Problems with Fat, Oil, and Grease (FOG) in Food Industry Wastewaters and Recovered FOG Recycling Methods Using Anaerobic Co-Digestion: A Short Review

Micro and macro analysis of restaurant wastewater containing fat, oil, grease (FOG): An approach based on prevention, control, and sustainable management

The number of restaurants is increasing day by day in almost all the developing countries, causing the increase in the generation of restaurant wastewater. Various activities (i.e., cleaning, washing, and cooking) going on in the restaurant kitchen lead to restaurant wastewater (RWW). RWW has high concentrations of chemical oxygen demand (COD), biochemical oxygen demand (BOD), nutrients such as potassium, phosphorus, and nitrogen, and solids. RWW also contains fats, oil, and grease (FOG) in alarmingly high concentration, which after congealing can constrict the sewer lines, leading to blockages, backups, and sanitatry sewer overflows (SSOs). The paper provides an insight to the details of RWW containing FOG collected from a gravity grease interceptor at a specific site in Malaysia, and its expected consequences and the sustainable management plan as prevention, control, and mitigation (PCM) approach. The results showed that the concentrations of pollutants are very high as compared to the discharge standards given by Department of Environment, Malaysia. Maximum values for COD, BOD and FOG in the restaurant wastewater samples were found to be 9948, 3170, and 1640 mg/l, respectively. FAME and FESEM analysis are done on the RWW containing FOG. In the FOG, palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9c), linoleic acid (C18:2n6c) are the dominant lipid acids with a maximum of 41, 8.4, 43.2, and 11.5%, respectively. FESEM analysis showed formation of whitish layers fprmed due to the deposition of calcium salts. Furthermore, a novel design of indoor hydromechanical grease interceptor (HGI) was proposed in the study based on the Malaysian conditions of restaurant. The HGI was designed for a maximum flow rate of 132 L per minute and a maximum FOG capacity of 60 kg.

Primary Sludge from Dairy and Meat Processing Wastewater and Waste from Biomass Enzymatic Hydrolysis as Resources in Anaerobic Digestion and Co-Digestion Supplemented with Biodegradable Surfactants as Process Enhancers

Incorporation of various alternative resources as co-digestion substrates aids to reduce the consumption of agricultural crops for biogas production. However, the efficiency and limitations of these co-substrates is still not fully understood. Use of biomass waste remaining after enzymatic hydrolysis for high value chemical fermentation, meat processing and dairy wastewater primary sludge as co-substrates in an agricultural resource anaerobic digestion plant is tackled within this study. The results showed that anionic surfactants (<200 ppm) can be used to improve fat, oil and grease (FOG) solubility in water and, at the same time, enhance the biomethane potential of FOG-containing sludge by increasing it from 1374.5 to 1765 mLCH4/gVS for meat processing wastewater primary sludge, and from 534 to 740 mLCH4/gVS for dairy wastewater primary sludge, when agricultural digestate is used as a substrate and sludge loading is not more than 10% from the volatile solids loaded. At the same time, only 549.7 mLCH4/gVS was produced as 30-day BMP when 5% biomass hydrolysis waste was used. Biomass hydrolysis waste co-digestion with primary sludge from dairy and meat processing wastewaters has an antigenic effect, and separate substrate anaerobic digestion gave a better results, thus, showing that excessive combination of various waste resources can be inhibitory for biogas production and the appropriate substrate selection and combination is a technical challenge for the biogas industry.

Valorization of lipid-rich wastewaters: A theoretical analysis to tackle the competition between polyhydroxyalkanoate and triacylglyceride-storing populations

The lipid fraction of the effluents generated in several food-processing activities can be transformed into polyhydroxyalkanoates (PHAs) and triacylglycerides (TAGs), through open culture biotechnologies. Although competition between storing and non-storing populations in mixed microbial cultures (MMCs) has been widely studied, the right selective environment allowing for the robust enrichment of a community when different types of accumulators coexist is still not clear. In this research, comprehensive metabolic analyses of PHA and TAG synthesis and degradation, and concomitant respiration of external carbon, were used to understand and explain the changes observed in a laboratory-scale bioreactor fed with the lipid-rich fraction (mainly oleic acid) of a wastewater stream produced in the fish-canning industry. It was concluded that the mode of oxygen, carbon, and nitrogen supply determines the enrichment of the culture in specific populations, and hence the type of intracellular compounds preferentially accumulated. Coupled carbon and nitrogen feeding regime mainly selects for TAG producers whereas uncoupled feeding leads to PHA or TAG production function of the rate of carbon supply under specific aeration rates and feast and famine phases lengths.

Food-processing wastes

Literature published in 2018 and literature published in 2019 related to food-processing wastes treatment for industrial applications are reviewed. This review is a subsection of the Treatment Systems section of the annual Water Environment Federation literature review and covers the following food-processing industries and applications: general, meat and poultry, fruits and vegetables, dairy and beverage, and miscellaneous treatment of food wastes. PRACTITIONER POINTS: This article summarizes literature reviews published in 2018 and in 2019 related to food processing wastes treatment for industrial applications are reviewed. This review is a subsection of the Treatment Systems section of the annual Water Environment Federation literature review and covers the following food processing industries and applications: general, meat and poultry, fruits and vegetables, dairy and beverage, and miscellaneous treatment of food wastes.

Microwave vs. alkaline-microwave pretreatment for enhancing Thickened Waste Activated Sludge and fat, oil, and grease solubilization, degradation and biogas production

The effects of microwave (MW) and combined alkaline-MW pretreatments on the co-digestion of TWAS:FOG mixtures with 20, 40 and 60% FOG were investigated. MW pretreatment at a high temperature of 175ᵒC was shown to be the most effective MW pretreatment option in solubilizing TWAS:FOG mixtures and boosting methane yield. MW pretreatment at 175ᵒC resulted in maximum solubilization (%) of 68.2% for the 20%FOG samples and a maximum methane yield that was 137% higher than the control for samples with 60%FOG. The combined alkaline-MW (NaOH-MW) pretreatment at pH 10 proved to be not an effective option for TWAS:FOG pretreatment before the anaerobic co-digestion. Despite the benefits of MW pretreatment on the TWAS:FOG samples, including a significant increase in solubilization, dewaterability improvement, high VS reductions, and high methane yield productions, the energy analysis resulted in negative net energy values for all MW-pretreated samples.

Effect of Organic Loading Rate on Anaerobic Digestion Performance of Mesophilic (UASB) Reactor Using Cattle Slaughterhouse Wastewater as Substrate

In this study, the performance of a laboratory scale upflow anaerobic sludge blanket (UASB) reactor operating at mesophilic temperature (35 °C) was examined. Cattle slaughterhouse wastewater (CSWW) was used as the main substrate. The total and effective volumes of the reactor were 8 L and 6 L, respectively. Twelve different organic loading rates (OLR) were applied and the performance was evaluated. The chemical oxygen demand (COD) removal efficiency was more than 90% during batch study. In the continuous study, COD removal was also approximately 90% at OLR 0.4 g/L d⁻¹ which subsequently dropped to below 50% when the loading rate increased to 15 g/L d⁻¹. Approximately 5 L/d of biogas was obtained with high methane concentration at stages VI and XI corresponding to OLR of 2 and 10 g/L d⁻¹, respectively. It was observed that the concentration of volatile fatty acids was low and that the alkalinity of the wastewater was sufficient to avoid acidification. Specific methane yields of 0.36 and 0.38 LCH₄/g COD added were achieved at OLR 7 and 10 g/L d⁻¹. A hydraulic retention time (HRT) of 1 day was sufficient to remove greater than 70% of COD which correspond to 89% methane concentration. Parameters like soluble COD, NH₃-N, pH, alkalinity, total suspended solid (TSS), fats, oil, and grease were also investigated. The results show that the UASB reactor could serve as a good alternative for anaerobic treatment of CSWW and methane production.