Exploring The Co-composting Potentials of Raw Grease Trap and Grease Trap-Derived Soaps: Insights into Grease Trap Modification, Calcium Supplementation, and Microbial Community Analysis

General Atomics (GA) is developing Supercritical Water Partial Oxidation (SWPO) as a means of producing hydrogen from low-grade biomass and other waste feeds. The Phase I Pilot-scale Testing/Feasibility Studies have been successfully completed and the results of that effort are described in this report. The key potential advantage of the SWPO process is the use of partial oxidation in-situ to rapidly heat the gasification medium, resulting in less char formation and improved hydrogen yield. Another major advantage is that the high-pressure, high-density aqueous environment is ideal for reacting and gasifying organics of all types. The high water content of the medium encourages formation of hydrogen and hydrogen-rich products and is especially compatible with high water content feeds such as biomass materials. The high water content of the medium is also effective for gasification of hydrogen-poor materials such as coal. A versatile pilot plant for exploring gasification in supercritical water has been established at GA's facilities in San Diego. The Phase I testing of the SWPO process with wood and ethanol mixtures demonstrated gasification efficiencies of about 90%, comparable to those found in prior laboratory-scale SCW gasification work carried out at the University of Hawaii at Manoa (UHM), as well as other biomass gasification experience with conventional gasifiers. As in the prior work at UHM, a significant amount of the hydrogen found in the gas phase products is derived from the water/steam matrix. The studies at UHM utilized an indirectly heated gasifier with an activated carbon catalyst. In contrast, the GA studies utilized a directly heated gasifier without catalyst, plus a surrogate waste fuel. Attainment of comparable gasification efficiencies without catalysis is an important advancement for the GA process, and opens the way for efficient hydrogen production from low-value, dirty feed materials. The Phase I results indicate that a practical means to overcome limitations on biomass slurry feed concentration and preheat temperature is to coprocess an auxiliary high heating value material. SWPO coprocessing of two high-water content wastes, partially dewatered sewage sludge and trap grease, yields a scenario for the production of hydrogen at highly competitive prices. It is estimated that there are hundreds if not thousands of potential sites for this technology across the US and worldwide. The economics for plants processing 40 tpd sewage sludge solids augmented with grease trap waste are favorable over a significant range of cost parameters such as sludge disposal credit and capital financing. Hydrogen production costs for SWPO plants of this size are projected to be about $3/GJ or less. Economics may be further improved by future developments such as pumping of higher solids content sludges and improved gasifier nozzle designs to reduce char and improve hydrogen yields. The easiest market entry for SWPO is expected to be direct sales to municipal wastewater treatment plants for use with sewage sludge in conjunction with trap grease, as both of these wastes are ubiquitous and have reasonably well-defined negative value (i.e., the process can take credit for reduction of well-defined disposal costs for these streams). Additionally, waste grease is frequently recovered at municipal wastewater treatment plants where it is already contaminated with sewage. SWPO should also be favorable to other market applications in which low or negative value, high water content biomass is available in conjunction with a low or negative value fuel material. For biomass slurries primary candidates are sewage sludge, manure sludge, and shredded and/or composted organic municipal solid waste (MSW) slurries. For the high heating value stream primary candidates are trap grease, waste plastic or rubber slurries, and coal or coke slurries. Phase II of the SWPO program will be focused on verifying process improvements identified during Phase I, and then performing extended duration testing with the GA pilot plant. Tests of at least 100 hours duration using sewage sludge and trap grease as simultaneous feedstocks are a primary objective. Follow-on Phases III and IV of the SWPO program will develop and demonstrate a dedicated 5 tpd reduced-scale SWPO facility at a location such as the Encina municipal wastewater treatment plant. Subsequent to this demonstration, the technology will be ready for a commercial-scale demonstration. While there are clearly technical challenges that must still be addressed, SWPO represents an outstanding opportunity to further the dual goals of developing a hydrogen economy and practicing environmentally friendly waste disposal. It may well represent one of the few scenarios in which hydrogen may be produced economically from biomass at a relatively small scale. SWPO could thus play a pivotal role in the proliferation of distributed hydrogen generation.

In recent years many researchers show a high interest in co-digestion, simultaneous anaerobic decomposition of a homogenous mixture of at least two biodegradable waste. Anaerobic codigestion is reported to offer several benefits over digestion of separate materials, such as increased cost-efficiency, increased biodegradation of the treated materials, as well as increased biogas production. Most often sewage sludge is digested alone while co-digestion with other substrates could be beneficial. In this study, the feasibility of co-digestion sewage sludge and grease trap waste (GTW) from meatprocessing plant was investigated in lab-scale reactor experiment. The research was made on the sewage sludge coming from municipal wastewater treatment plant and grease trap waste coming from meat industry company. Anaerobic co-digestion was studied in semi-continuous experiment at 37oC. Feeding of reactors was performed once a day with hydraulic retention time (HRT) of 10 days. The grease trap waste accounted for 2, 4, 6, 8 and 10 % of the mixture on the volatile solids basis. The mixtures were analyzed for the following parameters: total solids, volatile solids, pH, volatile fatty acids and long chain fatty acids (LCFAs). The control of digestion process was made every day on the basis of the measurement of the biogas production. What is more, there was determined the volatile solid removal as well the biogas yield in order to assess the efficiency of co-digestion process. It was found that co-digestion of sewage sludge and grease trap waste improved both biogas production and methane content. Grease trap waste addition of 10% of feed VS increased the biogas production by 16 % as well as methane concentration (72 % of biogas) compared to the period when reactor was feed only with sewage sludge. Moreover, the addition of GTW to the anaerobic digestion of sewage sludge increased organic matter removal. Although, the significant variations in LCFAs reduction, the biogas production and methane yield increased with higher addition of GTW. The results of the present laboratory study revealed that the use of GTW as a co-substrate is considered to be interesting option for sewage sludge digestion due to increased methane production. However, the feed should be planned carefully with stepwise increase to the desired feed ratio in order to acclimatize the bacteria and to prevent reactor overloading.

Lipids are attractive substrates for anaerobic digestion due to their high methane production yield. However, high concentrations of lipids may cause problems in anaerobic processes. Typically, grease trap waste is mechanically removed and discharged, both generating environmental issues and wasting a potential energy source. In this study, grease trap waste from a dairy wastewater treatment plant was subjected to anaerobic digestion. Untreated and pretreated sugarcane bagasse was evaluated as fat adsorbents to reduce the inhibitory effect of the fatty waste. The bagasse pretreated by the organosolv method was the condition that most contributed to increased methane production (82%) from anaerobic digestion of dairy fatty waste at 0.5 g COD.g–1TVS concentration. Untreated bagasse provided the second‐best condition, followed by hydrothermally treated bagasse, presenting no statistical difference. The obtained results showed the potential of using sugarcane bagasse as a strategy to reduce the inhibitory effect of the fatty waste from the dairy grease trap, making this waste another possible source for generating biogas.

Package on-site grease traps are widely used in household and restaurant in Thailand for oil and grease removal although frequent failures in FOG removal have been reported. Theoretically, too small of operating hydraulic retention time (HRT) takes the blame, but some suppliers claim that their grease traps can be well operated even with HRT of 15 minutes. This study was to investigate the performance of grease trap with various HRTs (15 minutes to 20 hours) and FOG concentrations in the feed (50 to 600 mg/l). Results showed that the operating HRTs of 15, 30 and 60 minutes could represent a kind of shock hydraulic loading condition, which insufficient FOG removal efficiencies were observed. Also, the experiment to enhance the grease trap’s performance was set up by withdrawing certain volume of grease trap waste. The operating HRT of 60 minutes with the feed contained FOG of 200 mg/l and dishwashing detergent of 0.5% (v/v) was investigated for seven-day period. The experiment without daily withdrawal was operated in parallel as a control. The results showed that the FOG removal efficiencies in the control began to fall down to 50% on the fifth day of operation. The experiment with daily withdrawal showed more stable FOG removal efficiencies, which its efficiencies was still higher than 50% after seven days of the experiment. However, this could be said that the 15-litre package on-site grease trap fed with operating HRT of 60 minutes (or lower) could not maintain sufficient removal efficiency for long period (months).

Although it is known that immature composts can depress plant growth, few studies have quantified this effect in real-world scenarios with field-grown crops. Glasshouse and field trials were used to investigate the effect of maturation of grease trap compost (GTC) on plant growth. Grease trap waste was composted for 7-14 d in an in-vessel reactor with shredded green waste, sawdust and chicken manure and matured in windrows for up to 6 weeks. In the glasshouse trial, compost samples were mixed with an equal volume of coarse sand and were compared with a standard mix of 3 parts composted pine bark to 1 part coarse sand (v/v). In these trials, fresh GTC suppressed germination and growth of both radish and alyssum compared to the standard mix. Two weeks maturation reduced phytotoxicity of GTC but it was still phytotoxic relative to the standard mix. After 6 weeks maturation, GTC performed as well as the standard mix in all measures of plant growth and germination except for plant height of alyssum. Fresh and mature GTC were also used as soil conditioners in field trials on a commercial vegetable farm in the Werribee irrigation district, Victoria, Australia. Treatments consisted of GTC at 5 or 10 t ha−1, nil compost or a pelletised poultry manure product (Zest®) at 618 kg ha−1 arranged in a factorial design with 100% and 75% of the grower's standard fertilizer rate (741 kg ha−1 Rustica-Plus®). Head weight of lettuce was significantly reduced (by up to 18%) by the application of 10 t ha−1 of fresh GTC at the grower's standard fertiliser rate. When the fertiliser rate was reduced to 75%, the negative impact of fresh GTC was less apparent. In contrast to the first crop, the performance of mature GTC compared to the controls was independent of fertilizer rate (soil amendment x fertilizer interaction not significant at p<0.05). Application of 5 and 10 t ha−1 of mature GTC increased head weight of lettuce by 11% and 12% respectively compared to the control plus Zest® treatment. This research highlights the need of a better understanding of the maturity requirements of composts for use as soil amendments and growing media in horticultural production.

Characterisation of FOGs in grease trap waste from the processing of chickens in Thailand

Forty-eight (37.7 ± 3.4 kg, initial shrunk live weight) lambs were used in a 61 d experiment to evaluate the energy value of grease trap waste (GT) at four levels of supplementation (0%, 2%, 4%, and 6%). Supplemental GT replaced cracked corn in the basal diet. The GT contained 6.4% moisture, 3.1% impurities, and 79.8% total fatty acids (FA). Increasing GT level in diets did not affect dry matter intake and daily weight gain but linearly increased gain efficiency and estimated dietary net energy (NE). However, the ratio of observed-to-expected diet NE decreased with increased levels of GT. The estimated NE values for GT based on FA intake were in close agreement (98% and 102% of predicted, respectively) with those NE values determined by replacement technique for 2% and 4% supplementation level. However, the observed NE value for GT supplemented at the 6% level was 9% lower than predicted. Kidney–pelvic–heart fat increased as level of GT supplementation increased; otherwise, carcass characteristics and shoulder composition were not affected. We conclude that GT is a suitable alternative to conventional feed fats in diets for finishing lambs. The estimated NE of GT is 93% the energy value assigned by current standards for tallow and yellow grease.

Model development and evaluation of methane potential from anaerobic co-digestion of municipal wastewater sludge and un-dewatered grease trap waste

Anaerobic co-digestion of municipal wastewater sludge and un-dewatered grease trap waste for assessing direct feed of grease trap waste in municipal digesters

Enhancing biomethanation of municipal waste sludge with grease trap waste as a co-substrate

Current Australian legislation permits the beneficial application of grease trap waste (GTW) to agricultural soil, viewing it as a beneficial source of organic matter and soil conditioner containing no/low amounts of metals or pathogenic organisms. However, little is known about the influence of GTW on soil bacterial community. A field experiment was established at Menangle in south western Sydney in Australia to quantitatively assess the impacts of different types (GTW CO and GTW CL) and amounts of GTW application on the soil bacterial community and diversity. Furthermore, a municipal solid waste (MSW) compost was simultaneously examined to compare against the other organic wastes. Knowledge about the shifts in microbial community structure and diversity following the applications of organic wastes could help to evaluate the ecological consequences on the soil and thus to develop sound regulatory guidelines for the beneficial reuse of organic wastes in agricultural lands. Soil samples were collected from recycled organics plots treated with different types and quantity of organic wastes. The field experimental treatments included control (CK, without application of any organic wastes), low amount of GTW CO (COL), GTW CL (CLL), and MSW (ML), and high amounts of GTW CO (COH), GTW CL (CLH), and MSW compost (MH). Microbial DNA was extracted from soil samples and the 16S rRNA genes were polymerase chain reaction (PCR)-amplified. The PCR products were analyzed by denaturing gradient gel electrophoresis (DGGE), cloning, and sequencing. The bacterial community structures and diversity were assessed using the DGGE profiles and clone libraries constructed from the excised DGGE bands. DGGE-based analyses showed that application of the GTW CO, regardless of the amount applied, had significant negative effects on soil bacterial genotypic diversity and community structure compared with the control, while the applications of other organic wastes including the GTW CL and MSW had no clear effects. The effects of the rate of organic waste application on soil bacterial community characteristics varied with the types of organic wastes applied. Sequence-based analyses of 126 clones indicated that Proteobacteria (53.2%) was the dominant taxa at the experimental site, followed by Actinobacteria (9.5%), Bacteroidetes (7.9%), Firmicutes (7.9%), Gemmatimonadetes (5.6%), Chloroflexi (2.4%), Acidobacteria (1.6%) and the unclassified group (11.9%). In the COH treatment, Acidobacteria, Bacteroidetes, and Gemmatimonadetes were not detected; the percentages of Firmicutes, Proteobacteria, and Actinobacteria in the COH treatment were significantly different from those in CK. There is a significant positive correlation (r = 0.71, p = 0.002) between the C/N ratio of organic wastes and the bacterial genotypic communities. Both the type and the amount of GTW applied affected soil bacterial genotypic diversity and community structure. The different effects of various types of organic wastes on soil bacterial characteristics may be predicted by the differences in specific properties of organic wastes such as C/N ratio, as evidenced by the strong and significant positive relationship between the bacterial community distance and the environmental distance of C/N ratio. This also indicates that the C/N ratio of GTW applied can be a major driver for the shift in the soil bacterial community. Our results revealed that the effects of organic wastes on soil bacterial communities varied with the types of organic wastes, and depending on the rate of application. Application of the GTW CO led to significant shifts in soil bacterial community diversity and structure. The effects of different types of organic wastes on the soil bacterial characteristics can be predicted by the differences of specific properties of organic wastes, such as the C/N ratio. Sequence-based analyses of 126 clones indicated that Proteobacteria was the dominant taxa at the experimental site. Our results have important implications for developing sound regulatory guidelines for the beneficial reuse of organic wastes, indicating that GTW CO and similar organic waste treatments may not be suitable for application in agricultural soils due to its significant negative effect on soil bacterial community.

Experimental investigation of iron removal from wet phosphoric acid through chemical precipitation process

As byproducts generated by commercial and domestic food-related processes, FOGs (fats, oils, and grease) are the leading cause of sewer pipe blockages in the US and around the world. Grease trap waste (GTW) is a subcategory of FOG currently disposed of as waste, resulting in an economic burden for GTW generators and handlers. This presents a global need for both resource conservation and carbon footprint reduction, particularly through increased waste upcycling. Therefore, it is critical to better understand current GTW handling practices in the context of the urban food–energy–water cycle. This can be accomplished with firsthand data collection, such as onsite visits, phone discussions, and targeted questionnaires. GTW disposal methods were found to be regional and correspond to key geographical locations, with landfill operations mostly practiced in the Midwest regions, incineration mainly in the Northeast and Mid-Atlantic regions, and digestion mainly in the West of the US. Select GTW samples were analyzed to evaluate their potential reuse as low-cost feedstocks for biodiesel or renewable diesel, which are alternatives to petroleum diesel fuels. Various GTW lipid extraction technologies have been reviewed, and more studies were found on converting GTW into biodiesel rather than renewable diesel. The challenges for these two pathways are the high sulfur content in biodiesel and the metal contents in renewable diesel, respectively. GTW lipid extraction technologies should overcome these issues while producing minimum-viable products with higher market values.

This thesis evaluates the technical, economic, and environmental impacts of producing biofuels from greases that accumulate in wastewater systems. The research in this thesis is accomplished through performing four tasks: (1) identification of the statistical variability in wastewater grease composition and its subsequent impact on biodiesel production capacity, (2) exploration of processing methods and their performance in meeting biodiesel fuel specifications, (3) evaluation of the environmental performance of biodiesel produced from wastewater grease feedstock, and (4) analysis of economic and environmental feasibility of producing biodiesel from wastewater greases. The two wastewater greases investigated in this thesis are grease trap waste (GTW), which is collected at restaurants, and sewage scum grease (SSG), which is collected at wastewater resource recovery facilities (WRRFs). Because wastewater greases are heterogeneous, degraded, and contain large amounts of water, solids, and impurities, GTW and SSG require different chemistry and additional processing steps for biodiesel production compared to conventional biodiesel feedstocks. The composition variability and a variety of parameters including wastewater quality are assessed during a year-long longitudinal study of GTW and SSG. GTW is primarily composed of water and has low lipid content (4%); however, ambient settling of GTW produces a floating grease layer that concentrates the lipids (34%). The average lipid content SSG (21%) is comparable to the float grease in GTW; however, SSG lipid content exhibits seasonal variability that is not observed in GTW. SSG has higher lipid content in cooler months (15-40%) and lower lipid content in warmer months (3-21%). Both GTW and SSG lipids have similar free fatty acid content (75%) affects the reaction pathways used for conversion into biodiesel. Technical feasibility of biodiesel production is assessed using a variety of reactors and distillation techniques. A major hurdle to producing biodiesel is reducing sulfur content to meet fuel specifications; approximately 56% of wastewater grease biofuel samples in this project contain between 15-30 ppm sulfur, and only 23% are below the required fuel specification of 15 ppm sulfur. Sulfur contents are shown to decrease throughout biodiesel production with an overall sulfur reduction of 75-96%. This thesis presents life cycle assessment (LCA) and techno-economic analysis to determine the environmental impacts and economics of biodiesel produced from wastewater greases. A process model is used to incorporate experimental biodiesel processing results and to create an inventory of the materials and energy required for biodiesel production. Monte Carlo simulation is used to perform a sensitivity analysis utilizing the longitudinal study data for variability of composition and biodiesel plant capacities. LCA is used to compare the greenhouse gas emissions (GHG) of biodiesel production to current raw grease disposal (business as usual) and a variety of solid waste disposal facilities including anaerobic digestion, incineration, and landfilling. Each solid waste scenario produces biogenic fuels that are considered to displace an equal amount of an existing petroleum fuel; this replacement of the petroleum fuel is treated as a credit (negative value). The waste solid disposal is the highest contributor to GHG emissions (20-40%, depending on lipid content). Multiple solid waste disposals facilities are also analyzed and showed that landfilling has the highest GHG, followed by incineration, and anaerobic digestion has the lowest GHG emissions. Biodiesel production from wastewater greases has the potential to lower GHG emissions by 20-75% compared to current methods of disposal of wastewater greases.

Municipal wastewater treatment facilities have typically been limited to the role of accepting wastewater, treating it to required levels, and disposing of its treatment residuals. However, a new view is emerging which includes wastewater treatment facilities as regional resource recovery centers. This view is a direct result of increasingly stringent regulations, concerns over energy use, carbon footprint, and worldwide depletion of fossil fuel resources. Resources in wastewater include chemical and thermal energy, as well as nutrients, and water. A waste stream such as residual grease, which concentrates in the drainage from restaurants (referred to as Trap Waste), is a good example of a resource with an energy content that can be recovered for beneficial reuse. If left in wastewater, grease accumulates inside of the wastewater collection system and can lead to increased corrosion and pipe blockages that can cause wastewater overflows. Also, grease in wastewater that arrives at the treatment facility can impair the operation of preliminary treatment equipment and is only partly removed in the primary treatment process. In addition, residual grease increases the demand in treatment materials such as oxygen in the secondary treatment process. When disposed of in landfills, grease is likely to undergo anaerobic decay prior to landfill capping, resulting in the atmospheric release of methane, a greenhouse gas (GHG). This research project was therefore conceptualized and implemented by the San Francisco Public Utilities Commission (SFPUC) to test the feasibility of energy recovery from Trap Waste in the form of Biodiesel or Methane gas. The research goals are given below: To validate technology performance; To determine the costs and benefits [including economic, socioeconomic, and GHG emissions reduction] associated with co-locating this type of operation at a municipal wastewater treatment plant (WWTP); To develop a business case or model for replication of the program by other municipal agencies (as applicable). In order to accomplish the goals of the project, the following steps were performed: 1. Operation of a demonstration facility designed to receive 10,000 to 12,000 gallons of raw Trap Waste each day from private Trap Waste hauling companies. The demonstration facility was designed and built by Pacific Biodiesel Technologies (PBTech). The demonstration facility would also recover 300 gallons of Brown Grease per day from the raw Trap Waste. The recovered Brown Grease was expected to contain no more than 2% Moisture, Insolubles, and Unsaponifiables (MIU) combined. 2. Co-digestion of the side streams (generated during the recovery of 300 gallons of Brown Grease from the raw Trap Waste) with wastewater sludge in the WWTP's anaerobic digesters. The effects of the side streams on anaerobic digestion were quantified by comparison with baseline data. 3. Production of 240 gallons per day of ASTM D6751-S15 grade Biodiesel fuel via a Biodiesel conversion demonstration facility, with the use of recovered Brown Grease as a feedstock. The demonstration facility was designed and built by Blackgold Biofuels (BGB). Side streams from this process were also co-digested with wastewater sludge. Bench-scale anaerobic digestion testing was conducted on side streams from both demonstration facilities to determine potential toxicity and/or changes in biogas production in the WWTP anaerobic digester. While there is a lot of theoretical data available on the lab-scale production of Biodiesel from grease Trap Waste, this full-scale demonstration project was one of the first of its kind in the United States. The project's environmental impacts were expected to include: Reduction of greenhouse gas emissions by prevention of the release of methane at landfills. Although the combustion product of Biodiesel and Methane gas produced in the Anaerobic digester, Carbon Dioxide, is also a greenhouse gas; it is 20 times weaker for the same amount (per mole) released, making its discharge preferable to that of Methane. The use of Biodiesel in place of fossil-fuel derived Diesel was expected to reduce net Carbon Dioxide, Ash Particulate, Sulfate, Silicate, and Soot emissions, thereby improving air quality.