Dynamic Model of Stabilization Pond Systems

OCHOA, M. P.; ESTRADA, V.; DIAZ, M.S.

Atlanta

Congreso; AIChE Annual Meeting 2014; 2014

AIChE

Wastewater generation is inevitable and its discharge into surface waters leads to environmental problems such as odor, eutrophication, depletion of dissolved oxygen, loss of biodiversity and also health risk. For these reasons, standards for wastewater discharge have been enforced and are expected to become stricter. Resulting in a growing interest area of study [1]. Wastewater treatment in stabilization ponds mainly results from settling and complex symbiosis of bacteria and algae where the oxidation of organic matter is accomplished by bacteria in presence of dissolved oxygen supplied by algal photosynthesis and surface re-aeration [2]. In this work different configurations of stabilization ponds are considered. Dynamic modeling of each pond was implemented within a dynamic optimization environment and the whole system was simulated during a time horizon of four months. A detailed mechanistic model is constructed, based on first principles of mass conservation, of different types of systems of anaerobic, aerobic and facultative ponds in series. The main objective of the work is to compare the performance of the different configuration pond system, by the amount of organic matter in the effluent of the treatment plant. Model takes into account dynamic mass balances of biomass of algae, the main groups of bacteria: heterotrophic bacteria, autotrophic bacteria, fermenting bacteria, acetotrophic sulphate reducing bacteria and acetotrophic methanogenic bacteria. Also, mass balances for organic load are formulated, such as slowly biodegradable particulate COD, inert particulate COD, fermentation products, inert soluble COD, and fermentable readily biodegradable soluble COD. For nutrients, ammonium and ammonia nitrogen, nitrate and nitrite nitrogen, sulphate sulphur and dissolved oxygen. Finally, molecular nitrogen and methane emissions are considered in the model. For the whole time horizon, we find that the conventional configuration is better than the actual configuration of the wastewater treatment plant under study [3]. Even though the differences are not as high as expected, this fact influences the total energy consumption by the aerators of the aerobic ponds. The results provide useful information on the complex relationship among micro-organisms, nutrients and organic matter concentration, as well as information about the impact of modification in the pond system that can be used to improve the control of the effluent composition.