Performance of UASB reactors in two stages under different HRT and OLR treating residual waters of swine farming

Rose M. Duda,Estevão Urbinati,Roberto A. de Oliveira

doi:10.1590/s0100-69162013000200015

Abstract

In this study it was evaluated the effects of hydraulic retention time (HRT) and Organic Loading Rate (OLR) on the performance of UASB (Upflow Anaerobic Sludge Blanket) reactors in two stages treating residual waters of swine farming. The system consisted of two UASB reactors in pilot scale, installed in series, with volumes of 908 and 188 L, for the first and second stages (R1 and R2), respectively. The HRT applied in the system of anaerobic treatment in two stages (R1 + R2) was of 19.3, 29.0 and 57.9 h. The OLR applied in the R1 ranged from 5.5 to 40.1 kg CODtotal (m³ d)-1. The average removal efficiencies of chemical oxygen demand (COD) and total suspended solids (TSS) ranged, respectively, from 66.3 to 88.2% and 62.5 to 89.3% in the R1, and from 85.5 to 95.5% and 76.4 to 96.1% in the system (R1 + R2). The volumetric production of methane in the system (R1 + R2) ranged from 0.295 to 0.721 m³CH4 (m³ reactor d)-1. It was found that the OLR applied were not limiting to obtain high efficiencies of CODtotal and TSS removal and methane production. The inclusion of the UASB reactor in the second stage contributed to increase the efficiencies of CODtotal and TSS removal, especially, when the treatment system was submitted to the lowest HRT and the highest OLR.

Highlights

According to FAO (2010), the swine meat is the most consumed worldwide, which makes the swine farming an important source of animal protein for the human population, exerting important role in food security
The UASB reactor (R1): With Organic Loading Rate (OLR) around 5kg CODtotal (m3 d)-1, the decrease in hydraulic retention time (HRT) from 48 to 16 h caused no reduction in CODtotal and total suspended solids (TSS) removal efficiencies, increased the removal of CODdiss and the production of methane;
- The smallest average temperatures resulted in reduced production of methane when it was applied to higher OLR of 40.1 kg chemical oxygen demand (COD) (m3 d)-1, but promoted physical removal of suspended solids, disallowing the reduction of the removal efficiencies of COD and TSS

Summary

Introduction

According to FAO (2010), the swine meat is the most consumed worldwide, which makes the swine farming an important source of animal protein for the human population, exerting important role in food security. It is one of the activities that most accentuate its participation in the impact caused to the environment, especially with the adoption of confined systems (FERNANDES & OLIVEIRA, 2006). In such systems, the high levels of animal concentration per unit area, often cause an imbalance between the agricultural area available for nutrient recycling and the amount of excrements produced on the farm (MIRANDA, 2007), causing contamination of soil and groundwater when using the ground as the final destination. The swine excrements, when thrown into water bodies can cause impact superior than the equivalent domestic sewage. A pig with their excreta may impact up to 4.6 times more than a human, because while the biochemical oxygen demand (BOD5) per capita of pigs can reach 208 g d-1 per animal, for humans the BOD5 varies from 45 to 75 g d-1 per capita (PERDOMO & LIMA, 1998).

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Results

Conclusion