Evaluation of a polyacrylamide assisted solid/liquid separation system for the treatment of liquid pig manure

The effectiveness of a static gravity screen-roll press separator operated in tandem with a polyacrylamide assisted gravity belt thickener to separate solid and liquid components of liquid pig manure (raw slurry – RS) under production-scale conditions was evaluated. The system was operated from May to October in 2006 and 2007 each of two years processing 4 039 919 l in year 1 and 4 674 840 l in year 2 of raw slurry (RS1). The amount of biosolids produced was 363 690 l in year 1 and 439 103 l in year 2 resulting in a 91.8% collection rate of separated effluent (SE). Significant reductions were obtained in settleable solids (98.4% and 94.3%), total suspended solids (98.2% and 80.9%), total nitrogen (60.6% and 37.0%) and phosphorus (91.7% and 70.9%) concentrations comparing RS1 with SE for years 1 and 2, respectively. The N:P ratio of RS1 was improved from 3.6:1 to 17.1:1 in SE for year 1 and from 5.1:1 to 11.3:1 in SE for year 2. The cost to separate and apply to land SE via centre pivot irrigation was 0.28 US¢ l−1, comparative in price to the cost for direct injection of RS (0.24–0.44 US¢ l−1). The cost of utilising this system was similar to existing land application technology while the nutrient load in the SE was significantly reduced.