Small wastewater treatment plants from Delphin Water Systems of America work without chemicals and are safe for the environment. The fixed-bed method consists of polyethylene tubes with reticular gaps, on which microbes contained in the wastewater settle and degrade contaminations via their metabolism. The method results in lower bacteria sludge production, improved collection efficiency during the final clarification stage and a lower pollutant discharge. The purified water seeps in the subsoil without reservation. Systems are available in 1,600 to 52,835 gpd. 210/858-6120; www.delphin-mexico.com.