Sinks and sources of anammox bacteria in a wastewater treatment plant - screening with qPCR.

The deammonification process, which includes nitritation and anammox bacteria, is an energy-efficient nitrogen removal process. Starting up an anammox process in a wastewater treatment plant (WWTP) is still widely believed to require external seeding of anammox bacteria. To demonstrate the principle of a non-seeded anammox start-up, anammox bacteria in potential sources must be quantified. In this study, seven digesters, their substrates and reject water were sampled and quantitative polymerase chain reaction (qPCR) was used to quantify both total and viable anammox bacteria. The results show that mesophilic digesters fed with nitrifying sludge (with high sludge ages) can be classified as a reliable source of anammox bacteria. Sludge hygienization and dewatering of digestate reduce the amount of anammox bacteria by one to two orders of magnitude and can be considered as a sink. The sampled reject waters contained on average >4.0 × 104 copies mL-1 and the majority of these cells (>87%) were viable cells. Furthermore, plants with side-stream anammox treatment appear to have higher overall quantities of anammox bacteria than those without such treatment. The present study contributes to the development of sustainable strategies for both start-up of anammox reactors and the possibility of improving microbial management in WWTPs.

Rapid start-up of one-stage deammonification MBBR without addition of external inoculum.

In recent years, the anammox process has emerged as a useful method for robust and efficient nitrogen removal in wastewater treatment plants (WWTPs). This paper evaluates a one-stage deammonification (nitritation and anammox) start-up using carrier material without using anammox inoculum. A continuous laboratory-scale process was followed by full-scale operation with reject water from the digesters at Bekkelaget WWTP in Oslo, Norway. A third laboratory reactor was run in operational mode to verify the suitability of reject water from thermophilic digestion for the deammonification process. The two start-ups presented were run with indigenous bacterial populations, intermittent aeration and dilution, to favour growth of the anammox bacterial branches. Evaluation was done by chemical and fluorescence in situ hybridization analyses. The results demonstrate that anammox culture can be set up in a one-stage process only using indigenous anammox bacteria and that a full-scale start-up process can be completed in less than 120 days.

Impact of seeding on the start-up of one-stage deammonification MBBRs.

Treating nitrogen-rich reject water from anaerobically digested sludge with deammonification has become a very beneficial side stream process. One common technique is the one-stage moving bed bioreactors (MBBRs), which in comparison with the other deammonification techniques can be started up without seeding anammox bacteria. This study investigated the impact of biofilm seeding on the start-up of one-stage deammonification MBBRs. Two lab-scale reactors were run in parallel with partial nitritation for 56 days until 11% of the carrier area in one reactor was replaced with fully developed deammonification biofilm to work as the seeding material. The seeded reactor started nitrogen reduction immediately up to a plateau of 1.3 g N m⁻² d⁻¹; after another 54 days on day 110, the reduction significantly increased. At the same time, the non-seeded reactor also started to reduce nitrogen due to deammonification. The development was followed with both nitrogen analyses and fluorescence in situ hybridization analyses. On day 134, the biofilm in both reactors contained>90% anammox bacteria and reached maximum nitrogen removal rates of 7.5 and 5.6 g N m⁻² d⁻¹ in the seeded and non-seeded reactor, respectively. Over 80% of the inorganic nitrogen was reduced. In conclusion, the seeding did not contribute to a shorter start-up time or the achieved anammox enrichment, although it did contribute to a partial, immediate nitrogen reduction. The boundary conditions are the most important factors for a successful start-up in a deammonification MBBR system.

Identifying targets for increased biogas production through chemical and organic matter characterization of digestate from full-scale biogas plants: what remains and why?

BACKGROUND: This study examines the destiny of macromolecules in different full-scale biogas processes. From previous studies it is clear that the residual organic matter in outgoing digestates can have significant biogas potential, but the factors dictating the size and composition of this residual fraction and how they correlate with the residual methane potential (RMP) are not fully understood. The aim of this study was to generate additional knowledge of the composition of residual digestate fractions and to understand how they correlate with various operational and chemical parameters. The organic composition of both the substrates and digestates from nine biogas plants operating on food waste, sewage sludge, or agricultural waste was characterized and the residual organic fractions were linked to substrate type, trace metal content, ammonia concentration, operational parameters, RMP, and enzyme activity. RESULTS: Carbohydrates represented the largest fraction of the total VS (32-68%) in most substrates. However, in the digestates protein was instead the most abundant residual macromolecule in almost all plants (3-21 g/kg). The degradation efficiency of proteins generally lower (28-79%) compared to carbohydrates (67-94%) and fats (86-91%). High residual protein content was coupled to recalcitrant protein fractions and microbial biomass, either from the substrate or formed in the degradation process. Co-digesting sewage sludge with fat increased the protein degradation efficiency with 18%, possibly through a priming mechanism where addition of easily degradable substrates also triggers the degradation of more complex fractions. In this study, high residual methane production (> 140 L CH4/kg VS) was firstly coupled to operation at unstable process conditions caused mainly by ammonia inhibition (0.74 mg NH3-N/kg) and/or trace element deficiency and, secondly, to short hydraulic retention time (HRT) (55 days) relative to the slow digestion of agricultural waste and manure. CONCLUSIONS: Operation at unstable conditions was one reason for the high residual macromolecule content and high RMP. The outgoing protein content was relatively high in all digesters and improving the degradation of proteins represents one important way to increase the VS reduction and methane production in biogas plants. Post-treatment or post-digestion of digestates, targeting microbial biomass or recalcitrant protein fractions, is a potential way to achieve increased protein degradation.