Researchers at the Georgia Tech Research Institute (GTRI) recently commissioned a dynamic filtration system capable of improved screening of poultry wastewater and other liquid streams with a variety of organic solids. The efforts result from a goal of achieving process water solids separations with one technology that can rival screens (medium and microscreening). Research has culminated in a provisional patent application.
“Some facilities see wastewater treatment as a mandatory cost, while others have looked for ways to extract or produce additional value, such as anaerobic processes that produce methane or water reuse,” says John Pierson, principal research engineer and project director.
Pierson and his team started by looking at water reuse opportunities but with an additional focus on capturing potentially useful byproducts.
“You realize that one option is to treat different process streams separately before these are combined in wastewater like scalders and chillers, but the underlying issue remains removing the finer particles or microscreening, since that is where the flux rate really starts to drop off,” explains Pierson.
Solids separation using physical means (filters, sieves, membranes) is typically described in terms of a flux rate or the volume of water through the filter area in a particular time period. Over time, the flux rate decreases as solids build up on the separation surface, reducing the amount of filtered water passed each minute even though the pressure builds in the direction of flow.
For primary and secondary screens, water is usually sprayed on the screens to wash the solids off as these are collected. However, microscreening systems are typically closed so that higher pressures can be delivered to yield needed flux rates. These higher pressure systems, including micro- and ultrafiltration, require more energy.
During the development of the dynamic filtration system, researchers processed coffee grounds and yeast at chemical oxygen demand (COD) and total suspended solids (TSS) concentrations that are significantly higher than analogous values for poultry liquid streams. By doing this, they realized they could capture greater than 95 percent of solids with a cascade of 212-micron screens followed by 75-micron screens. With surrogate chiller water and then actual marination effluents, they captured more than 90 percent of the protein.
“The advantage of the system is that we can backwash at any time during processing based on pressure buildup or a decrease in flow or throughput. And the way the system works, we are always keeping particles concentrated but not entrained in the separation surface, allowing us to remove that material during filtering,” says Pierson.
The current prototype can process roughly one liter per minute, but researchers are designing a scaled-up device capable of flow rates useful for poultry processing. Additionally, researchers have tested the system with 2-micron and 0.22-micron filters, resulting in a concentration of pathogens in the processed liquid stream.
Moving forward the team plans to conduct tests to quantify floatable materials including fats, oils, and greases and examine chiller water and other poultry liquid streams.
“We think we can build a system that uses one technological approach to remove solids and microbial contamination from the liquid stream. USDA water reuse guidelines remain our focus, but we think we can also either capture useful byproducts or produce a drier product to be sent to rendering,” says Pierson.
Funding for development of the dynamic filtration system is provided by GTRI’s Agricultural Technology Research Program (ATRP) with additional funding from the U.S. Poultry & Egg Association’s Harold E. Ford Foundation.