A new flocculant tannic acid for improving separation efficiency and lowering gas emissions from liquid and solid fractions of dairy slurry

This study examined a hypothesis that tannic acid, as a flocculant, may achieve the dual goals of improving solidliquid separation efficiency (SE) of dairy slurry and mitigating gas emissions during the storage of both liquid fraction (LF) and solid fraction (SF) compared to conventional flocculants, cationic polyacrylamide (cPAM) and polyaluminium chloride (PAC). Gas emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ammonia (NH3) from the storage of LF and SF were monitored over a two-month period. Tannic acid demonstrated a similar capability to improve the separation efficiencies of dry matter, organic matter, and total nitrogen in dairy slurry as PAM and PAC did compared to CK (mechanical separator). Compared to CK, tannic acid reduced integrated nitrogen loss from both SF and LF by 36.1%, while PAC significantly increased the total nitrogen losses by 51.4% due to enhanced NH3 and N2O emissions; PAM had a negligible impact on integrated nitrogen losses (a slight increase of 5.6%) but resulted in a trade-off between NH3 from LF and N2O from SF. Compared to CK, the use of PAC, PAM, and tannic acid reduced integrated CO2-e emissions of SF and LF during storage by 35.8%, 58.5%, and 69.4%, respectively, with only tannic acid achieving a co-reduction of long- and short-lived gases (i.e., N2O and CH4) from both fractions. This study demonstrated that tannic acid can be an efficient flocculant to improve the separation efficiency of dairy slurry and achieve a simultaneous reduction in N loss and GHG emissions from the separated solid and liquid fractions.