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MBT scrubber effluent: Wastewater or fertiliser?

The design of waste air cleaning in Mechanical Biological Treatment (MBT) plants frequently includes acid scrubbing followed by biofiltration. The main purpose of the former process is to remove ammonia from the exhaust air, which produces odours and is toxic for the biofilter microorganisms. The ammonia is then solubilised as ammonium sulphate or ammonium nitrate, according to the acid used in the scrubber (sulphuric or nitric acid, respectively). When the washing solution reaches a preset conductivity, it is partially discharged and replaced by fresh water. As a consequence, an effluent with high ammonia concentration is produced, which is difficult and expensive to treat in a waste water treatment plant. Yet, if we see it in the agronomical perspective, an ammonia rich solution may not be a pollutant but a fertiliser.

Further Authors:
H. Ribeiro - Technical University of Lisbon
D. Catalino - AMARSUL S.A.

The objective of the present study was to evaluate the potential of the scrubber effluent from Amarsul MBT plant in Setúbal, Portugal, to be used as a nitrogen liquid fertiliser. The experiments were carried out with wheat and grass. These species were selected so that land application of the product could be performed all around the year. In the wheat experiment, nitrogen fertilisation supplied by the scrubber effluent was compared to the conventional fertilisation with ammonium sulphate. Results showed that the obtained yields, considering grain and straw fresh and dry weight, were not significantly different, independently from the nitrogen source. No significant differences were also observed in the grass experiment, in which three nitrogen applications were carried out: one at the beginning of the experiment and the other two following the first and second cuts. Grass yield was determined after each cut. In both experiments, soil analysis indicated a more expressive drop in pH (relative to the control) for the treatment with mineral fertilisation, comparing to that receiving scrubber effluent. The composition of the scrubber effluent was determined in order to detect eventual pollutants such as heavy metals, organic compounds and pathogens. The results show that it fulfils the quality required in Portuguese legislation for irrigation water (DL 236/98) and for sewage sludge used in agriculture (DL 276/2009). Besides evaluating the agronomic and environmental quality of the potential fertiliser, it is important to optimise the product logistics, considering storage in the MBT plant and transport to the client site. Hence, different scrubber operation regimes were tested with the objective of maximising the ammonium sulphate concentration of the effluent, without causing damage to the equipment or affecting the odour removal performance. Results demonstrated that it is possible to reach compatibility between air treatment operation requests and fertiliser logistics. This study demonstrates that the scrubber effluent from exhaust air treatment in Amarsul MBT plant could be an environmentally safe good quality ammonia fertiliser, with high potential under an agronomic point of view.

Copyright:	© European Compost Network ECN e.V.
Quelle:	Orbit 2012 (Juni 2012)
Seiten:	8
Preis:	€ 0,00
Autor:	Dr. Maria J. Sebastião E. Vasconcelos
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