Long-term performance and operational strategies of a poultry slaughterhouse waste stabilization pond system in a tropical climate

This paper discusses the performance of a poultry slaughterhouse wastewater treatment plant (WWTP) in a tropical country and operating strategies that were applied over 84 months to this WWTP. The WWTP consisted of a dissolved air flotation (DAF) system, anaerobic ponds (APs) and a facultative pond (FP). The organic loading rates applied to the APs ranged from 0.26 to 1.05 kg BOD/m(3) day, and the hydraulic retention time ranged from 2.2 to 3.8 days. The resultant COD and BUD removal efficiencies were 42 +/- 11% and 38 +/- 15%, respectively. The FP surface loading was up to 983 kg BOD/ha day. The main observed events in the WWTP processes over this period were organic overload, low chemical oxygen demand (COD) and biochemical oxygen demand (BUD) removal efficiencies and color change from green to reddish at the FP. Molecular biology techniques were used to identify microbial groups in the FP in the period of low organic matter removal efficiency and when the liquid became reddish. Sunny conditions favored anoxygenic photosynthesis, the growth of purple nonsulfur bacteria (such as Rhodocyclales-like organisms), and green nonsulfur bacteria (such as Chloroflexi-like organisms). Mechanical aeration at the inlet of the FP restored the water to its original color and increased the COD and BUD removal efficiencies. Based on the BUD removal efficiencies of 89%, after the installation of aerators, the operating strategies illustrate the WWTP system's capacity and versatility to adapt to load variations. (C) 2012 Elsevier B.V. All rights reserved.