Annick Monballiu

Performance analysis and optimization of autotrophic nitrogen removal in different reactor configurations: a modelling study.

The autotrophic nitrogen removal process (partial nitritation combined with the Anammox process) is a new and sustainable nitrogen removal technique for nitrogen‐rich streams. A modelling study has been performed to define optimal process conditions (temperature, oxygen supply, pH and biomass retention) and to investigate the influence of chemical oxygen demand, nitrogen loading rate and hydraulic retention time on three alternative reactor configurations: a single oxygen‐limited partial nitritation reactor, a single Anammox reactor, and a combination of partial nitritation and Anammox in a single reactor. The model applied was compared to experimental data from the literature and gave good agreement for all three reactor configurations. The simulations revealed that a system with separated partial nitritation and Anammox offered a wider range of optimal process conditions than a one‐reactor system. The key factors in the successful operation of partial nitritation were found to be control of aeration, ammonium loading rate and temperature. Heterotrophs remained present in all three reactor systems and it was confirmed that interaction between heterotrophs and Anammox and between heterotrophs and ammonium oxidizers was possible.

Evaluation and thermodynamic calculation of ureolytic magnesium ammonium phosphate precipitation from UASB effluent at pilot scale

The removal of phosphate as magnesium ammonium phosphate (MAP, struvite) has gained a lot of attention. A novel approach using ureolytic MAP crystallization (pH increase by means of bacterial ureases) has been tested on the anaerobic effluent of a potato processing company in a pilot plant and compared with NuReSys(®) technology (pH increase by means of NaOH). The pilot plant showed a high phosphate removal efficiency of 83 ± 7%, resulting in a final effluent concentration of 13 ± 7 mg · L(-1) PO(4)-P. Calculating the evolution of the saturation index (SI) as a function of the remaining concentrations of Mg(2+), PO(4)-P and NH(4)(+) during precipitation in a batch reactor, resulted in a good estimation of the effluent PO(4)-P concentration of the pilot plant, operating under continuous mode. X-ray diffraction (XRD) analyses confirmed the presence of struvite in the small single crystals observed during experiments. The operational cost for the ureolytic MAP crystallization treating high phosphate concentrations (e.g. 100 mg · L(-1) PO(4)-P) was calculated as 3.9 € kg(-1) P(removed). This work shows that the ureolytic MAP crystallization, in combination with an autotrophic nitrogen removal process, is competitive with the NuReSys(®) technology in terms of operational cost and removal efficiency but further research is necessary to obtain larger crystals.

Stevia-based sweeteners as a promising alternative to table sugar: The effect on Listeria monocytogenes and Salmonella Typhimurium growth dynamics

Sugar is commonly substituted with stevia-based products in food industry and in our daily-life. This substitution results in a change in food product characteristic formula and properties that may affect the growth dynamics of food pathogenic and spoilage bacteria. This work studies the effect of table sugar (TS), laboratory sucrose (LS), commercial stevia (St) and steviol glycosides (SG) on the growth dynamics of Salmonella Typhimurium and Listeria monocytogenes. Experiments were carried out in general and minimal culture media at 3 equivalent concentration levels in terms of sweetness intensity (TS and LS at 3, 9 and 15% (w/v); St at 0.3, 0.9 and 1.5% (w/v); and SG at 0.01, 0.03 and 0.05% (w/v)). Incubation temperatures were: 4, 8 and 20°C for general media, and for minimal media 20°C. To decipher the role of these sweeteners, their concentration evolution in minimal media was determined via HPLC analysis. The results revealed slow maximum specific growth rates (μmax) of S. Typhimurium in general media with increasing concentrations of TS and LS at 20°C; and reduced maximum cell population (Nmax) at 8°C. The growth of L. monocytogenes in general culture media remains invariable independently of the sweetener added, except at 4°C. At this critical temperature, the presence of TS, LS and St seems to facilitate the growth of L. monocytogenes, presenting higher μmax values in comparison to SG and the control. Varying bacterial response to changes in media formulation suggests that further research is required, focusing on revealing the microbial dynamics in structured media, as well as in real food products.

The fate of nitrite and nitrate during anaerobic digestion

ABSTRACT Anaerobic digestion is widely used to produce renewable energy. However, the main drawback is the limited conversion efficiency of organic matter. Applying an advanced oxidation process as a digestate post-treatment is able to increase this conversion efficiency but will also lead to the oxidation of ammonium to nitrite or nitrate. In this lab-scale study, the fate of the latter in the digester was investigated. Nitrite and nitrate were therefore added in concentrations that could arise from rate-limiting ammonium concentrations (1.25–5 g L−1 N). The study clearly demonstrated that nitrite and nitrate were denitrified during the subsequent digestion process resulting in the formation of nitrogen gas. After a concentration-dependent adaptation period, in which some biogas was produced, the added nitrite was denitrified in amounts proportional to the amounts of electron donor present. This denitrification, however, strongly reduces the possibility that Anammox bacteria can develop. Nitrate was also denitrified in amounts proportional to the amounts of electron donor, but biogas production was not completely blocked in this case. Moreover, high concentrations of nitrite and nitrate inhibited their own denitrification. The methane formed was used as electron donor for the further denitrification of nitrate and nitrite when no other readily available electron donor was present. After addition of either nitrite or nitrate and their denitrification, the biogas production did not recover properly.

Autotrophic nitrogen removal after ureolytic phosphate precipitation to remove both endogenous and exogenous nitrogen

Anaerobic digestion yields effluents rich in ammonium and phosphate and poor in biodegradable organic carbon, thereby making them less suitable for conventional biological nitrogen and phosphorus removal. In addition, the demand for fertilizers is increasing, energy prices are rising and global phosphate reserves are declining. This requires both changes in wastewater treatment technologies and implementation of new processes. In this contribution a description is given of the combination of a ureolytic phosphate precipitation (UPP) and an autotrophic nitrogen removal (ANR) process on the anaerobic effluent of a potato processing company. The results obtained show that it is possible to recover phosphate as struvite and to remove the nitrogen with the ANR process. The ANR process was performed in either one or two reactors (partial nitritation + Anammox). The one-reactor configuration operated stably when the dissolved oxygen was kept between 0.1 and 0.35 mg L(-1). The best results for the two-reactor system were obtained when part of the effluent of the UPP was fully nitrified in a nitritation reactor and mixed in a 3:5 volumetric ratio with untreated ammonium-containing effluent. A phosphate and nitrogen removal efficiency of respectively 83 ± 1% and of 86 ± 7% was observed during this experiment.

Calcium phosphate precipitation in nitrified wastewater from the potato-processing industry

ABSTRACT Increasing environmental concerns and the awareness of the finite nature of natural resources make the valorization of waste materials to become a real challenge. The objective of the current research is to investigate the possibility of phosphate recovery as calcium phosphate salts from the wastewater from the potato-processing industry. Batch tests demonstrated that at high pH, struvite and calcium carbonate precipitations are competitive processes and that bicarbonate inhibits the precipitation of calcium phosphate salts. A biological nitrification of the wastewater removed the buffering capacity, the competitive formation of struvite and paved the way for phosphate precipitation as calcium phosphate salts as it also led to the simultaneous removal of (bi)carbonates. It is demonstrated that 75% of the phosphate precipitated as calcium phosphate at a [Ca2+]/[P] ratio of 2.5 at pH 8.5 and as such it provides a convenient alternative for the currently applied struvite processes in the agro-industrial industry.

Fractionating magnesium ion from seawater for struvite recovery using electrodialysis with monovalent selective membranes

As the consumption of global phosphorus reserves accelerates, recovering phosphorus as struvite (MgNH4PO4·6H2O) from wastewater is an important option for phosphorus recycling. However, magnesium source is one of the major limiting factors for struvite recovery. In this work, different from previous studies where seawater was used directly as magnesium source in struvite precipitation, an electrodialysis stack equipped with monovalent selective cation-exchange membranes was designed to fractionate Mg2+ from seawater for struvite recovery. Results revealed that Mg2+ fractionation was achieved effectively. The comparison on applying the driving force for ionic transport showed that constant voltage was more preferable than constant current due to its higher Mg2+ separation efficiency, current efficiency and lower energy consumption. Increasing voltage from 7 V to 13 V would improve Mg2+ permeation ratio from 72.9% to 80.5% into the product stream but simultaneously increased the energy consumption from 5.40 (kWh/kg MgCl2) to 11.69 (kWh/kg MgCl2). In addition, the investigation on the influence of Ca2+ co-existence and further struvite recovery experiments revealed that the variation of Ca2+ concentrations in seawater did not influence Mg2+ fractionation significantly, nevertheless it might reduce struvite recovery efficiency through forming calcium phosphate.