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

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.