Digestate treatment with algae-bacteria consortia: A field pilot-scale experimentation in a sub-optimal climate area

This paper addresses the efficiency of a microalgae-based agricultural digestate treatment at pilot-scale in an outdoor raceway pond (880 L, pH-dependent CO₂ dosage) and in a bubble column (74.5 L, air-bubbling). Specifically, nitrogen removal, evolution of the algae-bacteria consortium, and the actual process applicability in the Po Valley climate are discussed. The performance of the two reactors varied seasonally. The average algal productivity in the raceway was 32.4 ± 33.1 mg TSS·L^-1·d^-1 (8.2 ± 8.5 g TSS·m^-2·d^-1) while in the PBR it was 25.6 ± 26.8 mg TSS·L^-1·d^-1; the average nitrogen removal was 20 ± 29% (maximum 78%) and 22 ± 29% (maximum 71%) in the raceway and in the column, respectively. Nevertheless, nitrification had a key role as 61 ± 24% and 52 ± 32% of the nitrogen load was oxidized in the raceway and in the column, respectively.