[P006] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P03-416] Neutralizer selection and excess sludge utilization in microaerobic activated sludge system to convert wastewater nitrogen to ammonium

○Tomo Aoyagi¹, Akihiko Terada², Tomoyuki Hori¹ (1. National Institute of Advanced Industrial Science and Technology (Japan), 2. Tokyo University of Agriculture and Technology (Japan))

Keywords:

ammonium conversion,excessive waste sludge,microaerobic activated sludge system,neutralizer,stable isotope probing (SIP),wastewater treatment

Nitrogen compounds in wastewater are currently removed by microbial nitrification and denitrification in activated sludge systems. Meanwhile, there are increasing interests in recycling of the nitrogen compounds as resources, such as raw material and fuel. Recently, microaerobic activated sludge system has been proposed to convert the nitrogen compounds to ammonium. It is essential to suppress microbial nitrification under low aeration conditions for ammonium retention, while removing carbon compounds almost completely. In this study, with a focus on the lab-scale system treating industrial wastewater, we first investigated the effective neutralizer to minimize elements that caused membrane fouling in the following ammonium concentration systems, then examined the availability of excess waste sludge as nitrogen source. Two laboratory-scale (22.5-L) microaerobic reactors with activated sludge as the seed collected from a sewage treatment plant were fed with an acidic (pH 1.5) fermentation industrial wastewater containing high concentrations of organic matters (700-mg/L total nitrogen, 500-mg/L NH₄⁺ and 1200-mg/L total organic carbon [TOC]). The reactors were operated at pH >6.0 and hydraulic retention time (HRT) of 3 or 4 days. In the first experiment to test the effective neutralizer (slaked lime or sodium hydroxide), microaerobic conditions were formed with the low aeration and high biomass (i.e., mixed liquor suspended solids), preventing the nitrification reactions. The maximum NH₄⁺ conversion and average TOC degradation rates were at approximately 80% and >95%, respectively. During the operation with slaked lime, high concentrations of Ca²⁺ (possible membrane foulants) remained in the treated wastewater. The dominant prokaryotes were almost same between the operations with these two neutralizers, while the eukaryotes were largely different. The results indicated that sodium hydroxide was better neutralizer than the Ca²⁺-rich slaked lime. In the second experiments, the NH₄⁺ conversion rates increased with the addition of the hydrolyzed excess sludge, although decreases in the TOC degradation rates were obvious. It was confirmed that the effective sludge concentrations available as the nitrogen source were about 20% chemical oxygen demand load of the influent. High-sensitivity stable isotope probing (SIP) was applied to identify the sludge microorganisms capable of degrading the hydrolyzed microbial cells (i.e., model excess sludge material) for ammonium yield. The identified 6 microbial species increased with the addition of the hydrolyzed excess sludge, while exhibiting different transition patterns in the microaerobic system. Thus, these 6 species would play different roles in conversion of the excess sludge to NH₄⁺, possibly due to their different ecophysiological characteristics.

This presentation is partially based on results obtained from the project JPNP 18016 commissioned by the New Energy and Industrial Technology Development Organization (NEDO).