Production of Biomass (Algae-Bacteria) by Using a Mixture of Settled Swine and Sewage as Substrate

This paper presents the use of a mixture of settled swine and sewage as substrate for biomass production, mainly constituted by microalgae Chlorella vulgaris and aerobic bacteria, growing outdoor at different dilution rates in a continuous mode. The experiments were carried out in 16-litre volume laboratory ponds operating at hydraulic retention times (HRT) in a range of 4–14 days equivalent to dilution rates (D) in a range of 0.250–0.071 d⁻¹. Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total biochemical oxygen demand (TBOD₅), total suspended solids (TSS), volatile suspended solids (VSS), total Chlorophyll (Σ C), total Kjeldahl nitrogen (TKN), ammonia nitrogen, total phosphorous, orthophosphate and pH were monitored. An empirical relationship between the dilution rate (D) and the removal efficiencies of TCOD, SCOD, TBOD₅, TKN and total phosphorous was found. The occurrence of an inhibition process for TCOD, TBOD₅, TKN and total phosphorous removals was observed. The Andrews kinetic model was successfully applied to these experimental data, while the Monod model was more suitable for studying the variation of the SCOD removal rate with the effluent SCOD concentration. The maximum microalgal biomass productivity was found to be in the range of 93–98 mg VSS_A/L d (37.2–39.2 g/m²d) at dilution rates in the range of 0.167–0.250 d⁻¹, where VSS_A is the concentration of microalgae expressed in VSS. In the case of the bacteria, the productivity increased linearly with the dilution rate being maximum at a D value of 0.25 d⁻¹. It was concluded that the mixture of pre-treated swine and sewage used as substrate, contributed to the obtention of a high biomass (microalgae-bacteria) production, providing a simple technology feasible to be applied in developing countries.

Key Words:

• Mixed swine and sewage waste
• Kinetics
• Biomass production
• Continuous culture
• Dilution rate.

ACKNOWLEDGMENTS

The authors wish to express their gratitude to the “Ministerio de Educación y Ciencia” (Spanish Government), the program of Scientific Cooperation with Iberoamérica (Spanish Foreign Ministry) and “Consejería de Educación y Ciencia” of the “Junta de Andalucía” for providing financial support. We also wish to thank the “Ministerio de Ciencia Tecnología y Medio Ambiente” of Cuba and “The Alexander von Humboldt Foundation” of Germany.

Notes

*Average values of 15 samples, with a variance coefficient of less than 5% in all cases.

*Values are the averages of 11 determinations taken over 11 days after the steady-state conditions had been reached. The differences between the observed values were less than 3% in all cases.

*The variability coefficients for these constants were equal to or lower than 5% in all cases.

*The variability coefficients for these constants were less than 5% in all cases.

*Values are the averages of 11 determinations taken over 11 days after the steady-state conditions had been reached. The differences between the observed values were less than 3% in all cases.