(53b) Development of a Proposal for Improvement for the Prototype Recycling Domestic Wastewater of the  Fundación Universitaria Los Libertadores

A prototype of grey water recycling was designed and constructed by students of mechanical engineering from Fundación Universitaria Los Libertadores in Bogotá, Colombia in 2012. During its operation, problems concerning to strong smells were detected, especially in closed rest rooms such as apartments, and problems of corrosion in mechanical devices such as pumps.

The present project consisted in developing an improvement of this recycling domestic wastewater prototype in order to adapt it for implementation in bathrooms of homes, with treatments to avoid odors and corrosion.

The project began with the diagnosis of the current state of collected gray water in the prototype, where the parameters were evaluated, based on the Resolution 1207 of 2014, Resolution 631 of 2015. A characterization of domestic waste water collected in the shower of a residential apartment was made. Water characterization included a quantifying of the following parameters: pH, chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), total suspended solids (TSS), settleable solids, fats and oils, phenolic semivolatile compounds and active substances to methylene blue.

According to the results obtained in the characterization of water, critical indicators (COD, BOD5 and TSS) of residual effluent were analyzed in order to choose a chemical treatment which allows improve water quality and odors mitigation, being essential the coagulation and flocculation. The coagulant selection was done by development experiments method.

During the experiments development, coagulant alternatives were selected by performing a screening matrix, taking into account evaluation factors such as optimal use, the required pH, the corrosive action on the system, required speed for floc formation, among others. As a result, coagulating alternatives such as aluminum sulfate, aluminum polychloride and ferric chloride were obtained. Selected coagulants were used in the experimental development, using the technique of “test jugs”, which allowed the modeling in laboratory, of the process to be implemented in the prototype, checking the effectiveness of treatment of domestic grey water and making the determination of the right dosage.

The best alternative coagulant was the Aluminum Sulfate with a dosage of 200 ppm, because it showed the greatest decrease in the evaluated parameters (COD BOD₅ and TSS) with respect to the original sample of water and satisfying the regulations.

By applying the coagulant, the pH values were between 3.91 and 4.92, which are not within the range of the standard, between 6 and 9. Therefore, it is necessary to correct the pH with potassium hydroxide. This correction had to be done after the coagulant is added.

Development of experiments, allowed to evaluate the behavior of treated grey water in the recycling system of domestic prototype. Unit operations involved in the process were: coagulation, flocculation, sedimentation and filtration; therefore the chemical treatment to be implemented, consists of implementing these unit operations in the running of prototype.

Regarding diagnosis of the prototype, a visual inspection and metallographic testing of pump components was done, in order to identify the existence of corrosion. By means of these methods, the deterioration of the casing was observed together with the presence of stress corrosion and oxygen in the pump impeller. Also some failings concerning to aesthetics and functioning of the equipment were identified. Therefore, the modification in dimensions of the storage tank was proposed together with the adaptation to chemical treatment, and the inclusion of control instruments to ensure the correct operation of the equipment in an apartment.

Once the improvements were selected to adapt them to the running of equipment, its specifications of operation, assembly, maintenance and adjustment of the equipment were determined in order to guarantee the grey water quality. The specifications of the proposed improvements in the prototype, include both the modification of the storage tank and equipment, and the relocation of some elements such as filters, valves, level sensor, electrical stirrer, pump metering, among others. These improvements take into account not only the proper functioning of equipment but also the maintenance.

With the selection of the prototype improvements and technical specifications, its financial viability was analyzed in a case study for an apartment of middle class family, comparing the cash flows, with and without project, and evaluating financial indicators such as NPV, IRR and benefit / cost, in order to calculate the payback period of the project investment. As a result of this analysis, the project showed to be financially viable. At the same time, the project has added values of positive impacts on the environment and the community.