Optimization of sewage treatment systems through microalgal biomass use for clean water and energy: defining management guidelines.

FRANCO, JUDITH; FERNÁNDEZ, ROMINA; ZÁRATE, CLAUDIA; GONZÁLEZ LEIVA, NANCY; MANRIQUE, SILVINA M

Las Vegas

Conferencia; Stepping Towards a Sustainable World; 2018

University of Sheffield UK

Stabilization ponds are one of the most commonly used systems for the treatment of sewage effluents (SE) due to the low investment, operation and maintenance costs. In many cases these systems do not achieve the removal of 100% of the organic load and in others, even when the discharge is carried out in compliance with the discharge limits, they often contaminate the receiving water bodies, given the variation in water flows and the cumulative effects on the environment. The integration of microalgae in complementary systems to the tertiary treatment ponds, could be a multiple solution. Its ability to grow with free access resources such as solar energy and CO2 and convert them into biomass by removing residual nutrients, would allow a greater degree of water purification and potential reuse for irrigation purposes, reduction of contamination in the surroundings of treatment plants and generation of algal biomass, with promising alternatives for the energy industry. We explored the capacity of Scenedesmus quadricauda - with positive results in other regions of the country - to grow in the SE from the Treatment Plant in the northern of Argentina (Salta). The algal growth was evaluated comparatively by cell count in Neubauer chamber. The standard culture was maintained in modified Detmer medium, inoculating 2.5x105 cells/ml in 3 litres (room temperature, 1820 lux, photoperiod 12:12, daily agitation). Essays were performed in all cases in triplicate, preparing a culture with standard culture and four SE concentrations: 25%, 50%, 75% and 100%. It was observed that the highest growth value was recorded on day 22 for a concentration of the 25% (7.52x106 cel / ml ± 4.92x105) and 50% (9.73x106 cel / ml ± 7.82x105); while for the solutions with 75% and 100%, the highest value obtained was on seventh day (3.16x105 cel / ml ± 1.81x105) and sixth day (4.25x105 cel / ml± 3.46x105), respectively. This implies a reduction in the growth of around three times when the effluent concentration increases from 50% to 75% and 100%. The greater concentration of effluent in the culture, the lower growth. For the concentrations of 75 and 100% effluent, the culture does not reach to duplicate the inicial number of cells and practically remains stationary. Because we have detected the proliferation of other microorganisms, especially the group of rotifers, it is possible that our species will not be able to compete when the concentration of effluent in the culture is greater than 50%. We are currently working with scaling (100 litres). If the observed trends are maintained, they can be valuable management guidelines for the design of the depuration system, with the incorporation of microalgae. Future studies will advance in the evaluation of the different alternatives of use of the algal biomass with energetic purposes.