Performance evaluation of a simple wastewater treatment system comprised by UASB reactor, shallow polishing ponds and coarse rock filter.

The work investigates a small full-scale wastewater treatment system comprised by the following units in series: UASB reactor, three polishing ponds and one coarse rock filter. The overall performance of the system is analyzed based on three years of monitoring using physical-chemical and biological parameters. Good organic matter, suspended solids and ammonia removal is achieved, together with excellent coliform removal (5.70 log units). Mean effluent concentrations of the main parameters are: BOD: 39 mg/L; COD: 109 mg/L; SS = 41 mg/L; ammonia: 10 mg/L; E. coli: 540 MPN/100 mL, indicating compliance with many regulations for effluent discharge and reuse. Main algal classes found in the ponds and final effluent were chlorophyta and euglenophyta. The system is completely unmechanized and has a relatively small total hydraulic retention time (less than 13 days), compared with most natural treatment processes. No sludge removal from the ponds and filter has been necessary so far.