Comparing different schemes of agricultural wastewater lagooning: depuration performance and microbiological characteristics

Since the number of factors influencing depuration efficiency and energy requirement is high, the choice of the most suitable aeration scheme in aerated lagooning systems treating agricultural wastewater is a difficult task. This study provides technicians and researchers with guidelines on air diffuser position, presence of inoculum and characteristics of microbial mass, focusing organic matter degradation and energy performance of aerated ponds treating citrus processing wastewater. Four experimental batch tanks were set up: three tanks were subject to low air flow rates and times, while a fourth tank was not aerated. The organic matter degradation in the aerated tanks was on average six times higher compared to the non-aerated tank. Positioning the air diffuser at mid-depth and consequent separation of tank contents into two layers determined a decrease in the depuration performance, presumably due to the reduced transfer of oxygen to wastewater. Although the ability of spontaneous microflora to adapt to essential oil concentrations up to 1400 mL L−1 was detected, the effect of inoculum (50% of wastewater with spontaneous microflora already adapted to high essential oil concentration) was not noticeable. Overall, the results of the investigation confirm the suitability of aerated lagoons subject to fine bubble aeration also for agricultural wastewater depuration.