Recent interest in the circular economy has inspired new technologies for nutrient recovery from agricultural waste. Many of these technologies produce fine struvite particles that are lost in effluent streams. The objective of this study was to optimize dosing of natural coagulants to aggregate struvite particles and maximize recovery. In particular, alginate, bentonite, and chitosan were applied to improve struvite recovery from poultry litter. A poultry litter slurry was prepared at pH 4 to mobilize nutrients into the water phase. The nutrient-rich extracts were dosed with sodium hydroxide to pH 9, where struvite particles precipitated. Batch reactors containing 20 mL of poultry litter extract were dosed with primary coagulant (0-50 mg L-1) and coagulant aid (0-75 mg L-1). Chitosan was used as the primary coagulant, while alginate and bentonite were employed as coagulant aids. After chitosan addition, the reactors were rapidly mixed (1 min), slowly mixed (14 min), dosed with coagulant aid, slowly mixed (10 min), and allowed to settle (30 min). The particle size distributions were measured, and heatmaps were developed for the 10th, 50th, and 90th percentile particle diameters as a function of the primary coagulant and coagulant aid concentrations. The application of 0 mg L-1 chitosan with 75 mg L-1 alginate yielded the largest struvite particles; note, the chitosan concentration had no measurable impact on the chitosan-alginate system. The 50 mg L-1 chitosan with 50 mg L-1 bentonite condition provided the best performance for the chitosan-bentonite system. To confirm scalability, 1-L jar tests were conducted under similar conditions as the batch reactors. Samples were collected from (i) the supernatant and (ii) rapidly mixed jars. The particle size distributions were measured in both samples, and the results confirmed that incorporation of natural coagulants into nutrient recovery operations improved collection of struvite-based products.

Optimization of natural coagulant dosing strategies for struvite recovery from poultry litter

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.