Chemical and modelling evaluation of five coagulants/flocculants for clarifying and recovering nutrients from liquid dairy manure (Australia)

Sequence of pictures: starting with manure in the foreground of dairy yards, then diluted manure in a tub, a jar tester with four beakers to which five chemicals are pointed, leading to separated solids and liquids with models for solid separation and turbidity removal . Chemical treatment of farm dairy effluent can recover nutrients, clarify it for reuse, and improve effluent management in grazing systems. However, the comparative performance of coagulants/flocculants, and models adapted to variable total solids (TS) concentrations, is limited for flushed manures from grazing systems. Aluminium sulphate, ferric sulphate, polyferric sulphate, polyacrylamide Zetag 8185®, and a tannin-based coagulant–flocculant, Tanfloc®, were compared using centrifuge-based jar tests on liquid dairy manure (0.5–3.0% TS). Tanfloc achieved the greatest turbidity removal, polyacrylamide displayed the highest TS separation, and metal salts were most effective in separating nutrients. Polynomial models using the dose and either the centrifuged liquid turbidity (459–9,485 NTU) or TS concentration (0.5–3.0% TS) accurately predicted turbidity removal or TS separation (R2 = 79.3–98.7%, Lin's concordance correlation coefficient >0.98). Models were validated using random-splitting, k-fold, and cluster-aware methods. Limitations include the length of storage and the manure dilution method, which affect ionic strength and colloidal stability; uncontrolled pH and temperature conditions; and centrifuge-derived responses that may not generalize to typical on-farm solid–liquid separators. Our results provide a basis for chemically treating liquid dairy manure. On-farm validation, pathogens, and chemical residue analysis are required before providing recommendations for operational use.