Nutrient Recovery from Anaerobically Treated Blackwater and Improving Its Effluent Quality through Microalgae Biomass Production

Melesse Eshetu Moges,Arve Heistad,Thorsten Heidorn

doi:10.3390/w12020592

Melesse Eshetu Moges, Arve Heistad + Show 1 more

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https://doi.org/10.3390/w12020592

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Abstract

The blackwater stream of domestic wastewater contains energy and the majority of nutrients that can contribute to a circular economy. Hygienically safe and odor-free nutrient solution produced from anaerobically treated source-separated blackwater through an integrated post-treatment unit can be used as a source of liquid fertilizer. However, the high water content in the liquid fertilizer represents a storage or transportation challenge when utilized on agricultural areas, which are often situated far from the urban areas. Integration of microalgae into treated source-separated blackwater (BW) has been shown to effectively assimilate and recover phosphorus (P) and nitrogen (N) in the form of green biomass to be used as slow release biofertilizer and hence close the nutrient loop. With this objective, a lab-scale flat panel photobioreactor was used to cultivate Chlorella sorokiniana strain NIVA CHL 176 in a chemostat mode of operation. The growth of C. sorokiniana on treated source-separated blackwater as a substrate was monitored by measuring dry biomass concentration at a dilution rate of 1.38 d−1, temperature of 37 °C and pH of 7. The results indicate that the N and P recovery rates of C. sorokiniana were 99 mg N L−1d−1 and 8 mg P L−1d−1 for 10% treated BW and reached 213 mg N L−1d−1 and 35 mg P L−1d−1, respectively when using 20% treated BW as a substrate. The corresponding biomass yield on light, N and P on the 20% treated BW substrate were 0.37 g (mol photon)−1, 9.1 g g−1 and 54.1 g g−1, respectively, and up to 99% of N and P were removed from the blackwater.

Highlights

There is an increasing interest in biogas production from organic wastes, wastewater sludge and animal waste using anaerobic digestion (AD)
This study demonstrates the growth of Chlorella sorokiniana strain NIVA CHL176 in diluted treated blackwater
An average of up to 2 g biomass L−1 d−1 or 50 g m−2 d−1 was produced in flat panel photobioreactors with short light paths of 30 mm and a continuous irradiance of ca. 1450 μmol photons m−2 s−1

Summary

Introduction

There is an increasing interest in biogas production from organic wastes, wastewater sludge and animal waste using anaerobic digestion (AD). The increasing amount of AD effluent and the need for its appropriate disposal presents a challenge for biogas plants. This would be a serious problem if the direct use of AD effluents as fertilizer in agriculture is not permitted, or even if permitted, the large agricultural area required may not be available in the near vicinity of biogas plants and often result in long transportation distances [6]. Storage, transportation and application of the nutrient solution for use in agricultural fields becomes a challenge

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