Wastewater Characterization and Treatment: Influence in Bio-Hydrogen and Methane Production

Environmental conservation issues increasingly grow in importance and bring about changes in the way of addressing and optimizing industrial processes from their very conception, weighing environmental conditions and sustainability aspects. In particular, this paper deals with the issue of wastewater treatment including biohydrogen and methane recovery, and lays emphasis on effluent characterization and treatment system selection. In this context, complex mathematical models are developed whose solution correspond to optimal treatment systems configurations, minimizing costs and serving restrictions of dumping against scenarios of theoretical and practical interest. These models perform a superstructure that enables the description of reactors, kinetics of removing pollutants (C, N), and operational issues and design considerations. The importance of selecting a suitable scheme of degradation is made clear in previous works. It is also relevant to include the description of inhibitions factors; i.e. that physicochemical and biochemical process kinetics becomes decisive, irrespective of the reactor type to be designed. On the other hand, effluent characterization is based on parameters which measure the concentration of contaminants: chemical and biological oxygen demands, and volatile suspended solids, described mainly as volatile fatty acids, carbohydrates, and protein percentages.

The objective is to calculate optimal solutions that ponder biofuel recovery in wastewater treatment, taking into account: (a) different levels of pollution and (b) different alternatives using simple or combined methods of biological treatment. The objective function is net present value (NPV) minimization, which considers investment and operation costs, thus satisfying allowed discharge limits. For the studied cases, alternatives that involve biohydrogen production in an initial anaerobic stage (at low pH) in effluents with high organic load and a proper C/N ratio are attractive. Depending on methane’s tentative price (as a gas substitute), some alternatives including this recovery before an aerobic treatment stage are feasible. So, it is essential to identify the biofuel production cost component in each case. When effluent complexity increases, the concentration of suspended solids in the treated effluent decreases, resulting in a high NPV. The models were implemented in a (general Process Modeling System, gPROMS) software that allows simulating several scenarios and becomes an essential tool for decision-making.