Effects of swine manure dilution with lagoon effluent on microbial communities and odor formation in pit recharge systems

Authors: HWANG, OKHWA - National Institute Of Animal Science; Emmett, Bryan; ANDERSEN, DANIEL - Iowa State University; HOWE, ADINA - Iowa State University; Ro, Kyoung; Trabue, Steven - Steve

Submitted to: Journal of Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2024
Publication Date: 5/1/2024
Citation: Hwang, O., Emmett, B.D., Andersen, D., Howe, A., Ro, K.S., Trabue, S.L. 2024. Effects of swine manure dilution with lagoon effluent on microbial communities and odor formation in pit recharge systems. Journal of Environmental Management. 358 Article 120884. https://doi.org/10.1016/j.jenvman.2024.120884.
DOI: https://doi.org/10.1016/j.jenvman.2024.120884

Interpretive Summary: Swine odors in manure originate from the breakdown of undigested feed material by microorganisms. A pit recharge system (PRS) is a manure management system in which swine manure is held in shallow pits until drained and "recharged" with new liquids from lagoon effluent. These systems in general control odor by managing organic solids in manure. However, little is known about the role of microorganism in PRS to control odor and the role that recharge rate/dilution ratio has in controlling odor for PRS. A study was conducted to understand the role of both microorganisms and PRS recharge rate has in the control of swine odor. In PRS, the microbial community was controlled by both manure source and the recharge rate or dilution ratio of the manure to lagoon effluent. Odor formation was largely controlled by both manure solids and pH and the source of the manure. In PRS, microorganisms had a small role in odor control. This research is important to growers and engineers working in manure management systems who are interested in reducing odors from swine production.

Technical Abstract: Pit recharge systems (PRS) lower odor by managing organic solids in swine finishing operations. This study determined the impact the PRS recharge rate (i.e., manure dilution ratio) had on manure microbiome and odor formation using bioreactors dynamically loaded at 5% of the system's storage capacity (1 L). Manure to lagoon effluent ratios were 10:0; 7:3; 5:5; and 2:8 corresponding to control deep-pit, and recharge rates of 14, 10, 4 days, respectively. Manure microbial membership and chemical concentrations were measured to identify the interactions between microbiota and manure chemical concentrations. The microbial community structure was significantly impacted by manure dilution and manure barn source. Firmicutes and Proteobacteria were the dominant phylum in manure and lagoon effluent, respectively and both significantly decreased or increased with dilution, respectively. Key microbial species were Clostridium saudiense in manure and Pseudomonas caeni, in lagoon effluent whose percentages either declined by 8.9% or increased by 17.6%, respectively, for each increase in manure volume. Odor formation in manure was largely explained by the manure’s solids content and pH (greater than 75% of variance) with microbial community structure having a significant but minor role (less than 5% of variance) shown by canonical analysis. Increasing the PRS recharge rates limited the rise of dissolved organic carbon in manure and odorant accumulation as increasing proportions of aerobic organisms slowed the rise of manure odorant accumulation. The metabolic interactions of aerobic and anaerobic microorganisms in PRS contribute to odor control.