Sand and synthetic medium filtration of advanced primary treatment effluent from Mexico City

Abstract

One of the best options for handling Mexico City's 74.5 m 3/s of wastewater is to use advanced primary treatment (APT), filter and disinfect the effluent before it is reused in agriculture. The final effluent must contain less than 1 helminth egg (HE) per liter and less than 1000 fecal coliforms (MPN)/100 mL while still retaining nutrients and organic matter for their agronomic benefits. Sand and synthetic filters were tested on the effluent of a 12 L/s pilot APT plant. The average APT effluent concentration of helminth eggs was 1.2 HE/L and both filters produced effluent concentrations ranging from 0 to 0.52 HE/L. Although the removal efficiencies of the sand and synthetic filters were similar, the synthetic filter had several important advantages over the sand filter: (a) The filtration rate of the synthetic filter was more than 5.8 times that of the sand filter and the production rate per run per area was 2.1 times than of the sand filter. (b) The synthetic filter required less than 1% of the raw wastewater for backwashing, while the sand filter required twice as much filtered wastewater. Although, the synthetic filter has higher capital costs and has a more complex design and operation, the overall costs would most likely be lower due to its higher production rate.