(Jose) Emiliano Detta Silvera
Membrane Bioreactors (MBRS) as a Sustainable Solution for Wastewater Treatment in Mega Cities
|In recent years, the rate of urbanization has been increasing throughout the world. This phenomenon affects all countries and its effects pose tremendous challenges for society particularly for mega-cities in the developing world. Lack of planning and uncontrolled growth makes it difficult for local governments to provide adequate infrastructural services, one of them being the safe provision of water and its disposal.
Mexico City is the best example to illustrate the problem. The current situation in the city is unsustainable with aquifer overexploitation rates of millions of cubic metres a year. Nearby systems cannot supply sufficient water in the short term and the current pumping costs and energy consumption are excessive. Maintaining the hydrological balance of the basin is of vital importance to achieve sustainability of supply. Therefore, wastewater treatment and aquifer recharge must be a priority. However, this balance has to be achieved with a reasonable amount of energy, appropriate technologies and effective policies.
In this context, a new technology (membrane bioreactors, MBRs) was identified as one suitable solution for wastewater treatment due to the land constraints in the city that make it difficult to locate conventional wastewater treatment plants. The technology was evaluated and different options for its implementation were explored (decentralised and centralised). In addition, these were compared with the current system and with the solutions promoted by the National Water Commission.
Overall, there are still several concerns about the technology’s operation, costs and energy consumption. MBRs are still at an initial maturity stage with some problems to be overcome, such as supply issues and homogenisation of standards. Costs are still a barrier for MBR implementation in developing country mega-cities, especially where legal requirements oblige authorities to choose a technology based on the least cost. However, there are considerable opportunities for MBR retrofitting in existing plants for mega-cities. Moreover, retrofitting seems to be technically feasible, economically viable and environmentally sustainable if compared with the current system in Mexico City.