An assessment of using anaerobic baffled reactor to upgrade wastewater stabilization ponds: a pilot study

Abstract

Operating wastewater treatment facilities is a challenge in developing countries. A research to fi nd more sustainable alternatives is required with emphasize on modifi cation, upgrade and optimization of these systems. Accordingly, a case study over a wastewater stabilization pond (WSP) of Hoveizeh, Iran, is carried out. It is realized that the facultative ponds have been encountered high purple sulfur bacteria (PSBs) bloom as a consequence of high organic loads. In fact, the overall effi ciency of 70% in soluble COD removal is barely achieved in the system. This is recognized that volatile fatty acids (VFAs) have been motivated to be accumulated to more than 190 mg/L within the anaerobic ponds by high organic load. Hence, the ratio of VFAs to alkalinity is exceeded 0.6 and H 2 S concentration is increased in the facultative pond. It is observed that the infl uent COD is correlated logarithmically to the H 2 S concentration (R 2 = 0.9) and the latter itself is correlated in third order to the chlorophyll A (R 2 = 0.92) representing PSBs growth. Since this phenomenon is attributed to the accumulation of VFAs, it is recommended to use anaerobic baffl ed reactor (ABR) as a modifi cation to control the process. For this purpose, a bench-scale ABR with 48 l volume and six compartments were fed with domestic wastewater and operated for 7 months in three hydraulic retention times (HRT) of 36, 24 and 18 hours. It is observed that the effi ciency of soluble COD removal in the anaerobic part can be promoted from 45% to 70% by ABR with 24-h retention time while the effl uent of COD and VFAs are limited to 170 and 70 mg/L, respectively. Besides, the overall effi ciency of ABR has not been changed signifi cantly in a range of 36-18 h HRT. Consequently, it is found that ABR as an effi cient, economical and environmentally sound option can be considered as a sustainable alternative to upgrade WSPs operationally.