The aim of this research was to study the biological feasibility of the Partial Nitritation/Anammox (PN/A) technology to remove nitrogen from municipal mainstream wastewaters. During stable process operations at summer temperatures (23.2 ± 1.3°C), the total nitrogen removal rate was 0.223 ± 0.029 kg N (m3 d)−1 while at winter temperatures (13.4 ± 1.1°C) the total nitrogen removal rate was 0.097 ± 0.016 kg N (m3 d)−1. Nitrite-oxidizing bacteria (NOB) suppression was successfully achieved at the complete temperature range of municipal mainstream wastewater. Despite the presence of NOB as observed in activity tests, their activity could be successfully suppressed due to a relative low dissolved oxygen concentration. An overcapacity of ammonia-oxidizing bacteria and anammox activity was always present. Long-term stability is a focus point for future research, especially in relation to the stability of the biological oxygen demand removing step, preceding the PN/A reactor.@en

De doelstelling van het CENIRELTA project was aan te tonen dat Anammox in de hoofdstroom van een rwzi een effectieve, robuuste, kosten-efficiënte en duurzame technologie biedt voor de verwijdering van stikstof uit huishoudelijk afvalwater. De effectiviteit en robuustheid van het hoofdstroom Anammox proces zijn beproefd op rwzi Dokhaven in Rotterdam. In hoofdstuk 2 wordt ingegaan op het materiaal en de methode op basis waarvan dit project is uitgevoerd. Daarna volgt een hoofdstuk met resultaten van de full scale A-trap op Dokhaven en sliblijn op slibverwerkingsbedrijf Sluisjesdijk. Hoofdstuk 4 focust uitsluitend op de resultaten van de demonstratie-installatie die gedurende 3,5 jaar operationeel is geweest op rwzi Dokhaven. In dit hoofdstuk komen ook de belangrijkste conclusies en aanbevelingen terug van dit specifieke onderdeel van het CENIRELTA project. In hoofdstuk 5 staan de resultaten van de economische analyse van het CENIRELTA concept voor een groene weide situatie. In hoofdstuk 6 komt kort de inpassing van de hoofdstroom Anammox op rwzi Dokhaven aan bod, met oog voor technologische en technische aspecten. Tot slot wordt er stilgestaan bij de hoofdconclusies en aanbevelingen van het CENIRELTA project.@en

The implementation of autotrophic nitrogen removal in the mainstream of a municipal wastewater treatment plant is currently pursued. Among the crucial unknown factors are the kinetic properties of anaerobic ammonium oxidising (anammox) bacteria at low temperatures. In this study we investigated the adaptation of a fast-growing anammox culture to a lower temperature. In a membrane bioreactor a highly enriched anammox community was obtained at 30°C, 25°C and 20°C. This culture was exposed to long- and short-term temperature changes. In short-term experiments the decrease in biomass-specific activity due to decrease in temperature can be described by an activation energy of 64 ± 28 kJ mol−1. Prolonged cultivation (months) implies that cultivation at low temperatures resulted in deterioration of biomass-specific activity (EaLT 239 kJ mol−1). The growth rate and specific anammox activity in the system decreased from 0.33 d−1 and 4.47 g NO2-N g VSS−1 d−1 at 30°C to 0.0011 d−1 and 0.037 g NO2-N g VSS−1 d−1 at 20°C. The reason for the deterioration of the system was related to the required long SRT in the system. The long SRT leads to an increase of non-active and non-anammox cells in the reactor, thereby decreasing the biomass-specific activity.@en

Partial nitritation was stably achieved in a bench-scale airlift reactor (1.5L) containing granular sludge. Continuous operation at 20 °C treating low-strength synthetic wastewater (50 mg N-NH4 +/L and no COD) achieved nitrogen loading rates of 0.8 g N-NH4 +/(L·d) during partial nitritation. The switch between nitrite-oxidizing bacteria (NOB) repression and NOB proliferation was observed when ammonium concentrations in the reactor were below 2–5 mg N-NH4 +/L for DO concentrations lower than 4 mg O2/L at 20 °C. Nitrospira spp. were detected to be the dominant NOB population during the entire reactor operation, whereas Nitrobacter spp. were found to be increasing in numbers over time. Stratification of the granule structure, with ammonia-oxidizing bacteria (AOB) occupying the outer shell, was found to be highly important in the repression of NOB in the long term. The pH gradient in the granule, containing a pH difference of ca. 0.4 between the granule surface and the granule centre, creates a decreasing gradient of ammonia towards the centre of the granule. Higher residual ammonium concentration enhances the ammonium oxidation rate of those cells located further away from the granule surface, where the competition for oxygen between AOB and NOB is more important, and it contributes to the stratification of both populations in the biofilm.@en

Currently wastewater treatment plants (WWTP) consume a lot of energy and surface area. While the incoming water contains chemical energy (BOD) and reusable resources which are not effectively utilized. The ideal is to develop a treatment scheme which allows for the efficient removal of pollutants while minimizing the energy input and maximizing the recovery of energy and resources present in the wastewater. This thesis describes the potential and feasibility of implementing of the partial nitritation/anammox (PN/A) process in the mainstream of a municipal WWTP. Implementation of this technology will allow a complete re-design of the conventional wastewater treatment scheme from an energy consuming into an energy producing system. In wastewater treatment plants nitrogen is currently removed in two sequential microbial conversions: nitrification and denitrification. For the nitrification step oxygen is needed and for the denitrification step anoxic conditions and BOD are required. The PN/A technology can be used to optimize the municipal mainstream wastewater treatment technology. In the PN/A process the incomplete oxidation of ammonium to nitrite (by aerobic ammonium oxidising bacteria, AOB) is combined with the anaerobic ammonium oxidation (by anammox bacteria). The first advantage is; due to the autotrophic nature of the pathways used, there is no longer a need for carbon to remove nitrogen through denitrification. The carbon in the wastewater can therefore be used for different means for instance for the production of biogas. A second advantage of the PN/A technology is the use of biofilms for (part of) the biomass. Biofilms/granules can lead to higher biomass concentrations in the reactor and therefore higher volumetric loading rates can be applied. Biofilms are easier to separate from water compared to sludge flocs, so a more compact sludge retention system can be built (compared to current secondary clarifiers). Thirdly all nitrogen conversions can take place in the same reactor, omitting the two different zones/tanks for nitrification/denitrification. @en