Simultaneous Heterotrophic Nitrification and Aerobic Denitrification of Water after Sludge Dewatering in Two Sequential Moving Bed Biofilm Reactors (MBBR).

Eshetu Janka,Sandeep Gyawali,Shuai Wang,Alireza Rasti,Sabin Pathak

doi:10.3390/ijerph19031841

Abstract

Water after sludge dewatering, also known as reject water from anaerobic digestion, is recycled back to the main wastewater treatment inlet in the wastewater treatment plant Porsgrunn, Norway, causing periodic process disturbance due to high ammonium of 568 (±76.7) mg/L and total chemical oxygen demand (tCOD) of 2825 (±526) mg/L. The main aim of this study was the simultaneous treatment of reject water ammonium and COD using two pilot-scale sequential moving bed biofilm reactors (MBBR) implemented in the main wastewater treatment stream. The two pilot MBBRs each had a working volume of 67.4 L. The biofilm carriers used had a protected surface area of 650 m2/m3 with a 60% filling ratio. The results indicate that the combined ammonia removal efficiency (ARE) in both reactors was 65.9%, while the nitrite accumulation rate (NAR) and nitrate production rate (NPR) were 80.2 and 19.8%, respectively. Over 28% of the reject water’s tCOD was removed in both reactors. The heterotrophic nitrification and oxygen tolerant aerobic denitrification were the key biological mechanisms found for the ammonium removal in both reactors. The dominant bacterial family in both reactors was Alcaligenaceae, capable of simultaneous heterotrophic nitrification and denitrification. Moreover, microbial families that were found with equal potential for application of simultaneous heterotrophic nitrification and aerobic denitrification including Cloacamonaceae, Alcaligenaceae, Comamonadaceae, Microbacteriaceae, and Anaerolinaceae.

Highlights

In conventional wastewater treatment processes, the reject water, which is the water after sludge dewatering from anaerobic digestion effluent, is directly recycled into the main inlet without any pre-treatment
The effluent of the moving bed biofilm reactors (MBBR) R1 fed as an inlet for MBBR R2 had a specific ammonium loading rate (SALR) of 25.8 (±7.3) mg/m2 ·d
The dominant bacterial family Alcaligenaceae found in both reactors are capable of simultaneous nitrification and denitrification

Summary

Introduction

In conventional wastewater treatment processes, the reject water, which is the water after sludge dewatering from anaerobic digestion effluent, is directly recycled into the main inlet without any pre-treatment. Reject water that is recycled to the inlet is about 1–2% of the main flow. Reject water is highly concentrated wastewater that contains up to 25% of the total nitrogen load of the mainstream [1]. The main reject water constituents are ammonium The COD in reject water is associated with a low fraction of biodegradable substances. The high ammonium and COD concentration in reject water may cause process disturbance when recycled in the main treatment system. To avoid overload and process disturbance in the main treatment process, the biological treatment of reject water is vital [2]

Objectives

Methods

Results

Discussion

Conclusion