(505a) Additive-Free Treatment of High-Strength Agricultural Wastewaters Using Ultrafiltration

The rendering industry protects the environment by processing animal by-products into pet and livestock feed ingredients, materials, fuels, among other products, rather than entering them into a landfill. During this processing, rendering plants generate large volumes of highly impaired wastewater containing high total suspended solids, fats, oils and greases, and proteins. Most facilities use dissolved air flotation (DAF) for primary treatment of their wastewaters, with a very high operating cost of roughly US $3.20/1000 gal of wastewater.

In this contribution, we will discuss our latest work on the use of membrane filtration for the additive-free treatment of high-strength rendering facility wastewaters. The objectives of the present project are to 1) evaluate the performance of ultrafiltration (UF) membranes in the primary treatment of rendering wastewater; 2) understand how cross-flow filtration operating conditions (i.e., cross-flow velocity, transmembrane pressure, and total suspended solids) impact membrane performance; 3) measure the threshold flux for UF membranes; 4) evaluate cleaning protocols for UF membranes.

Our results have demonstrated that UF membranes can efficiently purify the wastewater without the polymeric and pH-adjusting additives required by DAF. Ultrafiltration with a membrane characterized by a pure water permeability of 0.1 L/(m²·h)/kPa reduced turbidity of the wastewater nearly 100%, chemical oxygen demand by 80%, and total solids by 90%. Operating below threshold flux enabled long-term, steady state measurements. Based on membrane performance, a mathematical model was proposed to predict flux behavior under different operating conditions.

In addition to experimental work, a preliminary cost analysis was done to compare the operating costs (energy and consumables) of the membrane ultrafiltration process to DAF. Assuming a conservative membrane lifetime of 1 year, the results suggest that the application of UF membranes in treating rendering wastewaters can reduce the operating cost to slightly less than $1.00/1000 gal of wastewater. In addition to the significantly lower projected operating costs for the membrane process, there are likely to be other economic benefits associated with the removal of chemical additives from the process.