UASB reactor followed by constructed wetland and UV radiation as an appropriate technology for municipal wastewater treatment in Mediterranean countries

Abstract

This paper describes a new wastewater treatment concept which was assessed to be technically and economically feasible for suburban and rural areas in Mediterranean countries. The treatment consists of a two-step anaerobic high-rate reactor like UASB reactor followed by vertical flow constructed wetland (CW) and UV radiation. It fulfills the defined criteria, as meeting the standards for water reuse, costs especially for energy are low, sewage sludge production is limited and operation and maintenance are simple. Although there are much experience and data available about design and operation of CW and UV radiation, the knowledge about anaerobic treatment of municipal wastewater in UASB reactor at moderate temperature is limited. Therefore bench-scale experiments with pre-settled high-strength municipal wastewater were carried out in a one step UASB reactor of 55 liters. The results show a satisfactory effluent quality at fluctuating HRT. During 9 months of continuous operation, total COD removal was 46% and 60% with HRT of 8 to 16 hours and more than 24 hours, respectively. Below an HRT of 24 hours, the removal of suspended solids was limited, sludge wash-out took place due to fluctuating HRT. The removal of colloidal COD was satisfying with around 60% for all HRT. These results indicate that combined with a second high rate anaerobic reactor and/or a settler after the UASB reactor, constructed wetland and UV radiation, an adequate tertiary effluent for water reuse in irrigation will be achieved.