly contributes to the formation of fatbergs, leading to blockages in sewer lines. Previous studies have mainly utilised aqueous solutions containing specific inorganic constituents, leaving the mechanisms of fat, oil, and grease (FOG) deposit formation in complex wastewater containing both organic and inorganic matter largely unexplored. This study aims to (i) examine how organic and inorganic constituents, food particles and sanitary products impact FOG formation and (ii) perform rheological analysis and modelling to determine the properties of FOG deposits and evaluate the pumping power needed to prevent blockages. FOG deposit formation was studied in a batch process using UCO, and the amount of the deposits produced was expressed as mass per volume of UCO added. Results showed that alkaline hydrolysis at pH 9 promoted FOG deposition by 57.2 % (1.80 mg/mL UCO) compared to acidic pH 5 (1.11 mg/mL UCO). Wastewater-containing organics slightly enhanced the amount of FOG deposits, likely due to the reactions between Ca and carbohydrate source, as indicated by a significant increase in Ca content. Wet wipes and facial tissues substantially increased FOG deposits, reaching concentrations of 5.59 mg/mL UCO and 4.10 mg/mL UCO, respectively. This was attributed to the aggregation caused by their large, porous fibre structures, which effectively trap sewer solids. Based on friction loss and pressure drop, a pumping power over 55.6 W would be required to pump out FOG deposits containing facial tissues and wet wipes along a 15 m long, 100 mm diameter sewer pipe. This study highlights the impact of improper disposal practices on FOG formation and sewer system inefficiencies, emphasising the need for better waste management.

Waste cooking oils as a sustainable feedstock for bio-based application: A systematic review

Waste cooking oils (WCOs) are common wastes and promising green, eco-friendly and sustainable feedstocks for bio-based applications. While the primary valorisation strategy revolves around the concept of waste-to energy, new research trends have emerged in the last decade. This systematic review provides a comprehensive analysis of the current state of the art in the conversion of WCOs into bio-based molecules. Based on the PRISMA methodology, 64 papers were selected using different databases and sources, such as: PubMed, ScienceDirect, Scopus and MDPI. The data extraction process focused on studies reporting the biological and chemical conversion of WCOs into value-added bioproducts. Many of the selected publications deal with the development of bioactive molecules, including biosurfactants, with application in pharmaceuticals, food, cosmetics, and bioremediation. Bioconversion processes mainly featured engineered Yarrowia lipolytica and Escherichia coli strains, even if additional microorganisms were also employed. In the same way, different chemical processes have been thoroughly studied. A smaller segment of research is directed to the production of feed supplements and soaps. Regulatory constraints limit further development in feed supplements due to potential contaminants, while soap production needs further stability studies. The present systematic review shows promising outcomes in the valorisation of WCOs through the development of value-added molecules and products. Despite the wide range of applications, these findings identify that the scalability and economic sustainability of the selected processes require further investigation. This study seeks to summarize the current state of the art and identify potential gaps to advance the industrialization of WCOs valorisation.

Uncovering the impact of metals on the formation and physicochemical properties of fat, oil and grease deposits in the sewer system

The deposition of fats, oil, and grease (FOG) in sewers reduces conveyance capacity and leads to sanitary sewer overflows. The major contributing factor lies in the indiscriminate disposal of used cooking oil (UCO) via kitchen sinks. While prior investigations have mostly highlighted the significance of Ca2+ from concrete biocorrosion, the influence of common metal ions (e.g., Mg2+, Na+, K+) found in kitchen wastewater on FOG deposition has received limited attention in the existing literature. This study aimed to elucidate the roles of Ca, Mg, Na and K in FOG deposition in sewers and examine the influence of metal ions, fat/oil sources, and free fatty acids (FFAs) on the physicochemical and rheological properties of FOG deposits. To examine FOG deposit formation, synthetic wastewater containing 0.1 g/L of each metal ion was mixed with 40 mL of fat/oil and agitated for 8 h. Following FOG deposition, three distinct phases were observed: unreacted oil, FOG deposit and wastewater. The composition of these phases was influenced by the composition of metal ions and FFA in the wastewater. Mg produced the highest amount of FOG of 242.5 ± 10.6 mL compared to Ca (72.5 ± 3.5 mL) when each FFAs content in UCO was increased by 10 mg/mL. Molar concentration, valency and the solubility of metal ion sources were identified to influence the formation of FOG deposits via saponification and aggregation reaction. Furthermore, Fourier-Transform Infrared spectroscopy indicated that the FOG deposits in this study were similar to those collected from the field. This study showed that the use of Mg(OH)2 as a biocorrosion control measure would increase FOG deposition and highlights the need for a comprehensive understanding of its roles in real sewage systems.

Effectiveness of grease interceptors in food service establishments for controlling fat, oil and grease deposition in the sewer system

The water industry worldwide experiences numerous sewer blockages each year, partially attributed to the accumulation of fat, oil and grease (FOG). Managing this issue involves various strategies, including the requirement for installation of grease interceptors (GIs) installation. However, the claimed efficacy of commercial GIs of eliminating 99 % of FOG has been questioned for many years because FOG deposit formation occurs despite food service establishments (FSEs) using GIs, therefore detailed understanding of FOG wastewater compositions and its removal by GIs is required. This study provides an insight into the key FOG components such as FOG particle size, metals and fatty acid (FA) profile in GI influent and effluent, and within the GI, at three different FSEs. Analysis of FAs identified substantial proportions of extra-long-chain FAs in the effluents, including arachidic (C20:0), behenic (C22:0), mead (C20:3), lignoceric (C24:0), and nervonic (C24:1) acids. In contrast, the household kitchen released palmitic (C16:0), oleic (C18:1) and linoleic (C18:2) acids. It was further observed that scums effectively remove the larger FOG particles, leaving only 10 % below 75.4 μm. Notably, FSEs which employed automatic dishwashers produced up to 80.4 % of particles ≤45 μm, whereas FSEs and household kitchen which used handwash sinks generated only 36.9 % and 26.3 % of particles ≤45 μm, respectively. This study demonstrated that the commercial GIs do not remove FOG entirely but clearly demonstrated that they discharge high concentrations of FOG with extra-long FFAs which were attributed to the occurrence of microbial activity and hydrolysis of triglycerides within the GI, potentially contributing to FOG deposition.

Tackling fat, oil, and grease (FOG) build-up in sewers: Insights into deposit formation and sustainable in-sewer management techniques

The increasing global demand for fatty products, population growth, and the expansion of food service establishments (FSEs) present significant challenges for the wastewater industry. This is often due to the build-up of fat, oil and grease (FOG) in sewers, which reduces capacity and leads to sanitary sewer overflows. It is crucial to develop economic and sustainable in-sewer FOG management techniques to minimise maintenance costs and service disruptions caused by the removal of FOG deposits from sewers. This study aims to understand the process of FOG deposit formation in both concrete and non-concrete sewers. Compared to fresh cooking oil, disposal of used cooking oil in households and FSE sinks results in the formation of highly adhesive and viscous FOG deposits. This occurs due to hydrolysis during frying, which increases the concentration of fatty acids, particularly palmitic acid, in the used cooking oil. Furthermore, metal ions from food waste, wastewater, and dishwashing detergents contribute to the saponification and aggregation reactions which cause FOG deposition in both concrete and non-concrete sewers. However, the leaching of Ca2+ ions exacerbates FOG deposition in cement-concrete sewers. The article concludes by suggesting future research perspectives and proposes implementation strategies for microbially induced concrete corrosion (MICC) control to manage FOG deposition in sewers. One such strategy involves applying superhydrophobic coating materials with low surface free energy and high surface roughness to the interior surfaces of the sewer. This approach would help repel wastewater carrying FOG deposit components, potentially disrupting the interaction between FOG components, and reducing the adhesion of FOG deposits to sewer surfaces.