Combined anaerobic-wetland wastewater treatment system for communities in Michoacán, Mexico

Abstract

In Mexico, the National Water Commission, hereinafter CONAGUA, records in its latest inventory about three thousand wastewater treatment plants, WWTP, of which approximately one thousand are in operation and according to data from the private industry only 100 are in optimal operating conditions. The widely used activated sludge system with more than 50% of the volume treatment is an excessively expensive system for Mexican municipalities, since, being extremely inefficient in the energy conversion with only 30% of it, the operators prefer to turn it off and pay the fine for not treating it. This type of systems invented more than a hundred years ago and which are also used to treat a mixture of industrial and domestic effluents “end-of-pipe treatment” is not capable of removing all contaminants. It has been shown that drugs such as cocaine, nonilphenol and endocrine disruptors flow through these WWTPs without suffering any degradation, hydrocarbons, medicines such as diclofenac are also not eliminated. Dyes from the textile industry cannot be degraded by this type of treatment. The mechanical aeration systems are complex to operate and require specialized personnel. An alternative is the cell treatment or at source and right there seek its reuse or alleviate the burden of the municipal WWTP. In the state of Michoacán, the local CONAGUA registers 116 activated sludge WWTPs that present the same problem of inoperability due to inefficiency energy and cost overruns that are beyond municipal budgets. This article presents a system combined for five thousand inhabitants consisting of a sand remover, a grease and oil trap, a digester or anaerobic reactor and an artificial wetland polish. This type of system is based on the use of the energy of gravity that allows lowering operating costs and is much less complex to operate than the activated sludge system.