Component analysis of fat, oil and grease in wastewater: challenges and opportunities

Characterisation and anaerobic digestion of fat, oil and grease (FOG) waste from wastewater treatment plants

The materials removed in the oil separation units of wastewater treatment plants can be referred to as fat, oil and grease (FOG) waste. FOG waste accumulation in treatment plants can cause clogging of pipes, production of excessive scums and foams, and negatively affect air/liquid oxygen transfer. While conventional disposal routes of this material can be limited by its water and organic content, FOG can represent a source of bio-energy other than bio-diesel production. This research determined the chemical and physical characteristics of FOG waste collected at four different wastewater treatment plants and defined the potential for energy recovery via dark fermentation and anaerobic digestion as treatment options for final disposal. The FOG samples featured markedly distinct physical aspects in connection with the oil separation technologies: solid agglomerate with a high content of lipids from vortex-type separation and semi-solid agglomerate with a low content of oils and fats from horizontal-flow chambers. All FOG waste presented high potential for methane production with values ranging from 460 to 865 Nm3CH4/tVS but low yields of biological hydrogen via dark fermentation. This study addresses a knowledge gap in the scientific literature on the characteristics of FOG waste from treatment plants and defines possible routes for sustainable management via bio-energy recovery.

Sampling strategy, quantification, characterization and hazard potential assessment of greywater from ships in the Baltic Sea

Ship-generated greywater contains a variety of pollutants which, through various pathways, usually are discharged into the sea. To understand the seasonal variation in greywater volumes, the contaminant concentrations in, and the potential hazard of, ship-generated greywater streams, a four-phase strategy for sampling, characterization and hazard assessment of greywater was developed and implemented. Eight greywater streams, sampled from five ships, were characterized for selected pollutants. The metals Zn, Cu, Mn and the metalloid, As, collectively contributed 98 % to the Hazard Index. Laundry greywater had the highest average concentration of phosphorus (42 mg/l) while galley greywater had the highest average concentration of nitrogen (30 mg/l). The geometric means of COD-Cr, BOD5, TSS and P exceeded the IMO resolution MEPC 227(64) guideline values for sewage effluent from Advanced Wastewater Treatment Plants. The results establish the basis for and contribute to discussions on, the optimization of ship-generated greywater management and the establishment of potential regulatory strategies in the Baltic Region.

Effective grease separator management is the key to enhancing bioenergy recovery of fat, oil, and grease (FOG) and contributing to a circular bio-economy

Management of fat, oil and grease (FOG) is crucial for the recovery of renewable resources and the protection of sewer systems. This study aims to identify the potential quantities and qualities of FOG that can be acquired through optimised grease separator (GS) management approaches in hotels and restaurants during seasonal tourism. A technical survey of 20 GS from hotels and restaurants in the federal state of Tyrol, Austria was conducted. The findings revealed that 55 % of the GS were in poor condition, often due to infrequent maintenance and limited operator's knowledge. The FOG layer quality and quantity was monitored over three years and physicochemical parameters including total residue, volatile solids, total organic carbon, lipid content, and biomethane yield, were analysed. An optimised management approach, which involved up to 4 GS emptying per season, revealed a significant increase in FOG quantity for the majority of the inspected establishments, with an overall doubling of the acquired FOG volume. Based on these results, the energy potential of GS is presented in three potential management scenarios. The energy recovered from GS increased by 246 %. This highlights the importance of proper GS management in the hospitality sector, which can play a critical role in promoting environmental sustainability and renewable energy production.

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.

Elucidating the impact of sanitary waste on the formation of fat, oil and grease deposits in sewer systems

The accumulation of fat, oil and grease (FOG) deposits in sanitary sewer systems is a significant cause of sewer overflows, mainly due to their tendency to adhere to pipe walls. The aim of this study is to (i) develop laboratory-prepared FOG deposits using a mixture of iron (Fe) and aluminium (Al) metal ions, fatty acids, saccharides and cooked oils, in addition to various sanitary waste materials such as paper towels, wipes and pads and (ii) examine the characteristics of these FOG deposits. The goals of this study were to (i) gain a deeper understanding of the impact of sanitary waste on the formation of FOG deposits and (ii) discuss the detailed physiochemical properties of these FOG deposits. The findings revealed that FOG deposits can vary in nature, appearing as either a smooth, paste-like substance or a coarse, semi-solid material, depending on the types of waste present in the sewer. Analysis of the fatty acid profile indicated that the FOG deposits with wipes have the highest viscosity (3.2 × 104 Pa s) and larger composition of smaller chain saturated fatty acids (caprylic acid 0.64%, undecanoic acid 5.61%, lauric acid 4.65%, myristic acid 3.21% and palmitic 8.38%). In contrast, FOG deposits with Fe and Al metal impurities have higher heat resistance and thermal stability (melting point of 125 °C) and have larger composition of long chain fatty acids. Furthermore, FTIR analysis confirmed that these FOG deposits are composed of metallic salts of fatty acids, aligning with samples from sewer lines. Our results suggest that FOG deposit formation involves the aggregation of excess calcium, which compresses free fatty acid micelles, and a saponification reaction between the calcium aggregates and free fatty acids. This research illuminates the complex processes behind FOG deposit formation and their varied characteristics, providing valuable insights into potential strategies for preventing FOG-related sewer blockages.

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.

The impact of olive mill wastewater on soil properties, nutrient and heavy metal availability - A study case from Syrian vertisols

Olive oil mill wastewater (OMW) is an environmental concern in olive oil producers' regions due to its use in agricultural soils as an organic amendment. However, OMW can also be used as organic fertilizer due to their high organic matter and nutrient levels, but its use, when it occurs without environmental management, can cause serious environmental implications for soils and waters. This work evaluated the impact of different OMW levels on a set of physicochemical parameters from an agricultural vertisol where wheat grew (Triticum aestivum L var. Douma 1). A set of physicochemical parameters were conducted before adding different levels of OMW (0, 5, 10 and 15 L m-2) at two soil depths (0-30 and 30-60 cm) and for the two growing seasons to determine: i) the effect of OMW treatments on the studied physicochemical soil properties (bulk density, soil porosity, soil pH, electrical conductivity and organic matter), ii) available primary (N, P, K) and secondary macronutrients (Ca, Mg and Na), ii) micronutrients (Cu Fe, Mn and Zn), and iv) available heavy metals (Cd and Pb). The results indicated that soil physicochemical parameters were slightly improved, mainly due to improvement in organic matter, macro- and micronutrients, usually proportionally to the olive mill wastewater dose. Cadmium and Pb were within the permissible limits. The increased OMW had different behaviour on the soil nutritional balances of different elements, leading to nutrient imbalances, although in some cases, they were improved. However, the plant growth was not affected, and it was improved under 10 L m-2 and 15 L m-2 doses. The results offer valuable data about the use of OMW as organic fertilizer for crops and their potential impact on soil properties.