Behaviour of doxycycline, oxytetracycline, tetracycline and flumequine during manure up-cycling for fertilizer production.

The fate of four widely used veterinary antibiotics (doxycycline, flumequine, oxytetracycline and tetracycline) during manure upcycling was investigated at laboratory and pilot scale. The pilot was operated continuously, while the laboratory scale in batch mode. Both set-ups consisted of anaerobic digestion, ammonia stripping and a solid liquid separation step. A partial nitritation anammox process was used to treat the laboratory scale effluent. In the pilot installation, pig manure as feed, natural occurring antibiotics levels were reduced by 92% for doxycycline, 88% for flumequine, 95% for oxytetracycline and 100% for tetracycline. In the laboratory scale set-up, antibiotic free sludge was used and the four substances were spiked. The input antibiotics concentration was reduced by 85% for doxycycline, 46% for flumequine, 97% for oxytetracycline and 100% for tetracycline. In both set-ups the centrifuge cake was identified as the major emission pathway for residual antibiotics. Manure upcycling, while producing fertilizers, can be considered effective in reducing the residual antibiotic load.

Nitrous oxide emissions of a mesh separated single stage deammonification reactor.

It is widely accepted that partial nitrification by ANAMMOX has the potential to become one of the key processes in wastewater treatment. However, large greenhouse gas emissions have been panobserved in many cases. A novel mesh separated reactor, developed to allow continuous operation of deammonification at smaller scale without external biomass selection, was compared to a conventional single-chamber deammonification sequencing batch reactor (SBR), where both were equally-sized pilot-scale reactors. The mesh reactor consisted of an aerated and an anoxic zone separated by a mesh. The resulting differences in the structure of the microbial community were detected by next-generation sequencing. When both systems were operated in a sequencing batch mode, both systems had comparable nitrous oxide emission factors in the range of 4% to 5% of the influent nitrogen load. A significant decrease was observed after switching from sequencing batch mode to continuous operation.

New hybrid reactor concept incorporating a filter mesh for nitritation-anammox treatment of sludge return liquid.

A new approach to perform partial nitritation-anammox in a single tank was investigated. The tank incorporated a mesh (opening size 1.0 × 1.2 mm) as permeable barrier to create two distinct reaction zones (aerated and anoxic). The study reports on the operation and optimization of a 13 L laboratory scale reactor to treat sludge reject water with an NH4-N concentration of ∼750 mg·L-1. Performance throughout 250 days at increasing nitrogen loading rates is presented. The maximum loading rate applied was 1.5 kg NH4-N·m-3·d-1 at a hydraulic retention time of 12 h. Typical composition of the effluent was ∼50 mg·L-1 NH4-N; <5-10 mg·L-1 NO2-N and ∼60 mg·L-1 NO3-N. The corresponding average N removal rates were 85% for total nitrogen and 90% for NH4-N, respectively. Process control was very simple. It comprised only regulation of the aeration rate to maintain a pre-set pH (7.1) in the nitritation zone. Performance data clearly indicate that the investigated reactor configuration offers distinct advantages over currently installed processes. It demonstrated high robustness without the need for sophisticated process control. Apparently, the use of a permeable mesh to establish different reaction conditions in a single reactor provides new features of high potential.

Influence of the gas composition on the efficiency of ammonia stripping of biogas digestate.

Impact of strip gas composition on side stream ammonia stripping, a technology aiming at the reduction of high ammonia levels in anaerobic reactors, was investigated. Evaluation of the effect of oxygen contact during air stripping showed a distinct, though lower than perceived, inhibition of anaerobic microflora. To circumvent, the feasibility and possible constraints of biogas and flue gas as alternatives in side stream stripping were studied. Experiments, with ammonia bicarbonate model solution and digestate, were conducted. It was demonstrated that the stripping performance is negatively correlated to the CO2 level in the strip gas with a progressive performance loss towards higher concentrations. In contrast to biogas with its high CO2 content, the efficiency reduction observed for flue gas was significantly less pronounced. The later provides the additional benefit that its high thermal energy can be re-utilized in the stripping unit and it is therefore considered a viable alternative for air.