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Integration of a Coagulation/Flocculation step in a biological sequencing batch reactor for COD and nitrogen removal of supernatant of anaerobically digested piggery wastewater

Dosta, J., Rovira, J., Galí, A., Macé, S., Mata-Álvarez, J.
Bioresource technology 2008 v.99 no.13 pp. 5722-5730
aeration, air, ammonia, anaerobic digestion, bioactive properties, biomass, chemical oxygen demand, coagulation, dissolved oxygen, effluents, flocculation, nitrites, nitrogen, nitrogen content, wastewater
The supernatant from mesophilic anaerobic digestion of piggery wastewater is characterised by a high amount of COD (4.1gCODL⁻¹), ammonium (2.3g [formula removed]) and suspended solids (2.5gSSL⁻¹). This effluent can be efficiently treated by means of a Sequencing Batch Reactor (SBR) strategy for biological COD, SS and nitrogen removal including a Coagulation/Flocculation step. Total COD and SS reduction yields higher than 66% and 74%, respectively, and a total nitrogen removal (via nitrite) of more than 98% were reached when working with HRT 2.7 days, SRT 12 days, temperature 32°C, three aerobic/anoxic periods, without external control of pH and under limited aeration flow. The inhibition of nitrite oxidizing biomass was achieved by the working free ammonia concentration and the restricted air supply (dissolved oxygen concentration below 1mgO₂ L⁻¹). Since a part of the total COD was colloidal and/or refractory, a Coagulation/Flocculation step was implemented inside the SBR operating strategy to meet a suitable effluent quality to be discharged. Several Jar-Tests demonstrated that the optimal concentration of FeCl₃ was 800mgL⁻¹. A respirometric assay showed that this coagulant dosage did not affect the biological activity of nitrifying/denitrifying biomass.