Biogas from mono- and co-digestion of microalgal biomass grown on piggery wastewater.

Biogas production has been suggested as a valid valorization solution for microalgal/bacteria biomass (MAB) grown on wastewater. This research is aimed at assessing the feasibility to use MAB grown in an outdoor raceway fed on piggery wastewater for biogas production. Batch and continuous anaerobic tests were conducted on the sole MAB and on a blend of MAB and carbonaceous substrates (deproteinated cheese whey and cellulose) to improve the carbon/nitrogen ratio. Results of batch biochemical methane potential tests confirmed that the sole microalgal/bacteria biomass was poorly degradable (119 NmLCH4·gCOD -1), while blending it with deproteinated cheese whey or cellulose (80% of carbonaceous material and 20% of MAB, as chemical oxygen demand (COD)) had no synergistic effects on the methane yield, although slight improvements in the degradation kinetics were observed. Continuous anaerobic degradation tests (at an organic loading rate of 1.5 gCOD·L-1·d-1, 35 °C and 30 days of hydraulic retention time) increased the overall methane yield from 81 NmLCH4·gCOD -1 (sole MAB) to 216 NmLCH4·gCOD -1 (MAB and deproteinated cheese whey) and 122 NmLCH4·gCOD -1 (MAB and cheese whey). However, data confirm that no evident synergistic effects were obtained.

Piggery wastewater treatment with algae-bacteria consortia: Pilot-scale validation and techno-economic evaluation at farm level.

The efficiency of an outdoor pilot-scale raceway pond treating the wastewaters generated by a large-scale piggery farm in Northern Italy was evaluated. The biomass productivity over 208 days of experimentation was 10.7 ± 6.5 g TSS·m-2·d-1, and ammoniacal nitrogen, orthophosphate, and COD average removal efficiencies were 90%, 90%, and 59%, respectively. Results were used to perform a comprehensive techno-economic analysis for integrating algae-based processes in farms of different sizes (100-10000 pigs). The amount of N disposed of on agricultural land could be reduced from 91% to 21%, increasing the fraction returned to the atmosphere from 2.4% to 63%, and the fraction in the biomass from 6.2% to 16%. For intensive farming, the release of 110 t N·ha-1·y-1 contained in the digestate could be avoided by including algae-bacteria processes. The biomass production cost was as low as 1.9 €·kg-1, while the cost for nitrogen removal was 4.3 €·kg N-1.

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 ±â€¯33.1 mg TSS·L-1·d-1 (8.2 ±â€¯8.5 g TSS·m-2·d-1) while in the PBR it was 25.6 ±â€¯26.8 mg TSS·L-1·d-1; the average nitrogen removal was 20 ±â€¯29% (maximum 78%) and 22 ±â€¯29% (maximum 71%) in the raceway and in the column, respectively. Nevertheless, nitrification had a key role as 61 ±â€¯24% and 52 ±â€¯32% of the nitrogen load was oxidized in the raceway and in the column, respectively.