Cost-effective clarification and nutrient recovery of liquid dairy manure treated with aluminium sulphate and a tannin-based coagulant-flocculant

ABSTRACT

Sequence of text and pictures showing Tanfloc with alum or pH adjustment applied to liquid manure, indicating that combining Tanfloc with alum improves turbidity removal, reduces costs, and increases phosphorus separation.

Tannin-based coagulant-flocculants, such as Tanfloc, are proposed as environmentally friendly alternatives to clarify water and recover nutrients from farm dairy effluent. However, cost and dosage requirements limit their use, and their performance when combined with metal salts remains poorly investigated. This study evaluated the performance and cost-effectiveness of combining Tanfloc with aluminium sulphate (alum) for turbidity removal and nutrient separation from manure (0.5–3.0% total solids). We used jar testing and response surface methods to compare performance with Tanfloc alone (pH 4.0–8.0). Although pH influenced turbidity removal (>99%), and separation of TN (77–79%) and TP (63–75%), alum inclusion enhanced turbidity removal at sub-optimal Tanfloc dosages with similar TN separation across treatments, and increased TP separation to 94–97%. Minimizing residual turbidity (6 NTU) using Tanfloc with pH adjustment cost $23.6 AUD/m3, while combining Tanfloc with alum reduced it to $15.6 AUD/m3. Aiming for moderate clarification (∼50 NTU) did not affect nutrient separation and reduced chemical costs to $2.9 AUD/m3. This study provides a cost-effective strategy to improve nutrient recovery and effluent quality, which may support future reuse on dairy farms. Pathogen analysis, field validation, and assessment of long-term alum effects in soil are required before on-farm implementation.