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

One of the best options for handling Mexico City's 74.5 m(3)/s of wastewate r is to use advanced primary treatment (APT), filter and disinfect the effl uent before it is reused in agriculture. The final effluent must contain le ss than helminth egg (HE) per liter and less than 1000 fecal coliforms (MPN )/100 mL while still retaining nutrients and organic matter for their agron omic 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 fillers produced effluent concentrations ranging from 0 to 0.52 HE/L. Although the removal efficiencies of the sand and syn thetic filters were similar, the synthetic filter had several important adv antages over the sand filter: (a) The filtration rate of the synthetic filt er was more than 5.8 times that of the sand filter and the production rate per run per al ea was 2.1 times than of the sand filler. (b) The synthetic filter required less than 1% of the raw wastewater for backwashing, while t he sand filler required twice as much filtered wastewater. Although, the sy nthetic filter has higher capital costs and has a more complex design and o peration, the overall costs would most likely be lower due to its higher pr oduction rate. (C) 1999 Elsevier Science Ltd. All rights reserved.