PRETREATMENT OF ANIMAL FAT THROUGH COARSE SAND FILTERS. Rashmi Singh Gaur, Ling Cai, Karen M. Mancl, and Olli H. Tuovinen

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1 PRETREATMENT OF ANIMAL FAT THROUGH COARSE SAND FILTERS Rashmi Singh Gaur, Ling Cai, Karen M. Mancl, and Olli H. Tuovinen Abstract Wastewaters with high contents of fat, oil and grease can be difficult to treat because of their slow rate of microbial transformations. Traditional preliminary treatment facilities to remove fat, oil and grease from wastewater prior to treatment create disposal problems and increase treatment costs. The objective of this study was to investigate the pretreatment performance of coarse sand and with or without a pea gravel pre-filter cap. Ideally, a successful pretreatment would change to COD/BOD 5 ratio to 1., implying that all organic matter is readily biodegradable. In this work, the ratios ranged from 1. to 3. following the pre-treatment step. This study indicated that the sand filter bioreactors with a 4-inch (1.16 cm) coarse sand layer was the most efficient in converting COD to BOD 5 as compared with other bioreactors, although none of the experimental bioreactors failed to support the conversion. Introduction Restaurants, food processing plants and dairy industries produce wastewater containing high levels of animal fat. The accumulation of animal fat can cause problems in wastewater treatment plants, such as blockages in drainage systems, scum formation on the surface of septic tanks and accumulation on interior pipe surfaces, and may eventually cause clogging and shutdown of treatment plant units. In 24, the U.S. EPA set wastewater discharge standards for meat and poultry products industries. This regulation has affected about 17 facilities that discharge wastewater from slaughtering, rendering and related processes such as cleaning, cutting, and smoking of metal products. Discharge limits of conventional pollutants, ammonia and nitrogen, were reduced in this new rule. It also set up national effluent limitations for poultry processes for the first time. Because of the new limits for meat and poultry related facilities, research on developing and testing methods for treating animal fat has become urgent. Wastewaters with high levels of fat, oil and grease can be difficult to treat because of the formation of flocs with poor settling characteristics in mixed liquor processes (Hopwood, 1977). Pre-treatment to remove fat, oil and grease from wastewater is also problematic because of disposal problems. Sand filters, relying on active biofilms that coat sand particles, have been used for wastewater treatment for over a century (Mancl and Peeples, 1991). Treatment of high fat turkey processing wastewater using layered sand filters has been evaluated (Kang, 24). Filters constructed with fine sand topped with a layer of coarse sand and a pea gravel cap provided sufficient treatment with long R.S. Gaur, Postdoctoral Research Associate, L. Cai, Visiting Scientist, and K.M Mancl, Professor, Food, Agricultural and Biological Engineering ( O.H. Tuovinen, Professor, Department of Microbiology, Ohio State University, Columbus, Ohio 4321.

2 filter runs to meet effluent standards. Some benefits of layered sand bioreactors in degrading fat were presented by Liu et al. (2). The biodegradation of butterfat supplemented with detergent formulation was assessed in layered sand biofilters with different configurations. The two- and threelayer filters had comparable performance measured as removal of chemical oxygen demand (COD) and biochemical oxygen demand (BOD 5 ), but the three-layer sand filters lasted longer before clogging. The in-series filters were the best design for COD and BOD 5 removal but they were prone to clog. However, Liu et al (2) did not explore the appropriate depth of the coarse sand layer to optimize the pre-treatment. Sand bioreactors are resistant to transient temporal changes such as ph or toxic metals and they need a minimum of care and maintenance and have a low operating cost as compared to the activated sludge process. Sand filtration systems are biofilm-driven processes, whereby microbial biofilms are established on sand grains and the resulting microbial communities are responsible for biotransformation, biodegradation, mineralization, and nutrient assimilation processes involved in wastewater purification. Biofilms containing lipolytic microorganisms are best suited for degrading fat and oil substrates. Lipases in these organisms act on fatty acid chains of triglycerides at the lipidwater interface (Brune and Götz, 1992). The hydrolytic enzyme reaction releases fatty acids, which can be utilized through the beta-oxidation pathway as carbon and energy sources (Ratledge, 1994). The objective of this study was to investigate the pre-treatment performance of coarse sand and the pea gravel. Specifically, the depth of coarse sand and a pea gravel layer were evaluated for the pretreatment of turkey processing wastewater. The goal of the pre-treatment of this wastewater in this study was to convert recalcitrant organic matter, taking longer than five days to degrade, to a more readily biodegradable form. It was hypothesized that under appropriate experimental conditions the pre-treatment would increase the BOD 5 of the wastewater passing through the sand filter column. Pre-treatment studies on sand filtration will be helpful in scaling up of the process for commercial applications. Materials and methods Artificial wastewater used in this study contained 4 mg purified turkey fat per liter of mineral salts solution, which was based on the formulation of BOD 5 (APHA, 1998). The pre-treatment of turkey fat was evaluated using bench-scale sand filter bioreactors. Twenty PVC columns (12 inch for coarse sand columns; 24 inch for coarse sand with a 6 inch pea gravel cap columns and 1.6 inch internal diameter) were constructed and fitted with an end cap. A hole (.25 inch) was drilled at the bottom to drain the effluent. All columns were coarse sand biofilters of varying depth and each had a 1-inch supporting layer of pea gravel at the bottom, followed by a varying depth (2, 4, 6, 8 or 1 inches) of coarse sand. An additional set of columns had a 6-inch layer of pea gravel on the top of the coarse sand layer (Figure 1). All columns were operated in duplicates.

3 Effluent Effluent Pea Gravel Coarse Sand Fig. 1. Column design used in this study. Each design was tested with duplicate columns. The columns were inoculated from the sand bioreactors used for treating turkey processing wastewater. After ten days of batch mode incubation, artificial turkey fat wastewater was loaded to the columns once a day. The columns were operated at 22±2 C. Each sand bioreactor received 172 ml of artificial wastewater (132 l/m 2 /day; 3.25 gal/ft 2 /day) from the top and the effluent was drained by gravity immediately from the bottom. During the first month of operation, effluent samples were collected once a week and analyzed for BOD 5 and COD (APHA, 1998). Subsequently, the samples were analyzed biweekly for next three months and thereafter once every 5-6 days. Results and Discussion Changes in the BOD 5 concentration over time in the coarse sand bioreactors are presented in Figure 2. The first thirty days of the time course can be regarded as the stabilization period of the sand bioreactors whereby microorganisms were colonized as a biofilm and acclimated to turkey fat in the wastewater. A fresh sample of turkey fat obtained from the turkey processing facility was used in the artificial wastewater starting on day 34. Subsequently, the results for days 43 and 54 showed some fluctuation and then assumed a more or less a stable pattern.

4 BOD5 (mg O2/L) Fig. 2. Changes in the BOD 5 concentration over time in coarse sand columns without pea gravel. In general, the BOD 5 concentration increased upon passage through the sand bioreactor regardless of the depth of the coarse sand layer. Notable exceptions from this trend were seen on day 161, 366, and the first 3 days of feeding the bioreactors with artificial wastewater. These results indicate that fat biodegradation was occurring in the columns, converting fat to more readily biodegradable fractions, thus contributing to BOD 5. This biotransformation was faster than the consumption of BOD 5 in the experimental columns because otherwise there would have been a net decrease in the concentration of BOD 5. A similar trend in the efficiencies of bioreactors with a pea gravel cap on the top was observed as shown in Figure 3. Most effluent BOD 5 data points were higher than for the influent, again indicating that BOD 5 formation and consumption were concurrent and their relative rates varied.

5 BOD5 (mg O2/L) Fig. 3. Changes in the BOD 5 concentration over time in coarse sand columns with a pea gravel cap. Sand filter bioreactors with a pea gravel layer on the top showed comparatively more COD removal than those without pea gravel (Figures 4 and 5). The decrease in COD values in effluent samples as compared to influent may be attributed to entrapment of fat in the pea gravel layer. The biodegradation essentially takes place in the coarse sand layer. This pea gravel layer acts as a sieve to trap suspended solids and fat globules, thereby extending the filter operation before clogging. Biofilm communities on the surface of pea gravel act upon trapped organic matter but the major biodegradation activity is associated with the biofilm in coarse sand layer. Previous work has demonstrated that pea gravel layer extends the filter operation before clogging as compared to bioreactors without pea gravel (Kang, 24).

6 COD (mg O2/L) COD (mg O2/L) Fig. 4. Changes in the COD concentration over time in coarse sand columns without pea gravel Fig. 5. Changes in the COD concentration over time in coarse sand columns with a pea gravel cap. The COD/BOD ratio for the effluent was lower than that of influent, except for first 5 days of column operation due to the fluctuation in BOD 5 and COD values. These fluctuations may be attributed to acclimatization. It is theorized that particulate organic matter was mostly strained by pea gravel and the remaining fraction accumulated in the void space between pea gravel and coarse

7 COD/BOD Ratio sand because there was a decrease of the particle size (from pea gravel to coarse sand) at this interface. The COD/BOD 5 ratio for the influent is higher than for the effluent, indicating that fat has been partially degraded to BOD 5 fractions (Figures 6 and 7). The COD/BOD 5 ratio close to 1. would be the target in this work because it would imply that organic matter is in biodegradable form based on the 5-day assay period and should be treatable in sand biofilters or other treatment systems. The measured ratios varied in the range of 1. to 3. (Tables 1 and 2). Of the experimental columns tested, the 4-inch coarse sand layer design was deemed the most efficient although the other columns were at times inseparable in performance Fig. 6. Changes in the COD/BOD 5 ratios over time in coarse sand columns without pea gravel.

8 COD/BOD Ratio Fig. 7. Changes in the COD/BOD 5 ratios over time in coarse sand columns with pea gravel. Table 1. COD/BOD ratios in columns without pea gravel. Days Ratio(COD/BOD)

9 Table 2. COD/BOD ratios in columns with pea gravel. Days Ratio(COD/BOD) Conclusions This study evaluated the pretreatment of turkey fat-containing wastewater in bioreactors with a varying depth of coarse sand and also for bioreactors with a pea gravel cap. Animal fat is difficult to treat because its biodegradation is too slow for the hydraulic retention time in municipal wastewater treatment facilities. Sand bioreactors showed that it is feasible to pre-treat high fat-containing wastewater, a process that would eliminate fat disposal and reduce the cost of removal. The present work suggested that the bioreactors with a 4-inch (1.2 cm) coarse sand layer was the most efficient in converting COD to BOD as compared with other bioreactors. The 6-inch pea gravel layer on the top slightly enhanced the conversion of slowly degradable carbon to BOD 5, possibly due to a longer duration of filter run. The accumulation of biomass in the upper pea gravel layer is beneficial in the treatment, promoting biodegradation and removal of COD from the influent. To ensure longer runs without clogging, filter systems should be designed to balance COD loading with appropriate capacity of utilization. To be utilized as pretreatment layer of biofilter, the recommended optimal depth of a coarse sand layer is 4 inches with a 6-inch pea gravel cap on the top. The pea gravel layer functions as a sieve for trapping organic particulates, promotes microbial degradation by removing COD of the influent and ensures longer filter runs. Acknowledgements This research was funded in part through a grant by Whitewater Processing, Inc. Support for L.C. was provided by the Institut National Des Sciences Appliquées. Salary and partial research support to K.M.M. were provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center. Additional research support from the BAAS Memorial Endowment Fund is gratefully acknowledged.

10 References APHA Standard methods for the examination of water and wastewater. 2 th edn. American Public Health association, Washington, D.C. Brune, K.A. and F. Götz Degradation of lipids by bacterial lipases. In Winkelmann, G. (Ed.), Microbial Degradation of Natural Products. VCH, Weinheim, pp Hopwood, D Effluent treatment in meat and poultry processing industries. Process Biochem. 12 (5-8), 44, 46. Kang, Y.W. 24. Biological Treatment of Turkey Processing Wastewater with Sand Filtration. Ph.D. Thesis, Ohio State University, Columbus, Ohio. Liu, Q., K.M. Mancl, and O.H. Tuovinen. 2. High fat wastewater remediation using layered sand filter biofilm systems. In Proceedings of the Eighth International Symposium on Animal, Agricultural and Food Processing Waste, American Society of Agricultural Engineers, St. Joseph, MI, pp Mancl, K.M. and J.A. Peeples, J.A One hundred years later: reviewing the work of Massachusetts State Board of Health on the intermittent sand filtration of wastewater from small communities. In Proceedings of the Sixth National Symposium on Individual and Small Community Sewage Systems, American Society of Agricultural Engineers, St. Joseph, MI, pp Ratledge, C Biodegradation of oils, fats and fatty acids. In Ratledge C. (Ed.), Biochemistry of Microbial Degradation. Kluwer, Dordrecht, pp