The combination of the anaerobic digestion (AD) process with a microbial electrolysis cell (MEC) coupled to an ammonia stripping unit as a post-treatment was assessed both in series operation, to improve the quality of the effluent, and in loop configuration recirculating the effluent, to increase the AD robustness. The MEC allowed maintaining the chemical oxygen demand removal of the whole system of 46±5% despite the AD destabilization after doubling the organic and nitrogen loads, while recovering 40±3% of ammonia. The AD-MEC system, in loop configuration, helped to recover the AD (55% increase in methane productivity) and attained a more stable and robust operation. The microbial population assessment revealed an enhancement of AD methanogenic archaea numbers and a shift in eubacterial population. The AD-MEC combined system is a promising strategy for stabilizing AD against organic and nitrogen overloads, while improving the quality of the effluent and recovering nutrients for their reutilization.

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12A Microbial fuel Cell (MFC) was used to study nitrogen dynamics and its feasibility for high

Both raw and anaerobically digested pig slurries were investigated in batch assays in two chambered bioelectrochemical systems (BES) run in Microbial Fuel Cell (MFC) and Microbial Electrolysis Cell (MEC) mode. Chemical Oxygen Demand (COD) removal, nitrogen recovery, cation transport and anode microbial population evolutions were assessed. The Anaerobic Digestion-MEC (AD-MEC) integrated system achieved the highest COD removal (60% in 48h); while the maximum NH4(+) removal efficiency (40%, with an ammonia flux of 8.86g N-NH4(+) d(-1)m(-2)) was achieved in MFC mode fed with digested pig slurry in 24h. On the other hand, the high pH (12.1) achieved in MEC mode (NaCl solution as catholyte), could favour ammonium recovery in a subsequent stripping and absorption process. Ammonia was the main cation involved in maintaining the electroneutrality between both compartments. Regarding microbial population, Desulfuromonadaceae, a known family of exoelectrogenic bacteria, was enriched under MEC mode, whereas hydrogenotrophic and methylotrophic methanogen phylotypes belonging to Thermoplasmatales were also favoured against acetotrophic Methanosaetaceae. From these results, the integration of anaerobic digestion in BES seems to be an interesting alternative for the treatment of complex substrates, since a polished effluent can be obtained and ammonium can be simultaneously recovered for further reuse as fertilizer.

BACKGROUNDThe formation of struvite (MgNH4PO4 6H(2)O) from digested slurry is an opportunity to recover nutrients as a slow-release fertilizer. A series of batch and continuous experiments were conducted to assay the influence of operational parameters, total solids and organic matter content on the quality and size of struvite crystals formed. Finally, the agronomic bioavailability of struvite was assessed in a greenhouse experiment.; RESULTSIn terms of process conditions an optimum pH of 9 was found, while changes in temperature (from 25 degrees C to 36 degrees C) showed to exert no influence whatsoever. On the other hand, though the presence of Na+ didn't affect the efficiency, high amounts of Ca2+ decreased the percentage of Mg2+ and NH4+ removed. CO2 stripping presented a reduction in the reagents required (NaOH) to raise the pH, with a similar removal efficiency and good quality of the struvite obtained. Nevertheless, the presence of organic matter resulted in a reduction on the size of struvite crystals. Agronomic assays showed that struvite P availability is similar to that of synthesis ammonium phosphate fertilizers.; CONCLUSIONSThe results point to struvite precipitation as a good strategy to recover nutrients from digested manure and to improve nutrient management. (c) 2014 Society of Chemical IndustryPostprint (published version