Helminth Egg Removal Capacity of UASB Reactors under Subtropical Conditions

Rosa-Elena Yaya-Beas,Katarzyna Kujawa-Roeleveld,Jules Van Lier,Christian Ayala-Limaylla,Grietje Zeeman

doi:10.3390/w7052402

Abstract

This research was conducted to study the anaerobic sludge filtration capacity regarding helminth egg removal in upflow anaerobic sludge blanket (UASB) reactors. Two 25 L lab-scale UASB reactors were operated at an ambient temperature which varied between 17.1 and 28.6 °C. Ascaris suum egg was selected as the model egg considering its similarity in terms of size and morphology to Ascaris lumbricoides, a human pathogen. Ascaris suum eggs were obtained from female parasites of infected pigs. The anaerobic sludge filtration capacity was performed applying upflow velocities between 0.09 and 0.68 m·h−1. Three sludge bed heights in the range of 0.30–0.40 m, 0.50–0.60 m and 0.60–0.70 m were applied. These sludge bed heights corresponded to 19%–25%, 31%–38% and 38%–44% of the total reactor height, respectively. Under the mentioned conditions, the average helminth egg removal efficiency was reciprocally correlated to the imposed upflow velocity. The studied lab-scale reactors reported an average helminth egg removal between 34%–100%, 30%–91% and 34%–56%, when the sludge bed in the UASB reactor was 19%–25%, 31%–38% and 38%–44% of the total reactor height, respectively. The decreased filtration capacity at increasing sludge bed heights might be likely related to biogas production and channeling formation. The average helminth egg removal efficiency in the control experiments performed without any sludge bed, by plain sedimentation, varied between 44% and 66%.

Highlights

When treated wastewater is intended to be used for agricultural purposes, the presence of pathogens may limit its application potential [1,2]
This study demonstrated that with an increased sludge bed height there is a reduction in the sludge filtration capacity for helminth egg removal
If treated wastewater is used for irrigation purposes, the upflow anaerobic sludge blanket (UASB) reactor must be followed by an adequate post-treatment unit

Summary

Introduction

When treated wastewater is intended to be used for agricultural purposes, the presence of pathogens may limit its application potential [1,2]. Due to their shell resistance, helminth eggs are the most persistent pathogens to inactivation [3,4]. In developing countries, high concentrations of helminth eggs are present in domestic wastewater, which cause parasitic diseases like ascariasis, taeniasis and trichuriasis [5,6,7]. Processes like alkaline pre- and post-stabilization, by, for example, adding lime or other alkaline compound to the sludge, and thermophilic anaerobic digestion have shown high residual concentrations of worm eggs, i.e., more than 1 egg·g−1 TS, and

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