Excessive phosphorus in wastewater discharge from poultry processing plants can degrade water quality and harm aquatic life in adjacent waterways. This makes effective wastewater treatment to remove the phosphorus in effluent a top priority for poultry processors. Chemical precipitation is the removal method used by most processors, but it is expensive and results in the production of sludge, which must be disposed of, further adding to treatment costs. Novel technologies such as nanomaterials are now being studied as potentially low-cost and environmentally friendly wastewater treatment alternatives.
Here, continuing work by the Georgia Tech Research Institute (GTRI) is showing promise as researchers have developed a magnetic nanoparticle (MNP)-based phosphorus removal method. It uses a proprietary MNP to capture and then remove phosphorus from poultry processing wastewater.
“We have made a functionalized magnetic nanoparticle to provide selective bindings to various phosphorus species in wastewater. The phosphorus removal method is not only economical and environmentally friendly but also makes it possible to achieve both phosphorus recovery in poultry processing wastewater and long-term water reuse,” says Dr. Jie Xu, GTRI principal research scientist and project director.
Xu and her team have been granted a provisional patent for their phosphorus removal chemistry, which when applied to the surface of an MNP attracts and attaches phosphorus species contained in the wastewater sample. These phosphorus-attached MNPs are then easily removed from the wastewater by an external magnet.
Initial experiments using the MNPs in poultry processing wastewater resulted in greater than 90-percent removal efficiency. The method was also tested in poultry rinsing water, tap water, and municipal wastewaters, and resulted in similarly high phosphate removal efficiencies.
And the method has been shown to be a very effective adsorbent even in the presence of other anions and organic materials like fats and proteins. This allows the MNPs to be used in a variety of wastewater treatment applications.
“The adsorption process only takes about 30 minutes, and the treatment process only requires one step. There is no filtration, centrifugation, or chemical addition,” says Xu.
The complete process is carried out in a continuous flow-through device where the MNPs can be regenerated for repeated use, currently up to 10 times, which lowers treatment costs. Residual MNP particles in the treated wastewater are negligible, and the method does not generate a large amount of sludge compared to chemical precipitation, meaning processors can reduce disposal costs. An added benefit long-term is the recovered phosphorus can be converted into a value-added product like fertilizer.
The team recently performed wastewater characterization and phosphorus speciation studies to understand the effectiveness of the MNP treatment method on different phosphorus species in the presence of other pollutants in various wastewater samples.
“A critical research aspect is characterizing the MNP technology as well as the target liquid stream,” says Xu. “For the MNP technology, the characterization includes assessments before, during, and after deployment. In all cases, the mechanism of performance and efficacy are the focus, both with regard to liquid stream improvement and MNP performance.”
Working with a local poultry wastewater treatment plant, the team collected samples from different liquid streams, including raw effluent, effluent of dissolved air flotation (DAF), effluent of biological treatment, effluent of chemical DAF, and the final effluent of the equalization pond. The samples were characterized with high contamination levels of COD (chemical oxygen demand), FOG (fats, oils, grease), TSS (total suspended solids), and TP (total phosphorus) .
Results showed that treatment of the collected wastewater samples with the MNP not only reduced TP significantly (more than 90 percent) in all the samples, but also decreased the levels of other contaminants, including COD, TSS, and FOG. However, there is an inherent tradeoff between the TP removal efficiency when these other constituents are present, notes Xu. So, she suggests, if the main focus is the removal of TP, deploying the MNP technology after the primary DAF system might yield the best results.
The team also conducted phosphorus speciation analyses on the samples from the same liquid streams as in the characterization studies. According to Xu, most discharge permit limits are based on total phosphorus, so all forms of phosphorus in the final effluent need to be considered for phosphorus removal. Results showed that almost all reactive phosphorus (orthophosphate) and organic phosphorus either in soluble or particulate forms were removed by the MNPs, which is preferable over acid-hydrolyzable phosphorus (polyphosphate).
“These tests confirm that our MNP is effective at removing phosphorus as well as reducing contaminant levels in various poultry wastewater streams,” says Xu. “We are encouraged by these results and are working on optimizing our synthesis method so that the MNP can ultimately be produced and used at a low cost to processors.”