Designing a sanitation system for floating communities

Abstract

An increasing trend of urbanization, land shortages and frequent floodings have created unfavorable living circumstances for Philippine inhabitants. Finch Floating Homes aims to repurpose the permanently flooded ricefields in Hagonoy into flood-proof, typhoon-resilient, affordable housing. The floating neighborhood will serve as storm-resilient living and have an educational purpose on circular living and recovering resources. The pilot floating home is equipped according to current sanitation practices, a septic tank. The septic tanks are usually emptied in drainage fields or surface water. With the aim of circularity in mind, an alternative sanitation had to be designed.

The neighborhood aspects and social implications were analyzed after which a set of eight design criteria were drafted. With the design criteria a framework was set up for selecting a flexible sanitation system that fits a range of desired effluent qualities. The framework offered treatment compartments that can be combined depending upon the location and effluent requirements. Three different treatment scenarios were compared based on the effluent qualities and costs. Scenario 2 containing a UASB-septic tank as primary treatment and a polishing step with water hyacinths, was found to be the most cost-effective. A final effluent concentration of 3 g/L COD, 0,05 mg/L NH3 and between 53 and 134 mg/L P was reached. And based on the die-off of E.coli, a pathogen removal of 5 log units was achieved.

Next, the conceptualization was laid out. The platforms on which the houses float, were made up of standard modules that were prefabricated and assembled on-site. Rainbarrels in wooden frames provided floating ability. The UASB-septic tank had similar dimensions as the rainbarrels, meaning no specialized treatment platform had to be built since the reactor could take the place of a rainbarrel. The disinfection tubes are placed on top of the platform and could be added at any time if the effluent quality demands a low pathogen level.
The final polishing pond was constructed from locally sourced materials and can be built in any shape that suits the neighborhood as long as the surface area is 17 m2.

The treatment system also offered possibilities for resource recovery in the form of biogas, irrigation water, fertilizer and reuse of the plant mass (food, extra COD, fabric raw materials). The residents could benefit from the biogas in the form of a communal kitchen suitable for social gatherings. The fertilizer and irrigation water were applied in communal gardens. Communal areas aided in improving relations between neighbors which created a pleasant environment.

The final treatment design was a scalable, affordable and sustainable treatment system with a range of resource recovery possibilities.