Kusum, Sennetc

Samrin Ahmed Kusum is a PhD candidate at the North Carolina State University. She completed her undergraduate studies from the Bangladesh University of Engineering and Technology and received M.S from the same institution in 2016. She is now working as a graduate research assistant in the project "Understanding the FOG Deposit Adhesion Mechanism on Different Sewer Line Surfaces" under the supervision of Dr. Joel Ducoste. Her research aims to enhance the sewer line conveyance to reduce Sanitary Sewer Overflows. She loves to travel and take photographs. You can reach her at skusum@ncsu.edu.

Titles from this speaker

Description: Factors that Influence the Formation and Surface Adhesion of Fat, Oil, and Grease...

Factors that Influence the Formation and Surface Adhesion of Fat, Oil, and Grease (FOG) Deposits

Abstract

The sewer collection system is an important infrastructure that protects the public health by safe disposal of wastewater. Sewer lines are designed for a certain carrying capacity, which is reduced by blockages, resulting in the risk of flooding and the occurrence of Sanitary Sewer Overflows (SSOs) that release raw contaminated sewage. According to the US Environmental Protection Agency, around 25% of the 23,000 to 75,000 SSOs are due to sewer line blockages related to fat, oil, and grease (FOG) deposits. Research studies have been conducted to understand the FOG deposit formation mechanism, sources of chemical constituents involved in FOG deposit formation, and engineering solutions to overcome the FOG-related SSO problems (He et al. 2017). These studies have shown that the long-chain free fatty acids (LCFFAs) from FOG discharge undergo a saponification reaction with calcium ion present in wastewater to form insoluble calcium soap known as FOG deposits that can adhere to sewer line surfaces to reduce its carrying capacity. The primary sources of FOG discharge are the food service establishments and domestic kitchen sinks, whereas sources of calcium can be attributed to the background wastewater as well as concrete structure corrosion. Previous research suggests that calcium released from concrete corrosion may have a more adverse impact on the FOG deposits accumulation on sewer line surfaces (Iasmin et al., 2014). The main contributor of calcium from concrete is the cement used as a binder. Research shows that the substitution of Portland cement by Supplementary Cementitious Materials (SCMs) such as Fly Ash (FA) reduces the calcium leaching potential of concrete exposed to corrosive media (RoziÃ¨re et al. 2009). In the research discussed in this presentation, we will evaluate the use of FA to replace a large volume of cement to produce an alternative binder material for sewer line construction that reduces the calcium leaching from concrete corrosion, therefore, reducing the FOG deposit formation. We will also explore different factors such as- porosity and pore size, surface roughness, and surface pH of different sewer line construction materials to understand the FOG deposits adhesion mechanism. In our study, two High Volume Fly Ash (HVFA) concrete materials, Concrete-50 and Concrete-75, were produced by keeping the water to cementitious material ratio at 0.42 using 50% and 75% replacement of cement by FA, respectively. Additionally, control samples, Concrete-0, were cast with no FA replacement and used as a standard to study the effect of FA replacement. HVFA samples were tested for compressive strength (ASTM C39-15) and chemical durability (ASTM C267) to check their suitability as sewer line construction materials. Concrete samples were also tested for their calcium leaching potential at pH 5 and 7 by submerging them into Deionized Water (DI) for 90 days. The FOG deposit formation test was performed at pH 7 for a 30 days testing period by submerging concrete samples in synthetic wastewater prepared by mixing oleic acid as the LCFFA source, canola oil, distilled water, and calcium chloride as a background calcium source. The compressive strength test results show that after 90 days of sealed curing, Concrete-50 is well above 4 ksi; a threshold compressive strength used for sewer line construction materials. The chemical durability test results showed that 50% FA replacement enhanced the durability of concrete against corrosive media. After 90 days of leaching under corrosive conditions, Concrete-50 and Concrete-75 samples showed 75% and 86% reduction in calcium leaching, respectively, when compared with the standard Concrete-0 sample. The calcium leaching potential from HVFA samples also revealed that the calcium ion diffusion flux of the HVFA samples was almost similar and lower than the Concrete-0 samples. This observation suggests that FA replacement can reduce the porosity of concrete; thereby, reduce the calcium leaching potential from sewer lines under corrosive media. In addition to the calcium leaching potential, HVFA samples were also tested for heavy metals such as Arsenic (As), Cadmium (Cd), Chromium (Cr), Selenium (Se), Mercury (Hg), and Lead (Pb) leaching potential. After 90 days of leaching test, the cumulative toxic ion concentration for Concrete-50 and Concrete-75 samples did not exceed the pollutant discharge limit provided by USEPA clean water act. FOG deposition formation test results showed that 50% and 75% FA replacement can reduce FOG deposit formation by 55% and 67%, respectively. Therefore, results from this study suggests that a significant decrease in calcium release can be achieved through the use of FA as a cement replacement, which can eventually reduce the FOG deposit formation. To understand the FOG deposits adhesion mechanism on different sewer line surfaces, a combined FOG deposit formation test was conducted by submerging Concrete-0, Concrete-50, Concrete-75, Vitrified Clay Pipe, and PVC pipe into the synthetic wastewater for 30 days of the testing period. This test results revealed a similar FOG deposit formation trend (highest FOG deposition on Concrete-0 samples and lowest FOG deposition on Concrete-75 samples); however, no FOG deposits were found on PVC and Vitrified clay pipes surfaces. Hence, we hypothesize that the FOG deposit adhesion phenomena are primarily controlled by the sewer line material's surface properties in addition to the availability of calcium and LCFFAs. In the next phase of this study, to understand the effect of porosity, pore size, and surface pH on FOG deposit adhesion mechanism, porous ceramic materials with controlled pore size will be used for the FOG deposit formation test. Whereas, to study the effect of surface roughness on FOG deposits adhesion phenomena, HVFA and PVC samples will be prepared at different surface roughness and tested for the FOG deposition test. Results from these tests will be able to identify the key factors that affect the FOG deposits adhesion mechanism. According to Clean Watershed Needs Survey (USEPA, 2016), the total need for replacing sewer lines is $42 billion on top of $25 billion and $18 billion in the new collector and new inceptor sewers, respectively. Therefore, the present study will reduce the future sewer line construction and maintenance cost by reusing FA as an alternative sewer line construction material. Additionally, by studying the FOG deposit adhesion mechanism, this research will provide wastewater collection system utilities with strategies to develop new construction materials or potentially design future coatings that can enhance existing alternative materials to limit or reduce the FOG deposit accumulation on the sewer surface.

The following conference paper was presented at Collection Systems 2021: A Virtual Event, March 23-25, 2021.

SpeakerKusum, Sennetc

Presentation time

13:40:00

14:00:00

Session time

13:00:00

14:00:00

SessionAsset Management

Session number5

Session locationSimu-live

TopicAsset Management, Collection Systems, Condition Assessment, FOG, Innovative Technology, Predictive Analytics, Risk Management, Sanitary Sewer Overflow