Assessment of microalgae and nitrifiers activity in a consortium in a continuous operation and the effect of oxygen depletion

Background: Industrial wastewaters with a high content of nitrogen are a relevant environmental problem. Currently, treatments to remove nitrogen are not efficient, so is necessary to develop alternative methods. The objective of this study is to investigate a consortium of microalgae - nitrifying, that due to the symbiosis between them could be an interesting alternative. Results: In this study, it was possible to obtain a consortium of nitrifying bacteria (NB) and microalgae (MA) capable of operating with low requirements of dissolved oxygen, using aerobic sludge from wastewater treatment plants. During the operation, this consortium presents removal percentages above 98% of ammonia, even at concentrations of DO of 0.5 mg O2 L-1. It is estimated that the removal was caused both by the action of nitrifying bacteria and microalgae. It was determined that approximately 60% of the ammonia feed was oxidized to nitrate by nitrifying bacteria, while the algae assimilated 40% of the nitrogen feed at steady state. A methodology for measuring the specific activities of nitrifying bacteria and microalgae by comparing the rates in the variation inorganic nitrogen compounds was established with satisfactory results. An average specific activity of 0.05 and 0.02 g NH4 + gVSS-1 d-1 for nitrifying bacteria and microalgae was determined, respectively. Conclusions: The consortium it can be obtained in a single continuous operation, and has a high capacity for nitrogen removal with low oxygen content. The consortium could prove to be a more economical method compared to traditional.

Effect of sulphate concentration and sulphide desorption on the combined removal of organic matter and sulphate from wastewaters using expanded granular sludge bed (EGSB) reactors

During the application of anaerobic processes to high sulphate concentration wastewaters, operational problems are expected due to the occurrence of sulphate reduction. Sulphide production reduces effluent quality and may produce inhibition. The application of Expanded Granular Sludge Bed (EGSB) reactors for the combined removal of organic matter and sulphate was studied at different COD/sulphate and 3 values of pH. During the EGSB reactor operation, most of the sulphide remains in the liquid phase reducing effluent quality. The inclusion of a desorption column in the recirculation of the EGSB reactor promotes mass transfer to the gas phase, reducing the sulphide concentration in the liquid phase, significantly decreasing the chemical oxygen demand of the effluent.