Treatment of Source-Separated Blackwater: A Decentralized Strategy for Nutrient Recovery towards a Circular Economy

Melesse Eshetu Moges,Arve Heistad,Daniel Todt

doi:10.3390/w10040463

Abstract

Using a filter medium for organic matter removal and nutrient recovery from blackwater treatment is a novel concept and has not been investigated sufficiently to date. This paper demonstrates a combined blackwater treatment and nutrient-recovery strategy and establishes mechanisms for a more dependable source of plant nutrients aiming at a circular economy. Source-separated blackwater from a student dormitory was used as feedstock for a sludge blanket anaerobic-baffled reactor. The effluent from the reactor, with 710 mg L−1 NH4–N and 63 mg L−1 PO4–P, was treated in a sequence of upflow and downflow filtration columns using granular activated carbon, Cocos char and polonite as filter media at a flow rate of 600 L m−2 day−1 and organic loading rate of 430 g chemical oxygen demand (COD) m−2 day−1. Filtration treatment of the anaerobic effluent with carbon adsorbents removed 80% of the residual organic matter, more than 90% of suspended solids, and turbidity while releasing more than 76% NH4–N and 85% of PO4–P in the liquid phase. The treatment train also removed total coliform bacteria and E. coli in the effluent, achieving concentrations below detection limit after the integration of ultraviolet (UV) light. These integrated technological pathways ensure simultaneous nutrient recovery as a nutrient solution, pathogen inactivation, and reduction of active organic substances. The treated nutrient-rich water can be applied as a source of value creation for various end-use options.

Highlights

Population growth and rapid urbanization during the early 1900s led to the development of synthetic fertilizers to supplement crop production and meet the world’s food demand [1,2].Harnessing P from phosphate rock reserves, K from potash reserves and N fixed from the atmosphere by the Haber–Bosch process helped to spawn the Green Revolution, and resulted in a rapid intensification of anthropogenic flows of N, P and K over the last century [3]
Up to 86% of the total P was recorded in the effluent of the anaerobic digestion, of which 82% was in the soluble fraction
This study demonstrated opportunities for a combined treatment and sustainable resource recovery from source-separated blackwater through systematic integration of a sludge blanket anaerobic-baffled reactor and a novel compacted filtration system

Summary

Introduction

Population growth and rapid urbanization during the early 1900s led to the development of synthetic fertilizers to supplement crop production and meet the world’s food demand [1,2].Harnessing P from phosphate rock reserves, K from potash reserves and N fixed from the atmosphere by the Haber–Bosch process helped to spawn the Green Revolution, and resulted in a rapid intensification of anthropogenic flows of N, P and K over the last century [3]. Phosphorus and nitrogen from agricultural food products are transported into cities and eventually end up in domestic wastewater streams. Nearly 20% of manufactured nitrogen and phosphorous is contained in domestic wastewater [4,5]. Most modern cities established centralized sewer systems with a network of collection pipes for transporting domestic wastewater to a municipal wastewater treatment plant, and with that improved public health and environmental quality [8,9]. In these systems, enormous volumes of freshwater are required to transport the small volume of human excreta from the toilet to the

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