In southwest Ohio a small turkey processing plant was facing closure. The permitted lagoon system that had treated the plant wastewater for decades created odors and threatened the groundwater. The company was looking for a way to treat the high-strength, high-fat-content wastewater in an affordable way. Pretreating the wastewater with dissolved air floatation (DAF) and constructing a sewer extension to the municipal treatment plant in the neighboring city was deemed cost prohibitive.
The company instead constructed and now operates a sand/gravel bioreactor system under permit from the Ohio EPA and discharges treated wastewater to the Whitewater River. Starting operation in the summer of 2013, the system meets all discharge requirements with treatment costs of $3.90 per 1,000 gal. The treatment system removes and treats fats, oil, and grease (FOG), eliminating the need for a DAF unit. The system was simple to construct on-site using locally available materials and labor.
Sand/Gravel Bioreactor System
Constructed in a 4-feet deep, PVC-lined excavation, layers of specially sized sand and gravel form the biofilm-based treatment system. Research at The Ohio State University showed that microorganisms grow on the surface of sand and gravel particles and filter out and consume the organic matter (CBOD5), FOG, and total suspended solids (TSS). The microbes in the biofilm also convert ammonia to nitrate making the treated wastewater safe to discharge. The overall system is diagramed in Figure 1 and begins with a grease trap and a screen as the primary treatment. Note that if sanitary wastewater is excluded from the grease trap and screen, the captured FOG can be sold to a renderer. The wastewater is then intermittently pumped on to the top of a sand/gravel bioreactor to provide secondary treatment. Final treatment is seasonal with ultraviolet light disinfection during summer months (May through October) and an ion-exchange system for ammonia removal during winter months, as needed, before stream discharge.
The sand/gravel bioreactor system is designed for surface wastewater application of 1.5 gallons per ft2 per day (6 cm a day) with an additional 50% excess capacity for flexibility in operation and to handle peak flows. The bioreactors are constructed with layers of sand and gravel as specified by OSU research. The bottom 6-inch (15 cm) layer of washed rock surrounds the drainage pipe and is topped with 6 inches (15 cm) of pea gravel as shown in Figure 2. The treatment system was built up on top of the drainage system in three layers. The bottom layer is 18 inches (45 cm) of fine sand, the middle layer is 6 inches (15 cm) of coarse sand, and the top layer is 6 inches (15 cm) of pea gravel. The washed, fine sand should have an effective size of 0.3 to 1 mm and a uniformity coefficient less than 4.0. The coarse sand should have an effective size of 2 to 3 mm and a uniformity coefficient less than 2.0. The pea gravel should have an effective size of 3.5–10 mm and a uniformity coefficient less than 2.0. The washed rock should be 2–3 cm size fraction.
The wastewater is applied in about four doses throughout the day. A tank accumulates the wastewater dose, and a pump delivers the wastewater to a series of laterals on the top of the sand/gravel bioreactor to evenly distribute it over the bioreactor area (Kang, Mancl, and Gustafson 2005; Liu and Mancl 2015).
Sand/Gravel Bioreactor Performance
The system constructed for the turkey processing plant is dosed with wastewater that ranges from 567 to 2040 mg/l CBOD5, 166 to 1540 mg/l TSS, 42 to 374 mg/l FOG and 18 to 44 mg/l ammonia-N. The Ohio EPA permit requires that the system meet the discharge limits as presented in Table 1.
|Pollutant||Seven-Day Limit (mg/l)||30-Day Limit (mg/l)|
|Organic matter (CBOD5)||15||10|
|Total Suspended Solids (TSS)||18||12|
|Fats, Oil, and Grease (FOG)||Not applicable||8|
|Ammonia – N (Summer)||1.5||1|
|Ammonia – N (Winter)||4.5||3|
Sand/gravel bioreactors easily meet CBOD5, TSS, and FOG limits throughout the year. If the treated effluent is discharged into a stream, ammonia levels are very important because ammonia is toxic to fish. Sand/gravel bioreactors easily remove ammonia in warm weather. However, in Ohio, late spring is a challenging time for ammonia removal because the air temperature is rising but the sand and gravel are still cold. An ion-exchange system can be used during this time of year to remove excess ammonia to meet effluent limits. A simple color-changing ammonia test can be used by the system operator to check the ammonia levels to determine when the ion-exchange system is needed. An ion-exchange system works just like a water softener and is recharged with salt.
Because a sand/gravel bioreactor system in southwest Ohio discharges to a stream, disinfection is required during the summer months. The sand/gravel treated wastewater is very clear, which allows an ultraviolet (UV) light system to be used for disinfection (Vedachalam, Huang, and Mancl 2011). Figures 3 through 7 provide information on the effluent of a working, sand/gravel bioreactor system in SW Ohio.
The construction of a sand/gravel bioreactor wastewater treatment system is a sound, economic choice for a small-scale food processing plant. The treatment system removes FOG, eliminating the need for a DAF unit. The system is also simple to construct on-site using locally available materials and labor. A sand/gravel bioreactor system is compatible with the high-strength and high-fat-content wastewater discharged from a meat processing plant. With the addition of an ion-exchange system for cold weather and a UV light disinfection system for the summer, this system can meet all Ohio effluent discharge requirements.
Kang, Young Woon, Karen Mancl, and Olli Tuovinen. 2007. Treatment of Turkey Processing Wastewater with Sand Filtration. Bioresource Technology. 98(7): 1460-1466. https://doi.org/10.1016/j.biortech.2006.03.006.
Kang, Young Woon, Karen Mancl, and Robert Gustafson. 2005. Mound Systems: Pressure Distribution of Wastewater. Extension Bulletin 829. The Ohio State University.
Liu, Kun, and Karen Mancl. 2015. Sand and Media Bioreactors: Pressure Distribution of Wastewater Design and Construction in Metric Units. Extension Bulletin 829.1. The Ohio State University. PDF.
Mancl, Karen, Ryan Kopp, and Olli Tuovinen. 2018. Treatment of meat-processing wastewater with a full-scale, low-cost sand/gravel bioreactor system. Applied Engineering in Agriculture. 34(2): 403-409. Doi.org/10.13031/aea.12683.
Tao, Jing, and Karen Mancl. 2011. Sand and Media Bioreactors for Wastewater Treatment for Ohio Communities. Extension Bulletin 876. The Ohio State University. DOI:10.13031/2013.25431.
Vedachalam, Sridhar, XiXi Huang, and Karen Mancl. 2011. Reuse of Reclaimed Wastewater – Disinfection to Protect Public Health. Extension Bulletin 943. The Ohio State University. PDF.