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

Continuous assays with a microbial electrolysis cell (MEC) fed with digested pig slurry were performed to evaluate its stability and robustness to malfunction periods of an anaerobic digestion (AD) reactor and its feasibility as a strategy to recover ammonia. When performing punctual pulses of volatile fatty acids (VFA) in the anode compartment of the MEC, simulating a malfunction of the AD process, an increase in the current density was produced (up to 14 times, reaching values of 3500mAm(-2)) as a result of the added chemical oxygen demand (COD), especially when acetate was used. Furthermore, ammonium diffusion from the anode to the cathode compartment was enhanced and the removal efficiency achieved up to 60% during daily basis VFA pulses. An AD-MEC combined system has proven to be a robust and stable configuration to obtain a high quality effluent, with a lower organic and ammonium content.

Methanogenic archaea enrichment of a granular sludge was undertaken in an upflow anaerobic sludge blanket (UASB) reactor fed with methanol in order to enrich methylotrophic and hydrogenotrophic methanogenic populations. A microbial community assessment, in terms of microbial composition and activity-throughout the different stages of the feeding process with methanol and acetate-was performed using specific methanogenic activity (SMA) assays, quantitative real-time polymerase chain reaction (qPCR), and high-throughput sequencing of 16S ribosomal RNA (rRNA) genes from DNA and complementary DNA (cDNA). Distinct methanogenic enrichment was revealed by qPCR of mcrA gene in the methanol-fed community, being two orders of magnitude higher with respect to the initial inoculum, achieving a final mcrA/16S rRNA ratio of 0.25. High-throughput sequencing analysis revealed that the resulting methanogenic population was mainly composed by methylotrophic archaea (Methanomethylovorans and Methanolobus genus), being also highly active according to the RNA-based assessment. SMA confirmed that the methylotrophic pathway, with a direct conversion of methanol to CH, was the main step of methanol degradation in the UASB. The biomass from the UASB, enriched in methanogenic archaea, may bear great potential as additional inoculum for bioreactors to carry out biogas production and other related processes.

AD and an electromethanogenic biocathode were operated as an integrated system. Methane production of 79 L m-3 d-1 was achieved in the biocathode. Ammonium removal in the MEC anode compartment achieved 14.46 g N-NH 4 + m-2 d-1. The MEC stabilised the AD when the organic and nitrogen loading rates were doubled.