Davide Scaglione

Autotrophic nitrogen removal by a two-step SBR process applied to mixed agro-digestate

The aim of this research was to evaluate the applicability of partial-nitritation/anammox processes for biological N removal from a centrifuge supernatant coming from a full scale anaerobic digester fed on a mixture of piggery manure, poultry manure, and agro-wastes. Stable partial nitritation was achieved at pilot-scale (650L SBR), obtaining a suitable influent for the anammox lab-scale SBR reactor (3L). The anammox lab scale reactor was fed with increasing fractions of the partial nitritation effluent, blended with synthetic wastewater. In the last 100days no dilution was used. The nitrogen loading rate applied to the anammox reactor was 0.5-0.6gNL(-)(1)d(-)(1) and the average nitrogen removal was 91±10%. During the first days of operation with undiluted supernatant, the maximum anammox activity in the SBR decreased, but recovered afterwards, suggesting the ability of the anammox biomass to acclimate to the wastewater. N2O emissions in both reactors were also measured.

Comparison based on environmental effects of nitrogen management techniques in a manure digestate case study

Due to climate issues and favourable energy market, biogas is spreading as a manure management technique. Digestate is rich in nutrient and has to be handled in order to respect the ‘nitrate directive’ that limits nitrogen field application in areas defined as vulnerable. In this study, we compared different nitrogen management scenarios: a non-treatment option, a biological short-cut nitrification, a complete autotrophic process (anammox) and ammonia stripping from membrane filtration concentrate. The environmental effect comparison was obtained with ‘Cross media effects analysis’ and life cycle assessment (LCA). The results were different in some aspects, especially the impacts on eutrophication. According to cross media, the best process is DENO 2, while LCA shows similar impacts for all techniques and the best solution would be the no-treatment option. The main reason to adopt a digestate treatment technique is the lack of area for a correct disposal. If LCA eutrophication results are multiplied with the hectares necessary for each technology, a result similar to that of cross media is obtained.

Inhibition on anammox bacteria upon exposure to digestates from biogas plants treating the organic fraction of municipal solid waste and the role of conductivity.

The aim of this research was to evaluate the applicability of the anammox process for removing nitrogen from the supernatant originating from the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW). The short term inhibitory potential of this concentrated wastewater was evaluated by means of batch tests in terms of maximum specific anammox activity reduction. A total of 20 real wastewater samples were tested originating from 4 different full scale anaerobic digestion plants treating OFMSW. Activity reduction between 73% and 89% was observed in the presence of undiluted real wastewaters. The specific activity remained stable for 6-7days after the initial reduction, thus suggesting its treatability even without dilution. The inhibitory effect of both the real and synthetic saline media tested could be modelled as a function of conductivity. IC50 of 6.1mS/cm was obtained for exposure to the tested liquid fraction of biowaste digestate.

Microcalorimetric and manometric tests to assess anammox activity

The present study compares two experimental methods to evaluate Anammox activity based on the assessment of (1) the N(2) production rate by a manometric device, as previously proposed, and (2) the heat production rate by a microcalorimeter. Two samples of Anammox suspended biomass were taken from a pilot-plant, and their specific Anammox activity measured by both techniques. Both methods were successfully applied. As for calorimetric tests, they were performed for the first time on Anammox enriched sludge samples. Comparisons between the specific Anammox activities estimated by manometry and calorimetry and between expected (from the reaction enthalpy) and measured heat productions were performed. Promising results were obtained.

Complete Autotrophic Process for Nitrogen Removal from Ink-jet Printing Wastewater

Lab-scale results on the treatability of ammonium-rich wastewater from textile digital printing highlight the feasibility of an innovative biological process, based on purely autotrophic bacterial populations: ammonium oxidising bacteria (AOB) and anaerobic ammonium oxidisers (AAO). Activity of AOB has been measured through pH/DO-stat titration and that of AAO has been assessed through manometric tests, on raw mixed wastewater coming from textile-print factories (0.5 to 0-6 gN/L as ammonium nitrogen). AOB activity showed a reduction of 20-40% if compared with maximum activity on a synthetic medium. AAO activity tests showed a residual specific maximum anammox activity (SAA) of 0.1-0.4 gN2-N/gVSS/d, 40-60% of the control values obtained with synthetic wastewater. Activity tests confirmed treatability of the textile wastewater by AAO. Tests have been performed also on concentrated wastewater (2 to 3 gN/L as ammonium nitrogen) from the first rinsing bath. In this case, strong inhibition (between 80 and 100%) of anammox activity was observed. Careful operation of a continuous-flow completely mixed bioreactor can overcome this drawback, as pH and effluent ammonium concentration in the reactor are controlled.