This study investigated the interactions between naturally occurring bacteria and the microalgae Chlorella vulgaris within a lab scale photobioreactor treating ammonia-rich swine wastewater digestate effluent. Nitrification and denitrification were assessed by targeting ammonia monoxygenases (amoA), nitrate (narG), nitrite (nirS), nitric oxide (norB) and nitrous oxide (nosZ) reductases genes. Oxygen produced from microalgae photosynthesis stimulated nitrification. Under limiting carbon availability (i.e., <1.44 for mg TOC/mg NO2-N and 1.72 for mg TOC/mg NO3-N), incomplete denitrification led to accumulation of NO2 and NO3. Significant N2O emission (up to 118 μg N2O-N) was linked to NO2 metabolism in Chlorella. The addition of acetate as external carbon source recovered heterotrophic denitrification activity suppressing N2O emission. Effluent methane concentrations trapped within photobioreactor was removed concomitantly with ammonia. Overall, closed photobioreactors can be built to effectively remove nitrogen and mitigate simultaneously greenhouse gases emissions that would occur otherwise in open microalgae-based wastewater treatment systems.

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O óxido nitroso (N2O) é altamente impactante ao meio ambiente por ser um dos três gases mais importantes quando considerado o alto potencial de efeito estufa e a baixa quantidade emitida para a atmosfera. A preocupação com a geração de N2O no tratamento de efluentes tem crescido nas duas últimas décadas. Muitos estudos vêm sendo realizados com o objetivo de avaliar as condições de geração e emissão de N2O em etapas de remoção de nitrogênio no tratamento, tanto em escala laboratorial quanto em estações de tratamento de efluentes. Essas pesquisas demonstram que, sob certas condições, ambos os processos podem produzir e emitir grandes quantidades de N2O para a atmosfera, o que remete à importância de mais investigações para determinar as condições específicas que minimizem a produção e a emissão de N2O nesse caso.

BACKGROUND: Considering biological nitrogen removal, the partial nitritation connected with the anaerobic ammonium oxidation (anammox) process is a promising alternative for nitrogen elimination at high loading rates. The objective of the present study was to evaluate the establishment and operation of a partial nitritation process in an airlift reactor with simultaneous removal of total organic carbon and suspended solids using swine wastewater.RESULTS: The partial nitritation reactor was inoculated with a nitrifying sludge at 2.1 gTSS L−1 and fed with an UASB reactor effluent. High organic carbon loading rates, above 2 kgTOC m−3 d−1 have been shown to be potential inhibitors of the partial nitritation process due to competition between autotrophic and heterotrophic bacteria. In this study, the partial nitritation process was established using undiluted swine wastewater, with HRT of 24 h, 1.84 mgO2 L−1 (SD = 0.41) DO, loading rate of 1.14 gTOC L−1 d−1 and 0.91 gN‐NH3 L−1 d−1 for more than 100 consecutive days. At the same time, the system proved to be an effective tool in TOC and TSS removal, reaching 84.9% (SD = 9.3) and 83.1% (SD = 0.1), respectively.CONCLUSION: This result enhances partial nitritation application as a technology for high load nitrogen converting, and allows the possibility of connection with anammox reactors. Copyright © 2012 Society of Chemical Industry

The aim of the conducted research was to assess the effectiveness of the nitrification process, at different concentrations of ammonium nitrogen, in biologically treated wastewater in one of the largest municipal and industrial wastewater treatment plants in Poland. The studies also attempted to acclimate nitrifying bacteria to the limited concentration of ammonium nitrogen and determined the efficiency of nitrification under the influence of acclimated activated sludge in the biological wastewater treatment system. The obtained results indicate that the concentration of ammonium nitrogen above 60.00 mg·dm−3 inhibits nitrification, even after increasing the biomass of nitrifiers. The increase in the efficiency of the nitrification process in the tested system can be obtained by using the activated sludge inoculated with nitrifiers. For this purpose, nitrifiers should be preacclimated, at least for a period of time, allowing them to colonize the activated sludge. The acclimated activated sludge allows reducing the amount of ammonium nitrogen in treated sewage by approx. 35.0%. The process of stable nitrification in the biological treatment system was observed nine days after introducing the acclimated activated sludge into the aeration chamber.